OpenImageIO 2.3

Programmer Documentation

Editor: Larry Gritz, lg@openimageio.org

OpenImageIO (OIIO) is a library for reading, writing, and processing images in a wide variety of file formats, using a format-agnostic API. OIIO emphasizes formats and functionality used in professional, large-scale visual effects and feature film animation, and it is used ubiquitously by large VFX studios, as well as incorporated into many commercial products.

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Contents

The code that implements OpenImageIO is licensed under the BSD 3-clause (also sometimes known as “new BSD” or “modified BSD”) license (https://github.com/OpenImageIO/oiio):


Copyright (c) 2008-present by Contributors to the OpenImageIO project. All Rights Reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

  1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

  2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

  3. Neither the name of the copyright holder nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS “AS IS” AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.


This manual and other text documentation about OpenImageIO are licensed under the Creative Commons Attribution 3.0 Unported License.

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OpenImageIO incorporates code from several other software packages with compatible licenses. Copies of their licenses are reproduced here: https://github.com/OpenImageIO/oiio/blob/master/THIRD-PARTY.md

Introduction

Welcome to OpenImageIO!


I kinda like “Oy-e-oh” with a bit of a groaning Yiddish accent, as in
“OIIO, did you really write yet another file I/O library?”

Dan Wexler


Overview

OpenImageIO provides simple but powerful ImageInput and ImageOutput APIs that abstract the reading and writing of 2D image file formats. They don’t support every possible way of encoding images in memory, but for a reasonable and common set of desired functionality, they provide an exceptionally easy way for an application using the APIs support a wide — and extensible — selection of image formats without knowing the details of any of these formats.

Concrete instances of these APIs, each of which implements the ability to read and/or write a different image file format, are stored as plugins (i.e., dynamic libraries, DLL’s, or DSO’s) that are loaded at runtime. The OpenImageIO distribution contains such plugins for several popular formats. Any user may create conforming plugins that implement reading and writing capabilities for other image formats, and any application that uses OpenImageIO would be able to use those plugins.

The library also implements the helper class ImageBuf, which is a handy way to store and manipulate images in memory. ImageBuf itself uses ImageInput and ImageOutput for its file I/O, and therefore is also agnostic as to image file formats. A variety of functions in the ImageBufAlgo namespace are available to perform common image processing operations on ImageBuf’s.

The ImageCache class transparently manages a cache so that it can access truly vast amounts of image data (thousands of image files totaling hundreds of GB to several TBs) very efficiently using only a tiny amount (tens of megabytes to a few GB at most) of runtime memory. Additionally, a TextureSystem class provides filtered MIP-map texture lookups, atop the nice caching behavior of ImageCache.

Finally, the OpenImageIO distribution contains several utility programs that operate on images, each of which is built atop this functionality, and therefore may read or write any image file type for which an appropriate plugin is found at runtime. Paramount among these utilities oiiotool, a command-line image processing engine, and iv, an image viewing application. Additionally, there are programs for converting images among different formats, comparing image data between two images, and examining image metadata.

All of this is released as “open source” software using the very permissive “BSD 3-clause” license. So you should feel free to use any or all of OpenImageIO in your own software, whether it is private or public, open source or proprietary, free or commercial. You may also modify it on your own. You are encouraged to contribute to the continued development of OpenImageIO and to share any improvements that you make on your own, though you are by no means required to do so.

Simplifying Assumptions

OpenImageIO is not the only image library in the world. Certainly there are many fine libraries that implement a single image format (including the excellent libtiff, libjpeg, and OpenEXR that OpenImageIO itself relies on). Many libraries attempt to present a uniform API for reading and writing multiple image file formats. Most of these support a fixed set of image formats, though a few of these also attempt to provide an extensible set by using the plugin approach.

But in our experience, these libraries are all flawed in one or more ways: (1) They either support only a few formats, or many formats but with the majority of them somehow incomplete or incorrect. (2) Their APIs are not sufficiently expressive as to handle all the image features we need (such as tiled images, which is critical for our texture library). (3) Their APIs are too complete, trying to handle every possible permutation of image format features, and as a result are horribly complicated.

The third sin is the most severe, and is almost always the main problem at the end of the day. Even among the many open source image libraries that rely on extensible plugins, we have not found one that is both sufficiently flexible and has APIs anywhere near as simple to understand and use as those of OpenImageIO.

Good design is usually a matter of deciding what not to do, and OpenImageIO is no exception. We achieve power and elegance only by making simplifying assumptions. Among them:

  • OpenImageIO only deals with ordinary 2D images, and to a limited extent 3D volumes, and image files that contain multiple (but finite) independent images within them. OpenImageIO’s support of “movie” files is limited to viewing them as a sequence of separate frames within the file, but not as movies per se (for example, no support for dealing with audio or synchronization).

  • Pixel data are presented as 8- 16- or 32-bit int (signed or unsigned), 16- 32- or 64-bit float. NOTHING ELSE. No \(<8\) bit images, or pixel value boundaries that aren’t byte boundaries. Files with \(<8\) will appear to the client application as 8-bit unsigned grayscale images.

  • Only fully elaborated, non-compressed data are accepted and returned by the API. Compression or special encodings are handled entirely within an OpenImageIO plugin.

  • Color space is by default converted to grayscale or RGB. Non-spectral color models, such as XYZ, CMYK, or YUV, are converted to RGB upon reading. (There is a way to override this and ask for raw pixel values.)

  • All color channels can be treated (by apps or readers/writers) as having the same data format (though there is a way to deal with per-channel formats for apps and readers/writers that truly need it).

  • All image channels in a subimage are sampled at the same resolution. For file formats that allow some channels to be subsampled, they will be automatically up-sampled to the highest resolution channel in the subimage.

  • Color information is always in the order R, G, B, and the alpha channel, if any, always follows RGB, and Z channel (if any) always follows alpha. So if a file actually stores ABGR, the plugin is expected to rearrange it as RGBA.

It’s important to remember that these restrictions apply to data passed through the APIs, not to the files themselves. It’s perfectly fine to have an OpenImageIO plugin that supports YUV data, or 4 bits per channel, or any other exotic feature. You could even write a movie-reading ImageInput (despite OpenImageIO’s claims of not supporting movies) and make it look to the client like it’s just a series of images within the file. It’s just that all the nonconforming details are handled entirely within the OpenImageIO plugin and are not exposed through the main OpenImageIO APIs.

Historical Origins

OpenImageIO is the evolution of concepts and tools I’ve been working on for two decades.

In the 1980’s, every program I wrote that output images would have a simple, custom format and viewer. I soon graduated to using a standard image file format (TIFF) with my own library implementation. Then I switched to Sam Leffler’s stable and complete libtiff.

In the mid-to-late-1990’s, I worked at Pixar as one of the main implementors of PhotoRealistic RenderMan, which had display drivers that consisted of an API for opening files and outputting pixels, and a set of DSO/DLL plugins that each implement image output for each of a dozen or so different file format. The plugins all responded to the same API, so the renderer itself did not need to know how to the details of the image file formats, and users could (in theory, but rarely in practice) extend the set of output image formats the renderer could use by writing their own plugins.

This was the seed of a good idea, but PRMan’s display driver plugin API was abstruse and hard to use. So when I started Exluna in 2000, Matt Pharr, Craig Kolb, and I designed a new API for image output for our own renderer, Entropy. This API, called “ExDisplay,” was C++, and much simpler, clearer, and easier to use than PRMan’s display drivers.

NVIDIA’s Gelato (circa 2002), whose early work was done by myself, Dan Wexler, Jonathan Rice, and Eric Enderton, had an API called “ImageIO.” ImageIO was much more powerful and descriptive than ExDisplay, and had an API for reading as well as writing images. Gelato was not only “format agnostic” for its image output, but also for its image input (textures, image viewer, and other image utilities). We released the API specification and headers (though not the library implementation) using the BSD open source license, firmly repudiating any notion that the API should be specific to NVIDIA or Gelato.

For Gelato 3.0 (circa 2007), we refined ImageIO again (by this time, Philip Nemec was also a major influence, in addition to Dan, Eric, and myself 1). This revision was not a major overhaul but more of a fine tuning. Our ideas were clearly approaching stability. But, alas, the Gelato project was canceled before Gelato 3.0 was released, and despite our prodding, NVIDIA executives would not open source the full ImageIO code and related tools.

1

Gelato as a whole had many other contributors; those I’ve named here are the ones I recall contributing to the design or implementation of the ImageIO APIs.

After I left NVIDIA, I was determined to recreate this work once again – and ONLY once more – and release it as open source from the start. Thus, OpenImageIO was born. I started with the existing Gelato ImageIO specification and headers (which were BSD licensed all along), and made further refinements since I had to rewrite the entire implementation from scratch anyway. I think the additional changes are all improvements.

Over the years and with the help of dozens of open source contributors, OpenImageIO has expanded beyond the original simple image format input/output to encompass a wide range of image-related functionality. It has grown into a foundational technology in many products and tools, particularly for the production of animation and visual effects for motion pictures (but also many other uses and fields). This is the software you have in your hands today.

Acknowledgments

OpenImageIO incorporates, depends upon, or dynamically links against several other open source packages, detailed below. These other packages are all distributed under licenses that allow them to be used by OpenImageIO. Where not specifically noted, they are all using the same BSD license that OpenImageIO uses. Any omissions or inaccuracies in this list are inadvertent and will be fixed if pointed out. The full original licenses can be found in the relevant parts of the source code.

OpenImageIO incorporates, distributes, or contains derived works of:

OpenImageIO Has the following build-time dependencies (using system installs, referencing as git submodules, or downloading as part of the build), including link-time dependencies against dynamic libraries:

Image I/O API Helper Classes

Data Type Descriptions: TypeDesc

There are two kinds of data that are important to OpenImageIO:

  • Internal data is in the memory of the computer, used by an application program.

  • Native file data is what is stored in an image file itself (i.e., on the “other side” of the abstraction layer that OpenImageIO provides).

Both internal and file data is stored in a particular data format that describes the numerical encoding of the values. OpenImageIO understands several types of data encodings, and there is a special class, TypeDesc, that allows their enumeration and is described in the header file OpenImageIO/typedesc.h. A TypeDesc describes a base data format type, aggregation into simple vector and matrix types, and an array length (if it’s an array).

The remainder of this section describes the C++ API for TypeDesc. See Section Python Bindings for the corresponding Python bindings.

struct OIIO::TypeDesc

A TypeDesc describes simple data types.

It frequently comes up (in my experience, with renderers and image handling programs) that you want a way to describe data that is passed through APIs through blind pointers. These are some simple classes that provide a simple type descriptor system. This is not meant to be comprehensive for example, there is no provision for structs, unions, pointers, const, or ‘nested’ type definitions. Just simple integer and floating point, common aggregates such as 3-points, and reasonably-lengthed arrays thereof.

Public Types

enum BASETYPE

BASETYPE is a simple enum describing the base data types that correspond (mostly) to the C/C++ built-in types.

Values:

enumerator UNKNOWN

unknown type

enumerator NONE

void/no type

enumerator UINT8

8-bit unsigned int values ranging from 0..255, (C/C++ unsigned char).

enumerator UCHAR
enumerator INT8

8-bit int values ranging from -128..127, (C/C++ char).

enumerator CHAR
enumerator UINT16

16-bit int values ranging from 0..65535, (C/C++ unsigned short).

enumerator USHORT
enumerator INT16

16-bit int values ranging from -32768..32767, (C/C++ short).

enumerator SHORT
enumerator UINT32

32-bit unsigned int values (C/C++ unsigned int).

enumerator UINT
enumerator INT32

signed 32-bit int values (C/C++ int).

enumerator INT
enumerator UINT64

64-bit unsigned int values (C/C++ unsigned long long on most architectures).

enumerator ULONGLONG
enumerator INT64

signed 64-bit int values (C/C++ long long on most architectures).

enumerator LONGLONG
enumerator HALF

16-bit IEEE floating point values (OpenEXR half).

enumerator FLOAT

32-bit IEEE floating point values, (C/C++ float).

enumerator DOUBLE

64-bit IEEE floating point values, (C/C++ double).

enumerator STRING

Character string.

enumerator PTR

A pointer value.

enumerator LASTBASE
enum AGGREGATE

AGGREGATE describes whether our TypeDesc is a simple scalar of one of the BASETYPE’s, or one of several simple aggregates.

Note that aggregates and arrays are different. A TypeDesc(FLOAT,3) is an array of three floats, a TypeDesc(FLOAT,VEC3) is a single 3-component vector comprised of floats, and TypeDesc(FLOAT,3,VEC3) is an array of 3 vectors, each of which is comprised of 3 floats.

Values:

enumerator SCALAR

A single scalar value (such as a raw int or float in C). This is the default.

enumerator VEC2

2 values representing a 2D vector.

enumerator VEC3

3 values representing a 3D vector.

enumerator VEC4

4 values representing a 4D vector.

enumerator MATRIX33

9 values representing a 3x3 matrix.

enumerator MATRIX44

16 values representing a 4x4 matrix.

enum VECSEMANTICS

VECSEMANTICS gives hints about what the data represent (for example, if a spatial vector quantity should transform as a point, direction vector, or surface normal).

Values:

enumerator NOXFORM

No semantic hints.

enumerator NOSEMANTICS

No semantic hints.

enumerator COLOR

Color.

enumerator POINT

Point: a spatial location.

enumerator VECTOR

Vector: a spatial direction.

enumerator NORMAL

Normal: a surface normal.

enumerator TIMECODE

indicates an int[2] representing the standard 4-byte encoding of an SMPTE timecode.

enumerator KEYCODE

indicates an int[7] representing the standard 28-byte encoding of an SMPTE keycode.

enumerator RATIONAL

A VEC2 representing a rational number val[0] / val[1]

enumerator BOX

A VEC2[2] or VEC3[2] that represents a 2D or 3D bounds (min/max)

Public Functions

inline constexpr TypeDesc(BASETYPE btype = UNKNOWN, AGGREGATE agg = SCALAR, VECSEMANTICS semantics = NOSEMANTICS, int arraylen = 0) noexcept

Construct from a BASETYPE and optional aggregateness, semantics, and arrayness.

inline constexpr TypeDesc(BASETYPE btype, int arraylen) noexcept

Construct an array of a non-aggregate BASETYPE.

inline constexpr TypeDesc(BASETYPE btype, AGGREGATE agg, int arraylen) noexcept

Construct an array from BASETYPE, AGGREGATE, and array length, with unspecified (or moot) semantic hints.

TypeDesc(string_view typestring)

Construct from a string (e.g., “float[3]”). If no valid type could be assembled, set base to UNKNOWN.

Examples: 

TypeDesc("int") == TypeDesc(TypeDesc::INT)            // C++ int32_t
TypeDesc("float") == TypeDesc(TypeDesc::FLOAT)        // C++ float
TypeDesc("uint16") == TypeDesc(TypeDesc::UINT16)      // C++ uint16_t
TypeDesc("float[4]") == TypeDesc(TypeDesc::FLOAT, 4)  // array
TypeDesc("point") == TypeDesc(TypeDesc::FLOAT,
                              TypeDesc::VEC3, TypeDesc::POINT)

inline constexpr TypeDesc(const TypeDesc &t) noexcept

Copy constructor.

const char *c_str() const

Return the name, for printing and whatnot. For example, “float”, “int[5]”, “normal”

inline constexpr size_t numelements() const noexcept

Return the number of elements: 1 if not an array, or the array length. Invalid to call this for arrays of undetermined size.

inline constexpr size_t basevalues() const noexcept

Return the number of basetype values: the aggregate count multiplied by the array length (or 1 if not an array). Invalid to call this for arrays of undetermined size.

inline constexpr bool is_array() const noexcept

Does this TypeDesc describe an array?

inline constexpr bool is_unsized_array() const noexcept

Does this TypeDesc describe an array, but whose length is not specified?

inline constexpr bool is_sized_array() const noexcept

Does this TypeDesc describe an array, whose length is specified?

inline size_t size() const noexcept

Return the size, in bytes, of this type.

inline constexpr TypeDesc elementtype() const noexcept

Return the type of one element, i.e., strip out the array-ness.

inline size_t elementsize() const noexcept

Return the size, in bytes, of one element of this type (that is, ignoring whether it’s an array).

inline constexpr TypeDesc scalartype() const

Return just the underlying C scalar type, i.e., strip out the array-ness and the aggregateness.

size_t basesize() const noexcept

Return the base type size, i.e., stripped of both array-ness and aggregateness.

bool is_floating_point() const noexcept

True if it’s a floating-point type (versus a fundamentally integral type or something else like a string).

bool is_signed() const noexcept

True if it’s a signed type that allows for negative values.

inline constexpr bool is_unknown() const noexcept

Shortcut: is it UNKNOWN?

inline constexpr operator bool() const noexcept

if (typedesc) is the same as asking whether it’s not UNKNOWN.

size_t fromstring(string_view typestring)

Set *this to the type described in the string. Return the length of the part of the string that describes the type. If no valid type could be assembled, return 0 and do not modify *this.

inline constexpr bool operator==(const TypeDesc &t) const noexcept

Compare two TypeDesc values for equality.

inline constexpr bool operator!=(const TypeDesc &t) const noexcept

Compare two TypeDesc values for inequality.

inline constexpr bool equivalent(const TypeDesc &b) const noexcept

Member version of equivalent.

inline constexpr bool is_vec2(BASETYPE b = FLOAT) const noexcept

Is this a 2-vector aggregate (of the given type, float by default)?

inline constexpr bool is_vec3(BASETYPE b = FLOAT) const noexcept

Is this a 3-vector aggregate (of the given type, float by default)?

inline constexpr bool is_vec4(BASETYPE b = FLOAT) const noexcept

Is this a 4-vector aggregate (of the given type, float by default)?

inline constexpr bool is_box2(BASETYPE b = FLOAT) const noexcept

Is this an array of aggregates that represents a 2D bounding box?

inline constexpr bool is_box3(BASETYPE b = FLOAT) const noexcept

Is this an array of aggregates that represents a 3D bounding box?

inline void unarray(void) noexcept

Demote the type to a non-array

bool operator<(const TypeDesc &x) const noexcept

Test for lexicographic ‘less’, comes in handy for lots of STL containers and algorithms.

Public Members

unsigned char basetype

C data type at the heart of our type.

unsigned char aggregate

What kind of AGGREGATE is it?

unsigned char vecsemantics

Hint: What does the aggregate represent?

unsigned char reserved

Reserved for future expansion.

int arraylen

Array length, 0 = not array, -1 = unsized.

Public Static Functions

static BASETYPE basetype_merge(TypeDesc a, TypeDesc b)

Given base data types of a and b, return a basetype that is a best guess for one that can handle both without any loss of range or precision.

Friends

inline friend friend constexpr bool operator== (const TypeDesc &t, BASETYPE b) noexcept

Compare a TypeDesc to a basetype (it’s the same if it has the same base type and is not an aggregate or an array).

inline friend friend constexpr bool operator!= (const TypeDesc &t, BASETYPE b) noexcept

Compare a TypeDesc to a basetype (it’s the same if it has the same base type and is not an aggregate or an array).

inline friend friend constexpr bool equivalent (const TypeDesc &a, const TypeDesc &b) noexcept

TypeDesc’s are equivalent if they are equal, or if their only inequality is differing vector semantics.

A number of static constexpr TypeDesc aliases for common types exist in the outer OpenImageIO scope:

TypeUnknown TypeFloat TypeColor TypePoint TypeVector TypeNormal
TypeMatrix33 TypeMatrix44 TypeMatrix TypeHalf
TypeInt TypeUInt TypeInt32 TypeUInt32 TypeInt64 TypeUInt64
TypeInt16 TypeUInt16 TypeInt8 TypeUInt8
TypeFloat2 TypeVector2 TypeVector2i TypeFloat4
TypeString TypeTimeCode TypeKeyCode
TypeBox2 TypeBox2i TypeBox3 TypeBox3i
TypeRational TypePointer

The only types commonly used to store pixel values in image files are scalars of UINT8, UINT16, float, and half (the last only used by OpenEXR, to the best of our knowledge).

Note that the TypeDesc (which is also used for applications other than images) can describe many types not used by OpenImageIO. Please ignore this extra complexity; only the above simple types are understood by OpenImageIO as pixel storage data types, though a few others, including string and MATRIX44 aggregates, are occasionally used for metadata for certain image file formats (see Sections sec-imageoutput-metadata, sec-imageinput-metadata, and the documentation of individual ImageIO plugins for details).

Non-owning string views: string_view

class OIIO::string_view

A string_view is a non-owning, non-copying, non-allocating reference to a sequence of characters. It encapsulates both a character pointer and a length.

A function that takes a string input (but does not need to alter the string in place) may use a string_view parameter and accept input that is any of char* (C string), string literal (constant char array), a std::string (C++ string), or OIIO ustring. For all of these cases, no extra allocations are performed, and no extra copies of the string contents are performed (as they would be, for example, if the function took a const std::string& argument but was passed a char* or string literal).

Furthermore, a function that returns a copy or a substring of one of its inputs (for example, a substr()-like function) may return a string_view rather than a std::string, and thus generate its return value without any allocation or copying. Upon assignment to a std::string or ustring, it will properly auto-convert.

There are two important caveats to using this class:

  1. The string_view merely refers to characters owned by another string, so the string_view may not be used outside the lifetime of the string it refers to. Thus, string_view is great for parameter passing, but it’s not a good idea to use a string_view to store strings in a data structure (unless you are really sure you know what you’re doing).

  2. Because the run of characters that the string_view refers to may not be 0-terminated, it is important to distinguish between the data() method, which returns the pointer to the characters, and the c_str() method, which is guaranteed to return a valid C string that is 0-terminated. Thus, if you want to pass the contents of a string_view to a function that expects a 0-terminated string (say, fopen), you must call fopen(my_string_view.c_str()). Note that the usual case is that the string_view does refer to a 0-terminated string, and in that case c_str() returns the same thing as data() without any extra expense; but in the rare case that it is not 0-terminated, c_str() will incur extra expense to internally allocate a valid C string.

Public Functions

inline constexpr string_view() noexcept

Default ctr.

inline constexpr string_view(const string_view &copy)

Copy ctr.

inline constexpr string_view(const charT *chars, size_t len)

Construct from char* and length.

inline constexpr string_view(const charT *chars)

Construct from char*, use strlen to determine length.

inline string_view(const std::string &str) noexcept

Construct from std::string. Remember that a string_view doesn’t have its own copy of the characters, so don’t use the string_view after the original string has been destroyed or altered.

inline std::string str() const

Convert a string_view to a std::string.

const char *c_str() const

Explicitly request a 0-terminated string. USUALLY, this turns out to be just data(), with no significant added expense (because most uses of string_view are simple wrappers of C strings, C++ std::string, or ustring all of which are 0-terminated). But in the more rare case that the string_view represents a non-0-terminated substring, it will force an allocation and copy underneath.

Caveats:

  1. This is NOT going to be part of the C++17 std::string_view, so it’s probably best to avoid this method if you want to have 100% drop-in compatibility with std::string_view.

  2. It is NOT SAFE to use c_str() on a string_view whose last char is the end of an allocation because that next char may only coincidentally be a ‘\0’, which will cause c_str() to return the string start (thinking it’s a valid C string, so why not just return its address?), if there’s any chance that the subsequent char could change from 0 to non-zero during the use of the result of c_str(), and thus break the assumption that it’s a valid C str.

inline operator std::string() const

Convert a string_view to a std::string.

inline constexpr bool empty() const noexcept

Is the string_view empty, containing no characters?

inline constexpr const_reference operator[](size_type pos) const

Element access of an individual character (beware: no bounds checking!).

inline constexpr const_reference at(size_t pos) const

Element access with bounds checking and exception if out of bounds.

inline size_type find(string_view s, size_t pos = 0) const noexcept

Find the first occurrence of substring s in *this, starting at position pos.

inline size_type find(charT c, size_t pos = 0) const noexcept

Find the first occurrence of character c in *this, starting at position pos.

inline size_type rfind(string_view s, size_t pos = npos) const noexcept

Find the last occurrence of substring s *this, but only those occurrences earlier than position pos.

inline size_type rfind(charT c, size_t pos = npos) const noexcept

Find the last occurrence of character c in *this, but only those occurrences earlier than position pos.


Efficient unique strings: ustring

class OIIO::ustring

A ustring is an alternative to char* or std::string for storing strings, in which the character sequence is unique (allowing many speed advantages for assignment, equality testing, and inequality testing).

The implementation is that behind the scenes there is a hash set of allocated strings, so the characters of each string are unique. A ustring itself is a pointer to the characters of one of these canonical strings. Therefore, assignment and equality testing is just a single 32- or 64-bit int operation, the only mutex is when a ustring is created from raw characters, and the only malloc is the first time each canonical ustring is created.

The internal table also contains a std::string version and the length of the string, so converting a ustring to a std::string (via ustring::string()) or querying the number of characters (via ustring::size() or ustring::length()) is extremely inexpensive, and does not involve creation/allocation of a new std::string or a call to strlen.

We try very hard to completely mimic the API of std::string, including all the constructors, comparisons, iterations, etc. Of course, the charaters of a ustring are non-modifiable, so we do not replicate any of the non-const methods of std::string. But in most other ways it looks and acts like a std::string and so most templated algorthms that would work on a “const std::string &” will also work on a ustring.

Usage guidelines:

Compared to standard strings, ustrings have several advantages:

  • Each individual ustring is very small in fact, we guarantee that a ustring is the same size and memory layout as an ordinary char*.

  • Storage is frugal, since there is only one allocated copy of each unique character sequence, throughout the lifetime of the program.

  • Assignment from one ustring to another is just copy of the pointer; no allocation, no character copying, no reference counting.

  • Equality testing (do the strings contain the same characters) is a single operation, the comparison of the pointer.

  • Memory allocation only occurs when a new ustring is constructed from raw characters the FIRST time subsequent constructions of the same string just finds it in the canonical string set, but doesn’t need to allocate new storage. Destruction of a ustring is trivial, there is no de-allocation because the canonical version stays in the set. Also, therefore, no user code mistake can lead to memory leaks.

But there are some problems, too. Canonical strings are never freed from the table. So in some sense all the strings “leak”, but they only leak one copy for each unique string that the program ever comes across. Also, creation of unique strings from raw characters is more expensive than for standard strings, due to hashing, table queries, and other overhead.

On the whole, ustrings are a really great string representation

  • if you tend to have (relatively) few unique strings, but many copies of those strings;

  • if the creation of strings from raw characters is relatively rare compared to copying or comparing to existing strings;

  • if you tend to make the same strings over and over again, and if it’s relatively rare that a single unique character sequence is used only once in the entire lifetime of the program;

  • if your most common string operations are assignment and equality testing and you want them to be as fast as possible;

  • if you are doing relatively little character-by-character assembly of strings, string concatenation, or other “string manipulation” (other than equality testing).

ustrings are not so hot

  • if your program tends to have very few copies of each character sequence over the entire lifetime of the program;

  • if your program tends to generate a huge variety of unique strings over its lifetime, each of which is used only a short time and then discarded, never to be needed again;

  • if you don’t need to do a lot of string assignment or equality testing, but lots of more complex string manipulation.

Public Functions

inline ustring(void) noexcept

Default ctr for ustring make an empty string.

inline explicit ustring(const char *str)

Construct a ustring from a null-terminated C string (char *).

inline explicit ustring(string_view str)

Construct a ustring from a string_view, which can be auto-converted from either a null-terminated C string (char *) or a C++ std::string.

inline ustring(const char *str, size_type pos, size_type n)

Construct a ustring from at most n characters of str, starting at position pos.

inline ustring(const char *str, size_type n)

Construct a ustring from the first n characters of str.

inline ustring(size_type n, char c)

Construct a ustring from n copies of character c.

inline ustring(const std::string &str, size_type pos, size_type n = npos)

Construct a ustring from an indexed substring of a std::string.

inline ustring(const ustring &str) noexcept

Copy construct a ustring from another ustring.

inline ustring(const ustring &str, size_type pos, size_type n = npos)

Construct a ustring from an indexed substring of a ustring.

inline ~ustring() noexcept

ustring destructor.

inline operator string_view() const noexcept

Conversion to string_view.

inline explicit operator std::string() const noexcept

Conversion to std::string (explicit only!).

inline const ustring &assign(const ustring &str)

Assign a ustring to *this.

inline const ustring &assign(const ustring &str, size_type pos, size_type n = npos)

Assign a substring of a ustring to *this.

inline const ustring &assign(const std::string &str)

Assign a std::string to *this.

inline const ustring &assign(const std::string &str, size_type pos, size_type n = npos)

Assign a substring of a std::string to *this.

inline const ustring &assign(const char *str)

Assign a null-terminated C string (char*) to *this.

inline const ustring &assign(const char *str, size_type n)

Assign the first n characters of str to *this.

inline const ustring &assign(size_type n, char c)

Assign n copies of c to *this.

inline const ustring &assign(string_view str)

Assign a string_view to *this.

inline const ustring &operator=(const ustring &str)

Assign a ustring to another ustring.

inline const ustring &operator=(const char *str)

Assign a null-terminated C string (char *) to a ustring.

inline const ustring &operator=(const std::string &str)

Assign a C++ std::string to a ustring.

inline const ustring &operator=(string_view str)

Assign a string_view to a ustring.

inline const ustring &operator=(char c)

Assign a single char to a ustring.

inline const char *c_str() const noexcept

Return a C string representation of a ustring.

inline const char *data() const noexcept

Return a C string representation of a ustring.

inline const std::string &string() const noexcept

Return a C++ std::string representation of a ustring.

inline void clear(void) noexcept

Reset to an empty string.

inline size_t length(void) const noexcept

Return the number of characters in the string.

inline size_t hash(void) const noexcept

Return a hashed version of the string.

inline size_t size(void) const noexcept

Return the number of characters in the string.

inline bool empty(void) const noexcept

Is the string empty i.e., is it nullptr or does it point to an empty string?

inline const_iterator begin() const noexcept

Return a const_iterator that references the first character of the string.

inline const_iterator end() const noexcept

Return a const_iterator that references the end of a traversal of the characters of the string.

inline const_reverse_iterator rbegin() const noexcept

Return a const_reverse_iterator that references the last character of the string.

inline const_reverse_iterator rend() const noexcept

Return a const_reverse_iterator that references the end of a reverse traversal of the characters of the string.

inline const_reference operator[](size_type pos) const noexcept

Return a reference to the character at the given position. Note that it’s up to the caller to be sure pos is within the size of the string.

inline size_type copy(char *s, size_type n, size_type pos = 0) const

Dump into character array s the characters of this ustring, beginning with position pos and copying at most n characters.

inline ustring substr(size_type pos = 0, size_type n = npos) const

Returns a substring of the ustring object consisting of n characters starting at position pos.

inline int compare(string_view str) const noexcept

Return 0 if *this is lexicographically equal to str, -1 if *this is lexicographically earlier than str, 1 if *this is lexicographically after str.

inline int compare(const char *str) const noexcept

Return 0 if *this is lexicographically equal to str, -1 if *this is lexicographically earlier than str, 1 if *this is lexicographically after str.

inline bool operator==(const ustring &str) const noexcept

Test two ustrings for equality are they comprised of the same sequence of characters. Note that because ustrings are unique, this is a trivial pointer comparison, not a char-by-char loop as would be the case with a char* or a std::string.

inline bool operator!=(const ustring &str) const noexcept

Test two ustrings for inequality are they comprised of different sequences of characters. Note that because ustrings are unique, this is a trivial pointer comparison, not a char-by-char loop as would be the case with a char* or a std::string.

inline bool operator==(const std::string &x) const noexcept

Test a ustring (*this) for lexicographic equality with std::string x.

inline bool operator==(string_view x) const noexcept

Test a ustring (*this) for lexicographic equality with string_view x.

inline bool operator==(const char *x) const noexcept

Test a ustring (this) for lexicographic equality with char x.

inline bool operator!=(const std::string &x) const noexcept

Test a ustring (*this) for lexicographic inequality with std::string x.

inline bool operator!=(string_view x) const noexcept

Test a ustring (*this) for lexicographic inequality with string_view x.

inline bool operator!=(const char *x) const noexcept

Test a ustring (this) for lexicographic inequality with char x.

inline bool operator<(const ustring &x) const noexcept

Test for lexicographic ‘less’, comes in handy for lots of STL containers and algorithms.

Public Static Functions

template<typename ...Args>
static inline ustring sprintf(const char *fmt, const Args&... args)

Construct a ustring in a printf-like fashion. In other words, something like: ustring s = ustring::sprintf(“blah %d %g”, (int)foo, (float)bar); The argument list is fully typesafe. The formatting of the string will always use the classic “C” locale conventions (in particular, ‘.’ as decimal separator for float values).

template<typename ...Args>
static inline ustring fmtformat(const char *fmt, const Args&... args)

Construct a ustring in a fmt::format-like fashion. In other words, something like: ustring s = ustring::fmtformat(“blah {} {}”, (int)foo, (float)bar); The argument list is fully typesafe. The formatting of the string will always use the classic “C” locale conventions (in particular, ‘.’ as decimal separator for float values).

template<typename ...Args>
static inline ustring format(const char *fmt, const Args&... args)

NOTE: Semi-DEPRECATED! This will someday switch to behave like fmt::format (or future std::format) but for now, it is back compatible and equivalent to sprintf.

static ustring concat(string_view s, string_view t)

Concatenate two strings, returning a ustring, implemented carefully to not perform any redundant copies or allocations. This is semantically equivalent to ustring::sprintf("%s%s", s, t), but is more efficient.

static std::string getstats(bool verbose = true)

Return the statistics output as a string.

static size_t memory()

Return the amount of memory consumed by the ustring table.

static size_t total_ustrings()

Return the total number of ustrings in the internal table.

static size_t hash_collisions(std::vector<ustring> *collisions = nullptr)

Return the total number ustrings that have the exact hash as another ustring. If collisions is passed, store all the colliding ustrings in the vector.

static const char *make_unique(string_view str)

Given a string_view, return a pointer to the unique version kept in the internal table (creating a new table entry if we haven’t seen this sequence of characters before). N.B.: this is equivalent to ustring(str).c_str(). It’s also the routine that is used directly by ustring’s internals to generate the canonical unique copy of the characters.

static inline bool is_unique(const char *str)

Is this character pointer a unique ustring representation of those characters? Useful for diagnostics and debugging.

static inline ustring from_unique(const char *unique)

Create a ustring from characters guaranteed to already be ustring-clean, without having to run through the hash yet again. Use with extreme caution!!!

Friends

inline friend friend int compare (const std::string &a, const ustring &b) noexcept

Return 0 if a is lexicographically equal to b, -1 if a is lexicographically earlier than b, 1 if a is lexicographically after b.

inline friend friend bool operator== (const std::string &a, const ustring &b) noexcept

Test for lexicographic equality between std::string a and ustring b.

inline friend friend bool operator== (string_view a, const ustring &b) noexcept

Test for lexicographic equality between string_view a and ustring b.

inline friend friend bool operator== (const char *a, const ustring &b) noexcept

Test for lexicographic equality between char* a and ustring b.

inline friend friend bool operator!= (const std::string &a, const ustring &b) noexcept

Test for lexicographic inequality between std::string a and ustring b.

inline friend friend bool operator!= (string_view a, const ustring &b) noexcept

Test for lexicographic inequality between string_view a and ustring b.

inline friend friend bool operator!= (const char *a, const ustring &b) noexcept

Test for lexicographic inequality between char* a and ustring b.

inline friend friend std::ostream & operator<< (std::ostream &out, const ustring &str)

Generic stream output of a ustring.

struct TableRep

Non-owning array views: span / cspan

template<typename T, oiio_span_size_type Extent = dynamic_extent>
class OIIO::span

span<T> is a non-owning, non-copying, non-allocating reference to a contiguous array of T objects known length. A ‘span` encapsulates both a pointer and a length, and thus is a safer way of passing pointers around (because the function called knows how long the array is). A function that might ordinarily take a T* and a length could instead just take a span<T>.

A span<T> is mutable (the values in the array may be modified). A non-mutable (i.e., read-only) reference would be span<const T>. Thus, a function that might ordinarily take a const T* and a length could instead take a span<const T>.

For convenience, we also define cspan<T> as equivalent to span<const T>.

A span may be initialized explicitly from a pointer and length, by initializing with a std::vector<T>, or by initalizing with a constant (treated as an array of length 1). For all of these cases, no extra allocations are performed, and no extra copies of the array contents are made.

Important caveat: The span merely refers to items owned by another array, so the span should not be used beyond the lifetime of the array it refers to. Thus, span is great for parameter passing, but it’s not a good idea to use a span to store values in a data structure (unless you are really sure you know what you’re doing).

Public Functions

inline constexpr span() noexcept

Default constructor the span points to nothing.

template<class U, oiio_span_size_type N>
inline constexpr span(const span<U, N> &copy) noexcept

Copy constructor (copies the span pointer and length, NOT the data).

constexpr span(const span &copy) noexcept = default

Copy constructor (copies the span pointer and length, NOT the data).

inline constexpr span(pointer data, size_type size) noexcept

Construct from T* and length.

inline constexpr span(pointer b, pointer e) noexcept

Construct from begin and end pointers.

inline constexpr span(T &data)

Construct from a single T&.

template<size_t N>
inline constexpr span(T (&data)[N])

Construct from a fixed-length C array. Template magic automatically finds the length from the declared type of the array.

template<class Allocator>
inline constexpr span(std::vector<T, Allocator> &v)

Construct from std::vector<T>.

template<class Allocator>
inline span(const std::vector<value_type, Allocator> &v)

Construct from const std::vector<T>. This turns const std::vector<T> into a span<const T> (the span isn’t const, but the data it points to will be).

template<size_t N>
inline constexpr span(std::array<value_type, N> &arr)

Construct from mutable element std::array.

template<size_t N>
inline constexpr span(const std::array<value_type, N> &arr)

Construct from read-only element std::array.

inline constexpr span(std::initializer_list<T> il)

Construct an span from an initializer_list.

inline span &operator=(const span &copy)

Assignment copies the pointer and length, not the data.

template<size_type Count>
inline constexpr span<element_type, Count> first() const

Subview containing the first Count elements of the span.

template<size_type Count>
inline constexpr span<element_type, Count> last() const

Subview containing the last Count elements of the span.

Additionally, there is a convenience template:

template<typename T>
using cspan = span<const T>

cspan<T> is a synonym for a non-mutable span<const T>.


Rectangular region of interest: ROI

struct OIIO::ROI

ROI is a small helper struct describing a rectangular region of interest in an image. The region is [xbegin,xend) x [begin,yend) x [zbegin,zend), with the “end” designators signifying one past the last pixel in each dimension, a la STL style.

ROI data members

The data members are: 

int xbegin, xend, ybegin, yend, zbegin, zend;
int chbegin, chend;

These describe the spatial extent [xbegin,xend) x [ybegin,yend) x [zbegin,zend) And the channel extent: [chbegin,chend)]

Spatial size functions.

The width, height, and depth of the region.

inline constexpr int width() const noexcept

Height.

inline constexpr int height() const noexcept

Width.

inline constexpr int depth() const noexcept

Depth.

Public Functions

inline constexpr ROI() noexcept

Default constructor is an undefined region. Note that this is also interpreted as All().

inline constexpr ROI(int xbegin, int xend, int ybegin, int yend, int zbegin = 0, int zend = 1, int chbegin = 0, int chend = 10000) noexcept

Constructor with an explicitly defined region.

inline constexpr bool defined() const noexcept

Is a region defined?

inline constexpr int nchannels() const noexcept

Number of channels in the region. Beware this defaults to a huge number, and to be meaningful you must consider std::min (imagebuf.nchannels(), roi.nchannels()).

inline constexpr imagesize_t npixels() const noexcept

Total number of pixels in the region.

inline constexpr bool contains(int x, int y, int z = 0, int ch = 0) const noexcept

Test if the coordinate is within the ROI.

inline constexpr bool contains(const ROI &other) const noexcept

Test if another ROI is entirely within our ROI.

Public Static Functions

static inline constexpr ROI All() noexcept

All() is an alias for the default constructor, which indicates that it means “all” of the image, or no region restriction. For example, float myfunc (ImageBuf &buf, ROI roi = ROI::All()); Note that this is equivalent to: float myfunc (ImageBuf &buf, ROI roi = {});

Friends

inline friend friend constexpr bool operator== (const ROI &a, const ROI &b) noexcept

Test equality of two ROIs.

inline friend friend constexpr bool operator!= (const ROI &a, const ROI &b) noexcept

Test inequality of two ROIs.

inline friend friend std::ostream & operator<< (std::ostream &out, const ROI &roi)

Stream output of the range.

In addition, there are several related helper functions that involve ROI:

inline constexpr ROI OIIO::roi_union(const ROI &A, const ROI &B) noexcept

Union of two regions, the smallest region containing both.

inline constexpr ROI OIIO::roi_intersection(const ROI &A, const ROI &B) noexcept

Intersection of two regions.

ROI get_roi(const ImageSpec &spec)
ROI get_roi_full(const ImageSpec &spec)

Return the ROI describing spec’s pixel data window (the x, y, z, width, height, depth fields) or the full (display) window (the full_x, full_y, full_z, full_width, full_height, full_depth fields), respectively.

void set_roi(const ImageSpec &spec, const ROI &newroi)
void set_roi_full(const ImageSpec &spec, const ROI &newroi)

Alters the spec so to make its pixel data window or the full (display) window match newroi.

Image Specification: ImageSpec

An ImageSpec is a structure that describes the complete format specification of a single image. It contains:

  • The image resolution (number of pixels) and origin. This specifies what is often called the “pixel data window.”

  • The full size and offset of an abstract “full” or “display” window. Differing full and data windows can indicate that the pixels are a crop region or a larger image, or contain overscan pixels.

  • Whether the image is organized into tiles, and if so, the tile size.

  • The native data format of the pixel values (e.g., float, 8-bit integer, etc.).

  • The number of color channels in the image (e.g., 3 for RGB images), names of the channels, and whether any particular channels represent alpha and depth.

  • A user-extensible (and format-extensible) list of any other arbitrarily-named and -typed data that may help describe the image or its disk representation.

The remainder of this section describes the C++ API for ImageSpec. See Section ImageSpec for the corresponding Python bindings.

class OIIO::ImageSpec

ImageSpec describes the data format of an image dimensions, layout, number and meanings of image channels.

The width, height, depth are the size of the data of this image, i.e., the number of pixels in each dimension. A depth greater than 1 indicates a 3D “volumetric” image. The x, y, z fields indicate the origin of the pixel data of the image. These default to (0,0,0), but setting them differently may indicate that this image is offset from the usual origin. Therefore the pixel data are defined over pixel coordinates [x … x+width-1] horizontally, [y … y+height-1] vertically, and [z … z+depth-1] in depth.

The analogous full_width, full_height, full_depth and full_x, full_y, full_z fields define a “full” or “display” image window over the region [full_x … full_x+full_width-1] horizontally, [full_y … full_y+full_height-1] vertically, and [full_z… full_z+full_depth-1] in depth.

Having the full display window different from the pixel data window can be helpful in cases where you want to indicate that your image is a crop window of a larger image (if the pixel data window is a subset of the full display window), or that the pixels include overscan (if the pixel data is a superset of the full display window), or may simply indicate how different non-overlapping images piece together.

For tiled images, tile_width, tile_height, and tile_depth specify that the image is stored in a file organized into rectangular tiles of these dimensions. The default of 0 value for these fields indicates that the image is stored in scanline order, rather than as tiles.

ImageSpec data members

The ImageSpec contains data fields for the values that are required to describe nearly any image, and an extensible list of arbitrary attributes that can hold metadata that may be user-defined or specific to individual file formats.

Here are the hard-coded data fields:

int x

origin (upper left corner) of pixel data

int y

origin (upper left corner) of pixel data

int z

origin (upper left corner) of pixel data

int width

width of the pixel data window

int height

height of the pixel data window

int depth

depth of pixel data, >1 indicates a “volume”

int full_x

origin of the full (display) window

int full_y

origin of the full (display) window

int full_z

origin of the full (display) window

int full_width

width of the full (display) window

int full_height

height of the full (display) window

int full_depth

depth of the full (display) window

int tile_width

tile width (0 for a non-tiled image)

int tile_height

tile height (0 for a non-tiled image)

int tile_depth

tile depth (0 for a non-tiled image, 1 for a non-volume image)

int nchannels

number of image channels, e.g., 4 for RGBA

TypeDesc format

Data format of the channels. Describes the native format of the pixel data values themselves, as a TypeDesc. Typical values would be TypeDesc::UINT8 for 8-bit unsigned values, TypeDesc::FLOAT for 32-bit floating-point values, etc.

std::vector<TypeDesc> channelformats

Optional per-channel data formats. If all channels of the image have the same data format, that will be described by format and channelformats will be empty (zero length). If there are different data formats for each channel, they will be described in the channelformats vector, and the format field will indicate a single default data format for applications that don’t wish to support per-channel formats (usually this will be the format of the channel that has the most precision).

std::vector<std::string> channelnames

The names of each channel, in order. Typically this will be “R”, “G”, “B”, “A” (alpha), “Z” (depth), or other arbitrary names.

int alpha_channel

The index of the channel that represents alpha (pixel coverage and/or transparency). It defaults to -1 if no alpha channel is present, or if it is not known which channel represents alpha.

int z_channel

The index of the channel that represents z or depth (from the camera). It defaults to -1 if no depth channel is present, or if it is not know which channel represents depth.

bool deep

True if the image contains deep data. If true, this indicates that the image describes contains “deep” data consisting of multiple samples per pixel. If false, it’s an ordinary image with one data value (per channel) per pixel.

ParamValueList extra_attribs

A list of arbitrarily-named and arbitrarily-typed additional attributes of the image, for any metadata not described by the hard-coded fields described above. This list may be manipulated with the attribute() and find_attribute() methods.

Public Functions

ImageSpec(TypeDesc format = TypeDesc::UNKNOWN) noexcept

Constructor: given just the data format, set all other fields to something reasonable.

inline ImageSpec(string_view format) noexcept

Constructor: given just the data format (as any type name recognized by the TypeDesc constructor), set all other fields to something reasonable.

ImageSpec(int xres, int yres, int nchans, TypeDesc fmt = TypeUInt8) noexcept

Constructs an ImageSpec with the given x and y resolution, number of channels, and pixel data format.

All other fields are set to the obvious defaults the image is an ordinary 2D image (not a volume), the image is not offset or a crop of a bigger image, the image is scanline-oriented (not tiled), channel names are “R”, “G”, “B”’ and “A” (up to and including 4 channels, beyond that they are named “channel *n*”), the fourth channel (if it exists) is assumed to be alpha.

inline ImageSpec(int xres, int yres, int nchans, string_view fmt) noexcept

Construct an ImageSpec with the given x and y resolution, number of channels, and pixel data format name (as any type name recognized by the TypeDesc constructor).

explicit ImageSpec(const ROI &roi, TypeDesc fmt = TypeUInt8) noexcept

Construct an ImageSpec whose dimensions (both data and “full”) and number of channels are given by the ROI, pixel data type by fmt, and other fields are set to their default values.

inline explicit ImageSpec(const ROI &roi, string_view fmt) noexcept

Construct an ImageSpec from an ROI giving dimensions, and the name of a data type that will be recognized by the TypeDesc constructor.

void set_format(TypeDesc fmt) noexcept

Set the data format, and clear any per-channel format information in channelformats.

inline void set_format(string_view fmt) noexcept

Set the data format, and clear any per-channel format information in channelformats. The fmt may be a string such as "uint8", or any other type name recognized by the TypeDesc constructor.

void default_channel_names() noexcept

Sets the channelnames to reasonable defaults for the number of channels. Specifically, channel names are set to “R”, “G”, “B,” and “A” (up to and including 4 channels, beyond that they are named “channel*n*”.

inline size_t channel_bytes() const noexcept

Returns the number of bytes comprising each channel of each pixel (i.e., the size of a single value of the type described by the format field).

size_t channel_bytes(int chan, bool native = false) const noexcept

Return the number of bytes needed for the single specified channel. If native is false (default), compute the size of one channel of this->format, but if native is true, compute the size of the channel in terms of the “native” data format of that channel as stored in the file.

size_t pixel_bytes(bool native = false) const noexcept

Return the number of bytes for each pixel (counting all channels). If native is false (default), assume all channels are in this->format, but if native is true, compute the size of a pixel in the “native” data format of the file (these may differ in the case of per-channel formats).

size_t pixel_bytes(int chbegin, int chend, bool native = false) const noexcept

Return the number of bytes for just the subset of channels in each pixel described by [chbegin,chend). If native is false (default), assume all channels are in this->format, but if native is true, compute the size of a pixel in the “native” data format of the file (these may differ in the case of per-channel formats).

imagesize_t scanline_bytes(bool native = false) const noexcept

Returns the number of bytes comprising each scanline, i.e., pixel_bytes(native) * width This will return std::numeric_limits<imagesize_t>max() in the event of an overflow where it’s not representable in an imagesize_t.

imagesize_t tile_pixels() const noexcept

Return the number of pixels comprising a tile (or 0 if it is not a tiled image). This will return std::numeric_limits<imagesize_t>max() in the event of an overflow where it’s not representable in an imagesize_t.

imagesize_t tile_bytes(bool native = false) const noexcept

Returns the number of bytes comprising an image tile, i.e., pixel_bytes(native) * tile_width * tile_height * tile_depth If native is false (default), assume all channels are in this->format, but if native is true, compute the size of a pixel in the “native” data format of the file (these may differ in the case of per-channel formats).

imagesize_t image_pixels() const noexcept

Return the number of pixels for an entire image. This will return std::numeric_limits<imagesize_t>max() in the event of an overflow where it’s not representable in an imagesize_t.

imagesize_t image_bytes(bool native = false) const noexcept

Returns the number of bytes comprising an entire image of these dimensions, i.e., pixel_bytes(native) * width * height * depth This will return std::numeric_limits<image size_t>max() in the event of an overflow where it’s not representable in an imagesize_t. If native is false (default), assume all channels are in this->format, but if native is true, compute the size of a pixel in the “native” data format of the file (these may differ in the case of per-channel formats).

inline bool size_t_safe() const noexcept

Verify that on this platform, a size_t is big enough to hold the number of bytes (and pixels) in a scanline, a tile, and the whole image. If this returns false, the image is much too big to allocate and read all at once, so client apps beware and check these routines for overflows!

void attribute(string_view name, TypeDesc type, const void *value)

Add a metadata attribute to extra_attribs, with the given name and data type. The value pointer specifies the address of the data to be copied.

inline void attribute(string_view name, unsigned int value)

Add an unsigned int attribute to extra_attribs.

inline void attribute(string_view name, int value)

Add an int attribute to extra_attribs.

inline void attribute(string_view name, float value)

Add a float attribute to extra_attribs.

inline void attribute(string_view name, string_view value)

Add a string attribute to extra_attribs.

void attribute(string_view name, TypeDesc type, string_view value)

Parse a string containing a textual representation of a value of the given type, and add that as an attribute to extra_attribs. Example: 

spec.attribute ("temperature", TypeString, "-273.15");

void erase_attribute(string_view name, TypeDesc searchtype = TypeDesc::UNKNOWN, bool casesensitive = false)

Searches extra_attribs for any attributes matching name (as a regular expression), removing them entirely from extra_attribs. If searchtype is anything other than TypeDesc::UNKNOWN, matches will be restricted only to attributes with the given type. The name comparison will be case-sensitive if casesensitive is true, otherwise in a case-insensitive manner.

ParamValue *find_attribute(string_view name, TypeDesc searchtype = TypeDesc::UNKNOWN, bool casesensitive = false)

Searches extra_attribs for an attribute matching name, returning a pointer to the attribute record, or NULL if there was no match. If searchtype is anything other than TypeDesc::UNKNOWN, matches will be restricted only to attributes with the given type. The name comparison will be exact if casesensitive is true, otherwise in a case-insensitive manner if caseinsensitive is false.

const ParamValue *find_attribute(string_view name, ParamValue &tmpparam, TypeDesc searchtype = TypeDesc::UNKNOWN, bool casesensitive = false) const

Search for the named attribute and return the pointer to its ParamValue record, or NULL if not found. This variety of find_attribute(} can retrieve items such as “width”, which are data members of the ImageSpec, but not in extra_attribs. The tmpparam is a storage area owned by the caller, which is used as temporary buffer in cases where the information does not correspond to an actual extra_attribs (in this case, the return value will be &tmpparam). The extra names it understands are:

  • "x" "y" "z" "width" "height" "depth" "full_x" "full_y" "full_z" "full_width" "full_height" "full_depth"

    Returns the ImageSpec fields of those names (despite the fact that they are technically not arbitrary named attributes in extra_attribs). All are of type int.

  • "datawindow"

    Without a type, or if requested explicitly as an int[4], returns the OpenEXR-like pixel data min and max coordinates, as a 4-element integer array: { x, y, x+width-1, y+height-1 }. If instead you specifically request as an int[6], it will return the volumetric data window, { x, y, z, x+width-1, y+height-1, z+depth-1 }.

  • "displaywindow"

    Without a type, or if requested explicitly as an int[4], returns the OpenEXR-like pixel display min and max coordinates, as a 4-element integer array: { full_x, full_y, full_x+full_width-1, full_y+full_height-1 }. If instead you specifically request as an int[6], it will return the volumetric display window, { full_x, full_y, full_z, full_x+full_width-1, full_y+full_height-1, full_z+full_depth-1 }.

EXAMPLES 

ImageSpec spec;           // has the info
Imath::Box2i dw;          // we want the displaywindow here
ParamValue tmp;           // so we can retrieve pseudo-values
TypeDesc int4("int[4]");  // Equivalent: TypeDesc int4(TypeDesc::INT,4);
const ParamValue* p = spec.find_attribute ("displaywindow", int4);
if (p)
    dw = Imath::Box2i(p->get<int>(0), p->get<int>(1),
                      p->get<int>(2), p->get<int>(3));

p = spec.find_attribute("temperature", TypeFloat);
if (p)
    float temperature = p->get<float>();

TypeDesc getattributetype(string_view name, bool casesensitive = false) const

If the named attribute can be found in the ImageSpec, return its data type. If no such attribute exists, return TypeUnknown.

This was added in version 2.1.

bool getattribute(string_view name, TypeDesc type, void *value, bool casesensitive = false) const

If the ImageSpec contains the named attribute and its type matches type, copy the attribute value into the memory pointed to by val (it is up to the caller to ensure there is enough space) and return true. If no such attribute is found, or if it doesn’t match the type, return false and do not modify val.

EXAMPLES: 

ImageSpec spec;
...
// Retrieving an integer attribute:
int orientation = 0;
spec.getattribute ("orientation", TypeInt, &orientation);

// Retrieving a string attribute with a char*:
const char* compression = nullptr;
spec.getattribute ("compression", TypeString, &compression);

// Alternately, retrieving a string with a ustring:
ustring compression;
spec.getattribute ("compression", TypeString, &compression);

Note that when passing a string, you need to pass a pointer to the char*, not a pointer to the first character. Also, the char* will end up pointing to characters owned by the ImageSpec; the caller does not need to ever free the memory that contains the characters.

This was added in version 2.1.

int get_int_attribute(string_view name, int defaultval = 0) const

Retrieve the named metadata attribute and return its value as an int. Any integer type will convert to int by truncation or expansion, string data will parsed into an int if its contents consist of of the text representation of one integer. Floating point data will not succeed in converting to an int. If no such metadata exists, or are of a type that cannot be converted, the defaultval will be returned.

float get_float_attribute(string_view name, float defaultval = 0) const

Retrieve the named metadata attribute and return its value as a float. Any integer or floating point type will convert to float in the obvious way (like a C cast), and so will string metadata if its contents consist of of the text representation of one floating point value. If no such metadata exists, or are of a type that cannot be converted, the defaultval will be returned.

string_view get_string_attribute(string_view name, string_view defaultval = string_view()) const

Retrieve any metadata attribute, converted to a string. If no such metadata exists, the defaultval will be returned.

std::string serialize(SerialFormat format, SerialVerbose verbose = SerialDetailed) const

Returns, as a string, a serialized version of the ImageSpec. The format may be either ImageSpec::SerialText or ImageSpec::SerialXML. The verbose argument may be one of: ImageSpec::SerialBrief (just resolution and other vital statistics, one line for SerialText, ImageSpec::SerialDetailed (contains all metadata in original form), or ImageSpec::SerialDetailedHuman (contains all metadata, in many cases with human-readable explanation).

std::string to_xml() const

Converts the contents of the ImageSpec as an XML string.

void from_xml(const char *xml)

Populates the fields of the ImageSpec based on the XML passed in.

std::pair<string_view, int> decode_compression_metadata(string_view defaultcomp = "", int defaultqual = -1) const

Hunt for the “Compression” and “CompressionQuality” settings in the spec and turn them into the compression name and quality. This handles compression name/qual combos of the form “name:quality”.

inline bool valid_tile_range(int xbegin, int xend, int ybegin, int yend, int zbegin, int zend) noexcept

Helper function to verify that the given pixel range exactly covers a set of tiles. Also returns false if the spec indicates that the image isn’t tiled at all.

inline TypeDesc channelformat(int chan) const

Return the channelformat of the given channel. This is safe even if channelformats is not filled out.

inline string_view channel_name(int chan) const

Return the channel name of the given channel. This is safe even if channelnames is not filled out.

inline void get_channelformats(std::vector<TypeDesc> &formats) const

Fill in an array of channel formats describing all channels in the image. (Note that this differs slightly from the member data channelformats, which is empty if there are not separate per-channel formats.)

int channelindex(string_view name) const

Return the index of the channel with the given name, or -1 if no such channel is present in channelnames.

inline ROI roi() const noexcept

Return pixel data window for this ImageSpec expressed as a ROI.

inline ROI roi_full() const noexcept

Return full/display window for this ImageSpec expressed as a ROI.

inline void set_roi(const ROI &r) noexcept

Set pixel data window parameters (x, y, z, width, height, depth) for this ImageSpec from an ROI. Does NOT change the channels of the spec, regardless of r.

inline void set_roi_full(const ROI &r) noexcept

Set full/display window parameters (full_x, full_y, full_z, full_width, full_height, full_depth) for this ImageSpec from an ROI. Does NOT change the channels of the spec, regardless of r.

inline void copy_dimensions(const ImageSpec &other)

Copy from other the image dimensions (x, y, z, width, height, depth, full*, nchannels, format) and data types. It does not copy arbitrary named metadata or channel names (thus, for an ImageSpec with lots of metadata, it is much less expensive than copying the whole thing with operator=()).

inline bool undefined() const noexcept

Returns true for a newly initialized (undefined) ImageSpec. (Designated by no channels and undefined data type true of the uninitialized state of an ImageSpec, and presumably not for any ImageSpec that is useful or purposefully made.)

inline AttrDelegate<ImageSpec> operator[](string_view name)

Array indexing by string will create an AttrDelegate that enables a convenient shorthand for adding and retrieving values from the spec:

  1. Assigning to the delegate adds a metadata attribute: 

    ImageSpec spec;
spec["foo"] = 42;                   // int
spec["pi"] = float(M_PI);           // float
spec["oiio:ColorSpace"] = "sRGB";   // string
spec["cameratoworld"] = Imath::Matrix44(...);  // matrix

    Be very careful, the attribute’s type will be implied by the C++ type of what you assign.

  2. String data may be retrieved directly, and for other types, the delegate supports a get<T>() that retrieves an item of type T: 

     std::string colorspace = spec["oiio:ColorSpace"];
 int dither = spec["oiio:dither"].get<int>();

This was added in version 2.1.

Public Static Functions

static inline void auto_stride(stride_t &xstride, stride_t &ystride, stride_t &zstride, stride_t channelsize, int nchannels, int width, int height) noexcept

Adjust the stride values, if set to AutoStride, to be the right sizes for contiguous data with the given format, channels, width, height.

static inline void auto_stride(stride_t &xstride, stride_t &ystride, stride_t &zstride, TypeDesc format, int nchannels, int width, int height) noexcept

Adjust the stride values, if set to AutoStride, to be the right sizes for contiguous data with the given format, channels, width, height.

static inline void auto_stride(stride_t &xstride, TypeDesc format, int nchannels) noexcept

Adjust xstride, if set to AutoStride, to be the right size for contiguous data with the given format and channels.

static std::string metadata_val(const ParamValue &p, bool human = false)

For a given parameter p, format the value nicely as a string. If human is true, use especially human-readable explanations (units, or decoding of values) for certain known metadata.


“Deep” pixel data: DeepData

class OIIO::DeepData

A DeepData holds the contents of an image of ``deep’’ pixels (multiple depth samples per pixel).

Public Functions

DeepData()

Construct an empty DeepData.

DeepData(const ImageSpec &spec)

Construct and init from an ImageSpec.

DeepData(const DeepData &d)

Copy constructor.

const DeepData &operator=(const DeepData &d)

Copy assignment.

void clear()

Reset the DeepData to be equivalent to its empty initial state.

void free()

In addition to performing the tasks of clear(), also ensure that all allocated memory has been truly freed.

void init(int64_t npix, int nchan, cspan<TypeDesc> channeltypes, cspan<std::string> channelnames)

Initialize the DeepData with the specified number of pixels, channels, channel types, and channel names, and allocate memory for all the data.

void init(const ImageSpec &spec)

Initialize the DeepData based on the ImageSpec’s total number of pixels, number and types of channels. At this stage, all pixels are assumed to have 0 samples, and no sample data is allocated.

bool initialized() const

Is the DeepData initialized?

bool allocated() const

Has the DeepData fully allocated? If no, it is still very inexpensive to call set_capacity().

int64_t pixels() const

Retrieve the total number of pixels.

int channels() const

Retrieve the number of channels.

string_view channelname(int c) const

Return the name of channel c.

TypeDesc channeltype(int c) const

Retrieve the data type of channel c.

size_t channelsize(int c) const

Return the size (in bytes) of one sample datum of channel c.

size_t samplesize() const

Return the size (in bytes) for all channels of one sample.

int samples(int64_t pixel) const

Retrieve the number of samples for the given pixel index.

void set_samples(int64_t pixel, int samps)

Set the number of samples for the given pixel. This must be called after init().

void set_all_samples(cspan<unsigned int> samples)

Set the number of samples for all pixels. The samples.size() is required to match pixels().

void set_capacity(int64_t pixel, int samps)

Set the capacity of samples for the given pixel. This must be called after init().

int capacity(int64_t pixel) const

Retrieve the capacity (number of allocated samples) for the given pixel index.

void insert_samples(int64_t pixel, int samplepos, int n = 1)

Insert n samples of the specified pixel, betinning at the sample position index. After insertion, the new samples will have uninitialized values.

void erase_samples(int64_t pixel, int samplepos, int n = 1)

Erase n samples of the specified pixel, betinning at the sample position index.

float deep_value(int64_t pixel, int channel, int sample) const

Retrieve the value of the given pixel, channel, and sample index, cast to a float.

uint32_t deep_value_uint(int64_t pixel, int channel, int sample) const

Retrieve the value of the given pixel, channel, and sample index, cast to a uint32.

void set_deep_value(int64_t pixel, int channel, int sample, float value)

Set the value of the given pixel, channel, and sample index, for floating-point channels.

void set_deep_value(int64_t pixel, int channel, int sample, uint32_t value)

Set the value of the given pixel, channel, and sample index, for integer channels.

void *data_ptr(int64_t pixel, int channel, int sample)

Retrieve the pointer to a given pixel/channel/sample, or NULL if there are no samples for that pixel. Use with care, and note that calls to insert_samples and erase_samples can invalidate pointers returned by prior calls to data_ptr.

void get_pointers(std::vector<void*> &pointers) const

Fill in the vector with pointers to the start of the first channel for each pixel.

bool copy_deep_sample(int64_t pixel, int sample, const DeepData &src, int64_t srcpixel, int srcsample)

Copy a deep sample from src to this DeepData. They must have the same channel layout. Return true if ok, false if the operation could not be performed.

bool copy_deep_pixel(int64_t pixel, const DeepData &src, int64_t srcpixel)

Copy an entire deep pixel from src to this DeepData, completely replacing any pixel data for that pixel. They must have the same channel layout. Return true if ok, false if the operation could not be performed.

bool split(int64_t pixel, float depth)

Split all samples of that pixel at the given depth zsplit. Samples that span z (i.e. z < zsplit < zback) will be split into two samples with depth ranges [z,zsplit] and [zsplit,zback] with appropriate changes to their color and alpha values. Samples not spanning zsplit will remain intact. This operation will have no effect if there are not Z and Zback channels present. Return true if any splits occurred, false if the pixel was not modified.

void sort(int64_t pixel)

Sort the samples of the pixel by their Z depth.

void merge_overlaps(int64_t pixel)

Merge any adjacent samples in the pixel that exactly overlap in z range. This is only useful if the pixel has previously been split at all sample starts and ends, and sorted by Z. Note that this may change the number of samples in the pixel.

void merge_deep_pixels(int64_t pixel, const DeepData &src, int srcpixel)

Merge the samples of src’s pixel into this DeepData’s pixel. Return true if ok, false if the operation could not be performed.

float opaque_z(int64_t pixel) const

Return the z depth at which the pixel reaches full opacity.

void occlusion_cull(int64_t pixel)

Remove any samples hidden behind opaque samples.


Global Attributes

These helper functions are not part of any other OpenImageIO class, they just exist in the OpenImageIO namespace as general utilities. (See Miscellaneous Utilities for the corresponding Python bindings.)

bool OIIO::attribute(string_view name, TypeDesc type, const void *val)

OIIO::attribute() sets a global attribute (i.e., a property or option) of OpenImageIO. The name designates the name of the attribute, type describes the type of data, and val is a pointer to memory containing the new value for the attribute.

If the name is known, valid attribute that matches the type specified, the attribute will be set to the new value and attribute() will return true. If name is not recognized, or if the types do not match (e.g., type is TypeFloat but the named attribute is a string), the attribute will not be modified, and attribute() will return false.

The following are the recognized attributes:

  • string options

    This catch-all is simply a comma-separated list of name=value settings of named options, which will be parsed and individually set. For example, 

    OIIO::attribute ("options", "threads=4,log_times=1");

    Note that if an option takes a string value that must itself contain a comma, it is permissible to enclose the value in either ‘single’ or “double” quotes.

  • int threads

    How many threads to use for operations that can be sped up by being multithreaded. (Examples: simultaneous format conversions of multiple scanlines read together, or many ImageBufAlgo operations.) The default is 0, meaning to use the full available hardware concurrency detected.

    Situations where the main application logic is essentially single threaded (i.e., one top-level call into OIIO at a time) should leave this at the default value, or some reasonable number of cores, thus allowing lots of threads to fill the cores when OIIO has big tasks to complete. But situations where you have many threads at the application level, each of which is expected to be making separate OIIO calls simultaneously, should set this to 1, thus having each calling thread do its own work inside of OIIO rather than spawning new threads with a high overall “fan out.”

  • int exr_threads

    Sets the internal OpenEXR thread pool size. The default is to use as many threads as the amount of hardware concurrency detected. Note that this is separate from the OIIO "threads" attribute.

  • string font_searchpath

    Colon-separated (or semicolon-separated) list of directories to search if fonts are needed. (Such as for ImageBufAlgo::render_text().)

  • string plugin_searchpath

    Colon-separated (or semicolon-separated) list of directories to search for dynamically-loaded format plugins.

  • int try_all_readers

    When nonzero (the default), a call to ImageInput::create() or ImageInput::open() that does not succeed in opening the file with the format reader implied by the file extension will try all available format readers to see if one of them can open the file. If this is zero, the only reader that will be tried is the one implied by the file extension.

  • int read_chunk

    When performing a read_image(), this is the number of scanlines it will attempt to read at a time (some formats are more efficient when reading and decoding multiple scanlines). The default is 256. The special value of 0 indicates that it should try to read the whole image if possible.

  • float[] missingcolor, string missingcolor

    This attribute may either be an array of float values, or a string containing a comma-separated list of the values. Setting this option globally is equivalent to always passing an ImageInput open-with-configuration hint "oiio:missingcolor" with the value.

    When set, it gives some ImageInput readers the option of ignoring any missing tiles or scanlines in the file, and instead of treating the read failure of an individual tile as a full error, will interpret is as an intentionally missing tile and proceed by simply filling in the missing pixels with the color specified. If the first element is negative, it will use the absolute value, but draw alternating diagonal stripes of the color. For example, 

    float missing[4] = { -1.0, 0.0, 0.0, 0.0 }; // striped red
OIIO::attribute ("missingcolor", TypeDesc("float[4]"), &missing);

    Note that only some file formats support files with missing tiles or scanlines, and this is only taken as a hint. Please see chap-bundledplugins_ for details on which formats accept a "missingcolor" configuration hint.

  • int debug

    When nonzero, various debug messages may be printed. The default is 0 for release builds, 1 for DEBUG builds (values > 1 are for OIIO developers to print even more debugging information), This attribute but also may be overridden by the OPENIMAGEIO_DEBUG environment variable.

  • int tiff:half

    When nonzero, allows TIFF to write half pixel data. N.B. Most apps may not read these correctly, but OIIO will. That’s why the default is not to support it.

  • int openexr:core

    When nonzero, use the new “OpenEXR core C library” when available, for OpenEXR >= 3.1. This is experimental, and currently defaults to 0.

  • int limits:channels (1024)

    When nonzero, the maximum number of color channels in an image. Image files whose headers indicate they have more channels might be assumed to be corrupted or malicious files. In situations when more channels are expected to be encountered, the application should raise this limit. The default is 1024 channels.

  • int limits:imagesize_MB (32768)

    When nonzero, the maximum size in MB of the uncompressed pixel data of a single 2D image. Images whose headers indicate that they are larger than this might be assumed to be corrupted or malicious files. The default is 32768 (32 GB of uncompressed pixel data equivalent to 64k x 64k x 4 channel x half). In situations when images larger than this are expected to be encountered, you should raise this limit.

  • int log_times

    When the "log_times" attribute is nonzero, ImageBufAlgo functions are instrumented to record the number of times they were called and the total amount of time spent executing them. It can be overridden by environment variable OPENIMAGEIO_LOG_TIMES. The totals will be recorded and can be retrieved as a string by using OIIO::getattribute("timing_report", ...). Additionally, if the value is 2 or more, the timing report will be printed to stdout upon application exit (not advised in contexts where it isn’t ok to print to the terminal via stdout, such as GUI apps or libraries).

    When enabled, there is a slight runtime performance cost due to checking the time at the start and end of each of those function calls, and the locking and recording of the data structure that holds the log information. When the log_times attribute is disabled, there is no additional performance cost.

bool OIIO::attribute(string_view name, int val)
bool OIIO::attribute(string_view name, float val)
bool OIIO::attribute(string_view name, string_view val)

Shortcuts for setting an attribute to a single int, float, or string.

bool OIIO::getattribute(string_view name, TypeDesc type, void *val)

Get the named global attribute of OpenImageIO, store it in *val. Return true if found and it was compatible with the type specified, otherwise return false and do not modify the contents of *val. It is up to the caller to ensure that val points to the right kind and size of storage for the given type.

In addition to being able to retrieve all the attributes that are documented as settable by the OIIO::attribute() call, getattribute() can also retrieve the following read-only attributes:

  • string format_list

  • string input_format_list

  • string output_format_list

    A comma-separated list of all the names of, respectively, all supported image formats, all formats accepted as inputs, and all formats accepted as outputs.

  • string extension_list

    For each format, the format name, followed by a colon, followed by a comma-separated list of all extensions that are presumed to be used for that format. Semicolons separate the lists for formats. For example, 

     "tiff:tif;jpeg:jpg,jpeg;openexr:exr"

  • string library_list

    For each format that uses a dependent library, the format name, followed by a colon, followed by the name and version of the dependency. Semicolons separate the lists for formats. For example, 

     "tiff:LIBTIFF 4.0.4;gif:gif_lib 4.2.3;openexr:OpenEXR 2.2.0"

  • string “timing_report” A string containing the report of all the log_times.

  • string hw:simd

  • string oiio:simd (read-only)

    A comma-separated list of hardware CPU features for SIMD (and some other things). The "oiio:simd" attribute is similarly a list of which features this build of OIIO was compiled to support.

    This was added in OpenImageIO 1.8.

  • float resident_memory_used_MB

    This read-only attribute can be used for debugging purposes to report the approximate process memory used (resident) by the application, in MB.

  • string timing_report

    Retrieving this attribute returns the timing report generated by the log_timing attribute (if it was enabled). The report is sorted alphabetically and for each named instrumentation region, prints the number of times it executed, the total runtime, and the average per call, like this: 

    IBA::computePixelStats        2   2.69ms  (avg   1.34ms)
IBA::make_texture             1  74.05ms  (avg  74.05ms)
IBA::mul                      8   2.42ms  (avg   0.30ms)
IBA::over                    10  23.82ms  (avg   2.38ms)
IBA::resize                  20   0.24s   (avg  12.18ms)
IBA::zero                     8   0.66ms  (avg   0.08ms)

bool getattribute(string_view name, int &val)
bool getattribute(string_view name, float &val)
bool getattribute(string_view name, char **val)
bool getattribute(string_view name, std::string &val)

Specialized versions of getattribute() in which the data type is implied by the type of the argument (for single int, float, or string). Two string versions exist: one that retrieves it as a std::string and another that retrieves it as a char *. In all cases, the return value is true if the attribute is found and the requested data type conversion was legal.

EXAMPLES:

int threads;
OIIO::getattribute ("threads", &threads);
std::string path;
OIIO::getattribute ("plugin_searchpath", path);
int get_int_attribute(string_view name, int defaultvalue = 0)
float get_float_attribute(string_view name, float defaultvalue = 0)
string_view get_string_attribute(string_view name, string_view defaultvalue = "")

Specialized versions of getattribute() for common types, in which the data is returned directly, and a supplied default value is returned if the attribute was not found.

EXAMPLES:

int threads = OIIO::get_int_attribute ("threads", 0);
string_view path = OIIO::get_string_attribute ("plugin_searchpath");

Miscellaneous Utilities

These helper functions are not part of any other OpenImageIO class, they just exist in the OIIO namespace as general utilities. (See Miscellaneous Utilities for the corresponding Python bindings.)

int OIIO::openimageio_version()

Returns a numeric value for the version of OpenImageIO, 10000 for each major version, 100 for each minor version, 1 for each patch. For example, OpenImageIO 1.2.3 would return a value of 10203. One example of how this is useful is for plugins to query the version to be sure they are linked against an adequate version of the library.

bool OIIO::has_error()

Is there a pending global error message waiting to be retrieved?

std::string OIIO::geterror(bool clear = true)

Returns any error string describing what went wrong if ImageInput::create() or ImageOutput::create() failed (since in such cases, the ImageInput or ImageOutput itself does not exist to have its own geterror() function called). This function returns the last error for this particular thread, and clear the pending error message unless clear is false; separate threads will not clobber each other’s global error messages.

void OIIO::declare_imageio_format(const std::string &format_name, ImageInput::Creator input_creator, const char **input_extensions, ImageOutput::Creator output_creator, const char **output_extensions, const char *lib_version)

Register the input and output ‘create’ routines and list of file extensions for a particular format.

bool OIIO::is_imageio_format_name(string_view name)

Is name one of the known format names?

inline std::map<std::string, std::vector<std::string>> OIIO::get_extension_map()

Utility: Parse the “extension_list” attribute into a std::map string keys are the names of all the file formats OIIO knows how to read, and whose values are vectors of strings of the file extensions associated with the file format. (Added in OIIO 2.2.13.)


Environment variables

There are a few special environment variables that can be used to control OpenImageIO at times that it is not convenient to set options individually from inside the source code.

OPENIMAGEIO_FONTS

A searchpath for finding fonts (for example, when using by ImageBufAlgo::render_text or oiiotool --text). This may contain a list of directories separated by “:” or “;”.

OPENIMAGEIO_OPTIONS

Allows you to seed the global OpenImageIO-wide options.

The value of the environment variable should be a comma-separated list of name=value settings. If a value is a string that itself needs to contain commas, it may be enclosed in single or double quotes.

Upon startup, the contents of this environment variable will be passed to a call to:

OIIO::attribute ("options", value);

OPENIMAGEIO_IMAGECACHE_OPTIONS

Allows you to seed the options for any ImageCache created.

The value of the environment variable should be a comma-separated list of name=value settings. If a value is a string that itself needs to contain commas, it may be enclosed in single or double quotes.

Upon creation of any ImageCache, the contents of this environment variable will be passed to a call to:

imagecache->attribute ("options", value);

OPENIMAGEIO_TEXTURE_OPTIONS

Allows you to seed the options for any TextureSystem created.

The value of the environment variable should be a comma-separated list of name=value settings. If a value is a string that itself needs to contain commas, it may be enclosed in single or double quotes.

Upon creation of any TextureSystem, the contents of this environment variable will be passed to a call to:

texturesys->attribute ("options", value);

OPENIMAGEIO_THREADS, CUE_THREADS

Either of these sets the default number of threads that OpenImageIO will use for its thread pool. If both are set, OPENIMAGEIO_THREADS will take precedence. If neither is set, the default will be 0, which means to use as many threads as there are physical cores on the machine.

ImageOutput: Writing Images

Image Output Made Simple

Here is the simplest sequence required to write the pixels of a 2D image to a file:

#include <OpenImageIO/imageio.h>
using namespace OIIO;
...

const char *filename = "foo.jpg";
const int xres = 640, yres = 480;
const int channels = 3;  // RGB
unsigned char pixels[xres * yres * channels];

std::unique_ptr<ImageOutput> out = ImageOutput::create (filename);
if (! out)
    return;
ImageSpec spec (xres, yres, channels, TypeDesc::UINT8);
out->open (filename, spec);
out->write_image (TypeDesc::UINT8, pixels);
out->close ();

This little bit of code does a surprising amount of useful work:

  • Search for an ImageIO plugin that is capable of writing the file foo.jpg), deducing the format from the file extension. When it finds such a plugin, it creates a subclass instance of ImageOutput that writes the right kind of file format.

    std::unique_ptr<ImageOutput> out = ImageOutput::create (filename);

  • Open the file, write the correct headers, and in all other important ways prepare a file with the given dimensions (640 x 480), number of color channels (3), and data format (unsigned 8-bit integer).

    ImageSpec spec (xres, yres, channels, TypeDesc::UINT8);
out->open (filename, spec);

  • Write the entire image, hiding all details of the encoding of image data in the file, whether the file is scanline- or tile-based, or what is the native format of data in the file (in this case, our in-memory data is unsigned 8-bit and we’ve requested the same format for disk storage, but if they had been different, write_image() would do all the conversions for us).

    out->write_image (TypeDesc::UINT8, &pixels);

  • Close the file.

    out->close ();

What happens when the file format doesn’t support the spec?

The open() call will fail (returning an empty pointer and set an appropriate error message) if the output format cannot accommodate what is requested by the ImageSpec. This includes:

  • Dimensions (width, height, or number of channels) exceeding the limits supported by the file format. 1

  • Volumetric (depth > 1) if the format does not support volumetric data.

  • Tile size >1 if the format does not support tiles.

  • Multiple subimages or MIP levels if not supported by the format.

1

One exception to the rule about number of channels is that a file format that supports only RGB, but not alpha, is permitted to silently drop the alpha channel without considering that to be an error.

However, several other mismatches between requested ImageSpec and file format capabilities will be silently ignored, allowing open() to succeed:

  • If the pixel data format is not supported (for example, a request for half pixels when writing a JPEG/JFIF file), the format writer may substitute another data format (generally, whichever commonly-used data format supported by the file type will result in the least reduction of precision or range).

  • If the ImageSpec requests different per-channel data formats, but the format supports only a single format for all channels, it may just choose the most precise format requested and use it for all channels.

  • If the file format does not support arbitrarily-named channels, the channel names may be lost when saving the file.

  • Any other metadata in the ImageSpec may be summarily dropped if not supported by the file format.

Advanced Image Output

Let’s walk through many of the most common things you might want to do, but that are more complex than the simple example above.

Writing individual scanlines, tiles, and rectangles

The simple example of Section Image Output Made Simple wrote an entire image with one call. But sometimes you are generating output a little at a time and do not wish to retain the entire image in memory until it is time to write the file. OpenImageIO allows you to write images one scanline at a time, one tile at a time, or by individual rectangles.

Writing individual scanlines

Individual scanlines may be written using the writescanline() API call:

unsigned char scanline[xres*channels];
out->open (filename, spec);
int z = 0;   // Always zero for 2D images
for (int y = 0;  y < yres;  ++y) {
    ... generate data in scanline[0..xres*channels-1] ...
    out->write_scanline (y, z, TypeDesc::UINT8, scanline);
}
out->close ();

The first two arguments to writescanline() specify which scanline is being written by its vertical (y) scanline number (beginning with 0) and, for volume images, its slice (z) number (the slice number should be 0 for 2D non-volume images). This is followed by a TypeDesc describing the data you are supplying, and a pointer to the pixel data itself. Additional optional arguments describe the data stride, which can be ignored for contiguous data (use of strides is explained in Section Data Strides).

All ImageOutput implementations will accept scanlines in strict order (starting with scanline 0, then 1, up to yres-1, without skipping any). See Section Random access and repeated transmission of pixels for details on out-of-order or repeated scanlines.

The full description of the writescanline() function may be found in Section ImageOutput Class Reference.

Writing individual tiles

Not all image formats (and therefore not all ImageOutput implementations) support tiled images. If the format does not support tiles, then writetile() will fail. An application using OpenImageIO should gracefully handle the case that tiled output is not available for the chosen format.

Once you create() an ImageOutput, you can ask if it is capable of writing a tiled image by using the supports("tiles") query:

std::unique_ptr<ImageOutput> out = ImageOutput::create (filename);
if (! out->supports ("tiles")) {
    // Tiles are not supported
}

Assuming that the ImageOutput supports tiled images, you need to specifically request a tiled image when you open() the file. This is done by setting the tile size in the ImageSpec passed to open(). If the tile dimensions are not set, they will default to zero, which indicates that scanline output should be used rather than tiled output.

int tilesize = 64;
ImageSpec spec (xres, yres, channels, TypeDesc::UINT8);
spec.tile_width = tilesize;
spec.tile_height = tilesize;
out->open (filename, spec);

In this example, we have used square tiles (the same number of pixels horizontally and vertically), but this is not a requirement of OpenImageIO. However, it is possible that some image formats may only support square tiles, or only certain tile sizes (such as restricting tile sizes to powers of two). Such restrictions should be documented by each individual plugin.

unsigned char tile[tilesize*tilesize*channels];
int z = 0;   // Always zero for 2D images
for (int y = 0;  y < yres;  y += tilesize) {
    for (int x = 0;  x < xres;  x += tilesize) {
        ... generate data in tile[] ..
        out->write_tile (x, y, z, TypeDesc::UINT8, tile);
    }
}
out->close ();

The first three arguments to writetile() specify which tile is being written by the pixel coordinates of any pixel contained in the tile: x (column), y (scanline), and z (slice, which should always be 0 for 2D non-volume images). This is followed by a TypeDesc describing the data you are supplying, and a pointer to the tile’s pixel data itself, which should be ordered by increasing slice, increasing scanline within each slice, and increasing column within each scanline. Additional optional arguments describe the data stride, which can be ignored for contiguous data (use of strides is explained in Section Data Strides).

All ImageOutput implementations that support tiles will accept tiles in strict order of increasing y rows, and within each row, increasing x column, without missing any tiles. See

The full description of the writetile() function may be found in Section ImageOutput Class Reference.

Writing arbitrary rectangles

Some ImageOutput implementations — such as those implementing an interactive image display, but probably not any that are outputting directly to a file — may allow you to send arbitrary rectangular pixel regions. Once you create() an ImageOutput, you can ask if it is capable of accepting arbitrary rectangles by using the supports("rectangles") query:

std::unique_ptr<ImageOutput> out = ImageOutput::create (filename);
if (! out->supports ("rectangles")) {
    // Rectangles are not supported
}

If rectangular regions are supported, they may be sent using the write_rectangle() API call:

unsigned int rect[...];
// ... generate data in rect[] ...
out->write_rectangle (xbegin, xend, ybegin, yend, zbegin, zend,
                      TypeDesc::UINT8, rect);

The first six arguments to write_rectangle() specify the region of pixels that is being transmitted by supplying the minimum and one-past-maximum pixel indices in x (column), y (scanline), and z (slice, always 0 for 2D non-volume images).

Note

OpenImageIO nearly always follows the C++ STL convention of specifying ranges as the half-open interval [begin,end) specifying the sequence begin, begin+1, ..., end-1 (but the sequence does not contain the end value itself).

The total number of pixels being transmitted is therefore:

(xend - xbegin) * (yend - ybegin) * (zend - zbegin)

This is followed by a TypeDesc describing the data you are supplying, and a pointer to the rectangle’s pixel data itself, which should be ordered by increasing slice, increasing scanline within each slice, and increasing column within each scanline. Additional optional arguments describe the data stride, which can be ignored for contiguous data (use of strides is explained in Section Data Strides).

Converting pixel data types

The code examples of the previous sections all assumed that your internal pixel data is stored as unsigned 8-bit integers (i.e., 0-255 range). But OpenImageIO is significantly more flexible.

You may request that the output image pixels be stored in any of several data types. This is done by setting the format field of the ImageSpec prior to calling open. You can do this upon construction of the ImageSpec, as in the following example that requests a spec that stores pixel values as 16-bit unsigned integers:

ImageSpec spec (xres, yres, channels, TypeDesc::UINT16);

Or, for an ImageSpec that has already been constructed, you may reset its format using the set_format() method.

ImageSpec spec(...);
spec.set_format(TypeDesc::UINT16);

Note that resetting the pixel data type must be done before passing the spec to open(), or it will have no effect on the file.

Individual file formats, and therefore ImageOutput implementations, may only support a subset of the pixel data types understood by the OpenImageIO library. Each ImageOutput plugin implementation should document which data formats it supports. An individual ImageOutput implementation is expected to always succeed, but if the file format does not support the requested pixel data type, it is expected to choose a data type that is supported, usually the data type that best preserves the precision and range of the originally-requested data type.

The conversion from floating-point formats to integer formats (or from higher to lower integer, which is done by first converting to float) is always done by rescaling the value so that 0.0 maps to integer 0 and 1.0 to the maximum value representable by the integer type, then rounded to an integer value for final output. Here is the code that implements this transformation (T is the final output integer type):

float value = quant_max * input;
T output = (T) clamp ((int)(value + 0.5), quant_min, quant_max);

Quantization limits for each integer type is as follows:

Data Format

min

max

UINT8

0

255

INT8

-128

127

UINT16

0

65535

INT16

-32768

32767

UINT

0

4294967295

INT

-2147483648

2147483647

Note that the default is to use the entire positive range of each integer type to represent the floating-point (0.0 - 1.0) range. Floating-point types do not attempt to remap values, and do not clamp (except to their full floating-point range).

It is not required that the pixel data passed to writeimage(), writescanline(), writetile(), or write_rectangle() actually be in the same data type as that requested as the native pixel data type of the file. You can fully mix and match data you pass to the various “write” routines and OpenImageIO will automatically convert from the internal format to the native file format. For example, the following code will open a TIFF file that stores pixel data as 16-bit unsigned integers (values ranging from 0 to 65535), compute internal pixel values as floating-point values, with writeimage() performing the conversion automatically:

std::unique_ptr<ImageOutput> out = ImageOutput::create ("myfile.tif");
ImageSpec spec (xres, yres, channels, TypeDesc::UINT16);
out->open (filename, spec);
...
float pixels [xres*yres*channels];
...
out->write_image (TypeDesc::FLOAT, pixels);

Note that writescanline(), writetile(), and write_rectangle() have a parameter that works in a corresponding manner.

Data Strides

In the preceeding examples, we have assumed that the block of data being passed to the “write” functions are contiguous, that is:

  • each pixel in memory consists of a number of data values equal to the declared number of channels that are being written to the file;

  • successive column pixels within a row directly follow each other in memory, with the first channel of pixel x immediately following last channel of pixel x-1 of the same row;

  • for whole images, tiles or rectangles, the data for each row immediately follows the previous one in memory (the first pixel of row y immediately follows the last column of row y-1);

  • for 3D volumetric images, the first pixel of slice z immediately follows the last pixel of of slice z-1.

Please note that this implies that data passed to writetile() be contiguous in the shape of a single tile (not just an offset into a whole image worth of pixels), and that data passed to write_rectangle() be contiguous in the dimensions of the rectangle.

The writescanline() function takes an optional xstride argument, and the writeimage(), writetile(), and write_rectangle() functions take optional xstride, ystride, and zstride values that describe the distance, in bytes, between successive pixel columns, rows, and slices, respectively, of the data you are passing. For any of these values that are not supplied, or are given as the special constant AutoStride, contiguity will be assumed.

By passing different stride values, you can achieve some surprisingly flexible functionality. A few representative examples follow:

  • Flip an image vertically upon writing, by using negative y stride:

    unsigned char pixels[xres*yres*channels];
int scanlinesize = xres * channels * sizeof(pixels[0]);
...
out->write_image (TypeDesc::UINT8,
                  (char *)pixels+(yres-1)*scanlinesize, // offset to last
                  AutoStride,                  // default x stride
                  -scanlinesize,               // special y stride
                  AutoStride);                 // default z stride

  • Write a tile that is embedded within a whole image of pixel data, rather than having a one-tile-only memory layout:

    unsigned char pixels[xres*yres*channels];
int pixelsize = channels * sizeof(pixels[0]);
int scanlinesize = xres * pixelsize;
...
out->write_tile (x, y, 0, TypeDesc::UINT8,
                 (char *)pixels + y*scanlinesize + x*pixelsize,
                 pixelsize,
                 scanlinesize);

  • Write only a subset of channels to disk. In this example, our internal data layout consists of 4 channels, but we write just channel 3 to disk as a one-channel image:

    // In-memory representation is 4 channel
const int xres = 640, yres = 480;
const int channels = 4;  // RGBA
const int channelsize = sizeof(unsigned char);
unsigned char pixels[xres*yres*channels];

// File representation is 1 channel
std::unique_ptr<ImageOutput> out = ImageOutput::create (filename);
ImageSpec spec (xres, yres, 1, TypeDesc::UINT8);
out->open (filename, spec);

// Use strides to write out a one-channel "slice" of the image
out->write_image (TypeDesc::UINT8,
                  (char *)pixels+3*channelsize, // offset to chan 3
                  channels*channelsize,         // 4 channel x stride
                  AutoStride,                   // default y stride
                  AutoStride);                  // default z stride
...

Please consult Section ImageOutput Class Reference for detailed descriptions of the stride parameters to each “write” function.

Writing a crop window or overscan region

The ImageSpec fields width, height, and depth describe the dimensions of the actual pixel data.

At times, it may be useful to also describe an abstract full or display image window, whose position and size may not correspond exactly to the data pixels. For example, a pixel data window that is a subset of the full display window might indicate a crop window; a pixel data window that is a superset of the full display window might indicate overscan regions (pixels defined outside the eventual viewport).

The ImageSpec fields full_width, full_height, and full_depth describe the dimensions of the full display window, and full_x, full_y, full_z describe its origin (upper left corner). The fields x, y, z describe the origin (upper left corner) of the pixel data.

These fields collectively describe an abstract full display image ranging from [full_x … full_x+full_width-1] horizontally, [full_y … full_y+full_height-1] vertically, and [full_z … full_z+full_depth-1] in depth (if it is a 3D volume), and actual pixel data over the pixel coordinate range [x … x+width-1] horizontally, [y … y+height-1] vertically, and [z … z+depth-1] in depth (if it is a volume).

Not all image file formats have a way to describe display windows. An ImageOutput implementation that cannot express display windows will always write out the width * height pixel data, may upon writing lose information about offsets or crop windows.

Here is a code example that opens an image file that will contain a 32x32 pixel crop window within an abstract 640 x 480 full size image. Notice that the pixel indices (column, scanline, slice) passed to the “write” functions are the coordinates relative to the full image, not relative to the crop widow, but the data pointer passed to the “write” functions should point to the beginning of the actual pixel data being passed (not the the hypothetical start of the full data, if it was all present).

int fullwidth = 640, fulllength = 480; // Full display image size
int cropwidth = 16, croplength = 16;  // Crop window size
int xorigin = 32, yorigin = 128;      // Crop window position
unsigned char pixels [cropwidth * croplength * channels]; // Crop size
...
std::unique_ptr<ImageOutput> out = ImageOutput::create(filename);
ImageSpec spec(cropwidth, croplength, channels, TypeDesc::UINT8);
spec.full_x = 0;
spec.full_y = 0;
spec.full_width = fullwidth;
spec.full_length = fulllength;
spec.x = xorigin;
spec.y = yorigin;
out->open(filename, spec);
...
int z = 0;   // Always zero for 2D images
for (int y = yorigin;  y < yorigin+croplength;  ++y) {
    out->write_scanline(y, z, TypeDesc::UINT8,
                        &pixels[(y-yorigin)*cropwidth*channels]);
}
out->close();

Writing metadata

The ImageSpec passed to open() can specify all the common required properties that describe an image: data format, dimensions, number of channels, tiling. However, there may be a variety of additional metadata that should be carried along with the image or saved in the file.

Note

Metadata refers to data about data, in this case, data about the image that goes beyond the pixel values and description thereof.

The remainder of this section explains how to store additional metadata in the ImageSpec. It is up to the ImageOutput to store these in the file, if indeed the file format is able to accept the data. Individual ImageOutput implementations should document which metadata they respect.

Channel names

In addition to specifying the number of color channels, it is also possible to name those channels. Only a few ImageOutput implementations have a way of saving this in the file, but some do, so you may as well do it if you have information about what the channels represent.

By convention, channel names for red, green, blue, and alpha (or a main image) should be named "R", "G", "B", and "A", respectively. Beyond this guideline, however, you can use any names you want.

The ImageSpec has a vector of strings called channelnames. Upon construction, it starts out with reasonable default values. If you use it at all, you should make sure that it contains the same number of strings as the number of color channels in your image. Here is an example:

int channels = 3;
ImageSpec spec (width, length, channels, TypeDesc::UINT8);
spec.channelnames.assign ({ "R", "G", "B" });

Here is another example in which custom channel names are used to label the channels in an 8-channel image containing beauty pass RGB, per-channel opacity, and texture s,t coordinates for each pixel.

int channels = 8;
ImageSpec spec (width, length, channels, TypeDesc::UINT8);
spec.channelnames.clear ();
spec.channelnames.assign ({ "R", "G", "B", "opacityR", "opacityG",
                            "opacityB", "texture_s", "texture_t" });

The main advantage to naming color channels is that if you are saving to a file format that supports channel names, then any application that uses OpenImageIO to read the image back has the option to retain those names and use them for helpful purposes. For example, the iv image viewer will display the channel names when viewing individual channels or displaying numeric pixel values in “pixel view” mode.

Specially-designated channels

The ImageSpec contains two fields, alpha_channel and z_channel, which can be used to designate which channel indices are used for alpha and z depth, if any. Upon construction, these are both set to -1, indicating that it is not known which channels are alpha or depth. Here is an example of setting up a 5-channel output that represents RGBAZ:

int channels = 5;
ImageSpec spec (width, length, channels, format);
spec.channelnames.assign({ "R", "G", "B", "A", "Z" });
spec.alpha_channel = 3;
spec.z_channel = 4;

There are advantages to designating the alpha and depth channels in this manner: Some file formats may require that these channels be stored in a particular order, with a particular precision, or the ImageOutput may in some other way need to know about these special channels.

Arbitrary metadata

For all other metadata that you wish to save in the file, you can attach the data to the ImageSpec using the attribute() methods. These come in polymorphic varieties that allow you to attach an attribute name and a value consisting of a single int, unsigned int, float, char*, or std::string, as shown in the following examples:

ImageSpec spec (...);

int i = 1;
spec.attribute ("Orientation", i);

float f = 72.0f;
spec.attribute ("dotsize", f);

std::string s = "Fabulous image writer 1.0";
spec.attribute ("Software", s);

These are convenience routines for metadata that consist of a single value of one of these common types. For other data types, or more complex arrangements, you can use the more general form of attribute(), which takes arguments giving the name, type (as a TypeDesc), number of values (1 for a single value, >1 for an array), and then a pointer to the data values. For example,

ImageSpec spec (...);

// Attach a 4x4 matrix to describe the camera coordinates
float mymatrix[16] = { ... };
spec.attribute ("worldtocamera", TypeMatrix, &mymatrix);

// Attach an array of two floats giving the CIE neutral color
float neutral[2] = { 0.3127, 0.329 };
spec.attribute ("adoptedNeutral", TypeDesc(TypeDesc::FLOAT, 2), &neutral);

Additionally, the ["key"] notation may be used to set metadata in the spec as if it were an associative array or dictionary:

// spec["key"] = value  sets the value of the metadata, using
// the type of value as a guide for the type of the metadata.
spec["Orientation"] = 1;   // int
spec["PixelAspectRatio"] = 1.0f;   // float
spec["ImageDescription"] = "selfie";  // string
spec["worldtocamera"] = Imath::M44f(...)  // matrix

In general, most image file formats (and therefore most ImageOutput implementations) are aware of only a small number of name/value pairs that they predefine and will recognize. Some file formats (OpenEXR, notably) do accept arbitrary user data and save it in the image file. If an ImageOutput does not recognize your metadata and does not support arbitrary metadata, that metadatum will be silently ignored and will not be saved with the file.

Each individual ImageOutput implementation should document the names, types, and meanings of all metadata attributes that they understand.

Color space hints

We certainly hope that you are using only modern file formats that support high precision and extended range pixels (such as OpenEXR) and keeping all your images in a linear color space. But you may have to work with file formats that dictate the use of nonlinear color values. This is prevalent in formats that store pixels only as 8-bit values, since 256 values are not enough to linearly represent colors without banding artifacts in the dim values.

Since this can (and probably will) happen, we have a convention for explaining what color space your image pixels are in. Each individual ImageOutput should document how it uses this (or not).

The ImageSpec::extra_attribs field should store metadata that reveals the color space of the pixels you are sending the ImageOutput (see Section Color information metadata for explanations of particular values).

The color space hints only describe color channels. You should always pass alpha, depth, or other non-color channels with linear values.

Here is a simple example of setting up the ImageSpec when you know that the pixel values you are writing are linear:

ImageSpec spec (width, length, channels, format);
spec.attribute ("oiio:ColorSpace", "Linear");

If a particular ImageOutput implementation is required (by the rules of the file format it writes) to have pixels in a particular color space, then it should try to convert the color values of your image to the right color space if it is not already in that space. For example, JPEG images must be in sRGB space, so if you declare your pixels to be "Linear", the JPEG ImageOutput will convert to sRGB.

If you leave the "oiio:ColorSpace" unset, the values will not be transformed, since the plugin can’t be sure that it’s not in the correct space to begin with.

Random access and repeated transmission of pixels

All ImageOutput implementations that support scanlines and tiles should write pixels in strict order of increasing z slice, increasing y scanlines/rows within each slice, and increasing x column within each row. It is generally not safe to skip scanlines or tiles, or transmit them out of order, unless the plugin specifically advertises that it supports random access or rewrites, which may be queried using:

auto out = ImageOutput::create (filename);
if (out->supports ("random_access"))
    ...

Similarly, you should assume the plugin will not correctly handle repeated transmissions of a scanline or tile that has already been sent, unless it advertises that it supports rewrites, which may be queried using:

if (out->supports("rewrite"))
    ...

Multi-image files

Some image file formats support storing multiple images within a single file. Given a created ImageOutput, you can query whether multiple images may be stored in the file:

auto out = ImageOutput::create(filename);
if (out->supports("multiimage"))
    ...

Some image formats allow you to do the initial open() call without declaring the specifics of the subimages, and simply append subimages as you go. You can detect this by checking

if (out->supports("appendsubimage"))
    ...

In this case, all you have to do is, after writing all the pixels of one image but before calling close(), call open() again for the next subimage and pass AppendSubimage as the value for the mode argument (see Section ImageOutput Class Reference for the full technical description of the arguments to open()). The close() routine is called just once, after all subimages are completed. Here is an example:

const char *filename = "foo.tif";
int nsubimages;     // assume this is set
ImageSpec specs[];  // assume these are set for each subimage
unsigned char *pixels[]; // assume a buffer for each subimage

// Create the ImageOutput
auto out = ImageOutput::create (filename);

// Be sure we can support subimages
if (subimages > 1 &&  (! out->supports("multiimage") ||
                       ! out->supports("appendsubimage"))) {
    std::cerr << "Does not support appending of subimages\n";
    return;
}

// Use Create mode for the first level.
ImageOutput::OpenMode appendmode = ImageOutput::Create;

// Write the individual subimages
for (int s = 0;  s < nsubimages;  ++s) {
    out->open (filename, specs[s], appendmode);
    out->write_image (TypeDesc::UINT8, pixels[s]);
    // Use AppendSubimage mode for subsequent levels
    appendmode = ImageOutput::AppendSubimage;
}
out->close ();

On the other hand, if out->supports("appendsubimage") returns false, then you must use a different open() variety that allows you to declare the number of subimages and their specifications up front.

Below is an example of how to write a multi-subimage file, assuming that you know all the image specifications ahead of time. This should be safe for any file format that supports multiple subimages, regardless of whether it supports appending, and thus is the preferred method for writing subimages, assuming that you are able to know the number and specification of the subimages at the time you first open the file.

const char *filename = "foo.tif";
int nsubimages;     // assume this is set
ImageSpec specs[];  // assume these are set for each subimage
unsigned char *pixels[]; // assume a buffer for each subimage

// Create the ImageOutput
auto out = ImageOutput::create (filename);

// Be sure we can support subimages
if (subimages > 1 &&  (! out->supports("multiimage") ||
                       ! out->supports("appendsubimage"))) {
    std::cerr << "Does not support appending of subimages\n";
    return;
}

// Open and declare all subimages
out->open (filename, nsubimages, specs);

// Write the individual subimages
for (int s = 0;  s < nsubimages;  ++s) {
    if (s > 0)  // Not needed for the first, which is already open
        out->open (filename, specs[s], ImageInput::AppendSubimage);
    out->write_image (TypeDesc::UINT8, pixels[s]);
}
out->close ();

In both of these examples, we have used writeimage(), but of course writescanline(), writetile(), and write_rectangle() work as you would expect, on the current subimage.

MIP-maps

Some image file formats support multiple copies of an image at successively lower resolutions (MIP-map levels, or an “image pyramid”). Given a created ImageOutput, you can query whether MIP-maps may be stored in the file:

auto out = ImageOutput::create (filename);
if (out->supports ("mipmap"))
    ...

If you are working with an ImageOutput that supports MIP-map levels, it is easy to write these levels. After writing all the pixels of one MIP-map level, call open() again for the next MIP level and pass ImageInput::AppendMIPLevel as the value for the mode argument, and then write the pixels of the subsequent MIP level. (See Section ImageOutput Class Reference for the full technical description of the arguments to open().) The close() routine is called just once, after all subimages and MIP levels are completed.

Below is pseudocode for writing a MIP-map (a multi-resolution image used for texture mapping):

const char *filename = "foo.tif";
const int xres = 512, yres = 512;
const int channels = 3;  // RGB
unsigned char *pixels = new unsigned char [xres*yres*channels];

// Create the ImageOutput
auto out = ImageOutput::create (filename);

// Be sure we can support either mipmaps or subimages
if (! out->supports ("mipmap") && ! out->supports ("multiimage")) {
    std::cerr << "Cannot write a MIP-map\n";
    return;
}
// Set up spec for the highest resolution
ImageSpec spec (xres, yres, channels, TypeDesc::UINT8);

// Use Create mode for the first level.
ImageOutput::OpenMode appendmode = ImageOutput::Create;

// Write images, halving every time, until we're down to
// 1 pixel in either dimension
while (spec.width >= 1 && spec.height >= 1) {
    out->open (filename, spec, appendmode);
    out->write_image (TypeDesc::UINT8, pixels);
    // Assume halve() resamples the image to half resolution
    halve (pixels, spec.width, spec.height);
    // Don't forget to change spec for the next iteration
    spec.width /= 2;
    spec.height /= 2;

    // For subsequent levels, change the mode argument to
    // open().  If the format doesn't support MIPmaps directly,
    // try to emulate it with subimages.
    if (out->supports("mipmap"))
        appendmode = ImageOutput::AppendMIPLevel;
    else
        appendmode = ImageOutput::AppendSubimage;
}
out->close ();

In this example, we have used writeimage(), but of course writescanline(), writetile(), and write_rectangle() work as you would expect, on the current MIP level.

Per-channel formats

Some image formats allow separate per-channel data formats (for example, half data for colors and float data for depth). When this is desired, the following steps are necessary:

  1. Verify that the writer supports per-channel formats by checking supports ("channelformats").

  2. The ImageSpec passed to open() should have its channelformats vector filled with the types for each channel.

  3. The call to write_scanline(), read_scanlines(), write_tile(), write_tiles(), or write_image() should pass a data pointer to the raw data, already in the native per-channel format of the file and contiguously packed, and specify that the data is of type TypeUnknown.

For example, the following code fragment will write a 5-channel image to an OpenEXR file, consisting of R/G/B/A channels in half and a Z channel in float:

// Mixed data type for the pixel
struct Pixel { half r,g,b,a; float z; };
Pixel pixels[xres*yres];

auto out = ImageOutput::create ("foo.exr");

// Double check that this format accepts per-channel formats
if (! out->supports("channelformats")) {
    return;
}

// Prepare an ImageSpec with per-channel formats
ImageSpec spec (xres, yres, 5, TypeDesc::FLOAT);
spec.channelformats.assign(
    { TypeHalf, TypeHalf, TypeHalf, TypeHalf, TypeFloat });
spec.channelnames.assign({ "R", "G", "B", "A", "Z" });
spec.alpha_channel = 3;
spec.z_channel = 4;

out->open (filename, spec);
out->write_image (TypeDesc::UNKNOWN, /* use channel formats */
                  pixels,            /* data buffer */
                  sizeof(Pixel));    /* pixel stride */

Writing “deep” data

Some image file formats (OpenEXR only, at this time) support the concept of “deep” pixels – those containing multiple samples per pixel (and a potentially differing number of them in each pixel). You can tell if a format supports deep images by checking supports("deepdata"), and you can specify a deep data in an ImageSpec by setting its deep field will be true.

Deep files cannot be written with the usual write_scanline(), write_scanlines(), write_tile(), write_tiles(), write_image() functions, due to the nature of their variable number of samples per pixel. Instead, ImageOutput has three special member functions used only for writing deep data:

bool write_deep_scanlines (int ybegin, int yend, int z,
                           const DeepData &deepdata);

bool write_deep_tiles (int xbegin, int xend, int ybegin, int yend,
                       int zbegin, int zend, const DeepData &deepdata);

bool write_deep_image (const DeepData &deepdata);

It is only possible to write “native” data types to deep files; that is, there is no automatic translation into arbitrary data types as there is for ordinary images. All three of these functions are passed deep data in a special DeepData structure, described in detail in Section “Deep” pixel data: DeepData.

Here is an example of using these methods to write a deep image:

// Prepare the spec for 'half' RGBA, 'float' z
int nchannels = 5;
ImageSpec spec (xres, yres, nchannels);
spec.channelnames.assign({ "R", "G", "B", "A", "Z" });
spec.channeltypes.assign ({ TypeHalf, TypeHalf, TypeHalf, TypeHalf,
                            TypeFloat });
spec.alpha_channel = 3;
spec.z_channel = 4;
spec.deep = true;

// Prepare the data (sorry, complicated, but need to show the gist)
DeepData deepdata;
deepdata.init (spec);
for (int y = 0;  y < yres;  ++y)
    for (int x = 0;  x < xres;  ++x)
        deepdata.set_samples(y*xres+x, ...samples for that pixel...);
deepdata.alloc ();  // allocate pointers and data
int pixel = 0;
for (int y = 0;  y < yres;  ++y)
    for (int x = 0;  x < xres;  ++x, ++pixel)
        for (int chan = 0;  chan < nchannels;  ++chan)
            for (int samp = 0; samp < deepdata.samples(pixel); ++samp)
                deepdata.set_deep_value (pixel, chan, samp, ...value...);

// Create the output
auto out = ImageOutput::create (filename);
if (! out)
    return;
// Make sure the format can handle deep data and per-channel formats
if (! out->supports("deepdata") || ! out->supports("channelformats"))
    return;

// Do the I/O (this is the easy part!)
out->open (filename, spec);
out->write_deep_image (deepdata);
out->close ();

Copying an entire image

Suppose you want to copy an image, perhaps with alterations to the metadata but not to the pixels. You could open an ImageInput and perform a read_image(), and open another ImageOutput and call write_image() to output the pixels from the input image. However, for compressed images, this may be inefficient due to the unnecessary decompression and subsequent re-compression. In addition, if the compression is lossy, the output image may not contain pixel values identical to the original input.

A special copy_image() method of ImageOutput is available that attempts to copy an image from an open ImageInput (of the same format) to the output as efficiently as possible with without altering pixel values, if at all possible.

Not all format plugins will provide an implementation of copy_image() (in fact, most will not), but the default implemenatation simply copies pixels one scanline or tile at a time (with decompression/recompression) so it’s still safe to call. Furthermore, even a provided copy_image() is expected to fall back on the default implementation if the input and output are not able to do an efficient copy. Nevertheless, this method is recommended for copying images so that maximal advantage will be taken in cases where savings can be had.

The following is an example use of copy_image() to transfer pixels without alteration while modifying the image description metadata:

// Open the input file
auto in = ImageInput::open ("input.jpg");

// Make an output spec, identical to the input except for metadata
ImageSpec out_spec = in->spec();
out_spec.attribute ("ImageDescription", "My Title");

// Create the output file and copy the image
auto out = ImageOutput::create ("output.jpg");
out->open (output, out_spec);
out->copy_image (in);

// Clean up
out->close ();
in->close ();

Opening for output with configuration settings/hints

Sometimes you will want to give the image file writer hints or requests related to how to write the data, hints which must be made in time for the initial opening of the file. For example, when writing to a file format that requires unassociated alpha, you may already have unpremultiplied colors to pass, rather than the more customary practice of passing associated colors and having them converted to unassociated while being output.

This is accomplished by setting certain metadata in the ImageSpec that is passed to ImageOutput::open(). These particular metadata entries will be understood to be hints that control choices about how to write the file, rather than as metadata to store in the file header.

Configuration hints are optional and advisory only – meaning that not all image file writers will respect them (and indeed, many of them are only sensible for certain file formats).

Some common output configuration hints that tend to be respected across many writers (but not all, check Chapter Bundled ImageIO Plugins to see what hints are supported by each writer, as well as writer-specific settings) are:

Input Configuration Attribute

Type

Meaning

Compression

string

Compression method (and sometimes quality level) to be used. Each output file format may have a different set of possible compression methods that are accepted.

oiio:ioproxy

ptr

Pointer to a Filesystem::IOProxy that will handle the I/O, for example by writing to a memory buffer.

oiio:BitsPerSample

int

Requests that the data in the file use a particular bits-per-sample that is not directly expressible by the ImageSpec.format or any of the usual C data types, for example, requesting 10 bits per sample in the output file.

oiio:dither

int

If nonzero and writing UINT8 values to the file from a source buffer of higher bit depth, will add a small amount of random dither to combat the appearance of banding.

oiio:RawColor

int

If nonzero, when writing images to certain formats that suppport or dictate non-RGB color models (such as YCbCr), this indicates that the input passed by the app will already be in this color model, and should not be automatically converted from RGB to the designated color space as the pixels are written.

oiio:UnassociatedAlpha

int

If nonzero and writing to a file format that allows or dictates unassociated alpha/color values, this hint indicates that the pixel data that will be passed are already in unassociated form and should not automatically be “un-premultiplied” by the writer in order to conform to the file format’s need for unassociated data.

Examples:

Below is an example where we are writing to a PNG file, which dictates that RGBA data is always unassociated (i.e., the color channels are not already premultiplied by alpha), and we already have unassociated pixel values we wish to write unaltered, without it assuming that it’s associated and automatically converteing to unassociated alpha:

unsigned char unassociated_pixels[xres*yres*channels];

ImageSpec spec (xres, yres, channels, TypeDesc::UINT8);
spec["oiio:UnassociatedAlpha"] = 1;

auto out = ImageOutput::create ("foo.png");
out->open ("foo.png", spec);
out->write_image (TypeDesc::UINT8, unassociated_pixels);
out->close ();

Custom I/O proxies (and writing the file to a memory buffer)

Some file format writers allow you to supply a custom I/O proxy object that can allow bypassing the usual file I/O with custom behavior, including the ability to fill an in-memory buffer with a byte-for-byte representation of the correctly formatted file that would have been written to disk.

Only some output format writers support this feature. To find out if a particular file format supports this feature, you can create an ImageOutput of the right type, and check if it supports the feature name "ioproxy":

auto out = ImageOutput::create (filename);
if (! out  ||  ! out->supports ("ioproxy")) {
    return;
}

ImageOutput writers that support "ioproxy" will respond to a special attribute, "oiio:ioproxy", which passes a pointer to a Filesystem::IOProxy* (see OpenImageIO’s filesystem.h for this type and its subclasses). IOProxy is an abstract type, and concrete subclasses include IOFile (which wraps I/O to an open FILE*) and IOVecOutput (which sends output to a std::vector<unsigned char>).

Here is an example of using a proxy that writes the “file” to a std::vector<unsigned char>:

// ImageSpec describing the image we want to write.
ImageSpec spec (xres, yres, channels, TypeDesc::UINT8);

std::vector<unsigned char> file_buffer;  // bytes will go here
Filesystem::IOVecOutput vecout (file_buffer);  // I/O proxy object

auto out = ImageOutput::create ("out.exr", &vecout);
out->open ("out.exr", spec);
out->write_image (...);
out->close ();

// At this point, file_buffer will contain the "file"

Custom search paths for plugins

When you call ImageOutput::create(), the OpenImageIO library will try to find a plugin that is able to write the format implied by your filename. These plugins are alternately known as DLL’s on Windows (with the .dll extension), DSO’s on Linux (with the .so extension), and dynamic libraries on Mac OS X (with the .dylib extension).

OpenImageIO will look for matching plugins according to search paths, which are strings giving a list of directories to search, with each directory separated by a colon :. Within a search path, any substrings of the form ${FOO} will be replaced by the value of environment variable FOO. For example, the searchpath "${HOME}/plugins:/shared/plugins" will first check the directory /home/tom/plugins (assuming the user’s home directory is /home/tom), and if not found there, will then check the directory /shared/plugins.

The first search path it will check is that stored in the environment variable OIIO_LIBRARY_PATH. It will check each directory in turn, in the order that they are listed in the variable. If no adequate plugin is found in any of the directories listed in this environment variable, then it will check the custom searchpath passed as the optional second argument to ImageOutput::create(), searching in the order that the directories are listed. Here is an example:

char *mysearch = "/usr/myapp/lib:${HOME}/plugins";
std::unique_ptr<ImageOutput> out = ImageOutput::create (filename, mysearch);
...

Error checking

Nearly every ImageOutput API function returns a bool indicating whether the operation succeeded (true) or failed (false). In the case of a failure, the ImageOutput will have saved an error message describing in more detail what went wrong, and the latest error message is accessible using the ImageOutput method geterror(), which returns the message as a std::string.

The exception to this rule is ImageOutput::create(), which returns NULL if it could not create an appropriate ImageOutput. And in this case, since no ImageOutput exists for which you can call its geterror() function, there exists a global geterror() function (in the OpenImageIO namespace) that retrieves the latest error message resulting from a call to create().

Here is another version of the simple image writing code from Section Image Output Made Simple, but this time it is fully elaborated with error checking and reporting:

#include <OpenImageIO/imageio.h>
using namespace OIIO;
...

const char *filename = "foo.jpg";
const int xres = 640, yres = 480;
const int channels = 3;  // RGB
unsigned char pixels[xres*yres*channels];

auto out = ImageOutput::create (filename);
if (! out) {
    std::cerr << "Could not create an ImageOutput for "
              << filename << ", error = "
              << OpenImageIO::geterror() << "\n";
    return;
}
ImageSpec spec (xres, yres, channels, TypeDesc::UINT8);

if (! out->open (filename, spec)) {
    std::cerr << "Could not open " << filename
              << ", error = " << out->geterror() << "\n";
    return;
}

if (! out->write_image (TypeDesc::UINT8, pixels)) {
    std::cerr << "Could not write pixels to " << filename
              << ", error = " << out->geterror() << "\n";
    return;
}

if (! out->close ()) {
    std::cerr << "Error closing " << filename
              << ", error = " << out->geterror() << "\n";
    return;
}

ImageOutput Class Reference

class OIIO::ImageOutput

ImageOutput abstracts the writing of an image file in a file format-agnostic manner.

Users don’t directly declare these. Instead, you call the create() static method, which will return a unique_ptr holding a subclass of ImageOutput that implements writing the particular format.

Creating an ImageOutput

static unique_ptr create(string_view filename, Filesystem::IOProxy *ioproxy = nullptr, string_view plugin_searchpath = "")

Create an ImageOutput that can be used to write an image file. The type of image file (and hence, the particular subclass of ImageOutput returned, and the plugin that contains its methods) is inferred from the name, if it appears to be a full filename, or it may also name the format.

Return

A unique_ptr that will close and free the ImageOutput when it exits scope or is reset. The pointer will be empty if the required writer was not able to be created.

Parameters

  • filename: The name of the file format (e.g., “openexr”), a file extension (e.g., “exr”), or a filename from which the the file format can be inferred from its extension (e.g., “hawaii.exr”). The filename is UTF-8 encoded.

  • plugin_searchpath: An optional colon-separated list of directories to search for OpenImageIO plugin DSO/DLL’s.

  • ioproxy: Optional pointer to an IOProxy to use (not supported by all formats, see supports("ioproxy")). The caller retains ownership of the proxy.

static inline unique_ptr create(const std::wstring &filename, Filesystem::IOProxy *ioproxy = nullptr, const std::wstring &plugin_searchpath = {})

Create an ImageOutput using a UTF-16 encoded wstring filename and plugin searchpath.

Opening and closing files for output

enum OpenMode

Modes passed to the open() call.

Values:

enumerator Create
enumerator AppendSubimage
enumerator AppendMIPLevel
inline virtual int supports(string_view feature) const

Given the name of a “feature”, return whether this ImageOutput supports output of images with the given properties. Most queries will simply return 0 for “doesn’t support” and 1 for “supports it,” but it is acceptable to have queries return other nonzero integers to indicate varying degrees of support or limits (but should be clearly documented as such).

Feature names that ImageOutput implementations are expected to recognize include:

  • "tiles" : Is this format writer able to write tiled images?

  • "rectangles" : Does this writer accept arbitrary rectangular pixel regions (via write_rectangle())? Returning 0 indicates that pixels must be transmitted via write_scanline() (if scanline-oriented) or write_tile() (if tile-oriented, and only if supports("tiles") returns true).

  • "random_access" : May tiles or scanlines be written in any order (0 indicates that they must be in successive order)?

  • "multiimage" : Does this format support multiple subimages within a file?

  • "appendsubimage" : Does this format support multiple subimages that can be successively appended at will via open(name,spec,AppendSubimage)? A value of 0 means that the format requires pre-declaring the number and specifications of the subimages when the file is first opened, with open(name,subimages,specs).

  • "mipmap" : Does this format support multiple resolutions for an image/subimage?

  • "volumes" : Does this format support “3D” pixel arrays (a.k.a. volume images)?

  • "alpha" : Can this format support an alpha channel?

  • "nchannels" : Can this format support arbitrary number of channels (beyond RGBA)?

  • "rewrite" : May the same scanline or tile be sent more than once? Generally, this is true for plugins that implement interactive display, rather than a saved image file.

  • "empty" : Does this plugin support passing a NULL data pointer to the various write routines to indicate that the entire data block is composed of pixels with value zero? Plugins that support this achieve a speedup when passing blank scanlines or tiles (since no actual data needs to be transmitted or converted).

  • "channelformats" : Does this format writer support per-channel data formats, respecting the ImageSpec’s channelformats field? If not, it only accepts a single data format for all channels and will ignore the channelformats field of the spec.

  • "displaywindow" : Does the format support display (“full”) windows distinct from the pixel data window?

  • "origin" : Does the image format support specifying a pixel window origin (i.e., nonzero ImageSpec x, y, z)?

  • "negativeorigin" : Does the image format allow data and display window origins (i.e., ImageSpec x, y, z, full_x, full_y, full_z) to have negative values?

  • "deepdata" : Does the image format allow “deep” data consisting of multiple values per pixel (and potentially a differing number of values from pixel to pixel)?

  • "arbitrary_metadata" : Does the image file format allow metadata with arbitrary names (and either arbitrary, or a reasonable set of, data types)? (Versus the file format supporting only a fixed list of specific metadata names/values.)

  • "exif" Does the image file format support Exif camera data (either specifically, or via arbitrary named metadata)?

  • "iptc" Does the image file format support IPTC data (either specifically, or via arbitrary named metadata)?

  • "ioproxy" Does the image file format support writing to an IOProxy?

  • "procedural" : Is this a purely procedural output that doesn’t write an actual file?

  • "thumbnail" : Does this format writer support adding a reduced resolution copy of the image via the thumbnail() method?

  • "thumbnail_after_write" : Does this format writer support calling thumbnail() after the scanlines or tiles have been specified? (Supporting "thumbnail" but not "thumbnail_after_write" means that any thumbnail must be supplied immediately after open(), prior to any of the write_*() calls.)

This list of queries may be extended in future releases. Since this can be done simply by recognizing new query strings, and does not require any new API entry points, addition of support for new queries does not break ``link compatibility’’ with previously-compiled plugins.

virtual bool open(const std::string &filename, const ImageSpec &newspec, OpenMode mode = Create) = 0

Open the file with given name, with resolution and other format data as given in newspec. It is legal to call open multiple times on the same file without a call to close(), if it supports multiimage and mode is AppendSubimage, or if it supports MIP-maps and mode is AppendMIPLevel this is interpreted as appending a subimage, or a MIP level to the current subimage, respectively.

Return

true upon success, or false upon failure.

Parameters

  • filename: The name of the image file to open, UTF-8 encoded.

  • newspec: The ImageSpec describing the resolution, data types, etc.

  • mode: Specifies whether the purpose of the open is to create/truncate the file (default: Create), append another subimage (AppendSubimage), or append another MIP level (AppendMIPLevel).

inline bool open(const std::wstring &filename, const ImageSpec &newspec, OpenMode mode = Create)

Open an ImageOutput using a UTF-16 encoded wstring filename.

inline virtual bool open(const std::string &filename, int subimages, const ImageSpec *specs)

Open a multi-subimage file with given name and specifications for each of the subimages. Upon success, the first subimage will be open and ready for transmission of pixels. Subsequent subimages will be denoted with the usual call of open(name,spec,AppendSubimage) (and MIP levels by open(name,spec,AppendMIPLevel)).

The purpose of this call is to accommodate format-writing libraries that must know the number and specifications of the subimages upon first opening the file; such formats can be detected by:: supports(“multiimage”) && !supports(“appendsubimage”) The individual specs passed to the appending open() calls for subsequent subimages must match the ones originally passed.

Return

true upon success, or false upon failure.

Parameters

  • filename: The name of the image file to open, UTF-8 encoded.

  • subimages: The number of subimages (and therefore the length of the specs[] array.

  • specs[]: Pointer to an array of ImageSpec objects describing each of the expected subimages.

inline const ImageSpec &spec(void) const

Return a reference to the image format specification of the current subimage. Note that the contents of the spec are invalid before open() or after close().

virtual bool close() = 0

Closes the currently open file associated with this ImageOutput and frees any memory or resources associated with it.

Writing pixels

Common features of all the write methods:

  • The format parameter describes the data type of the data[]. The write methods automatically convert the data from the specified format to the actual output data type of the file (as was specified by the ImageSpec passed to open()). If format is TypeUnknown, then rather than converting from format, it will just copy pixels assumed to already be in the file’s native data layout (including, possibly, per-channel data formats as specified by the ImageSpec’s channelformats field).

  • The stride values describe the layout of the data buffer: xstride is the distance in bytes between successive pixels within each scanline. ystride is the distance in bytes between successive scanlines. For volumetric images zstride is the distance in bytes between successive “volumetric planes”. Strides set to the special value AutoStride imply contiguous data, i.e., 

    xstride = format.size() * nchannels
ystride = xstride * width
zstride = ystride * height

  • Any range parameters (such as ybegin and yend) describe a “half open interval”, meaning that begin is the first item and end is one past the last item. That means that the number of items is end - begin.

  • For ordinary 2D (non-volumetric) images, any z or zbegin coordinates should be 0 and any zend should be 1, indicating that only a single image “plane” exists.

  • Scanlines or tiles must be written in successive increasing coordinate order, unless the particular output file driver allows random access (indicated by supports("random_access")).

  • All write functions return true for success, false for failure (after which a call to geterror() may retrieve a specific error message).

virtual bool write_scanline(int y, int z, TypeDesc format, const void *data, stride_t xstride = AutoStride)

Write the full scanline that includes pixels (*,y,z). For 2D non-volume images, z should be 0. The xstride value gives the distance between successive pixels (in bytes). Strides set to AutoStride imply “contiguous” data.

Return

true upon success, or false upon failure.

Parameters

  • y/z: The y & z coordinates of the scanline.

  • format: A TypeDesc describing the type of data.

  • data: Pointer to the pixel data.

  • xstride: The distance in bytes between successive pixels in data (or AutoStride).

virtual bool write_scanlines(int ybegin, int yend, int z, TypeDesc format, const void *data, stride_t xstride = AutoStride, stride_t ystride = AutoStride)

Write multiple scanlines that include pixels (*,y,z) for all ybegin <= y < yend, from data. This is analogous to write_scanline(y,z,format,data,xstride) repeatedly for each of the scanlines in turn (the advantage, though, is that some image file types may be able to write multiple scanlines more efficiently or in parallel, than it could with one scanline at a time).

Return

true upon success, or false upon failure.

Parameters

  • ybegin/yend: The y range of the scanlines being passed.

  • z: The z coordinate of the scanline.

  • format: A TypeDesc describing the type of data.

  • data: Pointer to the pixel data.

  • xstride/ystride: The distance in bytes between successive pixels and scanlines (or AutoStride).

virtual bool write_tile(int x, int y, int z, TypeDesc format, const void *data, stride_t xstride = AutoStride, stride_t ystride = AutoStride, stride_t zstride = AutoStride)

Write the tile with (x,y,z) as the upper left corner. The three stride values give the distance (in bytes) between successive pixels, scanlines, and volumetric slices, respectively. Strides set to AutoStride imply ‘contiguous’ data in the shape of a full tile, i.e., 

xstride = format.size() * spec.nchannels
ystride = xstride * spec.tile_width
zstride = ystride * spec.tile_height

Return

true upon success, or false upon failure.

Note

This call will fail if the image is not tiled, or if (x,y,z) is not the upper left corner coordinates of a tile.

Parameters

  • x/y/z: The upper left coordinate of the tile being passed.

  • format: A TypeDesc describing the type of data.

  • data: Pointer to the pixel data.

  • xstride/ystride/zstride: The distance in bytes between successive pixels, scanlines, and image planes (or AutoStride to indicate a “contiguous” single tile).

virtual bool write_tiles(int xbegin, int xend, int ybegin, int yend, int zbegin, int zend, TypeDesc format, const void *data, stride_t xstride = AutoStride, stride_t ystride = AutoStride, stride_t zstride = AutoStride)

Write the block of multiple tiles that include all pixels in 

[xbegin,xend) X [ybegin,yend) X [zbegin,zend)

This is analogous to calling write_tile(x,y,z,...) for each tile in turn (but for some file formats, passing multiple tiles may allow it to write more efficiently or in parallel).

The begin/end pairs must correctly delineate tile boundaries, with the exception that it may also be the end of the image data if the image resolution is not a whole multiple of the tile size. The stride values give the data spacing of adjacent pixels, scanlines, and volumetric slices (measured in bytes). Strides set to AutoStride imply contiguous data in the shape of the [begin,end) region, i.e., 

xstride = format.size() * spec.nchannels
ystride = xstride * (xend-xbegin)
zstride = ystride * (yend-ybegin)

Return

true upon success, or false upon failure.

Note

The call will fail if the image is not tiled, or if the pixel ranges do not fall along tile (or image) boundaries, or if it is not a valid tile range.

Parameters

  • xbegin/xend: The x range of the pixels covered by the group of tiles passed.

  • ybegin/yend: The y range of the pixels covered by the tiles.

  • zbegin/zend: The z range of the pixels covered by the tiles (for a 2D image, zbegin=0 and zend=1).

  • format: A TypeDesc describing the type of data.

  • data: Pointer to the pixel data.

  • xstride/ystride/zstride: The distance in bytes between successive pixels, scanlines, and image planes (or AutoStride).

virtual bool write_rectangle(int xbegin, int xend, int ybegin, int yend, int zbegin, int zend, TypeDesc format, const void *data, stride_t xstride = AutoStride, stride_t ystride = AutoStride, stride_t zstride = AutoStride)

Write a rectangle of pixels given by the range 

[xbegin,xend) X [ybegin,yend) X [zbegin,zend)

The stride values give the data spacing of adjacent pixels, scanlines, and volumetric slices (measured in bytes). Strides set to AutoStride imply contiguous data in the shape of the [begin,end) region, i.e., 

xstride = format.size() * spec.nchannels
ystride = xstride * (xend-xbegin)
zstride = ystride * (yend-ybegin)

Return

true upon success, or false upon failure.

Note

The call will fail for a format plugin that does not return true for supports("rectangles").

Parameters

  • xbegin/xend: The x range of the pixels being passed.

  • ybegin/yend: The y range of the pixels being passed.

  • zbegin/zend: The z range of the pixels being passed (for a 2D image, zbegin=0 and zend=1).

  • format: A TypeDesc describing the type of data.

  • data: Pointer to the pixel data.

  • xstride/ystride/zstride: The distance in bytes between successive pixels, scanlines, and image planes (or AutoStride).

virtual bool write_image(TypeDesc format, const void *data, stride_t xstride = AutoStride, stride_t ystride = AutoStride, stride_t zstride = AutoStride, ProgressCallback progress_callback = nullptr, void *progress_callback_data = nullptr)

Write the entire image of spec.width x spec.height x spec.depth pixels, from a buffer with the given strides and in the desired format.

Depending on the spec, this will write either all tiles or all scanlines. Assume that data points to a layout in row-major order.

Because this may be an expensive operation, a progress callback may be passed. Periodically, it will be called as follows: 

progress_callback (progress_callback_data, float done);

where done gives the portion of the image (between 0.0 and 1.0) that has been written thus far.

Return

true upon success, or false upon failure.

Parameters

  • format: A TypeDesc describing the type of data.

  • data: Pointer to the pixel data.

  • xstride/ystride/zstride: The distance in bytes between successive pixels, scanlines, and image planes (or AutoStride).

  • progress_callback/progress_callback_data: Optional progress callback.

virtual bool write_deep_scanlines(int ybegin, int yend, int z, const DeepData &deepdata)

Write deep scanlines containing pixels (*,y,z), for all y in the range [ybegin,yend), to a deep file. This will fail if it is not a deep file.

Return

true upon success, or false upon failure.

Parameters

  • ybegin/yend: The y range of the scanlines being passed.

  • z: The z coordinate of the scanline.

  • deepdata: A DeepData object with the data for these scanlines.

virtual bool write_deep_tiles(int xbegin, int xend, int ybegin, int yend, int zbegin, int zend, const DeepData &deepdata)

Write the block of deep tiles that include all pixels in the range 

[xbegin,xend) X [ybegin,yend) X [zbegin,zend)

The begin/end pairs must correctly delineate tile boundaries, with the exception that it may also be the end of the image data if the image resolution is not a whole multiple of the tile size.

Return

true upon success, or false upon failure.

Note

The call will fail if the image is not tiled, or if the pixel ranges do not fall along tile (or image) boundaries, or if it is not a valid tile range.

Parameters

  • xbegin/xend: The x range of the pixels covered by the group of tiles passed.

  • ybegin/yend: The y range of the pixels covered by the tiles.

  • zbegin/zend: The z range of the pixels covered by the tiles (for a 2D image, zbegin=0 and zend=1).

  • deepdata: A DeepData object with the data for the tiles.

virtual bool write_deep_image(const DeepData &deepdata)

Write the entire deep image described by deepdata. Depending on the spec, this will write either all tiles or all scanlines.

Return

true upon success, or false upon failure.

Parameters

  • deepdata: A DeepData object with the data for the image.

inline virtual bool set_thumbnail(const ImageBuf &thumb)

Specify a reduced-resolution (“thumbnail”) version of the image. Note that many image formats may require the thumbnail to be specified prior to writing the pixels.

Return

true upon success, false if it was not possible to write the thumbnail, or if this file format (or writer) does not support thumbnails.

Note

This method was added to OpenImageIO 2.3.

Parameters

  • thumb: A reference to an ImageBuf containing the thumbnail image.

Public Types

using unique_ptr = std::unique_ptr<ImageOutput>

unique_ptr to an ImageOutput.

typedef ImageOutput *(*Creator)()

Call signature of a function that creates and returns an ImageOutput*.

Public Functions

virtual const char *format_name(void) const = 0

Return the name of the format implemented by this class.

virtual bool copy_image(ImageInput *in)

Read the pixels of the current subimage of in, and write it as the next subimage of *this, in a way that is efficient and does not alter pixel values, if at all possible. Both in and this must be a properly-opened ImageInput and ImageOutput, respectively, and their current images must match in size and number of channels.

If a particular ImageOutput implementation does not supply a copy_image method, it will inherit the default implementation, which is to simply read scanlines or tiles from in and write them to *this. However, some file format implementations may have a special technique for directly copying raw pixel data from the input to the output, when both are the same file type and the same pixel data type. This can be more efficient than in->read_image() followed by out->write_image(), and avoids any unintended pixel alterations, especially for formats that use lossy compression.

Note: this method is NOT thread-safe, since it depends on persistent state in the ImageInput.

Return

true upon success, or false upon failure.

Parameters

  • in: A pointer to the open ImageInput to read from.

inline virtual bool set_ioproxy(Filesystem::IOProxy *ioproxy)

Set an IOProxy for this writer. This must be called prior to open(), and only for writers that support them (supports("ioproxy")). The caller retains ownership of the proxy.

Return

true for success, false for failure.

bool has_error() const

Is there a pending error message waiting to be retrieved, that resulted from an ImageOutput API call made by the this thread?

Note that any error() calls issued are thread-specific, and the geterror()/has_error() are expected to be called by the same thread that called whichever API function encountered an error.

std::string geterror(bool clear = true) const

Return the text of all pending error messages issued against this ImageOutput by the calling thread, and clear the pending error message unless clear is false. If no error message is pending, it will return an empty string.

Note that any error() calls issued are thread-specific, and the geterror()/has_error() are expected to be called by the same thread that called whichever API function encountered an error.

template<typename ...Args>
inline void error(const char *fmt, const Args&... args) const

Error reporting for the plugin implementation: call this with Strutil::format-like arguments. It is not necessary to have the error message contain a trailing newline. Use with caution! Some day this will change to be fmt-like rather than printf-like.

template<typename ...Args>
inline void errorf(const char *fmt, const Args&... args) const

Error reporting for the plugin implementation: call this with printf-like arguments. It is not necessary to have the error message contain a trailing newline.

template<typename ...Args>
inline void errorfmt(const char *fmt, const Args&... args) const

Error reporting for the plugin implementation: call this with std::format-like arguments. It is not necessary to have the error message contain a trailing newline.

void threads(int n)

Set the threading policy for this ImageOutput, controlling the maximum amount of parallelizing thread “fan-out” that might occur during large write operations. The default of 0 means that the global attribute("threads") value should be used (which itself defaults to using as many threads as cores; see Section Global Attributes_).

The main reason to change this value is to set it to 1 to indicate that the calling thread should do all the work rather than spawning new threads. That is probably the desired behavior in situations where the calling application has already spawned multiple worker threads.

int threads() const

Retrieve the current thread-spawning policy.

See

threads(int)

ImageInput: Reading Images

Image Input Made Simple

Here is the simplest sequence required to open an image file, find out its resolution, and read the pixels (converting them into 8-bit values in memory, even if that’s not the way they’re stored in the file):

#include <OpenImageIO/imageio.h>
using namespace OIIO;
...

auto inp = ImageInput::open(filename);
if (! inp)
    return;
const ImageSpec &spec = inp->spec();
int xres = spec.width;
int yres = spec.height;
int channels = spec.nchannels;
std::vector<unsigned char> pixels(xres * yres * channels);
inp->read_image(TypeDesc::UINT8, &pixels[0]);
inp->close();

Here is a breakdown of what work this code is doing:

  • Search for an ImageIO plugin that is capable of reading the file (foo.jpg), first by trying to deduce the correct plugin from the file extension, but if that fails, by opening every ImageIO plugin it can find until one will open the file without error. When it finds the right plugin, it creates a subclass instance of ImageInput that reads the right kind of file format, and tries to fully open the file. The open() method returns a std::unique_ptr<ImageInput> that will be automatically freed when it exits scope.

    auto inp = ImageInput::open (filename);

  • The specification, accessible as inp->spec(), contains vital information such as the dimensions of the image, number of color channels, and data type of the pixel values. This is enough to allow us to allocate enough space for the image in C++ (for Python, this is unnecessary, since read_image() will return a NumPy array to us).

    const ImageSpec &spec = inp->spec();
int xres = spec.width;
int yres = spec.height;
int channels = spec.nchannels;
std::vector<unsigned char> pixels (xres*yres*channels);

    Note that in this example, we don’t care what data format is used for the pixel data in the file — we will request unsigned 8 bit integers and rely on OpenImageIO’s ability to convert to our requested format from the native data format of the file.

  • Read the entire image, hiding all details of the encoding of image data in the file, whether the file is scanline- or tile-based, or what is the native format of the data in the file (in this case, we request that it be automatically converted to unsigned 8-bit integers).

    inp->read_image(TypeDesc::UINT8, &pixels[0]);

  • Close the file.

    inp->close();

  • When inp exits its scope, the ImageInput will automatically be destroyed and any resources used by the plugin will be released.

Advanced Image Input

Let’s walk through some of the most common things you might want to do, but that are more complex than the simple example above.

Reading individual scanlines and tiles

The simple example of Section Image Input Made Simple read an entire image with one call. But sometimes you want to read a large image a little at a time and do not wish to retain the entire image in memory as you process it. OpenImageIO allows you to read images one scanline at a time or one tile at a time.

Examining the ImageSpec reveals whether the file is scanline or tile-oriented: a scanline image will have spec.tile_width and spec.tile_height set to 0, whereas a tiled images will have nonzero values for the tile dimensions.

Reading scanlines

Individual scanlines may be read using the read_scanline() API call:

auto inp = ImageInput::open (filename);
const ImageSpec &spec = inp->spec();
if (spec.tile_width == 0) {
    std::vector<unsigned char> scanline (spec.width*spec.channels);
    for (int y = 0;  y < yres;  ++y) {
        inp->read_scanline (y, 0, TypeDesc::UINT8, &scanline[0]);
        // ... process data in scanline[0..width*channels-1] ...
    }
} else {
     //... handle tiles, or reject the file ...
}
inp->close ();

The first two arguments to read_scanline() specify which scanline is being read by its vertical (y) scanline number (beginning with 0) and, for volume images, its slice (z) number (the slice number should be 0 for 2D non-volume images). This is followed by a TypeDesc describing the data type of the pixel buffer you are supplying, and a pointer to the pixel buffer itself. Additional optional arguments describe the data stride, which can be ignored for contiguous data (use of strides is explained in Section Data Strides).

Nearly all ImageInput implementations will be most efficient reading scanlines in strict order (starting with scanline 0, then 1, up to yres-1, without skipping any). An ImageInput is required to accept read_scanline() requests in arbitrary order, but depending on the file format and reader implementation, out-of-order scanline reads may be inefficient.

There is also a read_scanlines() function that operates similarly, except that it takes a ybegin and yend that specify a range, reading all scanlines ybegin <= y < yend. For most image format readers, this is implemented as a loop over individual scanlines, but some image format readers may be able to read a contiguous block of scanlines more efficiently than reading each one individually.

The full descriptions of the read_scanline() and read_scanlines() functions may be found in Section ImageInput Class Reference.

Reading tiles

Once you open() an image file, you can find out if it is a tiled image (and the tile size) by examining the ImageSpec’s tile_width, tile_height, and tile_depth fields. If they are zero, it’s a scanline image and you should read pixels using read_scanline(), not read_tile().

auto inp = ImageInput::open(filename);
const ImageSpec &spec = inp->spec();
if (spec.tile_width == 0) {
    // ... read scanline by scanline ...
} else {
    // Tiles
    int tilesize = spec.tile_width * spec.tile_height;
    std::vector<unsigned char> tile(tilesize * spec.channels);
    for (int y = 0;  y < yres;  y += spec.tile_height) {
        for (int x = 0;  x < xres;  x += spec.tile_width) {
            inp->read_tile(x, y, 0, TypeDesc::UINT8, &tile[0]);
            // ... process the pixels in tile[] ..
        }
    }
}
inp->close ();

The first three arguments to read_tile() specify which tile is being read by the pixel coordinates of any pixel contained in the tile: x (column), y (scanline), and z (slice, which should always be 0 for 2D non-volume images). This is followed by a TypeDesc describing the data format of the pixel buffer you are supplying, and a pointer to the pixel buffer. Pixel data will be written to your buffer in order of increasing slice, increasing scanline within each slice, and increasing column within each scanline. Additional optional arguments describe the data stride, which can be ignored for contiguous data (use of strides is explained in Section Data Strides).

All ImageInput implementations are required to support reading tiles in arbitrary order (i.e., not in strict order of increasing y rows, and within each row, increasing x column, without missing any tiles).

The full description of the read_tile() function may be found in Section ImageInput Class Reference.

Converting formats

The code examples of the previous sections all assumed that your internal pixel data is stored as unsigned 8-bit integers (i.e., 0-255 range). But OpenImageIO is significantly more flexible.

You may request that the pixels be stored in any of several formats. This is done merely by passing the read function the data type of your pixel buffer, as one of the enumerated type TypeDesc.

It is not required that the pixel data buffer passed to read_image(), read_scanline(), or read_tile() actually be in the same data format as the data in the file being read. OpenImageIO will automatically convert from native data type of the file to the internal data format of your choice. For example, the following code will open a TIFF and read pixels into your internal buffer represented as float values. This will work regardless of whether the TIFF file itself is using 8-bit, 16-bit, or float values.

std::unique_ptr<ImageInput> inp = ImageInput::open ("myfile.tif");
const ImageSpec &spec = inp->spec();

int numpixels = spec.image_pixels()
float pixels = new float [numpixels * channels];

inp->read_image (TypeDesc::FLOAT, pixels);

Note that read_scanline() and read_tile() have a parameter that works in a corresponding manner.

You can, of course, find out the native type of the file simply by examining spec.format. If you wish, you may then allocate a buffer big enough for an image of that type and request the native type when reading, therefore eliminating any translation among types and seeing the actual numerical values in the file.

Data Strides

In the preceeding examples, we have assumed that the buffer passed to the read functions (i.e., the place where you want your pixels to be stored) is contiguous, that is:

  • each pixel in memory consists of a number of data values equal to the number of channels in the file;

  • successive column pixels within a row directly follow each other in memory, with the first channel of pixel x immediately following last channel of pixel x-1 of the same row;

  • for whole images or tiles, the data for each row immediately follows the previous one in memory (the first pixel of row y immediately follows the last column of row y-1);

  • for 3D volumetric images, the first pixel of slice z immediately follows the last pixel of of slice z-1.

Please note that this implies that read_tile() will write pixel data into your buffer so that it is contiguous in the shape of a single tile, not just an offset into a whole image worth of pixels.

The read_scanline() function takes an optional xstride argument, and the read_image() and read_tile() functions take optional xstride, ystride, and zstride values that describe the distance, in bytes, between successive pixel columns, rows, and slices, respectively, of your pixel buffer. For any of these values that are not supplied, or are given as the special constant AutoStride, contiguity will be assumed.

By passing different stride values, you can achieve some surprisingly flexible functionality. A few representative examples follow:

  • Flip an image vertically upon reading, by using negative y stride:

    unsigned char pixels[spec.width * spec.height * spec.nchannels];
int scanlinesize = spec.width * spec.nchannels * sizeof(pixels[0]);
...
in->read_image (TypeDesc::UINT8,
                (char *)pixels+(yres-1)*scanlinesize, // offset to last
                AutoStride,                  // default x stride
                -scanlinesize,               // special y stride
                AutoStride);                 // default z stride

  • Read a tile into its spot in a buffer whose layout matches a whole image of pixel data, rather than having a one-tile-only memory layout:

    int pixelsize = spec.nchannels * sizeof(pixels[0]);
int scanlinesize = xpec.width * pixelsize;
...
in->read_tile (x, y, 0, TypeDesc::UINT8,
               (char *)pixels + y*scanlinesize + x*pixelsize,
               pixelsize,
               scanlinesize);

Please consult Section ImageInput Class Reference for detailed descriptions of the stride parameters to each read function.

Reading channels to separate buffers

While specifying data strides allows writing entire pixels to buffers with arbitrary layouts, it is not possible to separate those pixels into multiple buffers (i.e. to write image data to a separate or planar memory layout: RRRRGGGGBBBB instead of the interleaved RGBRGBRGBRGB).

A workaround for this is to call read_scanlines, read_tiles or read_image repeatedly with arguments chbegin and chend of 0 <= chbegin < spec.nchannels and chend == chbegin + 1:

// one buffer for all three channels
unsigned char pixels[spec.width * spec.height * spec.nchannels];

for (int channel = 0; channel < spec.nchannels; ++channel) {
    file->read_image(
        // reading one channel at a time
        channel, channel + 1,
        TypeDesc::UINT8,
        // writing the data to offsets spaced `spec.width * spec.height`
        // apart
        &pixels[spec.width * spec.height * channel]);
}

For many formats, this is nearly as fast as reading the image with interleaved pixel data if the format stores the pixels in an interleaved layout and even slightly faster if the pixels are stored in separate planes in the file.

Reading metadata

The ImageSpec that is filled in by ImageInput::open() specifies all the common properties that describe an image: data format, dimensions, number of channels, tiling. However, there may be a variety of additional metadata that are present in the image file and could be queried by your application.

The remainder of this section explains how to query additional metadata in the ImageSpec. It is up to the ImageInput to read these from the file, if indeed the file format is able to carry additional data. Individual ImageInput implementations should document which metadata they read.

Channel names

In addition to specifying the number of color channels, the ImageSpec also stores the names of those channels in its channelnames field, which is a std::vector<std::string> in C++, or a tuple of strings in Python. Its length should always be equal to the number of channels (it’s the responsibility of the ImageInput to ensure this).

Only a few file formats (and thus ImageInput implementations) have a way of specifying custom channel names, so most of the time you will see that the channel names follow the default convention of being named "R", "G", "B", and "A", for red, green, blue, and alpha, respectively.

Here is example code that prints the names of the channels in an image:

auto inp = ImageInput::open (filename);
const ImageSpec &spec = inp->spec();
for (int i = 0;  i < spec.nchannels;  ++i)
    std::cout << "Channel " << i << " is "
              << spec.channelnames[i] << "\n";
Specially-designated channels

The ImageSpec contains two fields, alpha_channel and z_channel, which designate which channel numbers represent alpha and z depth, if any. If either is set to -1, it indicates that it is not known which channel is used for that data.

If you are doing something special with alpha or depth, it is probably safer to respect the alpha_channel and z_channel designations (if not set to -1) rather than merely assuming that, for example, channel 3 is always the alpha channel.

Arbitrary metadata

All other metadata found in the file will be stored in the ImageSpec’s extra_attribs field, which is a ParamValueList, which is itself essentially a vector of ParamValue instances. Each ParamValue stores one meta-datum consisting of a name, type (specified by a TypeDesc), number of values, and data pointer.

If you know the name and type of a specific piece of metadata you want to use, you can retrieve it using the ImageSpec::getattribute() method. In C++, this copies the value into your variable and returns true if the attribute was found, or false if it was not. In Python, getattribute() simply returns the value of the attribute itself, or None if no match was found.

auto in; = ImageInput::open(filename);
const ImageSpec &spec = inp->spec();
...
int orientation = 0;
bool ok = spec.getattribute("Orientation", TypeInt, &orientation);
if (!ok) {
    std::cout << "No integer orientation in the file\n";
}

By convention, ImageInput plugins will save all integer metadata as 32-bit integers (TypeDesc::INT or TypeDesc::UINT), even if the file format dictates that a particular item is stored in the file as a 8- or 16-bit integer. This is just to keep client applications from having to deal with all the types. Since there is relatively little metadata compared to pixel data, there’s no real memory waste of promoting all integer types to int32 metadata. Floating-point metadata and string metadata may also exist, of course.

For certain common types, there is an even simpler method for retrieving the metadata:

int i = spec.get_int_attribute ("Orientation", 0);
float f = spec.get_float_attribute ("PixelAspectRatio", 1.0f);
std::string s = spec.get_string_attribute ("ImageDescription", "");

This method simply returns the value. The second argument is the default value to use if the attribute named is not found. These versions will do automatic type conversion as well — for example, if you ask for a float and the attribute is really an int, it will return the proper float for it; or if the attribute is a UINT16 and you call get_int_attribute(), it will succeed, promoting to an int.

And finally, another convenience method lets you treat the spec itself as an associative array or dictionary:

// spec["key"].get<TYPE> tries to retrieve that type, or a default
// value (generally 0 or empty string) if not found.
int i = spec["Orientation"].get<int>();
float f = spec["PixelAspectRatio"].get<float>();
std::string s = spec["ImageDescription"].get<std::string>();

// An optional argument to get() lets you specify a different default
// value to return if the attribute is not found.
float f = spec["PixelAspectRatio"].get<float>(1.0f);

Note that when retrieving with this “dictionary” syntax, the C++ and Python behaviors are different: C++ requires a get<TYPE>() call to retrieve the full value, and a missing key will return a default value. Python will return the value directly (no get() needed), and a missing key will raise a KeyError exception.

It is also possible to step through all the metadata, item by item. This can be accomplished using the technique of the following example:

for (const auto &p : spec.extra_attribs) {
    printf ("    %s: %s\n", p.name().c_str(), p.get_string().c_str());
}

Each individual ImageInput implementation should document the names, types, and meanings of all metadata attributes that they understand.

Color space hints

We certainly hope that you are using only modern file formats that support high precision and extended range pixels (such as OpenEXR) and keeping all your images in a linear color space. But you may have to work with file formats that dictate the use of nonlinear color values. This is prevalent in formats that store pixels only as 8-bit values, since 256 values are not enough to linearly represent colors without banding artifacts in the dim values.

The ImageSpec::extra_attribs field may store metadata that reveals the color space the image file in the "oiio:ColorSpace" attribute (see Section Color information for explanations of particular values).

The ImageInput sets the "oiio:ColorSpace" metadata in a purely advisory capacity — the read will not convert pixel values among color spaces. Many image file formats only support nonlinear color spaces (for example, JPEG/JFIF dictates use of sRGB). So your application should intelligently deal with gamma-corrected and sRGB input, at the very least.

The color space hints only describe color channels. You should assume that alpha or depth (z) channels (designated by the alpha_channel and z_channel fields, respectively) always represent linear values and should never be transformed by your application.

Multi-image files and MIP-maps

Some image file formats support multiple discrete subimages to be stored in one file, and/or miltiple resolutions for each image to form a MIPmap. When you open() an ImageInput, it will by default point to the first (i.e., number 0) subimage in the file, and the highest resolution (level 0) MIP-map level. You can switch to viewing another subimage or MIP-map level using the seek_subimage() function:

auto inp = ImageInput::open (filename);
int subimage = 1;
int miplevel = 0;
if (inp->seek_subimage (subimage, miplevel)) {
    ... process the subimage/miplevel ...
} else {
    ... no such subimage/miplevel ...
}

The seek_subimage() function takes three arguments: the index of the subimage to switch to (starting with 0), the MIPmap level (starting with 0 for the highest-resolution level), and a reference to an ImageSpec, into which will be stored the spec of the new subimage/miplevel. The seek_subimage() function returns true upon success, and false if no such subimage or MIP level existed. It is legal to visit subimages and MIP levels out of order; the ImageInput is responsible for making it work properly. It is also possible to find out which subimage and MIP level is currently being viewed, using the current_subimage() and current_miplevel() functions, which return the index of the current subimage and MIP levels, respectively.

Below is pseudocode for reading all the levels of a MIP-map (a multi-resolution image used for texture mapping) that shows how to read multi-image files:

auto inp = ImageInput::open (filename);
int num_miplevels = 0;
while (inp->seek_subimage (0, num_miplevels, spec)) {
    const ImageSpec &spec = inp->spec();
    int npixels = spec.width * spec.height;
    int nchannels = spec.nchannels;
    unsigned char *pixels = new unsigned char [npixels * nchannels];
    inp->read_image(TypeDesc::UINT8, pixels);

    // ... do whatever you want with this level, in pixels ...

    delete [] pixels;
    ++num_miplevels;
}
// Note: we break out of the while loop when seek_subimage fails
// to find a next MIP level.

inp->close();

In this example, we have used read_image(), but of course read_scanline() and read_tile() work as you would expect, on the current subimage and MIP level.

Per-channel formats

Some image formats allow separate per-channel data formats (for example, half data for colors and float data for depth). If you want to read the pixels in their true native per-channel formats, the following steps are necessary:

  1. Check the ImageSpec’s channelformats vector. If non-empty, the channels in the file do not all have the same format.

  2. When calling read_scanline, read_scanlines, read_tile, read_tiles, or read_image, pass a format of TypeUnknown to indicate that you would like the raw data in native per-channel format of the file written to your data buffer.

For example, the following code fragment will read a 5-channel image to an OpenEXR file, consisting of R/G/B/A channels in half and a Z channel in float:

auto inp = ImageInput::open (filename);
const ImageSpec &spec = inp->spec();

// Allocate enough space
unsigned char *pixels = new unsigned char [spec.image_bytes(true)];

inp->read_image(TypeDesc::UNKNOWN, /* use native channel formats */
                pixels);           /* data buffer */

if (spec.channelformats.size() > 0) {
    ... the buffer contains packed data in the native
        per-channel formats ...
} else {
    ... the buffer contains all data per spec.format ...
}

Reading “deep” data

Some image file formats (OpenEXR only, at this time) support the concept of “deep” pixels – those containing multiple samples per pixel (and a potentially differing number of them in each pixel). You can tell an image is “deep” from its ImageSpec: the deep field will be true.

Deep files cannot be read with the usual read_scanline(), read_scanlines(), read_tile(), read_tiles(), read_image() functions, due to the nature of their variable number of samples per pixel. Instead, ImageInput has three special member functions used only for reading deep data:

bool read_native_deep_scanlines (int subimage, int miplevel,
                                 int ybegin, int yend, int z,
                                 int chbegin, int chend,
                                 DeepData &deepdata);

bool read_native_deep_tiles (int subimage, int miplevel,
                             int xbegin, int xend, int ybegin int yend,
                             int zbegin, int zend,
                             int chbegin, int chend, DeepData &deepdata);

bool read_native_deep_image (int subimage, int miplevel,
                             DeepData &deepdata);

It is only possible to read “native” data types from deep files; that is, there is no automatic translation into arbitrary data types as there is for ordinary images. All three of these functions store the resulting deep data in a special DeepData structure, described in detail in Section Reading “deep” data.

Here is an example of using these methods to read a deep image from a file and print all its values:

auto inp = ImageInput::open (filename);
if (! inp)
    return;
const ImageSpec &spec = inp.spec();
if (spec.deep) {
    DeepData deepdata;
    inp.read_native_deep_image (0, 0, deepdata);
    int p = 0;  // absolute pixel number
    for (int y = 0; y < spec.height;  ++y) {
        for (int x = 0;  x < spec.width;  ++x, ++p) {
            std::cout << "Pixel " << x << "," << y << ":\n";
            if (deepdata.samples(p) == 0)
                std::cout << "  no samples\n";
            else
                for (int c = 0;  c < spec.nchannels;  ++c) {
                    TypeDesc type = deepdata.channeltype(c);
                    std::cout << "  " << spec.channelnames[c] << ": ";
                    void *ptr = deepdata.pointers[p*spec.nchannels+c]
                    for (int s = 0; s < deepdata.samples(p); ++s) {
                        if (type.basetype == TypeDesc::FLOAT ||
                            type.basetype == TypeDesc::HALF)
                            std::cout << deepdata.deep_value(p, c, s) << ' ';
                        else if (type.basetype == TypeDesc::UINT32)
                            std::cout << deepdata.deep_value_uint(p, c, s) << ' ';
                    }
                    std::cout << "\n";
                }
        }
    }
}
inp.close ();

Opening for input with configuration settings/hints

Sometimes you will want to give the image file reader hints or requests for how to open the file or present its data, hints which must be made in time for the initial opening of the file. For example, in specific circumstances, you might want to request that an image with unassociated alpha not be automatically converted to associated alpha by multiplying the color channel values by the alpha (as would be customary by OIIO convention).

This is accomplished by using the ImageInput::open() or ImageInput::create() method varieties that take an additional config parameter. This is an ImageSpec object whose metadata contains the configuration hints.

Configuration hints are optional and advisory only – meaning that not all image file readers will respect them (and indeed, many of them are only sensible for certain file formats).

Some common input configuration hints that tend to be respected across many readers (but not all, check Chapter Bundled ImageIO Plugins to see what hints are supported by each reader) are:

Input Configuration Attribute

Type

Meaning

oiio:ioproxy

ptr

Pointer to a Filesystem::IOProxy that will handle the I/O, for example by reading from memory rather than the file system.

oiio:RawColor

int

If nonzero, reading images with non-RGB color models (such as YCbCr) will return unaltered pixel values (versus the default OIIO behavior of automatically converting to RGB).

oiio:UnassociatedAlpha

int

If nonzero, and the file contains unassociated alpha, this will cause the reader to leave alpha unassociated (versus the default of premultiplying color channels by alpha if the alpha channel is unassociated).

Examples:

Below is an example where we wish to read in an RGBA image in a format that tends to store it as unassociated alpha, but we DON’T want it to automatically be converted to associated alpha.

// Set up an ImageSpec that holds the configuration hints.
ImageSpec config;
config["oiio:UnassociatedAlpha"] = 1;

// Open the file, passing in the config.
auto inp = ImageInput::open (filename, config);
const ImageSpec &spec = inp->spec();
std::vector<unsigned char> pixels (spec.image_pixels() * spec.nchannels);
inp->read_image (TypeDesc::UINT8, pixels.data());
if (spec.get_int_attribute("oiio:UnassociatedAlpha"))
    printf("pixels holds unassociated alpha\n");
else
    printf("pixels holds associated alpha\n");

Custom I/O proxies (and reading the file from a memory buffer)

Some file format readers allow you to supply a custom I/O proxy object that can allow bypassing the usual file I/O with custom behavior, including the ability to read the file form an in-memory buffer rather than reading from disk.

Only some input format readers support this feature. To find out if a particular file format supports this feature, you can create an ImageInput of the right type, and check if it supports the feature name "ioproxy":

auto in = ImageInput::create(filename);
if (! in  ||  ! in->supports ("ioproxy")) {
    return;
}

ImageInput readers that support "ioproxy" will respond to a special attribute, "oiio:ioproxy", which passes a pointer to a Filesystem::IOProxy* (see OpenImageIO’s filesystem.h for this type and its subclasses). IOProxy is an abstract type, and concrete subclasses include IOFile (which wraps I/O to an open FILE*) and IOMemReader (which reads input from a block of memory).

Here is an example of using a proxy that reads the “file” from a memory buffer:

const void *buf = ...;   // pointer to memory block
size_t size = ...;       // length of memory block
Filesystem::IOMemReader memreader (buf, size);  // I/O proxy object

auto in = ImageInput::open ("in.exr", nullptr, &memreader);
in->read_image (...);
in->close();

// That will have read the "file" from the memory buffer

Custom search paths for plugins

Please see Section Global Attributes for discussion about setting the plugin search path via the attribute() function. For example:

std::string mysearch = "/usr/myapp/lib:/home/jane/plugins";
OIIO::attribute ("plugin_searchpath", mysearch);
auto inp = ImageInput::open (filename);
// ...

Error checking

Nearly every ImageInput API function returns a bool indicating whether the operation succeeded (true) or failed (false). In the case of a failure, the ImageInput will have saved an error message describing in more detail what went wrong, and the latest error message is accessible using the ImageInput method geterror(), which returns the message as a std::string.

The exceptions to this rule are static methods such as the static ImageInput::open() and ImageInput::create(), which return an empty pointer if it could not create an appropriate ImageInput (and open it, in the case of open(). In such a case, since no ImageInput is returned for which you can call its geterror() function, there exists a global geterror() function (in the OpenImageIO namespace) that retrieves the latest error message resulting from a call to static open() or create().

Here is another version of the simple image reading code from Section Image Input Made Simple, but this time it is fully elaborated with error checking and reporting:

#include <OpenImageIO/imageio.h>
using namespace OIIO;
...

const char *filename = "foo.jpg";
auto inp = ImageInput::open (filename);
if (! inp) {
    std::cerr << "Could not open " << filename
              << ", error = " << OIIO::geterror() << "\n";
    return;
}
const ImageSpec &spec = inp->spec();
int xres = spec.width;
int yres = spec.height;
int channels = spec.nchannels;
std::vector<unsigned char> pixels(xres * yres * channels);

if (! inp->read_image (TypeDesc::UINT8, &pixels[0])) {
    std::cerr << "Could not read pixels from " << filename
              << ", error = " << inp->geterror() << "\n";
    return;
}

if (! inp->close ()) {
    std::cerr << "Error closing " << filename
              << ", error = " << inp->geterror() << "\n";
    return;
}

ImageInput Class Reference

class OIIO::ImageInput

ImageInput abstracts the reading of an image file in a file format-agnostic manner.

Creating an ImageIntput

static unique_ptr open(const std::string &filename, const ImageSpec *config = nullptr, Filesystem::IOProxy *ioproxy = nullptr)

Create an ImageInput subclass instance that is able to read the given file and open it, returning a unique_ptr to the ImageInput if successful. The unique_ptr is set up with an appropriate deleter so the ImageInput will be properly closed and deleted when the unique_ptr goes out of scope or is reset. If the open fails, return an empty unique_ptr and set an error that can be retrieved by OIIO::geterror().

The config, if not nullptr, points to an ImageSpec giving hints, requests, or special instructions. ImageInput implementations are free to not respond to any such requests, so the default implementation is just to ignore config.

open() will first try to make an ImageInput corresponding to the format implied by the file extension (for example, "foo.tif" will try the TIFF plugin), but if one is not found or if the inferred one does not open the file, every known ImageInput type will be tried until one is found that will open the file.

Return

A unique_ptr that will close and free the ImageInput when it exits scope or is reset. The pointer will be empty if the required writer was not able to be created.

Parameters

  • filename: The name of the file to open, UTF-8 encoded.

  • config: Optional pointer to an ImageSpec whose metadata contains “configuration hints.”

  • ioproxy: Optional pointer to an IOProxy to use (not supported by all formats, see supports("ioproxy")). The caller retains ownership of the proxy.

static inline unique_ptr open(const std::wstring &filename, const ImageSpec *config = nullptr, Filesystem::IOProxy *ioproxy = nullptr)

Create and open an ImageInput using a UTF-16 encoded wstring filename.

static unique_ptr create(string_view filename, bool do_open = false, const ImageSpec *config = nullptr, Filesystem::IOProxy *ioproxy = nullptr, string_view plugin_searchpath = "")

Create and return an ImageInput implementation that is able to read the given file or format. If do_open is true (and the filename is the name of a file, not just a format), fully open it if possible (using the optional config configuration spec, if supplied), otherwise just create the ImageInput but don’t open it. The plugin_searchpath parameter is an override of the searchpath. colon-separated list of directories to search for ImageIO plugin DSO/DLL’s (not a searchpath for the image itself!).

If the filename parameter is the name of a file format (such as “openexr”), it will create an ImageInput that reads that particular format. If the name is a file extension (such as “exr” or “.exr”), it will guess the file format from the extension and return that type of ImageInput.

If filename is a full file name (such as “hawaii.exr”), it will create an ImageInput that reads the format implied by the file extension (“.tif”) and try to open the file with that reader. If the file can be opened and appears to be of the correct type, then that ImageInput (after being closed) will be returned to the caller. But if it fails (say, because the file type does not match the extension), then every known kind of image reader will be tried in turn, until one can be found that succeeds in opening that file. The create() file will fail entirely only if no known image reader type succeeds.

If the caller intends to immediately open the file, then it is often simpler to call static ImageInput::open().

Return

A unique_ptr that will close and free the ImageInput when it exits scope or is reset. The pointer will be empty if the required writer was not able to be created.

Parameters

  • filename: The name of an image file, or a file extension, or the name of a file format. The filename is UTF-8 encoded.

  • do_open: If true, not only create but also open the file.

  • config: Optional pointer to an ImageSpec whose metadata contains “configuration hints” for the ImageInput implementation.

  • ioproxy: Optional pointer to an IOProxy to use (not supported by all formats, see supports("ioproxy")). The caller retains ownership of the proxy. If this is not supplied, it is still possible to set the proxy with a call to set_proxy() prior to open().

  • plugin_searchpath: An optional colon-separated list of directories to search for OpenImageIO plugin DSO/DLL’s.

static inline unique_ptr create(const std::wstring &filename, bool do_open = false, const ImageSpec *config = nullptr, Filesystem::IOProxy *ioproxy = nullptr, string_view plugin_searchpath = "")

Create an ImageInput using a UTF-16 encoded wstring filename.

Reading pixels

Common features of all the read methods:

  • The format parameter describes the data type of the data[] buffer. The read methods automatically convert the data from the data type it is stored in the file into the format of the data buffer. If format is TypeUnknown it will just copy pixels of file’s native data layout (including, possibly, per-channel data formats as specified by the ImageSpec’s channelformats field).

  • The stride values describe the layout of the data buffer: xstride is the distance in bytes between successive pixels within each scanline. ystride is the distance in bytes between successive scanlines. For volumetric images zstride is the distance in bytes between successive “volumetric planes”. Strides set to the special value AutoStride imply contiguous data, i.e., 

    xstride = format.size() * nchannels
ystride = xstride * width
zstride = ystride * height

  • Any range parameters (such as ybegin and yend) describe a “half open interval”, meaning that begin is the first item and end is one past the last item. That means that the number of items is end - begin.

  • For ordinary 2D (non-volumetric) images, any z or zbegin coordinates should be 0 and any zend should be 1, indicating that only a single image “plane” exists.

  • Some read methods take a channel range [chbegin,chend) to allow reading of a contiguous subset of channels (chbegin=0, chend=spec.nchannels reads all channels).

  • ImageInput readers are expected to give the appearance of random access in other words, if it can’t randomly seek to the given scanline or tile, it should transparently close, reopen, and sequentially read through prior scanlines.

  • All read functions return true for success, false for failure (after which a call to geterror() may retrieve a specific error message).

virtual bool read_scanline(int y, int z, TypeDesc format, void *data, stride_t xstride = AutoStride)

Read the scanline that includes pixels (*,y,z) from the “current” subimage and MIP level. The xstride value gives the distance between successive pixels (in bytes). Strides set to AutoStride imply “contiguous” data.

Note

This variety of read_scanline is not re-entrant nor thread-safe. If you require concurrent reads to the same open ImageInput, you should use read_scanlines that has the subimage and miplevel passed explicitly.

Return

true upon success, or false upon failure.

Parameters

  • y/z: The y & z coordinates of the scanline. For 2D images, z should be 0.

  • format: A TypeDesc describing the type of data.

  • data: Pointer to the pixel data buffer.

  • xstride: The distance in bytes between successive pixels in data (or AutoStride).

inline bool read_scanline(int y, int z, float *data)

Simple read_scanline reads into contiguous float pixels.

virtual bool read_scanlines(int subimage, int miplevel, int ybegin, int yend, int z, int chbegin, int chend, TypeDesc format, void *data, stride_t xstride = AutoStride, stride_t ystride = AutoStride)

Read multiple scanlines that include pixels (*,y,z) for all ybegin <= y < yend in the specified subimage and mip level, into data, using the strides given and converting to the requested data format (TypeUnknown indicates no conversion, just copy native data types). Only channels [chbegin,chend) will be read/copied (chbegin=0, chend=spec.nchannels reads all channels, yielding equivalent behavior to the simpler variant of read_scanlines).

This version of read_scanlines, because it passes explicit subimage/miplevel, does not require a separate call to seek_subimage, and is guaranteed to be thread-safe against other concurrent calls to any of the read_* methods that take an explicit subimage/miplevel (but not against any other ImageInput methods).

Return

true upon success, or false upon failure.

Note

This call was changed for OpenImageIO 2.0 to include the explicit subimage and miplevel parameters. The previous versions, which lacked subimage and miplevel parameters (thus were dependent on a prior call to seek_subimage) are considered deprecated.

Parameters

  • subimage: The subimage to read from (starting with 0).

  • miplevel: The MIP level to read (0 is the highest resolution level).

  • ybegin/yend: The y range of the scanlines being passed.

  • z: The z coordinate of the scanline.

  • chbegin/chend: The channel range to read.

  • format: A TypeDesc describing the type of data.

  • data: Pointer to the pixel data.

  • xstride/ystride: The distance in bytes between successive pixels and scanlines (or AutoStride).

virtual bool read_tile(int x, int y, int z, TypeDesc format, void *data, stride_t xstride = AutoStride, stride_t ystride = AutoStride, stride_t zstride = AutoStride)

Read the tile whose upper-left origin is (x,y,z) into data[], converting if necessary from the native data format of the file into the format specified. The stride values give the data spacing of adjacent pixels, scanlines, and volumetric slices (measured in bytes). Strides set to AutoStride imply ‘contiguous’ data in the shape of a full tile, i.e., 

xstride = format.size() * spec.nchannels
ystride = xstride * spec.tile_width
zstride = ystride * spec.tile_height

Note

This variety of read_tile is not re-entrant nor thread-safe. If you require concurrent reads to the same open ImageInput, you should use read_tiles() that has the subimage and miplevel passed explicitly.

Return

true upon success, or false upon failure.

Note

This call will fail if the image is not tiled, or if (x,y,z) is not the upper left corner coordinates of a tile.

Parameters

  • x/y/z: The upper left coordinate of the tile being passed.

  • format: A TypeDesc describing the type of data.

  • data: Pointer to the pixel data.

  • xstride/ystride/zstride: The distance in bytes between successive pixels, scanlines, and image planes (or AutoStride to indicate a “contiguous” single tile).

inline bool read_tile(int x, int y, int z, float *data)

Simple read_tile reads into contiguous float pixels.

virtual bool read_tiles(int subimage, int miplevel, int xbegin, int xend, int ybegin, int yend, int zbegin, int zend, int chbegin, int chend, TypeDesc format, void *data, stride_t xstride = AutoStride, stride_t ystride = AutoStride, stride_t zstride = AutoStride)

Read the block of multiple tiles that include all pixels in 

[xbegin,xend) X [ybegin,yend) X [zbegin,zend)

This is analogous to calling read_tile(x,y,z,...) for each tile in turn (but for some file formats, reading multiple tiles may allow it to read more efficiently or in parallel).

The begin/end pairs must correctly delineate tile boundaries, with the exception that it may also be the end of the image data if the image resolution is not a whole multiple of the tile size. The stride values give the data spacing of adjacent pixels, scanlines, and volumetric slices (measured in bytes). Strides set to AutoStride imply contiguous data in the shape of the [begin,end) region, i.e., 

xstride = format.size() * spec.nchannels
ystride = xstride * (xend-xbegin)
zstride = ystride * (yend-ybegin)

This version of read_tiles, because it passes explicit subimage and miplevel, does not require a separate call to seek_subimage, and is guaranteed to be thread-safe against other concurrent calls to any of the read_* methods that take an explicit subimage/miplevel (but not against any other ImageInput methods).

Return

true upon success, or false upon failure.

Note

The call will fail if the image is not tiled, or if the pixel ranges do not fall along tile (or image) boundaries, or if it is not a valid tile range.

Parameters

  • subimage: The subimage to read from (starting with 0).

  • miplevel: The MIP level to read (0 is the highest resolution level).

  • xbegin/xend: The x range of the pixels covered by the group of tiles being read.

  • ybegin/yend: The y range of the pixels covered by the tiles.

  • zbegin/zend: The z range of the pixels covered by the tiles (for a 2D image, zbegin=0 and zend=1).

  • chbegin/chend: The channel range to read.

  • format: A TypeDesc describing the type of data.

  • data: Pointer to the pixel data.

  • xstride/ystride/zstride: The distance in bytes between successive pixels, scanlines, and image planes (or AutoStride).

virtual bool read_image(int subimage, int miplevel, int chbegin, int chend, TypeDesc format, void *data, stride_t xstride = AutoStride, stride_t ystride = AutoStride, stride_t zstride = AutoStride, ProgressCallback progress_callback = NULL, void *progress_callback_data = NULL)

Read the entire image of spec.width x spec.height x spec.depth pixels into a buffer with the given strides and in the desired data format.

Depending on the spec, this will read either all tiles or all scanlines. Assume that data points to a layout in row-major order.

This version of read_image, because it passes explicit subimage and miplevel, does not require a separate call to seek_subimage, and is guaranteed to be thread-safe against other concurrent calls to any of the read_* methods that take an explicit subimage/miplevel (but not against any other ImageInput methods).

Because this may be an expensive operation, a progress callback may be passed. Periodically, it will be called as follows: 

progress_callback (progress_callback_data, float done);

where done gives the portion of the image (between 0.0 and 1.0) that has been written thus far.

Return

true upon success, or false upon failure.

Parameters

  • subimage: The subimage to read from (starting with 0).

  • miplevel: The MIP level to read (0 is the highest resolution level).

  • chbegin/chend: The channel range to read.

  • format: A TypeDesc describing the type of data.

  • data: Pointer to the pixel data.

  • xstride/ystride/zstride: The distance in bytes between successive pixels, scanlines, and image planes (or AutoStride).

  • progress_callback/progress_callback_data: Optional progress callback.

virtual bool read_native_deep_scanlines(int subimage, int miplevel, int ybegin, int yend, int z, int chbegin, int chend, DeepData &deepdata)

Read deep scanlines containing pixels (*,y,z), for all y in the range [ybegin,yend) into deepdata. This will fail if it is not a deep file.

Return

true upon success, or false upon failure.

Parameters

  • subimage: The subimage to read from (starting with 0).

  • miplevel: The MIP level to read (0 is the highest resolution level).

  • chbegin/chend: The channel range to read.

  • ybegin/yend: The y range of the scanlines being passed.

  • z: The z coordinate of the scanline.

  • deepdata: A DeepData object into which the data for these scanlines will be placed.

virtual bool read_native_deep_tiles(int subimage, int miplevel, int xbegin, int xend, int ybegin, int yend, int zbegin, int zend, int chbegin, int chend, DeepData &deepdata)

Read into deepdata the block of native deep data tiles that include all pixels and channels specified by pixel range.

Return

true upon success, or false upon failure.

Note

The call will fail if the image is not tiled, or if the pixel ranges do not fall along tile (or image) boundaries, or if it is not a valid tile range.

Parameters

  • subimage: The subimage to read from (starting with 0).

  • miplevel: The MIP level to read (0 is the highest resolution level).

  • xbegin/xend: The x range of the pixels covered by the group of tiles being read.

  • ybegin/yend: The y range of the pixels covered by the tiles.

  • zbegin/zend: The z range of the pixels covered by the tiles (for a 2D image, zbegin=0 and zend=1).

  • chbegin/chend: The channel range to read.

  • deepdata: A DeepData object into which the data for these tiles will be placed.

virtual bool read_native_deep_image(int subimage, int miplevel, DeepData &deepdata)

Read the entire deep data image of spec.width x spec.height x spec.depth pixels, all channels, into deepdata.

Return

true upon success, or false upon failure.

Parameters

  • subimage: The subimage to read from (starting with 0).

  • miplevel: The MIP level to read (0 is the highest resolution level).

  • deepdata: A DeepData object into which the data for the image will be placed.

Reading native pixels – implementation overloads

Note

read_native_* methods are usually not directly called by user code (except for read_native_deep_* varieties). These are the methods that are overloaded by the ImageInput subclasses that implement the individual file format readers.

virtual bool read_native_scanline(int subimage, int miplevel, int y, int z, void *data) = 0

Read a single scanline (all channels) of native data into contiguous memory.

virtual bool read_native_scanlines(int subimage, int miplevel, int ybegin, int yend, int z, void *data)

Read a range of scanlines (all channels) of native data into contiguous memory.

virtual bool read_native_scanlines(int subimage, int miplevel, int ybegin, int yend, int z, int chbegin, int chend, void *data)

Read a range of scanlines (with optionally a subset of channels) of native data into contiguous memory.

virtual bool read_native_tile(int subimage, int miplevel, int x, int y, int z, void *data)

Read a single tile (all channels) of native data into contiguous memory. The base class read_native_tile fails. A format reader that supports tiles MUST overload this virtual method that reads a single tile (all channels).

virtual bool read_native_tiles(int subimage, int miplevel, int xbegin, int xend, int ybegin, int yend, int zbegin, int zend, void *data)

Read multiple tiles (all channels) of native data into contigious memory. A format reader that supports reading multiple tiles at once (in a way that’s more efficient than reading the tiles one at a time) is advised (but not required) to overload this virtual method. If an ImageInput subclass does not overload this, the default implementation here is simply to loop over the tiles, calling the single-tile read_native_tile() for each one.

virtual bool read_native_tiles(int subimage, int miplevel, int xbegin, int xend, int ybegin, int yend, int zbegin, int zend, int chbegin, int chend, void *data)

Read multiple tiles (potentially a subset of channels) of native data into contigious memory. A format reader that supports reading multiple tiles at once, and can handle a channel subset while doing so, is advised (but not required) to overload this virtual method. If an ImageInput subclass does not overload this, the default implementation here is simply to loop over the tiles, calling the single-tile read_native_tile() for each one (and copying carefully to handle the channel subset issues).

Public Types

using unique_ptr = std::unique_ptr<ImageInput>

unique_ptr to an ImageInput

typedef std::lock_guard<const ImageInput&> lock_guard

The presence of lock() and unlock() establish an ImageInput itself as having the BasicLockable concept and therefore can be used by std::lock_guard.

typedef ImageInput *(*Creator)()

Call signature of a function that creates and returns an ImageInput*.

Public Functions

virtual const char *format_name(void) const = 0

Return the name of the format implemented by this class.

inline virtual int supports(string_view feature) const

Given the name of a “feature”, return whether this ImageInput supports output of images with the given properties. Most queries will simply return 0 for “doesn’t support” and 1 for “supports it,” but it is acceptable to have queries return other nonzero integers to indicate varying degrees of support or limits (but should be clearly documented as such).

Feature names that ImageInput implementations are expected to recognize include:

  • "arbitrary_metadata" : Does this format allow metadata with arbitrary names and types?

  • "exif" : Can this format store Exif camera data?

  • "ioproxy" : Does this format reader support reading from an IOProxy?

  • "iptc" : Can this format store IPTC data?

  • "procedural" : Can this format create images without reading from a disk file?

  • "thumbnail" : Does this format reader support retrieving a reduced resolution copy of the image via the thumbnail() method?

This list of queries may be extended in future releases. Since this can be done simply by recognizing new query strings, and does not require any new API entry points, addition of support for new queries does not break ``link compatibility’’ with previously-compiled plugins.

virtual bool valid_file(const std::string &filename) const

Return true if the filename names a file of the type for this ImageInput. The implementation will try to determine this as efficiently as possible, in most cases much less expensively than doing a full open(). Note that there can be false positives: a file can appear to be of the right type (i.e., valid_file() returning true) but still fail a subsequent call to open(), such as if the contents of the file are truncated, nonsensical, or otherwise corrupted. The filename is UTF-8 encoded.

Return

true upon success, or false upon failure.

inline bool valid_file(const std::wstring &filename) const

Check valid vile using a UTF-16 encoded wstring filename.

virtual bool open(const std::string &name, ImageSpec &newspec) = 0

Opens the file with given name and seek to the first subimage in the file. Various file attributes are put in newspec and a copy is also saved internally to the ImageInput (retrievable via spec(). From examining newspec or spec(), you can discern the resolution, if it’s tiled, number of channels, native data format, and other metadata about the image.

Return

true if the file was found and opened successfully.

Parameters

  • name: Filename to open, UTF-8 encoded.

  • newspec: Reference to an ImageSpec in which to deposit a full description of the contents of the first subimage of the file.

inline bool open(const std::wstring &name, ImageSpec &newspec)

Open the ImageInput using a UTF-16 encoded wstring filename.

inline virtual bool open(const std::string &name, ImageSpec &newspec, const ImageSpec &config)

Open file with given name, similar to open(name,newspec). The config is an ImageSpec giving requests or special instructions. ImageInput implementations are free to not respond to any such requests, so the default implementation is just to ignore config and call regular open(name,newspec).

Return

true if the file was found and opened successfully.

Parameters

  • name: Filename to open, UTF-8 encoded.

  • newspec: Reference to an ImageSpec in which to deposit a full description of the contents of the first subimage of the file.

  • config: An ImageSpec whose metadata contains “configuration hints” for the ImageInput implementation.

inline bool open(const std::wstring &name, ImageSpec &newspec, const ImageSpec &config)

Open the ImageInput using a UTF-16 encoded wstring filename.

inline virtual const ImageSpec &spec(void) const

Return a reference to the image specification of the current subimage/MIPlevel. Note that the contents of the spec are invalid before open() or after close(), and may change with a call to seek_subimage(). It is thus not thread-safe, since the spec may change if another thread calls seek_subimage, or any of the read_*() functions that take explicit subimage/miplevel.

virtual ImageSpec spec(int subimage, int miplevel = 0)

Return a full copy of the ImageSpec of the designated subimage and MIPlevel. This method is thread-safe, but it is potentially expensive, due to the work that needs to be done to fully copy an ImageSpec if there is lots of named metadata to allocate and copy. See also the less expensive spec_dimensions(). Errors (such as having requested a nonexistent subimage) are indicated by returning an ImageSpec with format==TypeUnknown.

virtual ImageSpec spec_dimensions(int subimage, int miplevel = 0)

Return a copy of the ImageSpec of the designated subimage and miplevel, but only the dimension and type fields. Just as with a call to ImageSpec::copy_dimensions(), neither the channel names nor any of the arbitrary named metadata will be copied, thus this is a relatively inexpensive operation if you don’t need that information. It is guaranteed to be thread-safe. Errors (such as having requested a nonexistent subimage) are indicated by returning an ImageSpec with format==TypeUnknown.

inline virtual bool get_thumbnail(ImageBuf &thumb, int subimage)

Retrieve a reduced-resolution (“thumbnail”) version of the given subimage. It is guaranteed to be thread-safe.

Return

true upon success, false if no thumbnail was available, or if this file format (or reader) does not support thumbnails.

Note

This method was added to OpenImageIO 2.3.

Parameters

  • thumb: A reference to an ImageBuf which will be overwritten with the thumbnail image.

  • subimage: The index of the subimage in the file whose thumbnail is to be retrieved.

virtual bool close() = 0

Close an open ImageInput. The call to close() is not strictly necessary if the ImageInput is destroyed immediately afterwards, since it is required for the destructor to close if the file is still open.

Return

true upon success, or false upon failure.

inline virtual int current_subimage(void) const

Returns the index of the subimage that is currently being read. The first subimage (or the only subimage, if there is just one) is number 0.

inline virtual int current_miplevel(void) const

Returns the index of the MIPmap image that is currently being read. The highest-res MIP level (or the only level, if there is just one) is number 0.

inline virtual bool seek_subimage(int subimage, int miplevel)

Seek to the given subimage and MIP-map level within the open image file. The first subimage of the file has index 0, the highest- resolution MIP level has index 0. The new subimage’s vital statistics=may be retrieved by this->spec(). The reader is expected to give the appearance of random access to subimages and MIP levels in other words, if it can’t randomly seek to the given subimage/level, it should transparently close, reopen, and sequentially read through prior subimages and levels.

Return

true upon success, or false upon failure. A failure may indicate that no such subimage or MIP level exists in the file.

inline virtual bool set_ioproxy(Filesystem::IOProxy *ioproxy)

Set an IOProxy for this reader. This must be called prior to open(), and only for readers that support them (supports("ioproxy")). The caller retains ownership of the proxy.

Return

true for success, false for failure.

bool has_error() const

Is there a pending error message waiting to be retrieved, that resulted from an ImageInput API call made by the this thread?

Note that any error() calls issued are thread-specific, and the geterror()/has_error() are expected to be called by the same thread that called whichever API function encountered an error.

std::string geterror(bool clear = true) const

Return the text of all pending error messages issued against this ImageInput by the calling thread, and clear the pending error message unless clear is false. If no error message is pending, it will return an empty string.

Note that any error() calls issued are thread-specific, and the geterror()/has_error() are expected to be called by the same thread that called whichever API function encountered an error.

template<typename ...Args>
inline void error(const char *fmt, const Args&... args) const

Error reporting for the plugin implementation: call this with Strutil::format-like arguments. It is not necessary to have the error message contain a trailing newline. Use with caution! Some day this will change to be fmt-like rather than printf-like.

template<typename ...Args>
inline void errorf(const char *fmt, const Args&... args) const

Error reporting for the plugin implementation: call this with printf-like arguments. It is not necessary to have the error message contain a trailing newline.

template<typename ...Args>
inline void errorfmt(const char *fmt, const Args&... args) const

Error reporting for the plugin implementation: call this with std::format-like arguments. It is not necessary to have the error message contain a trailing newline.

void threads(int n)

Set the threading policy for this ImageInput, controlling the maximum amount of parallelizing thread “fan-out” that might occur during large read operations. The default of 0 means that the global attribute("threads") value should be used (which itself defaults to using as many threads as cores; see Section Global Attributes_).

The main reason to change this value is to set it to 1 to indicate that the calling thread should do all the work rather than spawning new threads. That is probably the desired behavior in situations where the calling application has already spawned multiple worker threads.

int threads() const

Retrieve the current thread-spawning policy.

See

threads(int)

void lock() const

There is a (hidden) internal recursive mutex to each ImageInput that can be used by the II to enforce thread safety. This is exposed via the obvious lock()/unlock()/try_lock() semantics.

Writing ImageIO Plugins

Plugin Introduction

As explained in Chapters ImageInput: Reading Images and ImageOutput: Writing Images, the ImageIO library does not know how to read or write any particular image formats, but rather relies on plugins located and loaded dynamically at run-time. This set of plugins, and therefore the set of image file formats that OpenImageIO or its clients can read and write, is extensible without needing to modify OpenImageIO itself.

This chapter explains how to write your own OpenImageIO plugins. We will first explain separately how to write image file readers and writers, then tie up the loose ends of how to build the plugins themselves.

Image Reader Plugins

A plugin that reads a particular image file format must implement a subclass of ImageInput (described in Chapter ImageInput: Reading Images). This is actually very straightforward and consists of the following steps, which we will illustrate with a real-world example of writing a JPEG/JFIF plug-in.

  1. Read the base class definition from imageio.h. It may also be helpful to enclose the contents of your plugin in the same namespace that the OpenImageIO library uses:

    #include <OpenImageIO/imageio.h>
OIIO_PLUGIN_NAMESPACE_BEGIN

// ... everything else ...

OIIO_PLUGIN_NAMESPACE_END

  2. Declare these public items:

    1. An integer called name_imageio_version that identifies the version of the ImageIO protocol implemented by the plugin, defined in imageio.h as the constant OIIO_PLUGIN_VERSION. This allows the library to be sure it is not loading a plugin that was compiled against an incompatible version of OpenImageIO.

    2. An function named name_imageio_library_version that identifies the underlying dependent library that is responsible for reading or writing the format (it may return nullptr to indicate that there is no dependent library being used for this format).

    3. A function named name_input_imageio_create that takes no arguments and returns an ImageInput * constructed from a new instance of your ImageInput subclass and a deleter. (Note that name is the name of your format, and must match the name of the plugin itself.)

    4. An array of char * called name_input_extensions that contains the list of file extensions that are likely to indicate a file of the right format. The list is terminated by a nullptr.

    All of these items must be inside an extern "C" block in order to avoid name mangling by the C++ compiler, and we provide handy macros OIIO_PLUGIN_EXPORTS_BEGIN and OIIO_PLUGIN_EXPORTS_END to make this easy. Depending on your compiler, you may need to use special commands to dictate that the symbols will be exported in the DSO; we provide a special OIIO_EXPORT macro for this purpose, defined in export.h.

    Putting this all together, we get the following for our JPEG example:

    OIIO_PLUGIN_EXPORTS_BEGIN
    OIIO_EXPORT int jpeg_imageio_version = OIIO_PLUGIN_VERSION;
    OIIO_EXPORT ImageInput *jpeg_input_imageio_create () {
        return new JpgInput;
    }
    OIIO_EXPORT const char *jpeg_input_extensions[] = {
        "jpg", "jpe", "jpeg", "jif", "jfif", "jfi", nullptr
    };
    OIIO_EXPORT const char* jpeg_imageio_library_version () {
      #define STRINGIZE2(a) #a
      #define STRINGIZE(a) STRINGIZE2(a)
      #ifdef LIBJPEG_TURBO_VERSION
        return "jpeg-turbo " STRINGIZE(LIBJPEG_TURBO_VERSION);
      #else
        return "jpeglib " STRINGIZE(JPEG_LIB_VERSION_MAJOR) "."
                STRINGIZE(JPEG_LIB_VERSION_MINOR);
      #endif
    }
OIIO_PLUGIN_EXPORTS_END

  3. The definition and implementation of an ImageInput subclass for this file format. It must publicly inherit ImageInput, and must overload the following methods which are “pure virtual” in the ImageInput base class:

    1. format_name() should return the name of the format, which ought to match the name of the plugin and by convention is strictly lower-case and contains no whitespace.

    2. open() should open the file and return true, or should return false if unable to do so (including if the file was found but turned out not to be in the format that your plugin is trying to implement).

    3. close() should close the file, if open.

    4. read_native_scanline() should read a single scanline from the file into the address provided, uncompressing it but keeping it in its naive data format without any translation.

    5. The virtual destructor, which should close() if the file is still open, addition to performing any other tear-down activities.

    Additionally, your ImageInput subclass may optionally choose to overload any of the following methods, which are defined in the ImageInput base class and only need to be overloaded if the default behavior is not appropriate for your plugin:

    1. supports(), only if your format supports any of the optional features described in the section describing ImageInput::supports.

    2. valid_file(), if your format has a way to determine if a file is of the given format in a way that is less expensive than a full open().

    3. seek_subimage(), only if your format supports reading multiple subimages within a single file.

    4. read_native_scanlines(), only if your format has a speed advantage when reading multiple scanlines at once. If you do not supply this function, the default implementation will simply call read_scanline() for each scanline in the range.

    5. read_native_tile(), only if your format supports reading tiled images.

    6. read_native_tiles(), only if your format supports reading tiled images and there is a speed advantage when reading multiple tiles at once. If you do not supply this function, the default implementation will simply call read_native_tile() for each tile in the range.

    7. Channel subset'' versions of ``read_native_scanlines() and/or read_native_tiles(), only if your format has a more efficient means of reading a subset of channels. If you do not supply these methods, the default implementation will simply use read_native_scanlines() or read_native_tiles() to read into a temporary all-channel buffer and then copy the channel subset into the user’s buffer.

    8. read_native_deep_scanlines() and/or read_native_deep_tiles(), only if your format supports “deep” data images.

    Here is how the class definition looks for our JPEG example. Note that the JPEG/JFIF file format does not support multiple subimages or tiled images.

    class JpgInput final : public ImageInput {
 public:
    JpgInput () { init(); }
    virtual ~JpgInput () { close(); }
    virtual const char * format_name (void) const override { return "jpeg"; }
    virtual bool open (const std::string &name, ImageSpec &spec) override;
    virtual bool read_native_scanline (int y, int z, void *data) override;
    virtual bool close () override;
 private:
    FILE *m_fd;
    bool m_first_scanline;
    struct jpeg_decompress_struct m_cinfo;
    struct jpeg_error_mgr m_jerr;

    void init () { m_fd = NULL; }
};

Your subclass implementation of open(), close(), and read_native_scanline() are the heart of an ImageInput implementation. (Also read_native_tile() and seek_subimage(), for those image formats that support them.)

The remainder of this section simply lists the full implementation of our JPEG reader, which relies heavily on the open source jpeg-6b library to perform the actual JPEG decoding.

// Copyright 2008-present Contributors to the OpenImageIO project.
// SPDX-License-Identifier: BSD-3-Clause
// https://github.com/OpenImageIO/oiio

#include <algorithm>
#include <cassert>
#include <cstdio>

#include <OpenImageIO/filesystem.h>
#include <OpenImageIO/fmath.h>
#include <OpenImageIO/imageio.h>
#include <OpenImageIO/tiffutils.h>

#include "jpeg_pvt.h"

OIIO_PLUGIN_NAMESPACE_BEGIN


// N.B. The class definition for JpgInput is in jpeg_pvt.h.


// Export version number and create function symbols
OIIO_PLUGIN_EXPORTS_BEGIN

OIIO_EXPORT int jpeg_imageio_version = OIIO_PLUGIN_VERSION;

OIIO_EXPORT const char*
jpeg_imageio_library_version()
{
#define STRINGIZE2(a) #a
#define STRINGIZE(a) STRINGIZE2(a)
#ifdef LIBJPEG_TURBO_VERSION
    return "jpeg-turbo " STRINGIZE(LIBJPEG_TURBO_VERSION) "/jp" STRINGIZE(
        JPEG_LIB_VERSION);
#else
    return "jpeglib " STRINGIZE(JPEG_LIB_VERSION_MAJOR) "." STRINGIZE(
        JPEG_LIB_VERSION_MINOR);
#endif
}

OIIO_EXPORT ImageInput*
jpeg_input_imageio_create()
{
    return new JpgInput;
}

OIIO_EXPORT const char* jpeg_input_extensions[]
    = { "jpg", "jpe", "jpeg", "jif", "jfif", "jfi", nullptr };

OIIO_PLUGIN_EXPORTS_END


static const uint8_t JPEG_MAGIC1 = 0xff;
static const uint8_t JPEG_MAGIC2 = 0xd8;


// For explanations of the error handling, see the "example.c" in the
// libjpeg distribution.


static void
my_error_exit(j_common_ptr cinfo)
{
    /* cinfo->err really points to a my_error_mgr struct, so coerce pointer */
    JpgInput::my_error_ptr myerr = (JpgInput::my_error_ptr)cinfo->err;

    /* Always display the message. */
    /* We could postpone this until after returning, if we chose. */
    //  (*cinfo->err->output_message) (cinfo);
    myerr->jpginput->jpegerror(myerr, true);

    /* Return control to the setjmp point */
    longjmp(myerr->setjmp_buffer, 1);
}



static void
my_output_message(j_common_ptr cinfo)
{
    JpgInput::my_error_ptr myerr = (JpgInput::my_error_ptr)cinfo->err;

    // Create the message
    char buffer[JMSG_LENGTH_MAX];
    (*cinfo->err->format_message)(cinfo, buffer);
    myerr->jpginput->jpegerror(myerr, false);

    // This function is called only for non-fatal problems, so we don't
    // need to do the longjmp.
    // longjmp(myerr->setjmp_buffer, 1);
}



static std::string
comp_info_to_attr(const jpeg_decompress_struct& cinfo)
{
    // Compare the current 6 samples with our known definitions
    // to determine the corresponding subsampling attr
    std::vector<int> comp;
    comp.push_back(cinfo.comp_info[0].h_samp_factor);
    comp.push_back(cinfo.comp_info[0].v_samp_factor);
    comp.push_back(cinfo.comp_info[1].h_samp_factor);
    comp.push_back(cinfo.comp_info[1].v_samp_factor);
    comp.push_back(cinfo.comp_info[2].h_samp_factor);
    comp.push_back(cinfo.comp_info[2].v_samp_factor);
    size_t size = comp.size();

    if (std::equal(JPEG_444_COMP, JPEG_444_COMP + size, comp.begin()))
        return JPEG_444_STR;
    else if (std::equal(JPEG_422_COMP, JPEG_422_COMP + size, comp.begin()))
        return JPEG_422_STR;
    else if (std::equal(JPEG_420_COMP, JPEG_420_COMP + size, comp.begin()))
        return JPEG_420_STR;
    else if (std::equal(JPEG_411_COMP, JPEG_411_COMP + size, comp.begin()))
        return JPEG_411_STR;
    return "";
}



void
JpgInput::jpegerror(my_error_ptr /*myerr*/, bool fatal)
{
    // Send the error message to the ImageInput
    char errbuf[JMSG_LENGTH_MAX];
    (*m_cinfo.err->format_message)((j_common_ptr)&m_cinfo, errbuf);
    errorf("JPEG error: %s (\"%s\")", errbuf, filename());

    // Shut it down and clean it up
    if (fatal) {
        m_fatalerr = true;
        close();
        m_fatalerr = true;  // because close() will reset it
    }
}



bool
JpgInput::valid_file(const std::string& filename, Filesystem::IOProxy* io) const
{
    // Check magic number to assure this is a JPEG file
    uint8_t magic[2] = { 0, 0 };
    bool ok          = true;

    if (io) {
        ok = (io->pread(magic, sizeof(magic), 0) == sizeof(magic));
    } else {
        FILE* fd = Filesystem::fopen(filename, "rb");
        if (!fd)
            return false;
        ok = (fread(magic, sizeof(magic), 1, fd) == 1);
        fclose(fd);
    }

    if (magic[0] != JPEG_MAGIC1 || magic[1] != JPEG_MAGIC2) {
        ok = false;
    }
    return ok;
}



bool
JpgInput::open(const std::string& name, ImageSpec& newspec,
               const ImageSpec& config)
{
    auto p = config.find_attribute("_jpeg:raw", TypeInt);
    m_raw  = p && *(int*)p->data();
    p      = config.find_attribute("oiio:ioproxy", TypeDesc::PTR);
    if (p)
        m_io = p->get<Filesystem::IOProxy*>();
    m_config.reset(new ImageSpec(config));  // save config spec
    return open(name, newspec);
}



bool
JpgInput::open(const std::string& name, ImageSpec& newspec)
{
    m_filename = name;

    if (m_io) {
        // If an IOProxy was passed, it had better be a File or a
        // MemReader, that's all we know how to use with jpeg.
        std::string proxytype = m_io->proxytype();
        if (proxytype != "file" && proxytype != "memreader") {
            errorf("JPEG reader can't handle proxy type %s", proxytype);
            return false;
        }
    } else {
        // If no proxy was supplied, create a file reader
        m_io = new Filesystem::IOFile(name, Filesystem::IOProxy::Mode::Read);
        m_local_io.reset(m_io);
    }
    if (!m_io || m_io->mode() != Filesystem::IOProxy::Mode::Read) {
        errorf("Could not open file \"%s\"", name);
        return false;
    }

    // Check magic number to assure this is a JPEG file
    uint8_t magic[2] = { 0, 0 };
    if (m_io->pread(magic, sizeof(magic), 0) != sizeof(magic)) {
        errorf("Empty file \"%s\"", name);
        close_file();
        return false;
    }

    if (magic[0] != JPEG_MAGIC1 || magic[1] != JPEG_MAGIC2) {
        close_file();
        errorf(
            "\"%s\" is not a JPEG file, magic number doesn't match (was 0x%x%x)",
            name, int(magic[0]), int(magic[1]));
        return false;
    }

    // Set up the normal JPEG error routines, then override error_exit and
    // output_message so we intercept all the errors.
    m_cinfo.err               = jpeg_std_error((jpeg_error_mgr*)&m_jerr);
    m_jerr.pub.error_exit     = my_error_exit;
    m_jerr.pub.output_message = my_output_message;
    if (setjmp(m_jerr.setjmp_buffer)) {
        // Jump to here if there's a libjpeg internal error
        // Prevent memory leaks, see example.c in jpeg distribution
        jpeg_destroy_decompress(&m_cinfo);
        close_file();
        return false;
    }

    // initialize decompressor
    jpeg_create_decompress(&m_cinfo);
    m_decomp_create = true;
    // specify the data source
    if (!strcmp(m_io->proxytype(), "file")) {
        auto fd = reinterpret_cast<Filesystem::IOFile*>(m_io)->handle();
        jpeg_stdio_src(&m_cinfo, fd);
    } else {
        auto buffer = reinterpret_cast<Filesystem::IOMemReader*>(m_io)->buffer();
        jpeg_mem_src(&m_cinfo, const_cast<unsigned char*>(buffer.data()),
                     buffer.size());
    }

    // Request saving of EXIF and other special tags for later spelunking
    for (int mark = 0; mark < 16; ++mark)
        jpeg_save_markers(&m_cinfo, JPEG_APP0 + mark, 0xffff);
    jpeg_save_markers(&m_cinfo, JPEG_COM, 0xffff);  // comment marker

    // read the file parameters
    if (jpeg_read_header(&m_cinfo, FALSE) != JPEG_HEADER_OK || m_fatalerr) {
        errorf("Bad JPEG header for \"%s\"", filename());
        return false;
    }

    int nchannels = m_cinfo.num_components;

    if (m_cinfo.jpeg_color_space == JCS_CMYK
        || m_cinfo.jpeg_color_space == JCS_YCCK) {
        // CMYK jpegs get converted by us to RGB
        m_cinfo.out_color_space = JCS_CMYK;  // pre-convert YCbCrK->CMYK
        nchannels               = 3;
        m_cmyk                  = true;
    }

    if (m_raw)
        m_coeffs = jpeg_read_coefficients(&m_cinfo);
    else
        jpeg_start_decompress(&m_cinfo);  // start working
    if (m_fatalerr)
        return false;
    m_next_scanline = 0;  // next scanline we'll read

    m_spec = ImageSpec(m_cinfo.output_width, m_cinfo.output_height, nchannels,
                       TypeDesc::UINT8);

    // Assume JPEG is in sRGB unless the Exif or XMP tags say otherwise.
    m_spec.attribute("oiio:ColorSpace", "sRGB");

    if (m_cinfo.jpeg_color_space == JCS_CMYK)
        m_spec.attribute("jpeg:ColorSpace", "CMYK");
    else if (m_cinfo.jpeg_color_space == JCS_YCCK)
        m_spec.attribute("jpeg:ColorSpace", "YCbCrK");

    // If the chroma subsampling is detected and matches something
    // we expect, then set an attribute so that it can be preserved
    // in future operations.
    std::string subsampling = comp_info_to_attr(m_cinfo);
    if (!subsampling.empty())
        m_spec.attribute(JPEG_SUBSAMPLING_ATTR, subsampling);

    for (jpeg_saved_marker_ptr m = m_cinfo.marker_list; m; m = m->next) {
        if (m->marker == (JPEG_APP0 + 1)
            && !strcmp((const char*)m->data, "Exif")) {
            // The block starts with "Exif\0\0", so skip 6 bytes to get
            // to the start of the actual Exif data TIFF directory
            decode_exif(string_view((char*)m->data + 6, m->data_length - 6),
                        m_spec);
        } else if (m->marker == (JPEG_APP0 + 1)
                   && !strcmp((const char*)m->data,
                              "http://ns.adobe.com/xap/1.0/")) {
            std::string xml((const char*)m->data, m->data_length);
            decode_xmp(xml, m_spec);
        } else if (m->marker == (JPEG_APP0 + 13)
                   && !strcmp((const char*)m->data, "Photoshop 3.0"))
            jpeg_decode_iptc((unsigned char*)m->data);
        else if (m->marker == JPEG_COM) {
            if (!m_spec.find_attribute("ImageDescription", TypeDesc::STRING))
                m_spec.attribute("ImageDescription",
                                 std::string((const char*)m->data,
                                             m->data_length));
        }
    }

    // Handle density/pixelaspect. We need to do this AFTER the exif is
    // decoded, in case it contains useful information.
    float xdensity = m_spec.get_float_attribute("XResolution");
    float ydensity = m_spec.get_float_attribute("YResolution");
    if (!xdensity || !ydensity) {
        xdensity = float(m_cinfo.X_density);
        ydensity = float(m_cinfo.Y_density);
        if (xdensity && ydensity) {
            m_spec.attribute("XResolution", xdensity);
            m_spec.attribute("YResolution", ydensity);
        }
    }
    if (xdensity && ydensity) {
        float aspect = ydensity / xdensity;
        if (aspect != 1.0f)
            m_spec.attribute("PixelAspectRatio", aspect);
        switch (m_cinfo.density_unit) {
        case 0: m_spec.attribute("ResolutionUnit", "none"); break;
        case 1: m_spec.attribute("ResolutionUnit", "in"); break;
        case 2: m_spec.attribute("ResolutionUnit", "cm"); break;
        }
    }

    read_icc_profile(&m_cinfo, m_spec);  /// try to read icc profile

    newspec = m_spec;
    return true;
}



bool
JpgInput::read_icc_profile(j_decompress_ptr cinfo, ImageSpec& spec)
{
    int num_markers = 0;
    std::vector<unsigned char> icc_buf;
    unsigned int total_length = 0;
    const int MAX_SEQ_NO      = 255;
    unsigned char marker_present
        [MAX_SEQ_NO
         + 1];  // one extra is used to store the flag if marker is found, set to one if marker is found
    unsigned int data_length[MAX_SEQ_NO + 1];  // store the size of each marker
    unsigned int data_offset[MAX_SEQ_NO + 1];  // store the offset of each marker
    memset(marker_present, 0, (MAX_SEQ_NO + 1));

    for (jpeg_saved_marker_ptr m = cinfo->marker_list; m; m = m->next) {
        if (m->marker == (JPEG_APP0 + 2)
            && !strcmp((const char*)m->data, "ICC_PROFILE")) {
            if (num_markers == 0)
                num_markers = GETJOCTET(m->data[13]);
            else if (num_markers != GETJOCTET(m->data[13]))
                return false;
            int seq_no = GETJOCTET(m->data[12]);
            if (seq_no <= 0 || seq_no > num_markers)
                return false;
            if (marker_present[seq_no])  // duplicate marker
                return false;
            marker_present[seq_no] = 1;  // flag found marker
            data_length[seq_no]    = m->data_length - ICC_HEADER_SIZE;
        }
    }
    if (num_markers == 0)
        return false;

    // checking for missing markers
    for (int seq_no = 1; seq_no <= num_markers; seq_no++) {
        if (marker_present[seq_no] == 0)
            return false;  // missing sequence number
        data_offset[seq_no] = total_length;
        total_length += data_length[seq_no];
    }

    if (total_length == 0)
        return false;  // found only empty markers

    icc_buf.resize(total_length * sizeof(JOCTET));

    // and fill it in
    for (jpeg_saved_marker_ptr m = cinfo->marker_list; m; m = m->next) {
        if (m->marker == (JPEG_APP0 + 2)
            && !strcmp((const char*)m->data, "ICC_PROFILE")) {
            int seq_no = GETJOCTET(m->data[12]);
            memcpy(&icc_buf[0] + data_offset[seq_no], m->data + ICC_HEADER_SIZE,
                   data_length[seq_no]);
        }
    }
    spec.attribute(ICC_PROFILE_ATTR, TypeDesc(TypeDesc::UINT8, total_length),
                   &icc_buf[0]);
    return true;
}



static void
cmyk_to_rgb(int n, const unsigned char* cmyk, size_t cmyk_stride,
            unsigned char* rgb, size_t rgb_stride)
{
    for (; n; --n, cmyk += cmyk_stride, rgb += rgb_stride) {
        // JPEG seems to store CMYK as 1-x
        float C = convert_type<unsigned char, float>(cmyk[0]);
        float M = convert_type<unsigned char, float>(cmyk[1]);
        float Y = convert_type<unsigned char, float>(cmyk[2]);
        float K = convert_type<unsigned char, float>(cmyk[3]);
        float R = C * K;
        float G = M * K;
        float B = Y * K;
        rgb[0]  = convert_type<float, unsigned char>(R);
        rgb[1]  = convert_type<float, unsigned char>(G);
        rgb[2]  = convert_type<float, unsigned char>(B);
    }
}



bool
JpgInput::read_native_scanline(int subimage, int miplevel, int y, int /*z*/,
                               void* data)
{
    if (!seek_subimage(subimage, miplevel))
        return false;
    if (m_raw)
        return false;
    if (y < 0 || y >= (int)m_cinfo.output_height)  // out of range scanline
        return false;
    if (m_next_scanline > y) {
        // User is trying to read an earlier scanline than the one we're
        // up to.  Easy fix: close the file and re-open.
        // Don't forget to save and restore any configuration settings.
        ImageSpec configsave;
        if (m_config)
            configsave = *m_config;
        ImageSpec dummyspec;
        int subimage = current_subimage();
        if (!close() || !open(m_filename, dummyspec, configsave)
            || !seek_subimage(subimage, 0))
            return false;  // Somehow, the re-open failed
        OIIO_DASSERT(m_next_scanline == 0 && current_subimage() == subimage);
    }

    // Set up our custom error handler
    if (setjmp(m_jerr.setjmp_buffer)) {
        // Jump to here if there's a libjpeg internal error
        return false;
    }

    void* readdata = data;
    if (m_cmyk) {
        // If the file's data is CMYK, read into a 4-channel buffer, then
        // we'll have to convert.
        m_cmyk_buf.resize(m_spec.width * 4);
        readdata = &m_cmyk_buf[0];
        OIIO_DASSERT(m_spec.nchannels == 3);
    }

    for (; m_next_scanline <= y; ++m_next_scanline) {
        // Keep reading until we've read the scanline we really need
        if (jpeg_read_scanlines(&m_cinfo, (JSAMPLE**)&readdata, 1) != 1
            || m_fatalerr) {
            errorf("JPEG failed scanline read (\"%s\")", filename());
            return false;
        }
    }

    if (m_cmyk)
        cmyk_to_rgb(m_spec.width, (unsigned char*)readdata, 4,
                    (unsigned char*)data, 3);

    return true;
}



bool
JpgInput::close()
{
    if (m_io) {
        // unnecessary?  jpeg_abort_decompress (&m_cinfo);
        if (m_decomp_create)
            jpeg_destroy_decompress(&m_cinfo);
        m_decomp_create = false;
        close_file();
    }
    init();  // Reset to initial state
    return true;
}



void
JpgInput::jpeg_decode_iptc(const unsigned char* buf)
{
    // APP13 blob doesn't have to be IPTC info.  Look for the IPTC marker,
    // which is the string "Photoshop 3.0" followed by a null character.
    if (strcmp((const char*)buf, "Photoshop 3.0"))
        return;
    buf += strlen("Photoshop 3.0") + 1;

    // Next are the 4 bytes "8BIM"
    if (strncmp((const char*)buf, "8BIM", 4))
        return;
    buf += 4;

    // Next two bytes are the segment type, in big endian.
    // We expect 1028 to indicate IPTC data block.
    if (((buf[0] << 8) + buf[1]) != 1028)
        return;
    buf += 2;

    // Next are 4 bytes of 0 padding, just skip it.
    buf += 4;

    // Next is 2 byte (big endian) giving the size of the segment
    int segmentsize = (buf[0] << 8) + buf[1];
    buf += 2;

    decode_iptc_iim(buf, segmentsize, m_spec);
}

OIIO_PLUGIN_NAMESPACE_END

Image Writers

A plugin that writes a particular image file format must implement a subclass of ImageOutput (described in Chapter ImageOutput: Writing Images). This is actually very straightforward and consists of the following steps, which we will illustrate with a real-world example of writing a JPEG/JFIF plug-in.

  1. Read the base class definition from imageio.h, just as with an image reader (see Section Image Reader Plugins).

  2. Declare four public items:

    1. An integer called name_imageio_version that identifies the version of the ImageIO protocol implemented by the plugin, defined in imageio.h as the constant OIIO_PLUGIN_VERSION. This allows the library to be sure it is not loading a plugin that was compiled against an incompatible version of OpenImageIO. Note that if your plugin has both a reader and writer and they are compiled as separate modules (C++ source files), you don’t want to declare this in both modules; either one is fine.

    2. A function named name_output_imageio_create that takes no arguments and returns an ImageOutput * constructed from a new instance of your ImageOutput subclass and a deleter. (Note that name is the name of your format, and must match the name of the plugin itself.)

    3. An array of char * called name_output_extensions that contains the list of file extensions that are likely to indicate a file of the right format. The list is terminated by a nullptr pointer.

    All of these items must be inside an extern "C" block in order to avoid name mangling by the C++ compiler, and we provide handy macros OIIO_PLUGIN_EXPORTS_BEGIN and OIIO_PLUGIN_EXPORTS_END to mamke this easy. Depending on your compiler, you may need to use special commands to dictate that the symbols will be exported in the DSO; we provide a special OIIO_EXPORT macro for this purpose, defined in export.h.

    Putting this all together, we get the following for our JPEG example:

    OIIO_PLUGIN_EXPORTS_BEGIN
    OIIO_EXPORT int jpeg_imageio_version = OIIO_PLUGIN_VERSION;
    OIIO_EXPORT ImageOutput *jpeg_output_imageio_create () {
        return new JpgOutput;
    }
    OIIO_EXPORT const char *jpeg_input_extensions[] = {
        "jpg", "jpe", "jpeg", nullptr
    };
OIIO_PLUGIN_EXPORTS_END

  3. The definition and implementation of an ImageOutput subclass for this file format. It must publicly inherit ImageOutput, and must overload the following methods which are “pure virtual” in the ImageOutput base class:

    1. format_name() should return the name of the format, which ought to match the name of the plugin and by convention is strictly lower-case and contains no whitespace.

    2. supports() should return true if its argument names a feature supported by your format plugin, false if it names a feature not supported by your plugin. See the description of ImageOutput::supports() for the list of feature names.

    3. open() should open the file and return true, or should return false if unable to do so (including if the file was found but turned out not to be in the format that your plugin is trying to implement).

    4. close() should close the file, if open.

    5. write_scanline() should write a single scanline to the file, translating from internal to native data format and handling strides properly.

    6. The virtual destructor, which should close() if the file is still open, addition to performing any other tear-down activities.

    Additionally, your ImageOutput subclass may optionally choose to overload any of the following methods, which are defined in the ImageOutput base class and only need to be overloaded if the default behavior is not appropriate for your plugin:

    1. write_scanlines(), only if your format supports writing scanlines and you can get a performance improvement when outputting multiple scanlines at once. If you don’t supply write_scanlines(), the default implementation will simply call write_scanline() separately for each scanline in the range.

    2. write_tile(), only if your format supports writing tiled images.

    3. write_tiles(), only if your format supports writing tiled images and you can get a performance improvement when outputting multiple tiles at once. If you don’t supply write_tiles(), the default implementation will simply call write_tile() separately for each tile in the range.

    4. write_rectangle(), only if your format supports writing arbitrary rectangles.

    5. write_image(), only if you have a more clever method of doing so than the default implementation that calls write_scanline() or write_tile() repeatedly.

    6. write_deep_scanlines() and/or write_deep_tiles(), only if your format supports “deep” data images.

It is not strictly required, but certainly appreciated, if a file format does not support tiles, to nonetheless accept an ImageSpec that specifies tile sizes by allocating a full-image buffer in open(), providing an implementation of write_tile() that copies the tile of data to the right spots in the buffer, and having close() then call write_scanlines() to process the buffer now that the image has been fully sent.

Here is how the class definition looks for our JPEG example. Note that the JPEG/JFIF file format does not support multiple subimages or tiled images.

class JpgOutput final : public ImageOutput {
 public:
    JpgOutput () { init(); }
    virtual ~JpgOutput () { close(); }
    virtual const char * format_name (void) const override { return "jpeg"; }
    virtual int supports (string_view property) const override { return false; }
    virtual bool open (const std::string &name, const ImageSpec &spec,
                       bool append=false) override;
    virtual bool write_scanline (int y, int z, TypeDesc format,
                                 const void *data, stride_t xstride) override;
    bool close ();
 private:
    FILE *m_fd;
    std::vector<unsigned char> m_scratch;
    struct jpeg_compress_struct m_cinfo;
    struct jpeg_error_mgr m_jerr;

    void init () { m_fd = NULL; }
};

Your subclass implementation of open(), close(), and write_scanline() are the heart of an ImageOutput implementation. (Also write_tile(), for those image formats that support tiled output.)

An ImageOutput implementation must properly handle all data formats and strides passed to write_scanline() or write_tile(), unlike an ImageInput implementation, which only needs to read scanlines or tiles in their native format and then have the super-class handle the translation. But don’t worry, all the heavy lifting can be accomplished with the following helper functions provided as protected member functions of ImageOutput that convert a scanline, tile, or rectangular array of values from one format to the native format(s) of the file.

const void *to_native_scanline(TypeDesc format, const void *data, stride_t xstride, std::vector<unsigned char> &scratch, unsigned int dither = 0, int yorigin = 0, int zorigin = 0)

Convert a full scanline of pixels (pointed to by data with the given format and strides into contiguous pixels in the native format (described by the ImageSpec returned by the spec() member function). The location of the newly converted data is returned, which may either be the original data itself if no data conversion was necessary and the requested layout was contiguous (thereby avoiding unnecessary memory copies), or may point into memory allocated within the scratch vector passed by the user. In either case, the caller doesn’t need to worry about thread safety or freeing any allocated memory (other than eventually destroying the scratch vector).

const void *to_native_tile(TypeDesc format, const void *data, stride_t xstride, stride_t ystride, stride_t zstride, std::vector<unsigned char> &scratch, unsigned int dither = 0, int xorigin = 0, int yorigin = 0, int zorigin = 0)

Convert a full tile of pixels (pointed to by data with the given format and strides into contiguous pixels in the native format (described by the ImageSpec returned by the spec() member function). The location of the newly converted data is returned, which may either be the original data itself if no data conversion was necessary and the requested layout was contiguous (thereby avoiding unnecessary memory copies), or may point into memory allocated within the scratch vector passed by the user. In either case, the caller doesn’t need to worry about thread safety or freeing any allocated memory (other than eventually destroying the scratch vector).

const void *to_native_rectangle(int xbegin, int xend, int ybegin, int yend, int zbegin, int zend, TypeDesc format, const void *data, stride_t xstride, stride_t ystride, stride_t zstride, std::vector<unsigned char> &scratch, unsigned int dither = 0, int xorigin = 0, int yorigin = 0, int zorigin = 0)

Convert a rectangle of pixels (pointed to by data with the given format, dimensions, and strides into contiguous pixels in the native format (described by the ImageSpec returned by the spec() member function). The location of the newly converted data is returned, which may either be the original data itself if no data conversion was necessary and the requested layout was contiguous (thereby avoiding unnecessary memory copies), or may point into memory allocated within the scratch vector passed by the user. In either case, the caller doesn’t need to worry about thread safety or freeing any allocated memory (other than eventually destroying the scratch vector).

For float to 8 bit integer conversions only, if dither parameter is nonzero, random dither will be added to reduce quantization banding artifacts; in this case, the specific nonzero dither value is used as a seed for the hash function that produces the per-pixel dither amounts, and the optional origin parameters help it to align the pixels to the right position in the dither pattern.


The remainder of this section simply lists the full implementation of our JPEG writer, which relies heavily on the open source jpeg-6b library to perform the actual JPEG encoding.

// Copyright 2008-present Contributors to the OpenImageIO project.
// SPDX-License-Identifier: BSD-3-Clause
// https://github.com/OpenImageIO/oiio

#include <cassert>
#include <cstdio>
#include <vector>

#include <OpenImageIO/filesystem.h>
#include <OpenImageIO/fmath.h>
#include <OpenImageIO/imageio.h>
#include <OpenImageIO/tiffutils.h>

#include "jpeg_pvt.h"

OIIO_PLUGIN_NAMESPACE_BEGIN

#define DBG if (0)


// References:
//  * JPEG library documentation: /usr/share/doc/libjpeg-devel-6b
//  * JFIF spec: https://www.w3.org/Graphics/JPEG/jfif3.pdf
//  * ITU T.871 (aka ISO/IEC 10918-5):
//      https://www.itu.int/rec/T-REC-T.871-201105-I/en



class JpgOutput final : public ImageOutput {
public:
    JpgOutput() { init(); }
    virtual ~JpgOutput() { close(); }
    virtual const char* format_name(void) const override { return "jpeg"; }
    virtual int supports(string_view feature) const override
    {
        return (feature == "exif" || feature == "iptc" || feature == "ioproxy");
    }
    virtual bool open(const std::string& name, const ImageSpec& spec,
                      OpenMode mode = Create) override;
    virtual bool write_scanline(int y, int z, TypeDesc format, const void* data,
                                stride_t xstride) override;
    virtual bool write_tile(int x, int y, int z, TypeDesc format,
                            const void* data, stride_t xstride,
                            stride_t ystride, stride_t zstride) override;
    virtual bool close() override;
    virtual bool copy_image(ImageInput* in) override;
    virtual bool set_ioproxy(Filesystem::IOProxy* ioproxy) override
    {
        m_io = ioproxy;
        return true;
    }

private:
    std::string m_filename;
    unsigned int m_dither;
    int m_next_scanline;  // Which scanline is the next to write?
    std::vector<unsigned char> m_scratch;
    struct jpeg_compress_struct m_cinfo;
    struct jpeg_error_mgr c_jerr;
    jvirt_barray_ptr* m_copy_coeffs;
    struct jpeg_decompress_struct* m_copy_decompressor;
    std::vector<unsigned char> m_tilebuffer;
    std::unique_ptr<Filesystem::IOProxy> m_io_local;
    Filesystem::IOProxy* m_io = nullptr;
    // m_outbuffer/m_outsize are used for jpeg-to-memory
    unsigned char* m_outbuffer = nullptr;
#if OIIO_JPEG_LIB_VERSION >= 94
    // libjpeg switched jpeg_mem_dest() from accepting a `unsigned long*`
    // to a `size_t*` in version 9d.
    size_t m_outsize = 0;
#else
    // libjpeg < 9d, and so far all libjpeg-turbo releases, have a
    // jpeg_mem_dest() declaration that needs this to be unsigned long.
    unsigned long m_outsize = 0;
#endif

    void init(void)
    {
        m_copy_coeffs       = NULL;
        m_copy_decompressor = NULL;
        m_io_local.reset();
        m_io = nullptr;
        clear_outbuffer();
    }

    void clear_outbuffer()
    {
        if (m_outbuffer) {
            free(m_outbuffer);
            m_outbuffer = nullptr;
        }
        m_outsize = 0;
    }

    void set_subsampling(const int components[])
    {
        jpeg_set_colorspace(&m_cinfo, JCS_YCbCr);
        m_cinfo.comp_info[0].h_samp_factor = components[0];
        m_cinfo.comp_info[0].v_samp_factor = components[1];
        m_cinfo.comp_info[1].h_samp_factor = components[2];
        m_cinfo.comp_info[1].v_samp_factor = components[3];
        m_cinfo.comp_info[2].h_samp_factor = components[4];
        m_cinfo.comp_info[2].v_samp_factor = components[5];
    }

    // Read the XResolution/YResolution and PixelAspectRatio metadata, store
    // in density fields m_cinfo.X_density,Y_density.
    void resmeta_to_density();
};



OIIO_PLUGIN_EXPORTS_BEGIN

OIIO_EXPORT ImageOutput*
jpeg_output_imageio_create()
{
    return new JpgOutput;
}

OIIO_EXPORT const char* jpeg_output_extensions[]
    = { "jpg", "jpe", "jpeg", "jif", "jfif", "jfi", nullptr };

OIIO_PLUGIN_EXPORTS_END



bool
JpgOutput::open(const std::string& name, const ImageSpec& newspec,
                OpenMode mode)
{
    if (mode != Create) {
        errorf("%s does not support subimages or MIP levels", format_name());
        return false;
    }

    // Save name and spec for later use
    m_filename = name;
    m_spec     = newspec;

    // Check for things this format doesn't support
    if (m_spec.width < 1 || m_spec.height < 1) {
        errorf("Image resolution must be at least 1x1, you asked for %d x %d",
               m_spec.width, m_spec.height);
        return false;
    }
    if (m_spec.depth < 1)
        m_spec.depth = 1;
    if (m_spec.depth > 1) {
        errorf("%s does not support volume images (depth > 1)", format_name());
        return false;
    }

    if (auto ioparam = m_spec.find_attribute("oiio:ioproxy", TypeDesc::PTR))
        m_io = ioparam->get<Filesystem::IOProxy*>();
    if (!m_io) {
        // If no proxy was supplied, create a file reader
        m_io = new Filesystem::IOFile(name, Filesystem::IOProxy::Write);
        m_io_local.reset(m_io);
    }
    if (!m_io || m_io->mode() != Filesystem::IOProxy::Write) {
        errorfmt("Could not open \"{}\"", name);
        m_io = nullptr;
        m_io_local.reset();
        return false;
    }

    m_cinfo.err = jpeg_std_error(&c_jerr);  // set error handler
    jpeg_create_compress(&m_cinfo);         // create compressor
    if (!strcmp(m_io->proxytype(), "file")) {
        auto fd = reinterpret_cast<Filesystem::IOFile*>(m_io)->handle();
        jpeg_stdio_dest(&m_cinfo, fd);  // set output stream
    } else {
        clear_outbuffer();
        jpeg_mem_dest(&m_cinfo, &m_outbuffer, &m_outsize);
    }

    // Set image and compression parameters
    m_cinfo.image_width  = m_spec.width;
    m_cinfo.image_height = m_spec.height;

    // JFIF can only handle grayscale and RGB. Do the best we can with this
    // limited format by truncating to 3 channels if > 3 are requested,
    // truncating to 1 channel if 2 are requested.
    if (m_spec.nchannels >= 3) {
        m_cinfo.input_components = 3;
        m_cinfo.in_color_space   = JCS_RGB;
    } else {
        m_cinfo.input_components = 1;
        m_cinfo.in_color_space   = JCS_GRAYSCALE;
    }

    resmeta_to_density();

    m_cinfo.write_JFIF_header = TRUE;

    if (m_copy_coeffs) {
        // Back door for copy()
        jpeg_copy_critical_parameters(m_copy_decompressor, &m_cinfo);
        DBG std::cout << "out open: copy_critical_parameters\n";
        jpeg_write_coefficients(&m_cinfo, m_copy_coeffs);
        DBG std::cout << "out open: write_coefficients\n";
    } else {
        // normal write of scanlines
        jpeg_set_defaults(&m_cinfo);  // default compression
        // Careful -- jpeg_set_defaults overwrites density
        resmeta_to_density();
        DBG std::cout << "out open: set_defaults\n";

        auto compqual = m_spec.decode_compression_metadata("jpeg", 98);
        if (Strutil::iequals(compqual.first, "jpeg"))
            jpeg_set_quality(&m_cinfo, clamp(compqual.second, 1, 100), TRUE);
        else
            jpeg_set_quality(&m_cinfo, 98, TRUE);  // not jpeg? default qual

        if (m_cinfo.input_components == 3) {
            std::string subsampling = m_spec.get_string_attribute(
                JPEG_SUBSAMPLING_ATTR);
            if (subsampling == JPEG_444_STR)
                set_subsampling(JPEG_444_COMP);
            else if (subsampling == JPEG_422_STR)
                set_subsampling(JPEG_422_COMP);
            else if (subsampling == JPEG_420_STR)
                set_subsampling(JPEG_420_COMP);
            else if (subsampling == JPEG_411_STR)
                set_subsampling(JPEG_411_COMP);
        }
        DBG std::cout << "out open: set_colorspace\n";

        // Save as a progressive jpeg if requested by the user
        if (m_spec.get_int_attribute("jpeg:progressive")) {
            jpeg_simple_progression(&m_cinfo);
        }

        jpeg_start_compress(&m_cinfo, TRUE);  // start working
        DBG std::cout << "out open: start_compress\n";
    }
    m_next_scanline = 0;  // next scanline we'll write

    // Write JPEG comment, if sent an 'ImageDescription'
    ParamValue* comment = m_spec.find_attribute("ImageDescription",
                                                TypeDesc::STRING);
    if (comment && comment->data()) {
        const char** c = (const char**)comment->data();
        jpeg_write_marker(&m_cinfo, JPEG_COM, (JOCTET*)*c, strlen(*c) + 1);
    }

    if (Strutil::iequals(m_spec.get_string_attribute("oiio:ColorSpace"), "sRGB"))
        m_spec.attribute("Exif:ColorSpace", 1);

    // Write EXIF info
    std::vector<char> exif;
    // Start the blob with "Exif" and two nulls.  That's how it
    // always is in the JPEG files I've examined.
    exif.push_back('E');
    exif.push_back('x');
    exif.push_back('i');
    exif.push_back('f');
    exif.push_back(0);
    exif.push_back(0);
    encode_exif(m_spec, exif);
    jpeg_write_marker(&m_cinfo, JPEG_APP0 + 1, (JOCTET*)&exif[0], exif.size());

    // Write IPTC IIM metadata tags, if we have anything
    std::vector<char> iptc;
    encode_iptc_iim(m_spec, iptc);
    if (iptc.size()) {
        static char photoshop[] = "Photoshop 3.0";
        std::vector<char> head(photoshop, photoshop + strlen(photoshop) + 1);
        static char _8BIM[] = "8BIM";
        head.insert(head.end(), _8BIM, _8BIM + 4);
        head.push_back(4);  // 0x0404
        head.push_back(4);
        head.push_back(0);  // four bytes of zeroes
        head.push_back(0);
        head.push_back(0);
        head.push_back(0);
        head.push_back((char)(iptc.size() >> 8));  // size of block
        head.push_back((char)(iptc.size() & 0xff));
        iptc.insert(iptc.begin(), head.begin(), head.end());
        jpeg_write_marker(&m_cinfo, JPEG_APP0 + 13, (JOCTET*)&iptc[0],
                          iptc.size());
    }

    // Write XMP packet, if we have anything
    std::string xmp = encode_xmp(m_spec, true);
    if (!xmp.empty()) {
        static char prefix[] = "http://ns.adobe.com/xap/1.0/";
        std::vector<char> block(prefix, prefix + strlen(prefix) + 1);
        block.insert(block.end(), xmp.c_str(), xmp.c_str() + xmp.length());
        jpeg_write_marker(&m_cinfo, JPEG_APP0 + 1, (JOCTET*)&block[0],
                          block.size());
    }

    m_spec.set_format(TypeDesc::UINT8);  // JPG is only 8 bit

    // Write ICC profile, if we have anything
    const ParamValue* icc_profile_parameter = m_spec.find_attribute(
        ICC_PROFILE_ATTR);
    if (icc_profile_parameter != NULL) {
        unsigned char* icc_profile
            = (unsigned char*)icc_profile_parameter->data();
        unsigned int icc_profile_length = icc_profile_parameter->type().size();
        if (icc_profile && icc_profile_length) {
            /* Calculate the number of markers we'll need, rounding up of course */
            int num_markers = icc_profile_length / MAX_DATA_BYTES_IN_MARKER;
            if ((unsigned int)(num_markers * MAX_DATA_BYTES_IN_MARKER)
                != icc_profile_length)
                num_markers++;
            int curr_marker     = 1; /* per spec, count strarts at 1*/
            size_t profile_size = MAX_DATA_BYTES_IN_MARKER + ICC_HEADER_SIZE;
            std::vector<unsigned char> profile(profile_size);
            while (icc_profile_length > 0) {
                // length of profile to put in this marker
                unsigned int length
                    = std::min(icc_profile_length,
                               (unsigned int)MAX_DATA_BYTES_IN_MARKER);
                icc_profile_length -= length;
                // Write the JPEG marker header (APP2 code and marker length)
                strncpy((char*)&profile[0], "ICC_PROFILE", profile_size);
                profile[11] = 0;
                profile[12] = curr_marker;
                profile[13] = (unsigned char)num_markers;
                memcpy(&profile[0] + ICC_HEADER_SIZE,
                       icc_profile + length * (curr_marker - 1), length);
                jpeg_write_marker(&m_cinfo, JPEG_APP0 + 2, &profile[0],
                                  ICC_HEADER_SIZE + length);
                curr_marker++;
            }
        }
    }

    m_dither = m_spec.get_int_attribute("oiio:dither", 0);

    // If user asked for tiles -- which JPEG doesn't support, emulate it by
    // buffering the whole image.
    if (m_spec.tile_width && m_spec.tile_height)
        m_tilebuffer.resize(m_spec.image_bytes());

    return true;
}



void
JpgOutput::resmeta_to_density()
{
    string_view resunit = m_spec.get_string_attribute("ResolutionUnit");
    if (Strutil::iequals(resunit, "none"))
        m_cinfo.density_unit = 0;
    else if (Strutil::iequals(resunit, "in"))
        m_cinfo.density_unit = 1;
    else if (Strutil::iequals(resunit, "cm"))
        m_cinfo.density_unit = 2;
    else
        m_cinfo.density_unit = 0;

    int X_density = int(m_spec.get_float_attribute("XResolution"));
    int Y_density = int(m_spec.get_float_attribute("YResolution", X_density));
    const float aspect = m_spec.get_float_attribute("PixelAspectRatio", 1.0f);
    if (aspect != 1.0f && X_density <= 1 && Y_density <= 1) {
        // No useful [XY]Resolution, but there is an aspect ratio requested.
        // Arbitrarily pick 72 dots per undefined unit, and jigger it to
        // honor it as best as we can.
        //
        // Here's where things get tricky. By logic and reason, as well as
        // the JFIF spec and ITU T.871, the pixel aspect ratio is clearly
        // ydensity/xdensity (because aspect is xlength/ylength, and density
        // is 1/length). BUT... for reasons lost to history, a number of
        // apps get this exactly backwards, and these include PhotoShop,
        // Nuke, and RV. So, alas, we must replicate the mistake, or else
        // all these common applications will misunderstand the JPEG files
        // written by OIIO and vice versa.
        Y_density = 72;
        X_density = int(Y_density * aspect + 0.5f);
        m_spec.attribute("XResolution", float(Y_density * aspect + 0.5f));
        m_spec.attribute("YResolution", float(Y_density));
    }
    while (X_density > 65535 || Y_density > 65535) {
        // JPEG header can store only UINT16 density values. If we
        // overflow that limit, punt and knock it down to <= 16 bits.
        X_density /= 2;
        Y_density /= 2;
    }
    m_cinfo.X_density = X_density;
    m_cinfo.Y_density = Y_density;
}



bool
JpgOutput::write_scanline(int y, int z, TypeDesc format, const void* data,
                          stride_t xstride)
{
    y -= m_spec.y;
    if (y != m_next_scanline) {
        errorf("Attempt to write scanlines out of order to %s", m_filename);
        return false;
    }
    if (y >= (int)m_cinfo.image_height) {
        errorf("Attempt to write too many scanlines to %s", m_filename);
        return false;
    }
    assert(y == (int)m_cinfo.next_scanline);

    // Here's where we do the dirty work of conforming to JFIF's limitation
    // of 1 or 3 channels, by temporarily doctoring the spec so that
    // to_native_scanline properly contiguizes the first 1 or 3 channels,
    // then we restore it.  The call to to_native_scanline below needs
    // m_spec.nchannels to be set to the true number of channels we're
    // writing, or it won't arrange the data properly.  But if we doctored
    // m_spec.nchannels permanently, then subsequent calls to write_scanline
    // (including any surrounding call to write_image) with
    // stride=AutoStride would screw up the strides since the user's stride
    // is actually not 1 or 3 channels.
    m_spec.auto_stride(xstride, format, m_spec.nchannels);
    int save_nchannels = m_spec.nchannels;
    m_spec.nchannels   = m_cinfo.input_components;

    data = to_native_scanline(format, data, xstride, m_scratch, m_dither, y, z);
    m_spec.nchannels = save_nchannels;

    jpeg_write_scanlines(&m_cinfo, (JSAMPLE**)&data, 1);
    ++m_next_scanline;

    return true;
}



bool
JpgOutput::write_tile(int x, int y, int z, TypeDesc format, const void* data,
                      stride_t xstride, stride_t ystride, stride_t zstride)
{
    // Emulate tiles by buffering the whole image
    return copy_tile_to_image_buffer(x, y, z, format, data, xstride, ystride,
                                     zstride, &m_tilebuffer[0]);
}



bool
JpgOutput::close()
{
    if (!m_io) {  // Already closed
        init();
        return true;
    }

    bool ok = true;

    if (m_spec.tile_width) {
        // We've been emulating tiles; now dump as scanlines.
        OIIO_DASSERT(m_tilebuffer.size());
        ok &= write_scanlines(m_spec.y, m_spec.y + m_spec.height, 0,
                              m_spec.format, &m_tilebuffer[0]);
        std::vector<unsigned char>().swap(m_tilebuffer);  // free it
    }

    if (m_next_scanline < spec().height && m_copy_coeffs == NULL) {
        // But if we've only written some scanlines, write the rest to avoid
        // errors
        std::vector<char> buf(spec().scanline_bytes(), 0);
        char* data = &buf[0];
        while (m_next_scanline < spec().height) {
            jpeg_write_scanlines(&m_cinfo, (JSAMPLE**)&data, 1);
            ++m_next_scanline;
        }
    }

    if (m_next_scanline >= spec().height || m_copy_coeffs) {
        DBG std::cout << "out close: about to finish_compress\n";
        jpeg_finish_compress(&m_cinfo);
        DBG std::cout << "out close: finish_compress\n";
    } else {
        DBG std::cout << "out close: about to abort_compress\n";
        jpeg_abort_compress(&m_cinfo);
        DBG std::cout << "out close: abort_compress\n";
    }
    DBG std::cout << "out close: about to destroy_compress\n";
    jpeg_destroy_compress(&m_cinfo);

    if (m_outsize) {
        // We had an IOProxy of some type that was not IOFile. JPEG doesn't
        // have fully general IO overloads, but it can write to memory
        // buffers, we did that, so now we have to copy that in one big chunk
        // to IOProxy.
        m_io->write(m_outbuffer, m_outsize);
    }

    m_io_local.reset();  // closes the file if we opened it locally
    init();

    return ok;
}



bool
JpgOutput::copy_image(ImageInput* in)
{
    if (in && !strcmp(in->format_name(), "jpeg")) {
        JpgInput* jpg_in    = dynamic_cast<JpgInput*>(in);
        std::string in_name = jpg_in->filename();
        DBG std::cout << "JPG copy_image from " << in_name << "\n";

        // Save the original input spec and close it
        ImageSpec orig_in_spec = in->spec();
        in->close();
        DBG std::cout << "Closed old file\n";

        // Re-open the input spec, with special request that the JpgInput
        // will recognize as a request to merely open, but not start the
        // decompressor.
        ImageSpec in_spec;
        ImageSpec config_spec;
        config_spec.attribute("_jpeg:raw", 1);
        in->open(in_name, in_spec, config_spec);

        // Re-open the output
        std::string out_name    = m_filename;
        ImageSpec orig_out_spec = spec();
        close();
        m_copy_coeffs       = (jvirt_barray_ptr*)jpg_in->coeffs();
        m_copy_decompressor = &jpg_in->m_cinfo;
        open(out_name, orig_out_spec);

        // Strangeness -- the write_coefficients somehow sets things up
        // so that certain writes only happen in close(), which MUST
        // happen while the input file is still open.  So we go ahead
        // and close() now, so that the caller of copy_image() doesn't
        // close the input file first and then wonder why they crashed.
        close();

        return true;
    }

    return ImageOutput::copy_image(in);
}

OIIO_PLUGIN_NAMESPACE_END

Tips and Conventions

OpenImageIO’s main goal is to hide all the pesky details of individual file formats from the client application. This inevitably leads to various mismatches between a file format’s true capabilities and requests that may be made through the OpenImageIO APIs. This section outlines conventions, tips, and rules of thumb that we recommend for image file support.

Readers

  • If the file format stores images in a non-spectral color space (for example, YUV), the reader should automatically convert to RGB to pass through the OIIO APIs. In such a case, the reader should signal the file’s true color space via a "Foo:colorspace" attribute in the ImageSpec.

  • “Palette” images should be automatically converted by the reader to RGB.

  • If the file supports thumbnail images in its header, the reader should provide an ImageInput::get_thumbnail() method, as well as store the thumbnail dimensions in the ImageSpec as attributes "thumbnail_width", "thumbnail_height", and "thumbnail_nchannels" (all of which should be int).

Writers

The overall rule of thumb is: try to always “succeed” at writing the file, outputting the closest approximation of the user’s data as possible. But it is permissible to fail the open() call if it is clearly nonsensical or there is no possible way to output a decent approximation of the user’s data. Some tips:

  • If the client application requests a data format not directly supported by the file type, silently write the supported data format that will result in the least precision or range loss.

  • It is customary to fail a call to open() if the ImageSpec requested a number of color channels plainly not supported by the file format. As an exception to this rule, it is permissible for a file format that does not support alpha channels to silently drop the fourth (alpha) channel of a 4-channel output request.

  • If the app requests a "Compression" not supported by the file format, you may choose as a default any lossless compression supported. Do not use a lossy compression unless you are fairly certain that the app wanted a lossy compression.

  • If the file format is able to store images in a non-spectral color space (for example, YUV), the writer may accept a "Foo:colorspace" attribute in the ImageSpec as a request to automatically convert and store the data in that format (but it will always be passed as RGB through the OIIO APIs).

  • If the file format can support thumbnail images in its header, and the ImageSpec contain attributes "thumbnail_width", "thumbnail_height", "thumbnail_nchannels", and "thumbnail_image", the writer should attempt to store the thumbnail if possible.

Bundled ImageIO Plugins

This chapter lists all the image format plugins that are bundled with OpenImageIO. For each plugin, we delineate any limitations, custom attributes, etc. The plugins are listed alphabetically by format name.


BMP

BMP is a bitmap image file format used mostly on Windows systems. BMP files use the file extension .bmp.

BMP is not a nice format for high-quality or high-performance images. It only supports unsigned integer 1-, 2-, 4-, and 8- bits per channel; only grayscale, RGB, and RGBA; does not support MIPmaps, multiimage, or tiles.

BMP Attributes

ImageSpec Attribute

Type

BMP header data or explanation

compression

string

The compression of the BMP file ("rle4" or "rle8", if RLE compression is used).

XResolution

float

hres

YResolution

float

vres

ResolutionUnit

string

always "m" (pixels per meter)

bmp:bitsperpixel

int

When not a whole number of bytes per channel, this describes the bits per pixel in the file (16 for R4G4B4, 8 for a 256-color palette image, 4 for a 16-color palette image, 1 for a 2-color palette image).

bmp:version

int

Version of the BMP file format

Configuration settings for BMP input

When opening a BMP ImageInput with a configuration (see Section Opening for input with configuration settings/hints), the following special configuration options are supported:

Input Configuration Attribute

Type

Meaning

bmp:monochrome_detect

int

If nonzero, try to detect when all palette entries are gray and pretend that it’s a 1-channel image to allow the calling app to save memory and time (even though the BMP format does not actually support grayscale images per se. It is 1 by default, but by setting the hint to 0, you can disable this behavior.

BMP Attributes

ImageSpec Attribute

Type

BMP header data or explanation

XResolution

float

hres

YResolution

float

vres

ResolutionUnit

string

always "m" (pixels per meter)

bmp:bitsperpixel

int

When not a whole number of bytes per channel, this describes the bits per pixel in the file (16 for R4G4B4, 8 for a 256-color palette image, 4 for a 16-color palette image, 1 for a 2-color palette image).

bmp:version

int

Version of the BMP file format

BMP Limitations

  • OIIO’s current implementation will only write uncompessed 8bpp (from a 1-channel source), 24bpp (if 3 channel), or 32bpp (if 4 channel). Reads, however, can handle RLE compression as well as 1, 4, or 16 bpp input.

  • Only 1, 3, and 4-channel images are supported with BMP due to limitations of the file format itself.

  • BMP only supports uint8 pixel data types. Requests for other pixel data types will automatically be converted to uint8.


Cineon

Cineon is an image file format developed by Kodak that is commonly used for scanned motion picture film and digital intermediates. Cineon files use the file extension .cin.


DDS

DDS (Direct Draw Surface) is an image file format designed by Microsoft for use in Direct3D graphics. DDS files use the extension .dds.

DDS is an awful format, with several compression modes that are all so lossy as to be completely useless for high-end graphics. Nevertheless, they are widely used in games and graphics hardware directly supports these compression modes. Alas.

OpenImageIO currently only supports reading DDS files, not writing them.

ImageSpec Attribute

Type

DDS header data or explanation

compression

string

Compression type

oiio:BitsPerSample

int

bits per sample

textureformat

string

Set correctly to one of "Plain Texture", "Volume Texture", or "CubeFace Environment".

dds:CubeMapSides

string

For environment maps, which cube faces are present (e.g., "+x -x +y -y" if x & y faces are present, but not z).

DICOM

DICOM (Digital Imaging and Communications in Medicine) is the standard format used for medical images. DICOM files usually have the extension .dcm.

OpenImageIO currently only supports reading DICOM files, not writing them.

ImageSpec Attribute

Type

DDS header data or explanation

oiio:BitsPerSample

int

Bits per sample.

dicom:*

any

DICOM header information and metadata is currently all preceded by the dicom: prefix.

DPX

DPX (Digital Picture Exchange) is an image file format used for motion picture film scanning, output, and digital intermediates. DPX files use the file extension .dpx.

Configuration settings for DPX input

When opening a DPX ImageInput with a configuration (see Section Opening for input with configuration settings/hints), the following special configuration options are supported:

Input Configuration Attribute

Type

Meaning

oiio:RawColor

int

If nonzero, reading images with non-RGB color models (such as YCbCr) will return unaltered pixel values (versus the default OIIO behavior of automatically converting to RGB).

oiio:ioproxy

ptr

Pointer to a Filesystem::IOProxy that will handle the I/O, for example by reading from memory rather than the file system.

Configuration settings for DPX output

When opening a DPX ImageOutput, the following special metadata tokens control aspects of the writing itself:

Output configuration Attribute

Type

Meaning

oiio:RawColor

int

If nonzero, writing images with non-RGB color models (such as YCbCr) will keep unaltered pixel values (versus the default OIIO behavior of automatically converting from RGB to the designated color space as the pixels are written).

oiio:ioproxy

ptr

Pointer to a Filesystem::IOProxy that will handle the I/O, for example by writing to memory rather than the file system.

oiio:dither

int

If nonzero and outputting UINT8 values in the file from a source of higher bit depth, will add a small amount of random dither to combat the appearance of banding.

Custom I/O Overrides

DPX input and output both support the “custom I/O” feature via the special "oiio:ioproxy" attributes (see Sections Custom I/O proxies (and writing the file to a memory buffer) and Custom I/O proxies (and reading the file from a memory buffer)) as well as the set_ioproxy() methods.

DPX Attributes

ImageSpec Attribute

Type

DPX header data or explanation

ImageDescription

string

Description of image element

Copyright

string

Copyright statement

Software

string

Creator

DocumentName

string

Project name

DateTime

string

Creation date/time

Orientation

int

the orientation of the DPX image data (see metadata:orientation)

compression

string

The compression type

PixelAspectRatio

float

pixel aspect ratio

oiio:BitsPerSample

int

the true bits per sample of the DPX file.

oiio:Endian

string

When writing, force a particular endianness for the output "little" or "big")

smpte:TimeCode

int[2]

SMPTE time code (vecsemantics will be marked as TIMECODE)

smpte:KeyCode

int[7]

SMPTE key code (vecsemantics will be marked as KEYCODE)

dpx:Transfer

string

Transfer characteristic

dpx:Colorimetric

string

Colorimetric specification

dpx:ImageDescriptor

string

ImageDescriptor

dpx:Packing

string

Image packing method

dpx:TimeCode

int

SMPTE time code

dpx:UserBits

int

SMPTE user bits

dpx:SourceDateTime

string

source time and date

dpx:FilmEdgeCode

string

FilmEdgeCode

dpx:Signal

string

Signal ("Undefined", "NTSC", "PAL", etc.)

dpx:UserData

UCHAR[*]

User data (stored in an array whose length is whatever it it was in the DPX file)

dpx:EncryptKey

int

Encryption key (-1 is not encrypted)

dpx:DittoKey

int

Ditto (0 = same as previous frame, 1 = new)

dpx:LowData

int

reference low data code value

dpx:LowQuantity

float

reference low quantity

dpx:HighData

int

reference high data code value

dpx:HighQuantity

float

reference high quantity

dpx:XScannedSize

float

X scanned size

dpx:YScannedSize

float

Y scanned size

dpx:FramePosition

int

frame position in sequence

dpx:SequenceLength

int

sequence length (frames)

dpx:HeldCount

int

held count (1 = default)

dpx:FrameRate

float

frame rate of original (frames/s)

dpx:ShutterAngle

float

shutter angle of camera (deg)

dpx:Version

string

version of header format

dpx:Format

string

format (e.g., "Academy")

dpx:FrameId

string

frame identification

dpx:SlateInfo

string

slate information

dpx:SourceImageFileName

string

source image filename

dpx:InputDevice

string

input device name

dpx:InputDeviceSerialNumber

string

input device serial number

dpx:Interlace

int

interlace (0 = noninterlace, 1 = 2:1 interlace

dpx:FieldNumber

int

field number

dpx:HorizontalSampleRate

float

horizontal sampling rate (Hz)

dpx:VerticalSampleRate

float

vertical sampling rate (Hz)

dpx:TemporalFrameRate

float

temporal sampling rate (Hz)

dpx:TimeOffset

float

time offset from sync to first pixel (ms)

dpx:BlackLevel

float

black level code value

dpx:BlackGain

float

black gain

dpx:BreakPoint

float

breakpoint

dpx:WhiteLevel

float

reference white level code value

dpx:IntegrationTimes

float

integration time (s)

dpx:EndOfLinePadding

int

Padded bytes at the end of each line

dpx:EndOfImagePadding

int

Padded bytes at the end of each image

Field3D

Field3d is an open-source volume data file format. Field3d files commonly use the extension .f3d. The official Field3D site is: https://github.com/imageworks/Field3D Currently, OpenImageIO only reads Field3d files, and does not write them.

Fields are comprised of multiple layers (which appear to OpenImageIO as subimages). Each layer/subimage may have a different name, resolution, and coordinate mapping. Layers may be scalar (1 channel) or vector (3 channel) fields, and the data may be half, float, or double.

OpenImageIO always reports Field3D files as tiled. If the Field3d file has a “block size”, the block size will be reported as the tile size. Otherwise, the tile size will be the size of the entire volume.

ImageSpec Attribute

Type

Field3d header data or explanation

ImageDescription

string

unique layer name

oiio:subimagename

string

unique layer name

field3d:partition

string

the partition name

field3d:layer

string

the layer (a.k.a. attribute) name

field3d:fieldtype

string

field type, one of: "dense", "sparse", or "MAC"

field3d:mapping

string

the coordinate mapping type

field3d:localtoworld

matrix of doubles

if a matrixMapping, the local-to-world transformation matrix

worldtolocal

matrix

if a matrixMapping, the world-to-local coordinate mapping

The “unique layer name” is generally the partition name + : + attribute name (example: "defaultfield:density"), with the following exceptions: (1) if the partition and attribute names are identical, just one is used rather than it being pointlessly concatenated (e.g., "density", not "density:density"); (2) if there are mutiple partitions + attribute combinations with identical names in the same file, “number” will be added after the partition name for subsequent layers (e.g., "default:density", "default.2:density", "default.3:density").


FITS

FITS (Flexible Image Transport System) is an image file format used for scientific applications, particularly professional astronomy. FITS files use the file extension .fits. Official FITS specs and other info may be found at: http://fits.gsfc.nasa.gov/

OpenImageIO supports multiple images in FITS files, and supports the following pixel data types: UINT8, UINT16, UINT32, FLOAT, DOUBLE.

FITS files can store various kinds of arbitrary data arrays, but OpenImageIO’s support of FITS is mostly limited using FITS for image storage. Currently, OpenImageIO only supports 2D FITS data (images), not 3D (volume) data, nor 1-D or higher-dimensional arrays.

ImageSpec Attribute

Type

FITS header data or explanation

Orientation

int

derived from FITS “ORIENTAT” field.

DateTime

string

derived from the FITS “DATE” field.

Comment

string

FITS “COMMENT” (*)

History

string

FITS “HISTORY” (*)

Hierarch

string

FITS “HIERARCH” (*)

other

all other FITS keywords will be added to the ImageSpec as arbitrary named metadata.

Note

If the file contains multiple COMMENT, HISTORY, or HIERARCH fields, their text will be appended to form a single attribute (of each) in OpenImageIO’s ImageSpec.


GIF

GIF (Graphics Interchange Format) is an image file format developed by CompuServe in 1987. Nowadays it is widely used to display basic animations despite its technical limitations.

ImageSpec Attribute

Type

GIF header data or explanation

gif:Interlacing

int

Specifies if image is interlaced (0 or 1).

FramesPerSecond

int[2] (rational)

Frames per second

oiio:Movie

int

If nonzero, indicates that it’s a multi-subimage file indended to represent an animation.

oiio:LoopCount

int

Number of times the animation should be played (0-65535, 0 stands for infinity).

gif:LoopCount

int

Deprecated synonym for oiio:LoopCount.

ImageDescription

string

The GIF comment field.

Configuration settings for GIF input

When opening a GIF ImageInput with a configuration (see Section Opening for input with configuration settings/hints), the following special configuration options are supported:

Input Configuration Attribute

Type

Meaning

oiio:ioproxy

ptr

Pointer to a Filesystem::IOProxy that will handle the I/O, for example by reading from memory rather than the file system.

Configuration settings for GIF output

When opening a GIF ImageOutput, the following special metadata tokens control aspects of the writing itself:

Output configuration Attribute

Type

Meaning

oiio:ioproxy

ptr

Pointer to a Filesystem::IOProxy that will handle the I/O, for example by writing to memory rather than the file system.

Custom I/O Overrides

GIF supports the “custom I/O” feature via the special "oiio:ioproxy" attributes (see Sections Custom I/O proxies (and writing the file to a memory buffer) and Custom I/O proxies (and reading the file from a memory buffer)) as well as the set_ioproxy() methods.

Limitations

  • GIF only supports 3-channel (RGB) images and at most 8 bits per channel.

  • Each subimage can include its own palette or use global palette. Palettes contain up to 256 colors of which one can be used as background color. It is then emulated with additional Alpha channel by OpenImageIO’s reader.


HDR/RGBE

HDR (High Dynamic Range), also known as RGBE (rgb with extended range), is a simple format developed for the Radiance renderer to store high dynamic range images. HDR/RGBE files commonly use the file extensions .hdr. The format is described in this section of the Radiance documentation: http://radsite.lbl.gov/radiance/refer/filefmts.pdf

RGBE does not support tiles, multiple subimages, mipmapping, true half or float pixel values, or arbitrary metadata. Only RGB (3 channel) files are supported.

RGBE became important because it was developed at a time when no standard file formats supported high dynamic range, and is still used for many legacy applications and to distribute HDR environment maps. But newer formats with native HDR support, such as OpenEXR, are vastly superior and should be preferred except when legacy file access is required.

ImageSpec Attribute

Type

RGBE header data or explanation

Orientation

int

encodes the orientation (see Section Display hints)

oiio:ColorSpace

string

Color space (see Section Color information).

oiio:Gamma

float

the gamma correction specified in the RGBE header (if it’s gamma corrected).

HEIF/HEIC/AVIF

HEIF is a container format for images compressed with various compression standards (HEIC is based on HEVC/H.265, AVIF is based on AV1). HEIC is used commonly for iPhone camera pictures, but it is not Apple-specific and will probably become more popular on other platforms in coming years. HEIF files usually use the file extension .HEIC or .AVIF depending on their main compression type.

HEIC and AVIF compression formats are lossy, but are higher visual quality than JPEG while taking <= half the file size. Currently, OIIO’s HEIF reader supports reading files as RGB or RGBA, uint8 pixel values. Multi-image files are currently supported for reading, but not yet writing. All pixel data is uint8, though we hope to add support for HDR (more than 8 bits) in the future.

Configuration settings for HEIF input

When opening an HEIF ImageInput with a configuration (see Section Opening for input with configuration settings/hints), the following special configuration attributes are supported:

Input Configuration Attribute

Type

Meaning

oiio:UnassociatedAlpha

int

If nonzero, and the file contains unassociated alpha, this will cause the reader to leave alpha unassociated (versus the default of premultiplying color channels by alpha if the alpha channel is unassociated).

Configuration settings for HEIF output

When opening an HEIF ImageOutput, the following special metadata tokens control aspects of the writing itself:

ImageSpec Attribute

Type

HEIF header data or explanation

Compression

string

If supplied, can be "heic" or "avif", but may optionally have a quality value appended, like "heic:90". Quality can be 1-100, with 100 meaning lossless. The default is 75.

ICO

ICO is an image file format used for small images (usually icons) on Windows. ICO files use the file extension .ico.

Attributes

ImageSpec Attribute

Type

ICO header data or explanation

oiio:BitsPerSample

int

the true bits per sample in the ICO file.

ico:PNG

int

if nonzero, will cause the ICO to be written out using PNG format.

Configuration settings for ICO output

When opening an ICO ImageOutput, the following special metadata tokens control aspects of the writing itself:

Output Configuration Attribute

Type

Meaning

oiio:dither

int

If nonzero and outputting UINT8 values in the file from a source of higher bit depth, will add a small amount of random dither to combat the appearance of banding.

Limitations

  • ICO only supports UINT8 and UINT16 formats; all output images will be silently converted to one of these.

  • ICO only supports small images, up to 256 x 256. Requests to write larger images will fail their open() call.


IFF

IFF files are used by Autodesk Maya and use the file extension .iff.

ImageSpec Attribute

Type

IFF header data or explanation

Artist

string

The IFF “author”

DateTime

string

Creation date/time

compression

string

The compression type ("none" or "rle" [default])

oiio:BitsPerSample

int

the true bits per sample of the IFF file.

Configuration settings for IFF output

When opening an IFF ImageOutput, the following special metadata tokens control aspects of the writing itself:

Output Configuration Attribute

Type

Meaning

oiio:dither

int

If nonzero and outputting UINT8 values in the file from a source of higher bit depth, will add a small amount of random dither to combat the appearance of banding.

JPEG

JPEG (Joint Photographic Experts Group), or more properly the JFIF file format containing JPEG-compressed pixel data, is one of the most popular file formats on the Internet, with applications, and from digital cameras, scanners, and other image acquisition devices. JPEG/JFIF files usually have the file extension .jpg, .jpe, .jpeg, .jif, .jfif, or .jfi. The JFIF file format is described by http://www.w3.org/Graphics/JPEG/jfif3.pdf.

Although we strive to support JPEG/JFIF because it is so widely used, we acknowledge that it is a poor format for high-end work: it supports only 1- and 3-channel images, has no support for alpha channels, no support for high dynamic range or even 16 bit integer pixel data, by convention stores sRGB data and is ill-suited to linear color spaces, and does not support multiple subimages or MIPmap levels. There are newer formats also blessed by the Joint Photographic Experts Group that attempt to address some of these issues, such as JPEG-2000, but these do not have anywhere near the acceptance of the original JPEG/JFIF format.

Attributes

ImageSpec Attribute

Type

JPEG header data or explanation

ImageDescription

string

the JPEG Comment field

Orientation

int

the image orientation

XResolution, YResolution, ResolutionUnit

The resolution and units from the Exif header

Compression

string

If supplied, must be "jpeg", but may optionally have a quality value appended, like "jpeg:90". Quality can be 1-100, with 100 meaning lossless.

ICCProfile

uint8[]

The ICC color profile

jpeg:subsampling

string

Describes the chroma subsampling, e.g., "4:2:0" (the default), "4:4:4", "4:2:2", "4:2:1".

Exif:*, IPTC:*, XMP:*, GPS:*

Extensive Exif, IPTC, XMP, and GPS data are supported by the reader/writer, and you should assume that nearly everything described Appendix Metadata conventions is properly translated when using JPEG files.

Configuration settings for JPEG input

When opening a JPEG ImageInput with a configuration (see Section Opening for input with configuration settings/hints), the following special configuration attributes are supported:

Input Configuration Attribute

Type

Meaning

oiio:ioproxy

ptr

Pointer to a Filesystem::IOProxy that will handle the I/O, for example by reading from memory rather than the file system.

Configuration settings for JPEG output

When opening a JPEG ImageOutput, the following special metadata tokens control aspects of the writing itself:

Output Configuration Attribute

Type

Meaning

oiio:dither

int

If nonzero and outputting UINT8 values in the file from a source of higher bit depth, will add a small amount of random dither to combat the appearance of banding.

oiio:ioproxy

ptr

Pointer to a Filesystem::IOProxy that will handle the I/O, for example by writing to a memory buffer.

jpeg:progressive

int

If nonzero, will write a progressive JPEG file.

Custom I/O Overrides

JPEG supports the “custom I/O” feature via the ImageInput::set_ioproxy() method and the special "oiio:ioproxy" attributes (see Section Custom I/O proxies (and reading the file from a memory buffer)).

Limitations

  • JPEG/JFIF only supports 1- (grayscale) and 3-channel (RGB) images. As a special case, OpenImageIO’s JPEG writer will accept n-channel image data, but will only output the first 3 channels (if n >= 3) or the first channel (if n <= 2), silently drop any extra channels from the output.

  • Since JPEG/JFIF only supports 8 bits per channel, OpenImageIO’s JPEG/JFIF writer will silently convert to UINT8 upon output, regardless of requests to the contrary from the calling program.

  • OpenImageIO’s JPEG/JFIF reader and writer always operate in scanline mode and do not support tiled image input or output.


JPEG-2000

JPEG-2000 is a successor to the popular JPEG/JFIF format, that supports better (wavelet) compression and a number of other extensions. It’s geared toward photography. JPEG-2000 files use the file extensions .jp2 or .j2k. The official JPEG-2000 format specification and other helpful info may be found at: http://www.jpeg.org/JPEG2000.htm

JPEG-2000 is not yet widely used, so OpenImageIO’s support of it is preliminary. In particular, we are not yet very good at handling the metadata robustly.

Attributes

ImageSpec Attribute

Type

JPEG-2000 header data or explanation

jpeg2000:streamformat

string

specifies the JPEG-2000 stream format ("none" or "jpc")

Configuration settings for JPEG-2000 input

When opening an JPEG-2000 ImageInput with a configuration (see Section Opening for input with configuration settings/hints), the following special configuration attributes are supported:

Input Configuration Attribute

Type

Meaning

oiio:UnassociatedAlpha

int

If nonzero, will leave alpha unassociated (versus the default of premultiplying color channels by alpha if the alpha channel is unassociated).

Configuration settings for JPEG-2000 output

When opening a JPEG-2000 ImageOutput, the following special metadata tokens control aspects of the writing itself:

Output Configuration Attribute

Type

Meaning

oiio:dither

int

If nonzero and outputting UINT8 values in the file from a source of higher bit depth, will add a small amount of random dither to combat the appearance of banding.

Movie formats (using ffmpeg)

The ffmpeg-based reader is capable of reading the individual frames from a variety of movie file formats, including:

Format

Extensions

AVI

.avi

QuickTime

.qt, .mov

MPEG-4

.mp4, .m4a, .m4v

3GPP files

.3gp, .3g2

Motion JPEG-2000

.mj2

Apple M4V

.m4v

MPEG-1/MPEG-2

.mpg

Currently, these files may only be read. Write support may be added in a future release. Also, currently, these files simply look to OIIO like simple multi-image files and not much support is given to the fact that they are technically movies (for example, there is no support for reading audio information).

Some special attributes are used for movie files:

ImageSpec Attribute

Type

Header data or explanation

oiio:Movie

int

Nonzero value for movie files

oiio:subimages

int

The number of frames in the movie, positive if it can be known without reading the entire file. Zero or not present if the number of frames cannot be determinend from reading from just the file header.

FramesPerSecond

int[2] (rational)

Frames per second

Null format

The nullptr reader/writer is a mock-up that does not perform any actual I/O. The reader just returns constant-colored pixels, and the writer just returns directly without saving any data. This has several uses:

  • Benchmarking, if you want to have OIIO’s input or output truly take as close to no time whatsoever.

  • “Dry run” of applications where you don’t want it to produce any real output (akin to a Unix command that you redirect output to /dev/null).

  • Make “fake” input that looks like a file, but the file doesn’t exist (if you are happy with constant-colored pixels).

The filename allows a REST-ful syntax, where you can append modifiers that specify things like resolution (of the non-existent file), etc. For example:

foo.null?RES=640x480&CHANNELS=3

would specify a null file with resolution 640x480 and 3 channels. Token/value pairs accepted are:

RES=1024x1024

Set resolution (3D example: 256x256x100)

CHANNELS=4

Set number of channels

TILES=64x64

Makes it look like a tiled image with tile size

TYPE=uint8

Set the pixel data type

PIXEL=r,g,b,...

Set pixel values (comma separates channel values)

TEX=1

Make it look like a full MIP-mapped texture

attrib=value

Anything else will set metadata

OpenEXR

OpenEXR is an image file format developed by Industrial Light & Magic, and subsequently open-sourced. OpenEXR’s strengths include support of high dynamic range imagery (half and float pixels), tiled images, explicit support of MIPmaps and cubic environment maps, arbitrary metadata, and arbitrary numbers of color channels. OpenEXR files use the file extension .exr. The official OpenEXR site is http://www.openexr.com/.

Attributes

ImageSpec Attribute

Type

OpeneEXR header data or explanation

width, height, x, y

int

dataWindow

full_width, full_height, full_x, full_y

int

displayWindow

worldtocamera

matrix

worldToCamera

worldtoscreen

matrix

worldToScreen

worldtoNDC

matrix

worldToNDC

ImageDescription

string

comments

Copyright

string

owner

DateTime

string

capDate

PixelAspectRatio

float

pixelAspectRatio

ExposureTime

float

expTime

FNumber

float

aperture

compression

string

one of: "none", "rle", "zip", "zips", "piz", "pxr24", "b44", "b44a", "dwaa", or "dwab". If the writer receives a request for a compression type it does not recognize or is not supported by the version of OpenEXR on the system, it will use "zip" by default. For "dwaa" and "dwab", the dwaCompressionLevel may be optionally appended to the compression name after a colon, like this: "dwaa:200". (The default DWA compression value is 45.) For "zip" and "zips" compression, a level from 1 to 9 may be appended (the default is "zip:4"), but note that this is only honored when building against OpenEXR 3.1.3 or later.

textureformat

string

"Plain Texture" for MIP-mapped OpenEXR files, "CubeFace Environment" or "Latlong Environment" for OpenEXR environment maps. Non-environment non-MIP-mapped OpenEXR files will not set this attribute.

wrapmodes

string

wrapmodes

FramesPerSecond

int[2]

Frames per second playback rate (vecsemantics will be marked as RATIONAL)

captureRate

int[2]

Frames per second capture rate (vecsemantics will be marked as RATIONAL)

smpte:TimeCode

int[2]

SMPTE time code (vecsemantics will be marked as TIMECODE)

smpte:KeyCode

int[7]

SMPTE key code (vecsemantics will be marked as KEYCODE)

openexr:lineOrder

string

OpenEXR lineOrder attribute: "increasingY", "randomY", or "decreasingY".

openexr:roundingmode

int

the MIPmap rounding mode of the file.

openexr:dwaCompressionLevel

float

compression level for dwaa or dwab compression (default: 45.0).

other

All other attributes will be added to the ImageSpec by their name and apparent type.

Configuration settings for OpenEXR input

When opening an OpenEXR ImageInput with a configuration (see Section Opening for input with configuration settings/hints), the following special configuration attributes are supported:

Input Configuration Attribute

Type

Meaning

oiio:ioproxy

ptr

Pointer to a Filesystem::IOProxy that will handle the I/O, for example by reading from memory rather than the file system.

oiio:missingcolor

float or string

Either an array of float values or a string holding a comma-separated list of values, if present this is a request to use this color for pixels of any missing tiles or scanlines, rather than considering a tile/scanline read failure to be an error. This can be helpful when intentionally reading partially-written or incomplete files (such as an in-progress render).

Configuration settings for OpenEXR output

When opening an OpenEXR ImageOutput, the following special metadata tokens control aspects of the writing itself:

Output Configuration Attribute

Type

Meaning

oiio:RawColor

int

If nonzero, writing images with non-RGB color models (such as YCbCr) will keep unaltered pixel values (versus the default OIIO behavior of automatically converting from RGB to the designated color space as the pixels are written).

oiio:ioproxy

ptr

Pointer to a Filesystem::IOProxy that will handle the I/O, for example by writing to a memory buffer.

Custom I/O Overrides

OpenEXR input and output both support the “custom I/O” feature via the special "oiio:ioproxy" attributes (see Sections Custom I/O proxies (and writing the file to a memory buffer) and Custom I/O proxies (and reading the file from a memory buffer)) as well as the set_ioproxy() methods.

A note on channel names

The underlying OpenEXR library (libIlmImf) always saves channels into lexicographic order, so the channel order on disk (and thus when read!) will NOT match the order when the image was created.

But in order to adhere to OIIO’s convention that RGBAZ will always be the first channels (if they exist), OIIO’s OpenEXR reader will automatically reorder just those channels to appear at the front and in that order. All other channel names will remain in their relative order as presented to OIIO by libIlmImf.

Limitations

  • The OpenEXR format only supports HALF, FLOAT, and UINT32 pixel data. OpenImageIO’s OpenEXR writer will silently convert data in formats (including the common UINT8 and UINT16 cases) to HALF data for output.


OpenVDB

OpenVDB is an open-source volume data file format. OpenVDB files commonly use the extension .vdb. The official OpenVDB site is: http://www.openvdb.org/ Currently, OpenImageIO only reads OpenVDB files, and does not write them.

Volumes are comprised of multiple layers (which appear to OpenImageIO as subimages). Each layer/subimage may have a different name, resolution, and coordinate mapping. Layers may be scalar (1 channel) or vector (3 channel) fields, and the voxel data are always float. OpenVDB files always report as tiled, using the leaf dimension size.

ImageSpec Attribute

Type

OpenVDB header data or explanation

ImageDescription

string

Description of image element

oiio:subimagename

string

unique layer name

openvdb:indextoworld

matrix of doubles

conversion of voxel index to world space coordinates.

openvdb:worldtoindex

matrix of doubles

conversion of world space coordinates to voxel index.

worldtocamera

matrix

World-to-local coordinate mapping.

PNG

PNG (Portable Network Graphics) is an image file format developed by the open source community as an alternative to the GIF, after Unisys started enforcing patents allegedly covering techniques necessary to use GIF. PNG files use the file extension .png.

Attributes

ImageSpec Attribute

Type

PNG header data or explanation

ImageDescription

string

Description

Artist

string

Author

DocumentName

string

Title

DateTime

string

the timestamp in the PNG header

PixelAspectRatio

float

pixel aspect ratio

XResolution, YResolution, ResolutionUnit

resolution and units from the PNG header.

oiio:ColorSpace

string

Color space (see Section Color information).

oiio:Gamma

float

the gamma correction value (if specified).

ICCProfile

uint8[]

The ICC color profile

Configuration settings for PNG input

When opening an PNG ImageInput with a configuration (see Section Opening for input with configuration settings/hints), the following special configuration attributes are supported:

Input Configuration Attribute

Type

Meaning

oiio:UnassociatedAlpha

int

If nonzero, will leave alpha unassociated (versus the default of premultiplying color channels by alpha if the alpha channel is unassociated).

oiio:ioproxy

ptr

Pointer to a Filesystem::IOProxy that will handle the I/O, for example by reading from memory rather than the file system.

Configuration settings for PNG output

When opening an PNG ImageOutput, the following special metadata tokens control aspects of the writing itself:

Output Configuration Attribute

Type

Meaning

oiio:dither

int

If nonzero and outputting UINT8 values in the file from a source of higher bit depth, will add a small amount of random dither to combat the appearance of banding.

oiio:ioproxy

ptr

Pointer to a Filesystem::IOProxy that will handle the I/O, for example by writing to a memory buffer.

png:compressionLevel

int

Compression level for zip/deflate compression, on a scale from 0 (fastest, minimal compression) to 9 (slowest, maximal compression). The default is 6. PNG compression is always lossless.

png:filter

int

Controls the “row filters” that prepare the image for optimal compression. The default is 0 (PNG_NO_FILTERS), but other values (which may be “or-ed” or summed to combine their effects) are 8 (PNG_FILTER_NONE), 16 (PNG_FILTER_SUB), 32 (PNG_FILTER_UP), 64 (PNG_FILTER_AVG), or 128 (PNG_FILTER_PAETH).

Custom I/O Overrides

PNG input and output both support the “custom I/O” feature via the special "oiio:ioproxy" attributes (see Sections Custom I/O proxies (and writing the file to a memory buffer) and Custom I/O proxies (and reading the file from a memory buffer)) as well as the set_ioproxy() methods.

Limitations

  • PNG stupidly specifies that any alpha channel is “unassociated” (i.e., that the color channels are not “premultiplied” by alpha). This is a disaster, since it results in bad loss of precision for alpha image compositing, and even makes it impossible to properly represent certain additive glows and other desirable pixel values. OpenImageIO automatically associates alpha (i.e., multiplies colors by alpha) upon input and deassociates alpha (divides colors by alpha) upon output in order to properly conform to the OIIO convention (and common sense) that all pixel values passed through the OIIO APIs should use associated alpha.

  • PNG only supports UINT8 and UINT16 output; other requested formats will be automatically converted to one of these.


PNM / Netpbm

The Netpbm project, a.k.a. PNM (portable “any” map) defines PBM, PGM, and PPM (portable bitmap, portable graymap, portable pixmap) files. Without loss of generality, we will refer to these all collectively as “PNM.” These files have extensions .pbm, .pgm, and .ppm and customarily correspond to bi-level bitmaps, 1-channel grayscale, and 3-channel RGB files, respectively, or .pnm for those who reject the nonsense about naming the files depending on the number of channels and bitdepth.

PNM files are not much good for anything, but because of their historical significance and extreme simplicity (that causes many “amateur” programs to write images in these formats), OpenImageIO supports them. PNM files do not support floating point images, anything other than 1 or 3 channels, no tiles, no multi-image, no MIPmapping. It’s not a smart choice unless you are sending your images back to the 1980’s via a time machine.

Attributes

ImageSpec Attribute

Type

PNM header data or explanation

oiio:BitsPerSample

int

The true bits per sample of the file (1 for true PBM files, even though OIIO will report the format as UINT8).

pnm:binary

int

nonzero if the file itself used the PNM binary format, 0 if it used ASCII. The PNM writer honors this attribute in the ImageSpec to determine whether to write an ASCII or binary file.

Configuration settings for PNM output

When opening a PNM ImageOutput, the following special metadata tokens control aspects of the writing itself:

Output Configuration Attribute

Type

Meaning

oiio:dither

int

If nonzero and outputting UINT8 values in the file from a source of higher bit depth, will add a small amount of random dither to combat the appearance of banding.

PSD

PSD is the file format used for storing Adobe PhotoShop images. OpenImageIO provides limited read abilities for PSD, but not currently the ability to write PSD files.

Configuration settings for PSD input

When opening an ImageInput with a configuration (see Section Opening for input with configuration settings/hints), the following special configuration options are supported:

Input Configuration Attribute

Type

Meaning

oiio:RawColor

int

If nonzero, reading images with non-RGB color models (such as YCbCr or CMYK) will return unaltered pixel values (versus the default OIIO behavior of automatically converting to RGB).

Currently, the PSD format reader supports color modes RGB, CMYK, multichannel, grayscale, indexed, and bitmap. It does NOT currenty support Lab or duotone modes.


Ptex

Ptex is a special per-face texture format developed by Walt Disney Feature Animation. The format and software to read/write it are open source, and available from http://ptex.us/. Ptex files commonly use the file extension .ptex.

OpenImageIO’s support of Ptex is still incomplete. We can read pixels from Ptex files, but the TextureSystem doesn’t properly filter across face boundaries when using it as a texture. OpenImageIO currently does not write Ptex files at all.

ImageSpec Attribute

Type

Ptex header data or explanation

ptex:meshType

string

the mesh type, either "triangle" or "quad".

ptex:hasEdits

int

nonzero if the Ptex file has edits.

wrapmode

string

the wrap mode as specified by the Ptex file.

other

Any other arbitrary metadata in the Ptex file will be stored directly as attributes in the ImageSpec.

RAW digital camera files

A variety of digital camera “raw” formats are supported via this plugin that is based on the LibRaw library (http://www.libraw.org/).

Configuration settings for RAW input

When opening an ImageInput with a configuration (see Section Opening for input with configuration settings/hints), the following special configuration options are supported:

Input Configuration Attribute

Type

Meaning

raw:auto_bright

int

If nonzero, will use libraw’s exposure correction. (Default: 0)

raw:use_camera_wb

int

If 1, use libraw’s camera white balance adjustment. (Default: 1)

raw:use_camera_matrix

int

Whether to use the embedded color profile, if it’s present: 0 = never, 1 (default) = only for DNG files, 3 = always.

raw:adjust_maximum_thr

float

If nonzero, auto-adjusting maximum value. (Default:0.0)

raw:user_sat

int

If nonzero, sets the camera maximum value that will be normalized to appear saturated. (Default: 0)

raw:aber

float[2]

Red and blue scale factors for chromatic aberration correction when decoding the raw image. The default (1,1) means to perform no correction. This is an overall spatial scale, sensible values will be very close to 1.0.

raw:half_size

int

If nonzero, outputs the image in half size. (Default: 0)

raw:user_mul

float[4]

Sets user white balance coefficients. Only applies if raw:use_camera_wb is not equal to 0.

raw:ColorSpace

string

Which color primaries to use for the returned pixel values: raw, sRGB, sRGB-linear (sRGB primaries, but a linear transfer function), Adobe, Wide, ProPhoto, ProPhoto-linear, XYZ, ACES (only supported by LibRaw >= 0.18), DCI-P3 (LibRaw >= 0.21), Rec2020 (LibRaw >= 0.2). (Default: sRGB)

raw:Exposure

float

Amount of exposure before de-mosaicing, from 0.25 (2 stop darken) to 8 (3 stop brighten). (Default: 0, meaning no correction.)

raw:Demosaic

string

Force a demosaicing algorithm: linear, VNG, PPG, AHD (default), DCB, AHD-Mod, AFD, VCD, Mixed, LMMSE, AMaZE, DHT, AAHD, none.

raw:HighlightMode

int

Set libraw highlight mode processing: 0 = clip, 1 = unclip, 2 = blend, 3+ = rebuild. (Default: 0.)

raw:balance_clamped

int

If nonzero, balance any clamped highlight values in the image. Resolves issues where highlights take on an undesired hue shift due to incongruous channel sensor saturation. Enabling this option will change the output datatype to HALF. (Default: 0)

raw:apply_scene_linear_scale

int

If nonzero, applies an additional multiplication to the pixel values returned by libraw. See raw:camera_to_scene_linear_scale for more details. Enabling this option will change the output datatype to HALF. (Default: 0)

raw:camera_to_scene_linear_scale

float

Whilst the libraw pixel values are linear, they are normalized based on the whitepoint / sensor / ISO and shooting conditions. An additional multiplication is needed to bring exposure levels up so that a correctly photographed 18% grey card has pixel values at 0.18. Setting this metadata key implies raw:apply_scene_linear_scale. Enabling this option will change the output datatype to HALF. (Default: 2.2222222222222223 (1.0/0.45))

raw:user_flip

int

Set libraw user flip value : -1 ignored, other values are between [0; 8] with the same definition than the Exif orientation code.

RLA

RLA (Run-Length encoded, version A) is an early CGI renderer output format, originating from Wavefront Advanced Visualizer and used primarily by software developed at Wavefront. RLA files commonly use the file extension .rla.

Attributes

ImageSpec Attribute

Type

RLA header data or explanation

width, height, x, y

int

RLA “active/viewable” window.

full_width, full_height, full_x, full_y

int

RLA “full” window.

rla:FrameNumber

int

frame sequence number.

rla:Revision

int

file format revision number, currently 0xFFFE.

rla:JobNumber

int

job number ID of the file.

rla:FieldRendered

int

whether the image is a field-rendered (interlaced) one 0 for false, non-zero for true.

rla:FileName

string

name under which the file was orignally saved.

ImageDescription

string

RLA “Description” of the image.

Software

string

name of software used to save the image.

HostComputer

string

name of machine used to save the image.

Artist

string

RLA “UserName”: logon name of user who saved the image.

rla:Aspect

string

aspect format description string.

rla:ColorChannel

string

textual description of color channel data format (usually rgb).

rla:Time

string

description (format not standardized) of amount of time spent on creating the image.

rla:Filter

string

name of post-processing filter applied to the image.

rla:AuxData

string

textual description of auxiliary channel data format.

rla:AspectRatio

float

image aspect ratio.

rla:RedChroma

vec2 or vec3 of floats

red point XY (vec2) or XYZ (vec3) coordinates.

rla:GreenChroma

vec2 or vec3 of floats

green point XY (vec2) or XYZ (vec3) coordinates.

rla:BlueChroma

vec2 or vec3 of floats

blue point XY (vec2) or XYZ (vec3) coordinates.

rla:WhitePoint

vec2 or vec3 of floats

white point XY (vec2) or XYZ (vec3) coordinates.

oiio:ColorSpace

string

Color space (see Section Color information).

oiio:Gamma

float

the gamma correction value (if specified).

Configuration settings for RLA output

When opening a RLA ImageOutput, the following special metadata tokens control aspects of the writing itself:

Output Configuration Attribute

Type

Meaning

oiio:dither

int

If nonzero and outputting UINT8 values in the file from a source of higher bit depth, will add a small amount of random dither to combat the appearance of banding.

Limitations

  • OpenImageIO will only write a single image to each file, multiple subimages are not supported by the writer (but are supported by the reader).


SGI

The SGI image format was a simple raster format used long ago on SGI machines. SGI files use the file extensions sgi, rgb, rgba, bw, int, and inta.

The SGI format is sometimes used for legacy apps, but has little merit otherwise: no support for tiles, no MIPmaps, no multi-subimage, only 8- and 16-bit integer pixels (no floating point), only 1-4 channels.

Attributes

ImageSpec Attribute

Type

SGI header data or explanation

compression

string

The compression of the SGI file (rle, if RLE compression is used).

ImageDescription

string

Image name.

Configuration settings for SGI output

When opening an SGI ImageOutput, the following special metadata tokens control aspects of the writing itself:

Output Configuration Attribute

Type

Meaning

oiio:dither

int

If nonzero and outputting UINT8 values in the file from a source of higher bit depth, will add a small amount of random dither to combat the appearance of banding.

Softimage PIC

Softimage PIC is an image file format used by the SoftImage 3D application, and some other programs that needed to be compatible with it. Softimage files use the file extension .pic.

The Softimage PIC format is sometimes used for legacy apps, but has little merit otherwise, so currently OpenImageIO only reads Softimage files and is unable to write them.

ImageSpec Attribute

Type

PIC header data or explanation

compression

string

The compression of the SGI file (rle, if RLE compression is used).

ImageDescription

string

Comment

oiio:BitsPerSample

int

the true bits per sample of the PIC file.

Targa

Targa (a.k.a. Truevision TGA) is an image file format with little merit except that it is very simple and is used by many legacy applications. Targa files use the file extension .tga, or, much more rarely, .tpic. The official Targa format specification may be found at: http://www.dca.fee.unicamp.br/~martino/disciplinas/ea978/tgaffs.pdf

Attributes

ImageSpec Attribute

Type

TGA header data or explanation

ImageDescription

string

Comment

Artist

string

author

DocumentName

string

job name/ID

Software

string

software name

DateTime

string

TGA time stamp

targa:JobTime

string

TGA “job time.”

compression

string

values of none and rle are supported. The writer will use RLE compression if any unknown compression methods are requested.

targa:alpha_type

int

Meaning of any alpha channel (0 = none; 1 = undefined, ignore; 2 = undefined, preserve; 3 = useful unassociated alpha; 4 = useful associated alpha / premultiplied color).

targa:ImageID

string

Image ID

targa:JobTime

string

Job time

targa:version

int

TGA file format version (1 or 2)

PixelAspectRatio

float

pixel aspect ratio

oiio:BitsPerSample

int

the true bits per sample of the PIC file.

oiio:ColorSpace

string

Color space (see Section Color information).

oiio:Gamma

float

the gamma correction value (if specified).

If the TGA file contains a thumbnail, its dimensions will be stored in the attributes "thumbnail_width", "thumbnail_height", and "thumbnail_nchannels", and the thumbnail pixels themselves will be retrievable via ImageInput::get_thumbnail() or ImageBuf::thumbnail() or ImageCache::get_thumbnail().

Configuration settings for Targa input

When opening an Targa ImageInput with a configuration (see Section Opening for input with configuration settings/hints), the following special configuration attributes are supported:

Input Configuration Attribute

Type

Meaning

oiio:ioproxy

ptr

Pointer to a Filesystem::IOProxy that will handle the I/O, for example by reading from memory rather than the file system.

oiio:UnassociatedAlpha

int

If nonzero, and the file contains unassociated alpha, this will cause the reader to leave alpha unassociated (versus the default of premultiplying color channels by alpha if the alpha channel is unassociated).

Configuration settings for Targa output

When opening a Targa ImageOutput, the following special metadata tokens control aspects of the writing itself:

Output Configuration Attribute

Type

Meaning

oiio:dither

int

If nonzero and outputting UINT8 values in the file from a source of higher bit depth, will add a small amount of random dither to combat the appearance of banding.

Limitations

  • The Targa reader reserves enough memory for the entire image. Therefore it is not a good choice for high-performance image use such as would be used for ImageCache or TextureSystem.

  • Targa files only support 8- and 16-bit unsigned integers (no signed, floating point, or HDR capabilities); the OpenImageIO TGA writer will silently convert all output images to UINT8 (except if UINT16 is explicitly requested).

  • Targa only supports grayscale, RGB, and RGBA; the OpenImageIO TGA writer will fail its call to open() if it is asked create a file with more than 4 color channels.


Term (Terminal)

This experimental output-only “format” is actually a procedural output that writes a low-res representation of the image to the console output. It requires a terminal application that supports Unicode and 24 bit color extensions.

The term ImageOutput supports the following special metadata tokens to control aspects of the writing itself:

Output Configuration Attribute

Type

Meaning

term:method

string

May be one of iterm2, 24bit (default), 24bit-space, 256color, or dither.

term:fit

int

If 1 (the default), the image will be resized to fit on the console window.

The iterm2 mode is the best quality and is the default mode when actually running on a Mac and launching using iTerm2 as the terminal. This mode uses iTerm2’s nonstandard extension to directly output an pixel array to be visible in the terminal.

The default in other circumstances is the 24bit mode, which displays two approximately square pixels vertically in each character cell, by outputting the Unicode “upper half block” glyph (\u2508) with the foreground color set to the top pixel’s color and the background color set to the bottom pixel’s color.

If this doesn’t look right, or your terminal doesn’t support Unicode, the 24bit-space is an alternate mode that displays one elongated pixel in each character cell, writing a space character with the correct color.

There’s also a 256color method that just uses the 6x6x6 color space in the 256 color palette – which looks horrible – and an experimental dither which does a half-assed Floyd-Steinberg dithering, horizontally only, and frankly is not an improvement unless you squint really hard. These may change or be eliminted in the future.

In all cases, the image will automatically be resized to fit in the terminal and keep approximately the correct aspect ratio, as well as converted to sRGB so it looks kinda ok.


TIFF

TIFF (Tagged Image File Format) is a flexible file format created by Aldus, now controlled by Adobe. TIFF supports nearly everything anybody could want in an image format (and has extactly the complexity you would expect from such a requirement). TIFF files commonly use the file extensions .tif or, .tiff. Additionally, OpenImageIO associates the following extensions with TIFF files by default: .tx, .env, .sm, .vsm.

The official TIFF format specification may be found here: http://partners.adobe.com/public/developer/tiff/index.html The most popular library for reading TIFF directly is libtiff, available here: http://www.remotesensing.org/libtiff/ OpenImageIO uses libtiff for its TIFF reading/writing.

We like TIFF a lot, especially since its complexity can be nicely hidden behind OIIO’s simple APIs. It supports a wide variety of data formats (though unfortunately not half), an arbitrary number of channels, tiles and multiple subimages (which makes it our preferred texture format), and a rich set of metadata.

OpenImageIO supports the vast majority of TIFF features, including: tiled images (tiled) as well as scanline images; multiple subimages per file (multiimage); MIPmapping (using multi-subimage; that means you can’t use multiimage and MIPmaps simultaneously); data formats 8- 16, and 32 bit integer (both signed and unsigned), and 32- and 64-bit floating point; palette images (will convert to RGB); “miniswhite” photometric mode (will convert to “minisblack”).

The TIFF plugin attempts to support all the standard Exif, IPTC, and XMP metadata if present.

Configuration settings for TIFF input

When opening an ImageInput with a configuration (see Section Opening for input with configuration settings/hints), the following special configuration options are supported:

Input Configuration Attribute

Type

Meaning

oiio:UnassociatedAlpha

int

If nonzero, and the file contains unassociated alpha, this will cause the reader to leave alpha unassociated (versus the default of premultiplying color channels by alpha if the alpha channel is unassociated).

oiio:RawColor

int

If nonzero, reading images with non-RGB color models (such as YCbCr) will return unaltered pixel values (versus the default OIIO behavior of automatically converting to RGB).

oiio:ioproxy

ptr

Pointer to a Filesystem::IOProxy that will handle the I/O, for example by reading from memory rather than the file system.

Configuration settings for TIFF output

When opening an ImageOutput, the following special metadata tokens control aspects of the writing itself:

Output Configuration Attribute

Type

Meaning

oiio:BitsPerSample

int

Requests a rescaling to a specific bits per sample (such as writing 12-bit TIFFs).

oiio:dither

int

If nonzero and outputting UINT8 values in the file from a source of higher bit depth, will add a small amount of random dither to combat the appearance of banding.

oiio:ioproxy

ptr

Pointer to a Filesystem::IOProxy that will handle the I/O, for example by writing to memory rather than the file system.

oiio:UnassociatedAlpha

int

If nonzero, any alpha channel is understood to be unassociated, and the EXTRASAMPLES tag in the TIFF file will be set to reflect this).

tiff:write_exif

int

If zero, will not write any Exif data to the TIFF file. (The default is 1.)

tiff:half

int

If nonzero, allow writing TIFF files with half (16 bit float) pixels. The default of 0 will automatically translate to float pixels, since most non-OIIO applications will not properly read half TIFF files despite their being legal.

tiff:ColorSpace

string

Requests that the file be saved with a non-RGB color spaces. Choices are RGB, CMYK. (YCbCr, CIELAB, ICCLAB, ITULAB are not yet supported.)

tiff:zipquality

int

A time-vs-space knob for zip compression, ranging from 1-9 (default is 6). Higher means compress to less space, but taking longer to do so. It is strictly a time vs space tradeoff, the visual image quality is identical (lossless) no matter what the setting.

tiff:RowsPerStrip

int

Overrides TIFF scanline rows per strip with a specific request (if not supplied, OIIO will choose a reasonable default).

tiff:bigtiff

int

If nonzero, forces use of “bigtiff,” a nonstandard extension that allows files to be more than 4 GB (default: 0).

TIFF compression modes

The full list of possible TIFF compression mode values are as follows ($ ^*$ indicates that OpenImageIO can write that format, and is not part of the format name):

none $ ^*$ lzw $ ^*$ zip $ ^*$ ccitt_t4 ccitt_t6 ccittfax3 ccittfax4 ccittrle2 ccittrle $ ^*$ dcs isojbig IT8BL IT8CTPAD IT8LW IT8MP jp2000 jpeg $ ^*$ lzma next ojpeg packbits $ ^*$ pixarfilm pixarlog sgilog24 sgilog T43 T85 thunderscan

Custom I/O Overrides

TIFF input and output support the “custom I/O” feature via the ImageInput::set_ioproxy() method and the special "oiio:ioproxy" attributes (see Section Custom I/O proxies (and reading the file from a memory buffer)).

Limitations

OpenImageIO’s TIFF reader and writer have some limitations you should be aware of:

  • No separate per-channel data formats (not supported by libtiff).

  • Only multiples of 8 bits per pixel may be passed through OpenImageIO’s APIs, e.g., 1-, 2-, and 4-bits per pixel will be passed by OIIO as 8 bit images; 12 bits per pixel will be passed as 16, etc. But the oiio:BitsPerSample attribute in the ImageSpec will correctly report the original bit depth of the file. Similarly for output, you must pass 8 or 16 bit output, but oiio:BitsPerSample gives a hint about how you want it to be when written to the file, and it will try to accommodate the request (for signed integers, TIFF output can accommodate 2, 4, 8, 10, 12, and 16 bits).

  • JPEG compression is limited to 8-bit per channel, 3-channel files.

TIFF Attributes

ImageSpec Attribute

Type

TIFF header data or explanation

ImageSpec::x

int

XPosition

ImageSpec::y

int

YPosition

ImageSpec::full_width

int

PIXAR_IMAGEFULLWIDTH

ImageSpec::full_length

int

PIXAR_IMAGEFULLLENGTH

ImageDescription

string

ImageDescription

DateTime

string

DateTime

Software

string

Software

Artist

string

Artist

Copyright

string

Copyright

Make

string

Make

Model

string

Model

DocumentName

string

DocumentName

HostComputer

string

HostComputer

XResultion, YResolution

float

XResolution, YResolution

ResolutionUnit

string

ResolutionUnit (in or cm).

Orientation

int

Orientation

ICCProfile

uint8[]

The ICC color profile

textureformat

string

PIXAR_TEXTUREFORMAT

wrapmodes

string

PIXAR_WRAPMODES

fovcot

float

PIXAR_FOVCOT

worldtocamera

matrix

PIXAR_MATRIX_WORLDTOCAMERA

worldtoscreen

matrix

PIXAR_MATRIX_WORLDTOSCREEN

compression

string

based on TIFF Compression (one of none, lzw, zip, or others listed above).

tiff:compression

int

the original integer code from the TIFF Compression tag.

tiff:planarconfig

string

PlanarConfiguration (separate or contig). The OpenImageIO TIFF writer will honor such a request in the ImageSpec.

tiff:PhotometricInterpretation

int

Photometric

tiff:PageName

string

PageName

tiff:PageNumber

int

PageNumber

tiff:RowsPerStrip

int

RowsPerStrip

tiff:subfiletype

int

SubfileType

Exif:*

A wide variety of EXIF data are honored, and are all prefixed with Exif.

oiio:BitsPerSample

int

The actual bits per sample in the file (may differ from ImageSpec::format).

oiio:UnassociatedAlpha

int

Nonzero if the data returned by OIIO will have “unassociated” alpha.

tiff:UnassociatedAlpha

int

Nonzero if the data in the file had “unassociated” alpha (even if using the usual convention of returning associated alpha from the read methods).

Webp

WebP is an image file format developed by Google that is intended to be an open standard for lossy-compressed images for use on the web.

Attributes

ImageSpec Attribute

Type

WebP header data or explanation

oiio:Movie

int

If nonzero, indicates that it’s a multi-subimage file indended to represent an animation.

oiio:LoopCount

int

Number of times the animation should be played (0-65535, 0 stands for infinity).

webp:LoopCount

int

Deprecated synonym for oiio:LoopCount.

Configuration settings for WebP output

When opening a WebP ImageOutput, the following special metadata tokens control aspects of the writing itself:

Output Configuration Attribute

Type

Meaning

oiio:dither

int

If nonzero and outputting UINT8 values in the file from a source of higher bit depth, will add a small amount of random dither to combat the appearance of banding.

Limitations

  • WebP only supports 3-channel (RGB) or 4-channel (RGBA) images and must be 8-bit unsigned integer pixel values (uint8).


Zfile

Zfile is a very simple format for writing a depth (z) image, originally from Pixar’s PhotoRealistic RenderMan but now supported by many other renderers. It’s extremely minimal, holding only a width, height, world-to-screen and camera-to-screen matrices, and uncompressed float pixels of the z-buffer. Zfile files use the file extension .zfile.

ImageSpec Attribute

Type

Zfile header data or explanation

worldtocamera

matrix

NP

worldtoscreen

matrix

Nl

Cached Images

Image Cache Introduction and Theory of Operation

ImageCache is a utility class that allows an application to read pixels from a large number of image files while using a remarkably small amount of memory and other resources. Of course it is possible for an application to do this directly using ImageInput objects. But ImageCache offers the following advantages:

  • ImageCache presents an even simpler user interface than ImageInput — the only supported operations are asking for an ImageSpec describing a subimage in the file, retrieving for a block of pixels, and locking/reading/releasing individual tiles. You refer to images by filename only; you don’t need to keep track of individual file handles or ImageInput objects. You don’t need to explicitly open or close files.

  • The ImageCache is completely thread-safe; if multiple threads are accessing the same file, the ImageCache internals will handle all the locking and resource sharing.

  • No matter how many image files you are accessing, the ImageCache will maintain a reasonable number of simultaneously-open files, automatically closing files that have not been needed recently.

  • No matter how large the total pixels in all the image files you are dealing with are, the ImageCache will use only a small amount of memory. It does this by loading only the individual tiles requested, and as memory allotments are approached, automatically releasing the memory from tiles that have not been used recently.

In short, if you have an application that will need to read pixels from many large image files, you can rely on ImageCache to manage all the resources for you. It is reasonable to access thousands of image files totalling hundreds of GB of pixels, efficiently and using a memory footprint on the order of 50 MB.

Below are some simple code fragments that shows ImageCache in action:

#include <OpenImageIO/imagecache.h>
using namespace OIIO;

// Create an image cache and set some options
ImageCache *cache = ImageCache::create ();
cache->attribute ("max_memory_MB", 500.0f);
cache->attribute ("autotile", 64);

// Get a block of pixels from a file.
// (for brevity of this example, let's assume that 'size' is the
// number of channels times the number of pixels in the requested region)
float pixels[size];
cache->get_pixels ("file1.jpg", 0, 0, xbegin, xend, ybegin, yend,
                   zbegin, zend, TypeDesc::FLOAT, pixels);

// Get information about a file
ImageSpec spec;
bool ok = cache->get_imagespec ("file2.exr", spec);
if (ok)
    std::cout << "resolution is " << spec.width << "x"
              << spec.height << "\n";

// Request and hold a tile, do some work with its pixels, then release
ImageCache::Tile *tile;
tile = cache->get_tile ("file2.exr", 0, 0, x, y, z);
// The tile won't be freed until we release it, so this is safe:
TypeDesc format;
void *p = cache->tile_pixels (tile, format);
// Now p points to the raw pixels of the tile, whose data format
// is given by 'format'.
cache->release_tile (tile);
// Now cache is permitted to free the tile when needed

// Note that all files were referenced by name, we never had to open
// or close any files, and all the resource and memory management
// was automatic.

ImageCache::destroy (cache);

ImageCache API

class OIIO::ImageCache

Define an API to an abstract class that manages image files, caches of open file handles as well as tiles of pixels so that truly huge amounts of image data may be accessed by an application with low memory footprint.

Creating and destroying an image cache

ImageCache is an abstract API described as a pure virtual class. The actual internal implementation is not exposed through the external API of OpenImageIO. Because of this, you cannot construct or destroy the concrete implementation, so two static methods of ImageCache are provided:

static ImageCache *create(bool shared = true)

Create a ImageCache and return a raw pointer to it. This should only be freed by passing it to ImageCache::destroy()!

Return

A raw pointer to an ImageCache, which can only be freed with ImageCache::destroy().

See

ImageCache::destroy

Parameters

  • shared: If true, the pointer returned will be a shared ImageCache (so that multiple parts of an application that request an ImageCache will all end up with the same one). If shared is false, a completely unique ImageCache will be created and returned.

static void destroy(ImageCache *cache, bool teardown = false)

Destroy an allocated ImageCache, including freeing all system resources that it holds.

It is safe to destroy even a shared ImageCache, as the implementation of destroy() will recognize a shared one and only truly release its resources if it has been requested to be destroyed as many times as shared ImageCache’s were created.

Parameters

  • cache: Raw pointer to the ImageCache to destroy.

  • teardown: For a shared ImageCache, if the teardown parameter is true, it will try to truly destroy the shared cache if nobody else is still holding a reference (otherwise, it will leave it intact). This parameter has no effect if cache was not the single globally shared ImageCache.

Setting options and limits for the image cache

These are the list of attributes that can bet set or queried by attribute/getattribute:

  • int max_open_files : The maximum number of file handles that the image cache will hold open simultaneously. (Default = 100)

  • float max_memory_MB : The maximum amount of memory (measured in MB) used for the internal “tile cache.” (Default: 256.0 MB)

  • string searchpath : The search path for images: a colon-separated list of directories that will be searched in order for any image filename that is not specified as an absolute path. (Default: “”)

  • string plugin_searchpath : The search path for plugins: a colon-separated list of directories that will be searched in order for any OIIO plugins, if not found in OIIO’s lib directory. (Default: “”)

  • int autotile , int autoscanline : These attributes control how the image cache deals with images that are not “tiled” (i.e., are stored as scanlines).

    If autotile is set to 0 (the default), an untiled image will be treated as if it were a single tile of the resolution of the whole image. This is simple and fast, but can lead to poor cache behavior if you are simultaneously accessing many large untiled images.

    If autotile is nonzero (e.g., 64 is a good recommended value), any untiled images will be read and cached as if they were constructed in tiles of size: 

    - `autotile * autotile`
      if `autoscanline` is 0
- `width * autotile`
      if `autoscanline` is nonzero.

    In both cases, this should lead more efficient caching. The autoscanline determines whether the “virtual tiles” in the cache are square (if autoscanline is 0, the default) or if they will be as wide as the image (but only autotile scanlines high). You should try in your application to see which leads to higher performance.

  • int autoscanline : autotile using full width tiles

  • int automip : If 0 (the default), an untiled single-subimage file will only be able to utilize that single subimage. If nonzero, any untiled, single-subimage (un-MIP-mapped) images will have lower-resolution MIP-map levels generated on-demand if pixels are requested from the lower-res subimages (that don’t really exist). Essentially this makes the ImageCache pretend that the file is MIP-mapped even if it isn’t.

  • int accept_untiled : When nonzero, ImageCache accepts untiled images as usual. When zero, ImageCache will reject untiled images with an error condition, as if the file could not be properly read. This is sometimes helpful for applications that want to enforce use of tiled images only. (default=1)

  • int accept_unmipped : When nonzero, ImageCache accepts un-MIPmapped images as usual. When set to zero, ImageCache will reject un-MIPmapped images with an error condition, as if the file could not be properly read. This is sometimes helpful for applications that want to enforce use of MIP-mapped images only. (Default: 1)

  • int statistics:level : verbosity of statistics auto-printed.

  • int forcefloat : If set to nonzero, all image tiles will be converted to float type when stored in the image cache. This can be helpful especially for users of ImageBuf who want to simplify their image manipulations to only need to consider float data. The default is zero, meaning that image pixels are not forced to be float when in cache.

  • int failure_retries : When an image file is opened or a tile/scanline is read but a file error occurs, if this attribute is nonzero, it will try the operation again up to this many times before giving up and reporting a failure. Setting this to a small nonzero number (like 3) may help make an application more robust to occasional spurious networking or other glitches that would otherwise cause the entire long-running application to fail upon a single transient error. (Default: 0)

  • int deduplicate : When nonzero, the ImageCache will notice duplicate images under different names if their headers contain a SHA-1 fingerprint (as is done with maketx-produced textures) and handle them more efficiently by avoiding redundant reads. The default is 1 (de-duplication turned on). The only reason to set it to 0 is if you specifically want to disable the de-duplication optimization.

  • string substitute_image : When set to anything other than the empty string, the ImageCache will use the named image in place of all other images. This allows you to run an app using OIIO and (if you can manage to get this option set) automagically substitute a grid, zone plate, or other special debugging image for all image/texture use.

  • int unassociatedalpha : When nonzero, will request that image format readers try to leave input images with unassociated alpha as they are, rather than automatically converting to associated alpha upon reading the pixels. The default is 0, meaning that the automatic conversion will take place.

  • int max_errors_per_file : The maximum number of errors that will be printed for each file. The default is 100. If your output is cluttered with error messages and after the first few for each file you aren’t getting any helpful additional information, this can cut down on the clutter and the runtime. (default: 100)

  • int trust_file_extensions : When nonzero, assume that the file extensions of any texture requests correctly indicates the file format (when enabled, this reduces the number of file opens, at the expense of not being able to open files if their format do not actually match their filename extension). Default: 0

  • string options This catch-all is simply a comma-separated list of name=value settings of named options, which will be parsed and individually set. Example: 

     ic->attribute ("options", "max_memory_MB=512.0,autotile=1");

    Note that if an option takes a string value that must itself contain a comma, it is permissible to enclose the value in either single (` ‘ ‘ ) or double ( ” ” `) quotes.

Read-only attributes

Additionally, there are some read-only attributes that can be queried with getattribute() even though they cannot be set via attribute():

  • int total_files : The total number of unique file names referenced by calls to the ImageCache.

  • string[] all_filenames : An array that will be filled with the list of the names of all files referenced by calls to the ImageCache. (The array is of ustring or char*.)

  • int64 stat:cache_memory_used : Total bytes used by tile cache.

  • int stat:tiles_created , int stat:tiles_current , int stat:tiles_peak : Total times created, still allocated (at the time of the query), and the peak number of tiles in memory at any time.

  • int stat:open_files_created , int stat:open_files_current , int stat:open_files_peak : Total number of times a file was opened, number still opened (at the time of the query), and the peak number of files opened at any time.

  • int stat:find_tile_calls : Number of times a filename was looked up in the file cache.

  • int64 stat:image_size : Total size (uncompressed bytes of pixel data) of all images referenced by the ImageCache. (Note: Prior to 1.7, this was called stat:files_totalsize.)

  • int64 stat:file_size : Total size of all files (as on disk, possibly compressed) of all images referenced by the ImageCache.

  • int64 stat:bytes_read : Total size (uncompressed bytes of pixel data) read.

  • int stat:unique_files : Number of unique files opened.

  • float stat:fileio_time : Total I/O-related time (seconds).

  • float stat:fileopen_time : I/O time related to opening and reading headers (but not pixel I/O).

  • float stat:file_locking_time : Total time (across all threads) that threads blocked waiting for access to the file data structures.

  • float stat:tile_locking_time : Total time (across all threads) that threads blocked waiting for access to the tile cache data structures.

  • float stat:find_file_time : Total time (across all threads) that threads spent looking up files by name.

  • float stat:find_tile_time : Total time (across all threads) that threads spent looking up individual tiles.

The following member functions of ImageCache allow you to set (and in some cases retrieve) options that control the overall behavior of the image cache:

virtual bool attribute(string_view name, TypeDesc type, const void *val) = 0

Set a named attribute (i.e., a property or option) of the ImageCache.

Example: 

ImageCache *ic;
...
int maxfiles = 50;
ic->attribute ("max_open_files", TypeDesc::INT, &maxfiles);

const char *path = "/my/path";
ic->attribute ("searchpath", TypeDesc::STRING, &path);

// There are specialized versions for setting a single int,
// float, or string without needing types or pointers:
ic->attribute ("max_open_files", 50);
ic->attribute ("max_memory_MB", 4000.0f);
ic->attribute ("searchpath", "/my/path");

Note: When passing a string, you need to pass a pointer to the char*, not a pointer to the first character. (Rationale: for an int attribute, you pass the address of the int. So for a string, which is a char*, you need to pass the address of the string, i.e., a char**).

Return

true if the name and type were recognized and the attribute was set, or false upon failure (including it being an unrecognized attribute or not of the correct type).

Parameters

  • name: Name of the attribute to set.

  • type: TypeDesc describing the type of the attribute.

  • val: Pointer to the value data.

virtual bool attribute(string_view name, int val) = 0

Specialized attribute() for setting a single int value.

virtual bool attribute(string_view name, float val) = 0

Specialized attribute() for setting a single float value.

virtual bool attribute(string_view name, string_view val) = 0

Specialized attribute() for setting a single string value.

virtual bool getattribute(string_view name, TypeDesc type, void *val) const = 0

Get the named attribute, store it in *val. All of the attributes that may be set with the attribute() call may also be queried with getattribute().

Examples: 

ImageCache *ic;
...
int maxfiles;
ic->getattribute ("max_open_files", TypeDesc::INT, &maxfiles);

const char *path;
ic->getattribute ("searchpath", TypeDesc::STRING, &path);

// There are specialized versions for retrieving a single int,
// float, or string without needing types or pointers:
int maxfiles;
ic->getattribute ("max_open_files", maxfiles);
const char *path;
ic->getattribute ("searchpath", &path);

Note: When retrieving a string, you need to pass a pointer to the char*, not a pointer to the first character. Also, the char* will end up pointing to characters owned by the ImageCache; the caller does not need to ever free the memory that contains the characters.

Return

true if the name and type were recognized and the attribute was retrieved, or false upon failure (including it being an unrecognized attribute or not of the correct type).

Parameters

  • name: Name of the attribute to retrieve.

  • type: TypeDesc describing the type of the attribute.

  • val: Pointer where the attribute value should be stored.

virtual bool getattribute(string_view name, int &val) const = 0

Specialized attribute() for retrieving a single int value.

virtual bool getattribute(string_view name, float &val) const = 0

Specialized attribute() for retrieving a single float value.

virtual bool getattribute(string_view name, char **val) const = 0

Specialized attribute() for retrieving a single string value as a char*.

virtual bool getattribute(string_view name, std::string &val) const = 0

Specialized attribute() for retrieving a single string value as a std::string.

Opaque data for performance lookups

The ImageCache implementation needs to maintain certain per-thread state, and some methods take an opaque Perthread pointer to this record. There are three options for how to deal with it:

  1. Don’t worry about it at all: don’t use the methods that want Perthread pointers, or always pass nullptr for any `Perthread*1 arguments, and ImageCache will do thread-specific-pointer retrieval as necessary (though at some small cost).

  2. If your app already stores per-thread information of its own, you may call get_perthread_info(nullptr) to retrieve it for that thread, and then pass it into the functions that allow it (thus sparing them the need and expense of retrieving the thread-specific pointer). However, it is crucial that this pointer not be shared between multiple threads. In this case, the ImageCache manages the storage, which will automatically be released when the thread terminates.

  3. If your app also wants to manage the storage of the Perthread, it can explicitly create one with create_perthread_info(), pass it around, and eventually be responsible for destroying it with destroy_perthread_info(). When managing the storage, the app may reuse the Perthread for another thread after the first is terminated, but still may not use the same Perthread for two threads running concurrently.

typedef pvt::ImageCachePerThreadInfo Perthread

Define an opaque data type that allows us to have a pointer to certain per-thread information that the ImageCache maintains. Any given one of these should NEVER be shared between running threads.

typedef pvt::ImageCacheFile ImageHandle

Define an opaque data type that allows us to have a handle to an image (already having its name resolved) but without exposing any internals.

virtual Perthread *get_perthread_info(Perthread *thread_info = NULL) = 0

Retrieve a Perthread, unique to the calling thread. This is a thread-specific pointer that will always return the Perthread for a thread, which will also be automatically destroyed when the thread terminates.

Applications that want to manage their own Perthread pointers (with create_thread_info and destroy_thread_info) should still call this, but passing in their managed pointer. If the passed-in thread_info is not NULL, it won’t create a new one or retrieve a TSP, but it will do other necessary housekeeping on the Perthread information.

virtual Perthread *create_thread_info() = 0

Create a new Perthread. It is the caller’s responsibility to eventually destroy it using destroy_thread_info().

virtual void destroy_thread_info(Perthread *thread_info) = 0

Destroy a Perthread that was allocated by create_thread_info().

virtual ImageHandle *get_image_handle(ustring filename, Perthread *thread_info = NULL) = 0

Retrieve an opaque handle for fast image lookups. The filename is presumed to be UTF-8 encoded. The opaque pointer thread_info is thread-specific information returned by get_perthread_info(). Return NULL if something has gone horribly wrong.

inline ImageHandle *get_image_handle(const std::wstring &filename, Perthread *thread_info = NULL)

Get an ImageHandle using a UTF-16 encoded wstring filename.

virtual bool good(ImageHandle *file) = 0

Return true if the image handle (previously returned by get_image_handle()) is a valid image that can be subsequently read.

virtual ustring filename_from_handle(ImageHandle *handle) = 0

Given a handle, return the filename for that image.

This method was added in OpenImageIO 2.3.

Getting information about images

virtual std::string resolve_filename(const std::string &filename) const = 0

Given possibly-relative filename (UTF-8 encoded), resolve it and use the true path to the file, with searchpath logic applied.

virtual bool get_image_info(ustring filename, int subimage, int miplevel, ustring dataname, TypeDesc datatype, void *data) = 0

Get information or metadata about the named image and store it in *data.

Data names may include any of the following:

  • "exists" : Stores the value 1 (as an int) if the file exists and is an image format that OpenImageIO can read, or 0 if the file does not exist, or could not be properly read as an image. Note that unlike all other queries, this query will “succeed” (return true) even if the file does not exist.

  • "udim" : Stores the value 1 (as an int) if the file is a “virtual UDIM” or texture atlas file (as described in :ref:sec-texturesys-udim) or 0 otherwise.

  • "subimages" : The number of subimages in the file, as an int.

  • "resolution" : The resolution of the image file, which is an array of 2 integers (described as TypeDesc(INT,2)).

  • "miplevels" : The number of MIPmap levels for the specified subimage (an integer).

  • "texturetype" : A string describing the type of texture of the given file, which describes how the texture may be used (also which texture API call is probably the right one for it). This currently may return one of: "unknown", "Plain Texture", "Volume Texture", "Shadow", or "Environment".

  • "textureformat" : A string describing the format of the given file, which describes the kind of texture stored in the file. This currently may return one of: "unknown", "Plain Texture", "Volume Texture", "Shadow", "CubeFace Shadow", "Volume Shadow", "LatLong Environment", or "CubeFace Environment". Note that there are several kinds of shadows and environment maps, all accessible through the same API calls.

  • "channels" : The number of color channels in the file (an int).

  • "format" : The native data format of the pixels in the file (an integer, giving the TypeDesc::BASETYPE of the data). Note that this is not necessarily the same as the data format stored in the image cache.

  • "cachedformat" : The native data format of the pixels as stored in the image cache (an integer, giving the TypeDesc::BASETYPE of the data). Note that this is not necessarily the same as the native data format of the file.

  • "datawindow" : Returns the pixel data window of the image, which is either an array of 4 integers (returning xmin, ymin, xmax, ymax) or an array of 6 integers (returning xmin, ymin, zmin, xmax, ymax, zmax). The z values may be useful for 3D/volumetric images; for 2D images they will be 0).

  • "displaywindow" : Returns the display (a.k.a. “full”) window of the image, which is either an array of 4 integers (returning xmin, ymin, xmax, ymax) or an array of 6 integers (returning xmin, ymin, zmin, xmax, ymax, zmax). The z values may be useful for 3D/volumetric images; for 2D images they will be 0).

  • "worldtocamera" : The viewing matrix, which is a 4x4 matrix (an Imath::M44f, described as TypeDesc(FLOAT,MATRIX)), giving the world-to-camera 3D transformation matrix that was used when the image was created. Generally, only rendered images will have this.

  • "worldtoscreen" : The projection matrix, which is a 4x4 matrix (an Imath::M44f, described as TypeDesc(FLOAT,MATRIX)), giving the matrix that projected points from world space into a 2D screen coordinate system where $x$ and $y$ range from -1 to +1. Generally, only rendered images will have this.

  • "worldtoNDC" : The projection matrix, which is a 4x4 matrix (an Imath::M44f, described as TypeDesc(FLOAT,MATRIX)), giving the matrix that projected points from world space into a 2D NDC coordinate system where $x$ and $y$ range from 0 to +1. Generally, only rendered images will have this.

  • "averagecolor" : If available in the metadata (generally only for files that have been processed by maketx), this will return the average color of the texture (into an array of float).

  • "averagealpha" : If available in the metadata (generally only for files that have been processed by maketx), this will return the average alpha value of the texture (into a float).

  • "constantcolor" : If the metadata (generally only for files that have been processed by maketx) indicates that the texture has the same values for all pixels in the texture, this will retrieve the constant color of the texture (into an array of floats). A non-constant image (or one that does not have the special metadata tag identifying it as a constant texture) will fail this query (return false).

  • "constantalpha" : If the metadata indicates that the texture has the same values for all pixels in the texture, this will retrieve the constant alpha value of the texture (into a float). A non-constant image (or one that does not have the special metadata tag identifying it as a constant texture) will fail this query (return false).

  • "stat:tilesread" : Number of tiles read from this file (int64).

  • "stat:bytesread" : Number of bytes of uncompressed pixel data read from this file (int64).

  • "stat:redundant_tiles" : Number of times a tile was read, where the same tile had been rad before. (int64).

  • "stat:redundant_bytesread" : Number of bytes (of uncompressed pixel data) in tiles that were read redundantly. (int64).

  • "stat:redundant_bytesread" : Number of tiles read from this file (int).

  • "stat:image_size" : Size of the uncompressed image pixel data of this image, in bytes (int64).

  • "stat:file_size" : Size of the disk file (possibly compressed) for this image, in bytes (int64).

  • "stat:timesopened" : Number of times this file was opened (int).

  • "stat:iotime" : Time (in seconds) spent on all I/O for this file (float).

  • "stat:mipsused" : Stores 1 if any MIP levels beyond the highest resolution were accessed, otherwise 0. (int)

  • "stat:is_duplicate" : Stores 1 if this file was a duplicate of another image, otherwise 0. (int)

  • Anything else : For all other data names, the the metadata of the image file will be searched for an item that matches both the name and data type.

Return

true if get_image_info() is able to find the requested dataname for the image and it matched the requested datatype. If the requested data was not found or was not of the right data type, return false. Except for the "exists" query, a file that does not exist or could not be read properly as an image also constitutes a query failure that will return false.

Parameters

  • filename: The name of the image, as a UTF-8 encoded ustring.

  • subimage/miplevel: The subimage and MIP level to query.

  • dataname: The name of the metadata to retrieve.

  • datatype: TypeDesc describing the data type.

  • data: Pointer to the caller-owned memory where the values should be stored. It is the caller’s responsibility to ensure that data points to a large enough storage area to accommodate the datatype requested.

virtual bool get_image_info(ImageHandle *file, Perthread *thread_info, int subimage, int miplevel, ustring dataname, TypeDesc datatype, void *data) = 0

A more efficient variety of get_image_info() for cases where you can use an ImageHandle* to specify the image and optionally have a Perthread* for the calling thread.

virtual bool get_imagespec(ustring filename, ImageSpec &spec, int subimage = 0, int miplevel = 0, bool native = false) = 0

Copy the ImageSpec associated with the named image (the first subimage & miplevel by default, or as set by subimage and miplevel).

Return

true upon success, false upon failure failure (such as being unable to find, open, or read the file, or if it does not contain the designated subimage or MIP level).

Parameters

  • filename: The name of the image, as a UTF-8 encoded ustring.

  • spec: ImageSpec into which will be copied the spec for the requested image.

  • subimage/miplevel: The subimage and MIP level to query.

  • native: If false (the default), then the spec retrieved will accurately describe the image stored internally in the cache, whereas if native is true, the spec retrieved will reflect the contents of the original file. These may differ due to use of certain ImageCache settings such as "forcefloat" or "autotile".

virtual bool get_imagespec(ImageHandle *file, Perthread *thread_info, ImageSpec &spec, int subimage = 0, int miplevel = 0, bool native = false) = 0

A more efficient variety of get_imagespec() for cases where you can use an ImageHandle* to specify the image and optionally have a Perthread* for the calling thread.

virtual const ImageSpec *imagespec(ustring filename, int subimage = 0, int miplevel = 0, bool native = false) = 0

Return a pointer to an ImageSpec associated with the named image (the first subimage & MIP level by default, or as set by subimage and miplevel) if the file is found and is an image format that can be read, otherwise return nullptr.

This method is much more efficient than get_imagespec(), since it just returns a pointer to the spec held internally by the ImageCache (rather than copying the spec to the user’s memory). However, the caller must beware that the pointer is only valid as long as nobody (even other threads) calls invalidate() on the file, or invalidate_all(), or destroys the ImageCache.

Return

A pointer to the spec, if the image is found and able to be opened and read by an available image format plugin, and the designated subimage and MIP level exists.

Parameters

  • filename: The name of the image, as a UTF-8 encoded ustring.

  • subimage/miplevel: The subimage and MIP level to query.

  • native: If false (the default), then the spec retrieved will accurately describe the image stored internally in the cache, whereas if native is true, the spec retrieved will reflect the contents of the original file. These may differ due to use of certain ImageCache settings such as "forcefloat" or "autotile".

virtual const ImageSpec *imagespec(ImageHandle *file, Perthread *thread_info, int subimage = 0, int miplevel = 0, bool native = false) = 0

A more efficient variety of imagespec() for cases where you can use an ImageHandle* to specify the image and optionally have a Perthread* for the calling thread.

virtual bool get_thumbnail(ustring filename, ImageBuf &thumbnail, int subimage = 0) = 0

Copy into thumbnail any associated thumbnail associated with this image (for the first subimage by default, or as set by subimage).

Return

true upon success, false upon failure failure (such as being unable to find, open, or read the file, or if it does not contain a thumbnail).

Parameters

  • filename: The name of the image, as a UTF-8 encoded ustring.

  • thumbnail: ImageBuf into which will be copied the thumbnail, if it exists. If no thumbnail can be retrieved, thumb will be reset to an uninitialized (empty) ImageBuf.

  • subimage: The subimage to query.

virtual bool get_thumbnail(ImageHandle *file, Perthread *thread_info, ImageBuf &thumbnail, int subimage = 0) = 0

A more efficient variety of get_thumbnail() for cases where you can use an ImageHandle* to specify the image and optionally have a Perthread* for the calling thread.

Getting Pixels

virtual bool get_pixels(ustring filename, int subimage, int miplevel, int xbegin, int xend, int ybegin, int yend, int zbegin, int zend, int chbegin, int chend, TypeDesc format, void *result, stride_t xstride = AutoStride, stride_t ystride = AutoStride, stride_t zstride = AutoStride, int cache_chbegin = 0, int cache_chend = -1) = 0

For an image specified by name, retrieve the rectangle of pixels from the designated subimage and MIP level, storing the pixel values beginning at the address specified by result and with the given strides. The pixel values will be converted to the data type specified by format. The rectangular region to be retrieved includes begin but does not include end (much like STL begin/end usage). Requested pixels that are not part of the valid pixel data region of the image file will be filled with zero values.

Return

true for success, false for failure.

Parameters

  • filename: The name of the image, as a UTF-8 encoded ustring.

  • subimage/miplevel: The subimage and MIP level to retrieve pixels from.

  • xbegin/xend/ybegin/yend/zbegin/zend: The range of pixels to retrieve. The pixels retrieved include the begin value but not the end value (much like STL begin/end usage).

  • chbegin/chend: Channel range to retrieve. To retrieve all channels, use chbegin = 0, chend = nchannels.

  • format: TypeDesc describing the data type of the values you want to retrieve into result. The pixel values will be converted to this type regardless of how they were stored in the file.

  • result: Pointer to the memory where the pixel values should be stored. It is up to the caller to ensure that result points to an area of memory big enough to accommodate the requested rectangle (taking into consideration its dimensions, number of channels, and data format).

  • xstride/ystride/zstride: The number of bytes between the beginning of successive pixels, scanlines, and image planes, respectively. Any stride values set to AutoStride will be assumed to indicate a contiguous data layout in that dimension.

  • cache_chbegin/cache_chend: These parameters can be used to tell the ImageCache to read and cache a subset of channels (if not specified or if they denote a non-positive range, all the channels of the file will be stored in the cached tile).

virtual bool get_pixels(ImageHandle *file, Perthread *thread_info, int subimage, int miplevel, int xbegin, int xend, int ybegin, int yend, int zbegin, int zend, int chbegin, int chend, TypeDesc format, void *result, stride_t xstride = AutoStride, stride_t ystride = AutoStride, stride_t zstride = AutoStride, int cache_chbegin = 0, int cache_chend = -1) = 0

A more efficient variety of get_pixels() for cases where you can use an ImageHandle* to specify the image and optionally have a Perthread* for the calling thread.

virtual bool get_pixels(ustring filename, int subimage, int miplevel, int xbegin, int xend, int ybegin, int yend, int zbegin, int zend, TypeDesc format, void *result) = 0

A simplified get_pixels() where all channels are retrieved, strides are assumed to be contiguous.

virtual bool get_pixels(ImageHandle *file, Perthread *thread_info, int subimage, int miplevel, int xbegin, int xend, int ybegin, int yend, int zbegin, int zend, TypeDesc format, void *result) = 0

A more efficient variety of get_pixels() for cases where you can use an ImageHandle* to specify the image and optionally have a Perthread* for the calling thread.

Controlling the cache

typedef pvt::ImageCacheTile Tile

An opaque data type that allows us to have a pointer to a tile but without exposing any internals.

virtual void invalidate(ustring filename, bool force = true) = 0

Invalidate any loaded tiles or open file handles associated with the filename (UTF-8 encoded), so that any subsequent queries will be forced to re-open the file or re-load any tiles (even those that were previously loaded and would ordinarily be reused). A client might do this if, for example, they are aware that an image being held in the cache has been updated on disk. This is safe to do even if other procedures are currently holding reference-counted tile pointers from the named image, but those procedures will not get updated pixels until they release the tiles they are holding.

If force is true, this invalidation will happen unconditionally; if false, the file will only be invalidated if it has been changed since it was first opened by the ImageCache.

virtual void invalidate(ImageHandle *file, bool force = true) = 0

A more efficient variety of invalidate() for cases where you already have an ImageHandle* for the file you want to invalidate.

virtual void invalidate_all(bool force = false) = 0

Invalidate all loaded tiles and close open file handles. This is safe to do even if other procedures are currently holding reference-counted tile pointers from the named image, but those procedures will not get updated pixels (if the images change) until they release the tiles they are holding.

If force is true, everything will be invalidated, no matter how wasteful it is, but if force is false, in actuality files will only be invalidated if their modification times have been changed since they were first opened.

virtual void close(ustring filename) = 0

Close any open file handles associated with a named file (UTF-8 encoded), but do not invalidate any image spec information or pixels associated with the files. A client might do this in order to release OS file handle resources, or to make it safe for other processes to modify image files on disk.

virtual void close_all() = 0

close() all files known to the cache.

virtual Tile *get_tile(ustring filename, int subimage, int miplevel, int x, int y, int z, int chbegin = 0, int chend = -1) = 0

Find the tile specified by an image filename (UTF-8 encoded), subimage & miplevel, the coordinates of a pixel, and optionally a channel range. An opaque pointer to the tile will be returned, or nullptr if no such file (or tile within the file) exists or can be read. The tile will not be purged from the cache until after release_tile() is called on the tile pointer the same number of times that get_tile() was called (reference counting). This is thread-safe! If chend < chbegin, it will retrieve a tile containing all channels in the file.

virtual Tile *get_tile(ImageHandle *file, Perthread *thread_info, int subimage, int miplevel, int x, int y, int z, int chbegin = 0, int chend = -1) = 0

A slightly more efficient variety of get_tile() for cases where you can use an ImageHandle* to specify the image and optionally have a Perthread* for the calling thread.

See

get_pixels()

virtual void release_tile(Tile *tile) const = 0

After finishing with a tile, release_tile will allow it to once again be purged from the tile cache if required.

virtual TypeDesc tile_format(const Tile *tile) const = 0

Retrieve the data type of the pixels stored in the tile, which may be different than the type of the pixels in the disk file.

virtual ROI tile_roi(const Tile *tile) const = 0

Retrieve the ROI describing the pixels and channels stored in the tile.

virtual const void *tile_pixels(Tile *tile, TypeDesc &format) const = 0

For a tile retrived by get_tile(), return a pointer to the pixel data itself, and also store in format the data type that the pixels are internally stored in (which may be different than the data type of the pixels in the disk file). This method should only be called on a tile that has been requested by get_tile() but has not yet been released with release_tile().

virtual bool add_file(ustring filename, ImageInput::Creator creator = nullptr, const ImageSpec *config = nullptr, bool replace = false) = 0

The add_file() call causes a file to be opened or added to the cache. There is no reason to use this method unless you are supplying a custom creator, or configuration, or both.

If creator is not NULL, it points to an ImageInput::Creator that will be used rather than the default ImageInput::create(), thus instead of reading from disk, creates and uses a custom ImageInput to generate the image. The ‘creator’ is a factory that creates the custom ImageInput and will be called like this: 

 std::unique_ptr<ImageInput> in (creator());

Once created, the ImageCache owns the ImageInput and is responsible for destroying it when done. Custom ImageInputs allow “procedural” images, among other things. Also, this is the method you use to set up a “writable” ImageCache images (perhaps with a type of ImageInput that’s just a stub that does as little as possible).

If config is not NULL, it points to an ImageSpec with configuration options/hints that will be passed to the underlying ImageInput::open() call. Thus, this can be used to ensure that the ImageCache opens a call with special configuration options.

This call (including any custom creator or configuration hints) will have no effect if there’s already an image by the same name in the cache. Custom creators or configurations only “work” the FIRST time a particular filename is referenced in the lifetime of the ImageCache. But if replace is true, any existing entry will be invalidated, closed and overwritten. So any subsequent access will see the new file. Existing texture handles will still be valid.

virtual bool add_tile(ustring filename, int subimage, int miplevel, int x, int y, int z, int chbegin, int chend, TypeDesc format, const void *buffer, stride_t xstride = AutoStride, stride_t ystride = AutoStride, stride_t zstride = AutoStride, bool copy = true) = 0

Preemptively add a tile corresponding to the named image, at the given subimage, MIP level, and channel range. The tile added is the one whose corner is (x,y,z), and buffer points to the pixels (in the given format, with supplied strides) which will be copied and inserted into the cache and made available for future lookups. If chend < chbegin, it will add a tile containing the full set of channels for the image. Note that if the ‘copy’ flag is false, the data is assumed to be in some kind of persistent storage and will not be copied, nor will its pixels take up additional memory in the cache.

Errors and statistics

virtual bool has_error() const = 0

Is there a pending error message waiting to be retrieved?

virtual std::string geterror(bool clear = true) const = 0

Return the text of all pending error messages issued against this ImageCache, and clear the pending error message unless clear is false. If no error message is pending, it will return an empty string.

virtual std::string getstats(int level = 1) const = 0

Returns a big string containing useful statistics about the ImageCache operations, suitable for saving to a file or outputting to the terminal. The level indicates the amount of detail in the statistics, with higher numbers (up to a maximum of 5) yielding more and more esoteric information.

virtual void reset_stats() = 0

Reset most statistics to be as they were with a fresh ImageCache. Caveat emptor: this does not flush the cache itelf, so the resulting statistics from the next set of texture requests will not match the number of tile reads, etc., that would have resulted from a new ImageCache.

Texture Access: TextureSystem

Texture System Introduction and Theory of Operation

Coming soon. FIXME

Helper Classes

Imath

The texture functinality of OpenImageIO uses the excellent open source Imath types when it requires 3D vectors and transformation matrixes. Specifically, we use Imath::V3f for 3D positions and directions, and Imath::M44f for 4x4 transformation matrices. To use these yourself, we recommend that you:

// If using Imath 3.x:
#include <Imath/ImathVec.h>
#include <Imath/ImathMatrix.h>

// OR, if using OpenEXR 2.x, before Imath split off:
#include <OpenEXR/ImathVec.h>
#include <OpenEXR/ImathMatrix.h>

Please refer to the Imath documentation and header files for more complete information about use of these types in your own application. However, note that you are not strictly required to use these classes in your application — Imath::V3f has a memory layout identical to float[3] and Imath::M44f has a memory layout identical to float[16], so as long as your own internal vectors and matrices have the same memory layout, it’s ok to just cast pointers to them when passing as arguments to TextureSystem methods.

TextureOpt

TextureOpt is a structure that holds many options controlling single-point texture lookups. Because each texture lookup API call takes a reference to a TextureOpt, the call signatures remain uncluttered rather than having an ever-growing list of parameters, most of which will never vary from their defaults. Here is a brief description of the data members of a TextureOpt structure:

  • int firstchannel : The beginning channel for the lookup. For example, to retrieve just the blue channel, you should have firstchannel = 2 while passing nchannels = 1 to the appropriate texture function.

  • int subimage, ustring subimagename : Specifies the subimage or face within the file to use for the texture lookup. If subimagename is set (it defaults to the empty string), it will try to use the subimage that had a matching metadata "oiio:subimagename", otherwise the integer subimage will be used (which defaults to 0, i.e., the first/default subimage). Nonzero subimage indices only make sense for a texture file that supports subimages (like TIFF or multi-part OpenEXR) or separate images per face (such as Ptex). This will be ignored if the file does not have multiple subimages or separate per-face textures.

  • Wrap swrap, twrap : Specify the wrap mode for 2D texture lookups (and 3D volume texture lookups, using the additional rwrap field). These fields are ignored for shadow and environment lookups. These specify what happens when texture coordinates are found to be outside the usual [0,1] range over which the texture is defined. Wrap is an enumerated type that may take on any of the following values:

    • WrapBlack : The texture is black outside the [0,1] range.

    • WrapClamp : The texture coordinates will be clamped to [0,1], i.e., the value outside [0,1] will be the same as the color at the nearest point on the border.

    • WrapPeriodic : The texture is periodic, i.e., wraps back to 0 after going past 1.

    • WrapMirror : The texture presents a mirror image at the edges, i.e., the coordinates go from 0 to 1, then back down to 0, then back up to 1, etc.

    • WrapDefault : Use whatever wrap might be specified in the texture file itself, or some other suitable default (caveat emptor).

    The wrap mode does not need to be identical in the s and t directions.

  • float swidth, twidth : For each direction, gives a multiplier for the derivatives. Note that a width of 0 indicates a point sampled lookup (assuming that blur is also zero). The default width is 1, indicating that the derivatives should guide the amount of blur applied to the texture filtering (not counting any additional blur specified).

  • float sblur, tblur : For each direction, specifies an additional amount of pre-blur to apply to the texture (after derivatives are taken into account), expressed as a portion of the width of the texture. In other words, blur = 0.1 means that the texture lookup should act as if the texture was pre-blurred with a filter kernel with a width 1/10 the size of the full image. The default blur amount is 0, indicating a sharp texture lookup.

  • float fill : Specifies the value that will be used for any color channels that are requested but not found in the file. For example, if you perform a 4-channel lookup on a 3-channel texture, the last channel will get the fill value. (Note: this behavior is affected by the "gray_to_rgb" attribute described in the Section about TextureSystem attributes.

  • const float* missingcolor : If not NULL, indicates that a missing or broken texture should not be treated as an error, but rather will simply return the supplied color as the texture lookup color and texture() will return true. If the missingcolor field is left at its default (a NULL pointer), a missing or broken texture will be treated as an error and texture() will return false. Note: When not NULL, the data must point to nchannels contiguous floats.

  • Wrap rwrap, float rblur, rwidth : Specifies wrap, blur, and width for the third component of 3D volume texture lookups. These are not used for 2D texture or environment lookups.

  • MipMode mipmode : Determines if/how MIP-maps are used:

    • MipModeDefault : The default high-quality lookup (same as Aniso).

    • MipModeNoMIP : Just use highest-res image, no MIP mapping

    • MipModeOneLevel : Use just one mipmap level

    • MipModeTrilinear : Use two MIPmap levels (trilinear)

    • MipModeAniso : Use two MIPmap levels w/ anisotropic

  • InterpMode interpmode : Determines how we sample within a mipmap level:

    • InterpClosest : Force closest texel.

    • InterpBilinear : Force bilinear lookup within a mip level.

    • InterpBicubic : Force cubic lookup within a mip level.

    • InterpSmartBicubic : Bicubic when maxifying, else bilinear (default).

  • int anisotropic : Maximum anisotropic ratio (default: 32).

  • bool conservative_filter : When true (the default), filters conservatively in a way that chooses to sometimes over-blur rather than alias.

TextureSystem API

class OIIO::TextureSystem

Define an API to an abstract class that that manages texture files, caches of open file handles as well as tiles of texels so that truly huge amounts of texture may be accessed by an application with low memory footprint, and ways to perform antialiased texture, shadow map, and environment map lookups.

Creating and destroying a texture system

TextureSystem is an abstract API described as a pure virtual class. The actual internal implementation is not exposed through the external API of OpenImageIO. Because of this, you cannot construct or destroy the concrete implementation, so two static methods of TextureSystem are provided:

static TextureSystem *create(bool shared = true, ImageCache *imagecache = nullptr)

Create a TextureSystem and return a pointer to it. This should only be freed by passing it to TextureSystem::destroy()!

Return

A raw pointer to a TextureSystem, which can only be freed with TextureSystem::destroy().

See

TextureSystem::destroy

Parameters

  • shared: If shared is true, the pointer returned will be a shared TextureSystem, (so that multiple parts of an application that request a TextureSystem will all end up with the same one, and the same underlying ImageCache). If shared is false, a completely unique TextureCache will be created and returned.

  • imagecache: If shared is false and imagecache is not nullptr, the TextureSystem will use this as its underlying ImageCache. In that case, it is the caller who is responsible for eventually freeing the ImageCache after the TextureSystem is destroyed. If shared is false and imagecache is nullptr, then a custom ImageCache will be created, owned by the TextureSystem, and automatically freed when the TS destroys.

static void destroy(TextureSystem *ts, bool teardown_imagecache = false)

Destroy an allocated TextureSystem, including freeing all system resources that it holds.

It is safe to destroy even a shared TextureSystem, as the implementation of destroy() will recognize a shared one and only truly release its resources if it has been requested to be destroyed as many times as shared TextureSystem’s were created.

Parameters

  • ts: Raw pointer to the TextureSystem to destroy.

  • teardown_imagecache: For a shared TextureSystem, if the teardown_imagecache parameter is true, it will try to truly destroy the shared cache if nobody else is still holding a reference (otherwise, it will leave it intact). This parameter has no effect if ts was not the single globally shared TextureSystem.

Setting options and limits for the texture system

These are the list of attributes that can bet set or queried by attribute/getattribute:

All attributes ordinarily recognized by ImageCache are accepted and passed through to the underlying ImageCache. These include:

  • int max_open_files : Maximum number of file handles held open.

  • float max_memory_MB : Maximum tile cache size, in MB.

  • string searchpath : Colon-separated search path for texture files.

  • string plugin_searchpath : Colon-separated search path for plugins.

  • int autotile : If >0, tile size to emulate for non-tiled images.

  • int autoscanline : If nonzero, autotile using full width tiles.

  • int automip : If nonzero, emulate mipmap on the fly.

  • int accept_untiled : If nonzero, accept untiled images.

  • int accept_unmipped : If nonzero, accept unmipped images.

  • int failure_retries : How many times to retry a read failure.

  • int deduplicate : If nonzero, detect duplicate textures (default=1).

  • string substitute_image : If supplied, an image to substatute for all texture references.

  • int max_errors_per_file : Limits how many errors to issue for each file. (default: 100)

Texture-specific settings:

  • matrix44 worldtocommon / matrix44 commontoworld : The 4x4 matrices that provide the spatial transformation from “world” to a “common” coordinate system and back. This is mainly used for shadow map lookups, in which the shadow map itself encodes the world coordinate system, but positions passed to shadow() are expressed in “common” coordinates. You do not need to set commontoworld and worldtocommon separately; just setting either one will implicitly set the other, since each is the inverse of the other.

  • int gray_to_rgb : If set to nonzero, texture lookups of single-channel (grayscale) images will replicate the sole channel’s values into the next two channels, making it behave like an RGB image that happens to have all three channels with identical pixel values. (Channels beyond the third will get the “fill” value.) The default value of zero means that all missing channels will get the “fill” color.

  • int max_tile_channels : The maximum number of color channels in a texture file for which all channels will be loaded as a single cached tile. Files with more than this number of color channels will have only the requested subset loaded, in order to save cache space (but at the possible wasted expense of separate tiles that overlap their channel ranges). The default is 5.

  • int max_mip_res : NEW 2.1 Sets the maximum MIP-map resolution for filtered texture lookups. The MIP levels used will be clamped to those having fewer than this number of pixels in each dimension. This can be helpful as a way to limit disk I/O when doing fast preview renders (with the tradeoff that you may see some texture more blurry than they would ideally be). The default is 1 << 30, a value so large that no such clamping will be performed.

  • string latlong_up : The default “up” direction for latlong environment maps (only applies if the map itself doesn’t specify a format or is in a format that explicitly requires a particular orientation). The default is "y". (Currently any other value will result in z being “up.”)

  • int flip_t : If nonzero, t coordinates will be flipped 1-t for all texture lookups. The default is 0.

  • string options This catch-all is simply a comma-separated list of name=value settings of named options, which will be parsed and individually set. 

    ic->attribute ("options", "max_memory_MB=512.0,autotile=1");

    Note that if an option takes a string value that must itself contain a comma, it is permissible to enclose the value in either single \' or double " quotes.

Read-only attributes

Additionally, there are some read-only attributes that can be queried with getattribute() even though they cannot be set via attribute():

The following member functions of TextureSystem allow you to set (and in some cases retrieve) options that control the overall behavior of the texture system:

virtual bool attribute(string_view name, TypeDesc type, const void *val) = 0

Set a named attribute (i.e., a property or option) of the TextureSystem.

Example: 

TextureSystem *ts;
...
int maxfiles = 50;
ts->attribute ("max_open_files", TypeDesc::INT, &maxfiles);

const char *path = "/my/path";
ts->attribute ("searchpath", TypeDesc::STRING, &path);

// There are specialized versions for retrieving a single int,
// float, or string without needing types or pointers:
ts->getattribute ("max_open_files", 50);
ic->attribute ("max_memory_MB", 4000.0f);
ic->attribute ("searchpath", "/my/path");

Note: When passing a string, you need to pass a pointer to the char*, not a pointer to the first character. (Rationale: for an int attribute, you pass the address of the int. So for a string, which is a char*, you need to pass the address of the string, i.e., a char**).

Return

true if the name and type were recognized and the attribute was set, or false upon failure (including it being an unrecognized attribute or not of the correct type).

Parameters

  • name: Name of the attribute to set.

  • type: TypeDesc describing the type of the attribute.

  • val: Pointer to the value data.

virtual bool attribute(string_view name, int val) = 0

Specialized attribute() for setting a single int value.

virtual bool attribute(string_view name, float val) = 0

Specialized attribute() for setting a single float value.

virtual bool attribute(string_view name, string_view val) = 0

Specialized attribute() for setting a single string value.

virtual bool getattribute(string_view name, TypeDesc type, void *val) const = 0

Get the named attribute of the texture system, store it in *val. All of the attributes that may be set with the attribute() call may also be queried with getattribute().

Examples: 

TextureSystem *ic;
...
int maxfiles;
ts->getattribute ("max_open_files", TypeDesc::INT, &maxfiles);

const char *path;
ts->getattribute ("searchpath", TypeDesc::STRING, &path);

// There are specialized versions for retrieving a single int,
// float, or string without needing types or pointers:
int maxfiles;
ts->getattribute ("max_open_files", maxfiles);
const char *path;
ts->getattribute ("searchpath", &path);

Note: When retrieving a string, you need to pass a pointer to the char*, not a pointer to the first character. Also, the char* will end up pointing to characters owned by the ImageCache; the caller does not need to ever free the memory that contains the characters.

Return

true if the name and type were recognized and the attribute was retrieved, or false upon failure (including it being an unrecognized attribute or not of the correct type).

Parameters

  • name: Name of the attribute to retrieve.

  • type: TypeDesc describing the type of the attribute.

  • val: Pointer where the attribute value should be stored.

virtual bool getattribute(string_view name, int &val) const = 0

Specialized attribute() for retrieving a single int value.

virtual bool getattribute(string_view name, float &val) const = 0

Specialized attribute() for retrieving a single float value.

virtual bool getattribute(string_view name, char **val) const = 0

Specialized attribute() for retrieving a single string value as a char*.

virtual bool getattribute(string_view name, std::string &val) const = 0

Specialized attribute() for retrieving a single string value as a std::string.

Opaque data for performance lookups

The TextureSystem implementation needs to maintain certain per-thread state, and some methods take an opaque Perthread pointer to this record. There are three options for how to deal with it:

  1. Don’t worry about it at all: don’t use the methods that want Perthread pointers, or always pass nullptr for any `Perthread*1 arguments, and ImageCache will do thread-specific-pointer retrieval as necessary (though at some small cost).

  2. If your app already stores per-thread information of its own, you may call get_perthread_info(nullptr) to retrieve it for that thread, and then pass it into the functions that allow it (thus sparing them the need and expense of retrieving the thread-specific pointer). However, it is crucial that this pointer not be shared between multiple threads. In this case, the ImageCache manages the storage, which will automatically be released when the thread terminates.

  3. If your app also wants to manage the storage of the Perthread, it can explicitly create one with create_perthread_info(), pass it around, and eventually be responsible for destroying it with destroy_perthread_info(). When managing the storage, the app may reuse the Perthread for another thread after the first is terminated, but still may not use the same Perthread for two threads running concurrently.

virtual Perthread *get_perthread_info(Perthread *thread_info = nullptr) = 0

Retrieve a Perthread, unique to the calling thread. This is a thread-specific pointer that will always return the Perthread for a thread, which will also be automatically destroyed when the thread terminates.

Applications that want to manage their own Perthread pointers (with create_thread_info and destroy_thread_info) should still call this, but passing in their managed pointer. If the passed-in thread_info is not nullptr, it won’t create a new one or retrieve a TSP, but it will do other necessary housekeeping on the Perthread information.

virtual Perthread *create_thread_info() = 0

Create a new Perthread. It is the caller’s responsibility to eventually destroy it using destroy_thread_info().

virtual void destroy_thread_info(Perthread *threadinfo) = 0

Destroy a Perthread that was allocated by create_thread_info().

virtual TextureHandle *get_texture_handle(ustring filename, Perthread *thread_info = nullptr) = 0

Retrieve an opaque handle for fast texture lookups. The filename is presumed to be UTF-8 encoded. The opaque pointer thread_info is thread-specific information returned by get_perthread_info(). Return nullptr if something has gone horribly wrong.

inline TextureHandle *get_texture_handle(const std::wstring &filename, Perthread *thread_info = nullptr)

Get a TextureHandle using a UTF-16 encoded wstring filename.

virtual bool good(TextureHandle *texture_handle) = 0

Return true if the texture handle (previously returned by get_image_handle()) is a valid texture that can be subsequently read.

virtual ustring filename_from_handle(TextureHandle *handle) = 0

Given a handle, return the UTF-8 encoded filename for that texture.

This method was added in OpenImageIO 2.3.

Texture lookups

virtual bool texture(ustring filename, TextureOpt &options, float s, float t, float dsdx, float dtdx, float dsdy, float dtdy, int nchannels, float *result, float *dresultds = nullptr, float *dresultdt = nullptr) = 0

Perform a filtered 2D texture lookup on a position centered at 2D coordinates (s, t) from the texture identified by filename, and using relevant texture options. The nchannels parameter determines the number of channels to retrieve (e.g., 1 for a single value, 3 for an RGB triple, etc.). The filtered results will be stored in result[0..nchannels-1].

We assume that this lookup will be part of an image that has pixel coordinates x and y. By knowing how s and t change from pixel to pixel in the final image, we can properly filter or antialias the texture lookups. This information is given via derivatives dsdx and dtdx that define the change in s and t per unit of x, and dsdy and dtdy that define the change in s and t per unit of y. If it is impossible to know the derivatives, you may pass 0 for them, but in that case you will not receive an antialiased texture lookup.

Return

true upon success, or false if the file was not found or could not be opened by any available ImageIO plugin.

Parameters

  • filename: The name of the texture, as a UTF-8 encoded ustring.

  • options: Fields within options that are honored for 2D texture lookups include the following:

    • int firstchannel : The index of the first channel to look up from the texture.

    • int subimage / ustring subimagename : The subimage or face within the file, specified by either by name (if non-empty) or index. This will be ignored if the file does not have multiple subimages or separate per-face textures.

    • Wrap swrap, twrap : Specify the wrap mode for each direction, one of: WrapBlack, WrapClamp, WrapPeriodic, WrapMirror, or WrapDefault.

    • float swidth, twidth : For each direction, gives a multiplier for the derivatives.

    • float sblur, tblur : For each direction, specifies an additional amount of pre-blur to apply to the texture (after derivatives are taken into account), expressed as a portion of the width of the texture.

    • float fill : Specifies the value that will be used for any color channels that are requested but not found in the file. For example, if you perform a 4-channel lookup on a 3-channel texture, the last channel will get the fill value. (Note: this behavior is affected by the "gray_to_rgb" TextureSystem attribute.

    • const float *missingcolor : If not nullptr, specifies the color that will be returned for missing or broken textures (rather than being an error).

  • s/t: The 2D texture coordinates.

  • dsdxdtdxdsdydtdy: The differentials of s and t relative to canonical directions x and y. The choice of x and y are not important to the implementation; it can be any imposed 2D coordinates, such as pixels in screen space, adjacent samples in parameter space on a surface, etc. The st derivatives determine the size and shape of the ellipsoid over which the texture lookup is filtered.

  • nchannels: The number of channels of data to retrieve into result (e.g., 1 for a single value, 3 for an RGB triple, etc.).

  • result[]: The result of the filtered texture lookup will be placed into result[0..nchannels-1].

  • dresultds/dresultdt: If non-null, these designate storage locations for the derivatives of result, i.e., the rate of change per unit s and t, respectively, of the filtered texture. If supplied, they must allow for nchannels of storage.

virtual bool texture(TextureHandle *texture_handle, Perthread *thread_info, TextureOpt &options, float s, float t, float dsdx, float dtdx, float dsdy, float dtdy, int nchannels, float *result, float *dresultds = nullptr, float *dresultdt = nullptr) = 0

Slightly faster version of texture() lookup if the app already has a texture handle and per-thread info.

virtual bool texture3d(ustring filename, TextureOpt &options, const Imath::V3f &P, const Imath::V3f &dPdx, const Imath::V3f &dPdy, const Imath::V3f &dPdz, int nchannels, float *result, float *dresultds = nullptr, float *dresultdt = nullptr, float *dresultdr = nullptr) = 0

Perform a filtered 3D volumetric texture lookup on a position centered at 3D position P (with given differentials) from the texture identified by filename, and using relevant texture options. The filtered results will be stored in result[0..nchannels-1].

The P coordinate and dPdx, dPdy, and dPdz derivatives are assumed to be in some kind of common global coordinate system (usually “world” space) and will be automatically transformed into volume local coordinates, if such a transformation is specified in the volume file itself.

Return

true upon success, or false if the file was not found or could not be opened by any available ImageIO plugin.

Parameters

  • filename: The name of the texture, as a UTF-8 encoded ustring.

  • options: Fields within options that are honored for 3D texture lookups include the following:

    • int firstchannel : The index of the first channel to look up from the texture.

    • int subimage / ustring subimagename : The subimage or field within the volume, specified by either by name (if non-empty) or index. This will be ignored if the file does not have multiple subimages or separate per-face textures.

    • Wrap swrap, twrap, rwrap : Specify the wrap mode for each direction, one of: WrapBlack, WrapClamp, WrapPeriodic, WrapMirror, or WrapDefault.

    • float swidth, twidth, rwidth : For each direction, gives a multiplier for the derivatives.

    • float sblur, tblur, rblur : For each direction, specifies an additional amount of pre-blur to apply to the texture (after derivatives are taken into account), expressed as a portion of the width of the texture.

    • float fill : Specifies the value that will be used for any color channels that are requested but not found in the file. For example, if you perform a 4-channel lookup on a 3-channel texture, the last channel will get the fill value. (Note: this behavior is affected by the "gray_to_rgb" TextureSystem attribute.

    • const float *missingcolor : If not nullptr, specifies the color that will be returned for missing or broken textures (rather than being an error).

    • float time : A time value to use if the volume texture specifies a time-varying local transformation (default: 0).

  • P: The 2D texture coordinates.

  • dPdx/dPdy/dPdz: The differentials of P. We assume that this lookup will be part of an image that has pixel coordinates x and y and depth z. By knowing how P changes from pixel to pixel in the final image, and as we step in z depth, we can properly filter or antialias the texture lookups. This information is given via derivatives dPdx, dPdy, and dPdz that define the changes in P per unit of x, y, and z, respectively. If it is impossible to know the derivatives, you may pass 0 for them, but in that case you will not receive an antialiased texture lookup.

  • nchannels: The number of channels of data to retrieve into result (e.g., 1 for a single value, 3 for an RGB triple, etc.).

  • result[]: The result of the filtered texture lookup will be placed into result[0..nchannels-1].

  • dresultds/dresultdt/dresultdr: If non-null, these designate storage locations for the derivatives of result, i.e., the rate of change per unit s, t, and r, respectively, of the filtered texture. If supplied, they must allow for nchannels of storage.

virtual bool texture3d(TextureHandle *texture_handle, Perthread *thread_info, TextureOpt &options, const Imath::V3f &P, const Imath::V3f &dPdx, const Imath::V3f &dPdy, const Imath::V3f &dPdz, int nchannels, float *result, float *dresultds = nullptr, float *dresultdt = nullptr, float *dresultdr = nullptr) = 0

Slightly faster version of texture3d() lookup if the app already has a texture handle and per-thread info.

virtual bool environment(ustring filename, TextureOpt &options, const Imath::V3f &R, const Imath::V3f &dRdx, const Imath::V3f &dRdy, int nchannels, float *result, float *dresultds = nullptr, float *dresultdt = nullptr) = 0

Perform a filtered directional environment map lookup in the direction of vector R, from the texture identified by filename, and using relevant texture options. The filtered results will be stored in result[].

Return

true upon success, or false if the file was not found or could not be opened by any available ImageIO plugin.

Parameters

  • filename: The name of the texture, as a UTF-8 encode ustring.

  • options: Fields within options that are honored for environment lookups include the following:

    • int firstchannel : The index of the first channel to look up from the texture.

    • int subimage / ustring subimagename : The subimage or face within the file, specified by either by name (if non-empty) or index. This will be ignored if the file does not have multiple subimages or separate per-face textures.

    • float swidth, twidth : For each direction, gives a multiplier for the derivatives.

    • float sblur, tblur : For each direction, specifies an additional amount of pre-blur to apply to the texture (after derivatives are taken into account), expressed as a portion of the width of the texture.

    • float fill : Specifies the value that will be used for any color channels that are requested but not found in the file. For example, if you perform a 4-channel lookup on a 3-channel texture, the last channel will get the fill value. (Note: this behavior is affected by the "gray_to_rgb" TextureSystem attribute.

    • const float *missingcolor : If not nullptr, specifies the color that will be returned for missing or broken textures (rather than being an error).

  • R: The direction vector to look up.

  • dRdx/dRdy: The differentials of R with respect to image coordinates x and y.

  • nchannels: The number of channels of data to retrieve into result (e.g., 1 for a single value, 3 for an RGB triple, etc.).

  • result[]: The result of the filtered texture lookup will be placed into result[0..nchannels-1].

  • dresultds/dresultdt: If non-null, these designate storage locations for the derivatives of result, i.e., the rate of change per unit s and t, respectively, of the filtered texture. If supplied, they must allow for nchannels of storage.

virtual bool environment(TextureHandle *texture_handle, Perthread *thread_info, TextureOpt &options, const Imath::V3f &R, const Imath::V3f &dRdx, const Imath::V3f &dRdy, int nchannels, float *result, float *dresultds = nullptr, float *dresultdt = nullptr) = 0

Slightly faster version of environment() if the app already has a texture handle and per-thread info.

Batched texture lookups

virtual bool texture(ustring filename, TextureOptBatch &options, Tex::RunMask mask, const float *s, const float *t, const float *dsdx, const float *dtdx, const float *dsdy, const float *dtdy, int nchannels, float *result, float *dresultds = nullptr, float *dresultdt = nullptr) = 0

Perform filtered 2D texture lookups on a batch of positions from the same texture, all at once. The parameters s, t, dsdx, dtdx, and dsdy, dtdy are each a pointer to [BatchWidth] values. The mask determines which of those array elements to actually compute.

The float* results act like float[nchannels][BatchWidth], so that effectively result[0..BatchWidth-1] are the “red” result for each lane, result[BatchWidth..2*BatchWidth-1] are the “green” results, etc. The dresultds and dresultdt should either both be provided, or else both be nullptr (meaning no derivative results are required).

Return

true upon success, or false if the file was not found or could not be opened by any available ImageIO plugin.

Parameters

  • filename: The name of the texture, as a UTF-8 encode ustring.

  • options: A TextureOptBatch containing texture lookup options. This is conceptually the same as a TextureOpt, but the following fields are arrays of [BatchWidth] elements: sblur, tblur, swidth, twidth. The other fields are, as with TextureOpt, ordinary scalar values.

  • mask: A bit-field designating which “lanes” should be computed: if mask & (1<<i) is nonzero, then results should be computed and stored for result[...][i].

  • s/t: Pointers to the 2D texture coordinates, each as a float[BatchWidth].

  • dsdx/dtdx/dsdy/dtdy: The differentials of s and t relative to canonical directions x and y, each as a float[BatchWidth].

  • nchannels: The number of channels of data to retrieve into result (e.g., 1 for a single value, 3 for an RGB triple, etc.).

  • result[]: The result of the filtered texture lookup will be placed here, as float [nchannels][BatchWidth]. (Note the “SOA” data layout.)

  • dresultds/dresultdt: If non-null, these designate storage locations for the derivatives of result, and like result are in SOA layout: float [nchannels][BatchWidth]

virtual bool texture(TextureHandle *texture_handle, Perthread *thread_info, TextureOptBatch &options, Tex::RunMask mask, const float *s, const float *t, const float *dsdx, const float *dtdx, const float *dsdy, const float *dtdy, int nchannels, float *result, float *dresultds = nullptr, float *dresultdt = nullptr) = 0

Slightly faster version of texture() lookup if the app already has a texture handle and per-thread info.

virtual bool texture3d(ustring filename, TextureOptBatch &options, Tex::RunMask mask, const float *P, const float *dPdx, const float *dPdy, const float *dPdz, int nchannels, float *result, float *dresultds = nullptr, float *dresultdt = nullptr, float *dresultdr = nullptr) = 0

Perform filtered 3D volumetric texture lookups on a batch of positions from the same texture, all at once. The “point-like” parameters P, dPdx, dPdy, and dPdz are each a pointers to arrays of float value[3][BatchWidth] (or alternately like Imath::Vec3<FloatWide>). That is, each one points to all the x values for the batch, immediately followed by all the y values, followed by the z values. The mask determines which of those array elements to actually compute.

The various results arrays are also arranged as arrays that behave as if they were declared float result[channels][BatchWidth], where all the batch values for channel 0 are adjacent, followed by all the batch values for channel 1, etc.

Return

true upon success, or false if the file was not found or could not be opened by any available ImageIO plugin.

Parameters

  • filename: The name of the texture, as a UTF-8 encode ustring.

  • options: A TextureOptBatch containing texture lookup options. This is conceptually the same as a TextureOpt, but the following fields are arrays of [BatchWidth] elements: sblur, tblur, swidth, twidth. The other fields are, as with TextureOpt, ordinary scalar values.

  • mask: A bit-field designating which “lanes” should be computed: if mask & (1<<i) is nonzero, then results should be computed and stored for result[...][i].

  • P: Pointers to the 3D texture coordinates, each as a float[3][BatchWidth].

  • dPdx/dPdy/dPdz: The differentials of P relative to canonical directions x, y, and z, each as a float[3][BatchWidth].

  • nchannels: The number of channels of data to retrieve into result (e.g., 1 for a single value, 3 for an RGB triple, etc.).

  • result[]: The result of the filtered texture lookup will be placed here, as float [nchannels][BatchWidth]. (Note the “SOA” data layout.)

  • dresultds/dresultdt/dresultdr: If non-null, these designate storage locations for the derivatives of result, and like result are in SOA layout: float [nchannels][BatchWidth]

virtual bool texture3d(TextureHandle *texture_handle, Perthread *thread_info, TextureOptBatch &options, Tex::RunMask mask, const float *P, const float *dPdx, const float *dPdy, const float *dPdz, int nchannels, float *result, float *dresultds = nullptr, float *dresultdt = nullptr, float *dresultdr = nullptr) = 0

Slightly faster version of texture3d() lookup if the app already has a texture handle and per-thread info.

virtual bool environment(ustring filename, TextureOptBatch &options, Tex::RunMask mask, const float *R, const float *dRdx, const float *dRdy, int nchannels, float *result, float *dresultds = nullptr, float *dresultdt = nullptr) = 0

Perform filtered directional environment map lookups on a batch of directions from the same texture, all at once. The “point-like” parameters R, dRdx, and dRdy are each a pointers to arrays of float value[3][BatchWidth] (or alternately like Imath::Vec3<FloatWide>). That is, each one points to all the x values for the batch, immediately followed by all the y values, followed by the z values. The mask determines which of those array elements to actually compute.

The various results arrays are also arranged as arrays that behave as if they were declared float result[channels][BatchWidth], where all the batch values for channel 0 are adjacent, followed by all the batch values for channel 1, etc.

Return

true upon success, or false if the file was not found or could not be opened by any available ImageIO plugin.

Parameters

  • filename: The name of the texture, as a UTF-8 encode ustring.

  • options: A TextureOptBatch containing texture lookup options. This is conceptually the same as a TextureOpt, but the following fields are arrays of [BatchWidth] elements: sblur, tblur, swidth, twidth. The other fields are, as with TextureOpt, ordinary scalar values.

  • mask: A bit-field designating which “lanes” should be computed: if mask & (1<<i) is nonzero, then results should be computed and stored for result[...][i].

  • R: Pointers to the 3D texture coordinates, each as a float[3][BatchWidth].

  • dRdx/dRdy: The differentials of R relative to canonical directions x and y, each as a float[3][BatchWidth].

  • nchannels: The number of channels of data to retrieve into result (e.g., 1 for a single value, 3 for an RGB triple, etc.).

  • result[]: The result of the filtered texture lookup will be placed here, as float [nchannels][BatchWidth]. (Note the “SOA” data layout.)

  • dresultds/dresultdt: If non-null, these designate storage locations for the derivatives of result, and like result are in SOA layout: float [nchannels][BatchWidth]

virtual bool environment(TextureHandle *texture_handle, Perthread *thread_info, TextureOptBatch &options, Tex::RunMask mask, const float *R, const float *dRdx, const float *dRdy, int nchannels, float *result, float *dresultds = nullptr, float *dresultdt = nullptr) = 0

Slightly faster version of environment() if the app already has a texture handle and per-thread info.

Texture metadata and raw texels

virtual std::string resolve_filename(const std::string &filename) const = 0

Given possibly-relative ‘filename’ (UTF-8 encoded), resolve it using the search path rules and return the full resolved filename.

virtual bool get_texture_info(ustring filename, int subimage, ustring dataname, TypeDesc datatype, void *data) = 0

Get information or metadata about the named texture and store it in *data.

Data names may include any of the following:

  • exists (int): Stores the value 1 if the file exists and is an image format that OpenImageIO can read, or 0 if the file does not exist, or could not be properly read as a texture. Note that unlike all other queries, this query will “succeed” (return true) even if the file does not exist.

  • udim (int) : Stores the value 1 if the file is a “virtual UDIM” or texture atlas file (as described in Section :ref:sec-texturesys-udim) or 0 otherwise.

  • subimages (int) : The number of subimages/faces in the file, as an integer.

  • resolution (int[2] or int[3]): The resolution of the texture file, if an array of 2 integers (described as TypeDesc(INT,2)), or the 3D resolution of the texture file, which is an array of 3 integers (described as TypeDesc(INT,3)) The third value will be 1 unless it’s a volumetric (3D) image.

  • miplevels (int) : The number of MIPmap levels for the specified subimage (an integer).

  • texturetype (string) : A string describing the type of texture of the given file, which describes how the texture may be used (also which texture API call is probably the right one for it). This currently may return one of: “unknown”, “Plain Texture”, “Volume Texture”, “Shadow”, or “Environment”.

  • textureformat

    (string) : A string describing the format of the given file, which describes the kind of texture stored in the file. This currently may return one of: “unknown”, “Plain Texture”, “Volume Texture”, “Shadow”, “CubeFace Shadow”, “Volume

    Shadow”, “LatLong Environment”, or “CubeFace Environment”. Note that there are several kinds of shadows and environment maps, all accessible through the same API calls.

  • channels (int) : The number of color channels in the file.

  • format (int) : The native data format of the pixels in the file (an integer, giving the TypeDesc::BASETYPE of the data). Note that this is not necessarily the same as the data format stored in the image cache.

  • cachedformat (int) : The native data format of the pixels as stored in the image cache (an integer, giving the TypeDesc::BASETYPE of the data). Note that this is not necessarily the same as the native data format of the file.

  • datawindow (int[4] or int[6]): Returns the pixel data window of the image, which is either an array of 4 integers (returning xmin, ymin, xmax, ymax) or an array of 6 integers (returning xmin, ymin, zmin, xmax, ymax, zmax). The z values may be useful for 3D/volumetric images; for 2D images they will be 0).

  • displaywindow (matrix) : Returns the display (a.k.a. full) window of the image, which is either an array of 4 integers (returning xmin, ymin, xmax, ymax) or an array of 6 integers (returning xmin, ymin, zmin, xmax, ymax, zmax). The z values may be useful for 3D/volumetric images; for 2D images they will be 0).

  • worldtocamera (matrix) : The viewing matrix, which is a 4x4 matrix (an Imath::M44f, described as TypeMatrix44) giving the world-to-camera 3D transformation matrix that was used when the image was created. Generally, only rendered images will have this.

  • worldtoscreen (matrix) : The projection matrix, which is a 4x4 matrix (an Imath::M44f, described as TypeMatrix44) giving the matrix that projected points from world space into a 2D screen coordinate system where x and y range from -1 to +1. Generally, only rendered images will have this.

  • worldtoNDC (matrix) : The projection matrix, which is a 4x4 matrix (an Imath::M44f, described as TypeMatrix44) giving the matrix that projected points from world space into a 2D screen coordinate system where x and y range from 0 to +1. Generally, only rendered images will have this.

  • averagecolor (float[nchannels]) : If available in the metadata (generally only for files that have been processed by maketx), this will return the average color of the texture (into an array of floats).

  • averagealpha (float) : If available in the metadata (generally only for files that have been processed by maketx), this will return the average alpha value of the texture (into a float).

  • constantcolor (float[nchannels]) : If the metadata (generally only for files that have been processed by maketx) indicates that the texture has the same values for all pixels in the texture, this will retrieve the constant color of the texture (into an array of floats). A non-constant image (or one that does not have the special metadata tag identifying it as a constant texture) will fail this query (return false).

  • constantalpha (float) : If the metadata indicates that the texture has the same values for all pixels in the texture, this will retrieve the constant alpha value of the texture. A non-constant image (or one that does not have the special metadata tag identifying it as a constant texture) will fail this query (return false).

  • stat:tilesread (int64) : Number of tiles read from this file.

  • stat:bytesread (int64) : Number of bytes of uncompressed pixel data read

  • stat:redundant_tiles (int64) : Number of times a tile was read, where the same tile had been rad before.

  • stat:redundant_bytesread (int64) : Number of bytes (of uncompressed pixel data) in tiles that were read redundantly.

  • stat:redundant_bytesread (int) : Number of tiles read from this file.

  • stat:timesopened (int) : Number of times this file was opened.

  • stat:iotime (float) : Time (in seconds) spent on all I/O for this file.

  • stat:mipsused (int) : Stores 1 if any MIP levels beyond the highest resolution were accessed, otherwise 0.

  • stat:is_duplicate (int) : Stores 1 if this file was a duplicate of another image, otherwise 0.

  • Anything else : For all other data names, the the metadata of the image file will be searched for an item that matches both the name and data type.

Return

true if get_textureinfo() is able to find the requested dataname for the texture and it matched the requested datatype. If the requested data was not found or was not of the right data type, return false. Except for the "exists" query, a file that does not exist or could not be read properly as an image also constitutes a query failure that will return false.

Parameters

  • filename: The name of the texture, as a UTF-8 encode ustring.

  • subimage: The subimage to query. (The metadata retrieved is for the highest-resolution MIP level of that subimage.)

  • dataname: The name of the metadata to retrieve.

  • datatype: TypeDesc describing the data type.

  • data: Pointer to the caller-owned memory where the values should be stored. It is the caller’s responsibility to ensure that data points to a large enough storage area to accommodate the datatype requested.

virtual bool get_texture_info(TextureHandle *texture_handle, Perthread *thread_info, int subimage, ustring dataname, TypeDesc datatype, void *data) = 0

A more efficient variety of get_texture_info() for cases where you can use a TextureHandle* to specify the image and optionally have a Perthread* for the calling thread.

virtual bool get_imagespec(ustring filename, int subimage, ImageSpec &spec) = 0

Copy the ImageSpec associated with the named texture (the first subimage by default, or as set by subimage).

Return

true upon success, false upon failure failure (such as being unable to find, open, or read the file, or if it does not contain the designated subimage or MIP level).

Parameters

  • filename: The name of the texture, as a UTF-8 encode ustring.

  • subimage: The subimage to query. (The spec retrieved is for the highest-resolution MIP level of that subimage.)

  • spec: ImageSpec into which will be copied the spec for the requested image.

virtual bool get_imagespec(TextureHandle *texture_handle, Perthread *thread_info, int subimage, ImageSpec &spec) = 0

A more efficient variety of get_imagespec() for cases where you can use a TextureHandle* to specify the image and optionally have a Perthread* for the calling thread.

virtual const ImageSpec *imagespec(ustring filename, int subimage = 0) = 0

Return a pointer to an ImageSpec associated with the named texture if the file is found and is an image format that can be read, otherwise return nullptr.

This method is much more efficient than get_imagespec(), since it just returns a pointer to the spec held internally by the TextureSystem (rather than copying the spec to the user’s memory). However, the caller must beware that the pointer is only valid as long as nobody (even other threads) calls invalidate() on the file, or invalidate_all(), or destroys the TextureSystem and its underlying ImageCache.

Return

A pointer to the spec, if the image is found and able to be opened and read by an available image format plugin, and the designated subimage exists.

Parameters

  • filename: The name of the texture, as a UTF-8 encode ustring.

  • subimage: The subimage to query. (The spec retrieved is for the highest-resolution MIP level of that subimage.)

virtual const ImageSpec *imagespec(TextureHandle *texture_handle, Perthread *thread_info = nullptr, int subimage = 0) = 0

A more efficient variety of imagespec() for cases where you can use a TextureHandle* to specify the image and optionally have a Perthread* for the calling thread.

virtual bool get_texels(ustring filename, TextureOpt &options, int miplevel, int xbegin, int xend, int ybegin, int yend, int zbegin, int zend, int chbegin, int chend, TypeDesc format, void *result) = 0

For a texture specified by name, retrieve the rectangle of raw unfiltered texels from the subimage specified in options and at the designated miplevel, storing the pixel values beginning at the address specified by result. The pixel values will be converted to the data type specified by format. The rectangular region to be retrieved includes begin but does not include end (much like STL begin/end usage). Requested pixels that are not part of the valid pixel data region of the image file will be filled with zero values. Channels requested but not present in the file will get the options.fill value.

Return

true for success, false for failure.

Parameters

  • filename: The name of the texture, as a UTF-8 encode ustring.

  • options: A TextureOpt describing access options, including wrap modes, fill value, and subimage, that will be used when retrieving pixels.

  • miplevel: The MIP level to retrieve pixels from (0 is the highest resolution level).

  • xbegin/xend/ybegin/yend/zbegin/zend: The range of pixels to retrieve. The pixels retrieved include the begin value but not the end value (much like STL begin/end usage).

  • chbegin/chend: Channel range to retrieve. To retrieve all channels, use chbegin = 0, chend = nchannels.

  • format: TypeDesc describing the data type of the values you want to retrieve into result. The pixel values will be converted to this type regardless of how they were stored in the file or in the cache.

  • result: Pointer to the memory where the pixel values should be stored. It is up to the caller to ensure that result points to an area of memory big enough to accommodate the requested rectangle (taking into consideration its dimensions, number of channels, and data format).

virtual bool get_texels(TextureHandle *texture_handle, Perthread *thread_info, TextureOpt &options, int miplevel, int xbegin, int xend, int ybegin, int yend, int zbegin, int zend, int chbegin, int chend, TypeDesc format, void *result) = 0

A more efficient variety of get_texels() for cases where you can use a TextureHandle* to specify the image and optionally have a Perthread* for the calling thread.

Methods for UDIM patterns

virtual bool is_udim(ustring filename) = 0

Is the UTF-8 encoded filename a UDIM pattern?

This method was added in OpenImageIO 2.3.

virtual bool is_udim(TextureHandle *udimfile) = 0

Does the handle refer to a file that’s a UDIM pattern?

This method was added in OpenImageIO 2.3.

virtual TextureHandle *resolve_udim(ustring udimpattern, float s, float t) = 0

For a UDIM filename pattern (UTF-8 encoded) and texture coordinates, return the TextureHandle pointer for the concrete tile file it refers to, or nullptr if there is no corresponding tile (udim sets are allowed to be sparse).

This method was added in OpenImageIO 2.3.

virtual TextureHandle *resolve_udim(TextureHandle *udimfile, Perthread *thread_info, float s, float t) = 0

A more efficient variety of resolve_udim() for cases where you have the TextureHandle* that corresponds to the “virtual” UDIM file and optionally have a Perthread* for the calling thread.

This method was added in OpenImageIO 2.3.

virtual void inventory_udim(ustring udimpattern, std::vector<ustring> &filenames, int &nutiles, int &nvtiles) = 0

Produce a full inventory of the set of concrete files comprising the UDIM set specified by UTF-8 encoded udimpattern. The apparent number of texture atlas tiles in the u and v directions will be written to nutiles and nvtiles, respectively. The vector filenames will be sized to ntiles * nvtiles and filled with the the names of the concrete files comprising the atlas, with an empty ustring corresponding to any unpopulated tiles (the UDIM set is allowed to be sparse). The filename list is indexed as utile + vtile

This method was added in OpenImageIO 2.3.

virtual void inventory_udim(TextureHandle *udimfile, Perthread *thread_info, std::vector<ustring> &filenames, int &nutiles, int &nvtiles) = 0

A more efficient variety of inventory_udim() for cases where you have the TextureHandle* that corresponds to the “virtual” UDIM file and optionally have a Perthread* for the calling thread.

This method was added in OpenImageIO 2.3.

Controlling the cache

virtual void invalidate(ustring filename, bool force = true) = 0

Invalidate any cached information about the named file (UTF-8 encoded), including loaded texture tiles from that texture, and close any open file handle associated with the file. This calls ImageCache::invalidate(filename,force) on the underlying ImageCache.

virtual void invalidate_all(bool force = false) = 0

Invalidate all cached data for all textures. This calls ImageCache::invalidate_all(force) on the underlying ImageCache.

virtual void close(ustring filename) = 0

Close any open file handles associated with a UTF-8 encoded filename, but do not invalidate any image spec information or pixels associated with the files. A client might do this in order to release OS file handle resources, or to make it safe for other processes to modify textures on disk. This calls ImageCache::close(force) on the underlying ImageCache.

virtual void close_all() = 0

close() all files known to the cache.

Errors and statistics

virtual bool has_error() const = 0

Is there a pending error message waiting to be retrieved?

virtual std::string geterror(bool clear = true) const = 0

Return the text of all pending error messages issued against this TextureSystem, and clear the pending error message unless clear is false. If no error message is pending, it will return an empty string.

virtual std::string getstats(int level = 1, bool icstats = true) const = 0

Returns a big string containing useful statistics about the TextureSystem operations, suitable for saving to a file or outputting to the terminal. The level indicates the amount of detail in the statistics, with higher numbers (up to a maximum of 5) yielding more and more esoteric information. If icstats is true, the returned string will also contain all the statistics of the underlying ImageCache, but if false will only contain texture-specific statistics.

virtual void reset_stats() = 0

Reset most statistics to be as they were with a fresh TextureSystem. Caveat emptor: this does not flush the cache itself, so the resulting statistics from the next set of texture requests will not match the number of tile reads, etc., that would have resulted from a new TextureSystem.

Public Functions

virtual ImageCache *imagecache() const = 0

Return an opaque, non-owning pointer to the underlying ImageCache (if there is one).

UDIM texture atlases

Texture lookups

The texture() call supports virtual filenames that expand per lookup for UDIM tiled texture atlases. The substitutions will occur if the texture filename initially passed to texture() does not exist as a concrete file and contains one or more of the following substrings:

Pattern

Numbering scheme

Example expansion if u=0.5, v=2.5

<UDIM>

1001 + utile + vtile*10

1021

<u>

utile

u0

<v>

vtile

v2

<U>

utile + 1

u1

<V>

vtile + 1

v3

<UVTILE>

equivalent to <U>_<V>

u1_v3

_u##v##

utile, vtile

_u00v02

%(UDIM)d

synonym for <UDIM>

1021

where the tile numbers are derived from the input u,v texture coordinates as follows:

// Each unit square of texture is a different tile
utile = max (0, int(u));
vtile = max (0, int(v));
// Re-adjust the texture coordinates to the offsets within the tile
u = u - utile;
v = v - vtile;

Example:

ustring filename ("paint.<UDIM>.tif");
float s = 1.4, t = 3.8;
texsys->texture (filename, s, t, ...);

will retrieve from file paint.1032.tif at coordinates (0.4,0.8).

Handles of udim files

Calls to get_texture_handle(), when passing a UDIM pattern filename, will always succeed. But withing knowing a specific u and v, it has no way to know that the concrete file you will eventually ask for would not succeed, so this handle is for the overall “virtual” texture atlas.

You can retrieve the handle of a specific “tile” of the UDIM set by using

TextureHandle *resolve_udim(ustring udimpattern, float s, float t)
TextureHandle *resolve_udim(TextureHandle *udimfile, Perthread *thread_info, float s, float t)

Note: these will return nullptr if the UDIM tile for those coordinates is unpopulated.

Note also that the is_udim() method can be used to ask whether a filename or handle corresponds to a UDIM pattern (the whole set of atlas tiles):

bool is_udim(ustring filename)
bool is_udim(TextureHandle *udimfile)

Retrieving metadata from UDIM sets and tiles

Calls to get_texture_info() on UDIM file pattern will succeed if the metadata is found and has the same value in all of the populated “tiles” of a UDIM. If not all populated tile files have the same value for that attribute, the call will fail.

If you want to know the metadata at a specific texture coordinate, you can use a combination of resolve_udim() to find the handle for the corresponding concrete texture file for that “tile,” and then get_texture_info() to retrieve the metadata for the concrete file.

Full inventory of a UDIM set

You can get the range in u and v of the UDIM texture atlas, and the list of all of the concrete filenames of the corresponding tiles with this method:

void inventory_udim(ustring udimpattern, std::vector<ustring> &filenames, int &nutiles, int &nvtiles)
void inventory_udim(TextureHandle *udimfile, Perthread *thread_info, std::vector<ustring> &filenames, int &nutiles, int &nvtiles)

The indexing scheme is that filenames[u + v * nvtiles] is the name of the tile with integer indices (u,v), where 0 is the first index of each row or column.

The combination of inventory_udim() and get_texture_handle() of the listed filenames can be used to generate the corresponding handles for each UDIM tile.

Batched Texture Lookups

On CPU architectures with SIMD processing, texturing entire batches of samples at once may provide a large speedup compared to texturing each sample point individually. The batch size is fixed (for any build of OpenImageIO) and may be accessed with the following constant:

static constexpr int OIIO::Tex::BatchWidth = OIIO_TEXTURE_SIMD_BATCH_WIDTH

The SIMD width for batched texturing operations. This is fixed within any release of OpenImageIO, but may change from release to release and also may be overridden at build time. A typical batch size is 16.

typedef simd::VecType<float, OIIO_TEXTURE_SIMD_BATCH_WIDTH>::type OIIO::Tex::FloatWide

A type alias for a SIMD vector of floats with the batch width.

typedef simd::VecType<int, OIIO_TEXTURE_SIMD_BATCH_WIDTH>::type OIIO::Tex::IntWide

A type alias for a SIMD vector of ints with the batch width.

All of the batched calls take a run mask, which describes which subset of “lanes” should be computed by the batched lookup:

typedef uint64_t OIIO::Tex::RunMask

RunMask is defined to be an integer large enough to hold at least BatchWidth bits. The least significant bit corresponds to the first (i.e., [0]) position of all batch arrays. For each position i in the batch, the bit identified by (1 << i) controls whether that position will be computed.

enumerator RunMaskOn

The defined constant RunMaskOn contains the value with all bits 0..BatchWidth-1 set to 1.

Batched Options

TextureOptBatch is a structure that holds the options for doing an entire batch of lookups from the same texture at once. The members of TextureOptBatch correspond to the similarly named members of the single-point TextureOpt, so we refer you to Section TextureOpt for detailed explanations, and this section will only explain the differences between batched and single-point options. Members include:

  • int firstchannel :

  • int subimage, ustring subimagename :

  • Wrap swrap, twrap, rwrap :

  • float fill :

  • const float* missingcolor :

  • MipMode mipmode :

  • InterpMode interpmode :

  • int anisotropic :

  • bool conservative_filter :

    These fields are all scalars — a single value for each TextureOptBatch — which means that the value of these options must be the same for every texture sample point within a batch. If you have a number of texture lookups to perform for the same texture, but they have (for example) differing wrap modes or subimages from point to point, then you must split them into separate batch calls.

  • float sblur[Tex::BatchWidth] :

  • float tblur[Tex::BatchWidth] :

  • float rblur[Tex::BatchWidth] :

    These arrays hold the s, and t blur amounts, for each sample in the batch, respectively. (And the r blur amount, used only for volumetric texture3d() lookups.)

  • float swidth[Tex::BatchWidth] :

  • float twidth[Tex::BatchWidth] :

  • float rwidth[Tex::BatchWidth] :

    These arrays hold the s, and t filtering width multiplier for derivatives, for each sample in the batch, respectively. (And the r multiplier, used only for volumetric texture3d() lookups.)

Batched Texture Lookup Calls

bool TextureSystem::texture(ustring filename, TextureOptBatch &options, Tex::RunMask mask, const float *s, const float *t, const float *dsdx, const float *dtdx, const float *dsdy, const float *dtdy, int nchannels, float *result, float *dresultds = nullptr, float *dresultdt = nullptr)
bool TextureSystem::texture(TextureHandle *texture_handle, Perthread *thread_info, TextureOptBatch &options, Tex::RunMask mask, const float *s, const float *t, const float *dsdx, const float *dtdx, const float *dsdy, const float *dtdy, int nchannels, float *result, float *dresultds = nullptr, float *dresultdt = nullptr)

Perform filtered 2D texture lookups on a batch of positions from the same texture, all at once. The parameters s, t, dsdx, dtdx, and dsdy, dtdy are each a pointer to [BatchWidth] values. The mask determines which of those array elements to actually compute.

The various results are arranged as arrays that behave as if they were declared:

float result[channels][BatchWidth]

In other words, all the batch values for channel 0 are adjacent, followed by all the batch values for channel 1, etc. (This is “SOA” order.)

This function returns true upon success, or false if the file was not found or could not be opened by any available ImageIO plugin.

bool texture3d(ustring filename, TextureOptBatch &options, Tex::RunMask mask, const float *P, const float *dPdx, const float *dPdy, const float *dPdz, int nchannels, float *result, float *dresultds = nullptr, float *dresultdt = nullptr, float *dresultdr = nullptr)
bool texture3d(TextureHandle *texture_handle, Perthread *thread_info, TextureOptBatch &options, Tex::RunMask mask, const float *P, const float *dPdx, const float *dPdy, const float *dPdz, int nchannels, float *result, float *dresultds = nullptr, float *dresultdt = nullptr, float *dresultdr = nullptr)

Perform filtered 3D volumetric texture lookups on a batch of positions from the same texture, all at once. The “point-like” parameters P, dPdx, dPdy, and dPdz are each a pointers to arrays of float value[3][BatchWidth]. That is, each one points to all the x values for the batch, immediately followed by all the y values, followed by the z values.

The various results arrays are also arranged as arrays that behave as if they were declared float result[channels][BatchWidth], where all the batch values for channel 0 are adjacent, followed by all the batch values for channel 1, etc.

This function returns true upon success, or false if the file was not found or could not be opened by any available ImageIO plugin.

bool environment(ustring filename, TextureOptBatch &options, Tex::RunMask mask, const float *R, const float *dRdx, const float *dRdy, int nchannels, float *result, float *dresultds = nullptr, float *dresultdt = nullptr)
bool environment(TextureHandle *texture_handle, Perthread *thread_info, TextureOptBatch &options, Tex::RunMask mask, const float *R, const float *dRdx, const float *dRdy, int nchannels, float *result, float *dresultds = nullptr, float *dresultdt = nullptr)

Perform filtered directional environment map lookups on a batch of positions from the same texture, all at once. The “point-like” parameters R, dRdx, and dRdy are each a pointers to arrays of float value[3][BatchWidth]. That is, each one points to all the x values for the batch, immediately followed by all the y values, followed by the z values.

Perform filtered directional environment map lookups on a collection of directions all at once, which may be much more efficient than repeatedly calling the single-point version of environment(). The parameters R, dRdx, and dRdy are now VaryingRef’s that may refer to either a single or an array of values, as are many the fields in the options.

The various results arrays are also arranged as arrays that behave as if they were declared float result[channels][BatchWidth], where all the batch values for channel 0 are adjacent, followed by all the batch values for channel 1, etc.

This function returns true upon success, or false if the file was not found or could not be opened by any available ImageIO plugin.

ImageBuf: Image Buffers

ImageBuf Introduction and Theory of Operation

ImageBuf is a utility class that stores an entire image. It provides a nice API for reading, writing, and manipulating images as a single unit, without needing to worry about any of the details of storage or I/O.

All I/O involving ImageBuf (that is, calls to read or write) are implemented underneath in terms of ImageCache, ImageInput, and ImageOutput, and so support all of the image file formats supported by OIIO.

The ImageBuf class definition requires that you:

#include <OpenImageIO/imagebuf.h>
enum OIIO::ImageBuf::IBStorage

An ImageBuf can store its pixels in one of several ways (each identified by an IBStorage enumerated value):

Values:

enumerator UNINITIALIZED

An ImageBuf that doesn’t represent any image at all (either because it is newly constructed with the default constructor, or had an error during construction).

enumerator LOCALBUFFER

“Local storage” is allocated to hold the image pixels internal to the ImageBuf. This memory will be freed when the ImageBuf is destroyed.

enumerator APPBUFFER

The ImageBuf “wraps” pixel memory already allocated and owned by the calling application. The caller will continue to own that memory and be responsible for freeing it after the ImageBuf is destroyed.

enumerator IMAGECACHE

The ImageBuf is “backed” by an ImageCache, which will automatically be used to retrieve pixels when requested, but the ImageBuf will not allocate separate storage for it. This brings all the advantages of the ImageCache, but can only be used for read-only ImageBuf’s that reference a stored image file.

Constructing, destructing, resetting an ImageBuf

There are several ways to construct an ImageBuf. Each constructor has a corresponding reset method that takes the same arguments. Calling reset on an existing ImageBuf is equivalent to constructing a new ImageBuf from scratch (even if the ImageBuf, prior to reset, previously held an image).

Making an empty or uninitialized ImageBuf

OIIO::ImageBuf::ImageBuf()

Default constructor makes an empty/uninitialized ImageBuf. There isn’t much you can do with an uninitialized buffer until you call reset(). The storage type of a default-constructed ImageBuf is IBStorage::UNINITIALIZED.

inline void OIIO::ImageBuf::reset()

Destroy any previous contents of the ImageBuf and re-initialize it to resemble a freshly constructed ImageBuf using the default constructor (holding no image, with storage IBStorage::UNINITIALIZED).

Constructing a readable ImageBuf

explicit OIIO::ImageBuf::ImageBuf(string_view name, int subimage = 0, int miplevel = 0, ImageCache *imagecache = nullptr, const ImageSpec *config = nullptr, Filesystem::IOProxy *ioproxy = nullptr)

Construct a read-only ImageBuf that will be used to read the named file (at the given subimage and MIP-level, defaulting to the first in the file). But don’t read it yet! The image will actually be read lazily, only when other methods need to access the spec and/or pixels, or when an explicit call to init_spec() or read() is made, whichever comes first.

The implementation may end up either reading the entire image internally owned memory (if so, the storage will be LOCALBUFFER), or it may rely on being backed by an ImageCache (in this case, the storage will be IMAGECACHE) depending on the image size and other factors.

Parameters

  • name: The image to read.

  • subimage/miplevel: The subimage and MIP level to read (defaults to the first subimage of the file, highest-res MIP level).

  • imagecache: Optionally, a particular ImageCache to use. If nullptr, the default global/shared image cache will be used. If a custom ImageCache (not the global/shared one), it is important that the IC should not be destroyed while the ImageBuf is still alive.

  • config: Optionally, a pointer to an ImageSpec whose metadata contains configuration hints that set options related to the opening and reading of the file.

  • ioproxy: Optional pointer to an IOProxy to use when reading from the file. The caller retains ownership of the proxy.

void OIIO::ImageBuf::reset(string_view name, int subimage = 0, int miplevel = 0, ImageCache *imagecache = nullptr, const ImageSpec *config = nullptr, Filesystem::IOProxy *ioproxy = nullptr)

Destroy any previous contents of the ImageBuf and re-initialize it as if newly constructed with the same arguments, as a read-only representation of an existing image file.

Constructing a writable ImageBuf

explicit OIIO::ImageBuf::ImageBuf(const ImageSpec &spec, InitializePixels zero = InitializePixels::Yes)

Construct a writable ImageBuf with the given specification (including resolution, data type, metadata, etc.). The ImageBuf will allocate and own its own pixel memory and will free that memory automatically upon destruction, clear(), or reset(). Upon successful initialization, the storage will be reported as LOCALBUFFER.

Parameters

  • spec: An ImageSpec describing the image and its metadata. If not enough information is given to know how much memory to allocate (width, height, depth, channels, and data format), the ImageBuf will remain in an UNINITIALIZED state and will have no local pixel storage.

  • zero: After a successful allocation of the local pixel storage, this parameter controls whether the pixels will be initialized to hold zero (black) values (InitializePixels::Yes) or if the pixel memory will remain uninitialized (InitializePixels::No) and thus may hold nonsensical values. Choosing No may save the time of writing to the pixel memory if you know for sure that you are about to overwrite it completely before you will need to read any pixel values.

void OIIO::ImageBuf::reset(const ImageSpec &spec, InitializePixels zero = InitializePixels::Yes)

Destroy any previous contents of the ImageBuf and re-initialize it as if newly constructed with the same arguments, as a read/write image with locally allocated storage that can hold an image as described by spec. The optional zero parameter controls whether the pixel values are filled with black/empty, or are left uninitialized after being allocated.

Note that if the ImageSpec does not contain enough information to specify how much memory to allocate (width, height, channels, and data format), the ImageBuf will remain uninitialized (regardless of how zero is set).

bool OIIO::ImageBuf::make_writable(bool keep_cache_type = false)

Make the ImageBuf be writable. That means that if it was previously backed by an ImageCache (storage was IMAGECACHE), it will force a full read so that the whole image is in local memory. This will invalidate any current iterators on the image. It has no effect if the image storage is not IMAGECACHE.

Return

Return true if it works (including if no read was necessary), false if something went horribly wrong.

Parameters

  • keep_cache_type: If true, preserve any ImageCache-forced data types (you might want to do this if it is critical that the apparent data type doesn’t change, for example if you are calling make_writable() from within a type-specialized function).

Constructing an ImageBuf that “wraps” an application buffer

OIIO::ImageBuf::ImageBuf(const ImageSpec &spec, void *buffer, stride_t xstride = AutoStride, stride_t ystride = AutoStride, stride_t zstride = AutoStride)

Construct a writable ImageBuf that “wraps” existing pixel memory owned by the calling application. The ImageBuf does not own the pixel storage and will will not free/delete that memory, even when the ImageBuf is destroyed. Upon successful initialization, the storage will be reported as APPBUFFER.

Parameters

  • spec: An ImageSpec describing the image and its metadata. If not enough information is given to know the “shape” of the image (width, height, depth, channels, and data format), the ImageBuf will remain in an UNINITIALIZED state.

  • buffer: A pointer to the caller-owned memory containing the storage for the pixels. It must be already allocated with enough space to hold a full image as described by spec.

  • xstride/ystride/zstride: The distance in bytes between successive pixels, scanlines, and image planes in the buffer (or AutoStride to indicate “contiguous” data in any of those dimensions).

void OIIO::ImageBuf::reset(const ImageSpec &spec, void *buffer, stride_t xstride = AutoStride, stride_t ystride = AutoStride, stride_t zstride = AutoStride)

Destroy any previous contents of the ImageBuf and re-initialize it as if newly constructed with the same arguments, to “wrap” existing pixel memory owned by the calling application.

Reading and Writing disk images

bool OIIO::ImageBuf::read(int subimage = 0, int miplevel = 0, bool force = false, TypeDesc convert = TypeDesc::UNKNOWN, ProgressCallback progress_callback = nullptr, void *progress_callback_data = nullptr)

Read the particular subimage and MIP level of the image. Generally, this will skip the expensive read if the file has already been read into the ImageBuf (at the specified subimage and MIP level). It will clear and re-allocate memory if the previously allocated space was not appropriate for the size or data type of the image being read.

In general, read() will try not to do any I/O at the time of the read() call, but rather to have the ImageBuf “backed” by an ImageCache, which will do the file I/O on demand, as pixel values are needed, and in that case the ImageBuf doesn’t actually allocate memory for the pixels (the data lives in the ImageCache). However, there are several conditions for which the ImageCache will be bypassed, the ImageBuf will allocate “local” memory, and the disk file will be read directly into allocated buffer at the time of the read() call: (a) if the force parameter is true; (b) if the convert parameter requests a data format conversion to a type that is not the native file type and also is not one of the internal types supported by the ImageCache (specifically, float and UINT8); (c) if the ImageBuf already has local pixel memory allocated, or “wraps” an application buffer.

Note that read() is not strictly necessary. If you are happy with the filename, subimage and MIP level specified by the ImageBuf constructor (or the last call to reset()), and you want the storage to be backed by the ImageCache (including storing the pixels in whatever data format that implies), then the file contents will be automatically read the first time you make any other ImageBuf API call that requires the spec or pixel values. The only reason to call read() yourself is if you are changing the filename, subimage, or MIP level, or if you want to use force = true or a specific convert value to force data format conversion.

Return

true upon success, or false if the read failed (in which case, you should be able to retrieve an error message via geterror()).

Parameters

  • subimage/miplevel: The subimage and MIP level to read.

  • force: If true, will force an immediate full read into ImageBuf-owned local pixel memory (yielding a LOCALPIXELS storage buffer). Otherwise, it is up to the implementation whether to immediately read or have the image backed by an ImageCache (storage IMAGECACHE.)

  • convert: If set to a specific type (notUNKNOWN), the ImageBuf memory will be allocated for that type specifically and converted upon read.

  • progress_callback/progress_callback_data: If progress_callback is non-NULL, the underlying read, if expensive, may make several calls to progress_callback(progress_callback_data, portion_done) which allows you to implement some sort of progress meter. Note that if the ImageBuf is backed by an ImageCache, the progress callback will never be called, since no actual file I/O will occur at this time (ImageCache will load tiles or scanlines on demand, as individual pixel values are needed).

bool OIIO::ImageBuf::read(int subimage, int miplevel, int chbegin, int chend, bool force, TypeDesc convert, ProgressCallback progress_callback = nullptr, void *progress_callback_data = nullptr)

Read the file, if possible only allocating and reading a subset of channels, [chbegin..chend-1]. This can be a performance and memory improvement for some image file formats, if you know that any use of the ImageBuf will only access a subset of channels from a many-channel file.

Additional parameters:

Parameters

  • chbegin/chend: The subset (a range with “exclusive end”) of channels to read, if the implementation is able to read only a subset of channels and have a performance advantage by doing so. If chbegin is 0 and chend is either negative or greater than the number of channels in the file, all channels will be read. Please note that it is “advisory” and not guaranteed to be honored by the underlying implementation.

bool OIIO::ImageBuf::init_spec(string_view filename, int subimage, int miplevel)

Read the ImageSpec for the given file, subimage, and MIP level into the ImageBuf, but will not read the pixels or allocate any local storage (until a subsequent call to read()). This is helpful if you have an ImageBuf and you need to know information about the image, but don’t want to do a full read yet, and maybe won’t need to do the full read, depending on what’s found in the spec.

Note that init_spec() is not strictly necessary. If you are happy with the filename, subimage and MIP level specified by the ImageBuf constructor (or the last call to reset()), then the spec will be automatically read the first time you make any other ImageBuf API call that requires it. The only reason to call read() yourself is if you are changing the filename, subimage, or MIP level, or if you want to use force=true or a specific convert value to force data format conversion.

Return

true upon success, or false if the read failed (in which case, you should be able to retrieve an error message via geterror()).

Parameters

  • filename: The filename to read from (should be the same as the filename used when the ImageBuf was constructed or reset.)

  • subimage/miplevel: The subimage and MIP level to read.

bool OIIO::ImageBuf::write(string_view filename, TypeDesc dtype = TypeUnknown, string_view fileformat = string_view(), ProgressCallback progress_callback = nullptr, void *progress_callback_data = nullptr) const

Write the image to the named file, converted to the specified pixel data type dtype (TypeUnknown signifies to use the data type of the buffer), and file format (an empty fileformat means to infer the type from the filename extension).

By default, it will always try to write a scanline-oriented file, unless the set_write_tiles() method has been used to override this.

Return

true upon success, or false if the write failed (in which case, you should be able to retrieve an error message via geterror()).

Parameters

  • filename: The filename to write to.

  • dtype: Optional override of the pixel data format to use in the file being written. The default (UNKNOWN) means to try writing the same data format that as pixels are stored within the ImageBuf memory (or whatever type was specified by a prior call to set_write_format()). In either case, if the file format does not support that data type, another will be automatically chosen that is supported by the file type and loses as little precision as possible.

  • fileformat: Optional override of the file format to write. The default (empty string) means to infer the file format from the extension of the filename (for example, “foo.tif” will write a TIFF file).

  • progress_callback/progress_callback_data: If progress_callback is non-NULL, the underlying write, if expensive, may make several calls to progress_callback(progress_callback_data, portion_done) which allows you to implement some sort of progress meter.

bool OIIO::ImageBuf::write(ImageOutput *out, ProgressCallback progress_callback = nullptr, void *progress_callback_data = nullptr) const

Write the pixels of the ImageBuf to an open ImageOutput. The ImageOutput must have already been opened with a spec that indicates a resolution identical to that of this ImageBuf (but it may have specified a different pixel data type, in which case data conversions will happen automatically). This method does NOT close the file when it’s done (and so may be called in a loop to write a multi-image file).

Note that since this uses an already-opened ImageOutput, which is too late to change how it was opened, it does not honor any prior calls to set_write_format or set_write_tiles.

The main application of this method is to allow an ImageBuf (which by design may hold only a single image) to be used for the output of one image of a multi-subimage and/or MIP-mapped image file.

Return

true if all went ok, false if there were errors writing.

Parameters

  • out: A pointer to an already-opened ImageOutput to which the pixels of the ImageBuf will be written.

  • progress_callback/progress_callback_data: If progress_callback is non-NULL, the underlying write, if expensive, may make several calls to progress_callback(progress_callback_data, portion_done) which allows you to implement some sort of progress meter.

void OIIO::ImageBuf::set_write_format(TypeDesc format)

Set the pixel data format that will be used for subsequent write() calls that do not themselves request a specific data type request.

Note that this does not affect the variety of write() that takes an open ImageOutput* as a parameter.

Parameters

  • format: The data type to be used for all channels.

void OIIO::ImageBuf::set_write_format(cspan<TypeDesc> format)

Set the per-channel pixel data format that will be used for subsequent write() calls that do not themselves request a specific data type request.

Parameters

  • format: The type of each channel (in order). Any channel’s format specified as TypeUnknown will default to be whatever type is described in the ImageSpec of the buffer.

void OIIO::ImageBuf::set_write_tiles(int width = 0, int height = 0, int depth = 0)

Override the tile sizing for subsequent calls to the write() method (the variety that does not take an open ImageOutput*). Setting all three dimensions to 0 indicates that the output should be a scanline-oriented file.

This lets you write a tiled file from an ImageBuf that may have been read originally from a scanline file, or change the dimensions of a tiled file, or to force the file written to be scanline even if it was originally read from a tiled file.

In all cases, if the file format ultimately written does not support tiling, or the tile dimensions requested, a suitable supported tiling choice will be made automatically.

void OIIO::ImageBuf::set_write_ioproxy(Filesystem::IOProxy *ioproxy)

Supply an IOProxy to use for a subsequent call to write().

If a proxy is set but it later turns out that the file format selected does not support write proxies, then write() will fail with an error.

Getting and setting information about an ImageBuf

bool OIIO::ImageBuf::initialized() const

Returns true if the ImageBuf is initialized, false if not yet initialized.

IBStorage OIIO::ImageBuf::storage() const

Which type of storage is being used for the pixels? Returns an enumerated type describing the type of storage currently employed by the ImageBuf: UNINITIALIZED (no storage), LOCALBUFFER (the ImageBuf has allocated and owns the pixel memory), APPBUFFER (the ImageBuf “wraps” memory owned by the calling application), or IMAGECACHE (the image is backed by an ImageCache).

const ImageSpec &OIIO::ImageBuf::spec() const

Return a read-only (const) reference to the image spec that describes the buffer.

const ImageSpec &OIIO::ImageBuf::nativespec() const

Return a read-only (const) reference to the “native” image spec (that describes the file, which may be slightly different than the spec of the ImageBuf, particularly if the IB is backed by an ImageCache that is imposing some particular data format or tile size).

This may differ from spec() for example, if a data format conversion was requested, if the buffer is backed by an ImageCache which stores the pixels internally in a different data format than that of the file, or if the file had differing per-channel data formats (ImageBuf must contain a single data format for all channels).

ImageSpec &OIIO::ImageBuf::specmod()

Return a writable reference to the ImageSpec that describes the buffer. It’s ok to modify most of the metadata, but if you modify the spec’s format, width, height, or depth fields, you get the pain you deserve, as the ImageBuf will no longer have correct knowledge of its pixel memory layout. USE WITH EXTREME CAUTION.

string_view OIIO::ImageBuf::name(void) const

Returns the name of the buffer (name of the file, for an ImageBuf read from disk).

string_view OIIO::ImageBuf::file_format_name(void) const

Return the name of the image file format of the file this ImageBuf refers to (for example "openexr"). Returns an empty string for an ImageBuf that was not constructed as a direct reference to a file.

int OIIO::ImageBuf::subimage() const

Return the index of the subimage within the file that the ImageBuf refers to. This will always be 0 for an ImageBuf that was not constructed as a direct reference to a file, or if the file contained only one image.

int OIIO::ImageBuf::nsubimages() const

Return the number of subimages in the file this ImageBuf refers to. This will always be 1 for an ImageBuf that was not constructed as a direct reference to a file.

int OIIO::ImageBuf::miplevel() const

Return the index of the miplevel with a file’s subimage that the ImageBuf is currently holding. This will always be 0 for an ImageBuf that was not constructed as a direct reference to a file, or if the subimage within that file was not MIP-mapped.

int OIIO::ImageBuf::nmiplevels() const

Return the number of MIP levels of the current subimage within the file this ImageBuf refers to. This will always be 1 for an ImageBuf that was not constructed as a direct reference to a file, or if this subimage within the file was not MIP-mapped.

int OIIO::ImageBuf::nchannels() const

Return the number of color channels in the image. This is equivalent to spec().nchannels.

int xbegin() const
int xend() const
int ybegin() const
int yend() const
int zbegin() const
int zend() const

Returns the [begin,end) range of the pixel data window of the buffer. These are equivalent to spec().x, spec().x+spec().width, spec().y, spec().y+spec().height, spec().z, and spec().z+spec().depth, respectively.

int OIIO::ImageBuf::orientation() const

Return the current "Orientation" metadata for the image, per the table in sec-metadata-orientation_

void OIIO::ImageBuf::set_orientation(int orient)

Set the "Orientation" metadata for the image.

int oriented_width() const
int oriented_height() const
int oriented_x() const
int oriented_y() const
int oriented_full_width() const
int oriented_full_height() const
int oriented_full_x() const
int oriented_full_y() const

The oriented width, height, x, and y describe the pixel data window after taking the display orientation into consideration. The full versions the “full” (a.k.a. display) window after taking the display orientation into consideration.

ROI OIIO::ImageBuf::roi() const

Return pixel data window for this ImageBuf as a ROI.

ROI OIIO::ImageBuf::roi_full() const

Return full/display window for this ImageBuf as a ROI.

void OIIO::ImageBuf::set_origin(int x, int y, int z = 0)

Alters the metadata of the spec in the ImageBuf to reset the “origin” of the pixel data window to be the specified coordinates. This does not affect the size of the pixel data window, only its position.

void OIIO::ImageBuf::set_full(int xbegin, int xend, int ybegin, int yend, int zbegin, int zend)

Set the “full” (a.k.a. display) window to Alters the metadata of the spec in the ImageBuf to reset the “full” image size (a.k.a. “display window”) to 

[xbegin,xend) x [ybegin,yend) x [zbegin,zend)`

This does not affect the size of the pixel data window.

void OIIO::ImageBuf::set_roi_full(const ROI &newroi)

Set full/display window for this ImageBuf to a ROI. Does NOT change the channels of the spec, regardless of newroi.

bool OIIO::ImageBuf::contains_roi(ROI roi) const

Is the specified roi completely contained in the data window of this ImageBuf?

TypeDesc OIIO::ImageBuf::pixeltype() const

The data type of the pixels stored in the buffer (equivalent to spec().format).

int OIIO::ImageBuf::threads() const

Retrieve the current thread-spawning policy of this ImageBuf.

void OIIO::ImageBuf::threads(int n) const

Set the threading policy for this ImageBuf, controlling the maximum amount of parallelizing thread “fan-out” that might occur during expensive operations. The default of 0 means that the global attribute("threads") value should be used (which itself defaults to using as many threads as cores).

The main reason to change this value is to set it to 1 to indicate that the calling thread should do all the work rather than spawning new threads. That is probably the desired behavior in situations where the calling application has already spawned multiple worker threads.

Copying ImageBuf’s and blocks of pixels

const ImageBuf &OIIO::ImageBuf::operator=(const ImageBuf &src)

Copy assignment.

const ImageBuf &OIIO::ImageBuf::operator=(ImageBuf &&src)

Move assignment.

bool OIIO::ImageBuf::copy(const ImageBuf &src, TypeDesc format = TypeUnknown)

Try to copy the pixels and metadata from src to *this (optionally with an explicit data format conversion).

If the previous state of *this was uninitialized, owning its own local pixel memory, or referring to a read-only image backed by ImageCache, then local pixel memory will be allocated to hold the new pixels and the call always succeeds unless the memory cannot be allocated. In this case, the format parameter may request a pixel data type that is different from that of the source buffer.

If *this previously referred to an app-owned memory buffer, the memory cannot be re-allocated, so the call will only succeed if the app-owned buffer is already the correct resolution and number of channels. The data type of the pixels will be converted automatically to the data type of the app buffer.

Return

true upon success or false upon error/failure.

Parameters

  • src: Another ImageBuf from which to copy the pixels and metadata.

  • format: Optionally request the pixel data type to be used. The default of TypeUnknown means to use whatever data type is used by the src. If *this is already initialized and has APPBUFFER storage (“wrapping” an application buffer), this parameter is ignored.

ImageBuf OIIO::ImageBuf::copy(TypeDesc format) const

Return a full copy of this ImageBuf (optionally with an explicit data format conversion).

void OIIO::ImageBuf::copy_metadata(const ImageBuf &src)

Copy all the metadata from src to *this (except for pixel data resolution, channel types and names, and data format).

bool OIIO::ImageBuf::copy_pixels(const ImageBuf &src)

Copy the pixel data from src to *this, automatically converting to the existing data format of *this. It only copies pixels in the overlap regions (and channels) of the two images; pixel data in *this that do exist in src will be set to 0, and pixel data in src that do not exist in *this will not be copied.

inline void OIIO::ImageBuf::swap(ImageBuf &other)

Swap the entire contents with another ImageBuf.

Getting and setting pixel values

Getting and setting individual pixels – slow

float OIIO::ImageBuf::getchannel(int x, int y, int z, int c, WrapMode wrap = WrapBlack) const

Retrieve a single channel of one pixel.

Return

The data value, converted to a float.

Parameters

  • x/y/z: The pixel coordinates.

  • c: The channel index to retrieve.

  • wrap: WrapMode that determines the behavior if the pixel coordinates are outside the data window: WrapBlack, WrapClamp, WrapPeriodic, WrapMirror.

void OIIO::ImageBuf::getpixel(int x, int y, int z, float *pixel, int maxchannels = 1000, WrapMode wrap = WrapBlack) const

Retrieve the pixel value by x, y, z pixel indices, placing its contents in pixel[0..n-1] where n is the smaller of maxchannels the actual number of channels stored in the buffer.

Parameters

  • x/y/z: The pixel coordinates.

  • pixel: The results are stored in pixel[0..nchannels-1]. It is up to the caller to ensure that pixel points to enough memory to hold the required number of channels.

  • maxchannels: Optional clamp to the number of channels retrieved.

  • wrap: WrapMode that determines the behavior if the pixel coordinates are outside the data window: WrapBlack, WrapClamp, WrapPeriodic, WrapMirror.

void OIIO::ImageBuf::interppixel(float x, float y, float *pixel, WrapMode wrap = WrapBlack) const

Sample the image plane at pixel coordinates (x,y), using linear interpolation between pixels, placing the result in pixel[].

Parameters

  • x/y: The pixel coordinates. Note that pixel data values themselves are at the pixel centers, so pixel (i,j) is at image plane coordinate (i+0.5, j+0.5).

  • pixel: The results are stored in pixel[0..nchannels-1]. It is up to the caller to ensure that pixel points to enough memory to hold the number of channels in the image.

  • wrap: WrapMode that determines the behavior if the pixel coordinates are outside the data window: WrapBlack, WrapClamp, WrapPeriodic, WrapMirror.

void OIIO::ImageBuf::interppixel_bicubic(float x, float y, float *pixel, WrapMode wrap = WrapBlack) const

Bicubic interpolation at pixel coordinates (x,y).

void OIIO::ImageBuf::interppixel_NDC(float s, float t, float *pixel, WrapMode wrap = WrapBlack) const

Linearly interpolate at NDC coordinates (s,t), where (0,0) is the upper left corner of the display window, (1,1) the lower right corner of the display window.

Note

interppixel() uses pixel coordinates (ranging 0..resolution) whereas interppixel_NDC() uses NDC coordinates (ranging 0..1).

void OIIO::ImageBuf::interppixel_bicubic_NDC(float s, float t, float *pixel, WrapMode wrap = WrapBlack) const

Bicubic interpolation at NDC space coordinates (s,t), where (0,0) is the upper left corner of the display (a.k.a. “full”) window, (1,1) the lower right corner of the display window.

inline void OIIO::ImageBuf::setpixel(int x, int y, int z, cspan<float> pixel)

Set the pixel with coordinates (x,y,z) to have the values in span pixel[]. The number of channels copied is the minimum of the span length and the actual number of channels in the image.

inline void OIIO::ImageBuf::setpixel(int i, cspan<float> pixel)

Set the i-th pixel value of the image (out of width*height*depth), from floating-point values in span pixel[]. The number of channels copied is the minimum of the span length and the actual number of channels in the image.


Getting and setting regions of pixels – fast

bool OIIO::ImageBuf::get_pixels(ROI roi, TypeDesc format, void *result, stride_t xstride = AutoStride, stride_t ystride = AutoStride, stride_t zstride = AutoStride) const

Retrieve the rectangle of pixels spanning the ROI (including channels) at the current subimage and MIP-map level, storing the pixel values beginning at the address specified by result and with the given strides (by default, AutoStride means the usual contiguous packing of pixels) and converting into the data type described by format. It is up to the caller to ensure that result points to an area of memory big enough to accommodate the requested rectangle. Return true if the operation could be completed, otherwise return false.

bool OIIO::ImageBuf::set_pixels(ROI roi, TypeDesc format, const void *data, stride_t xstride = AutoStride, stride_t ystride = AutoStride, stride_t zstride = AutoStride)

Copy the data into the given ROI of the ImageBuf. The data points to values specified by format, with layout detailed by the stride values (in bytes, with AutoStride indicating “contiguous” layout). It is up to the caller to ensure that data points to an area of memory big enough to account for the ROI. If roi is set to ROI::all(), the data buffer is assumed to have the same resolution as the ImageBuf itself. Return true if the operation could be completed, otherwise return false.

Deep data in an ImageBuf

bool OIIO::ImageBuf::deep() const

Does this ImageBuf store deep data? Returns true if the ImageBuf holds a “deep” image, false if the ImageBuf holds an ordinary pixel-based image.

int OIIO::ImageBuf::deep_samples(int x, int y, int z = 0) const

Retrieve the number of deep data samples corresponding to pixel (x,y,z). Return 0 if not a deep image, or if the pixel is outside of the data window, or if the designated pixel has no deep samples.

void OIIO::ImageBuf::set_deep_samples(int x, int y, int z, int nsamples)

Set the number of deep samples for pixel (x,y,z). If data has already been allocated, this is equivalent to inserting or erasing samples.

void OIIO::ImageBuf::deep_insert_samples(int x, int y, int z, int samplepos, int nsamples)

Insert nsamples new samples, starting at position samplepos of pixel (x,y,z).

void OIIO::ImageBuf::deep_erase_samples(int x, int y, int z, int samplepos, int nsamples)

Remove nsamples samples, starting at position samplepos of pixel (x,y,z).

float OIIO::ImageBuf::deep_value(int x, int y, int z, int c, int s) const

Return the value (as a float) of sample s of channel c of pixel (x,y,z). Return 0 if not a deep image or if the pixel coordinates or channel number are out of range or if that pixel has no deep samples.

uint32_t OIIO::ImageBuf::deep_value_uint(int x, int y, int z, int c, int s) const

Return the value (as a uint32_t) of sample s of channel c of pixel (x,y,z). Return 0 if not a deep image or if the pixel coordinates or channel number are out of range or if that pixel has no deep samples.

void OIIO::ImageBuf::set_deep_value(int x, int y, int z, int c, int s, float value)

Set the value of sample s of channel c of pixel (x,y,z) to a float value (it is expected that channel c is a floating point type).

void OIIO::ImageBuf::set_deep_value(int x, int y, int z, int c, int s, uint32_t value)

Set the value of sample s of channel c of pixel (x,y,z) to a uint32_t value (it is expected that channel c is an integer type).

const void *OIIO::ImageBuf::deep_pixel_ptr(int x, int y, int z, int c, int s = 0) const

Return a pointer to the raw data of pixel (x,y,z), channel c, sample s. Return nullptr if the pixel coordinates or channel number are out of range, if the pixel/channel has no deep samples, or if the image is not deep. Use with caution these pointers may be invalidated by calls that adjust the number of samples in any pixel.

DeepData &OIIO::ImageBuf::deepdata()
const DeepData &OIIO::ImageBuf::deepdata() const

Returns a reference to the underlying DeepData for a deep image.

Error Handling

template<typename ...Args>
inline void OIIO::ImageBuf::errorf(const char *fmt, const Args&... args) const

Error reporting for ImageBuf: call this with printf-like arguments to report an error. It is not necessary to have the error message contain a trailing newline.

bool OIIO::ImageBuf::has_error(void) const

Returns true if the ImageBuf has had an error and has an error message ready to retrieve via geterror().

std::string OIIO::ImageBuf::geterror(bool clear = true) const

Return the text of all pending error messages issued against this ImageBuf, and clear the pending error message unless clear is false. If no error message is pending, it will return an empty string.

Miscellaneous

void *localpixels()
const void *localpixels() const

Return a raw pointer to the “local” pixel memory, if they are fully in RAM and not backed by an ImageCache, or nullptr otherwise. You can also test it like a bool to find out if pixels are local.

void *pixeladdr(int x, int y, int z = 0, int ch = 0)
const void *pixeladdr(int x, int y, int z = 0, int ch = 0) const

Return the address where pixel (x,y,z), channel ch, is stored in the image buffer. Use with extreme caution! Will return nullptr if the pixel values aren’t local in RAM.

int OIIO::ImageBuf::pixelindex(int x, int y, int z, bool check_range = false) const

Return the index of pixel (x,y,z). If check_range is true, return -1 for an invalid coordinate that is not within the data window.

static WrapMode OIIO::ImageBuf::WrapMode_from_string(string_view name)

Return the WrapMode corresponding to the name ("default", "black", "clamp", "periodic", "mirror"). For an unknown name, this will return WrapDefault.

Iterators – the fast way of accessing individual pixels

Sometimes you need to visit every pixel in an ImageBuf (or at least, every pixel in a large region). Using the getpixel() and setpixel() for this purpose is simple but very slow. But ImageBuf provides templated Iterator and ConstIterator types that are very inexpensive and hide all the details of local versus cached storage.

Note

ImageBuf::ConstIterator is identical to the Iterator, except that ConstIterator may be used on a const ImageBuf and may not be used to alter the contents of the ImageBuf. For simplicity, the remainder of this section will only discuss the Iterator.

An Iterator is associated with a particular ImageBuf. The Iterator has a current pixel coordinate that it is visiting, and an iteration range that describes a rectangular region of pixels that it will visits as it advances. It always starts at the upper left corner of the iteration region. We say that the iterator is done after it has visited every pixel in its iteration range. We say that a pixel coordinate exists if it is within the pixel data window of the ImageBuf. We say that a pixel coordinate is valid if it is within the iteration range of the iterator.

The Iterator<BUFT,USERT> is templated based on two types: BUFT the type of the data stored in the ImageBuf, and USERT type type of the data that you want to manipulate with your code. USERT defaults to float, since usually you will want to do all your pixel math with float. We will thus use Iterator<T> synonymously with Iterator<T,float>.

For the remainder of this section, we will assume that you have a float-based ImageBuf, for example, if it were set up like this:

ImageBuf buf ("myfile.exr");
buf.read (0, 0, true, TypeDesc::FLOAT);
template<>
Iterator<BUFT>(ImageBuf &buf, WrapMode wrap = WrapDefault)

Initialize an iterator that will visit every pixel in the data window of buf, and start it out pointing to the upper left corner of the data window. The wrap describes what values will be retrieved if the iterator is positioned outside the data window of the buffer.

template<>
Iterator<BUFT>(ImageBuf &buf, const ROI &roi, WrapMode wrap = WrapDefault)

Initialize an iterator that will visit every pixel of buf within the region described by roi, and start it out pointing to pixel (roi.xbegin, roi.ybegin, roi.zbegin). The wrap describes what values will be retrieved if the iterator is positioned outside the data window of the buffer.

template<>
Iterator<BUFT>(ImageBuf &buf, int x, int y, int z, WrapMode wrap = WrapDefault)

Initialize an iterator that will visit every pixel in the data window of buf, and start it out pointing to pixel (x, y, z). The wrap describes what values will be retrieved if the iterator is positioned outside the data window of the buffer.

Iterator::operator++()

The ++ operator advances the iterator to the next pixel in its iteration range. (Both prefix and postfix increment operator are supported.)

bool Iterator::done() const

Returns true if the iterator has completed its visit of all pixels in its iteration range.

ROI Iterator::range() const

Returns the iteration range of the iterator, expressed as an ROI.

int Iterator::x() const
int Iterator::y() const
int Iterator::z() const

Returns the x, y, and z pixel coordinates, respectively, of the pixel that the iterator is currently visiting.

bool Iterator::valid() const

Returns true if the iterator’s current pixel coordinates are within its iteration range.

bool Iterator::valid(int x, int y, int z = 0) const

Returns true if pixel coordinate (x, y, z) are within the iterator’s iteration range (regardless of where the iterator itself is currently pointing).

bool Iterator::exists() const

Returns true if the iterator’s current pixel coordinates are within the data window of the ImageBuf.

bool Iterator::exists(int x, int y, int z = 0) const

Returns true if pixel coordinate (x, y, z) are within the pixel data window of the ImageBuf (regardless of where the iterator itself is currently pointing).

USERT &Iterator::operator[](int i)

The value of channel i of the current pixel. (The wrap mode, set up when the iterator was constructed, determines what value is returned if the iterator points outside the pixel data window of its buffer.)

int Iterator::deep_samples() const

For deep images only, retrieves the number of deep samples for the current pixel.

void Iterator::set_deep_samples()

For deep images only (and non-const ImageBuf), set the number of deep samples for the current pixel. This only is useful if the ImageBuf has not yet had the deep_alloc() method called.

USERT Iterator::deep_value(int c, int s) const
uint32_t Iterator::deep_value_int(int c, int s) const

For deep images only, returns the value of channel c, sample number s, at the current pixel.

void Iterator::set_deep_value(int c, int s, float value)
void Iterator::set_deep_value(int c, int s, uint32_t value)

For deep images only (and non-cconst ImageBuf, sets the value of channel c, sample number s, at the current pixel. This only is useful if the ImageBuf has already had the deep_alloc() method called.

Example: Visiting all pixels to compute an average color

void print_channel_averages (const std::string &filename)
{
    // Set up the ImageBuf and read the file
    ImageBuf buf (filename);
    bool ok = buf.read (0, 0, true, TypeDesc::FLOAT);  // Force a float buffer
    if (! ok)
        return;

    // Initialize a vector to contain the running total
    int nc = buf.nchannels();
    std::vector<float> total (n, 0.0f);

    // Iterate over all pixels of the image, summing channels separately
    for (ImageBuf::ConstIterator<float> it (buf);  ! it.done();  ++it)
        for (int c = 0;  c < nc;  ++c)
            total[c] += it[c];

    // Print the averages
    imagesize_t npixels = buf.spec().image_pixels();
    for (int c = 0;  c < nc;  ++c)
        std::cout << "Channel " << c << " avg = " (total[c] / npixels) << "\n";
}

Example: Set all pixels in a region to black

bool make_black (ImageBuf &buf, ROI region)
{
    if (buf.spec().format != TypeDesc::FLOAT)
        return false;    // Assume it's a float buffer

    // Clamp the region's channel range to the channels in the image
    roi.chend = std::min (roi.chend, buf.nchannels);

    // Iterate over all pixels in the region...
    for (ImageBuf::Iterator<float> it (buf, region);  ! it.done();  ++it) {
        if (! it.exists())   // Make sure the iterator is pointing
            continue;        //   to a pixel in the data window
        for (int c = roi.chbegin;  c < roi.chend;  ++c)
            it[c] = 0.0f;  // clear the value
    }
    return true;
}

Dealing with buffer data types

The previous section on iterators presented examples and discussion based on the assumption that the ImageBuf was guaranteed to store float data and that you wanted all math to also be done as float computations. Here we will explain how to deal with buffers and files that contain different data types.

Strategy 1: Only have float data in your ImageBuf

When creating your own buffers, make sure they are float:

ImageSpec spec (640, 480, 3, TypeDesc::FLOAT); // <-- float buffer
ImageBuf buf ("mybuf", spec);

When using ImageCache-backed buffers, force the ImageCache to convert everything to float:

// Just do this once, to set up the cache:
ImageCache *cache = ImageCache::create (true /* shared cache */);
cache->attribute ("forcefloat", 1);
...
ImageBuf buf ("myfile.exr");   // Backed by the shared cache

Or force the read to convert to float in the buffer if it’s not a native type that would automatically stored as a float internally to the ImageCache:1

1

ImageCache only supports a limited set of types internally, currently float, half, uint8, uint16, and all other data types are converted to these automatically as they are read into the cache.

ImageBuf buf ("myfile.exr");   // Backed by the shared cache
buf.read (0, 0, false /* don't force read to local mem */,
          TypeDesc::FLOAT /* but do force conversion to float*/);

Or force a read into local memory unconditionally (rather than relying on the ImageCache), and convert to float:

ImageBuf buf ("myfile.exr");
buf.read (0, 0, true /*force read*/,
          TypeDesc::FLOAT /* force conversion */);

Strategy 2: Template your iterating functions based on buffer type

Consider the following alternate version of the make_black function from Section Example: Set all pixels in a region to black

template<type BUFT>
static bool make_black_impl (ImageBuf &buf, ROI region)
{
    // Clamp the region's channel range to the channels in the image
    roi.chend = std::min (roi.chend, buf.nchannels);

    // Iterate over all pixels in the region...
    for (ImageBuf::Iterator<BUFT> it (buf, region);  ! it.done();  ++it) {
        if (! it.exists())   // Make sure the iterator is pointing
            continue;        //   to a pixel in the data window
        for (int c = roi.chbegin;  c < roi.chend;  ++c)
            it[c] = 0.0f;  // clear the value
    }
    return true;
}

bool make_black (ImageBuf &buf, ROI region)
{
    if (buf.spec().format == TypeDesc::FLOAT)
        return make_black_impl<float> (buf, region);
    else if (buf.spec().format == TypeDesc::HALF)
        return make_black_impl<half> (buf, region);
    else if (buf.spec().format == TypeDesc::UINT8)
        return make_black_impl<unsigned char> (buf, region);
    else if (buf.spec().format == TypeDesc::UINT16)
        return make_black_impl<unsigned short> (buf, region);
    else {
        buf.error ("Unsupported pixel data format %s", buf.spec().format);
        retrn false;
    }
}

In this example, we make an implementation that is templated on the buffer type, and then a wrapper that calls the appropriate template specialization for each of 4 common types (and logs an error in the buffer for any other types it encounters).

In fact, imagebufalgo_util.h provides a macro to do this (and several variants, which will be discussed in more detail in the next chapter). You could rewrite the example even more simply:

#include <OpenImageIO/imagebufalgo_util.h>

template<type BUFT>
static bool make_black_impl (ImageBuf &buf, ROI region)
{
    ... same as before ...
}

bool make_black (ImageBuf &buf, ROI region)
{
    bool ok;
    OIIO_DISPATCH_COMMON_TYPES (ok, "make_black", make_black_impl,
                                 buf.spec().format, buf, region);
    return ok;
}

This other type-dispatching helper macros will be discussed in more detail in Chapter ImageBufAlgo: Image Processing.

ImageBufAlgo: Image Processing

ImageBufAlgo is a set of image processing functions that operate on ImageBuf’s. The functions are declared in the header file OpenImageIO/imagebufalgo.h and are declared in the namespace ImageBufAlgo.

ImageBufAlgo common principles

This section explains the general rules common to all ImageBufAlgo functions. Only exceptions to these rules will be explained in the subsequent listings of all the individual ImageBufAlgo functions.

Return values and error messages

Most ImageBufAlgo functions that produce image data come in two forms:

  1. Return an ImageBuf.

    The return value is a new ImageBuf containing the result image. In this case, an entirely new image will be created to hold the result. In case of error, the result image returned can have any error conditions checked with has_error() and geterror().

    // Method 1: Return an image result
ImageBuf dst = ImageBufAlgo::over (fg, bg);
if (dst.has_error())
    std::cout << "error: " << dst.geterror() << "\n";

  2. Pass a destination ImageBuf reference as the first parameter.

    The function is passed a destination ImageBuf where the results will be stored, and the return value is a bool that is true if the function succeeds or false if the function fails. Upon failure, the destination ImageBuf (the one that is being altered) will have an error message set.

    // Method 2: Write into an existing image
ImageBuf fg ("fg.exr"), bg ("bg.exr");
ImageBuf dst;   // will be the output image
bool ok = ImageBufAlgo::over (dst, fg, bg);
if (! ok)
    std::cout << "error: " << dst.geterror() << "\n";

The first option (return an ImageBuf directly) is a more compact and intuitive notation that is natural for most simple uses. But the second option (pass an ImageBuf& referring to an existing destination) offers additional flexibility, including more careful control over allocations, the ability to partially overwrite regions of an existing image, and the ability for the destination image to also be one of the input images (for example, add(A,A,B) adds B into existing image A, with no third image allocated at all).

For a small minority of ImageBufAlgo functions, there are only input images, and no image outputs (e.g., isMonochrome()). In such cases, the error message should be retrieved from the first input image.

Region of interest

Most ImageBufAlgo functions take an optional ROI parameter that restricts the operation to a range in x, y, z, and channels. The default-constructed ROI (also known as ROI::All()) means no region restriction – the whole image will be copied or altered.

For ImageBufAlgo functions that write into a destination ImageBuf parameter and it is already initialized (i.e. allocated with a particular size and data type), the operation will be performed on the pixels in the destination that overlap the ROI, leaving pixels in the destination which are outside the ROI unaltered.

For ImageBufAlgo functions that return an ImageBuf directly, or if their dst parameter is an uninitialized ImageBuf, the ROI (if set) determines the size of the result image. If the ROI is the default All, the result image size will be the union of the pixel data windows of the input images and have a data type determind by the data types of the input images.

Most ImageBufAlgo functions also respect the chbegin and chend members of the ROI, thus restricting the channel range on which the operation is performed. The default ROI constructor sets up the ROI to specify that the operation should be performed on all channels of the input image(s).

Constant and per-channel values

Many ImageBufAlgo functions take per-channel constant-valued arguments (for example, a fill color). These parameters are passed as cspan<float>. These are generally expected to have length equal to the number of channels. But you may also pass a single float which will be used as the value for all channels. (More generally, what is happening is that the last value supplied is replicated for any missing channel.)

Some ImageBufAlgo functions have parameters of type Image_or_Const, which may take either an ImageBuf reference, or a per-channel constant, or a single constant to be used for all channels.

Multithreading

All ImageBufAlgo functions take an optional nthreads parameter that signifies the maximum number of threads to use to parallelize the operation. The default value for nthreads is 0, which signifies that the number of thread should be the OIIO global default set by OIIO::attribute() (see Section Global Attributes), which itself defaults to be the detected level of hardware concurrency (number of cores available).

Generally you can ignore this parameter (or pass 0), meaning to use all the cores available in order to perform the computation as quickly as possible. The main reason to explicitly pass a different number (generally 1) is if the application is multithreaded at a high level, and the thread calling the ImageBufAlgo function just wants to continue doing the computation without spawning additional threads, which might tend to crowd out the other application threads.

Pattern generation

For the ImageBufAlgo functions in this section, there is no “source” image. Therefore, either an initialized dst must be supplied (to give a pre- allocated size and data type of the image), or else it is strictly necessary to supply an ROI parameter to specify the size of the new image (the data type in this case will always be float). It is an error if one of the pattern generation ImageBufAlgo functions is neither supplied a pre-allocated dst nor a non-default ROI.

zero() – create a black image

ImageBuf OIIO::ImageBufAlgo::zero(ROI roi, int nthreads = 0)

Create an all-black float image of size and channels as described by the ROI.

Result-as-parameter version:

bool OIIO::ImageBufAlgo::zero(ImageBuf &dst, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

Examples:

// Create a new 3-channel, 512x512 float image filled with 0.0 values.
ImageBuf zero = ImageBufAlgo::zero (ROI(0,512,0,512,0,1,0,3));

// Zero out an existing buffer, keeping it the same size and data type
ImageBuf A = ...;
...
ImageBufAlgo::zero (A);

// Zero out just the green channel, leave everything else the same
ROI roi = A.roi ();
roi.chbegin = 1; // green
roi.chend = 2;   // one past the end of the channel region
ImageBufAlgo::zero (A, roi);

// Zero out a rectangular region of an existing buffer
ImageBufAlgo::zero (A, ROI (0, 100, 0, 100));

fill() – fill a region with a solid color or gradient

group fill

Fill an image region with given channel values, either returning a new image or altering the existing dst image within the ROI. Note that the values arrays start with channel 0, even if the ROI indicates that a later channel is the first to be changed.

Three varieties of fill() exist: (a) a single set of channel values that will apply to the whole ROI, (b) two sets of values that will create a linearly interpolated gradient from top to bottom of the ROI, (c) four sets of values that will be bilinearly interpolated across all four corners of the ROI.

Functions

ImageBuf fill(cspan<float> values, ROI roi, int nthreads = 0)
ImageBuf fill(cspan<float> top, cspan<float> bottom, ROI roi, int nthreads = 0)
ImageBuf fill(cspan<float> topleft, cspan<float> topright, cspan<float> bottomleft, cspan<float> bottomright, ROI roi, int nthreads = 0)
bool fill(ImageBuf &dst, cspan<float> values, ROI roi = {}, int nthreads = 0)
bool fill(ImageBuf &dst, cspan<float> top, cspan<float> bottom, ROI roi = {}, int nthreads = 0)
bool fill(ImageBuf &dst, cspan<float> topleft, cspan<float> topright, cspan<float> bottomleft, cspan<float> bottomright, ROI roi = {}, int nthreads = 0)

Examples:

// Create a new 640x480 RGB image, with a top-to-bottom gradient
// from red to pink
float pink[3] = { 1, 0.7, 0.7 };
float red[3] = { 1, 0, 0 };
ImageBuf A = ImageBufAlgo::fill (red, pink, ROI(0, 640, 0, 480, 0, 1, 0, 3));

// Draw a filled red rectangle overtop existing image A.
ImageBufAlgo::fill (A, red, ROI(50, 100, 75, 175));
_images/fill.jpg

checker() – make a checker pattern

ImageBuf OIIO::ImageBufAlgo::checker(int width, int height, int depth, cspan<float> color1, cspan<float> color2, int xoffset, int yoffset, int zoffset, ROI roi, int nthreads = 0)

Create a checkerboard pattern of size given by roi, with origin given by the offset values, checker size given by the width, height, depth values, and alternating between color1[] and color2[]. The pattern is defined in abstract “image space” independently of the pixel data window of dst or the ROI.

Result-as-parameter version:

bool OIIO::ImageBufAlgo::checker(ImageBuf &dst, int width, int height, int depth, cspan<float> color1, cspan<float> color2, int xoffset = 0, int yoffset = 0, int zoffset = 0, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

Examples:

// Create a new 640x480 RGB image, fill it with a two-toned gray
// checkerboard, the checkers being 64x64 pixels each.
ImageBuf A (ImageSpec(640, 480, 3, TypeDesc::FLOAT);
float dark[3] = { 0.1, 0.1, 0.1 };
float light[3] = { 0.4, 0.4, 0.4 };
ImageBufAlgo::checker (A, 64, 64, 1, dark, light, 0, 0, 0);
_images/checker.jpg

Noise patterns

ImageBuf OIIO::ImageBufAlgo::noise(string_view noisetype, float A = 0.0f, float B = 0.1f, bool mono = false, int seed = 0, ROI roi = {}, int nthreads = 0)

Return an image of “noise” in every pixel and channel specified by the roi. There are several noise types to choose from, and each behaves differently and has a different interpretation of the A and B parameters:

  • “gaussian” adds Gaussian (normal distribution) noise values with mean value A and standard deviation B.

  • ”white” adds independent uniformly distributed values on range [A,B).

  • ”uniform” (synonym for “white”)

  • ”blue” adds “blue noise” uniformly distributed on range [A,B) but not independent; rather, they are chosen for good spectral properties for sampling and dither.

  • ”salt” changes to value A a portion of pixels given by B.

If the mono flag is true, a single noise value will be applied to all channels specified by roi, but if mono is false, a separate noise value will be computed for each channel in the region.

The random number generator is actually driven by a hash on the “image

space” coordinates and channel, independently of the pixel data window of

dst or the ROI. Choosing different seed values will result in a different pattern, but for the same seed value, the noise at a given pixel coordinate (x,y,z) channel c will is completely deterministic and repeatable.

Result-as-parameter version:

bool OIIO::ImageBufAlgo::noise(ImageBuf &dst, string_view noisetype, float A = 0.0f, float B = 0.1f, bool mono = false, int seed = 0, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

Examples:

// Create a new 256x256 field of grayscale white noise on [0,1)
ImageBuf A = ImageBufAlgo::noise ("uniform", 0.0f /*min*/, 1.0f /*max*/,
                     true /*mono*/, 1 /*seed*/, ROI(0,256,0,256,0,1,0,3));

// Create a new 256x256 field of grayscale white noise on [0,1)
ImageBuf B = ImageBufAlgo::noise ("blue", 0.0f /*min*/, 1.0f /*max*/,
                     true /*mono*/, 1 /*seed*/, ROI(0,256,0,256,0,1,0,3));

// Add color Gaussian noise to an existing image
ImageBuf C ("tahoe.jpg");
ImageBufAlgo::noise (C, "gaussian", 0.0f /*mean*/, 0.1f /*stddev*/,
                     false /*mono*/, 1 /*seed*/);

// Use salt and pepper noise to make occasional random dropouts
ImageBuf D ("tahoe.jpg");
ImageBufAlgo::noise (D, "salt", 0.0f /*value*/, 0.01f /*portion*/,
                     true /*mono*/, 1 /*seed*/);

noiseimg1

noiseimg2

noiseimg3

noiseimg4

white noise

blue noise

gaussian noise added

salt & pepper dropouts

const ImageBuf &OIIO::ImageBufAlgo::bluenoise_image()

Return a const reference to a periodic bluenoise texture with float data in 4 channels that are uncorrelated to each other. Note that unlike most other ImageBufAlgo functions, it does not return an ImageBuf by value, but by const reference.

Example:

const ImageBuf& A = ImageBufAlgo::bluenoise_image();

Drawing shapes: points, lines, boxes

bool OIIO::ImageBufAlgo::render_point(ImageBuf &dst, int x, int y, cspan<float> color = 1.0f, ROI roi = {}, int nthreads = 0)

Render a single point at (x,y) of the given color “over” the existing image dst. If there is no alpha channel, the color will be written unconditionally (as if the alpha is 1.0).

Examples:

ImageBuf A (ImageSpec (640, 480, 4, TypeDesc::FLOAT));
float red[4] = { 1, 0, 0, 1 };
ImageBufAlgo::render_point (A, 50, 100, red);

bool OIIO::ImageBufAlgo::render_line(ImageBuf &dst, int x1, int y1, int x2, int y2, cspan<float> color = 1.0f, bool skip_first_point = false, ROI roi = {}, int nthreads = 0)

Render a line from pixel (x1,y1) to (x2,y2) into dst, doing an “over” of the color (if it includes an alpha channel) onto the existing data in dst. The color should include as many values as roi.chend-1. The ROI can be used to limit the pixel area or channels that are modified, and default to the entirety of dst. If skip_first_point is true, the first point (x1, y1) will not be drawn (this can be helpful when drawing poly-lines, to avoid double-rendering of the vertex positions).

Examples:

ImageBuf A (ImageSpec (640, 480, 4, TypeDesc::FLOAT));
float red[4] = { 1, 0, 0, 1 };
ImageBufAlgo::render_line (A, 10, 60, 250, 20, red);
ImageBufAlgo::render_line (A, 250, 20, 100, 190, red, true);
_images/lines.png

bool OIIO::ImageBufAlgo::render_box(ImageBuf &dst, int x1, int y1, int x2, int y2, cspan<float> color = 1.0f, bool fill = false, ROI roi = {}, int nthreads = 0)

Render a filled or unfilled box with corners at pixels (x1,y1) and (x2,y2) into dst, doing an “over” of the color (if it includes an alpha channel) onto the existing data in dst. The color must include as many values as roi.chend-1. The ROI can be used to limit the pixel area or channels that are modified, and default to the entirety of dst. If fill is true, the box will be completely filled in, otherwise only its outlien will be drawn.

Examples:

ImageBuf A (ImageSpec (640, 480, 4, TypeDesc::FLOAT));
float cyan[4] = { 0, 1, 1, 1 };
float yellow_transparent[4] = { 0.5, 0.5, 0, 0.5 };
ImageBufAlgo::render_box (A, 150, 100, 240, 180, cyan);
ImageBufAlgo::render_box (A, 100, 50, 180, 140, yellow_transparent, true);
_images/box.png

Drawing text

bool OIIO::ImageBufAlgo::render_text(ImageBuf &dst, int x, int y, string_view text, int fontsize = 16, string_view fontname = "", cspan<float> textcolor = 1.0f, TextAlignX alignx = TextAlignX::Left, TextAlignY aligny = TextAlignY::Baseline, int shadow = 0, ROI roi = {}, int nthreads = 0)

Render a text string (encoded as UTF-8) into image dst. If the dst image is not yet initialized, it will be initialized to be a black background exactly large enough to contain the rasterized text. If dst is already initialized, the text will be rendered into the existing image by essentially doing an “over” of the character into the existing pixel data.

Note that any named fonts (if not a full pathname) will search for the fonts in the following places: (a) any directories named in the global “font_searchpath” attribute or the

$OPENIMAGEIO_FONTS environment variable; (b) any font-related subdirectories (fonts, Fonts, share/fonts, or Library/Fonts) underneath the directories in environment variables $HOME, $SystemRoot, $OpenImageIO_ROOT; (c) a number of common system font areas, including /usr/share/fonts, /Library/fonts, and C:/Windows/fonts; (d) in fonts directories one level up from the place where the currently running binary lives.
Parameters

  • dst: Destination ImageBuf text is rendered into this image.

  • x/y: The position to place the text.

  • text: The text to draw. Linefeed (\n) characters are respected as indications that the text spans multiple rows.

  • fontsize/fontname: Size and name of the font. If the name is not a full pathname to a font file, it will search for a matching font, defaulting to some reasonable system font if not supplied at all), and with a nominal height of fontsize (in pixels).

  • textcolor: Color for drawing the text, defaulting to opaque white (1.0,1.0,…) in all channels if not supplied. If provided, it is expected to point to a float array of length at least equal to R.spec().nchannels, or defaults will be chosen for you).

  • alignx/aligny: The default behavior is to align the left edge of the character baseline to (x,y). Optionally, alignx and aligny can override the alignment behavior, with horizontal alignment choices of TextAlignX::Left, Right, and Center, and vertical alignment choices of Baseline, Top, Bottom, or Center.

  • shadow: If nonzero, a “drop shadow” of this radius will be used to make the text look more clear by dilating the alpha channel of the composite (makes a black halo around the characters).

Examples:

ImageBufAlgo::render_text (ImgA, 50, 100, "Hello, world");
float red[] = { 1, 0, 0, 1 };
ImageBufAlgo::render_text (ImgA, 100, 200, "Go Big Red!",
                           60, "Arial Bold", red);

float white[] = { 1, 1, 1, 1 };
ImageBufAlgo::render_text (ImgB, 320, 240, "Centered",
                           60, "Arial Bold", white,
                           TextAlignX::Center, TextAlignY::Center);

textimg1

textimg2

ROI OIIO::ImageBufAlgo::text_size(string_view text, int fontsize = 16, string_view fontname = "")

The helper function text_size() merely computes the dimensions of the text, returning it as an ROI relative to the left side of the baseline of the first character. Only the x and y dimensions of the ROI will be used. The x dimension runs from left to right, and y runs from top to bottom (image coordinates). For a failure (such as an invalid font name), the ROI will return false if you call its defined() method. The text may contain linefeed characters to designate multiple lines of text.

Examples:

// Render text centered in the image, using text_size to find out
// the size we will need and adjusting the coordinates.
ImageBuf A (ImageSpec (640, 480, 4, TypeDesc::FLOAT));
ROI Aroi = A.roi();
ROI size = ImageBufAlgo::text_size ("Centered", 48, "Courier New");
if (size.defined()) {
    int x = Aroi.xbegin + Aroi.width()/2  - (size.xbegin + size.width()/2);
    int y = Aroi.ybegin + Aroi.height()/2 - (size.ybegin + size.height()/2);
    ImageBufAlgo::render_text (A, x, y, "Centered", 48, "Courier New");
}

Image transformations and data movement

Shuffling channels

ImageBuf OIIO::ImageBufAlgo::channels(const ImageBuf &src, int nchannels, cspan<int> channelorder, cspan<float> channelvalues = {}, cspan<std::string> newchannelnames = {}, bool shuffle_channel_names = false, int nthreads = 0)

Generic channel shuffling: return (or store in dst) a copy of src, but with channels in the order channelorder[0..nchannels-1] (or set to a constant value, designated by channelorder[i] = -1 and having the fill value in channelvalues[i]. In-place operation is allowed (i.e., dst and src the same image, but an extra copy will occur).

Parameters

  • nchannels: The total number of channels that will be set up in the dst image.

  • channelorder: For each channel in dst, the index of he src channel from which to copy. Any channelorder[i] < 0 indicates that the channel i should be filled with constant value channelvalues[i] rather than copy any channel from src. If channelorder itself is empty, the implied channel order will be {0, 1, ..., nchannels-1}, meaning that it’s only renaming, truncating, or extending channels, not reordering the channels that are already present.

  • channelvalues: Fill values for color channels in which channelorder[i] < 0. This can be empty if no channels are to be filled with constant values.

  • newchannelnames: An array of new channel names. Channels for which this specifies an empty string will have their name taken from the src channel that was copied. If newchannelnames is entirely empty, all channel names will simply be copied from src.

  • shuffle_channel_names: If true, the channel names will be taken from the corresponding channels of the source image be careful with this, shuffling both channel ordering and their names could result in no semantic change at all, if you catch the drift. If false (the default), the resulting dst image will have default channel names in the usual order (“R”, “G”, etc.).

Result-as-parameter version:

bool OIIO::ImageBufAlgo::channels(ImageBuf &dst, const ImageBuf &src, int nchannels, cspan<int> channelorder, cspan<float> channelvalues = {}, cspan<std::string> newchannelnames = {}, bool shuffle_channel_names = false, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

Examples:

// Copy the first 3 channels of an RGBA, drop the alpha
ImageBuf RGBA (...);   // assume it's initialized, 4 chans
ImageBuf RGB = ImageBufAlgo::channels (RGBA, 3, {} /*default ordering*/);

// Copy just the alpha channel, making a 1-channel image
ImageBuf Alpha = ImageBufAlgo::channels (RGBA, 1, 3 /*alpha_channel*/);

// Swap the R and B channels
int channelorder[] = { 2 /*B*/, 1 /*G*/, 0 /*R*/, 3 /*A*/ };
ImageBuf BRGA = ImageBufAlgo::channels (BRGA, RGBA, 4, channelorder);

// Add an alpha channel with value 1.0 everywhere to an RGB image,
// keep the other channels with their old ordering, values, and
// names.
int channelorder[] = { 0, 1, 2, -1 /*use a float value*/ };
float channelvalues[] = { 0 /*ignore*/, 0 /*ignore*/, 0 /*ignore*/, 1.0 };
std::string channelnames[] = { "", "", "", "A" };
ImageBuf RGBA = ImageBufAlgo::channels (RGB, 4, channelorder,
                                        channelvalues, channelnames);

ImageBuf OIIO::ImageBufAlgo::channel_append(const ImageBuf &A, const ImageBuf &B, ROI roi = {}, int nthreads = 0)

Append the channels of A and B together into dst over the region of interest. If the region passed is uninitialized (the default), it will be interpreted as being the union of the pixel windows of A and B (and all channels of both images). If dst is not already initialized, it will be resized to be big enough for the region.

Result-as-parameter version:

bool OIIO::ImageBufAlgo::channel_append(ImageBuf &dst, const ImageBuf &A, const ImageBuf &B, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

Examples:

ImageBuf RGBA ("rgba.exr");
ImageBuf Z ("z.exr");
ImageBuf RGBAZ = ImageBufAlgo::channel_append (RGBA, Z);

ImageBuf OIIO::ImageBufAlgo::copy(const ImageBuf &src, TypeDesc convert = TypeUnknown, ROI roi = {}, int nthreads = 0)

Return the specified region of pixels of src as specified by roi (which will default to the whole of src, optionally with the pixel type overridden by convert (if it is not TypeUnknown).

Result-as-parameter version:

bool OIIO::ImageBufAlgo::copy(ImageBuf &dst, const ImageBuf &src, TypeDesc convert = TypeUnknown, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized). If dst is not already initialized, it will be set to the same size as roi (defaulting to all of src)

Examples:

// Set B to be a copy of A, but converted to float
ImageBuf A ("A.exr");
ImageBuf B = ImageBufAlgo::copy (A, TypeDesc::FLOAT);

ImageBuf OIIO::ImageBufAlgo::crop(const ImageBuf &src, ROI roi = {}, int nthreads = 0)

Return the specified region of src as an image, without altering its position in the image plane.

Pixels from src which are outside roi will not be copied, and new black pixels will be added for regions of roi which were outside the data window of src.

Note that the crop operation does not actually move the pixels on the image plane or adjust the full/display window; it merely restricts which pixels are copied from src to dst. (Note the difference compared to cut()).

Result-as-parameter version:

bool OIIO::ImageBufAlgo::crop(ImageBuf &dst, const ImageBuf &src, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

Examples:

// Set B to be a 200x100 region of A starting at (50,50), trimming
// the exterior away but leaving that region in its original position.
ImageBuf A ("A.exr");
ImageBuf B = ImageBufAlgo::crop (A, ROI(50,250,50,150));

ImageBuf OIIO::ImageBufAlgo::cut(const ImageBuf &src, ROI roi = {}, int nthreads = 0)

Return the designated region of src, but repositioned to the image origin and with the full/display window set to exactly cover the new pixel data window. (Note the difference compared to crop()).

Result-as-parameter version:

bool OIIO::ImageBufAlgo::cut(ImageBuf &dst, const ImageBuf &src, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

Examples:

// Set B to be a 200x100 region of A starting at (50,50), but
// moved to the upper left corner so its new origin is (0,0).
ImageBuf A ("A.exr");
ImageBuf B = ImageBufAlgo::cut (A, ROI(50,250,50,150));

bool OIIO::ImageBufAlgo::paste(ImageBuf &dst, int xbegin, int ybegin, int zbegin, int chbegin, const ImageBuf &src, ROI srcroi = {}, int nthreads = 0)

Copy src pixels within srcroi into the dst image, offset so that source location (0,0,0) will be copied to destination location (xbegin,ybegin,zbegin). If the srcroi is ROI::All(), the entirety of the data window of src will be used. It will copy into channels[chbegin...], as many channels as are described by srcroi. Pixels or channels of src inside srcroi will replace the corresponding destination pixels entirely, whereas src pixels outside of srcroi will not be copied and the corresponding offset pixels of dst will not be altered.

Examples:

// Paste fg.exr on top of bg.exr, offset by (100,100)
ImageBuf Bg ("bg.exr");
ImageBuf Fg ("fg.exr");
ImageBufAlgo::paste (Bg, 100, 100, 0, 0, fg);
group rotateN

Return (or copy into dst) a rotated copy of the image pixels of src, in 90 degree increments. Pictorially: 

 rotate90             rotate180            rotate270
-----------          -----------          -----------
AB  -->  CA          AB  -->  DC          AB  -->  BD
CD       DB          CD       BA          CD       AC

Functions

ImageBuf rotate90(const ImageBuf &src, ROI roi = {}, int nthreads = 0)
ImageBuf rotate180(const ImageBuf &src, ROI roi = {}, int nthreads = 0)
ImageBuf rotate270(const ImageBuf &src, ROI roi = {}, int nthreads = 0)
bool rotate90(ImageBuf &dst, const ImageBuf &src, ROI roi = {}, int nthreads = 0)
bool rotate180(ImageBuf &dst, const ImageBuf &src, ROI roi = {}, int nthreads = 0)
bool rotate270(ImageBuf &dst, const ImageBuf &src, ROI roi = {}, int nthreads = 0)

Examples:

ImageBuf A ("grid.jpg");
ImageBuf R90 = ImageBufAlgo::rotate90 (A);
ImageBuf R180 = ImageBufAlgo::rotate180 (A);
ImageBuf R270 = ImageBufAlgo::rotate270 (A);

rotimg1

rotimg2

rotimg3

rotimg4

original

rotated 90

rotated 180

rotated 270
group flip-flop-transpose

Return (or copy into dst) a subregion of src, but with the scanlines exchanged vertically (flip), or columns exchanged horizontally (flop), or transposed across the diagonal by swapping rows for columns (transpose) within the display/full window. In other words, 

   flip                 flop               transpose
-----------          -----------          -----------
AB  -->  CD          AB  -->  BA          AB  -->  AC
CD       AB          CD       DC          CD       BD

Functions

ImageBuf flip(const ImageBuf &src, ROI roi = {}, int nthreads = 0)
ImageBuf flop(const ImageBuf &src, ROI roi = {}, int nthreads = 0)
ImageBuf transpose(const ImageBuf &src, ROI roi = {}, int nthreads = 0)
bool flip(ImageBuf &dst, const ImageBuf &src, ROI roi = {}, int nthreads = 0)
bool flop(ImageBuf &dst, const ImageBuf &src, ROI roi = {}, int nthreads = 0)
bool transpose(ImageBuf &dst, const ImageBuf &src, ROI roi = {}, int nthreads = 0)

Examples:

ImageBuf A ("grid.jpg");
ImageBuf B;
B = ImageBufAlgo::flip (A);
B = ImageBufAlgo::flop (A);
B = ImageBufAlgo::transpose (A);

flipimg1

flipimg2

flipimg3

flipimg4

original

flip

flop

transpose
ImageBuf OIIO::ImageBufAlgo::reorient(const ImageBuf &src, int nthreads = 0)

Return (or store into dst) a copy of src, but with whatever seties of rotations, flips, or flops are necessary to transform the pixels into the configuration suggested by the “Orientation” metadata of the image (and the “Orientation” metadata is then set to 1, ordinary orientation).

Result-as-parameter version:

bool OIIO::ImageBufAlgo::reorient(ImageBuf &dst, const ImageBuf &src, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

Examples:

ImageBuf A ("tahoe.jpg");
A = ImageBufAlgo::reorient (A);

ImageBuf OIIO::ImageBufAlgo::circular_shift(const ImageBuf &src, int xshift, int yshift, int zshift = 0, ROI roi = {}, int nthreads = 0)

Return a subregion of src, but circularly shifting by the given amount. To clarify, the circular shift of [0,1,2,3,4,5] by +2 is [4,5,0,1,2,3].

Result-as-parameter version:

bool OIIO::ImageBufAlgo::circular_shift(ImageBuf &dst, const ImageBuf &src, int xshift, int yshift, int zshift = 0, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

Examples:

ImageBuf A ("grid.jpg");
ImageBuf B = ImageBufAlgo::circular_shift (A, 70, 30);

cshiftimg1

cshiftimg2

group rotate

Rotate the src image by the angle (in radians, with positive angles clockwise). When center_x and center_y are supplied, they denote the center of rotation; in their absence, the rotation will be about the center of the image’s display window.

Only the pixels (and channels) of dst that are specified by roi will be copied from the rotated src; the default roi is to alter all the pixels in dst. If dst is uninitialized, it will be resized to be an ImageBuf large enough to hold the rotated image if recompute_roi is true, or will have the same ROI as src if recompute_roi is false. It is an error to pass both an uninitialized dst and an undefined roi.

The filter is used to weight the src pixels falling underneath it for each dst pixel. The caller may specify a reconstruction filter by name and width (expressed in pixels units of the dst image), or rotate() will choose a reasonable default high-quality default filter (lanczos3) if the empty string is passed, and a reasonable filter width if filterwidth is 0. (Note that some filter choices only make sense with particular width, in which case this filterwidth parameter may be ignored.)

Functions

ImageBuf rotate(const ImageBuf &src, float angle, string_view filtername = string_view(), float filterwidth = 0.0f, bool recompute_roi = false, ROI roi = {}, int nthreads = 0)
ImageBuf rotate(const ImageBuf &src, float angle, Filter2D *filter, bool recompute_roi = false, ROI roi = {}, int nthreads = 0)
ImageBuf rotate(const ImageBuf &src, float angle, float center_x, float center_y, string_view filtername = string_view(), float filterwidth = 0.0f, bool recompute_roi = false, ROI roi = {}, int nthreads = 0)
ImageBuf rotate(const ImageBuf &src, float angle, float center_x, float center_y, Filter2D *filter, bool recompute_roi = false, ROI roi = {}, int nthreads = 0)
bool rotate(ImageBuf &dst, const ImageBuf &src, float angle, string_view filtername = string_view(), float filterwidth = 0.0f, bool recompute_roi = false, ROI roi = {}, int nthreads = 0)
bool rotate(ImageBuf &dst, const ImageBuf &src, float angle, Filter2D *filter, bool recompute_roi = false, ROI roi = {}, int nthreads = 0)
bool rotate(ImageBuf &dst, const ImageBuf &src, float angle, float center_x, float center_y, string_view filtername = string_view(), float filterwidth = 0.0f, bool recompute_roi = false, ROI roi = {}, int nthreads = 0)
bool rotate(ImageBuf &dst, const ImageBuf &src, float angle, float center_x, float center_y, Filter2D *filter, bool recompute_roi = false, ROI roi = {}, int nthreads = 0)

Examples:

ImageBuf Src ("tahoe.exr");
ImageBuf Dst = ImageBufAlgo::rotate (Src, 45.0);

rotateimg1

rotateimg2

group resize

Set dst, over the region of interest, to be a resized version of the corresponding portion of src (mapping such that the “full” image window of each correspond to each other, regardless of resolution). If dst is not yet initialized, it will be sized according to roi.

The caller may either (a) explicitly pass a reconstruction filter, or (b) specify one by filtername and filterwidth. If filter is nullptr or if filtername is the empty string resize() will choose a reasonable high-quality default (blackman-harris when upsizing, lanczos3 when downsizing). The filter is used to weight the src pixels falling underneath it for each dst pixel; the filter’s size is expressed in pixel units of the dst image.

Functions

ImageBuf resize(const ImageBuf &src, string_view filtername = "", float filterwidth = 0.0f, ROI roi = {}, int nthreads = 0)
ImageBuf resize(const ImageBuf &src, Filter2D *filter, ROI roi = {}, int nthreads = 0)
bool resize(ImageBuf &dst, const ImageBuf &src, string_view filtername = "", float filterwidth = 0.0f, ROI roi = {}, int nthreads = 0)
bool resize(ImageBuf &dst, const ImageBuf &src, Filter2D *filter, ROI roi = {}, int nthreads = 0)

Examples:

Examples:

// Resize the image to 640x480, using the default filter
ImageBuf Src ("tahoe.exr");
ROI roi (0, 640, 0, 480, 0, 1, /*chans:*/ 0, Src.nchannels());
ImageBuf Dst = ImageBufAlgo::resize (Src, "", 0, roi);

ImageBuf OIIO::ImageBufAlgo::resample(const ImageBuf &src, bool interpolate = true, ROI roi = {}, int nthreads = 0)

Set dst, over the region of interest, to be a resized version of the corresponding portion of src (mapping such that the “full” image window of each correspond to each other, regardless of resolution). If dst is not yet initialized, it will be sized according to roi.

Unlike ImageBufAlgo::resize(), resample() does not take a filter; it just samples either with a bilinear interpolation (if interpolate is true, the default) or uses the single “closest” pixel (if interpolate is false). This makes it a lot faster than a proper resize(), though obviously with lower quality (aliasing when downsizing, pixel replication when upsizing).

For “deep” images, this function returns copies the closest source pixel needed, rather than attempting to interpolate deep pixels (regardless of the value of interpolate).

Result-as-parameter version:

bool OIIO::ImageBufAlgo::resample(ImageBuf &dst, const ImageBuf &src, bool interpolate = true, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

Examples:

// Resample quickly to 320x240, with default interpolation
ImageBuf Src ("tahoe.exr");
ROI roi (0, 320, 0, 240, 0, 1, /*chans:*/ 0, Src.nchannels());
ImageBuf Dst = ImageBufAlgo::resiresampleze (Src, true, roi);

group fit

Fit src into dst (to a size specified by roi, if dst is not initialized), resizing but preserving its original aspect ratio. Thus, it will resize to be the largest size with the same aspect ratio that can fit inside the region, but will not stretch to completely fill it in both dimensions.

The fillmode determines which of several methods will be used to determine how the image will fill the new frame, if its aspect ratio does not precisely match the original source aspect ratio:

  • ”width” exactly fills the width of the new frame, either cropping or letterboxing the height if it isn’t precisely the right size to preserve the original aspect ratio.

  • ”height” exactly fills the height of the new frame, either cropping or letterboxing the width if it isn’t precisely the right size to preserve the original aspect ratio.

  • ”letterbox” (the default) chooses whichever of “width” or “height” will maximally fill the new frame with no image data lost (it will only letterbox, never crop).

If exact is true, will result in an exact match on aspect ratio and centering (partial pixel shift if necessary), whereas exact=false will only preserve aspect ratio and centering to the precision of a whole pixel.

The filter is used to weight the src pixels falling underneath it for each dst pixel. The caller may specify a reconstruction filter by name and width (expressed in pixels units of the dst image), or rotate() will choose a reasonable default high-quality default filter (lanczos3) if the empty string is passed, and a reasonable filter width if filterwidth is 0. (Note that some filter choices only make sense with particular width, in which case this filterwidth parameter may be ignored.)

Functions

ImageBuf fit(const ImageBuf &src, string_view filtername = "", float filterwidth = 0.0f, string_view fillmode = "letterbox", bool exact = false, ROI roi = {}, int nthreads = 0)
ImageBuf fit(const ImageBuf &src, Filter2D *filter, string_view fillmode = "letterbox", bool exact = false, ROI roi = {}, int nthreads = 0)
bool fit(ImageBuf &dst, const ImageBuf &src, string_view filtername = "", float filterwidth = 0.0f, string_view fillmode = "letterbox", bool exact = false, ROI roi = {}, int nthreads = 0)
bool fit(ImageBuf &dst, const ImageBuf &src, Filter2D *filter, string_view fillmode = "letterbox", bool exact = false, ROI roi = {}, int nthreads = 0)

Examples:

// Resize to fit into a max of 640x480, preserving the aspect ratio
ImageBuf Src ("tahoe.exr");
ROI roi (0, 640, 0, 480, 0, 1, /*chans:*/ 0, Src.nchannels());
ImageBuf Dst = ImageBufAlgo::fit (Src, "", 0, true, roi);

group warp

Warp the src image using the supplied 3x3 transformation matrix.

Only the pixels (and channels) of dst that are specified by roi will be copied from the warped src; the default roi is to alter all the pixels in dst. If dst is uninitialized, it will be sized to be an ImageBuf large enough to hold the warped image if recompute_roi is true, or will have the same ROI as src if recompute_roi is false. It is an error to pass both an uninitialized dst and an undefined roi.

The caller may explicitly pass a reconstruction filter, or specify one by name and size, or if the name is the empty string resize() will choose a reasonable high-quality default if nullptr is passed. The filter is used to weight the src pixels falling underneath it for each dst pixel; the filter’s size is expressed in pixel units of the dst image.

Functions

ImageBuf warp(const ImageBuf &src, const Imath::M33f &M, string_view filtername = string_view(), float filterwidth = 0.0f, bool recompute_roi = false, ImageBuf::WrapMode wrap = ImageBuf::WrapDefault, ROI roi = {}, int nthreads = 0)
ImageBuf warp(const ImageBuf &src, const Imath::M33f &M, const Filter2D *filter, bool recompute_roi = false, ImageBuf::WrapMode wrap = ImageBuf::WrapDefault, ROI roi = {}, int nthreads = 0)
bool warp(ImageBuf &dst, const ImageBuf &src, const Imath::M33f &M, string_view filtername = string_view(), float filterwidth = 0.0f, bool recompute_roi = false, ImageBuf::WrapMode wrap = ImageBuf::WrapDefault, ROI roi = {}, int nthreads = 0)
bool warp(ImageBuf &dst, const ImageBuf &src, const Imath::M33f &M, const Filter2D *filter, bool recompute_roi = false, ImageBuf::WrapMode wrap = ImageBuf::WrapDefault, ROI roi = {}, int nthreads = 0)

Examples:

Imath::M33f M ( 0.7071068, 0.7071068, 0,
               -0.7071068, 0.7071068, 0,
               20,        -8.284271,  1);
ImageBuf Src ("tahoe.exr");
ImageBuf Dst = ImageBufAlgo::warp (dst, src, M, "lanczos3");

Image arithmetic

ImageBuf OIIO::ImageBufAlgo::add(Image_or_Const A, Image_or_Const B, ROI roi = {}, int nthreads = 0)

Compute per-pixel sum A + B, returning the result image.

A and B may each either be an ImageBuf&, or a cspan<float> giving a per- channel constant, or a single constant used for all channels. (But at least one must be an image.)

Result-as-parameter version:

bool OIIO::ImageBufAlgo::add(ImageBuf &dst, Image_or_Const A, Image_or_Const B, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

Examples:

// Add images A and B
ImageBuf A ("a.exr");
ImageBuf B ("b.exr");
ImageBuf Sum = ImageBufAlgo::add (A, B);

// Add 0.2 to channels 0-2, but not to channel 3
ImageBuf Sum = ImageBufAlgo::add (A, { 0.2f, 0.2f, 0.2f, 0.0f });

ImageBuf OIIO::ImageBufAlgo::sub(Image_or_Const A, Image_or_Const B, ROI roi = {}, int nthreads = 0)

Compute per-pixel signed difference A - B, returning the result image.

A and B may each either be an ImageBuf&, or a cspan<float> giving a per-channel constant, or a single constant used for all channels. (But at least one must be an image.)

Result-as-parameter version:

bool OIIO::ImageBufAlgo::sub(ImageBuf &dst, Image_or_Const A, Image_or_Const B, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

Examples:

ImageBuf A ("a.exr");
ImageBuf B ("b.exr");
ImageBuf Diff = ImageBufAlgo::sub (A, B);

ImageBuf OIIO::ImageBufAlgo::absdiff(Image_or_Const A, Image_or_Const B, ROI roi = {}, int nthreads = 0)

Compute per-pixel absolute difference abs(A - B), returning the result image.

A and B may each either be an ImageBuf&, or a cspan<float> giving a per- channel constant, or a single constant used for all channels. (But at least one must be an image.)

Result-as-parameter version:

bool OIIO::ImageBufAlgo::absdiff(ImageBuf &dst, Image_or_Const A, Image_or_Const B, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

Examples:

ImageBuf A ("a.exr");
ImageBuf B ("b.exr");
ImageBuf Diff = ImageBufAlgo::absdiff (A, B);

ImageBuf OIIO::ImageBufAlgo::abs(const ImageBuf &A, ROI roi = {}, int nthreads = 0)

Compute per-pixel absolute value abs(A), returning the result image.

Result-as-parameter version:

bool OIIO::ImageBufAlgo::abs(ImageBuf &dst, const ImageBuf &A, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

Examples:

ImageBuf A ("a.exr");
ImageBuf Abs = ImageBufAlgo::abs (A);

ImageBuf OIIO::ImageBufAlgo::mul(Image_or_Const A, Image_or_Const B, ROI roi = {}, int nthreads = 0)

Compute per-pixel product A * B, returning the result image.

Either both A and B are images, or one is an image and the other is a cspan<float> giving a per-channel constant or a single constant used for all channels.

Result-as-parameter version:

bool OIIO::ImageBufAlgo::mul(ImageBuf &dst, Image_or_Const A, Image_or_Const B, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

Examples:

// Pixel-by-pixel, channel-by-channel multiplication of A and B
ImageBuf A ("a.exr");
ImageBuf B ("b.exr");
ImageBuf Product = ImageBufAlgo::mul (A, B);

// In-place reduce intensity of A's channels 0-2 by 50%
ImageBufAlgo::mul (A, A, { 0.5f, 0.5f, 0.5f, 1.0f });

ImageBuf OIIO::ImageBufAlgo::div(Image_or_Const A, Image_or_Const B, ROI roi = {}, int nthreads = 0)

Compute per-pixel division A / B, returning the result image. Division by zero is defined to result in zero.

A is always an image, and B is either an image or a cspan<float> giving a per-channel constant or a single constant used for all channels.

Result-as-parameter version:

bool OIIO::ImageBufAlgo::div(ImageBuf &dst, Image_or_Const A, Image_or_Const B, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

Examples:

// Pixel-by-pixel, channel-by-channel division of A by B
ImageBuf A ("a.exr");
ImageBuf B ("b.exr");
ImageBuf Ratio = ImageBufAlgo::div (A, B);

// In-place reduce intensity of A's channels 0-2 by 50%
ImageBufAlgo::div (A, A, { 2.0f, 2.0f, 2.0f, 1.0f });

ImageBuf OIIO::ImageBufAlgo::mad(Image_or_Const A, Image_or_Const B, Image_or_Const C, ROI roi = {}, int nthreads = 0)

Compute per-pixel multiply-and-add A * B + C, returning the result image.

A, B, and C are each either an image, or a cspan<float> giving a per-channel constant or a single constant used for all channels. (Note: at least one must be an image.)

Result-as-parameter version:

bool OIIO::ImageBufAlgo::mad(ImageBuf &dst, Image_or_Const A, Image_or_Const B, Image_or_Const C, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

Examples:

// Pixel-by-pixel, channel-by-channel A * B + C
ImageBuf A ("a.exr");
ImageBuf B ("b.exr");
ImageBuf C ("c.exr");
ImageBuf Result = ImageBufAlgo::mad (A, B, C);

// Compute the "inverse" A, which is 1.0-A, as A*(-1) + 1
// Do this in-place, and only for the first 3 channels (leave any
// alpha channel, if present, as it is).
ImageBuf Ainv = ImageBufAlgo::mad (A, { -1.0, -1.0, -1.0, 1.0 },
                                      { 1.0, 1.0, 1.0, 0.0 });

ImageBuf OIIO::ImageBufAlgo::over(const ImageBuf &A, const ImageBuf &B, ROI roi = {}, int nthreads = 0)

Return the composite of A over B using the Porter/Duff definition of “over”, returning true upon success and false for any of a variety of failures (as described below).

A and B (and dst, if already defined/allocated) must have valid alpha channels identified by their ImageSpec alpha_channel field. If A or B do not have alpha channels (as determined by those rules) or if the number of non-alpha channels do not match between A and B, over() will fail, returning false.

If dst is not already an initialized ImageBuf, it will be sized to encompass the minimal rectangular pixel region containing the union of the defined pixels of A and B, and with a number of channels equal to the number of non-alpha channels of A and B, plus an alpha channel. However, if dst is already initialized, it will not be resized, and the “over” operation will apply to its existing pixel data window. In this case, dst must have an alpha channel designated and must have the same number of non-alpha channels as A and B, otherwise it will fail, returning false.

A, B, and dst need not perfectly overlap in their pixel data windows; pixel values of A or B that are outside their respective pixel data window will be treated as having “zero” (0,0,0…) value.

Result-as-parameter version:

bool OIIO::ImageBufAlgo::over(ImageBuf &dst, const ImageBuf &A, const ImageBuf &B, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

Examples:

ImageBuf A ("a.exr");
ImageBuf B ("b.exr");
ImageBuf Composite = ImageBufAlgo::over (A, B);

ImageBuf OIIO::ImageBufAlgo::zover(const ImageBuf &A, const ImageBuf &B, bool z_zeroisinf = false, ROI roi = {}, int nthreads = 0)

Just like ImageBufAlgo::over(), but inputs A and B must have designated ‘z’ channels, and on a pixel-by-pixel basis, the z values will determine which of A or B will be considered the foreground or background (lower z is foreground). If z_zeroisinf is true, then z=0 values will be treated as if they are infinitely far away.

Result-as-parameter version:

bool OIIO::ImageBufAlgo::zover(ImageBuf &dst, const ImageBuf &A, const ImageBuf &B, bool z_zeroisinf = false, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

Examples:

ImageBuf A ("a.exr");
ImageBuf B ("b.exr");
ImageBuf Composite = ImageBufAlgo::zover (A, B);

ImageBuf OIIO::ImageBufAlgo::invert(const ImageBuf &A, ROI roi = {}, int nthreads = 0)

Compute per-pixel value inverse 1.0 - A (which you can think of as roughly meaning switching white and black), returning the result image.

Tips for callers: (1) You probably want to set roi to restrict the operation to only the color channels, and not accidentally include alpha, z, or others. (2) There may be situations where you want to unpremult() before the invert, then premult() the result, so that you are computing the inverse of the unmasked color.

Result-as-parameter version:

bool OIIO::ImageBufAlgo::invert(ImageBuf &dst, const ImageBuf &A, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

Examples:

// Invert all channels of A
ImageBuf A ("a.exr");
ImageBuf Inverse = ImageBufAlgo::invert (Inverse, A);

// In this example, we are careful to deal with alpha in an RGBA image.
// First we copy A to Inverse, un-premultiply the color values by alpha,
// invert just the color channels in-place, and then re-premultiply the
// colors by alpha.
roi = A.roi();
roi.chend = 3;      // Restrict roi to only R,G,B
ImageBuf Inverse = ImageBufAlgo::unpremult (A);
ImageBufAlgo::invert (Inverse, Inverse, roi);
ImageBufAlgo::repremult (Inverse, Inverse);
_images/tahoe-small.jpg _images/invert.jpg


ImageBuf OIIO::ImageBufAlgo::pow(const ImageBuf &A, cspan<float> B, ROI roi = {}, int nthreads = 0)

Compute per-pixel raise-to-power A ^ B. returning the result image. It is permitted for dst and A to be the same image.

A is always an image, and B is either an image or a cspan<float> giving a per-channel constant or a single constant used for all channels.

Result-as-parameter version:

bool OIIO::ImageBufAlgo::pow(ImageBuf &dst, const ImageBuf &A, cspan<float> B, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

Examples:

// Gamma-correct by 2.2 channels 0-2 of the image, in-place
ImageBuf A ("a.exr");
const float g = 1.0f / 2.2f;
ImageBufAlgo::pow (A, A, { g, g, g, 1.0f });

ImageBuf OIIO::ImageBufAlgo::channel_sum(const ImageBuf &src, cspan<float> weights = 1.0f, ROI roi = {}, int nthreads = 0)

Converts a multi-channel image into a one-channel image via a weighted sum of channels: 

(channel[0]*weight[0] + channel[1]*weight[1] + ...)

returning the resulting one-channel image. The weights, if not supplied, default to { 1, 1, 1, ... }).

Result-as-parameter version:

bool OIIO::ImageBufAlgo::channel_sum(ImageBuf &dst, const ImageBuf &src, cspan<float> weights = 1.0f, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

Examples:

Compute luminance via a weighted sum of R,G,B (assuming Rec709 primaries and a linear scale):

// Compute luminance via a weighted sum of R,G,B
// (assuming Rec709 primaries and a linear scale)
float luma_weights[3] = { .2126, .7152, .0722, 0.0 };
ImageBuf A ("a.exr");
ImageBuf lum = ImageBufAlgo::channel_sum (A, luma_weights);

Max, min, clamp

group maxminclamp

max() and min() take the pixel-by-pixel, channel-by-channel maximum and minimum of two images, or of an image and a constant.

clamp() restricts values of an image to the range between per-channel minimum and maximum constant values.

Functions

ImageBuf max(Image_or_Const A, Image_or_Const B, ROI roi = {}, int nthreads = 0)

Compute per-pixel max(A, B), returning the result image.

Either both A and B are images, or one is an image and the other is a cspan<float> giving a per-channel constant or a single constant used for all channels.

bool max(ImageBuf &dst, Image_or_Const A, Image_or_Const B, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

ImageBuf min(Image_or_Const A, Image_or_Const B, ROI roi = {}, int nthreads = 0)

Compute per-pixel min(A, B), returning the result image.

Either both A and B are images, or one is an image and the other is a cspan<float> giving a per-channel constant or a single constant used for all channels.

bool min(ImageBuf &dst, Image_or_Const A, Image_or_Const B, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

ImageBuf clamp(const ImageBuf &src, cspan<float> min = -std::numeric_limits<float>::max(), cspan<float> max = std::numeric_limits<float>::max(), bool clampalpha01 = false, ROI roi = {}, int nthreads = 0)

Return pixels of src with pixel values clamped as follows:

Parameters

  • min: The minimum clamp value for each channel. If min is empty, no minimum clamping is performed.

  • max: The maximum clamp value for each channel. If max is empty, no maximum clamping is performed.

  • clampalpha01: If true, then additionally any alpha channel is clamped to the 0-1 range.

bool clamp(ImageBuf &dst, const ImageBuf &src, cspan<float> min = -std::numeric_limits<float>::max(), cspan<float> max = std::numeric_limits<float>::max(), bool clampalpha01 = false, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

Examples:

// min of images A and B, assign to MinImage
ImageBuf A ("a.exr");
ImageBuf B ("b.exr");
ImageBuf MinImage = ImageBufAlgo::min (Sum, A, B);

// Squash negative values in A by taking max(A, 0.0) for all channels
ImageBuf A ("a.exr");
ImageBufAlgo::max (A, A, 0.0f);

// Clamp image buffer A in-place to the [0,1] range for all pixels.
ImageBufAlgo::clamp (A, A, 0.0f, 1.0f);

// Just clamp alpha to [0,1] in-place
ImageBufAlgo::clamp (A, A, -std::numeric_limits<float>::max(),
                     std::numeric_limits<float>::max(), true);

// Clamp R & G to [0,0.5], leave other channels alone
std::vector<float> min (A.nchannels(), -std::numeric_limits<float>::max());
std::vector<float> max (A.nchannels(), std::numeric_limits<float>::max());
min[0] = 0.0f;  max[0] = 0.5f;
min[1] = 0.0f;  max[1] = 0.5f;
ImageBufAlgo::clamp (A, A, &min[0], &max[0], false);

group maxminchan

maxchan() computes a one-channel image that for each pixel, contains the maximum value of all channels of corresponding pixel of the source image. minchan() similarly computes the minimum value of all channels.

Version

2.3.10

Functions

ImageBuf maxchan(const ImageBuf &A, ROI roi = {}, int nthreads = 0)
bool maxchan(ImageBuf &dst, const ImageBuf &A, ROI roi = {}, int nthreads = 0)
ImageBuf minchan(const ImageBuf &src, ROI roi = {}, int nthreads = 0)
bool minchan(ImageBuf &dst, const ImageBuf &src, ROI roi = {}, int nthreads = 0)

Examples:

// Computes the maximum of R, G, B.
ImageBuf A ("rgb.exr");
ImageBuf B = ImageBufAlgo::maxchan (A);

ImageBuf OIIO::ImageBufAlgo::contrast_remap(const ImageBuf &src, cspan<float> black = 0.0f, cspan<float> white = 1.0f, cspan<float> min = 0.0f, cspan<float> max = 1.0f, cspan<float> scontrast = 1.0f, cspan<float> sthresh = 0.5f, ROI = {}, int nthreads = 0)

Return pixel values that are a contrast-remap of the corresponding values of the src image, transforming pixel value domain [black, white] to range [min, max], either linearly or with optional application of a smooth sigmoidal remapping (if scontrast != 1.0).

The following steps are performed, in order:

  1. Linearly rescale values [black, white] to [0, 1].

  2. If scontrast != 1, apply a sigmoidal remapping where a larger scontrast value makes a steeper slope, and the steepest part is at value sthresh (relative to the new remapped value after steps 1 & 2; the default is 0.5).

  3. Rescale the range of that result: 0.0 -> min and 1.0 -> max.

Values outside of the [black,white] range will be extrapolated to outside [min,max], so it may be prudent to apply a clamp() to the results.

The black, white, min, max, scontrast, sthresh parameters may each either be a single float value for all channels, or a span giving per-channel values.

You can use this function for a simple linear contrast remapping of [black, white] to [min, max] if you use the default values for sthresh. Or just a simple sigmoidal contrast stretch within the [0,1] range if you leave all other parameters at their defaults, or a combination of these effects. Note that if black == white, the result will be a simple binary thresholding where values < black map to min and values >= black map to max.

Result-as-parameter version:

bool OIIO::ImageBufAlgo::contrast_remap(ImageBuf &dst, const ImageBuf &src, cspan<float> black = 0.0f, cspan<float> white = 1.0f, cspan<float> min = 0.0f, cspan<float> max = 1.0f, cspan<float> scontrast = 1.0f, cspan<float> sthresh = 0.5f, ROI = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

Examples:

ImageBuf A ("tahoe.tif");

// Simple linear remap that stretches input 0.1 to black, and input
// 0.75 to white.
ImageBuf linstretch = ImageBufAlgo::contrast_remap (A, 0.1f, 0.75f);

// Remapping 0->1 and 1->0 inverts the colors of the image,
// equivalent to ImageBufAlgo::invert().
ImageBuf inverse = ImageBufAlgo::contrast_remap (A, 1.0f, 0.0f);

// Use a sigmoid curve to add contrast but without any hard cutoffs.
// Use a contrast parameter of 5.0.
ImageBuf sigmoid = ImageBufAlgo::contrast_remap (A, 0.0f, 1.0f,
                                                 0.0f, 1.0f, 5.0f);

crimage1

crimage2

crimage3

crimage4

original

linstretch

inverse

sigmoid

group saturate

Increase or decrease color saturation of the image.

The saturate operation returns (or copies into dst) the pixels of src within the ROI, and in the process adjusts the color saturation of the three consecutive channels starting with firstchannel based on the scale parameter: 0.0 fully desaturates to a greyscale image of percaptually equivalent luminance, 1.0 leaves the colors unchanged, scale values inside this range interpolate between them, and scale > 1 would increase apparent color saturation.

Channels that are within the range of roi.chbegin to roi.chend-1, but outside the range of firstchannel to firstchannel+2 are simply copied unaltered. Only three channels at a time can be desaturated, by default the first three channels, though firstchannel may be used to specify a different subset of channels. It is allowed for src and dst to be the same image.

Version

2.4+

Functions

ImageBuf saturate(const ImageBuf &src, float scale = 0.0f, int firstchannel = 0, ROI roi = {}, int nthreads = 0)
bool saturate(ImageBuf &dst, const ImageBuf &src, float scale = 0.0f, int firstchannel = 0, ROI roi = {}, int nthreads = 0)

Examples:

ImageBuf img("tahoe.exr");
ImageBuf grey = ImageBufAlgo::saturate (img, 0.0f);
ImageBuf colorful = ImageBufAlgo::saturate (img, 2.0f);

sat1

sat0

sat2

original

sat scale = 0

sat scale = 2

group color_map

Remap value range by spline or name

Return (or copy into dst) pixel values determined by looking up a color map using values of the source image, using either the channel specified by srcchannel, or the luminance of src’s RGB if srcchannel is -1. This happens for all pixels within the ROI (which defaults to all of src), and if dst is not already initialized, it will be initialized to the ROI and with color channels equal to channels.

In the variant that takes a knots parameter, this specifies the values of a linearly-interpolated color map given by knots[nknots*channels]. An input value of 0.0 is mapped to knots[0..channels-1] (one value for each color channel), and an input value of 1.0 is mapped to knots[(nknots-1)*channels..knots.size()-1].

In the variant that takes a mapname parameter, this is the name of a color map. Recognized map names include: “inferno”, “viridis”, “magma”, “plasma”, all of which are perceptually uniform, strictly increasing in luminance, look good when converted to grayscale, and work for people with all types of colorblindness. Also “turbo” has most of these properties (except for being strictly increasing in luminance) and is a nice rainbow-like pattern. Also supported are the following color maps that do not have those desirable qualities (and are thus not recommended, but are present for back-compatibility or for use by clueless people): “blue-red”, “spectrum”, and “heat”. In all cases, the implied channels is 3.

Functions

ImageBuf color_map(const ImageBuf &src, int srcchannel, int nknots, int channels, cspan<float> knots, ROI roi = {}, int nthreads = 0)
ImageBuf color_map(const ImageBuf &src, int srcchannel, string_view mapname, ROI roi = {}, int nthreads = 0)
bool color_map(ImageBuf &dst, const ImageBuf &src, int srcchannel, int nknots, int channels, cspan<float> knots, ROI roi = {}, int nthreads = 0)
bool color_map(ImageBuf &dst, const ImageBuf &src, int srcchannel, string_view mapname, ROI roi = {}, int nthreads = 0)

Examples:

// Use luminance of a.exr (assuming Rec709 primaries and a linear
// scale) and map to a spectrum-like palette:
ImageBuf A ("a.exr");
ImageBuf B = ImageBufAlgo::color_map (A, -1, "turbo");

// Use a custom color map
float mymap[] = { 0.25, 0.25, 0.25,  0, 0.5, 0,  1, 0, 0 };
B = ImageBufAlgo::color_map (A, -1 /* use luminance */,
                             3 /* num knots */, 3 /* channels */,
                             mymap);

cmimage1

cmimage2

cmimage3

cmimage4

cmimage5

original

inferno

viridis

turbo

custom values
group range

Nonlinear range remapping for contrast preservation

rangecompress() returns (or copy into dst) all pixels and color channels of src within region roi (defaulting to all the defined pixels of dst), rescaling their range with a logarithmic transformation. Alpha and z channels are not transformed.

rangeexpand() performs the inverse transformation (logarithmic back into linear).

If useluma is true, the luma of channels [roi.chbegin..roi.chbegin+2] (presumed to be R, G, and B) are used to compute a single scale factor for all color channels, rather than scaling all channels individually (which could result in a color shift).

The purpose of these function is as follows: Some image operations (such as resizing with a “good” filter that contains negative lobes) can have objectionable artifacts when applied to images with very high-contrast regions involving extra bright pixels (such as highlights in HDR captured or rendered images). By compressing the range pixel values, then performing the operation, then expanding the range of the result again, the result can be much more pleasing (even if not exactly correct).

Functions

ImageBuf rangecompress(const ImageBuf &src, bool useluma = false, ROI roi = {}, int nthreads = 0)
ImageBuf rangeexpand(const ImageBuf &src, bool useluma = false, ROI roi = {}, int nthreads = 0)
bool rangecompress(ImageBuf &dst, const ImageBuf &src, bool useluma = false, ROI roi = {}, int nthreads = 0)
bool rangeexpand(ImageBuf &dst, const ImageBuf &src, bool useluma = false, ROI roi = {}, int nthreads = 0)

Examples:

In this example, we resize the image to 640x480, using a Lanczos3 filter, which has negative lobes. To prevent those negative lobes from producing ringing or negative pixel values for HDR data, do range compression, then resize, then re-expand the range.

// 1. Read the original image
ImageBuf Src ("tahoeHDR.exr");

// 2. Range compress to a logarithmic scale
ImageBuf Compressed = ImageBufAlgo::rangecompress (Src);

// 3. Now do the resize
ImageBuf Dst = ImageBufAlgo::resize (Compressed, "lanczos3", 6.0f,
                                     ROI(0, 640, 0, 480));

// 4. Expand range to be linear again (operate in-place)
ImageBufAlgo::rangeexpand (Dst, Dst);

Image comparison and statistics

PixelStats OIIO::ImageBufAlgo::computePixelStats(const ImageBuf &src, ROI roi = {}, int nthreads = 0)

Compute statistics about the ROI of the src image, returning a PixelStats structure. Upon success, the returned vectors in the result structure will have size == src.nchannels(). If there is a failure, the vector sizes will be 0 and an error will be set in src.

The PixelStats structure is defined as follows in C++:

struct PixelStats {
    std::vector<float> min;
    std::vector<float> max;
    std::vector<float> avg;
    std::vector<float> stddev;
    std::vector<imagesize_t> nancount;
    std::vector<imagesize_t> infcount;
    std::vector<imagesize_t> finitecount;
};

Examples:

ImageBuf A ("a.exr");
auto stats = ImageBufAlgo::computePixelStats(A);
if (stats.min.size() == 0)
    return; // empty vectors means we could not get the stats
for (int c = 0;  c < A.nchannels();  ++c) {
    std::cout << "Channel " << c << ":\n";
    std::cout << "   min = " << stats.min[c] << "\n";
    std::cout << "   max = " << stats.max[c] << "\n";
    std::cout << "   average = " << stats.avg[c] << "\n";
    std::cout << "   standard deviation  = " << stats.stddev[c] << "\n";
    std::cout << "   # NaN values    = " << stats.nancount[c] << "\n";
    std::cout << "   # Inf values    = " << stats.infcount[c] << "\n";
    std::cout << "   # finite values = " << stats.finitecount[c] << "\n";
}

CompareResults OIIO::ImageBufAlgo::compare(const ImageBuf &A, const ImageBuf &B, float failthresh, float warnthresh, ROI roi = {}, int nthreads = 0)

Numerically compare two images. The difference threshold (for any individual color channel in any pixel) for a “failure” is failthresh, and for a “warning” is warnthresh. The results are stored in result. If roi is defined, pixels will be compared for the pixel and channel range that is specified. If roi is not defined, the comparison will be for all channels, on the union of the defined pixel windows of the two images (for either image, undefined pixels will be assumed to be black).

The CompareResults structure is defined in C++ as follows:

struct CompareResults {
    double meanerror, rms_error, PSNR, maxerror;
    int maxx, maxy, maxz, maxc;
    imagesize_t nwarn, nfail;
    bool error;
};

Examples:

ImageBuf A ("a.exr");
ImageBuf B ("b.exr");
auto comp = ImageBufAlgo::compare(A, B, 1.0f/255.0f, 0.0f);
if (comp.nwarn == 0 && comp.nfail == 0) {
    std::cout << "Images match within tolerance\n";
} else {
    std::cout << "Image differed: " << comp.nfail << " failures, "
              << comp.nwarn << " warnings.\n";
    std::cout << "Average error was " << comp.meanerror << "\n";
    std::cout << "RMS error was " << comp.rms_error << "\n";
    std::cout << "PSNR was " << comp.PSNR << "\n";
    std::cout << "largest error was " << comp.maxerror
              << " on pixel (" << comp.maxx << "," << comp.maxy
              << "," << comp.maxz << "), channel " << comp.maxc << "\n";
}

int OIIO::ImageBufAlgo::compare_Yee(const ImageBuf &A, const ImageBuf &B, CompareResults &result, float luminance = 100, float fov = 45, ROI roi = {}, int nthreads = 0)

Compare two images using Hector Yee’s perceptual metric, returning the number of pixels that fail the comparison. Only the first three channels (or first three channels specified by roi) are compared. Free parameters are the ambient luminance in the room and the field of view of the image display; our defaults are probably reasonable guesses for an office environment. The ‘result’ structure will store the maxerror, and the maxx, maxy, maxz of the pixel that failed most severely. (The other fields of the CompareResults are not used for Yee comparison.)

Works for all pixel types. But it’s basically meaningless if the first three channels aren’t RGB in a linear color space that sort of resembles AdobeRGB.

Return true on success, false on error.


bool OIIO::ImageBufAlgo::isConstantColor(const ImageBuf &src, float threshold = 0.0f, span<float> color = {}, ROI roi = {}, int nthreads = 0)

Do all pixels within the ROI have the same values for channels [roi.chbegin..roi.chend-1], within a tolerance of +/- threshold? If so, return true and store that color in color[chbegin...chend-1] (if color is not empty); otherwise return false. If roi is not defined (the default), it will be understood to be all of the defined pixels and channels of source.

Examples:

ImageBuf A ("a.exr");
std::vector<float> color (A.nchannels());
if (ImageBufAlgo::isConstantColor (A, color)) {
    std::cout << "The image has the same value in all pixels: ";
    for (int c = 0;  c < A.nchannels();  ++c)
        std::cout << (c ? " " : "") << color[c];
    std::cout << "\n";
} else {
    std::cout << "The image is not a solid color.\n";
}

bool OIIO::ImageBufAlgo::isConstantChannel(const ImageBuf &src, int channel, float val, float threshold = 0.0f, ROI roi = {}, int nthreads = 0)

Does the requested channel have a given value (within a tolerance of +/- threshold) for every channel within the ROI? (For this function, the ROI’s chbegin/chend are ignored.) Return true if so, otherwise return false. If roi is not defined (the default), it will be understood to be all of the defined pixels and channels of source.

Examples:

ImageBuf A ("a.exr");
int alpha = A.spec().alpha_channel;
if (alpha < 0)
    std::cout << "The image does not have an alpha channel\n";
else if (ImageBufAlgo::isConstantChannel (A, alpha, 1.0f))
    std::cout << "The image has alpha = 1.0 everywhere\n";
else
    std::cout << "The image has alpha != 1 in at least one pixel\n";

bool OIIO::ImageBufAlgo::isMonochrome(const ImageBuf &src, float threshold = 0.0f, ROI roi = {}, int nthreads = 0)

Is the image monochrome within the ROI, i.e., for every pixel within the region, do all channels [roi.chbegin, roi.chend) have the same value (within a tolerance of +/- threshold)? If roi is not defined (the default), it will be understood to be all of the defined pixels and channels of source.

Examples:

ImageBuf A ("a.exr");
ROI roi = get_roi (A.spec());
roi.chend = std::min (3, roi.chend);  // only test RGB, not alpha
if (ImageBufAlgo::isMonochrome (A, roi))
    std::cout << "a.exr is really grayscale\n";

bool OIIO::ImageBufAlgo::color_count(const ImageBuf &src, imagesize_t *count, int ncolors, cspan<float> color, cspan<float> eps = 0.001f, ROI roi = {}, int nthreads = 0)

Count how many pixels in the ROI match a list of colors. The colors to match are in: 

colors[0 ... nchans-1]
colors[nchans ... 2*nchans-1]
...
colors[(ncolors-1)*nchans ... (ncolors*nchans)-1]

and so on, a total of ncolors consecutively stored colors of nchans channels each (nchans is the number of channels in the image, itself, it is not passed as a parameter).

eps[0..nchans-1] are the error tolerances for a match, for each channel. Setting eps[c] = numeric_limits<float>max() will effectively make it ignore the channel. The default eps is 0.001 for all channels (this value is chosen because it requires exact matches for 8 bit images, but allows a wee bit of imprecision for float images.

Upon success, return true and store the number of pixels that matched each color count[0..ncolors-1]. If there is an error, returns false and sets an appropriate error message set in src.

Examples:

ImageBuf A ("a.exr");
int n = A.nchannels();

// Try to match two colors: pure red and green
std::vector<float> colors (2*n, numeric_limits<float>::max());
colors[0] = 1.0f; colors[1] = 0.0f; colors[2] = 0.0f;
colors[n+0] = 0.0f; colors[n+1] = 1.0f; colors[n+2] = 0.0f;

const int ncolors = 2;
imagesize_t count[ncolors];
ImageBufAlgo::color_count (A, count, ncolors);
std::cout << "Number of red pixels   : " << count[0] << "\n";
std::cout << "Number of green pixels : " << count[1] << "\n";

bool OIIO::ImageBufAlgo::color_range_check(const ImageBuf &src, imagesize_t *lowcount, imagesize_t *highcount, imagesize_t *inrangecount, cspan<float> low, cspan<float> high, ROI roi = {}, int nthreads = 0)

Count how many pixels in the image (within the ROI) are outside the value range described by low[roi.chbegin..roi.chend-1] and high[roi.chbegin..roi.chend-1] as the low and high acceptable values for each color channel.

The number of pixels containing values that fall below the lower bound will be stored in *lowcount, the number of pixels containing values that fall above the upper bound will be stored in *highcount, and the number of pixels for which all channels fell within the bounds will be stored in *inrangecount. Any of these may be NULL, which simply means that the counts need not be collected or stored. 

ImageBuf A ("a.exr");
ROI roi = get_roi (A.spec());
roi.chend = std::min (roi.chend, 4);  // only compare RGBA

float low[] = {0, 0, 0, 0};
float high[] = {1, 1, 1, 1};

imagesize_t lowcount, highcount, inrangecount;
ImageBufAlgo::color_range_check (A, &lowcount, &highcount, &inrangecount,
                                 low, high, roi);
std::cout << lowcount << " pixels had components < 0\n";
std::cout << highcount << " pixels had components > 1\n";
std::cout << inrangecount << " pixels were fully within [0,1] range\n";

ROI OIIO::ImageBufAlgo::nonzero_region(const ImageBuf &src, ROI roi = {}, int nthreads = 0)

Find the minimal rectangular region within roi (which defaults to the entire pixel data window of src) that consists of nonzero pixel values. In other words, gives the region that is a “shrink-wraps” of src to exclude black border pixels. Note that if the entire image was black, the ROI returned will contain no pixels.

For “deep” images, this function returns the smallest ROI that contains all pixels that contain depth samples, and excludes the border pixels that contain no depth samples at all.

Examples:

ImageBuf A ("a.exr");
ROI shrunk = ImageBufAlgo::nonzero_region (A);
if (shrunk.undefined())
    std::cout << "All pixels were empty\n";
else
    std::cout << "Non-empty region was " << shrunk << "\n";

std::string OIIO::ImageBufAlgo::computePixelHashSHA1(const ImageBuf &src, string_view extrainfo = "", ROI roi = {}, int blocksize = 0, int nthreads = 0)

Compute the SHA-1 byte hash for all the pixels in the specifed region of the image. If blocksize > 0, the function will compute separate SHA-1 hashes of each blocksize batch of scanlines, then return a hash of the individual hashes. This is just as strong a hash, but will NOT match a single hash of the entire image (blocksize==0). But by breaking up the hash into independent blocks, we can parallelize across multiple threads, given by nthreads (if nthreads is 0, it will use the global OIIO thread count). The extrainfo provides additional text that will be incorporated into the hash.

Examples:

ImageBuf A ("a.exr");
std::string hash;
hash = ImageBufAlgo::computePixelHashSHA1 (A, "", ROI::All(), 64);

std::vector<imagesize_t> OIIO::ImageBufAlgo::histogram(const ImageBuf &src, int channel = 0, int bins = 256, float min = 0.0f, float max = 1.0f, bool ignore_empty = false, ROI roi = {}, int nthreads = 0)

Compute a histogram of src, for the given channel and ROI. Return a vector of length bins that contains the counts of how many pixel values were in each of bins equally spaced bins covering the range of values [min,max]. Values < min count for bin 0, values > max count for bin nbins-1. If ignore_empty is true, no counts will be incremented for any pixels whose value is 0 in all channels.

If there was an error, the returned vector will be empty, and an error message will be retrievable from src.geterror().

Examples:

ImageBuf Src ("tahoe.exr");
const int bins = 4;
auto hist = ImageBufAlgo::histogram (Src, 0, bins, 0.0f, 1.0f);
std::cout << "Channel 0 of the image had:\n";
float binsize = (max-min)/nbins;
for (int i = 0;  i < nbins;  ++i)
    hist[i] << " pixels that are >= " << (min+i*binsize) << " and "
            << (i == nbins-1 ? " <= " : " < ")
            << (min+(i+1)*binsize) << "\n";

Convolutions and frequency-space algorithms

ImageBuf OIIO::ImageBufAlgo::make_kernel(string_view name, float width, float height, float depth = 1.0f, bool normalize = true)

Make a 1-channel float image of the named kernel. The size of the image will be big enough to contain the kernel given its size (width x height) and rounded up to odd resolution so that the center of the kernel can be at the center of the middle pixel. The kernel image will be offset so that its center is at the (0,0) coordinate. If normalize is true, the values will be normalized so that they sum to 1.0. If depth > 1, a volumetric kernel will be created. Use with caution!

Kernel names can be: “gaussian”, “sharp-gaussian”, “box”, “triangle”, “blackman-harris”, “mitchell”, “b-spline”, “catmull-rom”, “lanczos3”, “disk”, “binomial”, “laplacian”.

Note that “catmull-rom” and “lanczos3” are fixed-size kernels that don’t scale with the width, and are therefore probably less useful in most cases.

The ImageBuf that is returned indicates if there was an error, in which case return.has_error() will be true and return.geterror() can be used to retrieve an error message.

Examples:

ImageBuf K = ImageBufAlgo::make_kernel ("gaussian", 5.0f, 5.0f);

ImageBuf OIIO::ImageBufAlgo::convolve(const ImageBuf &src, const ImageBuf &kernel, bool normalize = true, ROI roi = {}, int nthreads = 0)

Return the convolution of src and a kernel. If roi is not defined, it defaults to the full size src. If normalized is true, the kernel will be normalized for the convolution, otherwise the original values will be used.

Result-as-parameter version:

bool OIIO::ImageBufAlgo::convolve(ImageBuf &dst, const ImageBuf &src, const ImageBuf &kernel, bool normalize = true, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized). If roi is not defined, it defaults to the full size of dst (or src, if dst was uninitialized). If dst is uninitialized, it will be allocated to be the size specified by roi.

Examples:

// Blur an image with a 5x5 Gaussian kernel
ImageBuf Src ("tahoe.exr");
ImageBuf K = ImageBufAlgo::make_kernel ("gaussian", 5.0f, 5.0f);
ImageBuf Blurred = ImageBufAlgo::convolve (Src, K);

convimage1

convimage2

original

blurred

ImageBuf OIIO::ImageBufAlgo::laplacian(const ImageBuf &src, ROI roi = {}, int nthreads = 0)

Return the Laplacian of the corresponding region of src. The Laplacian is the generalized second derivative of the image

\[ \frac{\partial^2 s}{\partial x^2} + \frac{\partial^2 s}{\partial y^2} \]
which is approximated by convolving the image with a discrete 3x3 Laplacian kernel, 
                [ 0  1  0 ]
                [ 1 -4  1 ]
                [ 0  1  0 ]

Result-as-parameter version:

bool OIIO::ImageBufAlgo::laplacian(ImageBuf &dst, const ImageBuf &src, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

Examples:

ImageBuf src ("tahoe.exr");
ImageBuf lap = ImageBufAlgo::laplacian (src);

lapimage1

lapimage2

original

Laplacian image

group fft-ifft

Fast Fourier Transform and inverse

Return (or copy into dst) the discrete Fourier transform (DFT), or its inverse, of the section of src denoted by roi, If roi is not defined, it will be all of src’s pixels.

fft() takes the discrete Fourier transform (DFT) of the section of src denoted by roi, returning it or storing it in dst. If roi is not defined, it will be all of src’s pixels. Only one channel of src may be transformed at a time, so it will be the first channel described by roi (or, again, channel 0 if roi is undefined). If not already in the correct format, dst will be re-allocated to be a 2-channel float buffer of size roi.width() x roi.height, with channel 0 being the “real” part and channel 1 being the the “imaginary” part. The values returned are actually the unitary DFT, meaning that it is scaled by 1/sqrt(npixels).

ifft() takes the inverse discrete Fourier transform, transforming a 2-channel complex (real and imaginary) frequency domain image and into a single-channel spatial domain image. src must be a 2-channel float image, and is assumed to be a complex frequency-domain signal with the “real” component in channel 0 and the “imaginary” component in channel 1. dst will end up being a float image of one channel (the real component is kept, the imaginary component of the spatial-domain will be discarded). Just as with fft(), the ifft() function is dealing with the unitary DFT, so it is scaled by 1/sqrt(npixels).

Functions

ImageBuf fft(const ImageBuf &src, ROI roi = {}, int nthreads = 0)
ImageBuf ifft(const ImageBuf &src, ROI roi = {}, int nthreads = 0)
bool fft(ImageBuf &dst, const ImageBuf &src, ROI roi = {}, int nthreads = 0)
bool ifft(ImageBuf &dst, const ImageBuf &src, ROI roi = {}, int nthreads = 0)

Examples:

ImageBuf Src ("tahoe.exr");

// Take the DFT of the first channel of Src
ImageBuf Freq = ImageBufAlgo::fft (Src);

// At this point, Freq is a 2-channel float image (real, imag)
// Convert it back from frequency domain to a spatial image
ImageBuf Spatial = ImageBufAlgo::ifft (Freq);

group complex-polar

Converting complex to polar and back

The polar_to_complex() function transforms a 2-channel image whose channels are interpreted as complex values (real and imaginary components) into the equivalent values expressed in polar form of amplitude and phase (with phase between 0 and \( 2\pi \).

The complex_to_polar() function performs the reverse transformation, converting from polar values (amplitude and phase) to complex (real and imaginary).

In either case, the section of src denoted by roi is transformed, storing the result in dst. If roi is not defined, it will be all of src’s pixels. Only the first two channels of src will be transformed.

The transformation between the two representations are: 

real = amplitude * cos(phase);
imag = amplitude * sin(phase);

amplitude = hypot (real, imag);
phase = atan2 (imag, real);

Functions

ImageBuf complex_to_polar(const ImageBuf &src, ROI roi = {}, int nthreads = 0)
bool complex_to_polar(ImageBuf &dst, const ImageBuf &src, ROI roi = {}, int nthreads = 0)
ImageBuf polar_to_complex(const ImageBuf &src, ROI roi = {}, int nthreads = 0)
bool polar_to_complex(ImageBuf &dst, const ImageBuf &src, ROI roi = {}, int nthreads = 0)

Examples:

// Suppose we have an FFT in frequency space values expressed as
// complex values (real, imaginary)
ImageBuf fft ("fft.exr");

// Convert to polar values (amplitude, phase)
ImageBuf Polar = ImageBufAlgo::complex_to_polar (fft);

// Convert from polar back to (real, imag)
ImageBuf Freq = ImageBufAlgo::polar_to_complex (Polar);

Image Enhancement / Restoration

ImageBuf OIIO::ImageBufAlgo::fixNonFinite(const ImageBuf &src, NonFiniteFixMode mode = NONFINITE_BOX3, int *pixelsFixed = nullptr, ROI roi = {}, int nthreads = 0)

fixNonFinite() returns in image containing the values of src (within the ROI), while repairing any non-finite (NaN/Inf) pixels. If pixelsFixed is not nullptr, store in it the number of pixels that contained non-finite value. It is permissible to operate in-place (with src and dst referring to the same image).

How the non-finite values are repaired is specified by one of the mode parameter, which is an enum of NonFiniteFixMode.

This function works on all pixel data types, though it’s just a copy for images with pixel data types that cannot represent NaN or Inf values.

Result-as-parameter version:
bool OIIO::ImageBufAlgo::fixNonFinite(ImageBuf &dst, const ImageBuf &src, NonFiniteFixMode mode = NONFINITE_BOX3, int *pixelsFixed = nullptr, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

Examples:

ImageBuf Src ("tahoe.exr");
int pixelsFixed = 0;
ImageBufAlgo::fixNonFinite (Src, Src, ImageBufAlgo::NONFINITE_BOX3,
                            &pixelsFixed);
std::cout << "Repaired " << pixelsFixed << " non-finite pixels\n";

ImageBuf OIIO::ImageBufAlgo::fillholes_pushpull(const ImageBuf &src, ROI roi = {}, int nthreads = 0)

Copy the specified ROI of src and fill any holes (pixels where alpha < 1) with plausible values using a push-pull technique. The src image must have an alpha channel. The dst image will end up with a copy of src, but will have an alpha of 1.0 everywhere within roi, and any place where the alpha of src was < 1, dst will have a pixel color that is a plausible “filling” of the original alpha hole.

Result-as-parameter version:
bool OIIO::ImageBufAlgo::fillholes_pushpull(ImageBuf &dst, const ImageBuf &src, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

Examples:

ImageBuf Src ("holes.exr");
ImageBuf Filled = ImageBufAlgo::fillholes_pushpull (Src);

ImageBuf OIIO::ImageBufAlgo::median_filter(const ImageBuf &src, int width = 3, int height = -1, ROI roi = {}, int nthreads = 0)

Return a median-filtered version of the corresponding region of src. The median filter replaces each pixel with the median value underneath the width x height window surrounding it. If height <= 0, it will be set to width, making a square window.

Median filters are good for removing high-frequency detail smaller than the window size (including noise), without blurring edges that are larger than the window size.

Result-as-parameter version:
bool OIIO::ImageBufAlgo::median_filter(ImageBuf &dst, const ImageBuf &src, int width = 3, int height = -1, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

Examples:

ImageBuf Noisy ("tahoe.exr");
ImageBuf Clean = ImageBufAlgo::median_filter (Noisy, 3, 3);

medimage1

medimage2

medimage3

original

with dropouts

median filtered

ImageBuf OIIO::ImageBufAlgo::unsharp_mask(const ImageBuf &src, string_view kernel = "gaussian", float width = 3.0f, float contrast = 1.0f, float threshold = 0.0f, ROI roi = {}, int nthreads = 0)

Return a sharpened version of the corresponding region of src using the “unsharp mask” technique. Unsharp masking basically works by first blurring the image (low pass filter), subtracting this from the original image, then adding the residual back to the original to emphasize the edges. Roughly speaking, 

 dst = src + contrast * thresh(src - blur(src))

The specific blur can be selected by kernel name and width (for example, “gaussian” is typical). As a special case, “median” is also accepted as the kernel name, in which case a median filter is performed rather than a blurring convolution (Gaussian and other blurs sometimes over-sharpen edges, whereas using the median filter will sharpen compact high-frequency details while not over-sharpening long edges).

The contrast is a multiplier on the overall sharpening effect. The thresholding step causes all differences less than threshold to be squashed to zero, which can be useful for suppressing sharpening of low-contrast details (like noise) but allow sharpening of higher-contrast edges.

Result-as-parameter version:
bool OIIO::ImageBufAlgo::unsharp_mask(ImageBuf &dst, const ImageBuf &src, string_view kernel = "gaussian", float width = 3.0f, float contrast = 1.0f, float threshold = 0.0f, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

Examples:

ImageBuf Blurry ("tahoe.exr");
ImageBuf Sharp = ImageBufAlgo::unsharp_mask (Blurry, "gaussian", 5.0f);

Morphological filters

ImageBuf OIIO::ImageBufAlgo::dilate(const ImageBuf &src, int width = 3, int height = -1, ROI roi = {}, int nthreads = 0)

Return a dilated version of the corresponding region of src. Dilation is defined as the maximum value of all pixels under nonzero values of the structuring element (which is taken to be a width x height square). If height is not set, it will default to be the same as width. Dilation makes bright features wider and more prominent, dark features thinner, and removes small isolated dark spots.

Result-as-parameter version:
bool OIIO::ImageBufAlgo::dilate(ImageBuf &dst, const ImageBuf &src, int width = 3, int height = -1, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).


ImageBuf OIIO::ImageBufAlgo::erode(const ImageBuf &src, int width = 3, int height = -1, ROI roi = {}, int nthreads = 0)

Return an eroded version of the corresponding region of src. Erosion is defined as the minimum value of all pixels under nonzero values of the structuring element (which is taken to be a width x height square). If height is not set, it will default to be the same as width. Erosion makes dark features wider, bright features thinner, and removes small isolated bright spots.

Result-as-parameter version:
bool OIIO::ImageBufAlgo::erode(ImageBuf &dst, const ImageBuf &src, int width = 3, int height = -1, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).


Dilation and erosion are basic morphological filters, and more complex ones are often constructed from them:

  • “open” is erode followed by dilate, and it keeps the overall shape while removing small bright regions;

  • “close” is dilate followed by erode, and it keeps the overall shape while removing small dark regions;

  • “morphological gradient” is dilate minus erode, which gives a bright perimeter edge;

  • “tophat” is the original source minus the “open”, which isolates local peaks;

  • “bottomhat” is the “close” minus the original source, which isolates dark holes.

    Examples:

    ImageBuf Source ("source.tif");

ImageBuf Dilated = ImageBufAlgo::dilate (Source, 3, 3);
ImageBuf Eroded  = ImageBufAlgo::erode (Source, 3, 3);

// Morphological "open" is dilate(erode((source))
ImageBuf Opened = ImageBufAlgo::dilate (Eroded, 3, 3);
// Morphological "close" is erode(dilate(source))
ImageBuf Closed = ImageBufAlgo::erode (Dilated, 3, 3);
// Morphological "gradient" is dilate minus erode
ImageBuf Gradient = ImageBufAlgo::sub (Dilated, Eroded);
// Tophat filter is source minus open
ImageBuf Tophat = ImageBufAlgo::sub (Source, Opened);
// Bottomhat filter is close minus source
ImageBuf Bottomhat = ImageBufAlgo::sub (Close, Source);

morph1

morph2

morph3

morph4

original

dilate

erode

open

morph5

morph6

morph7

morph8

close

gradient

tophat

bottomhat

Color space conversion

group colorconvert

Convert between color spaces

Return (or copy into dst) the pixels of src within the ROI, applying a color space transformation. In-place operations (dst == src) are supported.

The first three channels are presumed to be the color to be transformed, and the fourth channel (if it exists) is presumed to be alpha. Any additional channels will be simply copied unaltered.

If OIIO was built with OpenColorIO support enabled, then the transformation may be between any two spaces supported by the active OCIO configuration, or may be a “look” transformation created by ColorConfig::createLookTransform. If OIIO was not built with OpenColorIO support enabled, then the only transformations available are from “sRGB” to “linear” and vice versa.

Parameters

  • fromspace/tospace: For the varieties of colorconvert() that use named color spaces, these specify the color spaces by name.

  • context_key/context_value: For the varieties of colorconvert() that use named color spaces, these optionally specify a “key” name/value pair to establish a context (for example, a shot-specific transform).

  • processor: For the varieties of colorconvert() that have a processor paramater, it is a raw ColorProcessor* object that implements the color transformation. This is a special object created by a ColorConfig (see OpenImageIO/color.h for details).

  • unpremult: If true, unpremultiply the image (divide the RGB channels by alpha if it exists and is nonzero) before color conversion, then repremult after the after the color conversion. Passing unpremult=false skips this step, which may be desirable if you know that the image is “unassociated alpha” (a.k.a., “not pre-multiplied colors”).

  • colorconfig: An optional ColorConfig* specifying an OpenColorIO configuration. If not supplied, the default OpenColorIO color configuration found by examining the $OCIO environment variable will be used instead.

Functions

ImageBuf colorconvert(const ImageBuf &src, string_view fromspace, string_view tospace, bool unpremult = true, string_view context_key = "", string_view context_value = "", ColorConfig *colorconfig = nullptr, ROI roi = {}, int nthreads = 0)

Transform between named color spaces, returning an ImageBuf result.

ImageBuf colorconvert(const ImageBuf &src, const ColorProcessor *processor, bool unpremult, ROI roi = {}, int nthreads = 0)

Transform using a ColorProcessor, returning an ImageBuf result.

bool colorconvert(ImageBuf &dst, const ImageBuf &src, string_view fromspace, string_view tospace, bool unpremult = true, string_view context_key = "", string_view context_value = "", ColorConfig *colorconfig = nullptr, ROI roi = {}, int nthreads = 0)

Transform between named color spaces, storing reults into an existing ImageBuf.

bool colorconvert(ImageBuf &dst, const ImageBuf &src, const ColorProcessor *processor, bool unpremult, ROI roi = {}, int nthreads = 0)

Transform using a ColorProcessor, storing reults into an existing ImageBuf.

bool colorconvert(span<float> color, const ColorProcessor *processor, bool unpremult)

Apply a color transform in-place to just one color: color[0..nchannels-1]. nchannels should either be 3 or 4 (if 4, the last channel is alpha).

inline bool colorconvert(float *color, int nchannels, const ColorProcessor *processor, bool unpremult)

Examples:

ImageBuf Src ("tahoe.jpg");
ImageBuf Dst = ImageBufAlgo::colorconvert (Src, "sRGB", "acescg", true);

ImageBuf OIIO::ImageBufAlgo::colormatrixtransform(const ImageBuf &src, const Imath::M44f &M, bool unpremult = true, ROI roi = {}, int nthreads = 0)

Return a copy of the pixels of src within the ROI, applying a color transform specified by a 4x4 matrix. In-place operations (dst == src) are supported.

The first three channels are presumed to be the color to be transformed, and the fourth channel (if it exists) is presumed to be alpha. Any additional channels will be simply copied unaltered.

Version

2.1+

Parameters

  • M: A 4x4 matrix. Following Imath conventions, the color is a row vector and the matrix has the “translation” part in elements [12..14] (matching the memory layout of OpenGL or RenderMan), so the math is color * Matrix (NOT M*c).

  • unpremult: If true, unpremultiply the image (divide the RGB channels by alpha if it exists and is nonzero) before color conversion, then repremult after the after the color conversion. Passing unpremult=false skips this step, which may be desirable if you know that the image is “unassociated alpha” (a.k.a., “not pre-multiplied colors”).

Result-as-parameter version:
bool OIIO::ImageBufAlgo::colormatrixtransform(ImageBuf &dst, const ImageBuf &src, const Imath::M44f &M, bool unpremult = true, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

Examples:

ImageBuf Src ("tahoe.exr");
Imath::M44f M ( .8047379,  .5058794, -.3106172, 0,
               -.3106172,  .8047379,  .5058794, 0,
                .5058794, -.3106172,  .8047379, 0,
                 0,         0,         0,       1);
ImageBuf dst = ImageBufAlgo::colormatrixtransform (Src, M);

ccmat1

ccmat2

original

matrix applied

ImageBuf OIIO::ImageBufAlgo::ociolook(const ImageBuf &src, string_view looks, string_view fromspace, string_view tospace, bool unpremult = true, bool inverse = false, string_view context_key = "", string_view context_value = "", ColorConfig *colorconfig = nullptr, ROI roi = {}, int nthreads = 0)

Return a copy of the pixels of src within the ROI, applying an OpenColorIO “look” transform to the pixel values. In-place operations (dst == src) are supported.

The first three channels are presumed to be the color to be transformed, and the fourth channel (if it exists) is presumed to be alpha. Any additional channels will be simply copied unaltered.

Parameters

  • looks: The looks to apply (comma-separated).

  • fromspace/tospace: For the varieties of colorconvert() that use named color spaces, these specify the color spaces by name.

  • unpremult: If true, unpremultiply the image (divide the RGB channels by alpha if it exists and is nonzero) before color conversion, then repremult after the after the color conversion. Passing unpremult=false skips this step, which may be desirable if you know that the image is “unassociated alpha” (a.k.a., “not pre-multiplied colors”).

  • inverse: If true, it will reverse the color transformation and look application.

  • context_key/context_value: Optional key/value to establish a context (for example, a shot-specific transform).

  • colorconfig: An optional ColorConfig* specifying an OpenColorIO configuration. If not supplied, the default OpenColorIO color configuration found by examining the $OCIO environment variable will be used instead.

Result-as-parameter version:
bool OIIO::ImageBufAlgo::ociolook(ImageBuf &dst, const ImageBuf &src, string_view looks, string_view fromspace, string_view tospace, bool unpremult = true, bool inverse = false, string_view context_key = "", string_view context_value = "", ColorConfig *colorconfig = nullptr, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

Examples:

ImageBuf Src ("tahoe.jpg");
ImageBuf Dst = ImageBufAlgo::ociolook (Src, "look", "vd8", "lnf",
                                       true, false, "SHOT", "pe0012");

ImageBuf OIIO::ImageBufAlgo::ociodisplay(const ImageBuf &src, string_view display, string_view view, string_view fromspace = "", string_view looks = "", bool unpremult = true, string_view context_key = "", string_view context_value = "", ColorConfig *colorconfig = nullptr, ROI roi = {}, int nthreads = 0)

Return the pixels of src within the ROI, applying an OpenColorIO “display” transform to the pixel values. In-place operations (dst == src) are supported.

The first three channels are presumed to be the color to be transformed, and the fourth channel (if it exists) is presumed to be alpha. Any additional channels will be simply copied unaltered.

Parameters

  • display: The OCIO “display” to apply. If this is the empty string, the default display will be used.

  • view: The OCIO “view” to use. If this is the empty string, the default view for this display will be used.

  • fromspace: If fromspace is not supplied, it will assume that the source color space is whatever is indicated by the source image’s metadata or filename, and if that cannot be deduced, it will be assumed to be scene linear.

  • looks: The looks to apply (comma-separated). This may be empty, in which case no “look” is used. Note: this parameter value is not used when building against OpenColorIO 2.x.

  • unpremult: If true, unpremultiply the image (divide the RGB channels by alpha if it exists and is nonzero) before color conversion, then repremult after the after the color conversion. Passing unpremult=false skips this step, which may be desirable if you know that the image is “unassociated alpha” (a.k.a., “not pre-multiplied colors”).

  • inverse: If true, it will reverse the color transformation and display application.

  • context_key/context_value: Optional key/value to establish a context (for example, a shot-specific transform).

  • colorconfig: An optional ColorConfig* specifying an OpenColorIO configuration. If not supplied, the default OpenColorIO color configuration found by examining the $OCIO environment variable will be used instead.

Result-as-parameter version:
bool OIIO::ImageBufAlgo::ociodisplay(ImageBuf &dst, const ImageBuf &src, string_view display, string_view view, string_view fromspace = "", string_view looks = "", bool unpremult = true, string_view context_key = "", string_view context_value = "", ColorConfig *colorconfig = nullptr, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

Examples:

ImageBuf Src ("tahoe.exr");
ImageBuf Dst = ImageBufAlgo::ociodisplay (Src, "sRGB", "Film", "lnf",
                                          "", true, "SHOT", "pe0012");

ImageBuf OIIO::ImageBufAlgo::ociofiletransform(const ImageBuf &src, string_view name, bool unpremult = true, bool inverse = false, ColorConfig *colorconfig = nullptr, ROI roi = {}, int nthreads = 0)

Return the pixels of src within the ROI, applying an OpenColorIO “file” transform. In-place operations (dst == src) are supported.

The first three channels are presumed to be the color to be transformed, and the fourth channel (if it exists) is presumed to be alpha. Any additional channels will be simply copied unaltered.

Parameters

  • name: The name of the file containing the transform information.

  • unpremult: If true, unpremultiply the image (divide the RGB channels by alpha if it exists and is nonzero) before color conversion, then repremult after the after the color conversion. Passing unpremult=false skips this step, which may be desirable if you know that the image is “unassociated alpha” (a.k.a., “not pre-multiplied colors”).

  • inverse: If true, it will reverse the color transformation.

  • colorconfig: An optional ColorConfig* specifying an OpenColorIO configuration. If not supplied, the default OpenColorIO color configuration found by examining the $OCIO environment variable will be used instead.

Result-as-parameter version:
bool OIIO::ImageBufAlgo::ociofiletransform(ImageBuf &dst, const ImageBuf &src, string_view name, bool unpremult = true, bool inverse = false, ColorConfig *colorconfig = nullptr, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

Examples:

ImageBuf Src ("tahoe.exr");
ImageBuf Dst = ImageBufAlgo::ociofiletransform (Src, "footransform.csp");

group premult

Premultiply or un-premultiply color by alpha

The unpremult operation returns (or copies into dst) the pixels of src within the ROI, and in the process divides all color channels (those not alpha or z) by the alpha value, to “un-premultiply” them. This presumes that the image starts of as “associated alpha” a.k.a. “premultipled,” and you are converting to “unassociated alpha.” For pixels with alpha == 0, the color values are not modified.

The premult operation returns (or copies into dst) the pixels of src within the ROI, and in the process multiplies all color channels (those not alpha or z) by the alpha value, to “premultiply” them. This presumes that the image starts of as “unassociated alpha” a.k.a. “non-premultipled” and converts it to “associated alpha / premultipled.”

The repremult operation is like premult, but preserves the color values of pixels whose alpha is 0. This is intended for cases where you unpremult, do an operation (such as color transforms), then want to return to associated/premultiplied alpha in that case, you want to make sure that “glow” pixels (those with alpha=0 but RGB > 0) are preserved for the round trip, and not crushed to black. This use case is distinct from a simple premult that is a one-time conversion from unassociated to associated alpha.

All three operations are simply a copy if there is no identified alpha channel (and a no-op if dst and src are the same image).

Functions

ImageBuf unpremult(const ImageBuf &src, ROI roi = {}, int nthreads = 0)
bool unpremult(ImageBuf &dst, const ImageBuf &src, ROI roi = {}, int nthreads = 0)
ImageBuf premult(const ImageBuf &src, ROI roi = {}, int nthreads = 0)
bool premult(ImageBuf &dst, const ImageBuf &src, ROI roi = {}, int nthreads = 0)
ImageBuf repremult(const ImageBuf &src, ROI roi = {}, int nthreads = 0)
bool repremult(ImageBuf &dst, const ImageBuf &src, ROI roi = {}, int nthreads = 0)

Examples:

// Convert from unassociated alpha to associated alpha by
// straightforward multiplication of color by alpha.
ImageBuf Unassoc;  // Assume somehow this has unassociated alpha
ImageBuf Assoc = ImageBufAlgo::premult (Unassoc);

// Convert in-place from associated alpha to unassociated alpha,
// preserving the color of alpha==0 pixels.
ImageBuf A;
ImageBufAlgo::unpremult (A, A);

// Finish the round-trip back to associated, still preserving the
// color of alpha==0 pixels. This should result in exactly the same
// pixel values we started with (within precision limits).
ImageBufAlgo::repremult (A, A);

Import / export

group make_texture

The make_texture() function turns an image into a tiled, MIP-mapped, texture file and write it to disk (outputfilename).

The return value is true for success, false if an error occurred. If there was an error, any error message will be retrievable via the global OIIO::geterror() call (since there is no destination ImageBuf in which to store it).

Named fields in config:

  • format : Data format of the texture file (default: UNKNOWN = same format as the input)

  • tile_width/tile_height/tile_depth : Preferred tile size (default: 64x64x1)

Metadata in config.extra_attribs

  • compression (string) : Default: “zip”

  • fovcot (float) : Default: aspect ratio of the image resolution.

  • planarconfig (string) : Default: “separate”

  • worldtocamera (matrix) : World-to-camera matrix of the view.

  • worldtoscreen (matrix) : World-to-screen space matrix of the view.

  • worldtoNDC (matrix) : World-to-NDC space matrix of the view.

  • wrapmodes (string) : Default: “black,black”

  • maketx:verbose (int) : How much detail should go to outstream (0).

  • maketx:runstats (int) : If nonzero, print run stats to outstream (0).

  • maketx:resize (int) : If nonzero, resize to power of 2. (0)

  • maketx:nomipmap (int) : If nonzero, only output the top MIP level (0).

  • maketx:updatemode (int) : If nonzero, write new output only if the output file doesn’t already exist, or is older than the input file, or was created with different command-line arguments. (0)

  • maketx:constant_color_detect (int) : If nonzero, detect images that are entirely one color, and change them to be low resolution (default: 0).

  • maketx:monochrome_detect (int) : If nonzero, change RGB images which have R==G==B everywhere to single-channel grayscale (default: 0).

  • maketx:opaque_detect (int) : If nonzero, drop the alpha channel if alpha is 1.0 in all pixels (default: 0).

  • maketx:compute_average (int) : If nonzero, compute and store the average color of the texture (default: 1).

  • maketx:unpremult (int) : If nonzero, unpremultiply color by alpha before color conversion, then multiply by alpha after color conversion (default: 0).

  • maketx:incolorspace, maketx:outcolorspace (string) : These two together will apply a color conversion (with OpenColorIO, if compiled). Default: “”

  • maketx:colorconfig (string) : Specifies a custom OpenColorIO color config file. Default: “”

  • maketx:checknan (int) : If nonzero, will consider it an error if the input image has any NaN pixels. (0)

  • maketx:fixnan (string) : If set to “black” or “box3”, will attempt to repair any NaN pixels found in the input image (default: “none”).

  • maketx:set_full_to_pixels (int) : If nonzero, doctors the full/display window of the texture to be identical to the pixel/data window and reset the origin to 0,0 (default: 0).

  • maketx:filtername (string) : If set, will specify the name of a high-quality filter to use when resampling for MIPmap levels. Default: “”, use bilinear resampling.

  • maketx:highlightcomp (int) : If nonzero, performs highlight compensation range compression and expansion around the resize, plus clamping negative pixel values to zero. This reduces ringing when using filters with negative lobes on HDR images.

  • maketx:sharpen (float) : If nonzero, sharpens details when creating MIPmap levels. The amount is the contrast metric. The default is 0, meaning no sharpening.

  • maketx:nchannels (int) : If nonzero, will specify how many channels the output texture should have, padding with 0 values or dropping channels, if it doesn’t the number of channels in the input. (default: 0, meaning keep all input channels)

  • maketx:channelnames (string) : If set, overrides the channel names of the output image (comma-separated).

  • maketx:fileformatname (string) : If set, will specify the output file format. (default: “”, meaning infer the format from the output filename)

  • maketx:prman_metadata (int) : If set, output some metadata that PRMan will need for its textures. (0)

  • maketx:oiio_options (int) : (Deprecated; all are handled by default)

  • maketx:prman_options (int) : If nonzero, override a whole bunch of settings as needed to make textures that are compatible with PRMan. (0)

  • maketx:mipimages (string) : Semicolon-separated list of alternate images to be used for individual MIPmap levels, rather than simply downsizing. (default: “”)

  • maketx:full_command_line (string) : The command or program used to generate this call, will be embedded in the metadata. (default: “”)

  • maketx:ignore_unassoc (int) : If nonzero, will disbelieve any evidence that the input image is unassociated alpha. (0)

  • maketx:read_local_MB (int) : If nonzero, will read the full input file locally if it is smaller than this threshold. Zero causes the system to make a good guess at a reasonable threshold (e.g. 1 GB). (0)

  • maketx:forcefloat (int) : Forces a conversion through float data for the sake of ImageBuf math. (1)

  • maketx:hash (int) : Compute the sha1 hash of the file in parallel. (1)

  • maketx:allow_pixel_shift (int) : Allow up to a half pixel shift per mipmap level. The fastest path may result in a slight shift in the image, accumulated for each mip level with an odd resolution. (0)

  • maketx:bumpformat (string) : For the MakeTxBumpWithSlopes mode, chooses whether to assume the map is a height map (“height”), a normal map (“normal”), or automatically determine it from the number of channels (“auto”, the default).

  • maketx:uvslopes_scale (float) : If nonzero, when used in MakeTxBumpWithSlopes mode, this computes derivatives for the bumpslopes data in UV space rather than in texel space, and divides them by this scale factor. The default is 0, disabling the feature. If you use this feature, a suggested value is 256.

  • maketx:cdf

    (int) : If nonzero, will write a Gaussian CDF and Inverse Gaussian CDF as per-channel metadata in the texture, which can be used by shaders to implement Histogram-Preserving Blending. This is only useful when the texture being created is written to an image format that supports arbitrary metadata (e.g. OpenEXR). (See Burley, “On Histogram-Preserving Blending

    for Randomized Texture Tiling,” JCGT 8(4), 2019, and Heitz/Neyret, “High-Performance By-Example Noise using a Histogram-Preserving Blending Operator,” ACM SIGGRAPH / Eurographics Symposium on High-Performance Graphics 2018.) (default: 0)

  • maketx:cdfsigma (float) : When maketx:cdf is active, determines the CDF sigma (default: 1.0/6).

  • maketx:cdfbits (int) : When maketx:cdf is active, determines the number of bits to use for the size of the CDF table. (default: 8, meaning 256 bins)

Parameters

  • mode: Describes what type of texture file we are creating and may be one of:

    • MakeTxTexture : Ordinary 2D texture.

    • MakeTxEnvLatl : Latitude-longitude environment map

    • MakeTxEnvLatlFromLightProbe : Latitude-longitude environment map constructed from a “light probe” image.

    • MakeTxBumpWithSlopes : Bump/displacement map with extra slope data channels (6 channels total, containing both the height and 1st and 2nd moments of slope distributions) for bump-to-roughness conversion in shaders.

  • outputfilename: Name of the file in which to save the resulting texture.

  • config: An ImageSpec that contains all the information and special instructions for making the texture. Anything set in config (format, tile size, or named metadata) will take precedence over whatever is specified by the input file itself. Additionally, named metadata that starts with “maketx:” will not be output to the file itself, but may contain instructions controlling how the texture is created. The full list of supported configuration options is listed below.

  • outstream: If not nullptr, it should point to a stream (for example, &std::out, or a pointer to a local std::stringstream to capture output), which is where console output and errors will be deposited. Note that error messages will also be retrievable from OIIO::geterror().

Functions

bool make_texture(MakeTextureMode mode, const ImageBuf &input, string_view outputfilename, const ImageSpec &config, std::ostream *outstream = nullptr)

Version of make_texture that starts with an ImageBuf.

bool make_texture(MakeTextureMode mode, string_view filename, string_view outputfilename, const ImageSpec &config, std::ostream *outstream = nullptr)

Version of make_texture that starts with a filename and reads the input from that file, rather than being given an ImageBuf directly.

bool make_texture(MakeTextureMode mode, const std::vector<std::string> &filenames, string_view outputfilename, const ImageSpec &config, std::ostream *outstream = nullptr)

Version of make_texture that takes multiple filenames (reserved for future expansion, such as assembling several faces into a cube map).

Examples:

ImageBuf Input ("in.exr");
ImageSpec config;
config["maketx:highlightcomp"] = 1;
config["maketx:filtername"] = "lanczos3";
config["maketx:opaque_detect"] = 1;

bool ok = ImageBufAlgo::make_texture (ImageBufAlgo::MakeTxTexture,
                                      Input, "texture.exr", config);
if (! ok)
    std::cout << "make_texture error: " << OIIO::geterror() << "\n";

OpenCV interoperability is performed by the from_OpenCV() and to_OpenCV() functions:

ImageBuf OIIO::ImageBufAlgo::from_OpenCV(const cv::Mat &mat, TypeDesc convert = TypeUnknown, ROI roi = {}, int nthreads = 0)

Convert an OpenCV cv::Mat into an ImageBuf, copying the pixels (optionally converting to the pixel data type specified by convert, if not UNKNOWN, which means to preserve the original data type if possible). Return true if ok, false if it couldn’t figure out how to make the conversion from Mat to ImageBuf. If OpenImageIO was compiled without OpenCV support, this function will return an empty image with error message set.

bool OIIO::ImageBufAlgo::to_OpenCV(cv::Mat &dst, const ImageBuf &src, ROI roi = {}, int nthreads = 0)

Construct an OpenCV cv::Mat containing the contents of ImageBuf src, and return true. If it is not possible, or if OpenImageIO was compiled without OpenCV support, then return false. Note that OpenCV only supports up to 4 channels, so >4 channel images will be truncated in the conversion.

ImageBuf OIIO::ImageBufAlgo::capture_image(int cameranum = 0, TypeDesc convert = TypeUnknown)

Capture a still image from a designated camera. If able to do so, store the image in dst and return true. If there is no such device, or support for camera capture is not available (such as if OpenCV support was not enabled at compile time), return false and do not alter dst.

Examples:

ImageBuf WebcamImage = ImageBufAlgo::capture_image (0, TypeDesc::UINT8);
WebcamImage.write ("webcam.jpg");

Deep images

A number of ImageBufAlgo functions are designed to work with “deep” images. These are detailed below. In general, ImageBufAlgo functions not listed in this section should not be expected to work with deep images.

Functions specific to deep images


ImageBuf OIIO::ImageBufAlgo::deepen(const ImageBuf &src, float zvalue = 1.0f, ROI roi = {}, int nthreads = 0)

Return the “deep” equivalent of the “flat” input src. Turning a flat image into a deep one means:

  • If the src image has a “Z” channel: if the source pixel’s Z channel value is not infinite, the corresponding pixel of dst will get a single depth sample that copies the data from the source pixel; otherwise, dst will get an empty pixel. In other words, infinitely far pixels will not turn into deep samples.

  • If the src image lacks a “Z” channel: if any of the source pixel’s channel values are nonzero, the corresponding pixel of dst will get a single depth sample that copies the data from the source pixel and uses the zvalue parameter for the depth; otherwise, if all source channels in that pixel are zero, the destination pixel will get no depth samples.

If src is already a deep image, it will just copy pixel values from src.

Result-as-parameter version:
bool OIIO::ImageBufAlgo::deepen(ImageBuf &dst, const ImageBuf &src, float zvalue = 1.0f, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

Examples:

ImageBuf Flat ("RGBAZ.exr");
ImageBuf Deep = ImageBufAlgo::deepen (Flat);

ImageBuf OIIO::ImageBufAlgo::flatten(const ImageBuf &src, ROI roi = {}, int nthreads = 0)

Return the “flattened” composite of deep image src. That is, it converts a deep image to a simple flat image by front-to- back compositing the samples within each pixel. If src is already a non-deep/flat image, it will just copy pixel values from src to dst. If dst is not already an initialized ImageBuf, it will be sized to match src (but made non-deep).

Result-as-parameter version:
bool OIIO::ImageBufAlgo::flatten(ImageBuf &dst, const ImageBuf &src, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

Examples:

ImageBuf Deep ("deepalpha.exr");
ImageBuf Flat = ImageBufAlgo::flatten (Deep);

ImageBuf OIIO::ImageBufAlgo::deep_merge(const ImageBuf &A, const ImageBuf &B, bool occlusion_cull = true, ROI roi = {}, int nthreads = 0)

Return the deep merge of the samples of deep images A and B, overwriting any existing samples of dst in the ROI. If occlusion_cull is true, any samples occluded by an opaque sample will be deleted.

Result-as-parameter version:
bool OIIO::ImageBufAlgo::deep_merge(ImageBuf &dst, const ImageBuf &A, const ImageBuf &B, bool occlusion_cull = true, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

Examples:

ImageBuf DeepA ("hardsurf.exr");
ImageBuf DeepB ("volume.exr");
ImageBuf Merged = ImageBufAlgo::deep_merge (DeepA, DeepB);

ImageBuf OIIO::ImageBufAlgo::deep_holdout(const ImageBuf &src, const ImageBuf &holdout, ROI roi = {}, int nthreads = 0)

Return the samples of deep image src that are closer than the opaque frontier of deep image holdout, returning true upon success and false for any failures. Samples of src that are farther than the first opaque sample of holdout (for the corresponding pixel)will not be copied to dst. Image holdout is only used as the depth threshold; no sample values from holdout are themselves copied to dst.

Result-as-parameter version:
bool OIIO::ImageBufAlgo::deep_holdout(ImageBuf &dst, const ImageBuf &src, const ImageBuf &holdout, ROI roi = {}, int nthreads = 0)

Write to an existing image dst (allocating if it is uninitialized).

Examples:

ImageBuf Src ("image.exr");
ImageBuf Holdout ("holdout.exr");
ImageBuf Merged = ImageBufAlgo::deep_holdout (Src, Holdout);

General functions that also work for deep images

ImageBuf channels(const ImageBuf &src, int nchannels, cspan<int> channelorder, cspan<float> channelvalues = NULL, cspan<std::string> newchannelnames = {}, bool shuffle_channel_names = false)
bool channels(ImageBuf &dst, const ImageBuf &src, int nchannels, cspan<int> channelorder, cspan<float> channelvalues = NULL, cspan<std::string> newchannelnames = {}, bool shuffle_channel_names = false)

Reorder, rename, remove, or add channels to a deep image.

bool compare(const ImageBuf &A, const ImageBuf &B, float failthresh, float warnthresh, CompareResults &result, ROI roi = {}, int nthreads = 0)

Numerically compare two images.

bool computePixelStats(PixelStats &stats, const ImageBuf &src, ROI roi = {}, int nthreads = 0)

Compute per-channel statistics about the image.

ImageBuf crop(const ImageBuf &src, ROI roi = {}, int nthreads = 0)
bool crop(ImageBuf &dst, const ImageBuf &src, ROI roi = {}, int nthreads = 0)

Crop the specified region of src, discarding samples outside the ROI.

ROI nonzero_region(const ImageBuf &src, ROI roi = {}, int nthreads = 0)

For “deep” images, this function returns the smallest ROI that contains all pixels that contain depth samples, and excludes the border pixels that contain no depth samples at all.

ImageBuf add(const ImageBuf &A, cspan<float> B, ROI roi = {}, int nthreads = 0)
bool add(ImageBuf &dst, const ImageBuf &A, cspan<float> B, ROI roi = {}, int nthreads = 0)
ImageBuf sub(const ImageBuf &A, cspan<float> B, ROI roi = {}, int nthreads = 0)
bool sub(ImageBuf &dst, const ImageBuf &A, cspan<float> B, ROI roi = {}, int nthreads = 0)
ImageBuf mul(const ImageBuf &A, cspan<float> B, ROI roi = {}, int nthreads = 0)
bool mul(ImageBuf &dst, const ImageBuf &A, cspan<float> B, ROI roi = {}, int nthreads = 0)
ImageBuf div(const ImageBuf &A, cspan<float> B, ROI roi = {}, int nthreads = 0)
bool div(ImageBuf &dst, const ImageBuf &A, cspan<float> B, ROI roi = {}, int nthreads = 0)

Add, subtract, multiply, or divide all the samples in a deep image A by per-channel values B[].

ImageBuf fixNonFinite(const ImageBuf &src, NonFiniteFixMode mode = NONFINITE_BOX3, int *pixelsFixed = nullptr, ROI roi = {}, int nthreads = 0)
bool fixNonFinite(ImageBuf &dst, const ImageBuf &src, NonFiniteFixMode mode = NONFINITE_BOX3, int *pixelsFixed = nullptr, ROI roi = {}, int nthreads = 0)

Repair nonfinite (NaN or Inf) values, setting them to 0.0.

ImageBuf resample(const ImageBuf &src, bool interpolate = true, ROI roi = {}, int nthreads = 0)
bool resample(ImageBuf &dst, const ImageBuf &src, bool interpolate = true, ROI roi = {}, int nthreads = 0)

Compute a resized version of the corresponding portion of src (mapping such that the “full” image window of each correspond to each other, regardless of resolution), for each pixel merely copying the closest deep pixel of the source image (no true interpolation is done for deep images).

Python Bindings

Overview

OpenImageIO provides Python language bindings for much of its functionality.

You must ensure that the environment variable PYTHONPATH includes the python subdirectory of the OpenImageIO installation.

A Python program must import the OpenImageIO package:

import OpenImageIO

In most of our examples below, we assume that for the sake of brevity, we will alias the package name as follows:

import OpenImageIO as oiio
from OIIO import ImageInput, ImageOutput
from OIIO import ImageBuf, ImageSpec, ImageBufAlgo

TypeDesc

The TypeDesc class that describes data types of pixels and metadata, described in detail in Section Data Type Descriptions: TypeDesc, is replicated for Python.

class BASETYPE

The BASETYPE enum corresponds to the C++ TypeDesc::BASETYPE and contains the following values:

UNKNOWN NONE UINT8 INT8 UINT16 INT16 UINT32 INT32 UINT64 INT64
HALF FLOAT DOUBLE STRING PTR

These names are also exported to the OpenImageIO namespace.

class AGGREGATE

The AGGREGATE enum corresponds to the C++ TypeDesc::AGGREGATE and contains the following values:

SCALAR VEC2 VEC3 VEC4 MATRIX33 MATRIX44

These names are also exported to the OpenImageIO namespace.

class VECSEMANTICS

The VECSEMANTICS enum corresponds to the C++ TypeDesc::VECSEMANTICS and contains the following values:

NOSEMANTICS COLOR POINT VECTOR NORMAL TIMECODE KEYCODE RATIONAL

These names are also exported to the OpenImageIO namespace.

TypeUnknown TypeString TypeFloat TypeHalf
TypeInt TypeUInt TypeInt16 TypeUInt16
TypeColor TypePoint TypeVector TypeNormal
TypeFloat2 TypeVector2 TypeFloat4 TypeVector2i
TypeMatrix TypeMatrix33
TypeTimeCode TypeKeyCode TypeRational TypePointer

Pre-constructed TypeDesc objects for some common types, available in the outer OpenImageIO scope.

Example:

t = TypeFloat
str(typedesc)

Returns a string that describes the TypeDesc.

Example:

print (str(TypeDesc(oiio.UINT16)))

> int16
TypeDesc.basetype
TypeDesc.aggregate
TypeDesc.vecsemantics
TypeDesc.arraylen

Access to the raw fields in the TypeDesc.

Example:

t = TypeDesc(...)
if t.basetype == oiio.FLOAT :
    print ("It's made of floats")
int TypeDesc.size ()
int TypeDesc.basesize ()
TypeDesc TypeDesc.elementtype ()
int TypeDesc.numelements ()
int TypeDesc.elementsize ()

The size() is the size in bytes, of the type described. The basesize() is the size in bytes of the BASETYPE.

The elementtype() is the type of each array element, if it is an array, or just the full type if it is not an array. The elementsize() is the size, in bytes, of the elementtype (thus, returning the same value as size() if the type is not an array). The numelements() method returns arraylen if it is an array, or 1 if it is not an array.

Example:

t = TypeDesc("point[2]")
print "size =", t.size()
print ("elementtype =", t.elementtype())
print ("elementsize =", t.elementsize())

> size = 24
> elementtype = point
> elementsize = 12
typedesc == typedesc
typedesc != typedesc
TypeDesc.equivalent(typedesc)

Test for equality or inequality. The equivalent() method is more forgiving than ==, in that it considers POINT, VECTOR, and NORMAL vector semantics to not constitute a difference from one another.

Example:

f = TypeDesc("float")
p = TypeDesc("point")
v = TypeDesc("vector")
print ("float==point?", (f == p))
print ("vector==point?", (v == p))
print ("float.equivalent(point)?", f.equivalent(p))
print ("vector.equivalent(point)?", v.equivalent(p))

> float==point? False
> vector==point? False
> float.equivalent(point)? False
> vector.equivalent(point)? True

ROI

The ROI class that describes an image extent or region of interest, explained in deail in Section Rectangular region of interest: ROI, is replicated for Python.

ROI()
ROI(xbegin, xend, ybegin, yend, zbegin=0, zend=1, chbegin=0, chend=1000)

Construct an ROI with the given bounds. The constructor with no arguments makes an ROI that is “undefined.”

Example:

roi = ROI (0, 640, 0, 480, 0, 1, 0, 4)   # video res RGBA
ROI.xbegin
ROI.xend
ROI.ybegin
ROI.yend
ROI.zbegin
ROI.zend
ROI.chbegin
ROI.chend

The basic fields of the ROI (all of type int).

ROI.All

A pre-constructed undefined ROI understood to mean unlimited ROI on an image.

ROI.defined

True if the ROI is defined, False if the ROI is undefined.

ROI.width
ROI.height
ROI.depth
ROI.nchannels

The number of pixels in each dimension, and the number of channels, as described by the ROI. (All of type int.)

int ROI.npixels

The total number of pixels in the region described by the ROI (as an int).

ROI.contains(x, y, z=0, ch=0)

Returns True if the ROI contains the coordinate.

ROI.contains(other)

Returns True if the ROI other is entirel contained within this ROI.

ROI get_roi (imagespec)
ROI get_roi_full (imagespec)

Returns an ROI corresponding to the pixel data window of the given ImageSpec, or the display/full window, respectively.

Example:

spec = ImageSpec(...)
roi = oiio.get_roi(spec)
set_roi(imagespec, roi)
set_roi_full(imagespec, roi)

Alter the ImageSpec’s resolution and offset to match the passed ROI.

Example:

# spec is an ImageSpec
# The following sets the full (display) window to be equal to the
# pixel data window:
oiio.set_roi_full (spec, oiio.get_roi(spec))

ImageSpec

The ImageSpec class that describes an image, explained in deail in Section Image Specification: ImageSpec, is replicated for Python.

ImageSpec()
ImageSpec(typedesc)
ImageSpec(xres, yres, nchannels, typedesc)
ImageSpec(roi, typedesc)

Constructors of an ImageSpec. These correspond directly to the constructors in the C++ bindings.

Example:

import OpenImageIO as oiio
...

# default ctr
s = ImageSpec()

# construct with known pixel type, unknown resolution
s = ImageSpec(oiio.UINT8)

# construct with known resolution, channels, pixel data type
s = ImageSpec(640, 480, 4, "half")

# construct from an ROI
s = ImageSpec (ROI(0,640,0,480,0,1,0,3), TypeFloat)
ImageSpec.width, ImageSpec.height, ImageSpec.depth
ImageSpec.x, ImageSpec.y, ImageSpec.z

Resolution and offset of the image data (int values).

Example:

s = ImageSpec (...)
print ("Data window is ({},{})-({},{})".format (s.x, s.x+s.width-1,
                                                s.y, s.y+s.height-1))
ImageSpec.full_width, ImageSpec.full_height, ImageSpec.full_depth
ImageSpec.full_x, ImageSpec.full_y, ImageSpec.full_z

Resolution and offset of the “full” display window (int values).

ImageSpec.tile_width, ImageSpec.tile_height, ImageSpec.tile_depth

For tiled images, the resolution of the tiles (int values). Will be 0 for untiled images.

ImageSpec.format

A TypeDesc describing the pixel data.

ImageSpec.nchannels

An int giving the number of color channels in the image.

ImageSpec.channelnames

A tuple of strings containing the names of each color channel.

ImageSpec.channelformats

If all color channels have the same format, that will be ImageSpec.format, and channelformats will be None. However, if there are different formats per channel, they will be stored in channelformats as a tuple of TypeDesc objects.

Example:

if spec.channelformats == None:
    print ("All color channels are", str(spec.format))
else:
    print ("Channel formats: ")
    for t in spec.channelformats:
        print ("\t", t)
ImageSpec.alpha_channel
ImageSpec.z_channel

The channel index containing the alpha or depth channel, respectively, or -1 if either one does not exist or cannot be identified.

ImageSpec.deep

True if the image is a deep (multiple samples per pixel) image, of False if it is an ordinary image.

ImageSpec.extra_attribs

Direct access to the extra_attribs named metadata, appropriate for iterating over the entire list rather than searching for a particular named value.

  • len(extra_attribs) : Returns the number of extra attributes.

  • extra_attribs[i].name : The name of the indexed attribute.

  • extra_attribs[i].type : The type of the indexed attribute, as a TypeDesc.

  • extra_attribs[i].value : The value of the indexed attribute.

Example:

s = ImageSpec(...)
...
print ("extra_attribs size is", len(s.extra_attribs))
for i in range(len(s.extra_attribs)) :
    print (i, s.extra_attribs[i].name, str(s.extra_attribs[i].type), " :")
    print ("\t", s.extra_attribs[i].value)
print
Imagespec.roi

The ROI describing the pixel data window.

ImageSpec.roi_full

The ROI describing the “display window” (or “full size”).

ImageSpec.set_format(typedesc)

Given a TypeDesc, sets the format field and clear any per-channel formats in channelformats.

Example:

s = ImageSpec ()
s.set_format (TypeDesc("uint8"))
ImageSpec.default_channel_names()

Sets channel_names to the default names given the value of the nchannels field.

ImageSpec.channelindex(name)

Return (as an int) the index of the channel with the given name, or -1 if it does not exist.

ImageSpec.channel_bytes()

ImageSpec.channel_bytes (channel, native=False)} Returns the size of a single channel value, in bytes (as an int). (Analogous to the C++ member functions, see Section Image Specification: ImageSpec for details.)

ImageSpec.pixel_bytes()
ImageSpec.pixel_bytes(native=False)
ImageSpec.pixel_bytes(chbegin, chend, native=False)

Returns the size of a pixel, in bytes (as an int). (Analogous to the C++ member functions, see Section Image Specification: ImageSpec for details.)

ImageSpec.scanline_bytes(native=False)
ImageSpec.tile_bytes(native=False)
ImageSpec.image_bytes(native=False)

Returns the size of a scanline, tile, or the full image, in bytes (as an int). (Analogous to the C++ member functions, see Section Image Specification: ImageSpec for details.)

ImageSpec.tile_pixels()
ImageSpec.image_pixels()

Returns the number of pixels in a tile or the full image, respectively (as an int). (Analogous to the C++ member functions, see Section Image Specification: ImageSpec for details.)

ImageSpec.erase_attribute(name, searchtype=TypeUnknown, casesensitive=False)

Remove any specified attributes matching the regular expression name from the list of extra_attribs.

ImageSpec.attribute(name, int)
ImageSpec.attribute(name, float)
ImageSpec.attribute(name, string)
ImageSpec.attribute(name, typedesc, data)

Sets a metadata value in the extra_attribs. If the metadata item is a single int, float, or string, you can pass it directly. For other types, you must pass the TypeDesc and then the data (for aggregate types or arrays, pass multiple values as a tuple).

Example:

s = ImageSpec (...)
s.attribute ("foo_str", "blah")
s.attribute ("foo_int", 14)
s.attribute ("foo_float", 3.14)
s.attribute ("foo_vector", TypeDesc.TypeVector, (1, 0, 11))
s.attribute ("foo_matrix", TypeDesc.TypeMatrix,
             (1, 0, 0, 0, 0, 2, 0, 0, 0, 0, 1, 0, 1, 2, 3, 1))
ImageSpec.getattribute(name)
ImageSpec.getattribute(name, typedesc)

Retrieves a named metadata value from extra_attribs. The generic getattribute() function returns it regardless of type, or None if the attribute does not exist. The typed variety will only succeed if the attribute is actually of that type specified.

Example:

foo = s.getattribute ("foo")   # None if not found
foo = s.getattribute ("foo", oiio.FLOAT)  # None if not found AND float
ImageSpec.get_int_attribute(name, defaultval=0)
ImageSpec.get_float_attribute(name, defaultval=0.0)
ImageSpec.get_string_attribute(name, defaultval='')

Retrieves a named metadata value from extra_attribs, if it is found and is of the given type; returns the default value (or a passed value) if not found.

Example:

# If "foo" is not found, or if it's not an int, return 0
foo = s.get_int_attribute ("foo")

# If "foo" is not found, or if it's not a string, return "blah"
foo = s.get_string_attribute ("foo", "blah")
ImageSpec[key]

ImageSpec provides a Python dict-like interface for metadata, in addition to attribute() and getattribute().

The ImageSpec["key"] = value notation can be used to set an attribute (just like calling ImageSpec.attribute("key", value)). Also, ImageSpec["key"] can retrieve an attribute if it is present, or raise a KeyError exception if not found.

Like dictionaries, 'key' in spec is True if the attribute is present, and del spec['key'] will remove the attribute.

Examples:

# Same as: spec.attribute("Compression", comp)
spec["Compression"] = comp

# Same as:  comp = spec.getattribute("Compression")
# if it succeeds, or raises a KeyError if not found.
comp = spec["Compression"]

# Failed spec["key"] will raise a KeyError
try:
    r = spec["unknown"]
except:
    print("'unknown' key was not found")

# "key" in spec is True if the key is present
if "Compression" in spec:
    print("'Compression' metadata is present")

# del spec["key"] removes the key
del key["Compression"]

# ImageSpec.get("key") returns the value, or None if not found
comp = spec.get("Compression")
# and optionally, a default value may be passed
comp = spec.get("Compression", "none")

The basic ["key"] setting and retrieval was added in OpenImageIO in 2.1. The "key" in and del operators, and the get() method, were added in OpenImageIO 2.4.

ImageSpec.metadata_val(paramval, human=False)

For a ParamValue, format its value as a string.

ImageSpec.serialize(format='text', verbose='Detailed')

Return a string containing the serialization of the ImageSpec. The format may be either “text” or “XML”. The verbose may be one of “brief”, “detailed”, or “detailedhuman”.

ImageSpec.to_xml()

Equivalent to serialize("xml", "detailedhuman").

ImageSpec.from_xml(xml)

Initializes the ImageSpec from the information in the string xml containing an XML-serialized ImageSpec.

ImageSpec.channel_name(chan)

Returns a string containing the name of the channel with index chan.

ImageSpec.channelindex(name)

Return the integer index of the channel with the given name, or -1 if the name is not a name of one of the channels.

ImageSpec.channelformat(chan)

Returns a TypeDesc of the channel with index chan.

ImageSpec.get_channelformats()

Returns a tuple containing all the channel formats.

ImageSpec.valid_tile_range(xbegin, xend, ybegin, yend, zbegin, zend)

Returns True if the given tile range exactly covers a set of tiles, or False if it isn’t (or if the image is not tiled).

ImageSpec.copy_dimensions(other)

Copies from ImageSpec other only the fields describing the size and data types, but not the arbitrary named metadata or channel names.

ImageSpec.undefined()

Returns True for a newly initialized (undefined) ImageSpec.


Example: Header info

Here is an illustrative example of the use of ImageSpec, a working Python function that opens a file and prints all the relevant header information:

#!/usr/bin/env python
import OpenImageIO as oiio

# Print the contents of an ImageSpec
def print_imagespec (spec, subimage=0, mip=0) :
    if spec.depth <= 1 :
        print ("  resolution %dx%d%+d%+d" % (spec.width, spec.height, spec.x, spec.y))
    else :
        print ("  resolution %dx%d%x%d+d%+d%+d" %
               (spec.width, spec.height, spec.depth, spec.x, spec.y, spec.z))
    if (spec.width != spec.full_width or spec.height != spec.full_height
        or spec.depth != spec.full_depth) :
        if spec.full_depth <= 1 :
            print ("  full res   %dx%d%+d%+d" %
                   (spec.full_width, spec.full_height, spec.full_x, spec.full_y))
        else :
            print ("  full res   %dx%d%x%d+d%+d%+d" %
                   (spec.full_width, spec.full_height, spec.full_depth,
                    spec.full_x, spec.full_y, spec.full_z))
    if spec.tile_width :
        print ("  tile size  %dx%dx%d" %
               (spec.tile_width, spec.tile_height, spec.tile_depth))
    else :
        print "  untiled"
    if mip >= 1 :
        return
    print "  " + str(spec.nchannels), "channels:", spec.channelnames
    print "  format = ", str(spec.format)
    if len(spec.channelformats) > 0 :
        print "  channelformats = ", spec.channelformats
    print "  alpha channel = ", spec.alpha_channel
    print "  z channel = ", spec.z_channel
    print "  deep = ", spec.deep
    for i in spec.extra_attribs) :
        if type(i.value) == str :
            print " ", i.name, "= \"" + i.value + "\""
        else :
            print " ", i.name, "=", i.value


def poor_mans_iinfo (filename) :
    input = ImageInput.open (filename)
    if not input :
        print 'Could not open "' + filename + '"'
        print "\tError: ", oiio.geterror()
        return
    print 'Opened "' + filename + '" as a ' + input.format_name()
    sub = 0
    mip = 0
    while True :
        if sub > 0 or mip > 0 :
            print "Subimage", sub, "MIP level", mip, ":"
        print_imagespec (input.spec(), mip=mip)
        mip = mip + 1
        if input.seek_subimage (sub, mip) :
            continue    # proceed to next MIP level
        else :
            sub = sub + 1
            mip = 0
            if input.seek_subimage (sub, mip) :
                continue    # proceed to next subimage
        break  # no more MIP levels or subimages
    input.close ()

DeepData

The DeepData class describing “deep” image data (multiple depth sample per pixel), which is explained in deail in Section Reading “deep” data, is replicated for Python.

DeepData()

Constructs a DeepData object. It needs to have its init() and alloc() methods called before it can hold any meaningful data.

DeepData.init(npixels, nchannels, channeltypes, channelnames)

Initializes this DeepData to hold npixels total pixels, with nchannels color channels. The data types of the channels are described by channeltypes, a tuple of TypeDesc values (one per channel), and the names are provided in a tuple of string`s `channelnames. After calling init, you still need to set the number of samples for each pixel (using set_nsamples) and then call alloc() to actually allocate the sample memory.

DeepData.initialized()

Returns True if the DeepData is initialized at all.

DeepData.allocated()

Returns True if the DeepData has already had pixel memory allocated.

DeepData.pixels

This int field constains the total number of pixels in this collection of deep data.

DeepData.channels

This int field constains the number of channels.

DeepData.A_channel
DeepData.AR_channel
DeepData.AG_channel
DeepData.AB_channel
DeepData.Z_channel
DeepData.Zback_channel

The channel index of certain named channels, or -1 if they don’t exist. For AR_channel, AG_channel, AB_channel, if they don’t exist, they will contain the value of A_channel, and Zback_channel will contain the value of z_channel if there is no actual Zback.

DeepData.channelname(c)

Retrieve the name of channel C, as a string.

DeepData.channeltype(c)

Retrieve the data type of channel C, as a TypeDesc.

DeepData.channelsize(c)

Retrieve the size (in bytes) of one datum of channel C.

DeepData.samplesize()

Retrieve the packed size (in bytes) of all channels of one sample.

DeepData.set_samples(pixel, nsamples)

Set the number of samples for a given pixel (specified by integer index).

DeepData.samples(pixel)

Get the number of samples for a given pixel (specified by integer index).

DeepData.insert_samples(pixel, samplepos, n)

Insert n samples starting at the given position of an indexed pixel.

DeepData.erase_samples(pixel, samplepos, n)

Erase n samples starting at the given position of an indexed pixel.

DeepData.set_deep_value(pixel, channel, sample, value)

Set specific float value of a given pixel, channel, and sample index.

DeepData.set_deep_value_uint(pixel, channel, sample, value)

Set specific unsigned int value of a given pixel, channel, and sample index.

DeepData.deep_value(pixel, channel, sample, value)

Retrieve the specific value of a given pixel, channel, and sample index (for float channels.

DeepData.deep_value_uint(pixel, channel, sample)

Retrieve the specific value of a given pixel, channel, and sample index (for uint channels).

DeepData.copy_deep_sample(pixel, sample, src, srcpixel, srcsample)

Copy a deep sample from DeepData src into this DeepData.

DeepData.copy_deep_pixel(pixel, src, srcpixel)

Copy a deep pixel from DeepData src into this DeepData.

DeepData.split(pixel, depth)

Split any samples of the pixel that cross depth. Return True if any splits occurred, False if the pixel was unmodified.

DeepData.sort(pixel)

Sort the samples of the pixel by their Z depth.

DeepData.merge_overlaps(pixel)

Merge any adjacent samples in the pixel that exactly overlap in z range. This is only useful if the pixel has previously been split at all sample starts and ends, and sorted by depth.

DeepData.merge_deep_pixels(pixel, src, srcpixel)

Merge the samples of src’s pixel into this DeepData’s pixel.

DeepData.occlusion_cull(pixel)

Eliminate any samples beyond an opaque sample.

DeepData.opaque_z(pixel)

For the given pixel index. return the z value at which the pixel reaches full opacity.

ImageInput

See Chapter ImageInput: Reading Images for detailed explanations of the C++ ImageInput class APIs. The Python APIs are very similar. The biggest difference is that in C++, the various read_* functions write the pixel values into an already-allocated array that belongs to the caller, whereas the Python versions allocate and return an array holding the pixel values (or None if the read failed).

ImageInput.open(filename[, config_imagespec])

Creates an ImageInput object and opens the named file. Returns the open ImageInput upon success, or None if it failed to open the file (after which, OpenImageIO.geterror() will contain an error message). In the second form, the optional ImageSpec argument config contains attributes that may set certain options when opening the file.

Example:

input = ImageInput.open ("tahoe.jpg")
if input == None :
    print "Error:", oiio.geterror()
    return
ImageInput.close()

Closes an open image file, returning True if successful, False otherwise.

Example:

input = ImageInput.open (filename)
...
input.close ()
ImageInput.format_name()

Returns the format name of the open file, as a string.

Example:

input = ImageInput.open (filename)
if input :
    print filename, "was a", input.format_name(), "file."
    input.close ()
ImageInput.spec()

Returns an ImageSpec corresponding to the currently open subimage and MIP level of the file.

Example:

input = ImageInput.open (filename)
spec = input.spec()
print "resolution ", spec.width, "x", spec.height
ImageInput.spec(subimage, miplevel=0)

Returns a full copy of the ImageSpec corresponding to the designated subimage and MIP level.

ImageSpec ImageInput.spec_dimensions (subimage, miplevel=0)

Returns a partial copy of the ImageSpec corresponding to the designated subimage and MIP level, only copying the dimension fields and not any of the arbitrary named metadata (and is thus much less expensive).

ImageInput.current_subimage()

Returns the current subimage of the file.

ImageInput.current_miplevel()

Returns the current MIP level of the file.

ImageInput.seek_subimage(subimage, miplevel)

Repositions the file pointer to the given subimage and MIP level within the file (starting with 0). This function returns True upon success, False upon failure (which may include the file not having the specified subimage or MIP level).

Example:

input = ImageInput.open (filename)
mip = 0
while True :
    ok = input.seek_subimage (0, mip)
    if not ok :
        break
    spec = input.spec()
    print "MIP level", mip, "is", spec.width, "x", spec.height
ImageInput.read_image(format='float')
ImageInput.read_image(chbegin, chend, format='float')
ImageInput.read_image(subimage, miplevel, chbegin, chend, format='float')

Read the entire image and return the pixels as a NumPy array of values of the given format (described by a TypeDesc or a string, float by default). If the format is unknown, the pixels will be returned in the native format of the file. If an error occurs, None will be returned.

For a normal (2D) image, the array returned will be 3D indexed as [y][x][channel]. For 3D volumetric images, the array returned will be 4D with shape indexed as [z][y][x][channel].

Example:

input = ImageInput.open (filename)
spec = input.spec ()
pixels = input.read_image ()
print "The first pixel is", pixels[0][0]
print "The second pixel is", pixels[0][1]
input.close ()
ImageInput.read_scanline(y, z, format='float')

Read scanline number y from depth plane z from the open file, returning the pixels as a NumPy array of values of the given type (described by a TypeDesc or a string, float by default). If the type is TypeUnknown, the pixels will be returned in the native format of the file. If an error occurs, None will be returned.

The pixel array returned will be a 2D ndarray, indexed as [x][channel].

Example:

input = ImageInput.open (filename)
spec = input.spec ()
if spec.tile_width == 0 :
    for y in range(spec.y, spec.y+spec.height) :
        pixels = input.read_scanline (y, spec.z, "float")
        # process the scanline
else :
    print "It's a tiled file"
input.close ()
ImageInput.read_tile(x, y, z, format='float')

Read the tile whose upper left corner is pixel (x,y,z) from the open file, returning the pixels as a NumPy array of values of the given type (described by a TypeDesc or a string, float by default). If the type is TypeUnknown, the pixels will be returned in the native format of the file. If an error occurs, None will be returned.

For a normal (2D) image, the array of tile pixels returned will be a 3D ndarray indexed as [y][x][channel]. For 3D volumetric images, the array returned will be 4D with shape indexed as [z][y][x][channel].

Example:

input = ImageInput.open (filename)
spec = input.spec ()
if spec.tile_width > 0 :
    for z in range(spec.z, spec.z+spec.depth, spec.tile_depth) :
        for y in range(spec.y, spec.y+spec.height, spec.tile_height) :
            for x in range(spec.x, spec.x+spec.width, spec.tile_width) :
                pixels = input.read_tile (x, y, z, oiio.FLOAT)
                # process the tile
else :
    print "It's a scanline file"
input.close ()
ImageInput.read_scanlines(subimage, miplevel, ybegin, yend, z, chbegin, chend, format='float')
ImageInput.read_scanlines(ybegin, yend, z, chbegin, chend, format='float')
ImageInput.read_tiles(xbegin, xend, ybegin, yend, zbegin, zend, chbegin, chend, format='float')
ImageInput.read_tiles(subimage, miplevel, xbegin, xend, ybegin, yend, zbegin, zend, format='float')

Similar to the C++ routines, these functions read multiple scanlines or tiles at once, which in some cases may be more efficient than reading each scanline or tile separately. Additionally, they allow you to read only a subset of channels.

For normal 2D images, both read_scanlines and read_tiles will return a 3D array indexed as [z][y][x][channel].

For 3D volumetric images, both read_scanlines will return a 3D array indexed as [y][x][channel], and read_tiles will return a 4D array indexed as [z][y][x][channel],

Example:

input = ImageInput.open (filename)
spec = input.spec ()

# Read the whole image, the equivalent of
#     pixels = input.read_image (type)
# but do it using read_scanlines or read_tiles:
if spec.tile_width == 0 :
    pixels = input.read_scanlines (spec.y, spec.y+spec.height, 0,
                                   0, spec.nchannels)
else :
    pixels = input.read_tiles (spec.x, spec.x+spec.width,
                               spec.y, spec.y+spec.height,
                               spec.z, spec.z+spec.depth,
                               0, spec.nchannels)
ImageInput.read_native_deep_scanlines(subimage, miplevel, ybegin, yend, z, chbegin, chend)
ImageInput.read_native_deep_tiles(subimage, miplevel, xbegin, xend, ybegin, yend, zbegin, zend, chbegin, chend)
ImageInput.read_native_deep_image(subimage=0, miplevel=0)

Read a collection of scanlines, tiles, or an entire image of “deep” pixel data from the specified subimage and MIP level. The begin/end coordinates are all integer values. The value returned will be a DeepData if the read succeeds, or None if the read fails.

These methods are guaranteed to be thread-safe against simultaneous calls to any of the other other read_native calls that take an explicit subimage/miplevel.

ImageOutput.get_thumbnail(subimage: int = 0) → ImageBuf

Retrieve an ImageBuf containing reduced-resolution(“thumbnail”) version of the image. If no thumbnail could be retrieved, an empty ImageBuf will be returned.

ImageInput.geterror(clear=True)

Retrieves the error message from the latest failed operation on an ImageInput.

Example:

input = ImageInput.open (filename)
if not input :
    print "Open error:", oiio.geterror()
    # N.B. error on open must be retrieved with the global geterror(),
    # since there is no ImageInput object!
else :
    pixels = input.read_image (oiio.FLOAT)
    if not pixels :
        print "Read_image error:", input.geterror()
    input.close ()

Example: Reading pixel values from a file to find min/max

#!/usr/bin/env python
import OpenImageIO as oiio

def find_min_max (filename) :
    input = ImageInput.open (filename)
    if not input :
        print 'Could not open "' + filename + '"'
        print "\tError: ", oiio.geterror()
        return
    spec = input.spec()
    nchans = spec.nchannels
    pixels = input.read_image()
    if not pixels :
        print "Could not read:", input.geterror()
        return
    input.close()    # we're done with the file at this point
    minval = pixels[0][0]   # initialize to the first pixel value
    maxval = pixels[0][0]
    for y in range(spec.height) :
        for x in range(spec.width) :
            p = pixels[y][x]
            for c in range(nchans) :
                if p[c] < minval[c] :
                    minval[c] = p[c]
                if p[c] > maxval[c] :
                    maxval[c] = p[c]
    print "Min values per channel were", minval
    print "Max values per channel were", maxval

ImageOutput

See Chapter ImageOutput: Writing Images for detailed explanations of the C++ ImageOutput class APIs. The Python APIs are very similar.

ImageOutput.create(name, plugin_searchpath='')

Create a new ImageOutput capable of writing the named file format (which may also be a file name, with the type deduced from the extension). There is an optional parameter giving an colon-separated search path for finding ImageOutput plugins. The function returns an ImageOutput object, or None upon error (in which case, OpenImageIO.geterror() may be used to retrieve the error message).

Example:

import OpenImageIO as oiio
output = ImageOutput.create ("myfile.tif")
if not output :
    print "Error:", oiio.geterror()
ImageOutput.format_name()

The file format name of a created ImageOutput, as a string.

Example:

output = ImageOutput.create (filename)
if output :
    print "Created output", filename, "as a", output.format_name()
ImageOutput.supports(feature)

For a created ImageOutput, returns True if the file format supports the named feature (such as “tiles”, “mipmap”, etc., see Section ImageOutput Class Reference for the full list), or False if this file format does not support the feature.

Example:

output = ImageOutput.create (filename)
if output :
    print output.format_name(), "supports..."
    print "tiles?", output.supports("tiles")
    print "multi-image?", output.supports("multiimage")
    print "MIP maps?", output.supports("mipmap")
    print "per-channel formats?", output.supports("channelformats")
ImageOutput.open(filename, spec, mode='Create')

Opens the named output file, with an ImageSpec describing the image to be output. The mode may be one of “Create”, “AppendSubimage”, or “AppendMIPLevel”. See Section ImageOutput Class Reference for details. Returns True upon success, False upon failure (error messages retrieved via ImageOutput.geterror().)

Returns

True for success, False for failure.

Example:

output = ImageOutput.create (filename)
if not output :
    print "Error:", oiio.geterror()
spec = ImageSpec (640, 480, 3, "uint8")
ok = output.open (filename, spec)
if not ok :
    print "Could not open", filename, ":", output.geterror()
ImageOutput.open(filename, (imagespec, ...))

This variety of open() is used specifically for multi-subimage files. A tuple of ImageSpec objects is passed, one for each subimage that will be written to the file. After each subimage is written, then a regular call to open(name, newspec, AppendSubimage) moves on to the next subimage.

Returns

True for success, False for failure.

ImageOutput.close()

Closes an open output.

Returns

True for success, False for failure.

ImageOutput.spec()

Returns the ImageSpec of the currently-open output image.

ImageOutput.write_image(pixels)

Write the currently opened image all at once. The pixels parameter should be a Numpy ndarray containing data elements indexed as [y][x][channel] for normal 2D images, or for 3D volumetric images, as [z][y][x][channel], in other words, exactly matching the shape of array returned by ImageInput.read_image(). (It will also work fine if the array is 1D “flattened” version, as long as it contains the correct total number of values.) The data type is deduced from the contents of the array itself. Returns True upon success, False upon failure.

Example:

# This example reads a scanline file, then converts it to tiled
# and writes to the same name.

input = ImageInput.open (filename)
spec = input.spec ()
pixels = input.read_image ()
input.close ()

output = ImageOutput.create (filename)
if output.supports("tiles") :
    spec.tile_width = 64
    spec.tile_height = 64
    output.open (filename, spec)
    output.write_image (pixels)
    output.close ()
ImageOutput.write_scanline(y, z, pixels)
ImageOutput.write_scanlines(ybegin, yend, z, pixels)

Write one or many scanlines to the currently open file. Returns True upon success, False upon failure.

The pixels parameter should be a Numpy ndarray containing data elements indexed as [x][channel] for write_scanline or as [y][x][channels for write_scanlines, exactly matching the shape returned by ImageInput.read_scanline or ImageInput.read_scanlines. (It will also work fine if the array is 1D “flattened” version, as long as it contains the correct total number of values.)

Example:

# Copy a TIFF image to JPEG by copying scanline by scanline.
input = ImageInput.open ("in.tif")
spec = input.spec ()
output = ImageOutput.create ("out.jpg")
output.open (filename, spec)
for z in range(spec.z, spec.z+spec.depth) :
    for y in range(spec.y, spec.y+spec.height) :
        pixels = input.read_scanline (y, z)
        output.write_scanline (y, z, pixels)
output.close ()
input.close ()

# The same example, but copying a whole "plane" of scanlines at a time:
...
for z in range(spec.z, spec.z+spec.depth) :
    pixels = input.read_scanlines (spec.y, spec.y+spec.height, z)
    output.write_scanlines (spec.y, spec.y+spec.height, z, pixels)
...
ImageOutput.write_tile(x, y, z, pixels)
ImageOutput.write_tiles(xbegin, xend, ybegin, yend, zbegin, zend, pixels)

Write one or many tiles to the currently open file. Returns True upon success, False upon failure.

The pixels parameter should be a Numpy ndarray containing data elements indexed as [y][x][channel] for normal 2D images, or as [z][y][x][channels 3D volumetric images, exactly matching the shape returned by ImageInput.read_tile or ImageInput.read_tiles. (It will also work fine if the array is 1D “flattened” version, as long as it contains the correct total number of values.)

Example:

input = ImageInput.open (in_filename)
spec = input.spec ()
output = ImageOutput.create (out_filename)
output.open (out_filename, spec)
for z in range(spec.z, spec.z+spec.depth, spec.tile_depth) :
    for y in range(spec.y, spec.y+spec.height, spec.tile_height) :
        for x in range(spec.x, spec.x+spec.width, spec.tile_width) :
            pixels = input.read_tile (x, y, z)
            output.write_tile (x, y, z, pixels)
output.close ()
input.close ()

# The same example, but copying a whole row of of tiles at a time:
...
for z in range(spec.z, spec.z+spec.depth, spec.tile_depth) :
    for y in range(spec.y, spec.y+spec.height, spec.tile_height) :
        pixels = input.read_tiles (spec.x, spec.x+spec.width,
                                   y, y+tile_width, z, z+tile_width)
        output.write_tiles (spec.x, spec.x+spec.width,
                            y, y+tile_width, z, z+tile_width, pixels)
...
ImageOutput.write_deep_scanlinesa(ybegin, yend, z, deepdata)
ImageOutput.write_deep_tiles(xbegin, xend, ybegin, yend, zbegin, zend, deepdata)
ImageOutput.write_deep_image(deepdata)

Write a collection of scanlines, tiles, or an entire image of “deep” pixel data. The begin/end coordinates are all integer values, and deepdata should be a DeepData.

ImageOutput.set_thumbnail(thumb: ImageBuf)

Specify a reduced-resolution (“thumbnail”) version of the image, as an ImageBuf. Note that many image formats may require the thumbnail to be specified prior to writing the pixels. Return True for success, or False if a thumbnail could not be set.

ImageOutput.copy_image(imageinput)

Copy the current image of the open input to the open output. (The reason this may be preferred in some circumstances is that, if input and output were the same kind of input file format, they may have a special efficient technique to copy pixels unaltered, for example by avoiding the decompression/recompression round trip.)

Example:

input = ImageInput.open (in_filename)
spec = input.spec ()
output = ImageOutput.create (out_filename)
output.open (filename, spec)
output.copy_image (input)
output.close ()
input.close ()
ImageOuput.geterror(clear=True)

Retrieves the error message from the latest failed operation on an open file.

Example:

output = ImageOutput.create (filename)
if not output :
    print "Create error:", oiio.geterror()
    # N.B. error on create must be retrieved with the global geterror(),
    # since there is no ImageOutput object!
else :
    ok = output.open (filename, spec)
    if not ok :
        print "Open error:", output.geterror()
    ok = output.write_image (pixels)
    if not ok :
        print "Write error:", output.geterror()
    output.close ()

ImageBuf

See Chapter ImageBuf: Image Buffers for detailed explanations of the C++ ImageBuf class APIs. The Python APIs are very similar.

ImageBuf()

Construct a new, empty ImageBuf. The ImageBuf is uninitialized and is awaiting a call to reset() or copy() before it is useful.

ImageBuf(filename[, subimage, miplevel])

Construct a read-only ImageBuf that will read from the named file. Optionally, a specific subimage or MIP level may be specified (defaulting to 0).

Example:

import OpenImageIO as oiio
...
buf = ImageBuf ("grid.tif")
ImageBuf(filename, subimage, miplevel, config)

Construct a read-only ImageBuf that will read from the named file, with an ImageSpec config giving configuration hints.

Example:

import OpenImageIO as oiio
...
config = ImageSpec()
config.attribute("oiio:RawColor", 1)
buf = ImageBuf ("grid.tif", 0, 0, config)
ImageBuf(imagespec, zero=True)

Construct a writable ImageBuf of the dimensions and data format specified by an ImageSpec. The pixels will be initialized to black/empty values if zero is True, otherwise the pixel values will remain uninitialized.

Example:

spec = ImageSpec (640, 480, 3, "float")
buf = ImageBuf (spec)
ImageBuf(data)

Construct a writable ImageBuf of the dimensions of data, which is a NumPy ndarray of values indexed as [y][x][channel] for normal 2D images, or for 3D volumetric images, as [z][y][x][channel]. The data will be copied into the ImageBuf’s internal storage. The NumPy array may be strided for z, y, or x, but must have “contiguous” channel data within each pixel. The pixel data type is also deduced from the contents of the data array.

Note that this Python ImageBuf will contain its own copy of the data, so further changes to the data array will not affect the ImageBuf. This is different from the C++ ImageBuf constructor from a pointer, which will “wrap” the existing user-provided buffer but not make its own copy.

Example:

pixels = numpy.zeros ((640, 480, 3), dtype = numpy.float32)
buf = ImageBuf (pixels)
ImageBuf.clear()

Resets the ImageBuf to a pristine state identical to that of a freshly constructed ImageBuf using the default constructor.

Example:

buf = ImageBuf (...)

# The following two commands are equivalent:
buf = ImageBuf()     # 1 - assign a new blank ImageBuf
buf.clear()          # 2 - clear the existing ImageBuf
ImageBuf.reset(filename, subimage=0, miplevel=0, config=ImageSpec())

Restore the ImageBuf to a newly-constructed state, to read from a filename (optionally specifying a subimage, MIP level, and/or a “configuration” ImageSpec).

ImageBuf.reset(imagespec, zero=True)

Restore the ImageBuf to the newly-constructed state of a writable ImageBuf specified by an ImageSpec. The pixels will be iniialized to black/empty if zero is True, otherwise the pixel values will remain uninitialized.

ImageBuf.reset(data)

Reset the ImageBuf to be sized to the dimensions of data, which is a NumPy ndarray of values indexed as [y][x][channel] for normal 2D images, or for 3D volumetric images, as [z][y][x][channel]. The data will be copied into the ImageBuf’s internal storage. The NumPy array may be strided for z, y, or x, but must have “contiguous” channel data within each pixel. The pixel data type is also deduced from the contents of the data array.

Note that this Python ImageBuf will contain its own copy of the data, so further changes to the data array will not affect the ImageBuf. This is different from the C++ ImageBuf constructor from a pointer, which will “wrap” the existing user-provided buffer but not make its own copy.

ImageBuf.read(subimage=0, miplevel=0, force=False, convert=oiio.UNKNOWN)
ImageBuf.read(subimage, miplevel, chbegin, chend, force, convert)

Explicitly read the image from the file (of a file-reading ImageBuf), optionally specifying a particular subimage, MIP level, and channel range. If force is True, will force an allocation of memory and a full read (versus the default of relying on an underlying ImageCache). If convert is not the default of`UNKNOWN`, it will force the ImageBuf to convert the image to the specified data format (versus keeping it in the native format or relying on the ImageCache to make a data formatting decision).

Note that a call to read() is not necessary — any ImageBuf API call that accesses pixel values will trigger a file read if it has not yet been done. An explicit read() is generally only needed to change the subimage or miplevel, or to force an in-buffer read or format conversion.

The read() method will return True for success, or False if the read could not be performed (in which case, a geterror() call will retrieve the specific error message).

Example:

buf = ImageBuf ("mytexture.exr")
buf.read (0, 2, True)
# That forces an allocation and read of MIP level 2
ImageBuf.init_spec(filename, subimage=0, miplevel=0)

Explicitly read just the header from a file-reading ImageBuf (if the header has not yet been read), optionally specifying a particular subimage and MIP level. The init_spec() method will return True for success, or False if the read could not be performed (in which case, a geterror() call will retrieve the specific error message).

Note that a call to init_spec() is not necessary — any ImageBuf API call that accesses the spec will read it automatically it has not yet been done.

ImageBuf.write(filename, dtype='', fileformat='')

Write the contents of the ImageBuf to the named file. Optionally, dtype can override the pixel data type (by default, the pixel data type of the buffer), and fileformat can specify a particular file format to use (by default, it will infer it from the extension of the file name).

Example:

# No-frills conversion of a TIFF file to JPEG
buf = ImageBuf ("in.tif")
buf.write ("out.jpg")

# Convert to uint16 TIFF
buf = ImageBuf ("in.exr")
buf.write ("out.tif", "uint16")
ImageBuf.write(imageoutput)

Write the contents of the ImageBuf as the next subimage to an open ImageOutput.

Example:

buf = ImageBuf (...)   # Existing ImageBuf

out = ImageOutput.create("out.exr")
out.open ("out.exr", buf.spec())

buf.write (out)
out.close()
ImageBuf.make_writable(keep_cache_type=False)

Force the ImageBuf to be writable. That means that if it was previously backed by an ImageCache (storage was IMAGECACHE), it will force a full read so that the whole image is in local memory.

ImageBuf.set_write_format(format=oiio.UNKNOWN)
ImageBuf.set_write_tiles(width=0, height=0, depth=0)

Override the data format or tile size in a subsequent call to write(). The format argument to set_write_format may be either a single data type description for all channels, or a tuple giving the data type for each channel in order.

Example:

# Conversion to a tiled unsigned 16 bit integer file
buf = ImageBuf ("in.tif")
buf.set_write_format ("uint16")
buf.set_write_tiles (64, 64)
buf.write ("out.tif")
ImageBuf.spec()
ImageBuf.nativespec()

ImageBuf.spec() returns the ImageSpec that describes the contents of the ImageBuf. ImageBuf.nativespec() returns an ImageSpec that describes the contents of the file that the ImageBuf was read from (this may differ from ImageBuf.spec() due to format conversions, or any changes made to the ImageBuf after the file was read, such as adding metadata).

Handy rule of thumb: spec() describes the buffer, nativespec() describes the original file it came from.

Example:

buf = ImageBuf ("in.tif")
print "Resolution is", buf.spec().width, "x", buf.spec().height
ImageBuf.specmod()

ImageBuf.specmod() provides a reference to the writable ImageSpec inside the ImageBuf. Be very careful! It is safe to modify certain metadata, but if you change the data format or resolution fields, you will get the chaos you deserve.

Example:

# Read an image, add a caption metadata, write it back out in place
buf = ImageBuf ("file.tif")
buf.specmod().attribute ("ImageDescription", "my photo")
buf.write ("file.tif")
ImageBuf.has_thumbnail

Contains True if the ImageBuf contains thumbnail data, otherwise False.

ImageBuf.clear_thumbnail()

Remove any associated thumbnail from this buffer.

ImageBuf.set_thumbnail(thumb: ImageBuf)

Set the thumbnai associated with this buffer to thumb.

ImageBuf.thumbnail() → ImageBuf

Return an ImageBuf holding any thumbnail associated with this buffer.

ImageBuf.name

The file name of the image (as a string).

ImageBuf.file_format_name

The file format of the image (as a string).

ImageBuf.subimage
ImageBuf.miplevel
ImageBuf.nsubimages
ImageBuf.nmiplevels

Several fields giving information about the current subimage and MIP level, and the total numbers thereof in the file.

ImageBuf.xbegin
ImageBuf.xend
ImageBuf.ybegin
ImageBuf.yend
ImageBuf.zbegin
ImageBuf.zend

The range of valid pixel data window. Remember that the end is one past the last pixel.

ImageBuf.xmin
ImageBuf.xmax
ImageBuf.ymin
ImageBuf.ymax
ImageBuf.zmin
ImageBuf.zmax

The minimum and maximum (inclusive) coordinates of the pixel data window.

ImageBuf.orientation
ImageBuf.oriented_width
ImageBuf.oriented_height
ImageBuf.oriented_x
ImageBuf.oriented_y
ImageBuf.oriented_full_width
ImageBuf.oriented_full_height
ImageBuf.oriented_full_x
ImageBuf.oriented_full_y

The Orientation field gives the suggested display oriententation of the image (see Section Display hints).

The other fields are helpers that give the width, height, and origin (as well as “full” or “display” resolution and origin), taking the intended orientation into consideration.

ImageBuf.roi
ImageBuf.roi_full

These fields hold an ROI description of the pixel data window (roi) and the full (a.k.a. “display”) window (roi_full).

Example:

buf = ImageBuf ("tahoe.jpg")
print "Resolution is", buf.roi.width, "x", buf.roi.height
ImageBuf.set_origin(x, y, z=0)

Changes the “origin” of the data pixel data window to the specified coordinates.

Example:

# Shift the pixel data so the upper left is at pixel (10, 10)
buf.set_origin (10, 10)
ImageBuf.set_full(xbegin, xend, ybegin, yend, zbegin, zend)

Changes the “full” (a.k.a. “display”) window to the specified ROI.

Example:

buf.set_full (0, 1024, 0, 768, 0, 1)
ImageBuf.pixels_valid

Will be True if the file has already been read and the pixels are valid. (It is always True for writable ImageBuf’s.) There should be few good reasons to access these, since the spec and pixels will be automatically be read when they are needed.

ImageBuf.pixeltype()

Returns a TypeDesc describing the data type of the pixels stored within the ImageBuf.

ImageBuf.copy_metadata(other_imagebuf)

Replaces the metadata (all ImageSpec items, except for the data format and pixel data window size) with the corresponding metadata from the other ImageBuf.

ImageBuf.copy_pixels(other_imagebuf)

Replace the pixels in this ImageBuf with the values from the other ImageBuf.

ImageBuf ImageBuf.copy (format=TypeUnknown)

Return a full copy of this ImageBuf (with optional data format conversion, if format is supplied).

Example:

A = ImageBuf("A.tif")

# Make a separate, duplicate copy of A
B = A.copy()

# Make another copy of A, but converting to float pixels
C = A.copy ("float")
ImageBuf.copy(other_imagebuf, format=TypeUnknown)

Make this ImageBuf a complete copy of the other ImageBuf. If a format is provided, this will get the specified pixel data type rather than using the same pixel format as the source ImageBuf.

Example:

A = ImageBuf("A.tif")

# Make a separate, duplicate copy of A
B = ImageBuf()
B.copy (A)

# Make another copy of A, but converting to float pixels
C = ImageBuf()
C.copy (A, oiio.FLOAT)
ImageBuf.swap(other_imagebuf)

Swaps the content of this ImageBuf and the other ImageBuf.

Example:

A = ImageBuf("A.tif")
B = ImageBuf("B.tif")
A.swap (B)
# Now B contains the "A.tif" image and A contains the "B.tif" image
tuple ImageBuf.getpixel (x, y, z=0, wrap="black")

Retrieves pixel (x,y,z) from the buffer and return it as a tuple of float values, one for each color channel. The x, y, z values are int pixel coordinates. The optional wrap parameter describes what should happen if the coordinates are outside the pixel data window (and may be: “black”, “clamp”, “periodic”, “mirror”).

Example:

buf = ImageBuf ("tahoe.jpg")
p = buf.getpixel (50, 50)
print p

> (0.37, 0.615, 0.97)
ImageBuf.getchannel(x, y, z, channel, wrap='black')

Retrieves just a single channel value from pixel (x,y,z) from the buffer and returns it as a float value. The optional wrap parameter describes what should happen if the coordinates are outside the pixel data window (and may be: “black”, “clamp”, “periodic”, “mirror”).

Example:

buf = ImageBuf ("tahoe.jpg")
green = buf.getchannel (50, 50, 0, 1)
ImageBuf.interppixel(x, y, wrap='black')
ImageBuf.interppixel_bicubic(x, y, wrap='black')

Interpolates the image value (bilinearly or bicubically) at coordinates $(x,y)$ and return it as a tuple of float values, one for each color channel. The x, y values are continuous float coordinates in “pixel space.” The optional wrap parameter describes what should happen if the coordinates are outside the pixel data window (and may be: “black”, “clamp”, “periodic”, “mirror”).

Example:

buf = ImageBuf ("tahoe.jpg")
midx = float(buf.xbegin + buf.xend) / 2.0
midy = float(buf.ybegin + buf.yend) / 2.0
p = buf.interpixel (midx, midy)
# Now p is the interpolated value from right in the center of
# the data window
ImageBuf.interppixel_NDC(x, y, wrap='black')
ImageBuf.interppixel_bicubic_NDC(x, y, wrap='black')

Interpolates the image value (bilinearly or bicubically) at coordinates (x,y) and return it as a tuple of float values, one for each color channel. The x, y values are continuous, normalized float coordinates in “NDC space,”” where (0,0) is the upper left corner of the full (a.k.a. “display”) window, and (1,1) is the lower right corner of the full/display window. The wrap parameter describes what should happen if the coordinates are outside the pixel data window (and may be: “black”, “clamp”, “periodic”, “mirror”).

Example:

buf = ImageBuf ("tahoe.jpg")
p = buf.interpixel_NDC (0.5, 0.5)
# Now p is the interpolated value from right in the center of
# the display window
ImageBuf.setpixel(x, y, pixel_value)
ImageBuf.setpixel(x, y, z, pixel_value)

Sets pixel (x,y,z) to be the pixel_value, expressed as a tuple of float (one for each color channel).

Example:

buf = ImageBuf (ImageSpec (640, 480, 3, oiio.UINT8))

# Set the whole image to red (the dumb slow way, but it works):
for y in range(buf.ybegin, buf.yend) :
    for x in range(buf.xbegin, buf.xend) :
        buf.setpixel (x, y, (1.0, 0.0, 0.0))
ImageBuf.get_pixels(format=TypeFloat, roi=ROI.All)

Retrieves the rectangle of pixels (and channels) specified by roi from the image and returns them as an array of values with type specified by format.

As with the ImageInput read functions, the return value is a NumPy ndarray containing data elements indexed as [y][x][channel] for normal 2D images, or for 3D volumetric images, as [z][y][x][channel]). Returns True upon success, False upon failure.

Example:

buf = ImageBuf ("tahoe.jpg")
pixels = buf.get_pixels (oiio.FLOAT)  # no ROI means the whole image
ImageBuf.set_pixels(roi, data)

Sets the rectangle of pixels (and channels) specified by roi with values in the data, which is a NumPy ndarray of values indexed as [y][x][channel] for normal 2D images, or for 3D volumetric images, as [z][y][x][channel]. (It will also work fine if the array is 1D “flattened” version, as long as it contains the correct total number of values.) The data type is deduced from the contents of the array itself.

Example:

buf = ImageBuf (...)
pixels = (....)
buf.set_pixels (ROI(), pixels)
ImageBuf.has_error

This field will be True if an error has occurred in the ImageBuf.

ImageBuf.geterror(clear=True)

Retrieve the error message (and clear the has_error flag).

Example:

buf = ImageBuf ("in.tif")
buf.read ()   # force a read
if buf.has_error :
    print "Error reading the file:", buf.geterror()
buf.write ("out.jpg")
if buf.has_error :
    print "Could not convert the file:", buf.geterror()
ImageBuf.pixelindex(x, y, z, check_range=False)

Return the index of pixel (x,y,z).

ImageBuf.deep

Will be True if the file contains “deep” pixel data, or False for an ordinary images.

ImageBuf.deep_samples(x, y, z=0)

Return the number of deep samples for pixel (x,y,z).

ImageBuf.set_deep_samples(x, y, z, nsamples)

Set the number of deep samples for pixel (x,y,z).

ImageBuf.deep_insert_samples(x, y, z, samplepos, nsamples)
ImageBuf.deep_erase_samples(x, y, z, samplepos, nsamples)

Insert or erase nsamples samples starting at the given position of pixel (x,y,z).

ImageBuf.deep_value(x, y, z, channel, sample)
ImageBuf.deep_value_uint(x, y, z, channel, sample)

Return the value of the given deep sample (particular pixel, channel, and sample number) for a channel that is a float or an unsigned integer type, respectively.

ImageBuf.set_deep_value(x, y, z, channel, sample, value)
ImageBuf.set_deep_value_uint(x, y, z, channel, sample, value)

Set the value of the given deep sample (particular pixel, channel, and sample number) for a channel that is a float or an unsigned integer type, respectively.

DeepData ImageBuf.deepdata

A reference to the underlying DeepData of the image.


ImageBufAlgo

The C++ ImageBufAlgo functions are described in detail in Chapter ImageBufAlgo: Image Processing. They are also exposed to Python. For the majority of ImageBufAlgo functions, their use in Python is identical to C++; in those cases, we will keep our descriptions of the Python bindings minimal and refer you to Chapter ImageBufAlgo: Image Processing, saving the extended descriptions for those functions that differ from the C++ counterparts.

A few things about the paramters of the ImageBufAlgo function calls are identical among the functions, so we will explain once here rather than separately for each function:

  • dst is an existing ImageBuf, which will be modified (it may be an uninitialized ImageBuf, but it must be an ImageBuf).

  • src parameter is an initialized ImageBuf, which will not be modified (unless it happens to refer to the same image as dst.

  • roi, if supplied, is an roi specifying a region of interst over which to operate. If omitted, the region will be the entire size of the source image(s).

  • nthreads is the maximum number of threads to use. If not supplied, it defaults to 0, meaning to use as many threads as hardware cores available.

Just as with the C++ ImageBufAlgo functions, if dst is an uninitialized ImageBuf, it will be sized to reflect the roi (which, in turn, if undefined, will be sized to be the union of the ROI’s of the source images).

Pattern generation

ImageBuf ImageBufAlgo.zero (roi, nthreads=0)
ImageBufAlgo.zero(dst, roi=ROI.All, nthreads=0)

Zero out the destination buffer (or a specific region of it).

Example:

# Initialize buf to a 640x480 3-channel FLOAT buffer of 0 values
buf = ImageBufAlgo.zero (ROI(0, 640, 0, 480, 0, 1, 0, 3))
ImageBuf ImageBufAlgo.fill (values, roi=ROI.All, nthreads=0)
ImageBuf ImageBufAlgo.fill (top, bottom, roi=ROI.All, nthreads=0)
ImageBuf ImageBufAlgo.fill (topleft, topright, bottomleft, bottomright, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.fill (dst, values, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.fill (dst, top, bottom, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.fill (dst, topleft, topright, bottomleft, bottomright, roi=ROI.All, nthreads=0)

Return a filled float image of size roi, or set the the pixels of image dst within the ROI to a color or gradient.

Three fill optins are available: (a) if one color tuple is supplied, the whole ROI will be filled with that constant value, (b) if two color tuples are supplied, a linear gradient will be applied from top to bottom, (c) if four color cuples are supplied, the ROI will be be filled with values bilinearly interpolated from the four corner colors supplied.

Example:

# Draw a red rectangle into buf
buf = ImageBuf (ImageSpec(640, 480, 3, TypeDesc.FLOAT)
ImageBufAlgo.fill (buf, (1,0,0), ROI(50, 100, 75, 85))
ImageBuf ImageBufAlgo.checker(width, height, depth, color1, color2,  xoffset=0, yoffset=0, zoffset=0, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.checker(dst, width, height, depth, color1, color2,  xoffset=0, yoffset=0, zoffset=0, roi=ROI.All, nthreads=0)

Return (or copy into dst) a checkerboard pattern. The colors are specified as tuples giving the values for each color channel.

Example:

buf = ImageBuf(ImageSpec(640, 480, 3, oiio.UINT8))
ImageBufAlgo.checker (buf, 64, 64, 1, (0.1,0.1,0.1), (0.4,0.4,0.4))
ImageBuf ImageBufAlgo.noise (noisetype, A=0.0, B=0.1, mono=False, seed=0, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.noise (dst, noisetype, A=0.0, B=0.1, mono=False, seed=0, roi=ROI.All, nthreads=0)

Return an image of pseudorandom noise, or add pseudorandom noise to the specified region of existing region dst.

For noise type “white” (and its synonym “uniform”), the values are uniformly distributed on the range [A,B) and independently chosen for each pixel. For noise type “blue”, the range will still be uniformly distributed on [A,B) as with “white,” except that the values have better spectral properties for sampling and dithering purposes. For noise “gaussian”, the noise will have a normal distribution with mean A and standard deviation B. For noise “salt”, the value A will be stored in a random set of pixels whose proportion (of the overall image) is B.

For all noise types, choosing different seed values will result in a different pattern. If the mono flag is True, a single noise value will be applied to all channels specified by roi, but if mono is False, a separate noise value will be computed for each channel in the region.

Example:

buf = ImageBuf(ImageSpec(640, 480, 3, oiio.UINT8))
ImageBufAlgo.zero (buf)
ImageBufAlgo.noise (buf, 'white', 0.25, 0.75)
ImageBufAlgo.render_point(dst, x, y, color=(1, 1, 1, 1))

Render a point at pixel (x,y) of dst. The color (if supplied) is a tuple giving the per-channel colors. Return True for success, False for failure.

Example:

buf = ImageBuf(ImageSpec (640, 480, 4, oiio.FLOAT))
ImageBufAlgo.render_point (buf, 10, 20, (1,0,0,1))
bool ImageBufAlgo.render_line (dst, x1, y1, x2, y2, color=(1,1,1,1), skip_first_point=False)

Render a line from pixel $(x_1,y_1)$ to $(x_2,y_2)$ into dst. The color (if supplied) is a tuple giving the per-channel colors.

Example:

buf = ImageBuf(ImageSpec (640, 480, 4, oiio.FLOAT))
ImageBufAlgo.render_line (buf, 10, 10, 500, 20, (1,0,0,1))
bool ImageBufAlgo.render_box (dst, x1, y1, x2, y2, color=(1,1,1,1), filled=False)

Render a filled or unfilled box with corners at pixels $(x_1,y_1)$ and $(x_2,y_2)$ into dst. The color (if supplied) is a tuple giving the per-channel colors.

Example:

buf = ImageBuf(ImageSpec (640, 480, 4, oiio.FLOAT))
ImageBufAlgo.render_box (buf, 150, 100, 240, 180, (0,1,1,1))
ImageBufAlgo.render_box (buf, 100, 50, 180, 140, (0.5, 0.5, 0, 0.5), True)
bool ImageBufAlgo.render_text (dst, x, y, text, fontsize=16, fontname="", textcolor=(1,1,1,1), alignx="left", aligny="baseline", shadow=0, roi=ROI.All, nthreads=0)

Render antialiased text into dst. The textcolor (if supplied) is a tuple giving the per-channel colors. Choices for alignx are “left”, “right”, and “center”, and choices for aligny are “baseline”, “top”, “bottom”, and “center”.

Example:

buf = ImageBuf(ImageSpec (640, 480, 4, oiio.FLOAT))
ImageBufAlgo.render_text (buf, 50, 100, "Hello, world")
ImageBufAlgo.render_text (buf, 100, 200, "Go Big Red!",
                          60, "Arial Bold", (1,0,0,1))
ROI ImageBufAlgo.text_size (text, fontsize=16, fontname="")

Compute the size that will be needed for the text as an ROI and return it. The size will not be defined if an error occurred (such as not being a valid font name).

Example:

A = ImageBuf(ImageSpec (640, 480, 4, oiio.FLOAT))
Aroi = A.roi
size = ImageBufAlgo.text_size ("Centered", 40, "Courier New")
if size.defined :
    x = Aroi.xbegin + Aroi.width/2  - (size.xbegin + size.width/2)
    y = Aroi.ybegin + Aroi.height/2 - (size.ybegin + size.height/2)
    ImageBufAlgo.render_text (A, x, y, "Centered", 40, "Courier New")

# Note: this was for illustration. An easier way to do this is:
#   render_text (A, x, y, "Centered", 40, "Courier New", alignx="center")

Image transformations and data movement

ImageBuf ImageBufAlgo.channels(src, channelorder, newchannelnames=(), shuffle_channel_names=False, nthreads=0)
bool ImageBufAlgo.channels(dst, src, channelorder, newchannelnames=(), shuffle_channel_names=False, nthreads=0)

Return (or store in dst) shuffled channels of src, with channels in the order specified by the tuple channelorder. The length of channelorder specifies the number of channels to copy. Each element in the tuple channelorder may be one of the following:

  • int : specifies the index (beginning at 0) of the channel to copy.

  • str : specifies the name of the channel to copy.

  • float : specifies a constant value to use for that channel.

If newchannelnames is supplied, it is a tuple of new channel names. (See the C++ version for more full explanation.)

Example:

# Copy the first 3 channels of an RGBA, drop the alpha
RGBA = ImageBuf("rgba.tif")
RGB = ImageBufAlgo.channels (RGBA, (0,1,2))

# Copy just the alpha channel, making a 1-channel image
Alpha = ImageBufAlgo.channels (RGBA, ("A",))

# Swap the R and B channels
BGRA = ImageBufAlgo.channels (RGBA, (2, 1, 0, 3))

# Add an alpha channel with value 1.0 everywhere to an RGB image
RGBA = ImageBufAlgo.channels (RGB, ("R", "G", "B", 1.0),
                              ("R", "G", "B", "A"))
ImageBuf ImageBufAlgo.channel_append (A, B, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.channel_append (dst, A, B, roi=ROI.All, nthreads=0)

Append the channels of images A and B together into one image.

Example:

RGBA = ImageBuf ("rgba.exr")
Z = ImageBuf ("z.exr")
RGBAZ = ImageBufAlgo.channel_append (RGBA, Z)
ImageBuf ImageBufAlgo.copy (src, convert=TypeDesc.UNKNOWN, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.copy (dst, src, convert=TypeDesc.UNKNOWN, roi=ROI.All, nthreads=0)

Copy the specified region of pixels of src at the same locations, optionally with the pixel type overridden by convert (if it is not UNKNOWN).

Example:

# Copy A's upper left 200x100 region into B
B = ImageBufAlgo.copy (A, ROI(0,200,0,100))
ImageBuf ImageBufAlgo.crop (src, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.crop (dst, src, roi=ROI.All, nthreads=0)

Reset dst to be the specified region of src.

Example:

# Set B to be the upper left 200x100 region of A
A = ImageBuf ("a.tif")
B = ImageBufAlgo.crop (A, ROI(0,200,0,100))
ImageBuf ImageBufAlgo.cut (src, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.cut (dst, src, roi=ROI.All, nthreads=0)

Reset dst to be the specified region of src, but moved so that the resulting new image has its pixel data at the image plane origin.

Example:

# Set B to be the lower left 200x100 region of A, moved to the origin
A = ImageBuf ("a.tif")
B = ImageBufAlgo.cut (A, ROI(0,200,380,480))
bool ImageBufAlgo.paste (dst, xbegin, ybegin, zbegin, chbegin, src, srcroi=ROI.All, nthreads=0)

Copy the specified region of src into dst with the given offset (xbegin, ybegin, zbegin).

Example:

# Paste small.exr on top of big.exr at offset (100,100)
Big = ImageBuf ("big.exr")
Small = ImageBuf ("small.exr")
ImageBufAlgo.paste (Big, 100, 100, 0, 0, Small)
ImageBuf ImageBufAlgo.rotate90 (src, roi=ROI.All, nthreads=0)
ImageBuf ImageBufAlgo.rotate180 (src, roi=ROI.All, nthreads=0)
ImageBuf ImageBufAlgo.rotate270 (src, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.rotate90 (dst, src, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.rotate180 (dst, src, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.rotate270 (dst, src, roi=ROI.All, nthreads=0)

Copy while rotating the image by a multiple of 90 degrees.

Example:

A = ImageBuf ("tahoe.exr")
B = ImageBufAlgo.rotate90 (A)
ImageBuf ImageBufAlgo.flip (src, roi=ROI.All, nthreads=0)
ImageBuf ImageBufAlgo.flop (src, roi=ROI.All, nthreads=0)
ImageBuf ImageBufAlgo.transpose (src, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.flip (dst, src, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.flop (dst, src, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.transpose (dst, src, roi=ROI.All, nthreads=0)

Copy while reversing orientation vertically (flip) or horizontally (flop), or diagonally (transpose).

Example:

A = ImageBuf ("tahoe.exr")
B = ImageBufAlgo.flip (A)
ImageBuf ImageBufAlgo.reorient (src, nthreads=0)
bool ImageBufAlgo.reorient (dst, src, nthreads=0)

Copy src, applying whatever seties of rotations, flips, or flops are necessary to transform the pixels into the configuration suggested by the "Orientation" metadata of the image (and the "Orientation" metadata is then set to 1, ordinary orientation).

Example:

A = ImageBuf ("tahoe.jpg")
ImageBufAlgo.reorient (A, A)
ImageBuf ImageBufAlgo.circular_shift (src, xshift, yshift, zshift=0, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.circular_shift (dst, src, xshift, yshift, zshift=0, roi=ROI.All, nthreads=0)

Copy while circularly shifting by the given amount.

Example:

A = ImageBuf ("tahoe.exr")
B = ImageBufAlgo.circular_shift (A, 200, 100)
ImageBuf ImageBufAlgo.rotate (src, angle, filtername="", filtersize=0.0, recompute_roi=False, roi=ROI.All, nthreads=0)
ImageBuf ImageBufAlgo.rotate (src, angle, center_x, center_y, filtername="", filtersize=0.0, recompute_roi=False, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.rotate (dst, src, angle, filtername="", filtersize=0.0, recompute_roi=False, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.rotate (dst, src, angle, center_x, center_y, filtername="", filtersize=0.0, recompute_roi=False, roi=ROI.All, nthreads=0)

Copy arotated version of the corresponding portion of src. The angle is in radians, with positive values indicating clockwise rotation. If the filter and size are not specified, an appropriate default will be chosen.

Example:

Src = ImageBuf ("tahoe.exr")
Dst = ImageBufAlgo.rotate (Src, math.radians(45.0))
ImageBuf ImageBufAlgo.warp (src, M, filtername="", filtersize=0.0, wrap="default", recompute_roi=False, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.warp (dst, src, M, filtername="", filtersize=0.0, wrap="default", recompute_roi=False, roi=ROI.All, nthreads=0)

Compute a warped (transformed) copy of src, with the warp specified by M consisting of 9 floating-point numbers representing a 3x3 transformation matrix. If the filter and size are not specified, an appropriate default will be chosen.

Example:

M = (0.7071068, 0.7071068, 0, -0.7071068, 0.7071068, 0, 20, -8.284271, 1)
Src = ImageBuf ("tahoe.exr")
Dst = ImageBufAlgo.warp (Src, M)
ImageBuf ImageBufAlgo.resize (src, filtername="", filtersize=0.0, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.resize (dst, src, filtername="", filtersize=0.0, roi=ROI.All, nthreads=0)

Compute a high-quality resized version of the corresponding portion of src. If the filter and size are not specified, an appropriate default will be chosen.

Example:

# Resize the image to 640x480, using the default filter
Src = ImageBuf ("tahoe.exr")
Dst = ImageBufAlgo.resize (Src, roi=ROI(0,640,0,480,0,1,0,3))
ImageBuf ImageBufAlgo.resample (src, interpolate=True, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.resample (dst, src, interpolate=True, roi=ROI.All, nthreads=0)

Set dst, over the ROI, to be a low-quality (but fast) resized version of the corresponding portion of src, either using a simple “closest pixel” choice or by bilinaerly interpolating (depending on interpolate).

Example:

# Resample quickly to 320x240 to make a low-quality thumbnail
Src = ImageBuf ("tahoe.exr")
Dst = ImageBufAlgo.resample (Src, roi=ROI(0,640,0,480,0,1,0,3))
ImageBuf ImageBufAlgo.fit (src, filtername="", filtersize=0.0, fillmode="letterbox", exact=false, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.fit (dst, src, filtername="", filtersize=0.0, fillmode="letterbox", exact=false, roi=ROI.All, nthreads=0)

Fit src into the roi while preserving the original aspect ratio, without stretching. If the filter and size are not specified, an appropriate default will be chosen.

Example:

# Resize to fit into a max of 640x480, preserving the aspect ratio
Src = ImageBuf ("tahoe.exr")
Dst = ImageBufAlgo.fit (Src, roi=ROI(0,640,0,480,0,1,0,3))

Image arithmetic

ImageBuf ImageBufAlgo.add (A, B, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.add (dst, A, B, roi=ROI.All, nthreads=0)

Compute A + B. A and B each may be an ImageBuf, a float value (for all channels) or a tuple giving a float for each color channel.

Example:

# Add two images
buf = ImageBufAlgo.add (ImageBuf("a.exr"), ImageBuf("b.exr"))

# Add 0.2 to channels 0-2
ImageBufAlgo.add (buf, buf, (0.2,0.2,0.2,0))
ImageBuf ImageBufAlgo.sub (A, B, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.sub (dst, A, B, roi=ROI.All, nthreads=0)

Compute A - B. A and B each may be an ImageBuf, a float value (for all channels) or a tuple giving a float for each color channel.

Example:

buf = ImageBufAlgo.sub (ImageBuf("a.exr"), ImageBuf("b.exr"))
ImageBuf ImageBufAlgo.absdiff (A, B, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.absdiff (dst, A, B, roi=ROI.All, nthreads=0)

Compute abs(A - B). A and B each may be an ImageBuf, a float value (for all channels) or a tuple giving a float for each color channel.

Example:

buf = ImageBufAlgo.absdiff (ImageBuf("a.exr"), ImageBuf("b.exr"))
ImageBuf ImageBufAlgo.abs (A, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.abs (dst, A, roi=ROI.All, nthreads=0)

Compute abs(A). A is an ImageBuf.

Example:

buf = ImageBufAlgo.abs (ImageBuf("a.exr"))
ImageBuf ImageBufAlgo.mul (A, B, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.mul (dst, A, B, roi=ROI.All, nthreads=0)

Compute A * B (channel-by-channel multiplication). A and B each may be an ImageBuf, a float value (for all channels) or a tuple giving a float for each color channel.

Example:

# Multiply the two images
buf = ImageBufAlgo.mul (ImageBuf("a.exr"), ImageBuf("b.exr"))

# Reduce intensity of buf's channels 0-2 by 50%, in place
ImageBufAlgo.mul (buf, buf, (0.5, 0.5, 0.5, 1.0))
ImageBuf ImageBufAlgo.div (A, B, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.div (dst, A, B, roi=ROI.All, nthreads=0)

Compute A / B (channel-by-channel division), where x/0 is defined to be 0. A and B each may be an ImageBuf, a float value (for all channels) or a tuple giving a float for each color channel.

Example:

# Divide a.exr by b.exr
buf = ImageBufAlgo.div (ImageBuf("a.exr"), ImageBuf("b.exr"))

# Reduce intensity of buf's channels 0-2 by 50%, in place
ImageBufAlgo.div (buf, buf, (2.0, 2.0, 2.0, 1.0))
ImageBuf ImageBufAlgo.mad (A, B, C, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.mad (dst, A, B, C, roi=ROI.All, nthreads=0)

Compute A * B + C (channel-by-channel multiplication and addition). A, B, and C each may be an ImageBuf, a float value (for all channels) or a tuple giving a float for each color channel.

Example:

# Multiply a and b, then add c
buf = ImageBufAlgo.mad (ImageBuf("a.exr"),
                        (1.0f, 0.5f, 0.25f), ImageBuf("c.exr"))
ImageBuf ImageBufAlgo.invert (A, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.invert (dst, A, roi=ROI.All, nthreads=0)

Compute 1-A (channel by channel color inverse). A is an ImageBuf.

Example:

buf = ImageBufAlgo.invert (ImageBuf("a.exr"))
ImageBuf ImageBufAlgo.pow (A, B, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.pow (dst, A, B, roi=ROI.All, nthreads=0)

Compute pow (A, B) (channel-by-channel exponentiation). A is an ImageBuf, and B may be a float (a single power for all channels) or a tuple giving a float for each color channel.

Example:

# Linearize a 2.2 gamma-corrected image (channels 0-2 only)
img = ImageBuf ("a.exr")
buf = ImageBufAlgo.pow (img, (2.2, 2.2, 2.2, 1.0))
ImageBuf ImageBufAlgo.channel_sum (src, weights=(), roi=ROI.All, nthreads=0)
bool ImageBufAlgo.channel_sum (dst, src, weights=(), roi=ROI.All, nthreads=0)

Converts a multi-channel image into a 1-channel image via a weighted sum of channels. The weights is a tuple providing the weight for each channel (if not supplied, all channels will have weight 1.0).

Example:

# Compute luminance via a weighted sum of R,G,B
# (assuming Rec709 primaries and a linear scale)
ImageBuf()
weights = (.2126, .7152, .0722)
luma = ImageBufAlgo.channel_sum (ImageBuf("a.exr"), weights)
ImageBuf ImageBufAlgo.contrast_remap (src, black=0.0, white=1.0, min=0.0, max=1.0, sthresh=0.0, scontrast=1.0, ROI roi={}, int nthreads=0)
bool ImageBufAlgo.contrast_remap (ImageBuf &dst, src, black=0.0, white=1.0, min=0.0, max=1.0, sthresh=0.0, scontrast=1.0, ROI roi={}, int nthreads=0)

Return (or copy into dst) pixel values that are a contrast-remap of the corresponding values of the src image, transforming pixel value domain [black, white] to range [min, max], either linearly or with optional application of a smooth sigmoidal remapping (if scontrast != 1.0).

Example:

A = ImageBuf('tahoe.tif');

# Simple linear remap that stretches input 0.1 to black, and input
# 0.75 to white.
linstretch = ImageBufAlgo.contrast_remap (A, black=0.1, white=0.75)

# Remapping 0->1 and 1->0 inverts the colors of the image,
# equivalent to ImageBufAlgo.invert().
inverse = ImageBufAlgo.contrast_remap (A, black=1.0, white=0.0)

# Use a sigmoid curve to add contrast but without any hard cutoffs.
# Use a contrast parameter of 5.0.
sigmoid = ImageBufAlgo.contrast_remap (a, contrast=5.0)
ImageBuf ImageBufAlgo.saturate (src, scale=0.0, firstchannel=0, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.saturate (dst, src, scale=0.0, firstchannel=0, roi=ROI.All, nthreads=0)

Copy pixels from src to dst, and scale the saturation of channels firstchannel to firstchannel+2 by the scale factor.

This function was added in OpenImageIO 2.4.

Example:

# In-place reduce saturation by 50%
A = ImageBuf ("a.exr")
ImageBufAlgo.saturate (A, A, 0.5)
ImageBuf ImageBufAlgo.color_map (src, srcchannel, nknots, channels, knots, roi=ROI.All, nthreads=0)
ImageBuf ImageBufAlgo.color_map (src, srcchannel, mapname, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.color_map (dst, src, srcchannel, nknots, channels, knots, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.color_map (dst, src, srcchannel, mapname, roi=ROI.All, nthreads=0)

Return an image (or copy into dst) pixel values determined by applying the color map to the values of src, using either the channel specified by srcchannel, or the luminance of src’s RGB if srcchannel is -1.

In the first variant, the values linearly-interpolated color map are given by the tuple knots[nknots*channels].

In the second variant, just the name of a color map is specified. Recognized map names include: “inferno”, “viridis”, “magma”, “plasma”, all of which are perceptually uniform, strictly increasing in luminance, look good when converted to grayscale, and work for people with all types of colorblindness. The “turbo” color map is also nice in most of these ways (except for being strictly increasing in luminance). Also supported are the following color maps that do not have those desirable qualities (and are this not recommended): “blue-red”, “spectrum”, and “heat”. In all cases, the implied channels is 3.

Example:

heatmap = ImageBufAlgo.color_map (ImageBuf("a.jpg"), -1, "inferno")

heatmap = ImageBufAlgo.color_map (ImageBuf("a.jpg"), -1, 3, 3,
                        (0.25, 0.25, 0.25,  0, 0.5, 0,  1, 0, 0))
ImageBuf ImageBufAlgo.max (A, B, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.max (dst, A, B, roi=ROI.All, nthreads=0)

Compute per-pixel, per-channel max(A, B), returning the result image. At least one of A and B must be an ImageBuf, the other may also be an ImageBuf, or a float value (for all channels), or a tuple giving a float for each color channel.

Example:

# Make an image that for each pixel and channel, is the maximum
# value of that pixel and channel of A and B.
A = ImageBuf("a.exr")
B = ImageBuf("b.exr")
maximg = ImageBufAlgo.max (A, B)

# Do an in-place clamp image A so that all values are at least 0
# (thus ensuring that there are no negative values).
ImageBufAlgo.max (A, A, 0.0)
ImageBuf ImageBufAlgo.min (A, B, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.min (dst, A, B, roi=ROI.All, nthreads=0)

Compute per-pixel, per-channel min(A, B), returning the result image. At least one of A and B must be an ImageBuf, the other may also be an ImageBuf, or a float value (for all channels), or a tuple giving a float for each color channel.

Example:

# Make an image that for each pixel and channel, is the minimum
# value of that pixel and channel of A and B.
A = ImageBuf("a.exr")
B = ImageBuf("b.exr")
minimg = ImageBufAlgo.min (A, B)

# Do an in-place clamp image A so that the maximum value of each pixel
# is 0.5 (except for alpha, which may be up to 1.0):
ImageBufAlgo.min (A, A, (0.5, 0.5, 0.5, 1.0))
ImageBuf ImageBufAlgo.clamp (src, min, max, bool clampalpha01=False,  roi=ROI.All, nthreads=0)
bool ImageBufAlgo.clamp (dst, src, min, max, bool clampalpha01=False,  roi=ROI.All, nthreads=0)

Copy pixels while clamping between the min and max values. The min and max may either be tuples (one min and max value per channel), or single floats (same value for all channels). Additionally, if clampalpha01 is True, then any alpha channel is clamped to the 0–1 range.

Example:

# Clamp image buffer A in-place to the [0,1] range for all channels.
ImageBufAlgo.clamp (A, A, 0.0, 1.0)
ImageBuf ImageBufAlgo.maxchan (src, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.maxchan (dst, src, roi=ROI.All, nthreads=0)

Return a one-channel image where each pixel has the maximum value found in any of the channels of src in that corresponding pixel.

This function was added in OpenImageIO 2.3.10.

Example:

A = ImageBuf("rgb.exr")
max_of_rgb = ImageBufAlgo.maxchan (A)
ImageBuf ImageBufAlgo.minchan (src, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.minchan (dst, src, roi=ROI.All, nthreads=0)

Return a one-channel image where each pixel has the minimum value found in any of the channels of src in that corresponding pixel.

This function was added in OpenImageIO 2.3.10.

Example:

A = ImageBuf("rgb.exr")
min_of_rgb = ImageBufAlgo.minchan (A)
ImageBuf ImageBufAlgo.rangecompress (src, useluma=False, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.rangecompress (dst, src, useluma=False, roi=ROI.All, nthreads=0)
ImageBuf ImageBufAlgo.rangeexpand (src, useluma=False, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.rangeexpand (dst, src, useluma=False, roi=ROI.All, nthreads=0)

Copy from src, compressing (logarithmically) or expanding (by the inverse of the compressive transformation) the range of pixel values. Alpha and z channels are copied but not transformed.

If useluma is True, the luma of the first three channels (presumed to be R, G, and B) are used to compute a single scale factor for all color channels, rather than scaling all channels individually (which could result in a big color shift when performing rangecompress and rangeexpand).

Example:

# Resize the image to 640x480, using a Lanczos3 filter, which
# has negative lobes. To prevent those negative lobes from
# producing ringing or negative pixel values for HDR data,
# do range compression, then resize, then re-expand the range.

# 1. Read the original image
Src = ImageBuf ("tahoeHDR.exr")

# 2. Range compress to a logarithmic scale
Compressed = ImageBufAlgo.rangecompress (Src)

# 3. Now do the resize
roi = ROI (0, 640, 0, 480, 0, 1, 0, Compressed.nchannels)
Dst = ImageBufAlgo.resize (Compressed, "lanczos3", 6.0, roi)

# 4. Expand range to be linear again (operate in-place)
ImageBufAlgo.rangeexpand (Dst, Dst)
ImageBuf ImageBufAlgo.over (A, B, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.over (dst, A, B, roi=ROI.All, nthreads=0)

Composite ImageBuf A over ImageBuf B.

Example:

Comp = ImageBufAlgo.over (ImageBuf("fg.exr"), ImageBuf("bg.exr"))
ImageBuf ImageBufAlgo.zover (A, B, bool z_zeroisinf=False, roi=ROI.All, nthreads=0
bool ImageBufAlgo.zover (dst, A, B, bool z_zeroisinf=False, roi=ROI.All, nthreads=0)

Composite ImageBuf A and ImageBuf B using their respective Z channels to decide which is in front on a pixel-by-pixel basis.

Example:

Comp = ImageBufAlgo.zover (ImageBuf("fg.exr"), ImageBuf("bg.exr"))

Image comparison and statistics

PixelStats ImageBufAlgo.computePixelStats (src, roi=ROI.All, nthreads=0)

Compute statistics about the ROI of the image src. The PixelStats structure is defined as contining the following data fields: min, max, avg, stddev, nancount, infcount, finitecount, sum, sum2, each of which is a tuple with one value for each channel of the image.

Example:

A = ImageBuf("a.exr")
stats = ImageBufAlgo.computePixelStats (A)
print "   min = ", stats.min
print "   max = ", stats.max
print "   average = ", stats.avg
print "   standard deviation  = ", stats.stddev
print "   # NaN values    = ", stats.nancount
print "   # Inf values    = ", stats.infcount
print "   # finite values = ", stats.finitecount
CompareResults ImageBufAlgo.compare (A, B, failthresh, warnthresh, roi=ROI.All, nthreads=0)

Numerically compare two ImageBuf’s, A and B. The failthresh and warnthresh supply failure and warning difference thresholds. The return value is a CompareResults object, which is defined as a class having the following members:

meanerror, rms_error, PSNR, maxerror  # error statistics
maxx, maxy, maxz, maxc                # pixel of biggest difference
nwarn, nfail                          # number of warnings and failures
error                                 # True if there was an error

Example:

A = ImageBuf ("a.exr")
B = ImageBuf ("b.exr")
comp = ImageBufAlgo.compare (A, B, 1.0/255.0, 0.0)
if comp.nwarn == 0 and comp.nfail == 0 :
    print "Images match within tolerance"
else :
    print comp.nfail, "failures,", comp.nwarn, " warnings."
    print "Average error was " , comp.meanerror
    print "RMS error was" , comp.rms_error
    print "PSNR was" , comp.PSNR
    print "largest error was ", comp.maxerror
    print "  on pixel", (comp.maxx, comp.maxy, comp.maxz)
    print "  channel", comp.maxc
tuple ImageBufAlgo.isConstantColor (src, threshold=0.0, roi=ROI.All, nthreads=0)

If all pixels of src within the ROI have the same values (for the subset of channels described by roi), return a tuple giving that color (one float for each channel), otherwise return None.

Example:

A = ImageBuf ("a.exr")
color = ImageBufAlgo.isConstantColor (A)
if color != None :
    print "The image has the same value in all pixels:", color
else :
    print "The image is not a solid color."
bool ImageBufAlgo.isConstantChannel (src, channel, val, threshold=0.0, roi=ROI.All, nthreads=0)

Returns True if all pixels of src within the ROI have the given channel value val.

Example:

A = ImageBuf ("a.exr")
alpha = A.spec.alpha_channel
if alpha < 0 :
    print "The image does not have an alpha channel"
elif ImageBufAlgo.isConstantChannel (A, alpha, 1.0) :
    print "The image has alpha = 1.0 everywhere"
else :
    print "The image has alpha < 1 in at least one pixel"
bool ImageBufAlgo.isMonochrome (src, threshold=0.0, roi=ROI.All, nthreads=0)

Returns True if the image is monochrome within the ROI.

Example:

A = ImageBuf ("a.exr")
roi = A.roi
roi.chend = min (3, roi.chend)  # only test RGB, not alpha
if ImageBufAlgo.isMonochrome (A, roi) :
    print "a.exr is really grayscale"
ImageBufAlgo.color_range_check(src, low, high, roi=ROI.All, nthreads=0)

Count how many pixels in the src image (within the roi) are outside the value range described by low and hi (which each may be either one value or a tuple with per-channel values for each of roi.chbegin ... roi.chend. The result returned is a tuple containing three values: the number of values less than low, the number of values greater then hi, and the number of values within the range.

Example:

A = ImageBuf ("a.exr")
counts = ImageBufAlgo.color_range_check (A, 0.5, 0.75)
print ('{} values < 0.5, {} values > 0.75'.format(counts[0], counts[1])
ROI ImageBufAlgo.nonzero_region (src, roi=ROI.All, nthreads=0)

Returns an ROI that tightly encloses the minimal region within roi that contains all pixels with nonzero values.

Example:

A = ImageBuf ("a.exr")
nonzero_roi = ImageBufAlgo.nonzero_region(A)
std::string ImageBufAlgo.computePixelHashSHA1 (src, extrainfo = "", roi=ROI.All, blocksize=0, nthreads=0)

Compute the SHA-1 byte hash for all the pixels in the ROI of src.

Example:

A = ImageBuf ("a.exr")
hash = ImageBufAlgo.computePixelHashSHA1 (A, blocksize=64)
tuple histogram (src, channel=0, bins=256, min=0.0, max=1.0, ignore_empty=False, roi=ROI.All, nthreads=0)

Computes a histogram of the given channel of image src, within the ROI, returning a tuple of length bins containing count of pixels whose value was in each of the equally-sized range bins between min and max. If ignore_empty is True, pixels that are empty (all channels 0 including alpha) will not be counted in the total.

Convolutions

ImageBuf ImageBufAlgo.make_kernel (name, width, height, depth=1.0, normalize=True)}

Create a 1-channel float image of the named kernel and dimensions. If normalize is True, the values will be normalized so that they sum to 1.0.

If depth > 1, a volumetric kernel will be created. Use with caution!

Kernel names can be: “gaussian”, “sharp-gaussian”, “box”, “triangle”, “mitchell”, “blackman-harris”, “b-spline”, “catmull-rom”, “lanczos3”, “cubic”, “keys”, “simon”, “rifman”, “disk”, “binomial”, “laplacian”. Note that “catmull-rom” and “lanczos3” are fixed-size kernels that don’t scale with the width, and are therefore probably less useful in most cases.

Example:

K = ImageBufAlgo.make_kernel ("gaussian", 5.0, 5.0)
ImageBuf ImageBufAlgo.convolve (src, kernel, normalize=True, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.convolve (dst, src, kernel, normalize=True, roi=ROI.All, nthreads=0)

Replace the given ROI of dst with the convolution of src and a kernel (also an ImageBuf).

Example:

# Blur an image with a 5x5 Gaussian kernel
Src = ImageBuf ("tahoe.exr")
K = ImageBufAlgo.make_kernel (K, "gaussian", 5.0, 5.0)
Blurred = ImageBufAlgo.convolve (Src, K)
ImageBuf ImageBufAlgo.laplacian (src, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.laplacian (dst, src, roi=ROI.All, nthreads=0)

Replace the given ROI of dst with the Laplacian of the corresponding part of src.

Example:

Src = ImageBuf ("tahoe.exr")
L = ImageBufAlgo.laplacian (Src)
ImageBuf ImageBufAlgo.fft (src, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.fft (dst, src, roi=ROI.All, nthreads=0)
ImageBuf ImageBufAlgo.ifft (src, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.ifft (dst, src, roi=ROI.All, nthreads=0)

Compute the forward or inverse discrete Fourier Transform.

Example:

Src = ImageBuf ("tahoe.exr")

# Take the DFT of the first channel of Src
Freq = ImageBufAlgo.fft (Src)

# At this point, Freq is a 2-channel float image (real, imag)
# Convert it back from frequency domain to a spatial iamge
Spatial = ImageBufAlgo.ifft (Freq)
ImageBuf ImageBufAlgo.complex_to_polar (src, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.complex_to_polar (dst, src, roi=ROI.All, nthreads=0)
ImageBuf ImageBufAlgo.polar_to_complex (src, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.polar_to_complex (dst, src, roi=ROI.All, nthreads=0)

Transform a 2-channel image from complex (real, imaginary) representation to polar (amplitude, phase), or vice versa.

Example:

Polar = ImageBuf ("polar.exr")

Complex = ImageBufAlgo.polar_to_complex (Polar)

# At this point, Complex is a 2-channel complex image (real, imag)
# Convert it back from frequency domain to a spatial iamge
Spatial = ImageBufAlgo.ifft (Complex)

Image Enhancement / Restoration

ImageBuf ImageBufAlgo.fixNonFinite (src, mode=NONFINITE_BOX3, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.fixNonFinite (dst, src, mode=NONFINITE_BOX3, roi=ROI.All, nthreads=0)

Copy pixel values from src and repair any non-finite (NaN or Inf) pixels.

How the non-finite values are repaired is specified by one of the following modes:

OpenImageIO.NONFINITE_NONE
OpenImageIO.NONFINITE_BLACK
OpenImageIO.NONFINITE_BOX3

Example:

Src = ImageBuf ("tahoe.exr")
ImageBufAlgo.fixNonFinite (Src, Src, OpenImageIO.NONFINITE_BOX3)
ImageBuf ImageBufAlgo.fillholes_pushpull (src, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.fillholes_pushpull (dst, src, roi=ROI.All, nthreads=0)

Copy the specified ROI of src and fill any holes (pixels where alpha < 1) with plausible values using a push-pull technique. The src image must have an alpha channel. The dst image will end up with a copy of src, but will have an alpha of 1.0 everywhere, and any place where the alpha of src was < 1, dst will have a pixel color that is a plausible “filling” of the original alpha hole.

Example:

Src = ImageBuf ("holes.exr")
Filled = ImageBufAlgo.fillholes_pushpull (Src)
bool ImageBufAlgo.median_filter (dst, src, width=3, height=-1, roi=ROI.All, nthreads=0)

Replace the given ROI of dst with the width x height median filter of the corresponding region of src using the “unsharp mask” technique.

Example:

Noisy = ImageBuf ("tahoe.exr")
Clean = ImageBuf ()
ImageBufAlgo.median_filter (Clean, Noisy, 3, 3)
ImageBuf ImageBufAlgo.dilate (src, width=3, height=-1, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.dilate (dst, src, width=3, height=-1, roi=ROI.All, nthreads=0)
ImageBuf ImageBufAlgo.erode (src, width=3, height=-1, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.erode (dst, src, width=3, height=-1, roi=ROI.All, nthreads=0) }

Compute a dilated or eroded version of the corresponding region of src.

Example:

Source = ImageBuf ("source.tif")
Dilated = ImageBufAlgo.dilate (Source, 3, 3)
ImageBuf ImageBufAlgo.unsharp_mask (src, kernel="gaussian", width=3.0, contrast=1.0, threshold=0.0, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.unsharp_mask (dst, src, kernel="gaussian", width=3.0, contrast=1.0, threshold=0.0, roi=ROI.All, nthreads=0)

Compute a sharpened version of the corresponding region of src using the “unsharp mask” technique.

Example:

Blurry = ImageBuf ("tahoe.exr")
Sharp = ImageBufAlgo.unsharp_mask (Blurry, "gaussian", 5.0)

Color manipulation

ImageBuf ImageBufAlgo.colorconvert (src, fromspace, tospace, unpremult=True, context_key="", context_value="", colorconfig="", roi=ROI.All, nthreads=0)
bool ImageBufAlgo.colorconvert (dst, src, fromspace, tospace, unpremult=True, context_key="", context_value="", colorconfig="", roi=ROI.All, nthreads=0)

Apply a color transform to the pixel values.

Example:

Src = ImageBuf ("tahoe.jpg")
Dst = ImageBufAlgo.colorconvert (Src, "sRGB", "linear")
ImageBuf ImageBufAlgo.colormatrixtransform (src, M, unpremult=True, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.colormatrixtransform (dst, src, M, unpremult=True, roi=ROI.All, nthreads=0)

NEW in 2.1

Apply a 4x4 matrix color transform to the pixel values. The matrix can be any tuple of 16 float values.

Example:

Src = ImageBuf ("tahoe.jpg")
M = ( .8047379,  .5058794, -.3106172, 0,
     -.3106172,  .8047379,  .5058794, 0,
      .5058794, -.3106172,  .8047379, 0,
      0,         0,         0,       1)
Dst = ImageBufAlgo.colormatrixtransform (Src, M)
ImageBuf ImageBufAlgo.ociolook (src, looks, fromspace, tospace, unpremult=True, inverse=False, context_key="", context_value="", colorconfig="", roi=ROI.All, nthreads=0)
bool ImageBufAlgo.ociolook (dst, src, looks, fromspace, tospace, unpremult=True, inverse=False, context_key="", context_value="", colorconfig="", roi=ROI.All, nthreads=0)

Apply an OpenColorIO “look” transform to the pixel values.

Example:

Src = ImageBuf ("tahoe.jpg")
Dst = ImageBufAlgo.ociolook (Src, "look", "vd8", "lnf",
                        context_key="SHOT", context_value="pe0012")
ImageBuf ImageBufAlgo.ociodisplay (src, display, view, fromspace="", looks="", unpremult=True, context_key="", context_value="", colorconfig="", roi=ROI.All, nthreads=0)
bool ImageBufAlgo.ociodisplay (dst, src, display, view, fromspace="", looks="", unpremult=True, context_key="", context_value="", colorconfig="", roi=ROI.All, nthreads=0)

Apply an OpenColorIO “display” transform to the pixel values.

Example:

Src = ImageBuf ("tahoe.exr")
Dst = ImageBufAlgo.ociodisplay (Src, "sRGB", "Film", "lnf",
                          context_key="SHOT", context_value="pe0012")
ImageBuf ImageBufAlgo.ociofiletransform (src, name, unpremult=True, inverse=False, colorconfig="", roi=ROI.All, nthreads=0)
bool ImageBufAlgo.ociofiletransform (dst, src, name, unpremult=True, inverse=False, colorconfig="", roi=ROI.All, nthreads=0)

Apply an OpenColorIO “file” transform to the pixel values. In-place operations (dst and src being the same image) are supported.

Example:

Src = ImageBuf ("tahoe.exr")
Dst = ImageBufAlgo.ociofiletransform (Src, "foottransform.csp")
ImageBuf ImageBufAlgo.unpremult (src, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.unpremult (dst, src, roi=ROI.All, nthreads=0)
ImageBuf ImageBufAlgo.premult (src, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.premult (dst, src, roi=ROI.All, nthreads=0)
ImageBuf ImageBufAlgo.repremult (src, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.repremult (dst, src, roi=ROI.All, nthreads=0)

Copy pixels from src to dst, and un-premultiply, premultiply, or re-premultiply the colors by alpha.

unpremult divides colors by alpha, but preserves original color if alpha is 0. premult multiplies colors by alpha (even if alpha is 0). repreumlt is the true inverse of unpremult, multiplying color by alpha, but preserving color values in the alpha = 0 case.

Example:

# Convert in-place from associated alpha to unassociated alpha
A = ImageBuf ("a.exr")
ImageBufAlgo.unpremult (A, A)

Import / export

bool ImageBufAlgo.make_texture (mode, input, outputfilename, config=ImageSpec())

Turn an input image (either an ImageBuf or a string giving a filename) into a tiled, MIP-mapped, texture file and write to the file named by (outputfilename). The mode describes what type of texture file we are creating and may be one of the following:

OpenImageIO.MakeTxTexture
OpenImageIO.MakeTxEnvLatl
OpenImageIO.MakeTxEnvLatlFromLightProbe

The config, if supplied, is an ImageSpec that contains all the information and special instructions for making the texture. The full list of supported configuration options is given in Section Import / export.

The return value is True for success, False if errors occurred, in which case the error message will be retrievable from the global oiio.geterror().

Example:

# This command line:
#    maketx in.exr --hicomp --filter lanczos3 --opaque-detect \
#             -o texture.exr
# performs the same operations as:

import OpenImageIO as oiio

Input = oiio.ImageBuf ("in.exr")
config = oiio.ImageSpec()
config.attribute ("maketx:highlightcomp", 1)
config.attribute ("maketx:filtername", "lanczos3")
config.attribute ("maketx:opaque_detect", 1)
ok = oiio.ImageBufAlgo.make_texture (oiio.MakeTxTexture, Input,
                                "texture.exr", config)
if not ok :
    print("error:", oiio.geterror())
ImageBuf ImageBufAlgo::capture_image (cameranum, convert = OpenImageIO.UNKNOWN)

Capture a still image from a designated camera.

Example:

WebcamImage = ImageBufAlgo.capture_image (0, OpenImageIO.UINT8)
WebcamImage.write ("webcam.jpg")

Functions specific to deep images

ImageBuf ImageBufAlgo.deepen (src, zvalue=1.0, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.deepen (dst, src, zvalue=1.0, roi=ROI.All, nthreads=0)

Convert a flat image to a deep one that has one depth sample per pixel (but no depth samples for the pixels corresponding to those in the source image that have infinite “Z” or that had 0 for all color channels and no “Z” channel).

Example:

Deep = ImageBufAlgo.deepen (ImageBuf("az.exr"))
ImageBuf ImageBufAlgo.flatten (src, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.flatten (dst, src, roi=ROI.All, nthreads=0)

Composite the depth samples within each pixel of “deep” ImageBuf src to produce a “flat” ImageBuf.

Example:

Flat = ImageBufAlgo.flatten (ImageBuf("deepalpha.exr"))
ImageBuf ImageBufAlgo.deep_merge (A, B, occlusion_cull, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.deep_merge (dst, A, B, occlusion_cull, roi=ROI.All, nthreads=0)

Merge the samples of two deep images A and B into a deep result. If occlusion_cull is True, samples beyond the first opaque sample will be discarded, otherwise they will be kept.

Example:

DeepA = ImageBuf("hardsurf.exr")
DeepB = ImageBuf("volume.exr")
Merged = ImageBufAlgo.deep_merge (DeepA, DeepB)
ImageBuf ImageBufAlgo.deep_holdout (src, holdout, roi=ROI.All, nthreads=0)
bool ImageBufAlgo.deep_holdout (dst, src, holdout, roi=ROI.All, nthreads=0)

Return the pixels of src, but only copying the samples that are closer than the opaque frontier of image holdout. That is, holdout will serve as a depth holdout mask, but no samples from holdout will actually be copied to dst.

Example:

Img = ImageBuf("image.exr")
Mask = ImageBuf("mask.exr")
Thresholded = ImageBufAlgo.deep_holdout (Img, Mask)

Other ImageBufAlgo methods that understand deep images

In addition to the previously described methods that are specific to deep images, the following ImageBufAlgo methods (described in their respective sections) work with deep inputs:

ImageBufAlgo.add
ImageBufAlgo.channels
ImageBufAlgo.compare
ImageBufAlgo.computePixelStats
ImageBufAlgo.crop
ImageBufAlgo.div
ImageBufAlgo.fixNonFinite
ImageBufAlgo.mul
ImageBufAlgo.nonzero_region
ImageBufAlgo.resample
ImageBufAlgo.sub

Miscellaneous Utilities

In the main OpenImageIO module, there are a number of values and functions that are useful. These correspond to the C++ API functions explained in Section Global Attributes, please refer there for details.

openimageio_version

The OpenImageIO version number is an int, 10000 for each major version, 100 for each minor version, 1 for each patch. For example, OpenImageIO 1.2.3 would return a value of 10203.

geterror(clear=True)

Retrieves the latest global error, as a string.

attribute(name, typedesc, value)
attribute(name, int_value)
attribute(name, float_value)
attribute(name, str_value)

Sets a global attribute (see Section Global Attributes for details), returning True upon success, or False if it was not a recognized attribute.

Example:

oiio.attribute ("threads", 0)
getattribute(name, typedesc)
get_int_attribute(name, defaultval=0)
get_float_attribute(name, defaultval=0.0)
get_string_attribute(name, defaultval='')

Retrieves an attribute value from the named set of global OIIO options. (See Section Global Attributes.) The getattribute() function returns the value regardless of type, or None if the attribute does not exist. The typed variety will only succeed if the attribute is actually of that type specified. Type varity with the type in the name also takes a default value.

Example:

formats = oiio.get_string_attribute ("format_list")
is_imageio_format_name(name)

Returns True if name is the name of a known and supported file format, False if it is not.

Example:

>>> print (oiio.is_imageio_format_name('tiff'))
True
>>> print (oiio.is_imageio_format_name('Bob'))
False

Python Recipes

This section illustrates the Python syntax for doing many common image operations from Python scripts, but that aren’t already given as examples in the earlier function descriptions. All example code fragments assume the following boilerplate:

#!/usr/bin/env python

import OpenImageIO as oiio
from OpenImageIO import ImageBuf, ImageSpec, ImageBufAlgo

Subroutine to create a constant-colored image

# Create an ImageBuf holding a n image of constant color, given the
# resolution, data format (defaulting to UINT8), fill value, and image
# origin.
def make_constimage (xres, yres, chans=3, format=oiio.UINT8, value=(0,0,0),
                     xoffset=0, yoffset=0) :
    spec = ImageSpec (xres,yres,chans,format)
    spec.x = xoffset
    spec.y = yoffset
    b = ImageBuf (spec)
    oiio.ImageBufAlgo.fill (b, value)
    return b

The image is returned as an ImageBuf, then up to the caller what to do with it next.


Subroutine to save an image to disk, printing errors

# Save an ImageBuf to a given file name, with optional forced image format
# and error handling.
def write_image (image, filename, format=oiio.UNKNOWN) :
    if not image.has_error :
        image.write (filename, format)
    if image.has_error :
        print "Error writing", filename, ":", image.geterror()

Converting between file formats

img = ImageBuf ("input.png")
write_image (img, "output.tif")

Comparing two images and writing a difference image

A = ImageBuf ("A.tif")
B = ImageBuf ("B.tif")
compresults = ImageBufAlgo.compare (A, B, 1.0e-6, 1.0e-6)
if compresults.nfail > 0 :
    print "Images did not match, writing difference image diff.tif"
    diff = ImageBufAlgo.absdiff (A, B)
    image_write (diff, "diff.tif")

Changing the data format or bit depth

img = ImageBuf ("input.exr")
# presume that it's a "half" OpenEXR file
# write it back out as a "float" file:
write_image (img, "output.exr", oiio.FLOAT)

Changing the compression

The following command converts writes a TIFF file, specifically using LZW compression:

img = ImageBuf ("in.tif")
img.specmod().attribute ("compression", "lzw")
write_image (img, "compressed.tif")

The following command writes its results as a JPEG file at a compression quality of 50 (pretty severe compression):

img = ImageBuf ("big.jpg")
img.specmod().attribute ("quality", 50)
write_image (img, "small.jpg")

Converting between scanline and tiled images

img = ImageBuf ("scan.tif")
img.set_write_tiles (64, 64)
write_image (img, "tile.tif")

img = ImageBuf ("tile.tif")
img.set_write_tiles (0, 0)
write_image (img, "scan.tif")

Adding captions or metadata

img = ImageBuf ("foo.jpg")
# Add a caption:
img.specmod().attribute ("ImageDescription", "Hawaii vacation")
# Add keywords:
img.specmod().attribute ("keywords", "volcano,lava")
write_image (img, "foo.jpg")

Changing image boundaries

Change the origin of the pixel data window:

img = ImageBuf ("in.exr")
img.set_origin (256, 80)
write_image (img, "offset.exr")

Change the display window:

img = ImageBuf ("in.exr")
img.set_full (16, 1040, 16, 784)
write_image (img, "out.exr")

Change the display window to match the data window:

img = ImageBuf ("in.exr")
img.set_full (img.roi())
write_image (img, "out.exr")

Cut (trim and extract) a 128x128 region whose upper left corner is at location (900,300), moving the result to the origin (0,0) of the image plane and setting the display window to the new pixel data window:

img = ImageBuf ("in.exr")
b = ImageBufAlgo.cut (img, oiio.ROI(900,1028,300,428))
write_image (b, "out.exr")

Extract just the named channels from a complicted many-channel image, and add an alpha channel that is 1 everywhere

img = ImageBuf ("allmyaovs.exr")
b = ImageBufAlgo.channels (img, ("spec.R", "spec.G", "spec.B", 1.0))
write_image (b, "spec.tif")

Fade 30% of the way between two images

a = ImageBufAlgo.mul (ImageBuf("A.exr"), 0.7)
b = ImageBufAlgo.mul (ImageBuf("B.exr"), 0.3)
fade = ImageBufAlgo.add (a, b)
write_image (fade, "fade.exr")

Composite of small foreground over background, with offset

fg = ImageBuf ("fg.exr")
fg.set_origin (512, 89)
bg = ImageBuf ("bg.exr")
comp = ImageBufAlgo.over (fg, bg)
write_image (comp, "composite.exr")

Write multiple ImageBufs into one multi-subimage file

bufs = (...)   # Suppose that bufs is a tuple of ImageBuf
specs = (...)  # specs is a tuple of the specs that describe them

# Open with intent to write the subimages
out = ImageOutput.create ("multipart.exr")
out.open ("multipart.exr", specs)
for s in range(len(bufs)) :
    if s > 0 :
        out.open ("multipart.exr", specs[s], "AppendSubimage")
    bufs[s].write (out)
out.close ()

oiiotool: the OIIO Swiss Army Knife

Overview

The oiiotool program will read images (from any file format for which an ImageInput plugin can be found), perform various operations on them, and write images (in any format for which an ImageOutput plugin can be found).

The oiiotool utility is invoked as follows:

oiiotool args

oiiotool maintains an image stack, with the top image in the stack also called the current image. The stack begins containing no images.

oiiotool arguments consist of image names, actions, and flags.

  • Image names: When an image name is encountered, that image is pushed on the stack and becomes the new current image.

  • Actions: Alter the current image (replacing it with the alteration), or in some cases will pull more than one image off the stack (such as the current image and the next item on the stack) and then push a new result image onto the stack.

  • Flags: A small number of arguments are non-positional – the order doesn’t matter and their effect applies to the entire oiiotool execution.

Argument order matters!

oiiotool processes actions and inputs in order. Thus, the order of operations on the command line is extremely important. For example,

oiiotool in.tif -resize 640x480 -o out.tif

has the effect of reading in.tif (thus making it the current image), resizing it (taking the original off the stack, and placing the resized result back on the stack), and then writing the new current image to the file out.tif. Contrast that with the following subtly-incorrect command:

oiiotool in.tif -o out.tif -resize 640x480

has the effect of reading in.tif (thus making it the current image), saving the current image to the file out.tif (note that it will be an exact copy of in.tif), resizing the current image, and then… exiting. Thus, the resized image is never saved, and out.tif will be an unaltered copy of in.tif.

The exceptions to this are non-positional flags, which affect the entire oiiotool command regardless of where they appear on the command line.

Optional modifiers

Some arguments stand completely on their own (like --flip), others take one or more subsequent command line arguments (like --resize or -o):

oiiotool foo.jpg --flip --resize 640x480 -o out.tif

A few arguments take optional modifiers for options that are so rarely-used or confusing that they should not be required arguments. In these cases, they are appended to the command name, after a colon (:), and with a name=value format. Multiple optional modifiers can be chained together, with colon separators. As an example:

    oiiotool in.tif --text:x=400:y=600:color=1,0,0 "Hello" -o out.tif
                    \____/\____/\____/\__________/ \____/
                      |     |     |        |         |
       command -------+     |     |        |         +----- required argument
                            |     |        |
optional modifiers ---------+-----+--------+
(separated by ':')

The value itself may be a single- or double-quoted string, and this is how you would make a value that itself contains a : character (which would otherwise denote the beginning of the next modifier).

Frame sequences

It is also possible to have oiiotool operate on numbered sequences of images. In effect, this will execute the oiiotool command several times, making substitutions to the sequence arguments in turn.

Image sequences are specified by having filename arguments to oiiotool use either a numeric range wildcard (designated such as 1-10# or a printf-like notation 1-10%d), or spelling out a more complex pattern with --frames. For example:

oiiotool big.1-3#.tif --resize 100x100 -o small.1-3#.tif

oiiotool big.1-3%04d.tif --resize 100x100 -o small.1-3%04d.tif

oiiotool --frames 1-3 big.#.tif --resize 100x100 -o small.#.tif

oiiotool --frames 1-3 big.%04d.tif --resize 100x100 -o small.%04d.tif

Any of those will be the equivalent of having issued the following sequence of commands:

oiiotool big.0001.tif --resize 100x100 -o small.0001.tif
oiiotool big.0002.tif --resize 100x100 -o small.0002.tif
oiiotool big.0003.tif --resize 100x100 -o small.0003.tif

The frame range may be forwards (1-5) or backwards (5-1), and may give a step size to skip frames (1-5x2 means 1, 3, 5) or take the complement of the step size set (1-5y2 means 2, 4) and may combine subsequences with a comma.

If you are using the # or @ wildcards, then the wildcard characters themselves specify how many digits to pad with leading zeroes, with # indicating 4 digits and @ indicating one digit (these may be combined: #@@ means 6 digits). An optional --framepadding can also be used to override the number of padding digits. For example:

oiiotool --framepadding 3 --frames 3,4,10-20x2 blah.#.tif

would match blah.003.tif, blah.004.tif, blah.010.tif, blah.012.tif, blah.014.tif, blah.016.tif, blah.018.tif, blah.020.tif.

Alternately, you can use the printf notation, such as:

oiiotool --frames 3,4,10-20x2 blah.%03d.tif

When using frame ranges, keep in mind that by default, any error (such as an input file not being found) on any frame will exit oiiotool right away. However, the --skip-bad-frames command line option causes an error to skip the rest of the processing for that frame, but try to continue iteration with the next frame.

Two special command line arguments can be used to disable numeric wildcard expansion: --wildcardoff disables numeric wildcard expansion for subsequent command line arguments, until --wildcardon re-enables it for subsequent command line arguments. Turning wildcard expansion off for selected arguments can be helpful if you have arguments that must contain the wildcard characters themselves. For example:

oiiotool input.@@@.tif --wildcardoff --sattrib Caption "lg@openimageio.org" \
    --wildcardon -o output.@@@.tif

In this example, the @ characters in the filenames should be expanded into numeric file sequence wildcards, but the @ in the caption (denoting an email address) should not.

Stereo wildcards

oiiotool can also handle image sequences with separate left and right images per frame using views. The %V wildcard will match the full name of all views and %v will match the first character of each view. View names default to “left” and “right”, but may be overridden using the --views option. For example:

oiiotool --frames 1-5 blah_%V.#.tif

would match blah_left.0001.tif, blah_right.0001.tif, blah_left.0002.tif, blah_right.0002.tif, blah_left.0003.tif, blah_right.0003.tif, blah_left.0004.tif, blah_right.0004.tif, blah_left.0005.tif, blah_right.0005.tif, and

oiiotool --frames 1-5 blah_%v.#.tif

would match blah_l.0001.tif, blah_r.0001.tif, blah_l.0002.tif, blah_r.0002.tif, blah_l.0003.tif, blah_r.0003.tif, blah_l.0004.tif, blah_r.0004.tif, blah_l.0005.tif, blah_r.0005.tif, but

oiiotool --views left --frames 1-5 blah_%v.#.tif

would only match blah_l.0001.tif, blah_l.0002.tif, blah_l.0003.tif, blah_l.0004.tif, blah_l.0005.tif.

Expression evaluation and substitution

oiiotool can perform expression evaluation and substitution on command-line arguments. As command-line arguments are needed, they are scanned for containing braces { }. If found, the braces and any text they enclose will be evaluated as an expression and replaced by its result. The contents of an expression may be any of:

  • number

    A numerical value (e.g., 1 or 3.14159).

  • imagename.metadata

    The named metadata of an image.

    The imagename may be one of: TOP (the top or current image), IMG[i] describing the i-th image on the stack (thus TOP is a synonym for IMG[0], the next image on the stack is IMG[1], etc.), or IMG[name] to denote an image named by filename or by label name. Remember that the positions on the stack (including TOP) refer to at that moment, with successive commands changing the contents of the top image.

    The metadata may be any of:

    • the name of any standard metadata of the specified image (e.g., ImageDescription, or width)

    • filename : the name of the file (e.g., foo.tif)

    • file_extension : the extension of the file (e.g., tif)

    • geom : the pixel data size in the form 640x480+0+0)

    • full_geom : the “full” or “display” size)

    • MINCOLOR : the minimum value in each channel (channels are comma-separated)

    • MAXCOLOR : the maximum value in each channel (channels are comma-separated)

    • AVGCOLOR : the average pixel value of the image (channels are comma-separated)

    • METABRIEF : a string containing the brief one-line description that would be printed with oiiotool -info.

    • META : a multi-line string containing the full metadata that would be printed with oiiotool -info -v.

    • STATS : a multi-line string containing the image statistics that would be printed with oiiotool -stats.

  • imagename.’metadata’

    If the metadata name is not a “C identifier” (initial letter followed by any number of letter, number, or underscore), it is permissible to use single or double quotes to enclose the metadata name. For example, suppose you want to retrieve metadata named “foo/bar”, you could say

    {TOP.'foo/bar'}

    Without the quotes, it might try to retrieve TOP.foo (which doesn’t exist) and divide it by bar.

  • Arithmetic

    Sub-expressions may be joined by +, -, *, /, //, and % for arithmetic operations. (Note that like in Python 3, / is floating point division, while // signifies integer division.) Parentheses are supported, and standard operator precedence applies.

  • Special variables

    • FRAME_NUMBER : the number of the frame in this iteration of wildcard expansion.

    • FRAME_NUMBER_PAD : like FRAME_NUMBER, but 0-padded based on the value set on the command line by --framepadding.

  • Functions

    • getattribute(name) : returns the global attribute that would be retrieved by OIIO::getattribute(name, ...). The name may be enclosed in single or double quotes or be a single unquoted sequence of characters. (Added in OIIO 2.3.)

To illustrate how this works, consider the following command, which trims a four-pixel border from all sides and outputs a new image prefixed with “cropped_”, without needing to know the resolution or filename of the original image:

oiiotool input.exr -cut "{TOP.width-2*4}x{TOP.height-2*4}+{TOP.x+4}+{TOP.y+4}" \
    -o cropped_{TOP.filename}

If you should come across filenames that contain braces (these are vary rare, but have been known to happen), you temporarily disable expression evaluation with the --evaloff end --evalon flags. For example:

$ oiiotool --info "{weird}.exr"
> oiiotool ERROR: expression : syntax error at char 1 of `weird'

$ oiiotool --info --evaloff "{weird}.exr"
> {weird.exr}          : 2048 x 1536, 3 channel, half openexr

Dealing with multi-subimage/multi-part files

Some file formats allow storing multiple images in one file (notably OpenEXR, which calls them “multi-part”). There are some special behaviors to be aware of for multi-subimage files.

Using oiiotool for a simple input-to-output copy will preserve all of the subimages (assuming that the output format can accommodate multiple subimages):

oiiotool multipart.exr -o another.exr

Most oiiotool commands by default work on just the first subimage of their input, discarding the others. For example:

oiiotool multipart.exr --colorconvert lnf aces -o out.exr

In this example, only the first subimage in multipart.exr will be color transformed and output to out.exr. Any other subimages in the input will not be used or copied.

Using the -a command tells oiiotool to try to preserve all subimages from the inputs and apply all computations to all subimages:

oiiotool -a multipart.exr --colorconvert lnf aces -o out.exr

Now all subimages of multipart.exr will be transformed and output.

But that might not be enough. Perhaps there are some subimages that need the color conversion, and others that do not. Many oiiotool commands take an optional modifier :subimages=... that can restrict the operation to certain subimages. The argument is a comma-separated list of any of the following: (a) an integer index of a subimage to include, or a minus sign (-) followed by an integer index of a subimage to exclude; (b) the name (as returned by the metadata “oiio:subimagename”) of a subimage to include, or to exclude if preceded by a -; (c) the special string “all”, meaning all subimages. Examples:

# Color convert only subimages 0, 3, and 4, leave the rest as-is
oiiotool -a multipart.exr --colorconvert:subimages=0,3,4 lnf aces -o out.exr

# Color convert all subimages EXCEPT the one named "normal"
oiiotool -a multipart.exr --colorconvert:subimages=-normal lnf aces -o out.exr

oiiotool Tutorial / Recipes

This section will give quick examples of common uses of oiiotool to get you started. They should be fairly intuitive, but you can read the subsequent sections of this chapter for all the details on every command.

Printing information about images

To print the name, format, resolution, and data type of an image (or many images):

oiiotool --info *.tif

To also print the full metadata about each input image, use both --info and -v:

oiiotool --info -v *.tif

or:

oiiotool --info:verbose=1 *.tif

To print info about all subimages and/or MIP-map levels of each input image, use the -a flag:

oiiotool --info -v -a mipmap.exr

To print statistics giving the minimum, maximum, average, and standard deviation of each channel of an image, as well as other information about the pixels:

oiiotool --stats img_2012.jpg

The --info, --stats, -v, and -a flags may be used in any combination.

Converting between file formats

It’s a snap to convert among image formats supported by OpenImageIO (i.e., for which ImageInput and ImageOutput plugins can be found). The oiiotool utility will simply infer the file format from the file extension. The following example converts a PNG image to JPEG:

oiiotool lena.png -o lena.jpg

The first argument (lena.png) is a filename, causing oiiotool to read the file and makes it the current image. The -o command outputs the current image to the filename specified by the next argument.

Thus, the above command should be read to mean, “Read lena.png into the current image, then output the current image as lena.jpg (using whatever file format is traditionally associated with the .jpg extension).”

Comparing two images

To print a report of the differences between two images of the same resolution:

oiiotool old.tif new.tif --diff

If you also want to save an image showing just the differences:

oiiotool old.tif new.tif --diff --absdiff -o diff.tif

This looks complicated, but it’s really simple: read old.tif, read new.tif (pushing old.tif down on the image stack), report the differences between them, subtract new.tif from old.tif and replace them both with the difference image, replace that with its absolute value, then save that image to diff.tif.

Sometimes you want to compare images but allow a certain number of small difference, say allowing the comparison to pass as long as no more than 1% of pixels differs by more than 1/255, and as long as no single pixel differs by more than 2/255. You can do this with thresholds:

oiiotool old.tif new.tif --fail 0.004 -failpercent 1 --hardfail 0.008 --diff

Changing the data format or bit depth

Just use the -d option to specify a pixel data format for all subsequent outputs. For example, assuming that in.tif uses 16-bit unsigned integer pixels, the following will convert it to an 8-bit unsigned pixels:

oiiotool in.tif -d uint8 -o out.tif

For formats that support per-channel data formats, you can override the format for one particular channel using -d CHNAME=TYPE. For example, assuming rgbaz.exr is a float RGBAZ file, and we wish to convert it to be half for RGBA, and float for Z. That can be accomplished with the following command:

oiiotool rgbaz.tif -d half -d Z=float -o rgbaz2.exr

When converting from a high bit depth data type (like float or half) to a very low bit depth data type (such as uint8), you may notice “banding” artifacts in smooth gradients. To combat this, you can use the --dither option to add random dither before the low bit depth quantization, which has the effect of masking the banding:

oiiotool half.exr -d uint8 --dither -o out8.tif

Note that --dither turns dither on for all 8 bit (or fewer) output files. Alternately, you can enable dither for individual outputs using a modifier to -o (the value of the dither modifier is the random seed that will be used):

oiiotool half.exr -d uint8 -o:dither=1 out8.tif

Changing the compression

The following command converts writes a TIFF file, specifically using LZW compression:

oiiotool in.tif --compression lzw -o compressed.tif

The following command writes its results as a JPEG file at a compression quality of 50 (pretty severe compression), illustrating how some compression methods allow a quality metric to be optionally appended to the name:

iconvert --compression jpeg:50 50 big.jpg small.jpg

Converting between scanline and tiled images

Convert a scanline file to a tiled file with 16x16 tiles:

oiiotool s.tif --tile 16 16 -o t.tif

Convert a tiled file to scanline:

oiiotool t.tif --scanline -o s.tif

Adding captions or metadata

Add a caption to the metadata:

oiiotool foo.jpg --caption "Hawaii vacation" -o bar.jpg

Add keywords to the metadata:

oiiotool foo.jpg --keyword "volcano,lava" -o bar.jpg

Add other arbitrary metadata:

oiiotool in.exr --attrib "FStop" 22.0 \
        --attrib "IPTC:City" "Berkeley" -o out.exr

oiiotool in.exr --attrib:type=timecode smpte:TimeCode "11:34:04:00" \
        -o out.exr

oiiotool in.exr --attrib:type=int[4] FaceBBox "140,300,219,460" \
        -o out.exr

Changing image boundaries and borders

Change the origin of the pixel data window:

oiiotool in.exr --origin +256+80 -o offset.exr

Change the display window:

oiiotool in.exr --fullsize 1024x768+16+16 -o out.exr

Change the display window to match the data window:

oiiotool in.exr --fullpixels -o out.exr

Crop (trim) an image to a 128x128 region whose upper left corner is at location (900,300), leaving the remaining pixels in their original positions on the image plane (i.e., the resulting image will have origin at 900,300), and retaining its original display window:

oiiotool in.exr --crop 128x128+900+300 -o out.exr

Cut (trim and extract) a 128x128 region whose upper left corner is at location (900,300), moving the result to the origin (0,0) of the image plane and setting the display window to the new pixel data window:

oiiotool in.exr --cut 128x128+900+300 -o out.exr

Put a constant-color border around all sides of an image, without needing to know the resolution of the input image:

# BW: Border width
BW=40
COLOR=.2,.2,.2,1.0
oiiotool in.tif \
    --pattern constant:color=$COLOR "{TOP.width+2*$BW}x{TOP.height+2*$BW}" "{TOP.nchannels}" --paste "+$BW+$BW" \
    -o out.tif

Scale the values in an image

Reduce the brightness of the R, G, and B channels by 10%, but leave the A channel at its original value:

oiiotool original.exr --mulc 0.9,0.9,0.9,1.0 -o out.exr

Remove gamma-correction from an image

Convert a gamma-corrected image (with gamma = 2.2) to linear values:

oiiotool corrected.exr --powc 2.2,2.2,2.2,1.0 -o linear.exr

Resize an image

Resize to a specific resolution:

oiiotool original.tif --resize 1024x768 -o specific.tif

Resize both dimensions by a known scale factor:

oiiotool original.tif --resize 200% -o big.tif
oiiotool original.tif --resize 25% -o small.tif

Resize each dimension, independently, by known scale factors:

oiiotool original.tif --resize 300%x200% -o big.tif
oiiotool original.tif --resize 100%x25% -o small.tif

Resize to a known resolution in one dimension, with the other dimension automatically computed to preserve aspect ratio (just specify 0 as the resolution in the dimension to be automatically computed):

oiiotool original.tif --resize 200x0 -o out.tif
oiiotool original.tif --resize 0x1024 -o out.tif

Resize to fit into a given resolution, keeping the original aspect ratio and padding with black where necessary to fit into the specified resolution:

oiiotool original.tif --fit 640x480 -o fit.tif

Color convert an image

This command linearizes a JPEG assumed to be in sRGB, saving as an HDRI OpenEXR file:

oiiotool photo.jpg --colorconvert sRGB linear -o output.exr

And the other direction:

oiiotool render.exr --colorconvert linear sRGB -o fortheweb.png

This converts between two named color spaces (presumably defined by your facility’s OpenColorIO configuration):

oiiotool in.dpx --colorconvert lg10 lnf -o out.exr

Grayscale and RGB

Turn a single channel image into a 3-channel gray RGB:

oiiotool gray.tif --ch 0,0,0 -o rgb.tif

Convert a color image to luminance grayscale:

oiiotool RGB.tif --chsum:weight=.2126,.7152,.0722 -o luma.tif

Channel reordering and padding

Copy just the color from an RGBA file, truncating the A, yielding RGB only:

oiiotool rgba.tif --ch R,G,B -o rgb.tif

Zero out the red and green channels:

oiiotool rgb.tif --ch R=0,G=0,B -o justblue.tif

Swap the red and blue channels from an RGBA image:

oiiotool rgba.tif --ch R=B,G,B=R,A -o bgra.tif

Extract just the named channels from a many-channel image, as efficiently as possible (avoiding memory and I/O for the unused channels):

oiiotool -i:ch=R,G,B manychannels.exr -o rgb.exr

Add an alpha channel to an RGB image, setting it to 1.0 everywhere, and naming it “A” so it will be recognized as an alpha channel:

oiiotool rgb.tif --ch R,G,B,A=1.0 -o rgba.tif

Add an alpha channel to an RGB image, setting it to be the same as the R channel and naming it “A” so it will be recognized as an alpha channel:

oiiotool rgb.tif --ch R,G,B,A=R -o rgba.tif

Add a z channel to an RGBA image, setting it to 3.0 everywhere, and naming it “Z” so it will be recognized as a depth channel:

oiiotool rgba.exr --ch R,G,B,A,Z=3.0 -o rgbaz.exr

Copy metadata from one image to another

Suppose you have a (non-OIIO) application that consumes input Exr files and produces output Exr files, but along the way loses crucial metadata from the input files that you want carried along. This command will add all the metadata from the first image to the pixels of the second image:

oiiotool metaonly.exr pixelsonly.exr –pastemeta -o combined.exr

Fade between two images

Fade 30% of the way from A to B:

oiiotool A.exr --mulc 0.7 B.exr --mulc 0.3 --add -o fade.exr

Simple compositing

Simple “over” composite of aligned foreground and background:

oiiotool fg.exr bg.exr --over -o composite.exr

Composite of small foreground over background, with offset:

oiiotool fg.exr --origin +512+89 bg.exr --over -o composite.exr

Creating an animated GIF from still images

Combine several separate JPEG images into an animated GIF with a frame rate of 8 frames per second:

oiiotool foo??.jpg --siappendall --attrib FramesPerSecond 10.0 -o anim.gif

Frame sequences: composite a sequence of images

Composite foreground images over background images for a series of files with frame numbers in their names:

oiiotool fg.1-50%04d.exr bg.1-50%04d.exr --over -o comp.1-50%04d.exr

Or:

oiiotool --frames 1-50 fg.%04d.exr bg.%04d.exr --over -o comp.%04d.exr

Expression example: annotate the image with its caption

This command reads a file, and draws any text in the “ImageDescription” metadata, 30 pixels from the bottom of the image:

oiiotool input.exr --text:x=30:y={TOP.height-30} {TOP.ImageDescription} -o out.exr

Note that this works without needing to know the caption ahead of time, and will always put the text 30 pixels from the bottom of the image without requiring you to know the resolution.

Contrast enhancement: stretch pixel value range to exactly fit [0-1]

This command reads a file, subtracts the minimum pixel value and then divides by the (new) maximum value, per channel, thus expanding its pixel values to the full [0-1] range:

oiiotool input.tif -subc {TOP.MINCOLOR} -divc {TOP.MAXCOLOR} -o out.tif

Note that this is a naive way to improve contrast and because each channel is handled independently, it may result in color hue shifts.

Split a multi-image file into separate files

Take a multi-image TIFF file, split into its constituent subimages and output each one to a different file, with names sub0001.tif, sub0002.tif, etc.:

oiiotool multi.tif -sisplit -o:all=1 sub%04d.tif

oiiotool commands: general non-positional flags

--help

Prints full usage information to the terminal, as well as information about image formats supported, known color spaces, filters, OIIO build options and library dependencies.

-v

Verbose status messages — print out more information about what oiiotool is doing at every step.

-q

Quet mode — print out less information about what oiiotool is doing (only errors).

-n

No saved output — do not save any image files. This is helpful for certain kinds of tests, or in combination with --runstats or --debug, for getting detailed information about what a command sequence will do and what it costs, but without producing any saved output files.

--debug

Debug mode — print lots of information about what operations are being performed.

--runstats

Print timing and memory statistics about the work done by oiiotool.

-a

Performs all operations on all subimages and/or MIPmap levels of each input image. Without -a, generally each input image will really only read the top-level MIPmap of the first subimage of the file.

--no-clobber

Sets “no clobber” mode, in which existing images on disk will never be overridden, even if the -o command specifies that file.

--threads <n>

Use n execution threads if it helps to speed up image operations. The default (also if n=0) is to use as many threads as there are cores present in the hardware.

--cache <size>

Set the underlying ImageCache size (in MB). See Section ImageCache API.

--frames <seq>
--framepadding <n>

Describes the frame range to substitute for the # or %0Nd numeric wildcards. The sequence is a comma-separated list of subsequences; each subsequence is a single frame (e.g., 100), a range of frames (100-150), or a frame range with step (100-150x4 means 100,104,108,...).

The frame padding is the number of digits (with leading zeroes applied) that the frame numbers should have. It defaults to 4.

For example,

oiiotool –framepadding 3 –frames 3,4,10-20x2 blah.#.tif

would match blah.003.tif, blah.004.tif, blah.010.tif, blah.012.tif, blah.014.tif, blah.016.tif, blah.018.tif, blah.020.tif.

--views <name1,name2,...>

Supplies a comma-separated list of view names (substituted for %V and %v). If not supplied, the view list will be left,right.

--skip-bad-frames

When iterating over a frame range, if this option is used, any errors will cease processing that frame, but continue iterating with the next frame (rather than the default behavior of exiting immediately and not even attempting the other frames in the range).

--wildcardoff, --wildcardon

These positional options turn off (or on) numeric wildcard expansion for subsequent command line arguments. This can be useful in selectively disabling numeric wildcard expansion for a subset of the command line.

--evaloff, --evalon

These positional options turn off (or on) expression evaluation (things with { }) for subsequent command line arguments. This can be useful in selectively disabling expression evaluation expansion for a subset of the command line, for example if you actually have filenames containing curly braces.

--oiioattrib <name> <value>

Adds or replaces a global OpenImageIO attribute with the given name to have the specified value.

Optional appended modifiers include:

  • type= typename : Specify the metadata type.

If the optional type= specifier is used, that provides an explicit type for the metadata. If not provided, it will try to infer the type of the metadata from the value: if the value contains only numerals (with optional leading minus sign), it will be saved as int metadata; if it also contains a decimal point, it will be saved as float metadata; otherwise, it will be saved as a string metadata.

Examples:

oiiotool --oiioattrib debug 1 in.jpg -o out.jpg

oiiotool commands: reading and writing images

The commands described in this section read images, write images, or control the way that subsequent images will be written upon output.

Reading images

<filename>
-i <filename>

If a command-line option is the name of an image file, that file will be read and will become the new current image, with the previous current image pushed onto the image stack.

The -i command may be used, which allows additional options that control the reading of just that one file.

Optional appended modifiers include:

:now= int

If 1, read the image now, before proceeding to the next command.

:autocc= int

Enable or disable --autocc for this input image (the default is to use the global setting).

:unpremult= int

If autocc is used for this image, should any color transformation be done on unassociated colors (unpremultiplied by alpha). The default is 0.

:info= int

Print info about this file (even if the global --info was not used) if nonzero. If the value is 2, print full verbose info (like --info -v).

:infoformat= name

When printing info, the format may be one of: text (default) for readable text, or xml for an XML description of the image metadata.

:type= name

Upon reading, convert the pixel data to the named type. This can override the default behavior of internally storing whatever type is the most precise one found in the file.

:ch= name…

Causes the input to read only the specified channels. This is equivalent to following the input with a --ch command, except that by integrating into the -i, it potentially can avoid the I/O of the unneeded channels.

--iconfig <name> <value>

Sets configuration hint metadata that will apply to the next input file read. Input configuration hint settings are cleared after an image is read, and must be specified separately for every -i or image filename to read.

Optional appended modifiers include:

  • type= typename : Specify the metadata type.

If the optional type= specifier is used, that provides an explicit type for the metadata. If not provided, it will try to infer the type of the metadata from the value: if the value contains only numerals (with optional leading minus sign), it will be saved as int metadata; if it also contains a decimal point, it will be saved as float metadata; otherwise, it will be saved as a string metadata.

Examples:

oiiotool --iconfig "oiio:UnassociatedAlpha" 1 in.png -o out.tif

Options that control the reading of all images

These are all non-positional flags that affect how all images are read in the oiiotool command.

--autocc

Turns on automatic color space conversion: Every input image file will be immediately converted to a scene-referred linear color space, and every file written will be first transformed to an appropriate output color space based on the filename or type. Additionally, if the name of an output file contains a color space and that color space is associated with a particular data format, it will output that data format (akin to -d).

The rules for deducing color spaces are as follows, in order of priority:

  1. If the filename (input or output) contains as a substring the name of a color space from the current OpenColorIO configuration, that will be assumed to be the color space of input data (or be the requested color space for output).

  2. For input files, if the ImageInput set the "oiio:ColorSpace" metadata, it will be honored if the filename did not override it.

  3. When outputting to JPEG files, assume that sRGB is the desired output color space (since JPEG requires sRGB), but still this only occurs if the filename does not specify something different.

If the implied color transformation is unknown (for example, involving a color space that is not recognized), a warning will be printed, but it the rest of oiiotool processing will proceed (but without having transformed the colors of the image).

Optional appended modifiers include:

:unpremult= int

If nonzero, when autocc is performed on an image containing an alpha channel, the image will first be unpremultiplied by alpha, then color transformed, then re-premultipled by alpha, so that the color transformation is done with unassociated color values. The default is 0, meanining that the color transformation will be done directly on the associated color values.

Example:

If the input file in_lg10.dpx is in the lg10 color space, and you want to read it in, brighten the RGB uniformly by 10% (in a linear space, of course), and then save it as a 16 bit integer TIFF file encoded in the vd16 color space, you could specifiy the conversions explicitly:

oiiotool in_lg10.dpx --colorconvert lg10 linear \
                     --mulc 1.1,1.1,1.1,1.0 -colorconvert linear vd16 \
                     -d uint16 -o out_vd16.tif

or rely on the naming convention matching the OCIO color space names and use automatic conversion:

oiiotool --autocc in_lg10.dpx --mulc 1.1 -o out_vd16.tif
--autopremult (default), -no-autopremult

By default, OpenImageIO’s format readers convert any “unassociated alpha” (color values that are not “premultiplied” by alpha) to the usual associated/premultiplied convention. If the --no-autopremult flag is found, subsequent inputs will not do this premultiplication. It can be turned on again via --autopremult.

--autoorient

Automatically do the equivalent of --reorient on every image as it is read in, if it has a nonstandard orientation. This is generally a good idea to use if you are using oiiotool to combine images that may have different orientations.

--native

Normally, all images read by oiiotool are read into an ImageBuf backed by an underlying ImageCache, and are automatically converted to float pixels for internal storage (because any subsequent image processing is usually much faster and more accurate when done on floating-point values).

This option causes (1) input images to be stored internally in their native pixel data type rather than converted to float, and (2) to bypass the ImageCache (reading directly into an ImageBuf) if the pixel data type is not one of the types that is supported internally to ImageCache (UINT8, uint16, half, and float).

images whose pixels are comprised of data types that are not natively representable exactly in the ImageCache to bypass the ImageCache and be read directly into an ImageBuf.

The typical use case for this is when you know you are dealing with unusual pixel data types that might lose precision if converted to float (for example, if you have images with uint32 or double pixels). Another use case is if you are using oiiotool merely for file format or data format conversion, with no actual image processing math performed on the pixel values – in that case, you might save time and memory by bypassing the conversion to float.

--autotile <tilesize>

For the underlying ImageCache, turn on auto-tiling with the given tile size. Setting tilesize to 0 turns off auto-tiling (the default is off). If auto-tile is turned on, The ImageCache “autoscanline” feature will also be enabled. See Section ImageCache API for details.

--missingfile <value>

Determines the behavior when an input file is not found, and no file of that name exists at all. An error is always printed and the oiiotool program always has an error-indicating exit code. But how it proceeds with the rest of the commands may vary depending on the option value:

  • error : (default) Consider it a full error for that frame iteration.

  • black : After the error is printed, try to continue with the rest of the command, substituting an opaque black image for the missing file.

  • checkerAfter the error is printed, try to continue with the rest

    of the command, substituting a checkerboard image for the missing file.

Note that the resolution, channels, and format (but not arbitrary metadata) of the missing file substution image will be the same as the first image that was successfully read. If the first image requested is missing (thus, nothing had been successfully read when the missing image is needed), it will be HD resolution, 1920x1080, RGBA.

--info

Print metadata information about each input image as it is read. If verbose mode is turned on (-v), all the metadata for the image is printed. If verbose mode is not turned on, only the resolution and data format are printed.

Optional appended modifiers include:

  • format=name : The format name may be one of: text (default) for readable text, or xml for an XML description of the image metadata.

  • verbose=1 : If nonzero, the information will contain all metadata, not just the minimal amount.

Note that this is a non-positional flag that will cause metadata to be printed for every input file. There is a separate --printinfo action that immediately prints metadata about the current image at the top of the stack (see oiiotool commands that print information about the current image).

--metamatch <regex>, --no-metamatch <regex>

Regular expressions to restrict which metadata are output when using oiiotool --info -v. The --metamatch expression causes only metadata whose name matches to print; non-matches are not output. The --no-metamatch expression causes metadata whose name matches to be suppressed; others (non-matches) are printed. It is not advised to use both of these options at the same time (probably nothing bad will happen, but it’s hard to reason about the behavior in that case).

--stats

Print detailed statistical information about each input image as it is read.

Note that this is a non-positional flag that will cause statistics to be printed for every input file. There is a separate --printstats action that immediately prints statistics about the current image at the top of the stack (see oiiotool commands that print information about the current image).

--hash

Print the SHA-1 hash of the pixels of each input image as it is read.

--dumpdata

Print to the console the numerical values of every pixel, for each input image as it is read.

Optional appended modifiers include:

  • C= name : If present, will cause the output of the data to be in the correct syntax of declaring a C array with the given name. (This was added in OpenImageIO v2.3.9.)

  • empty= verbose : If 0, will cause deep images to skip printing of information about pixels with no samples.

Examples:

$ oiiotool --dumpdata image.exr
image.exr       :  256 x  256, 4 channel, float openexr
    Pixel (0, 0): 0.517036676 0.261921108 0.017822538 0.912108004
    Pixel (1, 0): 0.653315008 0.527794302 0.359594107 0.277836263
    ...

$ oiiotool --dumpdata:C=foo image.exr
// image.exr       :  256 x  256, 4 channel, float openexr
float foo[256][256][4] =
{
    /* (0, 0): */ { 0.517036676, 0.261921108, 0.017822538, 0.912108004 },
    /* (1, 0): */ { 0.653315008, 0.527794302, 0.359594107, 0.277836263 },
    ...
};

Writing images

-o <filename>

Outputs the current image to the named file. This does not remove the current image from the image stack, it merely saves a copy of it.

Optional appended modifiers include:

:type= name

Set the pixel data type (like -d) for this output image (e.g., :uint8, uint16, half, float, etc.).

:bits= int

Set the bits per pixel (if nonstandard for the datatype) for this output image.

:dither= int

Turn dither on or off for this output. When writing floating point data to an 8 bit or less data type in the file, dither can reduce banding artifacts. (default: 0)

:autocc= int

Enable or disable --autocc for this output image (the default is to use the global setting).

:unpremult= int

If autocc is used for this image, should any color transformation be done on unassociated colors (unpremultiplied by alpha). The default is 0.

:autocrop= int

Enable or disable autocrop for this output image.

:autotrim= int

Enable or disable --autotrim for this output image.

:separate= int, contig= int

Set separate or contiguous planar configuration for this output.

:fileformatname= string

Specify the desired output file format, overriding any guess based on file name extension.

:scanline= int

If nonzero, force scanline output.

:tile= int x int

Force tiling with given size.

:all= n

Output all images currently on the stack using a pattern. See further explanation below.

The all=n option causes all images on the image stack to be output, with the filename argument used as a pattern assumed to contain a %d, which will be substituted with the index of the image (beginning with n). For example, to take a multi-image TIFF and extract all the subimages and save them as separate files:

oiiotool multi.tif -sisplit -o:all=1 sub%04d.tif

This will output the subimges as separate files sub0001.tif, sub0002.tif, and so on.

-otex <filename>
-oenv <filename>
-obump <filename>

Outputs the current image to the named file, as a MIP-mapped texture or environment map, identical to that which would be output by maketx (Chapter Making Tiled MIP-Map Texture Files With maketx or oiiotool). The advantage of using oiiotool rather than maketx is simply that you can have a complex oiiotool command line sequence of image operations, culminating in a direct saving of the results as a texture map, rather than saving to a temporary file and then separately invoking maketx.

In addition to all the optional arguments of -o, optional appended arguments for -otex, -oenv, and -obump also include:

:wrap= string

Set the default $s$ and $t$ wrap modes of the texture, to one of: :black, clamp, periodic, mirror.

:swrap= string

Set the default $s$ wrap mode of the texture.

:twrap= string

Set the default $t$ wrap mode of the texture.

:resize= int

If nonzero, resize to a power of 2 before starting to create the MIPpmap levels. (default: 0)

:nomipmap= int

If nonzero, do not create MIP-map levels at all. (default: 0)

:updatemode= int

If nonzero, do not create and overwrite the existing texture if it appears to already match the source pixels. (default: 0)

:constant_color_detect= int

Detect images that are entirely one color, and change them to be low resolution. (default: 0)

:monochrome_detect= int

Detect monochrome (R=G=B) images and turn them into 1-channel textures. (default: 0)

:opaque_detect= int

Detect opaque (A=1) images and drop the alpha channel from the texture. (default: 0)

:compute_average= int

Compute and store the average color of the texture. (default: 1)

:unpremult= int

Unpremultiply colors before any per-MIP-level color conversions, and re-premultiply after. (default: 0)

:incolorspace= string

Specify color space conversion.

:outcolorspace= string

…

:highlightcomp= int

Use highlight compensation for HDR images when resizing for MIP-map levels. (default: 0)

:sharpen= float

Additional sharpening factor when resizing for MIP-map levels. (default: 0.0)

:filter= string

Specify the filter for MIP-map level resizing. (default: box)

:prman_metadata= int

Turn all all options required to make the resulting texture file compatible with PRMan (particular tile sizes, formats, options, and metadata). (default: 0)

:prman_options= int

Include the metadata that PRMan’s texture system wants. (default: 0)

:bumpformat= string

For -obump only, specifies the interpretation of 3-channel source images as one of: height, normal, auto (default).

:uvslopes_scale= float

For -obump only, specifies the amount to scale the bump-map slopes by. (default: 0.0, meaning not to use this feature)

:cdf= int

If nonzero, will add to the texture metadata the forward and inverse Gaussian CDF, which can be used by shaders to implement Histogram-Preserving blending. (default: 0)

:cdfsigma= float

In conjunction with cdf=1, specifies the sigma value to use for the CDF (default: 1.0/6.0).

:cdfbits= int

In conjunction with cdf=1, specifies the number of bits to use for the size of the CDF table (default: 8, meaning 256 bins).

Examples:

oiiotool in.tif -otex out.tx

oiiotool in.jpg --colorconvert sRGB linear -d uint16 -otex out.tx

oiiotool --pattern:checker 512x512 3 -d uint8 -otex:wrap=periodic checker.tx

oiiotool in.exr -otex:hilightcomp=1:sharpen=0.5 out.exr
-d <datatype>
-d <channelname>=<datatype>
-d <subimagename>.*=<datatype>
-d <subimagename>.<channelname>=<datatype>

Attempts to set the pixel data type of all subsequent outputs. If no channel or subimage name is given, sets all channels to be the specified data type. If a specific channel is named, then the data type will be overridden for just that channel (multiple -d commands may be used). If both a subimage name and channel name are specified, the hint is only for the named channel when encountered in a named subimage. And if the specification is of the form subimagename.*=type, then all channels of that subimage will be output with the given type.

Valid types are: uint8, sint8, uint16, sint16, half, float, double. The types uint10 and uint12 may be used to request 10- or 12-bit unsigned integers. If the output file format does not support them, uint16 will be substituted.

If the -d option is not supplied, the output data type will be deduced from the data format of the input files, if possible.

In any case, if the output file type does not support the requested data type, it will instead use whichever supported data type results in the least amount of precision lost.

--scanline

Requests that subsequent output files be scanline-oriented, if scanline orientation is supported by the output file format. By default, the output file will be scanline if the input is scanline, or tiled if the input is tiled.

--tile <x> <y>

Requests that subsequent output files be tiled, with the given \(x \times y\) tile size, if tiled images are supported by the output format. By default, the output file will take on the tiledness and tile size of the input file.

--compression <method>
--compression <method:quality>

Sets the compression method, and optionally a quality setting, for the output image. Each ImageOutput plugin will have its own set of methods that it supports.

Sets the compression method, and optionally a quality setting, for the output image. Each ImageOutput plugin will have its own set of methods that it supports.

--quality <q>

Sets the compression quality, on a 1-100 floating-point scale. This only has an effect if the particular compression method supports a quality metric (as JPEG does).

This is considered deprecated, and in general we now recommend just appending the quality metric to the --compression name:qual.

--dither

Turns on dither when outputting to 8-bit or less image files (does not affect other data types). This adds just a bit of noise that reduces visible banding artifacts. The dither seed will be selected based on a hash of the output filename, and therefore will be a different random pattern for different files. It only has an effect when outputting to a file of 8 or fewer bits per sample, and only when the data being saved starts off with higher than 8 bit precision.

--planarconfig <config>

Sets the planar configuration of subsequent outputs (if supported by their formats). Valid choices are: config for contiguous (or interleaved) packing of channels in the file (e.g., RGBRGBRGB…), separate for separate channel planes (e.g., RRRR…GGGG…BBBB…), or default for the default choice for the given format. This command will be ignored for output files whose file format does not support the given choice.

--adjust-time

When this flag is present, after writing each output, the resulting file’s modification time will be adjusted to match any "DateTime" metadata in the image. After doing this, a directory listing will show file times that match when the original image was created or captured, rather than simply when oiiotool was run. This has no effect on image files that don’t contain any "DateTime" metadata.

--noautocrop

For subsequent outputs, do not automatically crop images whose formats don’t support separate pixel data and full/display windows. Without this, the default is that outputs will be cropped or padded with black as necessary when written to formats that don’t support the concepts of pixel data windows and full/display windows. This is a non-issue for file formats that support these concepts, such as OpenEXR.

--autotrim

For subsequent outputs, if the output format supports separate pixel data and full/display windows, automatically trim the output so that it writes the minimal data window that contains all the non-zero valued pixels. In other words, trim off any all-black border rows and columns before writing the file.

--metamerge

When this flag is used, most image operations will try to merge the metadata found in all of their source input images into the output. The default (if this is not used) is that image oprations with multiple input images will just take metadata from the first source image.

(This was added for OpenImageIO 2.1.)

oiiotool commands that print information about the current image

--echo <message>

Prints the message to the console, at that point in the left-to-right execution of command line arguments. The message may contain expressions for substitution.

Optional appended modifiers include:

  • newline=n : The number of newlines to print after the message (default is 1, but 0 will suppress the newline, and a larger number will make more vertical space.

Examples:

oiiotool test.tif --resize 256x0 --echo "result is {TOP.width}x{TOP.height}"

This will resize the input to be 256 pixels wide and automatically size it vertically to preserve the original aspect ratio, and then print a message to the console revealing the resolution of the resulting image.

--list-formats

Prints the complete list of file formats supported by this build of OpenImageIO, and for each one, the list of file extensions that it presumes are associated with the file format. (Added in OIIO 2.2.13.)

--printinfo

Prints information and all metadata about the current image.

--printstats

Prints detailed statistical information about the current image.

Optional appended modifiers include:

  • :window= geom

    If present, restricts the statistics to a rectangular subset of the image. The default, if not present is to print the statistics of the full data window of the image. The rectangle can be specified using either of these image geometry notations:

    width x height [+-] xoffset [+-] yoffset

    xmin,ymin,xmax,ymax

  • :allsubimages= int

    If nonzero, stats will be printed about all subimages of the current image. (The default is zero, meaning that stats will only be printed for the first subimage of the current image.)

--colorcount r1,g1,b1,...:r2,g2,b2,...:...

Given a list of colors separated by colons or semicolons, where each color is a list of comma-separated values (for each channel), examine all pixels of the current image and print a short report of how many pixels matched each of the colors.

Optional appended modifiers include:

  • eps=r,g,b,... : Tolerance for matching colors (default: 0.001 for all channels).

Examples:

oiiotool test.tif --colorcount "0.792,0,0,1;0.722,0,0,1"

might produce the following output:

10290  0.792,0,0,1
11281  0.722,0,0,1

Notice that use of double quotes " " around the list of color arguments, in order to make sure that the command shell does not interpret the semicolon (;) as a statement separator. An alternate way to specify multiple colors is to separate them with a colon (:), for example:

oiiotool test.tif --colorcount 0.792,0,0,1:0.722,0,0,1

Another example:

oiiotool test.tif --colorcount:eps=.01,.01,.01,1000 "0.792,0,0,1"

This example sets a larger epsilon for the R, G, and B channels (so that, for example, a pixel with value [0.795,0,0] would also match), and by setting the epsilon to 1000 for the alpha channel, it effectively ensures that alpha will not be considered in the matching of pixels to the color value.

--rangecheck Rlow,Glow,Blow,...  Rhi,Bhi,Ghi,...

Given a two colors (each a comma-separated list of values for each channel), print a count of the number of pixels in the image that has channel values outside the [low,hi] range. Any channels not specified will assume a low of 0.0 and high of 1.0.

Example:

oiiotool test.exr --rangecheck 0,0,0 1,1,1

might produce the following output:

    0  < 0,0,0
  221  > 1,1,1
65315  within range
--diff
--fail <A> --failpercent <B> --hardfail <C>
--warn <A> --warnpercent <B> --hardwarn <C>

This command computes the difference of the current image and the next image on the stack, and prints a report of those differences (how many pixels differed, the maximum amount, etc.). This command does not alter the image stack.

The --fail, --failpercent, and --hardfail options set thresholds for FAILURE: if more than B % of pixels (on a 0-100 floating point scale) are greater than A different, or if any pixels are more than C different. The defaults are to fail if more than 0% (any) pixels differ by more than 0.00001 (1e-6), and C is infinite.

The --warn, --warnpercent, and hardwarn options set thresholds for WARNING: if more than B % of pixels (on a 0-100 floating point scale) are greater than A different, or if any pixels are more than C different. The defaults are to warn if more than 0% (any) pixels differ by more than 0.00001 (1e-6), and C is infinite.

--pdiff

This command computes the difference of the current image and the next image on the stack using a perceptual metric, and prints whether or not they match according to that metric. This command does not alter the image stack.

oiiotool commands that change the current image metadata

This section describes oiiotool commands that alter the metadata of the current image, but do not alter its pixel values. Only the current (i.e., top of stack) image is affected, not any images further down the stack.

If the -a flag has previously been set, these commands apply to all subimages or MIPmap levels of the current top image. Otherwise, they only apply to the highest-resolution MIPmap level of the first subimage of the current top image.

--attrib <name> <value>
--sattrib <name> <value>

Adds or replaces metadata with the given name to have the specified value.

Optional appended modifiers include:

  • type= typename : Specify the metadata type.

If the optional type= specifier is used, that provides an explicit type for the metadata. If not provided, it will try to infer the type of the metadata from the value: if the value contains only numerals (with optional leading minus sign), it will be saved as int metadata; if it also contains a decimal point, it will be saved as float metadata; otherwise, it will be saved as a string metadata.

The --sattrib command is equivalent to --attrib:type=string.

Examples:

oiiotool in.jpg --attrib "IPTC:City" "Berkeley" -o out.jpg

oiiotool in.jpg --attrib:type=string "Name" "0" -o out.jpg

oiiotool in.exr --attrib:type=matrix worldtocam \
        "1,0,0,0,0,1,0,0,0,0,1,0,2.3,2.1,0,1" -o out.exr

oiiotool in.exr --attrib:type=timecode smpte:TimeCode "11:34:04:00" \
        -o out.exr
--caption <text>

Sets the image metadata "ImageDescription". This has no effect if the output image format does not support some kind of title, caption, or description metadata field. Be careful to enclose *text in quotes if you want your caption to include spaces or certain punctuation!

--keyword <text>

Adds a keyword to the image metadata "Keywords". Any existing keywords will be preserved, not replaced, and the new keyword will not be added if it is an exact duplicate of existing keywords. This has no effect if the output image format does not support some kind of keyword field.

Be careful to enclose *text in quotes if you want your keyword to include spaces or certain punctuation. For image formats that have only a single field for keywords, OpenImageIO will concatenate the keywords, separated by semicolon (;), so don’t use semicolons within your keywords.

--clear-keywords

Clears all existing keywords in the current image.

--nosoftwareattrib

When set, this prevents the normal adjustment of “Software” and “ImageHistory” metadata to reflect what oiiotool is doing.

--sansattrib

When set, this edits the command line inserted in the “Software” and “ImageHistory” metadata to omit any verbose --attrib and --sattrib commands.

--eraseattrib <pattern>

Removes any metadata whose name matches the regular expression pattern. The pattern will be case insensitive.

Examples:

# Remove one item only
oiiotool in.jpg --eraseattrib "smpte:TimeCode" -o no_timecode.jpg

# Remove all GPS tags
oiiotool in.jpg --eraseattrib "GPS:.*" -o no_gps_metadata.jpg

# Remove all metadata
oiiotool in.exr --eraseattrib ".*" -o no_metadata.exr
--orientation <orient>

Explicitly sets the image’s "Orientation" metadata to a numeric value (see Section Display hints for the numeric codes). This only changes the metadata field that specifies how the image should be displayed, it does NOT alter the pixels themselves, and so has no effect for image formats that don’t support some kind of orientation metadata.

--orientcw
--orientccw
--orient180

Adjusts the image’s "Orientation" metadata by rotating the suggested viewing orientation \(90^\circ\) clockwise, \(90^\circ\) degrees counter-clockwise, or \(180^\circ\), respectively, compared to its current setting. This only changes the metadata field that specifies how the image should be displayed, it does NOT alter the pixels themselves, and so has no effect for image formats that don’t support some kind of orientation metadata.

See the --rotate90, --rotate180, --rotate270, and --reorient commands for true rotation of the pixels (not just the metadata).

--origin <neworigin>

Set the pixel data window origin, essentially translating the existing pixel data window to a different position on the image plane. The new data origin is in the form:

[+-]x[+-]y

Examples:

--origin +20+10           x=20, y=10
--origin +0-40            x=0, y=-40
--originoffset <offset>

Alter the data window origin, translating the existing pixel data window by this relative amount. The offset is in the form:

[+-]x[+-]y

Examples:

# Assuming the old origin was +100+20...
--originoffset +20+10           # new x=120, y=30
--originoffset +0-40            # new x=100, y=-20
--fullsize <size>

Set the display/full window size and/or offset. The size is in the form

width x height [+-] xoffset [+-] yoffset

If either the offset or resolution is omitted, it will remain unchanged.

Examples:

--fullsize 1920x1080

resolution w=1920, h=1080, offset unchanged

--fullsize -20-30

resolution unchanged, x=-20, y=-30

--fullsize 1024x768+100+0

resolution w=1024, h=768, offset x=100, y=0
--fullpixels

Set the full/display window range to exactly cover the pixel data window.

--chnames <name-list>

Rename some or all of the channels of the top image to the given comma-separated list. Any completely empty channel names in the list will not be changed. For example:

oiiotool in.exr --chnames ",,,A,Z" -o out.exr

will rename channel 3 to be “A” and channel 4 to be “Z”, but will leave channels 0–3 with their old names.

Optional appended modifiers include:

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files). Only included subimages will have their channels renamed.

oiiotool commands that shuffle channels or subimages

--selectmip <level>

If the current image is MIP-mapped, replace the current image with a new image consisting of only the given level of the MIPmap. Level 0 is the highest resolution version, level 1 is the next-lower resolution version, etc.

--unmip

If the current image is MIP-mapped, discard all but the top level (i.e., replacing the current image with a new image consisting of only the highest-resolution level). Note that this is equivalent to --selectmip 0.

--subimage <n>

If the current image has multiple subimages, replace it with just the specified subimage. The subimage specifier n is either an integer giving the index of the subimage to extract (starting with 0), or the name of the subimage to extract (comparing to the "oiio:subimagename" metadata).

Additionally, this command can be used to remove one subimage (leaving the others) by using the optional modifier --subimage:delete=1.

--sisplit

Remove the top image from the stack, split it into its constituent subimages, and push them all onto the stack (first to last).

--siappend

Replaces the top two (or more) images on the stack with a single new multi-subimage comprised of the original images appended together as subimages within the same single image.

Optional appended modifiers include:

:n= number-of-subimages

Specify the number (if more than 2) of images to combine into a single multi-subimage image. This will be clamped between 2 and the total number of images on the stack.

--siappendall

Replace all of the individual images on the stack with a single new image comprised of the subimages of all original images appended together.

--ch <channellist>

Replaces the top image with a new image whose channels have been reordered as given by the channellist. The channellist is a comma-separated list of channel designations, each of which may be

  • an integer channel index of the channel to copy,

  • the name of a channel to copy,

  • newname = oldname, which copies a named channel and also renames it,

  • = float, which will set the channel to a constant value, or

  • newname = float, which sets the channel to a constant value as well as names the new channel.

Example channel lists include: R,G,B, R=0.0,G,B,A=1.0, R=B,G,B=R, 4,5,6,A.

Channel numbers outside the valid range of input channels, or unknown names, will be replaced by black channels. If the channellist is shorter than the number of channels in the source image, unspecified channels will be omitted.

If the channel list does not specify any changes (neither order, nor name, nor value), then this will just leave the images as-is, without any unnecessary expense or pointless copying of images in memory.

--chappend

Replaces the top two (or more) images on the stack with a single new image comprised of the channels of the input images appended together.

Optional appended modifiers include:

:n= number-of-subimages

Specify the number (if more than 2) of images whose channels should be combined into a single image. This will be clamped between 2 and the total number of images on the stack.

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

oiiotool commands that adjust the image stack

--pop

Pop the image stack, discarding the current image and thereby making the next image on the stack into the new current image.

--dup

Duplicate the current image and push the duplicate on the stack. Note that this results in both the current and the next image on the stack being identical copies.

--swap

Swap the current image and the next one on the stack.

--label <name>

Gives a name to (and saves) the current image at the top of the stack. Thereafter, the label name may be used to refer to that saved image, in the usual manner that an ordinary input image would be specified by filename.

oiiotool commands that make entirely new images

--create <size> <channels>

Create new black image with the given size and number of channels, pushing it onto the image stack and making it the new current image.

The size is in the form

width x height [+-] xoffset [+-] yoffset

If the offset is omitted, it will be x=0, y=0. Optional appended arguments include:

  • type= name : Create the image in memory with the named data type (default: float).

Examples:

--create 1920x1080 3         # RGB with w=1920, h=1080, x=0, y=0
--create 1024x768+100+0 4    # RGBA with w=1024, h=768, x=100, y=0
--create:type=uint8 1920x1080 3  # RGB, store internally as uint8
--pattern <patternname> <size> <channels>

Create new image with the given size and number of channels, initialize its pixels to the named pattern, and push it onto the image stack to make it the new current image.

The size is in the form

width x height [+-] xoffset [+-] yoffset

If the offset is omitted, it will be x=0, y=0. Optional appended arguments include:

  • type= name : Create the image in memory with the named data type (default: float).

The patterns recognized include the following:

  • black : A black image (all pixels 0.0)

  • constant : A constant color image, defaulting to white, but the color can be set with the optional :color=r,g,b,... arguments giving a numerical value for each channel.

  • checker : A black and white checkerboard pattern. The optional modifier :width= sets the width of the checkers (defaulting to 8 pixels), :height= sets the height of the checkers (defaulting to equal height and width). Optional modifiers :color1=r,g,b,... and :color2=r,g,b,... set the colors of the alternating squares (defaulting to black and white, respectively).

  • fill : A constant color or gradient, depending on the optional colors. Argument :color=r,g,b,... results in a constant color. Argument :top=r,g,b,...:bottom=... results in a top-to-bottom gradient. Argument :left=r,g,b,...:right=... results in a left-to-right gradient. Argument :topleft=r,g,b,...:topright=...:bottomleft=...:bottomright=... results in a 4-corner bilinear gradient.

  • noise : Create a noise image, with the option :type= specifying the kind of noise: (1) gaussian (default) for normal distribution noise with mean and standard deviation given by :mean= and :stddev=, respectively (defaulting to 0 and 0.1); (2) white (or uniform) for uniformly-distributed white noise over the range of values given by options :min= and :max= (defaults: 0 and 0.1); (3) blue for uniformly-distributed blue noise over the range of values given by options :min= and :max= (defaults: 0 and 0.1); (4) salt for “salt and pepper” noise where a portion of pixels given by option portion= (default: 0.1) is replaced with value given by option value= (default: 0). For any of these noise types, the option seed= can be used to change the random number seed and mono=1 can be used to make monochromatic noise (same value in all channels).

Examples:

A constant 4-channel, 640x480 image with all pixels (0.5, 0.5, 0.1, 1):

--pattern constant:color=0.3,0.5,0.1,1.0 640x480 4

A 256x256 RGB image with a 16-pixel-wide checker pattern:

--pattern checker:width=16:height=16 256x256 3
_images/checker.jpg

Horizontal, vertical, or 4-corner gradients:

--pattern fill:top=0.1,0.1,0.1:bottom=0,0,0.5 640x480 3
--pattern fill:left=0.1,0.1,0.1:right=0,0.75,0 640x480 3
--pattern fill:topleft=.1,.1,.1:topright=1,0,0:bottomleft=0,1,0:botromright=0,0,1 640x480 3
_images/gradient.jpg _images/gradienth.jpg _images/gradient4.jpg

The first example puts uniform noise independently in 3 channels, while the second generates a single greyscale noise and replicates it in all channels.

oiiotool --pattern noise:type=uniform:min=1:max=1 256x256 3 -o colornoise.jpg
oiiotool --pattern noise:type=uniform:min=0:max=1:mono=1 256x256 3 -o greynoise.jpg}
_images/unifnoise3.jpg _images/unifnoise1.jpg

Generate Gaussian noise with mean 0.5 and standard deviation 0.2 for each channel:

oiiotool --pattern noise:type=gaussian:mean=0.5:stddev=0.2 256x256 3 -o gaussnoise.jpg
_images/gaussnoise.jpg
--kernel <name> <size>

Create new 1-channel float image big enough to hold the named kernel and size (size is expressed as width x height, e.g. 5x5). The width and height are allowed to be floating-point numbers. The kernel image will have its origin offset so that the kernel center is at (0,0), and and will be normalized (the sum of all pixel values will be 1.0).

Kernel names can be: gaussian, sharp-gaussian, box, triangle, blackman-harris, mitchell, b-spline, cubic, keys, simon, rifman, disk. There are also catmull-rom and lanczos3 (and its synonym, nuke-lanczos6), but they are fixed-size kernels that don’t scale with the width, and are therefore probably less useful in most cases.

Examples:

oiiotool --kernel gaussian 11x11 -o gaussian.exr
--capture

Capture a frame from a camera device, pushing it onto the image stack and making it the new current image. Optional appended arguments include:

  • camera= num : Select which camera number to capture (default: 0).

Examples:

--capture               # Capture from the default camera
--capture:camera=1      # Capture from camera #1

oiiotool commands that do image processing

--add
--addc <value>
--addc <value0,value1,value2...>

Replace the two top images with a new image that is the pixel-by-pixel sum of those images (--add), or add a constant color value to all pixels in the top image (--addc).

For --addc, if a single constant value is given, it will be added to all color channels. Alternatively, a series of comma-separated constant values (with no spaces!) may be used to specifiy a different value to add to each channel in the image.

Optional appended modifiers include:

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

Examples:

oiiotool imageA.tif imageB.tif --add -o sum.jpg

oiiotool tahoe.jpg --addc 0.5 -o addc.jpg
_images/tahoe-small.jpg _images/addc.jpg

--sub
-- subc <value>
-- subc <value0,value1,value2...>

Replace the two top images with a new image that is the pixel-by-pixel difference between the first and second images (--sub), or subtract a constant color value from all pixels in the top image (--subc).

For --subc, if a single constant value is given, it will be subtracted from all color channels. Alternatively, a series of comma-separated constant values (with no spaces!) may be used to specifiy a different value to subtract from each channel in the image.

Optional appended modifiers include:

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

--mul
-- mulc <value>
-- mulc <value0,value1,value2...>

Replace the two top images with a new image that is the pixel-by-pixel multiplicative product of those images (--mul), or multiply all pixels in the top image by a constant value (--mulc).

For --mulc, if a single constant value is given, it will be multiplied to all color channels. Alternatively, a series of comma-separated constant values (with no spaces!) may be used to specifiy a different value to multiply with each channel in the image.

Optional appended modifiers include:

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

Example:

# Scale image brightness to 20% of its original
oiiotool tahoe.jpg --mulc 0.2 -o mulc.jpg
_images/tahoe-small.jpg _images/mulc.jpg

--div
-- divc <value>
-- divc <value0,value1,value2...>

Replace the two top images with a new image that is the pixel-by-pixel, channel-by-channel result of the first image divided by the second image (--div), or divide all pixels in the top image by a constant value (--divc). Division by zero is defined as resulting in 0.

For --divc, if a single constant value is given, all color channels will have their values divided by the same value. Alternatively, a series of comma-separated constant values (with no spaces!) may be used to specifiy a different multiplier for each channel in the image, respectively.

Optional appended modifiers include:

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

--mad

Replace the three top images A, B, and C (C being the top of stack, B below it, and A below B), and compute A*B+C, placing the result on the stack. Note that A B C --mad is equivalent to A B --mul C --add, though using --mad may be somewhat faster and preserve more precision.

Optional appended modifiers include:

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

--invert

Replace the top image with its color inverse. By default, it only inverts the first three channels in order to preserve alpha, but you can override the channel range of the inversion with optional modifiers chbegin and chend. Channels outside this range will simply be copied, without inversion.

Optional appended modifiers include:

:chbegin= int

Override the beginning of the range of channels to be inverted (defaults to 0.)

:chend= int

Override the end of the range of channels to be inverted (defaults to 3). Remember that this is one more than the index of the last channel to be inverted.

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

Example:

oiiotool tahoe.jpg --inverse -o inverse.jpg
_images/tahoe-small.jpg _images/invert.jpg
--absdiff
--absdiffc <value>
--absdiffc <value0,value1,value2...>

Replace the two top images with a new image that is the absolute value of the difference between the first and second images (--absdiff), or replace the top image by the absolute value of the difference between each pixel and a constant color (--absdiffc).

Optional appended modifiers include:

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

--abs

Replace the current image with a new image that has each pixel consisting of the absolute value of the old pixel value.

Optional appended modifiers include:

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

--powc <value>
--powc <value0,value1,value2...>

Raise all the pixel values in the top image to a constant power value. If a single constant value is given, all color channels will have their values raised to this power. Alternatively, a series of comma-separated constant values (with no spaces!) may be used to specifiy a different exponent for each channel in the image, respectively.

Optional appended modifiers include:

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

--noise

Alter the top image to introduce noise, with the option :type= specifying the kind of noise: (1) gaussian (default) for normal distribution noise with mean and standard deviation given by :mean= and :stddev=, respectively (defaulting to 0 and 0.1); (2) white (or uniform) for uniformly-distributed independent noise over the range of values given by options :min= and :max= (defaults: 0 and 0.1); (3) blue is also uniformly distributed between :min= and :max= (defaults: 0 and 0.1), but rather than independent values, low frequencies are supressed; (4) salt for “salt and pepper” noise where a portion of pixels given by option portion= (default: 0.1) is replaced with value given by option value= (default: 0).

Optional appended modifiers include:

:seed= int

Can be used to change the random number seed.

:mono=1

Make monochromatic noise (same value in all channels).

:nchannels= int

Limit which channels are affected by the noise.

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

Example:

# Add color gaussian noise to an image
oiiotool tahoe.jpg --noise:type=gaussian:stddev=0.1 -o noisy.jpg

# Simulate bad pixels by turning 1% of pixels black, but only in RGB
# channels (leave A alone)
oiiotool tahoe-rgba.tif --noise:type=salt:value=0:portion=0.01:mono=1:nchannels=3 \
    -o dropouts.tif

noiseimg1

noiseimg2

noiseimg3

noiseimg4

white noise

blue noise

gaussian noise added

salt & pepper dropouts

--chsum

Replaces the top image by a copy that contains only 1 color channel, whose value at each pixel is the sum of all channels of the original image. Using the optional weight allows you to customize the weight of each channel in the sum.

Optional appended modifiers include:

weight= r,g,…

Specify the weight of each channel (default: 1).

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

Example:

oiiotool RGB.tif --chsum:weight=.2126,.7152,.0722 -o luma.tif
_images/tahoe-small.jpg _images/luma.jpg

--contrast

Remap pixel values from [black, white] to [min, max], with an optional smooth sigmoidal contrast stretch as well.

Optional appended modifiers include:

black= vals

Specify black value(s), default 0.0.

white= vals

Specify white value(s), default 1.0.

min= vals

Specify the minimum range value(s), default 0.0.

max= vals

Specify the maximum range value(s), default 1.0.

scontrast= vals

Specify sigmoidal contrast slope value(s),

default 1.0. sthresh= vals

Specify sigmoidal threshold value(s) giving the position of maximum slope, default 0.5.

clamp= on

If on is nonzero, will optionally clamp all result channels to [min,max].

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

Each vals may be either a single floating point value for all channels, or a comma-separated list of per-channel values.

Examples:

oiiotool tahoe.tif --contrast:black=0.1:white=0.75 -o linstretch.tif
oiiotool tahoe.tif --contrast:black=1.0:white=0.0:clamp=0 -o inverse.tif
oiiotool tahoe.tif --contrast:scontrast=5 -o sigmoid.tif

crimage1

crimage2

crimage3

crimage4

original

linstretch

inverse

sigmoid
--saturate <scale>

Scale the saturation of the first three color channels of the image by the scale: 0.0 fully desaturates the image into its greyscale luminance equivalent image, 1.0 leaves the image unchanged, scale values inside this range interpolate between them, and scale > 1 would increase apparent color saturation.

Optional appended modifiers include:

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

Examples:

oiiotool tahoe.exr --saturate 0 -o grey.exr
oiiotool tahoe.exr --saturate 2 -o colorful.exr

sat1

sat2

sat2

original

sat scale = 0

sat scale = 2

This command was added in OIIO 2.4.

--colormap <mapname>

Creates an RGB color map based on the luminance of the input image. The mapname may be one of: “magma”, “inferno”, “plasma”, “viridis”, “turbo”, “blue-red”, “spectrum”, and “heat”. Or, mapname may also be a comma-separated list of RGB triples, to form a custom color map curve.

Note that “magma”, “inferno”, “plasma”, “viridis” are perceptually uniform, strictly increasing in luminance, look good when converted to grayscale, and work for people with all types of colorblindness. The “turbo” color map also shares all of these qualities except for being strictly increasing in luminance. These are all desirable qualities that are lacking in the other, older, crappier maps (blue-red, spectrum, and heat). Don’t be fooled by the flashy “spectrum” colors — it is an empirically bad color map compared to the preferred ones.

Optional appended modifiers include:

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

Example:

oiiotool tahoe.jpg --colormap inferno -o inferno.jpg
oiiotool tahoe.jpg --colormap viridis -o viridis.jpg
oiiotool tahoe.jpg --colormap turbo -o turbo.jpg
oiiotool tahoe.jpg --colormap .25,.25,.25,0,.5,0,1,0,0 -o custom.jpg

cmimage1

cmimage2

cmimage3

cmimage4

cmimage5

original

inferno

viridis

turbo

custom values
--paste <location>

Takes two images – the first is the “foreground” and the second is the “background” – and uses the pixels of the foreground to replace those of the backgroud, with foreground pixel (0,0) being pasted to the background at the location specified (expressed as +xpos+ypos, e.g., +100+50, or of course using - for negative offsets). Only pixels within the actual data region of the foreground image are pasted in this manner.

Note that if location is +0+0, the foreground image’s data region will be copied to its same position in the background image (this is useful if you are pasting an image that already knows its correct data window offset).

Optional appended modifiers include:

  • mergeroi=1 : If the value is nonzero, the result image will be sized to be the union of the input images (versus being the same data window as the background image). (The mergeroi modifier was added in OIIO 2.1.)

  • all=1 : If the value is nonzero, will paste all images on the image stack, not just the top two images. This can be useful to paste-merge many images at once, for example, if you have rendered a large image in abutting tiles and wish to re-assemble them into a single image. (The all modifier was added in OIIO 2.1.)

Examples:

# Result will be the size of bg, but with fg on top and with an
# offset of (100,100).
oiiotool fg.exr bg.exr -paste +100+100 -o out.exr

# Use "merge" mode, so result will be sized to contain both fg
# and bg. Also, paste fg into its natural position given by its
# data window.
oiiotool fg.exr bg.exr -paste:mergeroi=1 +0+0 -o out.exr

# Merge many non-overlapping "tiles" into one combined image
oiiotool img*.exr -paste:mergeroi=1:all=1 +0+0 -o combined.exr
--pastemeta <location>

Takes two images – the first will be a source of metadata only, and the second the source of pixels – and produces a new copy of the second image with the metadata from the first image added.

The output image’s pixels will come only from the second input. Metadata from the second input will be preserved if no identically-named metadata was present in the first input image.

Examples:

# Add all the metadata from meta.exr to pixels.exr and write the
# combined image to out.exr.
oiiotool meta.exr pixels.exr --pastemeta -o out.exr
--mosaic <size>

Removes \(w \times h\) images from the stack, dictated by the size, and turns them into a single image mosaic – an image that comprises \(w \times h\) “cells” each containing one of the constituent images.

If there are fewer images on the stack than the number of cells requested, the last cells will be black.

By default, the size of the “cell” is simply the largest of the constituent images, but the optional fit parameter can instead dictate the cell size and constituent images will be resized to fit this cell size.

Optional appended modifiers include:

  • fit= WxH : Sets the dimensions to which the constituent images will be resized as they are assembled into the mosaic.

  • pad= num : Select the number of pixels of black padding to add between images (default: 0).

Examples:

oiiotool left.tif right.tif --mosaic:pad=16 2x1 -o out.tif

oiiotool 0.tif 1.tif 2.tif 3.tif 4.tif --mosaic:pad=16:fit=320x240 2x2 -o out.tif
_images/mosaic.jpg
--over

Replace the two top images with a new image that is the Porter/Duff “over” composite with the first image as the foreground and the second image as the background. Both input images must have the same number and order of channels and must contain an alpha channel.

Optional appended modifiers include:

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

--zover

Replace the two top images with a new image that is a depth composite of the two images – the operation is the Porter/Duff “over” composite, but each pixel individually will choose which of the two images is the foreground and which background, depending on the “Z” channel values for that pixel (larger Z means farther away). Both input images must have the same number and order of channels and must contain both depth/Z and alpha channels. Optional appended modifiers include:

zeroisinf= num

If nonzero, indicates that z=0 pixels should be treated as if they were infinitely far away. (The default is 0, meaning that “zero means zero.””).

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

--rotate90

Replace the current image with a new image that is rotated 90 degrees clockwise.

Optional appended modifiers include:

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

Example:

oiiotool grid.jpg --rotate90 -o rotate90.jpg
_images/grid-small.jpg _images/rotate90.jpg
--rotate180

Replace the current image with a new image that is rotated by 180 degrees.

Optional appended modifiers include:

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

Example:

oiiotool grid.jpg --rotate180 -o rotate180.jpg
_images/grid-small.jpg _images/rotate180.jpg
--rotate270

Replace the current image with a new image that is rotated 270 degrees clockwise (or 90 degrees counter-clockwise).

Optional appended modifiers include:

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

Example:

oiiotool grid.jpg --rotate270 -o rotate270.jpg
_images/grid-small.jpg _images/rotate270.jpg
--flip

Replace the current image with a new image that is flipped vertically, with the top scanline becoming the bottom, and vice versa.

Optional appended modifiers include:

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

Example:

oiiotool grid.jpg --flip -o flip.jpg
_images/grid-small.jpg _images/flip.jpg
--flop

Replace the current image with a new image that is flopped horizontally, with the leftmost column becoming the rightmost, and vice versa.

Optional appended modifiers include:

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

Example:

oiiotool grid.jpg --flop -o flop.jpg
_images/grid-small.jpg _images/flop.jpg
--reorient

Replace the current image with a new image that is rotated and/or flipped as necessary to move the pixels to match the Orientation metadata that describes the desired display orientation.

Example:

oiiotool tahoe.jpg --reorient -o oriented.jpg
--transpose

Replace the current image with a new image that is reflected about the x-y axis (x and y coordinates and sizes are swapped).

Optional appended modifiers include:

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

Example:

oiiotool grid.jpg --transpose -o transpose.jpg
_images/grid-small.jpg _images/transpose.jpg
--cshift <offset>

Circularly shift the pixels of the image by the given offset (expressed as +10+100 to move by 10 pixels horizontally and 100 pixels vertically, or +50-30 to move by 50 pixels horizontally and -30 pixels vertically. Circular shifting means that the pixels wrap to the other side as they shift.

Optional appended modifiers include:

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

Example:

oiiotool grid.jpg --cshift +70+30 -o cshift.jpg
_images/grid-small.jpg _images/cshift.jpg
--crop <size>

Replace the current image with a new copy with the given size, cropping old pixels no longer needed, padding black pixels where they previously did not exist in the old image, and adjusting the offsets if requested.

The size is in the form

width x height [+-] xoffset [+-] yoffset

or

xmin,ymin,xmax,ymax

Note that crop does not reposition pixels, it only trims or pads to reset the image’s pixel data window to the specified region.

If oiiotool’s global -a flag is used (all subimages), or if the optional --crop:allsubimages=1 is employed, the crop will be applied identically to all subimages.

Examples:

# Both of these crop to a 100x120 region that begins at x=35,y=40
oiiotool tahoe.exr --crop 100x120+35+40 -o crop.exr
oiiotool tahoe.exr --crop 35,40,134,159 -o crop.exr
_images/tahoe-small.jpg _images/crop.jpg
--croptofull

Replace the current image with a new image that is cropped or padded as necessary to make the pixel data window exactly cover the full/display window.

--trim

Replace the current image with a new image that is cropped to contain the minimal rectangular ROI that contains all of the nonzero-valued pixels of the original image.

Examples:

oiiotool greenrect.exr -trim -o trimmed.jpg

.. image:: figures/pretrim.jpg
   :width: 1.5 in
.. image:: figures/trim.jpg
   :width: 1.5 in
--cut <size>

Replace the current image with a new copy with the given size, cropping old pixels no longer needed, padding black pixels where they previously did not exist in the old image, repositioning the cut region at the image origin (0,0) and resetting the full/display window to be identical to the new pixel data window. (In other words, --cut is equavalent to --crop followed by --origin +0+0 --fullpixels.)

The size is in the form

width x height [+-] xoffset [+-] yoffset

or

xmin,ymin,xmax,ymax

Examples:

# Both of these crop to a 100x120 region that begins at x=35,y=40
oiiotool tahoe.exr --cut 100x120+35+40 -o cut.exr
oiiotool tahoe.exr --cut 35,40,134,159 -o cut.exr
_images/tahoe-small.jpg _images/cut.jpg

--resample <size>

Replace the current image with a new image that is resampled to the given pixel data resolution rapidly, but at a low quality, either by simple bilinear interpolation or by just copying the “closest” pixel. The size is in the form of any of these:

width x height

width x height [+-] xoffset [+-] yoffset

xmin,ymin,xmax,ymax

wscale% x hscale%

if width or height is 0, that dimension will be automatically computed so as to preserve the original aspect ratio.

Optional appended modifiers include:

interp= bool

If set to zero, it will just copy the “closest” pixel; if nonzero, bilinear interpolation of the surrounding 4 pixels will be used.

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

Examples (suppose that the original image is 640x480):

--resample 1024x768         # new resolution w=1024, h=768
--resample 50%              # reduce resolution to 320x240
--resample 300%             # increase resolution to 1920x1440
--resample 400x0            # new resolution will be 400x300
--resize <size>

Replace the current image with a new image whose display (full) size is the given pixel data resolution and offset. The size is in the form

width x height

width x height [+-] xoffset [+-] yoffset

xmin,ymin,xmax,ymax

scale%

wscale% x hscale%

if width or height is 0, that dimension will be automatically computed so as to preserve the original aspect ratio.

Optional appended modifiers include:

filter= name

Filter name. The default is blackman-harris when increasing resolution, lanczos3 when decreasing resolution.

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

Examples (suppose that the original image is 640x480):

--resize 1024x768         # new resolution w=1024, h=768
--resize 50%              # reduce resolution to 320x240
--resize 300%             # increase resolution to 1920x1440
--resize 400x0            # new resolution will be 400x300
--fit <size>

Replace the current image with a new image that is resized to fit into the given pixel data resolution, keeping the original aspect ratio and padding with black pixels if the requested image size does not have the same aspect ratio. The size is in the form

width x height

width x height [+-] xoffset [+-] yoffset

Optional appended modifiers include:

  • filter= name : Filter name. The default is blackman-harris when increasing resolution, lanczos3 when decreasing resolution.

  • fillmode= mode : determines which of several methods will be used to determine how the image will fill the new frame, if its aspect ratio does not precisely match the original source aspect ratio:

    • “width” exactly fills the width of the new frame, either cropping or letterboxing the height if it isn’t precisely the right size to preserve the original aspect ratio.

    • “height” exactly fills the height of the new frame, either cropping or letterboxing the width if it isn’t precisely the right size to preserve the original aspect ratio.

    • “letterbox” (the default) chooses whichever of “width” or “height” will maximally fill the new frame with no image data lost (it will only letterbox, never crop).

  • pad= p : If the argument is nonzero, will pad with black pixels to make the resulting image exactly the size specified, if the source and desired size are not the same aspect ratio.

  • exact= e : If the argument is nonzero, will result in an exact match on aspect ratio and centering (partial pixel shift if necessary), whereas the default (0) will only preserve aspect ratio and centering to the precision of a whole pixel.

  • wrap= w : For “exact” aspect ratio fitting, this determines the wrap mode used for the resizing kernel (default: black, other choices include clamp, periodic, mirror).

Examples:

oiiotool in.exr --fit:pad=1:exact=1 640x480 -o out.exr

oiiotool in.exr --fit 1024x1024 -o out.exr
_images/tahoe-small.jpg _images/fit-width.jpg _images/fit-height.jpg _images/fit-letterbox.jpg

Examples of an image being fit into a frame that is wider than the original aspect ratio with fill mode: (a) original, (b) “width”, (c) “height”, (d) “letterbox”.

_images/tahoe-small.jpg _images/fitv-width.jpg _images/fitv-height.jpg _images/fitv-letterbox.jpg

Examples of an image being fit into a frame that is narrower than the original aspect ratio with fill mode: (a) original, (b) “width”, (c) “height”, (d) “letterbox”.

--pixelaspect <aspect>

Replace the current image with a new image that scales up the width or height in order to match the requested pixel aspect ratio. If displayed in a manner that honors the PixelAspectRatio, it should look the same, but it will have different pixel dimensions than the original. It will always be the same or higher resolution, so it does not lose any detail present in the original.

As an example, if you have a 512x512 image with pixel aspect ratio 1.0, --pixelaspect 2.0 will result in a 512x1024 image that has “PixelAspectRatio” metadata set to 2.0.

Optional appended modifiers include:

  • filter= name : Filter name. The default is lanczos3.

Examples:

oiiotool mandrill.tif --pixelaspect 2.0 -o widepixels.tif
--rotate <angle>

Replace the current image with a new image that is rotated by the given angle (in degrees). Positive angles mean to rotate counter-clockwise, negative angles mean clockwise. By default, the center of rotation is at the exact center of the display window (a.k.a. “full” image), but can be explicitly set with the optional center=x,y option.

Optional appended modifiers include:

center= x,y

Alternate center of rotation.

filter= name

Filter name. The default is lanczos3.

recompute_roi= val

If nonzero, recompute the pixel data window to exactly hold the transformed image (default=0).

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

Examples:

oiiotool mandrill.tif --rotate 45 -o rotated.tif

oiiotool mandrill.tif --rotate:center=80,91.5:filter=lanczos3 45 -o rotated.tif
_images/grid-small.jpg _images/rotate45.jpg
--warp <M33>

Replace the current image with a new image that is warped by the given 3x3 matrix (presented as a comma-separated list of values, without any spaces).

Optional appended modifiers include:

filter= name

Filter name. The default is lanczos3.

recompute_roi= val

If nonzero, recompute the pixel data window to exactly hold the transformed image (default=0).

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

Examples:

oiiotool mandrill.tif --warp "0.707,0.707,0,-0.707,0.707,0,128,-53.02,1" -o warped.tif
--convolve

Use the top image as a kernel to convolve the next image farther down the stack, replacing both with the result.

Optional appended modifiers include:

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

Examples:

# Use a kernel image already prepared
oiiotool image.exr kernel.exr --convolve -o output.exr

# Construct a kernel image on the fly with --kernel
oiiotool image.exr --kernel gaussian 5x5 --convolve -o blurred.exr
--blur <size>

Blur the top image with a blur kernel of the given size expressed as width x height. (The sizes may be floating point numbers.)

Optional appended modifiers include:

kernel= name

Kernel name. The default is gaussian.

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

Examples:

oiiotool image.jpg --blur 5x5 -o blurred.jpg

oiiotool image.jpg --blur:kernel=bspline 7x7 -o blurred.jpg

convimage1

convimage2

original

blurred
--median <size>

Perform a median filter on the top image with a window of the given size expressed as width x height. (The sizes are integers.) This helps to eliminate noise and other unwanted high-frequency detail, but without blurring long edges the way a --blur command would.

Optional appended modifiers include:

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

Examples:

oiiotool noisy.jpg --median 3x3 -o smoothed.jpg

medimage1

medimage2

medimage3

original

with dropouts

median filtered
--dilate <size>
--erode <size>

Perform dilation or erosion on the top image with a window of the given size expressed as width x height. (The sizes are integers.) Dilation takes the maximum of pixel values inside the window, and makes bright features wider and more prominent, dark features thinner, and removes small isolated dark spots. Erosion takes the minimum of pixel values inside the window, and makes dark features wider, bright features thinner, and removes small isolated bright spots.

Optional appended modifiers include:

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

Examples:

oiiotool orig.tif --dilate 3x3 -o dilate.tif
oiiotool orig.tif --erode 3x3 -o erode.tif
oiiotool orig.tif --erode 3x3 --dilate 3x3 -o open.tif
oiiotool orig.tif --dilate 3x3 --erode 3x3 -o close.tif
oiiotool orig.tif --dilate 3x3 --erode 3x3 -sub -o gradient.tif
oiiotool orig.tif open.tif -o tophat.tif
oiiotool close.tif orig.tif -o bottomhat.tif

morph1

morph2

morph3

morph4

original

dilate

erode

open

morph5

morph6

morph7

morph8

close

gradient

tophat

bottomhat
--laplacian

Calculates the Laplacian of the top image.

Optional appended modifiers include:

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

Examples:

oiiotool tahoe.jpg --laplacian tahoe-laplacian.exr

lapimage1

lapimage2

original

Laplacian image
--unsharp

Unblur the top image using an “unsharp mask.””

Optional appended modifiers include:

kernel= name

Name of the blur kernel (default: gaussian). If the kernel name is median, the unsarp mask algorithm will use a median filter rather than a blurring filter in order to compute the low-frequency image.

width= w

Width of the blur kernel (default: 3).

contrast= c

Contrast scale (default: 1.0)

threshold= t

Threshold for applying the difference (default: 0)

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

Examples:

oiiotool image.jpg --unsharp -o sharper.jpg

oiiotool image.jpg --unsharp:width=5:contrast=1.5 -o sharper.jpg

oiiotool image.jpg --unsharp:kernel=median -o sharper.jpg
# Note: median filter helps emphasize compact high-frequency details
# without over-sharpening long edges as the default unsharp filter
# sometimes does.
--fft
--ifft

Performs forward and inverse unitized discrete Fourier transform. The forward FFT always transforms only the first channel of the top image on the stack, and results in a 2-channel image (with real and imaginary channels). The inverse FFT transforms the first two channels of the top image on the stack (assuming they are real and imaginary, respectively) and results in a single channel result (with the real component only of the spatial domain result).

Optional appended modifiers include:

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

Examples:

# Select the blue channel and take its DCT
oiiotool image.jpg --ch 2 --fft -o fft.exr

# Reconstruct from the FFT
oiiotool fft.exr --ifft -o reconstructed.exr

# Output the power spectrum: real^2 + imag^2
oiiotool fft.exr --dup --mul --chsum -o powerspectrum.exr
--polar
--unpolar

The --polar transforms a 2-channel image whose channels are interpreted as complex values (real and imaginary components) into the equivalent values expressed in polar form of amplitude and phase (with phase between 0 and \(2\pi\)).

The unpolar performs the reverse transformation, converting from polar values (amplitude and phase) to complex (real and imaginary).

Optional appended modifiers include:

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

Examples:

oiiotool complex.exr --polar -o polar.exr
oiiotool polar.exr --unpolar -o complex.exr
--fixnan <streategy>

Replace the top image with a copy in which any pixels that contained NaN or Inf values (hereafter referred to collectively as “nonfinite”) are repaired. If strategy is black, nonfinite values will be replaced with 0. If strategy is box3, nonfinite values will be replaced by the average of all the finite values within a 3x3 region surrounding the pixel. If strategy is error, nonfinite values will be left alone, but it will result in an error that will terminate oiiotool.

--max
--maxc <value>
--maxc <value0,value1,value2...>
--min
--minc <value>
--minc <value0,value1,value2...>

Replace the two top images with a new image that is the pixel-by-pixel maximum of those images (--max) or minimum (--min) of the corresponding pixels of each image, or the min/max of each pixel of one image with a constant color (--maxc, --minc).

For --maxc and --minc, if a single constant value is given, it will be used for all color channels. Alternatively, a series of comma-separated constant values (with no spaces) may be used to specifiy a different value to add to each channel in the image.

Optional appended modifiers include:

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

Examples:

oiiotool imageA.tif imageB.tif –min -o minimum.tif

# Clamp all channels to a mimimum of 0 (all negative values are # changed to 0). oiiotool input.exr –minc 0.0 -o nonegatives.exr

--clamp

Replace the top image with a copy in which pixel values have been clamped. Optional arguments include:

Optional appended modifiers include:

  • min= val : Specify a minimum value for all channels.

  • min= val0,val1,… : Specify minimum value for each channel individually.

  • max= val : Specify a maximum value for all channels.

  • max= val0,val1,… : Specify maximum value for each channel individually.

  • clampalpha= val : If val is nonzero, will additionally clamp the alpha channel to [0,1]. (Default: 0, no additional alpha clamp.)

If no value is given for either the minimum or maximum, it will NOT clamp in that direction. For the variety of minimum and maximum that specify per-channel values, a missing value indicates that the corresponding channel should not be clamped.

Examples:

  • --clamp:min=0 : Clamp all channels to a mimimum of 0 (all negative values are changed to 0).

  • --clamp:min=0:max=1 : Clamp all channels to [0,1].

  • --clamp:clampalpha=1 : Clamp the designated alpha channel to [0,1].

  • --clamp:min=,,0:max=,,3.0 : Clamp the third channel to [0,3], do not clamp & other channels.

--maxchan
--minchan

Replace the top image with a single channel image that, for each pixel, contains the maximum value (for --maxchan) or minimum value (for --minchan) of all the channels in the corresponding pixel of the original image.

This command was first added to OpenImageIO 2.4.0.

Optional appended modifiers include:

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

Examples:

oiiotool RGB.tif –maxchan -o max_of_RGB.tif

--rangecompress
--rangeexpand

Range compression re-maps input values to a logarithmic scale. Range expansion is the inverse mapping back to a linear scale. Range compression and expansion only applies to color channels; alpha or z channels will not be modified.

By default, this transformation will happen to each color channel independently. But if the optional luma argument is nonzero and the image has at least 3 channels and the first three channels are not alpha or depth, they will be assumed to be RGB and the pixel scaling will be done using the luminance and applied equally to all color channels. This can help to preserve color even when remapping intensity.

Optional appended modifiers include:

luma= val

val is 0, turns off the luma behavior.

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

Range compression and expansion can be useful in cases where high contrast super-white (> 1) pixels (such as very bright highlights in HDR captured or rendered images) can produce undesirable artifacts, such as if you resize an HDR image using a filter with negative lobes – which could result in objectionable ringing or even negative result pixel values. For example:

oiiotool hdr.exr --rangecompress --resize 512x512 --rangeexpand -o resized.exr
--fillholes

Replace the top image with a copy in which any pixels that had \(\alpha < 1\) are “filled” in a smooth way using data from surrounding \(\alpha > 0\) pixels, resulting in an image that is \(\alpha = 1\) and plausible color everywhere. This can be used both to fill internal “holes” as well as to extend an image out.

--box <x1,y1,x2,y2>

Draw (rasterize) a filled or unfilled a box with opposite corners (x1,y1) and (x2,y2). Additional optional arguments include:

color= r,g,b,…

specify the color of the lines

fill= bool

if nonzero, fill in the box

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

The default color, if not supplied, is opaque white.

Examples:

oiiotool checker.exr --box:color=0,1,1,1 150,100,240,180 \
             --box:color=0.5,0.5,0,0.5:fill=1 100,50,180,140 -o out.exr
_images/box.png
--line <x1,y1,x2,y2,...>

Draw (rasterize) an open polyline connecting the list of pixel positions, as a comma-separated list of alternating x and y values. Additional optional arguments include:

color= r,g,b,…

specify the color of the line

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

The default color, if not supplied, is opaque white.

Examples:

oiiotool checker.exr --line:color=1,0,0 10,60,250,20,100,190 -o out.exr
_images/lines.png
--point <x1,y1,x2,y2,...>

Draw single points at the list of pixel positions, as a comma-separated list of alternating x and y values. Additional optional arguments include:

color= r,g,b,…

specify the color of the line

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

The default color, if not supplied, is opaque white.

Examples:

oiiotool checker.exr --point:color=1,0,0 10,60,250,20,100,190 -o out.exr
_images/points.png
--fill <size>

Alter the top image by filling the ROI specified by size. The fill can be a constant color, vertical gradient, horizontal gradient, or four-corner gradient.

Optional modifiers for constant color:

color= r,g,b,…

the color of the constant

Optional modifiers for vertical gradient:

top= r,g,b,…

the color for the top edge of the region

bottom= r,g,b,…

the color for the bottom edge of the region

Optional modifiers for horizontal gradient:

left= r,g,b,…

the color for the left edge of the region

right= r,g,b,…

the color for the right edge of the region

Optional modifiers for 4-corner gradient:

topleft= r,g,b,…

the color for the top left corner of the region

topright= r,g,b,…

the color for the top right corner of the region

bottomleft= r,g,b,…

the color for the bottom left corner of the region

bottomright= r,g,b,…

the color for the bottom right corner of the region

Examples:

# make a grey-to-blue vertical gradient
oiiotool --create 640x480 3 \
    --fill:top=0.1,0.1,0.1:bottom=0,0,0.5 640x480 -o gradient.tif

# make a grey-to-green horizontal gradient
oiiotool --create 640x480 3 \
    --fill:left=0.1,0.1,0.1:right=0,0.75,0 640x480 -o gradient.tif

# four-corner interpolated gradient
oiiotool --create 640x480 3 \
    -fill:topleft=.1,.1,.1:topright=1,0,0:bottomleft=0,1,0:botromright=0,0,1 \
        640x480 -o gradient.tif
--text <words>

Draw (rasterize) text overtop of the current image.

Optional appended modifiers include:

x= xpos

x position (in pixel coordinates) of the text

y= ypos

y position (in pixel coordinates) of the text

size= size

font size (height, in pixels)

font= name

font name, full path to the font file on disk (use double quotes "name" if the path name includes spaces or a colon)

color= r,g,b,…

specify the color of the text

xalign= val

controls horizontal text alignment: left (default), right, center.

yalign= val

controls vertical text alignment: base (default), top, bottom, center.

shadow= size

if nonzero, will make a dark shadow halo to make the text more clear on bright backgrounds.

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

The default positions the text starting at the center of the image, drawn 16 pixels high in opaque white in all channels (1,1,1,…), and using a default font (which may be system dependent).

Examples:

oiiotool --create 320x240 3 --text:x=10:y=400:size=40 "Hello world" \
    --text:x=100:y=200:font="Arial Bold":color=1,0,0:size=60 "Go Big Red!" \
    --tocolorspace sRGB -o text.jpg

oiiotool --create 320x240 3 --text:x=160:y=120:xalign=center "Centered" \
    --tocolorspace sRGB -o textcentered.jpg

oiiotool tahoe-small.jpg \
        --text:x=160:y=40:xalign=center:size=40:shadow=0 "shadow = 0" \
        --text:x=160:y=80:xalign=center:size=40:shadow=1 "shadow = 1" \
        --text:x=160:y=120:xalign=center:size=40:shadow=2 "shadow = 2" \
        --tocolorspace sRGB -o textshadowed.jpg

Note that because of slightly differing fonts and versions of Freetype available, we do not expect drawn text to be pixel-for-pixel identical on different platforms supported by OpenImageIO.

oiiotool commands for color management

Many of the color management commands depend on an installation of OpenColorIO (http://opencolorio.org).

If OIIO has been compiled with OpenColorIO support and the environment variable $OCIO is set to point to a valid OpenColorIO configuration file, you will have access to all the color spaces that are known by that OCIO configuration. Alternately, you can use the --colorconfig option to explicitly point to a configuration file. If no valid configuration file is found (either in $OCIO or specified by --colorconfig} or OIIO was not compiled with OCIO support, then the only color space transformats available are linear to Rec709 (and vice versa) and linear to sRGB (and vice versa).

If you ask for oiiotool help (oiiotool --help), at the very bottom you will see the list of all color spaces, looks, and displays that oiiotool knows about.

--iscolorspace <colorspace>

Alter the metadata of the current image so that it thinks its pixels are in the named color space. This does not alter the pixels of the image, it only changes oiiotool’s understanding of what color space those those pixels are in.

--colorconfig <filename>

Instruct oiiotool to read an OCIO configuration from a custom location. Without this, the default is to use the $OCIO environment variable as a guide for the location of the configuration file.

--colorconvert <fromspace> <tospace>

Replace the current image with a new image whose pixels are transformed from the named fromspace color space into the named tospace (disregarding any notion it may have previously had about the color space of the current image). Optional appended modifiers include:

  • key= name, value= str :

    Adds a key/value pair to the “context” that OpenColorIO will used when applying the look. Multiple key/value pairs may be specified by making each one a comma-separated list.

  • unpremult= val :

    If the numeric val is nonzero, the pixel values will be “un-premultipled” (divided by alpha) prior to the actual color conversion, and then re-multipled by alpha afterwards. The default is 0, meaning the color transformation not will be automatically bracketed by divide-by-alpha / mult-by-alpha operations.

  • strict= val :

    When nonzero (the default), an inability to perform the color transform will be a hard error. If strict is 0, inability to find the transformation will just print a warning and simply copy the image without changing colors.

    :subimages= indices-or-names

    Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

--tocolorspace <tospace>

Replace the current image with a new image whose pixels are transformed from their existing color space (as best understood or guessed by OIIO) into the named tospace. This is equivalent to a use of oiiotool --colorconvert where the fromspace is automatically deduced.

Optional appended modifiers include:

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

--ccmatrix <m00,m01,...>

NEW 2.1

Replace the current image with a new image whose colors are transformed according to the 3x3 or 4x4 matrix formed from the 9 or 16 comma-separated floating-point values in the subsequent argument (spaces are allowed only if the whole collection of values is enclosed in quotes so that they are a single command-line argument).

The values fill in the matrix left to right, first row, then second row, etc. This means that colors are treated as “row vectors” that are post-multiplied by the matrix (C*M).

Optional appended modifiers include:

  • unpremult= val :

    If the numeric val is nonzero, the pixel values will be “un-premultipled” (divided by alpha) prior to the actual color conversion, and then re-multipled by alpha afterwards. The default is 0, meaning the color transformation not will be automatically bracketed by divide-by-alpha / mult-by-alpha operations.

  • invert= val :

    If nonzero, this will cause the matrix to be inverted before being applied.

  • transpose= val :

    If nonzero, this will cause the matrix to be transposed (this allowing you to more easily specify it as if the color values were column vectors and the transformation as M*C).

    :subimages= indices-or-names

    Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

Example:

# Convert ACES to ACEScg using a matrix
oiiotool aces.exr --ccmatrix:transpose=1 \
    "1.454,-0.237,-0.215,-0.077,1.176,-0.010,0.008,-0.006, 0.998" \
    -o acescg.exr
--ociolook <lookname>

Replace the current image with a new image whose pixels are transformed using the named OpenColorIO look description. Optional appended arguments include:

  • from= val

    Assume the image is in the named color space. If no from= is supplied, it will try to deduce it from the image’s metadata or previous --iscolorspace directives. If no such hints are available, it will assume the pixel data are in the default linear scene-referred color space.

  • to= val

    Convert to the named space after applying the look.

  • inverse= val

    If val is nonzero, inverts the color transformation and look application.

  • key= name, value= str

    Adds a key/value pair to the “context” that OpenColorIO will used when applying the look. Multiple key/value pairs may be specified by making each one a comma-separated list.

  • unpremult= val :

    If the numeric val is nonzero, the pixel values will be “un-premultipled” (divided by alpha) prior to the actual color conversion, and then re-multipled by alpha afterwards. The default is 0, meaning the color transformation not will be automatically bracketed by divide-by-alpha / mult-by-alpha operations.

    :subimages= indices-or-names

    Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

This command is only meaningful if OIIO was compiled with OCIO support and the environment variable $OCIO is set to point to a valid OpenColorIO configuration file. If you ask for oiiotool help (oiiotool --help), at the very bottom you will see the list of all looks that oiiotool knows about.

Examples:

oiiotool in.jpg --ociolook:from=vd8:to=vd8:key=SHOT:value=pe0012 match -o cc.jpg
--ociodisplay <displayname> <viewname>

Replace the current image with a new image whose pixels are transformed using the named OpenColorIO “display” transformation given by the displayname and viewname. An empty string for displayname means to use the default display, and an empty string for viewname means to use the default view on that display.

Optional appended modifiers include:

from= val

Assume the image is in the named color space. If no from= is supplied, it will try to deduce it from the image’s metadata or previous --iscolorspace directives. If no such hints are available, it will assume the pixel data are in the default linear scene-referred color space.

key= name, value= str

Adds a key/value pair to the “context” that OpenColorIO will used when applying the look. Multiple key/value pairs may be specified by making each one a comma-separated list.

unpremult= val :

If the numeric val is nonzero, the pixel values will be “un-premultipled” (divided by alpha) prior to the actual color conversion, and then re-multipled by alpha afterwards. The default is 0, meaning the color transformation not will be automatically bracketed by divide-by-alpha / mult-by-alpha operations.

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

This command is only meaningful if OIIO was compiled with OCIO support and the environment variable $OCIO is set to point to a valid OpenColorIO configuration file. If you ask for oiiotool help (oiiotool --help), at the very bottom you will see the list of all looks that oiiotool knows about.

Examples:

oiiotool in.exr --ociodisplay:from=lnf:key=SHOT:value=pe0012 sRGB Film -o cc.jpg
--ociofiletransform <name>

Replace the current image with a new image whose pixels are transformed using the named OpenColorIO file transform. Optional appended arguments include:

  • inverse= val :

    If val is nonzero, inverts the color transformation.

  • unpremult= val :

    If the numeric val is nonzero, the pixel values will be “un-premultipled” (divided by alpha) prior to the actual color conversion, and then re-multipled by alpha afterwards. The default is 0, meaning the color transformation not will be automatically bracketed by divide-by-alpha / mult-by-alpha operations.

    :subimages= indices-or-names

    Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

Examples:

oiiotool in.jpg --ociofiletransform footransform.csp -o out.jpg
--unpremult

Divide all color channels (those not alpha or z) of the current image by the alpha value, to “un-premultiply” them. This presumes that the image starts of as “associated alpha,” a.k.a. “premultipled.” Pixels in which the alpha channel is 0 will not be modified (since the operation is undefined in that case). This is a no-op if there is no identified alpha channel.

Optional appended modifiers include:

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

--premult

Multiply all color channels (those not alpha or z) of the current image by the alpha value, to “premultiply’’ them. This presumes that the image starts of as “unassociated alpha,’’ a.k.a. “non-premultipled.”

Optional appended modifiers include:

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).


oiiotool commands for deep images

A number of oiiotool operations are designed to work with “deep” images. These are detailed below. In general, operations not listed in this section should not be expected to work with deep images.

Commands specific to deep images

--deepen

If the top image is not deep, then turn it into the equivalent “deep” image. Pixels with non-infinite $z$ or with any non-zero color channels will get a single depth sample in the resulting deep image. Pixels in the source that have 0 in all channels, and either no “Z” channel or a $z$ value indicating an infinite distance, will result in a pixel with no depth samples.

Optional appended modifiers include:

z= val

The depth to use for deep samples if the source image did not have a “Z” channel. (The default is 1.0.)

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

--flatten

If the top image is “deep,” then “flatten” it by compositing the depth samples in each pixel.

Optional appended modifiers include:

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

--deepmerge

Replace the two top images with a new deep image that is the “deep merge” of the inputs. Both input images must be deep images, have the same number and order of channels and must contain an alpha channel and depth channel.

Optional appended modifiers include:

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).

--deepholdout

Replace the two top images with a new deep image that is the ``deep holdout’’ of the first image by the second — that is, the samples from the first image that are closer than the opaque frontier of the second image. Both input inputs must be deep images.

Optional appended modifiers include:

:subimages= indices-or-names

Include/exclude subimages (see Dealing with multi-subimage/multi-part files).


General commands that also work for deep images

--addc, --subc, --mulc, --divc

Adding, subtracting, multiplying, or dividing a per-channel constant will work for deep images, performing the operation for every sample in the image.

--autotrim

For subsequent outputs, automatically --trim before writing the file.

--ch <channellist>

Reorder, rename, remove, or add channels to a deep image. See Section oiiotool commands that shuffle channels or subimages

--crop <size>

Crop (adjust the pixel data window), removing pixels or adding empty pixels as needed.

--paste <position>

Replace one image’s pixels with another’s (at an arbitary offset).

(This functionality was extended to deep images in OIIO 2.1.)

--resample <size>

Resampling (resize without filtering or interpolation, just choosing the closest deep pixel to copy for each output pixel).

Optional appended modifiers include:

  • interp= val : If 0, the “closest” single pixel will be copied for each sample. If 1, the nearest 4 pixels will be interpolated to produce each sample. (Default: 1)

--diff

Report on the difference of the top two images.

--dumpdata

Print to the console detailed information about the values in every pixel.

Optional appended modifiers include:

  • empty= val : If 0, will cause deep images to skip printing of information about pixels with no samples, and cause non-deep images to skip printing information about pixels that are entirely 0.0 value in all channels.

--info

Prints information about each input image as it is read.

--trim

Replace the current image with a new image that is cropped to contain the minimal rectangular ROI that contains all of the non-empty pixels of the original image.

--scanline
--tile <x> <y>

Convert to scanline or to tiled representations upon output.

--stats

Prints detailed statistical information about each input image as it is read.

--fixnan <streategy>

Replace the top image with a copy in which any pixels that contained NaN or Inf values (hereafter referred to collectively as “nonfinite”) are repaired. The strategy may be either black or error.

Getting Image information With iinfo

The iinfo program will print either basic information (name, resolution, format) or detailed information (including all metadata) found in images. Because iinfo is built on top on OpenImageIO, it will print information about images of any formats readable by ImageInput plugins on hand.

Using iinfo

The iinfo utility is invoked as follows:

iinfo options filename

Where filename (and any following strings) names the image file(s) whose information should be printed. The image files may be of any format recognized by OpenImageIO (i.e., for which ImageInput plugins are available).

In its most basic usage, it simply prints the resolution, number of channels, pixel data type, and file format type of each of the files listed:

$ iinfo img_6019m.jpg grid.tif lenna.png

img_6019m.jpg : 1024 x  683, 3 channel, uint8 jpeg
grid.tif      :  512 x  512, 3 channel, uint8 tiff
lenna.png     :  120 x  120, 4 channel, uint8 png

The -s flag also prints the uncompressed sizes of each image file, plus a sum for all of the images:

$ iinfo -s img_6019m.jpg grid.tif lenna.png

img_6019m.jpg : 1024 x  683, 3 channel, uint8 jpeg (2.00 MB)
grid.tif      :  512 x  512, 3 channel, uint8 tiff (0.75 MB)
lenna.png     :  120 x  120, 4 channel, uint8 png (0.05 MB)
Total size: 2.81 MB

The -v option turns on emph{verbose mode}, which exhaustively prints all metadata about each image:

img_6019m.jpg : 1024 x  683, 3 channel, uint8 jpeg
    channel list: R, G, B
    Color space: sRGB
    ImageDescription: "Family photo"
    Make: "Canon"
    Model: "Canon EOS DIGITAL REBEL XT"
    Orientation: 1 (normal)
    XResolution: 72
    YResolution: 72
    DateTime: "2008:05:04 19:51:19"
    Exif:YCbCrPositioning: 2
    ExposureTime: 0.004
    FNumber: 11
    Exif:ExposureProgram: 2 (normal program)
    Exif:ISOSpeedRatings: 400
    Exif:DateTimeOriginal: "2008:05:04 19:51:19"
    Exif:DateTimeDigitized: "2008:05:04 19:51:19"
    Exif:ShutterSpeedValue: 7.96579 (1/250 s)
    Exif:ApertureValue: 6.91887 (f/11)
    Exif:ExposureBiasValue: 0
    Exif:MeteringMode: 5 (pattern)
    Exif:Flash: 16 (no flash, flash suppression)
    Exif:FocalLength: 27 (27 mm)
    Exif:ColorSpace: 1
    Exif:PixelXDimension: 2496
    Exif:PixelYDimension: 1664
    Exif:FocalPlaneXResolution: 2855.84
    Exif:FocalPlaneYResolution: 2859.11
    Exif:FocalPlaneResolutionUnit: 2 (inches)
    Exif:CustomRendered: 0 (no)
    Exif:ExposureMode: 0 (auto)
    Exif:WhiteBalance: 0 (auto)
    Exif:SceneCaptureType: 0 (standard)
    Keywords: "Carly; Jack"

If the input file has multiple subimages, extra information summarizing the subimages will be printed:

$ iinfo img_6019m.tx

img_6019m.tx : 1024 x 1024, 3 channel, uint8 tiff (11 subimages)

$ iinfo -v img_6019m.tx

img_6019m.tx : 1024 x 1024, 3 channel, uint8 tiff
    11 subimages: 1024x1024 512x512 256x256 128x128 64x64 32x32 16x16 8x8 4x4 2x2 1x1
    channel list: R, G, B
    tile size: 64 x 64
    ...

Furthermore, the -a option will print information about all individual subimages:

$ iinfo -a ../sample-images/img_6019m.tx

img_6019m.tx : 1024 x 1024, 3 channel, uint8 tiff (11 subimages)
 subimage  0: 1024 x 1024, 3 channel, uint8 tiff
 subimage  1:  512 x  512, 3 channel, uint8 tiff
 subimage  2:  256 x  256, 3 channel, uint8 tiff
 subimage  3:  128 x  128, 3 channel, uint8 tiff
 subimage  4:   64 x   64, 3 channel, uint8 tiff
 subimage  5:   32 x   32, 3 channel, uint8 tiff
 subimage  6:   16 x   16, 3 channel, uint8 tiff
 subimage  7:    8 x    8, 3 channel, uint8 tiff
 subimage  8:    4 x    4, 3 channel, uint8 tiff
 subimage  9:    2 x    2, 3 channel, uint8 tiff
 subimage 10:    1 x    1, 3 channel, uint8 tiff


$ iinfo -v -a img_6019m.tx
img_6019m.tx : 1024 x 1024, 3 channel, uint8 tiff
    11 subimages: 1024x1024 512x512 256x256 128x128 64x64 32x32 16x16 8x8 4x4 2x2 1x1
 subimage  0: 1024 x 1024, 3 channel, uint8 tiff
    channel list: R, G, B
    tile size: 64 x 64
    ...
 subimage  1:  512 x  512, 3 channel, uint8 tiff
    channel list: R, G, B
    ...
...

iinfo command-line options

--help

Prints usage information to the terminal.

-v

Verbose output — prints all metadata of the image files.

-a

Print information about all subimages in the file(s).

-f

Print the filename as a prefix to every line. For example:

$ iinfo -v -f img_6019m.jpg

img_6019m.jpg : 1024 x  683, 3 channel, uint8 jpeg
img_6019m.jpg : channel list: R, G, B
img_6019m.jpg : Color space: sRGB
img_6019m.jpg : ImageDescription: "Family photo"
img_6019m.jpg : Make: "Canon"
...
-m pattern

Match the pattern (specified as an extended regular expression) against data metadata field names and print only data fields whose names match. The default is to print all data fields found in the file (if -v is given).

For example:

$ iinfo -v -f -m ImageDescription test*.jpg

test3.jpg :     ImageDescription: "Birthday party"
test4.jpg :     ImageDescription: "Hawaii vacation"
test5.jpg :     ImageDescription: "Bob's graduation"
test6.jpg :     ImageDescription: <unknown>

Note: the -m option is probably not very useful without also using the -v and -f options.

--hash

Displays a SHA-1 hash of the pixel data of the image (and of each subimage if combined with the -a flag).

-s

Show the image sizes, including a sum of all the listed images.

Converting Image Formats With iconvert

Overview

The iconvert program will read an image (from any file format for which an ImageInput plugin can be found) and then write the image to a new file (in any format for which an ImageOutput plugin can be found). In the process, iconvert can optionally change the file format or data format (for example, converting floating-point data to 8-bit integers), apply gamma correction, switch between tiled and scanline orientation, or alter or add certain metadata to the image.

The iconvert utility is invoked as follows:

iconvert optiions input output

Where input and output name the input image and desired output filename. The image files may be of any format recognized by OpenImageIO (i.e., for which ImageInput plugins are available). The file format of the output image will be inferred from the file extension of the output filename (e.g., foo.tif will write a TIFF file).

Alternately, any number of files may be specified as follows:

iconvert --inplace [options] file1 file2 …

When the --inplace option is used, any number of file names \(\ge 1\) may be specified, and the image conversion commands are applied to each file in turn, with the output being saved under the original file name. This is useful for applying the same conversion to many files, or simply if you want to replace the input with the output rather than create a new file with a different name.

iconvert Recipes

This section will give quick examples of common uses of iconvert.

Converting between file formats

It’s a snap to converting among image formats supported by OpenImageIO (i.e., for which ImageInput and ImageOutput plugins can be found). The iconvert utility will simply infer the file format from the file extension. The following example converts a PNG image to JPEG:

iconvert lena.png lena.jpg

Changing the data format or bit depth

Just use the -d option to specify a pixel data format. For example, assuming that in.tif uses 16-bit unsigned integer pixels, the following will convert it to an 8-bit unsigned pixels:

iconvert -d uint8 in.tif out.tif

Changing the compression

The following command converts writes a TIFF file, specifically using zip compression:

iconvert --compression zip in.tif out.tif

The following command writes its results as a JPEG file at a compression quality of 50 (pretty severe compression), illustrating how some compression methods allow a quality metric to be optionally appended to the name:

iconvert --compression jpeg:50 50 big.jpg small.jpg

Gamma-correcting an image

The following gamma-corrects the pixels, raising all pixel values to \(x^{1/2.2}\) upon writing:

iconvert -g 2.2 in.tif out.tif

Converting between scanline and tiled images

Convert a scanline file to a tiled file with $16 x 16$ tiles:

iconvert --tile 16 16 s.tif t.tif

Convert a tiled file to scanline:

iconvert --scanline t.tif s.tif

Converting images in place

You can use the --inplace flag to cause the output to emph{replace} the input file, rather than create a new file with a different name. For example, this will re-compress all of your TIFF files to use ZIP compression (rather than whatever they currently are using):

iconvert --inplace --compression zip *.tif

Change the file modification time to the image capture time

Many image formats (including JPEGs from digital cameras) contain an internal time stamp indicating when the image was captured. But the time stamp on the file itself (what you’d see in a directory listing from your OS) most likely shows when the file was last copied, not when it was created or captured. You can use the following command to re-stamp your files so that the file system modification time matches the time that the digital image was originally captured:

iconvert --inplace --adjust-time *.jpg

Add captions, keywords, IPTC tags

For formats that support it, you can add a caption/image description, keywords, or arbitrary string metadata:

iconvert --inplace --adjust-time --caption "Hawaii vacation" *.jpg

iconvert --inplace --adjust-time --keyword "John" img18.jpg img21.jpg

iconvert --inplace --adjust-time --attrib IPTC:State "HI" \
          --attrib IPTC:City "Honolulu" *.jpg

iconvert command-line options

--help

Prints usage information to the terminal.

-v

Verbose status messages.

--threads n

Use n execution threads if it helps to speed up image operations. The default (also if \(n=0\)) is to use as many threads as there are cores present in the hardware.

--inplace

Causes the output to replace the input file, rather than create a new file with a different name.

Without this flag, iconvert expects two file names, which will be used to specify the input and output files, respectively.

But when --inplace option is used, any number of file names \(\ge 1\) may be specified, and the image conversion commands are applied to each file in turn, with the output being saved under the original file name. This is useful for applying the same conversion to many files.

For example, the following example will add the caption “Hawaii vacation” to all JPEG files in the current directory:

iconvert --inplace --adjust-time --caption "Hawaii vacation" *.jpg
-d datatype

Attempt to sets the output pixel data type to one of: UINT8, sint8, uint16, sint16, half, float, double.

The types uint10 and uint12 may be used to request 10- or 12-bit unsigned integers. If the output file format does not support them, uint16 will be substituted.

If the -d option is not supplied, the output data type will be the same as the data format of the input file, if possible.

In any case, if the output file type does not support the requested data type, it will instead use whichever supported data type results in the least amount of precision lost.

-g gamma

Applies a gamma correction of \(1/\mathrm{gamma}\) to the pixels as they are output.

--sRGB

Explicitly tags the image as being in sRGB color space. Note that this does not alter pixel values, it only marks which color space those values refer to (and only works for file formats that understand such things). An example use of this command is if you have an image that is not explicitly marked as being in any particular color space, but you know that the values are sRGB.

--tile x y

Requests that the output file be tiled, with the given \(x \times y\) tile size, if tiled images are supported by the output format. By default, the output file will take on the tiledness and tile size of the input file.

--scanline

Requests that the output file be scanline-oriented (even if the input file was tile-oriented), if scanline orientation is supported by the output file format. By default, the output file will be scanline if the input is scanline, or tiled if the input is tiled.

--separate
--contig

Forces either “separate” (e.g., RRR…GGG…BBB) or “contiguous” (e.g., RGBRGBRGB…) packing of channels in the file. If neither of these options are present, the output file will have the same kind of channel packing as the input file. Of course, this is ignored if the output file format does not support a choice or does not support the particular choice requested.

--compression method
--compression method:quality

Sets the compression method, and optionally a quality setting, for the output image. Each ImageOutput plugin will have its own set of methods that it supports.

By default, the output image will use the same compression technique as the input image (assuming it is supported by the output format, otherwise it will use the default compression method of the output plugin).

--quality q

Sets the compression quality to q, on a 1–100 floating-point scale. This only has an effect if the particular compression method supports a quality metric (as JPEG does).

DEPRECATED(2.1): This is considered deprecated, and in general we now recommend just appending the quality metric to the compression name:qual.

--no-copy-image

Ordinarily, iconvert will attempt to use ImageOutput::copy_image underneath to avoid de/recompression or alteration of pixel values, unless other settings clearly contradict this (such as any settings that must alter pixel values). The use of --no-copy-image will force all pixels to be decompressed, read, and compressed/written, rather than copied in compressed form. We’re not exactly sure when you would need to do this, but we put it in just in case.

--adjust-time

When this flag is present, after writing the output, the resulting file’s modification time will be adjusted to match any "DateTime" metadata in the image. After doing this, a directory listing will show file times that match when the original image was created or captured, rather than simply when iconvert was run. This has no effect on image files that don’t contain any "DateTime" metadata.

--caption text

Sets the image metadata "ImageDescription". This has no effect if the output image format does not support some kind of title, caption, or description metadata field. Be careful to enclose text in quotes if you want your caption to include spaces or certain punctuation!

--keyword text

Adds a keyword to the image metadata "Keywords". Any existing keywords will be preserved, not replaced, and the new keyword will not be added if it is an exact duplicate of existing keywords. This has no effect if the output image format does not support some kind of keyword field.

Be careful to enclose text in quotes if you want your keyword to include spaces or certain punctuation. For image formats that have only a single field for keywords, OpenImageIO will concatenate the keywords, separated by semicolon (;), so don’t use semicolons within your keywords.

--clear-keywords

Clears all existing keywords in the image.

--attrib text

Sets the named image metadata attribute to a string given by text. For example, you could explicitly set the IPTC location metadata fields with:

iconvert --attrib "IPTC:City" "Berkeley" in.jpg out.jpg
--orientation orient

Explicitly sets the image’s "Orientation" metadata to a numeric value (see Display hints for the numeric codes). This only changes the metadata field that specifies how the image should be displayed, it does NOT alter the pixels themselves, and so has no effect for image formats that don’t support some kind of orientation metadata.

--rotcw
--rotccw
--rot180

Adjusts the image’s "Orientation" metadata by rotating it \(90^\circ\) clockwise, \(90^\circ\) degrees counter-clockwise, or \(180^\circ\), respectively, compared to its current setting. This only changes the metadata field that specifies how the image should be displayed, it does NOT alter the pixels themselves, and so has no effect for image formats that don’t support some kind of orientation metadata.

Searching Image Metadata With igrep

The igrep program search one or more image files for metadata that match a string or regular expression.

Using igrep

The igrep utility is invoked as follows:

igrep [options] pattern filename …

Where pattern is a POSIX.2 regular expression (just like the Unix/Linux grep(1) command), and filename (and any following names) specify images or directories that should be searched. An image file will “match” if any of its metadata contains values contain substring that are recognized regular expression. The image files may be of any format recognized by OpenImageIO (i.e., for which ImageInput plugins are available).

Example:

$ igrep Jack *.jpg
bar.jpg: Keywords = Carly; Jack
foo.jpg: Keywords = Jack
test7.jpg: ImageDescription = Jack on vacation

igrep command-line options

--help

Prints usage information to the terminal.

-d

Print directory names as it recurses. This only happens if the -r option is also used.

-E

Interpret the pattern as an extended regular expression (just like egrep or grep -E).

-f

Match the expression against the filename, as well as the metadata within the file.

-i

Ignore upper/lower case distinctions. Without this flag, the expression matching will be case-sensitive.

-l

Simply list the matching files by name, surpressing the normal output that would include the metadata name and values that matched. For example:

$ igrep Jack *.jpg
bar.jpg: Keywords = Carly; Jack
foo.jpg: Keywords = Jack
test7.jpg: ImageDescription = Jack on vacation

$ igrep -l Jack *.jpg
bar.jpg
foo.jpg
test7.jpg
-r

Recurse into directories. If this flag is present, any files specified that are directories will have any image file contained therein to be searched for a match (an so on, recursively).

-v

Invert the sense of matching, to select image files that do not match the expression.

Comparing Images With idiff

Overview

The idiff program compares two images, printing a report about how different they are and optionally producing a third image that records the pixel-by-pixel differences between them. There are a variety of options and ways to compare (absolute pixel difference, various thresholds for warnings and errors, and also an optional perceptual difference metric).

Because idiff is built on top on OpenImageIO, it can compare two images of any formats readable by ImageInput plugins on hand. They may have any (or different) file formats, data formats, etc.

Using idiff

The idiff utility is invoked as follows:

idiff [options] image1 image2

Where input1 and input2 are the names of two image files that should be compared. They may be of any format recognized by OpenImageIO (i.e., for which image-reading plugins are available).

If the two input images are not the same resolutions, or do not have the same number of channels, the comparison will return FAILURE immediately and will not attempt to compare the pixels of the two images. If they are the same dimensions, the pixels of the two images will be compared, and a report will be printed including the mean and maximum error, how many pixels were above the warning and failure thresholds, and whether the result is PASS, WARNING, or FAILURE. For example:

$ idiff a.jpg b.jpg

Comparing "a.jpg" and "b.jpg"
  Mean error = 0.00450079
  RMS error = 0.00764215
  Peak SNR = 42.3357
  Max error  = 0.254902 @ (700, 222, B)
  574062 pixels (82.1%) over 1e-06
  574062 pixels (82.1%) over 1e-06
FAILURE

The “mean error” is the average difference (per channel, per pixel). The “max error” is the largest difference in any pixel channel, and will point out on which pixel and channel it was found. It will also give a count of how many pixels were above the warning and failure thresholds.

The metadata of the two images (e.g., the comments) are not currently compared; only differences in pixel values are taken into consideration.

Raising the thresholds

By default, if any pixels differ between the images, the comparison will fail. You can allow some differences to still pass by raising the failure thresholds. The following example will allow images to pass the comparison test, as long as no more than 10% of the pixels differ by 0.004 (just above a 1/255 threshold):

idiff -fail 0.004 -failpercent 10 a.jpg b.jpg

But what happens if a just a few pixels are very different? Maybe you want that to fail, also. The following adjustment will fail if at least 10% of pixels differ by 0.004, or if any pixel differs by more than 0.25:

idiff -fail 0.004 -failpercent 10 -hardfail 0.25 a.jpg b.jpg

If none of the failure criteria are met, and yet some pixels are still different, it will still give a WARNING. But you can also raise the warning threshold in a similar way:

idiff -fail 0.004 -failpercent 10 -hardfail 0.25 \
         -warn 0.004 -warnpercent 3 a.jpg b.jpg

The above example will PASS as long as fewer than 3% of pixels differ by more than 0.004. If it does, it will be a WARNING as long as no more than 10% of pixels differ by 0.004 and no pixel differs by more than 0.25, otherwise it is a FAILURE.

Output a difference image

Ordinary text output will tell you how many pixels failed or were warnings, and which pixel had the biggest difference. But sometimes you need to see visually where the images differ. You can get idiff to save an image of the differences between the two input images:

idiff -o diff.tif -abs a.jpg b.jpg

The -abs flag saves the absolute value of the differences (i.e., all positive values or zero). If you omit the -abs, pixels in which a.jpg have smaller values than b.jpg will be negative in the difference image (be careful in this case of using a file format that doesn’t support negative values).

You can also scale the difference image with the -scale, making them easier to see. And the -od flag can be used to output a difference image only if the comparison fails, but not if the images pass within the designated threshold (thus saving you the trouble and space of saving a black image).

idiff Command Line Argument Reference

The various command-line options are discussed below:

General options

--help

Prints usage information to the terminal.

-v

Verbose output — more detail about what it finds when comparing images, even when the comparison does not fail.

-q

Quiet mode – output nothing for successful match), output only minimal error messages to stderr for failure / no match. The shell return code also indicates success or failure (successful match returns 0, failure returns nonzero).

-a

Compare all subimages. Without this flag, only the first subimage of each file will be compared.

Thresholds and comparison options

-fail A
-failpercent B
-hardfail C

Sets the threshold for FAILURE: if more than B % of pixels (on a 0-100 floating point scale) are greater than A different, or if any pixels are more than C different. The defaults are to fail if more than 0% (any) pixels differ by more than 0.00001 (1e-6), and C is infinite.

-warn A
-warnpercent B
-hardwarn C

Sets the threshold for WARNING: if more than B % of pixels (on a 0-100 floating point scale) are greater than A different, or if any pixels are more than C different. The defaults are to warn if more than 0% (any) pixels differ by more than 0.00001 (1e-6), and C is infinite.

-p

Does an additional test on the images to attempt to see if they are perceptually different (whether you are likely to discern a difference visually), using Hector Yee’s metric. If this option is enabled, the statistics will additionally show a report on how many pixels failed the perceptual test, and the test overall will fail if more than the “fail percentage” failed the perceptual test.

Difference image output

-o outputfile

Outputs a difference image to the designated file. This difference image pixels consist are each of the value of the corresponding pixel from image1 minus the value of the pixel image2.

The file extension of the output file is used to determine the file format to write (e.g., out.tif will write a TIFF file, out.jpg will write a JPEG, etc.). The data format of the output file will be format of whichever of the two input images has higher precision (or the maximum precision that the designated output format is capable of, if that is less than either of the input imges).

Note that pixels whose value is lower in image1 than in image2, this will result in negative pixels (which may be clamped to zero if the image format does not support negative values)), unless the -abs option is also used.

-abs

Will cause the output image to consist of the absolute value of the difference between the two input images (so all values in the difference image \(\ge 0\).

-scale factor

Scales the values in the difference image by the given (floating point) factor. The main use for this is to make small actual differences more visible in the resulting difference image by giving a large scale factor.

-od

Causes a difference image to be produce only if the image comparison fails. That is, even if the -o option is used, images that are within the comparison threshold will not write out a useless black (or nearly black) difference image.

Process return codes

The idiff program will return a code that can be used by scripts to indicate the results:

0

OK: the images match within the warning and error thresholds.

1

Warning: the errors differ a little, but within error thresholds.

2

Failure: the errors differ a lot, outside error thresholds.

3

The images weren’t the same size and couldn’t be compared.

4

File error: could not find or open input files, etc.

Making Tiled MIP-Map Texture Files With maketx or oiiotool

Overview

The TextureSystem (Chapter chap-texturesystem_) will exhibit much higher performance if the image files it uses as textures are tiled (versus scanline) orientation, have multiple subimages at different resolutions (MIP-mapped), and include a variety of header or metadata fields appropriately set for texture maps. Any image that you intend to use as input to TextureSystem, therefore, should first be converted to have these properties. An ordinary image will work as a texture, but without this additional step, it will be drastically less efficient in terms of memory, disk or network I/O, and time.

This can be accomplished programmatically using the ImageBufAlgo make_texture() function (see Section Import / export for C++ and Section Import / export for Python).

OpenImageIO includes two command-line utilities capable of converting ordinary images into texture files: maketx and oiiotool. 1

1

Why are there two programs? Historical artifact – maketx existed first, and much later oiiotool was extended to be capable of directly writing texture files. If you are simply converting an image into a texture, maketx is more straightforward and foolproof, in that you can’t accidentally forget to turn it into a texture, as you might do with and much later oiiotool was extended to be capable of directly writing texture files.

maketx

The maketx program will convert ordinary images to efficient textures. The maketx utility is invoked as follows:

maketx [options] input… -o output

Where input and output name the input image and desired output filename. The input files may be of any image format recognized by OpenImageIO (i.e., for which ImageInput plugins are available). The file format of the output image will be inferred from the file extension of the output filename (e.g., :filename:`foo.tif` will write a TIFF file).

Command-line arguments are:

--help

Prints usage information to the terminal.

-v

Verbose status messages, including runtime statistics and timing.

--runstats

Print runtime statistics and timing.

-o outputname

Sets the name of the output texture.

--threads <n>

Use n execution threads if it helps to speed up image operations. The default (also if n=0) is to use as many threads as there are cores present in the hardware.

--format <formatname>

Specifies the image format of the output file (e.g., “tiff”, “OpenEXR”, etc.). If --format is not used, maketx will guess based on the file extension of the output filename; if it is not a recognized format extension, TIFF will be used by default.

-d <datatype>

Attempt to sets the output pixel data type to one of: UINT8, sint8, uint16, sint16, half, float, double.

If the -d option is not supplied, the output data type will be the same as the data format of the input file.

In either case, the output file format itself (implied by the file extension of the output filename) may trump the request if the file format simply does not support the requested data type.

--tile <x> <y>

Specifies the tile size of the output texture. If not specified, maketx will make 64 x 64 tiles.

--separate

Forces “separate” (e.g., RRR…GGG…BBB) packing of channels in the output file. Without this option specified, “contiguous” (e.g., RGBRGBRGB…) packing of channels will be used for those file formats that support it.

--compression <method>
--compression <method:quality>

Sets the compression method, and optionally a quality setting, for the output image (the default is to try to use “zip” compression, if it is available).

-u

Ordinarily, textures are created unconditionally (which could take several seconds for large input files if read over a network) and will be stamped with the current time.

The -u option enables update mode: if the output file already exists, and has the same time stamp as the input file, and the command-lie arguments that created it are identical to the current ones, then the texture will be left alone and not be recreated. If the output file does not exist, or has a different time stamp than the input file, or was created using different command line arguments, then the texture will be created and given the time stamp of the input file.

--wrap <wrapmode>
--swrap <wrapmode>, --twrap <wrapmode>

Sets the default wrap mode for the texture, which determines the behavior when the texture is sampled outside the [0,1] range. Valid wrap modes are: black, clamp, periodic, mirror. The default, if none is set, is black. The --wrap option sets the wrap mode in both directions simultaneously, while the --swrap and --twrap may be used to set them individually in the s (horizontal) and t (vertical) diretions.

Although this sets the default wrap mode for a texture, note that the wrap mode may have an override specified in the texture lookup at runtime.

--resize

Causes the highest-resolution level of the MIP-map to be a power-of-two resolution in each dimension (by rounding up the resolution of the input image). There is no good reason to do this for the sake of OIIO’s texture system, but some users may require it in order to create MIP-map images that are compatible with both OIIO and other texturing systems that require power-of-2 textures.

--filter <name>

By default, the resizing step that generates successive MIP levels uses a triangle filter to bilinearly combine pixels (for MIP levels with even number of pixels, this is also equivalent to a box filter, which merely averages groups of 4 adjacent pixels). This is fast, but for source images with high frequency content, can result in aliasing or other artifacts in the lower-resolution MIP levels.

The --filter option selects a high-quality filter to use when resizing to generate successive MIP levels. Choices include lanczos3 (our best recommendation for highest-quality filtering, a 3-lobe Lanczos filter), box, triangle, catrom, blackman-harris, gaussian, mitchell, bspline, cubic, keys, simon, rifman, radial-lanczos3, disk, sinc.

If you select a filter with negative lobes (including lanczos3, sinc, lanczos3, keys, simon, rifman, or catrom), and your source image is an HDR image with very high contrast regions that include pixels with values >1, you may also wish to use the --rangecompress option to avoid ringing artifacts.

--hicomp

Perform highlight compensation. When HDR input data with high-contrast highlights is turned into a MIP-mapped texture using a high-quality filter with negative lobes (such as lanczos3), objectionable ringing could appear near very high-contrast regions with pixel values >1. This option improves those areas by using range compression (transforming values from a linear to a logarithmic scale that greatly compresses the values > 1) prior to each image filtered-resize step, and then expanded back to a linear format after the resize, and also clamping resulting pixel values to be non-negative. This can result in some loss of energy, but often this is a preferable alternative to ringing artifacts in your upper MIP levels.

--sharpen <contrast>

EXPERIMENTAL: USE AT YOUR OWN RISK!

This option will run an additional sharpening filter when creating the successive MIP-map levels. It uses an unsharp mask (much like in Section sec-iba-unsharpmask) to emphasize high-frequency details to make features “pop” visually even at high MIP-map levels. The contrast controls the degree to which it does this. Probably a good value to enhance detail but not go overboard is 0.5 or even 0.25. A value of 1.0 may make strage artifacts at high MIP-map levels. Also, if you simultaneously use --filter unsharp-median, a slightly different variant of unsharp masking will be used that employs a median filter to separate out the low-frequencies, this may tend to help emphasize small features while not over-emphasizing large edges.

--nomipmap

Causes the output to not be MIP-mapped, i.e., only will have the highest-resolution level.

--nchannels <n>

Sets the number of output channels. If n is less than the number of channels in the input image, the extra channels will simply be ignored. If n is greater than the number of channels in the input image, the additional channels will be filled with 0 values.

--chnames a,b,...

Renames the channels of the output image. All the channel names are concatenated together, separated by commas. A “blank” entry will cause the channel to retain its previous value (for example, --chnames ,,,A will rename channel 3 to be “A” and leave channels 0-2 as they were.

--checknan

Checks every pixel of the input image to ensure that no NaN or Inf values are present. If such non-finite pixel values are found, an error message will be printed and maketx will terminate without writing the output image (returning an error code).

--fixnan streategy

Repairs any pixels in the input image that contained NaN or Inf values (hereafter referred to collectively as “nonfinite”). If strategy is black, nonfinite values will be replaced with 0. If strategy is box3, nonfinite values will be replaced by the average of all the finite values within a 3x3 region surrounding the pixel.

--fullpixels

Resets the “full” (or “display”) pixel range to be the “data” range. This is used to deal with input images that appear, in their headers, to be crop windows or overscanned images, but you want to treat them as full 0–1 range images over just their defined pixel data.

--Mcamera <...16 floats...>
--Mscreen <...16 floats...>

Sets the camera and screen matrices (sometimes called Nl and NP, respectively, by some renderers) in the texture file, overriding any such matrices that may be in the input image (and would ordinarily be copied to the output texture).

--prman-metadata

Causes metadata “PixarTextureFormat” to be set, which is useful if you intend to create an OpenEXR texture or environment map that can be used with PRMan as well as OIIO.

--attrib <name> <value>

Adds or replaces metadata with the given name to have the specified value.

It will try to infer the type of the metadata from the value: if the value contains only numerals (with optional leading minus sign), it will be saved as int metadata; if it also contains a decimal point, it will be saved as float metadata; otherwise, it will be saved as a string metadata.

For example, you could explicitly set the IPTC location metadata fields with:

oiiotool --attrib "IPTC:City" "Berkeley" in.jpg out.jpg
--sattrib <name> <value>

Adds or replaces metadata with the given name to have the specified value, forcing it to be interpreted as a string. This is helpful if you want to set a string metadata to a value that the --attrib command would normally interpret as a number.

--sansattrib

When set, this edits the command line inserted in the “Software” and “ImageHistory” metadata to omit any verbose --attrib and --sattrib commands.

--constant-color-detect

Detects images in which all pixels are identical, and outputs the texture at a reduced resolution equal to the tile size, rather than filling endless tiles with the same constant color. That is, by substituting a low-res texture for a high-res texture if it’s a constant color, you could save a lot of save disk space, I/O, and texture cache size. It also sets the "ImageDescription" to contain a special message of the form ConstantColor=[r,g,...].

--monochrome-detect

Detects multi-channel images in which all color components are identical, and outputs the texture as a single-channel image instead. That is, it changes RGB images that are gray into single-channel gray scale images.

--opaque-detect

Detects images that have a designated alpha channel for which the alpha value for all pixels is 1.0 (fully opaque), and omits the alpha channel from the output texture. So, for example, an RGBA input texture where A=1 for all pixels will be output just as RGB. The purpose is to save disk space, texture I/O bandwidth, and texturing time for those textures where alpha was present in the input, but clearly not necessary.

--ignore-unassoc

Ignore any header tags in the input images that indicate that the input has “unassociated” alpha. When this option is used, color channels with unassociated alpha will not be automatically multiplied by alpha to turn them into associated alpha. This is also a good way to fix input images that really are associated alpha, but whose headers incorrectly indicate that they are unassociated alpha.

--prman

PRMan is will crash in strange ways if given textures that don’t have its quirky set of tile sizes and other specific metadata. If you want maketx to generate textures that may be used with either OpenImageIO or PRMan, you should use the --prman option, which will set several options to make PRMan happy, overriding any contradictory settings on the command line or in the input texture.

Specifically, this option sets the tile size (to 64x64 for 8 bit, 64x32 for 16 bit integer, and 32x32 for float or half images), uses “separate” planar configuration (--separate), and sets PRMan-specific metadata (--prman-metadata). It also outputs sint16 textures if uint16 is requested (because PRMan for some reason does not accept true uint16 textures), and in the case of TIFF files will omit the Exif directory block which will not be recognized by the older version of libtiff used by PRMan.

OpenImageIO will happily accept textures that conform to PRMan’s expectations, but not vice versa. But OpenImageIO’s TextureSystem has better performance with textures that use maketx’s default settings rather than these oddball choices. You have been warned!

--oiio

This sets several options that we have determined are the optimal values for OpenImageIO’s TextureSystem, overriding any contradictory settings on the command line or in the input texture.

Specifically, this is the equivalent to using

--separate --tile 64 64

--colorconvert <inspace> <outspace>

Convert the color space of the input image from inspace to tospace. If OpenColorIO is installed and finds a valid configuration, it will be used for the color conversion. If OCIO is not enabled (or cannot find a valid configuration, OIIO will at least be able to convert among linear, sRGB, and Rec709.

--colorconfig <name>

Explicitly specify a custom OpenColorIO configuration file. Without this, the default is to use the $OCIO environment variable as a guide for the location of the OpenColorIO configuration file.

--unpremult

When undergoing some color conversions, it is helpful to “un-premultiply” the alpha before converting color channels, and then re-multiplying by alpha. Caveat emptor – if you don’t know exactly when to use this, you probably shouldn’t be using it at all.

--mipimage <filename>

Specifies the name of an image file to use as a custom MIP-map level, instead of simply downsizing the last one. This option may be used multiple times to specify multiple levels. For example:

maketx 256.tif --mipimage 128.tif --mipimage 64.tif -o out.tx

This will make a texture with the first MIP level taken from 256.tif, the second level from 128.tif, the third from 64.tif, and then subsequent levels will be the usual downsizings of 64.tif.

--envlatl

Creates a latitude-longitude environment map, rather than an ordinary texture map.

--lightprobe

Creates a latitude-longitude environment map, but in contrast to --envlatl, the original input image is assumed to be formatted as a light probe image. (See http://www.pauldebevec.com/Probes/ for examples and an explanation of the geometric layout.)

--bumpslopes

For a single channel input image representing height (that you would ordinarily use for a bump or displacement), this produces a 6-channel texture that contains the first and second moments of bump slope, which can be used to implement certain bump-to-roughness techniques. The channel layout is as follows:

index

channel name

data at MIP level 0

0

b0_h

\(h\) (height)

1

b1_dhds

\(\partial h / \partial s\)

2

b2_dhdt

\(\partial h / \partial t\)

3

b3_dhds2

\((\partial h / \partial s)^2\)

4

b4_dhdt2

\((\partial h / \partial t)^2\)

5

b5_dhdsdt

\((\partial h / \partial s) \cdot (\partial h / \partial t)\)

(The strange channel names are to guarantee they are in alphabetical order, to prevent reordering by OpenEXR. And also note that the simple relationships between channels 1 & 2, and 3-6, is only for the highest- resolution level of the MIP-map, and will differ for the lower-res filtered versions, and those differences is what gives us the slope momets that we need.)

A reference for explaining how this can be used is here:

Christophe Hery, Michael Kass, and Junhi Ling. “Geometry into Shading.” Technical Memo 14-04, Pixar Animation Studios, 2014. https://graphics.pixar.com/library/BumpRoughness

--bumpformat <bformat>

In conjunction with --bumpslopes, this option can specify the strategy for determining whether a 3-channel source image specifies a height map or a normal map. The value “height” indicates it is a height map (only the first channel will be used). The value “normal” indicates it is a normal map (all three channels will be used for x, y, z). The default value, “auto”, indicates that it should be interpreted as a height map if and only if the R, G, B channel values are identical in all pixels, otherwise it will be interpreted as a 3-channel normal map.

--uvslopes_scale <scalefactor>

Used in conjunction with --bumpslopes, this computes derivatives for the bumpslopes data in UV space rather than in texel space, and divides them by a scale factor. If the value is 0 (default), this is disabled. For a nonzero value, it will be the scale factor. If you use this feature, a suggested value is 256.

(This option was added for OpenImageIO 2.3.)

--cdf
--cdfsigma <SIGMA>
--cdfbits <BITS>

When --cdf is used, the output texture will write a Gaussian CDF and Inverse Gaussian CDF as per-channel metadata in the texture, which can be used by shaders to implement Histogram-Preserving Blending. This is only useful when the texture being created is written to an image format that supports arbitrary metadata (e.g. OpenEXR).

When --cdf has been enabled, the additional options --cdfsigma may be used to specify the CDF sigma value (defaulting to 1.0/6.0), and --cdfbits specifies the number of bits to use for the size of the CDF table (defaulting to 8, which means 256 bins).

References:

  • Histogram-Preserving Blending for Randomized Texture Tiling,” JCGT 8(4), 2019.

  • Heitz/Neyret, “High-Performance By-Example Noise using a Histogram-Preserving Blending Operator,” ACM SIGGRAPH / Eurographics Symposium on High-Performance Graphics 2018.)

  • Benedikt Bitterli https://benedikt-bitterli.me/histogram-tiling/

These options were first added in OpenImageIO 2.3.10.

oiiotool

The oiiotool utility (Chapter oiiotool: the OIIO Swiss Army Knife) is capable of writing textures using the -otex option, and lat-long environment maps using the -oenv option. Roughly speaking,

maketx [maketx-options] input -o output

is equivalent to

oiiotool input [oiiotool-options] -otex output

and

maketx -envlatl [maketx-options] input -o output

is equivalent to

oiiotool input [oiiotool-options] -oenv output

However, the notation for the various options are not identical between the two programs, as will be explained by the remainder of this section.

The most important difference between oiiotool and maketx is that oiiotool can do so much more than convert an existing input image to a texture – literally any image creation or manipulation you can do via oiiotool may be output directly as a full texture file using -otex (or as a lat-long environment map using -oenv).

Note that it is vitally important that you use one of the texture output commands (-otex or -oenv) when creating textures with oiiotool — if you inadvertently forget and use an ordinary -o, you will end up with an output image that is much less efficient to use as a texture.

Command line arguments useful when creating textures

As with any use of oiiotool, you may use the following to control the run generally:

--help
-v
--runstats
--threads <n>

and as with any use of oiiotool, you may use the following command-line options to control aspects of the any output files (including those from -otex and -oenv, as well as -o). Only brief descriptions are given below, please consult Chapter oiiotool for detailed explanations.

-d <datatype>

Specify the pixel data type (UINT8, uint16, half, float, etc.) if you wish to override the default of writing the same data type as the first input file read.

--tile <x> <y>

Explicitly override the tile size (though you are strongly urged to use the default, and not use this command).

--compression <method>

Explicitly override the default compression methods when writing the texture file.

--ch <channellist>

Shuffle, add, delete, or rename channels (see sec-oiiotool-ch).

--chnames a,b,...

Renames the channels of the output image.

--fixnan <stretegy>

Repairs any pixels in the input image that contained NaN or Inf values (if the strategy is box3 or black), or to simply abort with an error message (if the strategy is error).

--fullpixels

Resets the “full” (or “display”) pixel range to be the “data” range.

--planarconfig separate

Forces “separate” (e.g., RRR…GGG…BBB) packing of channels in the output texture. This is almost always a bad choice, unless you know that the texture file must be readable by PRMan, in which case it is required.

--attrib <name> <value>

oiiotool’s --attrib command may be used to set attributes in the metadata of the output texture.

--attrib:type=matrix worldtocam <...16 comma-separated floats...>
--attrib:type=matrix screentocam <...16 comma-separated floats...>

Set/override the camera and screen matrices.

Optional arguments to -otex and -oenv

As with many oiiotool commands, the -otex and -oenv may have various optional arguments appended, in the form :name=value (see Section sec-oiiotooloptionalargs).

Optional arguments supported by -otex and -oenv include all the same options as -o (Section Writing images) and also the following (explanations are brief, please consult Section sec-maketx for more detailed explanations of each, for the corresponding maketx option):

Appended Option

maketx equivalent

wrap= string

--wrap

swrap= string

--swrap

twrap= string

--twrap

resize=1

--resize

nomipmap=1

--nomipmap

updatemode=1

-u

monochrome_detect=1

--monochrome-detect

opaque_detect=1

--opaque-detect

unpremult=1

--unpremult

incolorspace= name

--incolorspace

outcolorspace= name

--outcolorspace

hilightcomp=1

--hicomp

sharpen= float

--sharpen

filter= string

--filter

prman_metadata=1

--prman

prman_options=1

--prman-metadata

Examples

oiiotool in.tif -otex out.tx

oiiotool in.jpg --colorconvert sRGB linear -d uint16 -otex out.tx

oiiotool --pattern:checker 512x512 3 -d uint8 -otex:wrap=periodic checker.tx

oiiotool in.exr -otex:hilightcomp=1:sharpen=0.5 out.exr

Metadata conventions

The ImageSpec class, described thoroughly in Image Specification: ImageSpec, provides the basic description of an image that are essential across all formats — resolution, number of channels, pixel data format, etc. Individual images may have additional data, stored as name/value pairs in the extra_attribs field. Though literally anything can be stored in extra_attribs — it’s specifically designed for format- and user-extensibility — this chapter establishes some guidelines and lays out all of the field names that OpenImageIO understands.

Description of the image

"ImageDescription" : string

The image description, title, caption, or comments.

"Keywords" : string

Semicolon-separated keywords describing the contents of the image. (Semicolons are used rather than commas because of the common case of a comma being part of a keyword itself, e.g., “Kurt Vonnegut, Jr.” or “Washington, DC.””)

"Artist" : string

The artist, creator, or owner of the image.

Any copyright notice or owner of the image.

"DateTime" : string

The creation date of the image, in the following format: YYYY:MM:DD HH:MM:SS (exactly 19 characters long, not including a terminating NULL). For example, 7:30am on Dec 31, 2008 is encoded as "2008:12:31 07:30:00".

Usually this is simply the time that the image data was last modified. It may be wise to also store the "Exif:DateTimeOriginal" and "Exif:DateTimeDigitized" (see Section Exif metadata) to further distinguish the original image and its conversion to digital media.

"DocumentName" : string

The name of an overall document that this image is a part of.

"Software" : string

The software that was used to create the image.

"HostComputer" : string

The name or identity of the computer that created the image.

Display hints

"Orientation" : int

y default, image pixels are ordered from the top of the display to the ottom, and within each scanline, from left to right (i.e., the same rdering as English text and scan progression on a CRT). But the “Orientation”` field can suggest that it should be displayed with different orientation, according to the TIFF/EXIF conventions:

0

normal (top to bottom, left to right)

1

flipped horizontally (top to botom, right to left)

2

rotated \(180^\circ\) (bottom to top, right to left)

3

flipped vertically (bottom to top, left to right)

4

transposed (left to right, top to bottom)

5

rotated \(90^\circ\) clockwise (right to left, top to bottom)

6

transverse (right to left, bottom to top)

7

rotated \(90^\circ\) counter-clockwise (left to right, bottom to top)
"PixelAspectRatio" : float

The aspect ratio (\(x/y\)) of the size of individual pixels, with square pixels being 1.0 (the default).

"XResolution" : float
"YResolution" : float
"ResolutionUnit" : string

The number of horizontal (x) and vertical (y) pixels per resolution unit. This ties the image to a physical size (where applicable, such as with a scanned image, or an image that will eventually be printed).

Different file formats may dictate different resolution units. For example, the TIFF ImageIO plugin supports none, in, and cm.

"oiio:Movie" : int

If nonzero, a hint that a multi-image file is meant to be interpreted as an animation (i.e., that the subimages are a time sequence).

"oiio:subimages" : int

If nonzero, the number of subimages in the file. Not all image file formats can know this without reading the entire file, and in such cases, this attribute will not be set or will be 0. If the value is present and greater than zero, it can be trusted, but if not, nothing should be inferred and you will have to repeatedly seek to subimages to find out how many there are.

"FramesPerSecond" : rational

For a multi-image file intended to be played back as an animation, the frame refresh rate. (It’s technically a rational, but it may be retrieved as a float also, if you are ok with imprecision.)

Color information

"oiio:ColorSpace" : string

The name of the color space of the color channels. Values incude:

  • "Linear" : Color pixel values are known to be scene-linear and using facility-default color primaries (presumed sRGB/Rec709 color primaries if otherwise unknown.

  • "sRGB" : Using standard sRGB response and primaries.

  • "Rec709" : Using standard Rec709 response and primaries.

  • "ACES" : ACES color space encoding.

  • "AdobeRGB" : Adobe RGB color space.

  • "KodakLog" : Kodak logarithmic color space.

  • "GammaCorrectedX.Y" : Color values have been gamma corrected (raised to the power \(1/\gamma\)). The X.Y is the numeric value of the gamma exponent.

  • arbitrary : The name of any color space known to OpenColorIO (if OCIO support is present).

"oiio:Gamma" : float

If the color space is “GammaCorrectedX.Y”, this value is the gamma exponent. (Optional/deprecated; if present, it should match the suffix of the color space.)

"oiio:BorderColor" : float[nchannels]

The color presumed to be filling any parts of the display/full image window that are not overlapping the pixel data window. If not supplied, the default is black (0 in all channels).

"ICCProfile" : uint8[]

The ICC color profile takes the form of an array of bytes (unsigned 8 bit chars). The length of the array is the length of the profile blob.

Disk file format info/hints

"oiio:BitsPerSample" : int

Number of bits per sample in the file.

Note that this may not match the reported ImageSpec::format, if the plugin is translating from an unsupported format. For example, if a file stores 4 bit grayscale per channel, the "oiio:BitsPerSample" may be 4 but the format field may be TypeDesc::UINT8 (because the OpenImageIO APIs do not support fewer than 8 bits per sample).

"oiio:UnassociatedAlpha" : int

Whether the data in the file stored alpha channels (if any) that were unassociated with the color (i.e., color not “premultiplied” by the alpha coverage value).

"planarconfig" : string

contig indicates that the file has contiguous pixels (RGB RGB RGB…), whereas separate indicate that the file stores each channel separately (RRR…GGG…BBB…).

Note that only contiguous pixels are transmitted through the OpenImageIO APIs, but this metadata indicates how it is (or should be) stored in the file, if possible.

"compression" : string

Indicates the type of compression the file uses. Supported compression modes will vary from file format to file format, and each reader/writer plugin should document the modes it supports. If ImageOutput::open is called with an ImageSpec that specifies an compression mode not supported by that ImageOutput, it will choose a reasonable default. As an example, the OpenEXR writer supports none, rle, zip, zips, piz, pxr24, b44, b44a, dwaa, or dwab.

he compression name is permitted to have a quality value to be appended fter a colon, for example dwaa:60. The exact meaning and range of he quality value can vary between different file formats and compression odes, and some don’t support quality values at all (it will be ignored if ot supported, or if out of range).

"CompressionQuality" : int

DEPRECATED(2.1)

This is a deprecated methods of separately specifying the compression quality. Indicates the quality of compression to use (0–100), for those plugins and compression methods that allow a variable amount of compression, with higher numbers indicating higher image fidelity.

Substituting an IOPRoxy for custom I/O overrides

Format readers and writers that respond positively to supports("ioproxy") have the ability to read or write using an I/O proxy object. Among other things, this lets an ImageOutput write the file to a memory buffer rather than saving to disk, and for an ImageInput to read the file from a memory buffer. This behavior is controlled by a special attributes

"oiio:ioproxy" : pointer

Pointer to a Filesystem::IOProxy that will handle the I/O.

An explanation of how this feature is used may be found in Sections Custom I/O proxies (and reading the file from a memory buffer) and Custom I/O proxies (and writing the file to a memory buffer).

In addition to communicating IOProxy information via this attribute, it is also allowed (and probably preferred) to directly supply the IOProxy information via calls to ImageInput::open(), create(), and set_ioproxy(), ImageOutput::create() and set_ioproxy(), and ImageBuf::ImageBuf(), reset(), and set_write_ioproxy().

Photographs or scanned images

The following metadata items are specific to photos or captured images.

"Make" : string

For captured or scanned image, the make of the camera or scanner.

"Model" : string

For captured or scanned image, the model of the camera or scanner.

"ExposureTime" : float

The exposure time (in seconds) of the captured image.

"FNumber" : float

The f/stop of the camera when it captured the image.

Thumbnails / postage stamps / preview images

Some image file formats allow for storing a thumbnail – a lower-resolution image suitable for an icon or other small preview. These are retrievable separately via ImageInput::get_thumbnail(), ImageBuf::thumbnail(), or ImageCache::get_thumbnail(). In addition, if a thumbnail is available, the ImageSpec should also contain the following metadata:

"thumbnail_width" : int

The thumbnail width, in pixels.

"thumbnail_height" : int

The thumbnail height, in pixels.

"thumbnail_nchannels" : int

The number of color channels in the thumbnail image.

Texture Information

Several standard metadata are very helpful for images that are intended to be used as textures (especially for OpenImageIO’s TextureSystem).

"textureformat" : string

The kind of texture that this image is intended to be. We suggest the following names:

Plain Texture

Ordinary 2D texture

Volume Texture

3D volumetric texture

Shadow

Ordinary z-depth shadow map

CubeFace Shadow

Cube-face shadow map

Volume Shadow

Volumetric (“deep”) shadow map

LatLong Environment

Latitude-longitude (rectangular) environment map

CubeFace Environment

Cube-face environment map
"wrapmodes" : string

Give the intended texture wrap mode indicating what happens with texture coordinates outside the \([0...1]\) range. We suggest the following names: black, periodic, clamp, mirror. If the wrap mode is different in each direction, they should simply be separated by a comma. For example, black means black wrap in both directions, whereas clamp,periodic means to clamp in \(u\) and be periodic in \(v\).

"fovcot" : float

The cotangent (\(x/y\)) of the field of view of the original image (which may not be the same as the aspect ratio of the pixels of the texture, which may have been resized).

"worldtocamera" : matrix44

For shadow maps or rendered images this item (of type TypeDesc::PT_MATRIX) is the world-to-camera matrix describing the camera position.

"worldtoscreen" : matrix44

For shadow maps or rendered images this item (of type TypeDesc::PT_MATRIX) is the world-to-screen matrix describing the full projection of the 3D view onto a \([-1...1] \times [-1...1]\) 2D domain.

"worldtoNDC" : matrix44

For shadow maps or rendered images this item (of type TypeDesc::PT_MATRIX) is the world-to-NDC matrix describing the full projection of the 3D view onto a \([0...1] \times [0...1]\) 2D domain.

"oiio:updirection" : string

For environment maps, indicates which direction is “up” (valid values are y or z), to disambiguate conventions for environment map orientation.

"oiio:sampleborder" : int

If not present or 0 (the default), the conversion from pixel integer coordinates \((i,j)\) to texture coordinates \((s,t)\) follows the usual convention of \(s = (i+0.5)/\mathit{xres}\) and \(t = (j+0.5)/\mathit{yres}\). However, if this attribute is present and nonzero, the first and last row/column of pixels lie exactly at the \(s\) or \(t = 0\) or \(1\) boundaries, i.e., \(s = i/(\mathit{xres}-1)\) and \(t = j/(\mathit{yres}-1)\).

"oiio:ConstantColor" : string

If present, is a hint that the texture has the same value in all pixels, and the metadata value is a string containing the channel values as a comma-separated list (no spaces, for example: 0.73,0.9,0.11,1.0).

"oiio:AverageColor" : string

If present, is a hint giving the average value of all pixels in the texture, as a string containing a comma-separated list of the channel values (no spaces, for example: 0.73,0.9,0.11,1.0).

"oiio:SHA-1" : string

f present, is a 40-byte SHA-1 hash of the input image (possibly salted with arious maketx options) that can serve to quickly compare two separate extures to know if they contain the same pixels. While it’s not, echnically, 100% guaranteed that no separate textures will match, it’s so stronomically unlikely that we discount the possibility (you’d be rendering ovies for centuries before finding a single match).

Exif metadata

The following Exif metadata tags correspond to items in the “standard” set of metadata.

Exif tag

OpenImageIO metadata convention

ColorSpace

(reflected in “oiio:ColorSpace”)

ExposureTime

ExposureTime

FNumber

FNumber

The other remaining Exif metadata tags all include the Exif: prefix to keep it from clashing with other names that may be used for other purposes.

"Exif:ExposureProgram" : int

The exposure program used to set exposure when the picture was taken:

0

unknown

1

manual

2

normal program

3

aperture priority

4

shutter priority

5

Creative program (biased toward depth of field)

6

Action program (biased toward fast shutter speed)

7

Portrait mode (closeup photo with background out of focus)

8

Landscape mode (background in focus)
"Exif:SpectralSensitivity" : string

The camera’s spectral sensitivity, using the ASTM conventions.

"Exif:ISOSpeedRatings" : int

The ISO speed and ISO latitude of the camera as specified in ISO 12232.

"Exif:DateTimeOriginal" : string
"Exif:DateTimeDigitized" : string

Date and time that the original image data was generated or captured, and the time/time that the image was stored as digital data. Both are in YYYY:MM:DD HH:MM:SS format.

To clarify the role of these (and also with respect to the standard DateTime metadata), consider an analog photograph taken in 1960 (Exif:DateTimeOriginal), which was scanned to a digital image in 2010 (Exif:DateTimeDigitized), and had color corrections or other alterations performed in 2015 (DateTime).

"Exif:CompressedBitsPerPixel" : float

The compression mode used, measured in compressed bits per pixel.

"Exif:ShutterSpeedValue" : float

Shutter speed, in APEX units: \(-\log_2(\mathit{exposure time})\)

"Exif:ApertureValue" : float

Aperture, in APEX units: \(2 \log_2 (\mathit{fnumber})\)

"Exif:BrightnessValue" : float

Brightness value, assumed to be in the range of \(-99.99\) – \(99.99\).

"Exif:ExposureBiasValue" : float

Exposure bias, assumed to be in the range of \(-99.99\) – \(99.99\).

"Exif:MaxApertureValue" : float

Smallest F number of the lens, in APEX units: \(2 \log_2 (\mathit{fnumber})\)

"Exif:SubjectDistance" : float

Distance to the subject, in meters.

"Exif:MeteringMode" : int

The metering mode:

0

unknown

1

average

2

center-weighted average

3

spot

4

multi-spot

5

pattern

6

partial

255

other
"Exif:LightSource" : int

The kind of light source:

0

unknown

1

daylight

2

tungsten (incandescent light)

4

flash

9

fine weather

10

cloudy weather

11

shade

12

daylight fluorescent (D 5700-7100K)

13

day white fluorescent (N 4600-5400K)

14

cool white fuorescent (W 3900 - 4500K)

15

white fluorescent (WW 3200 - 3700K)

17

standard light A

18

standard light B

19

standard light C

20

D55

21

D65

22

D75

23

D50

24

ISO studio tungsten

255

other light source
"Exif:Flash" int}

A sum of:

1

if the flash fired

0

no strobe return detection function

4

strobe return light was not detected

6

strobe return light was detected

8

compulsary flash firing

16

compulsary flash suppression

24

auto-flash mode

32

no flash function (0 if flash function present)

64

red-eye reduction supported (0 if no red-eye reduction mode)
"Exif:FocalLength" : float

Actual focal length of the lens, in mm.

"Exif:SecurityClassification" : string

Security classification of the image: C = confidential, R = restricted, S = secret, T = top secret, U = unclassified.

"Exif:ImageHistory" : string

Image history.

"Exif:SubsecTime" : string

Fractions of a second to augment the "DateTime" (expressed as text of the digits to the right of the decimal).

"Exif:SubsecTimeOriginal" : string

Fractions of a second to augment the Exif:DateTimeOriginal (expressed as text of the digits to the right of the decimal).

"Exif:SubsecTimeDigitized" : string

Fractions of a second to augment the Exif:DateTimeDigital (expressed as text of the digits to the right of the decimal).

"Exif:PixelXDimension" : int
"Exif:PixelYDimension" : int

The x and y dimensions of the valid pixel area.

"Exif:FlashEnergy" : float

Strobe energy when the image was captures, measured in Beam Candle Power Seconds (BCPS).

"Exif:FocalPlaneXResolution" : float
"Exif:FocalPlaneYResolution" : float
"Exif:FocalPlaneResolutionUnit" : int

The number of pixels in the x and y dimension, per resolution unit. The codes for resolution units are:

1

none

2

inches

3

cm

4

mm

5

\(\mu m\)
"Exif:ExposureIndex" : float

The exposure index selected on the camera.

"Exif:SensingMethod" : int

The image sensor type on the camra:

1

undefined

2

one-chip color area sensor

3

two-chip color area sensor

4

three-chip color area sensor

5

color sequential area sensor

7

trilinear sensor

8

color trilinear sensor
"Exif:FileSource" : int

The source type of the scanned image, if known:

1

film scanner

2

reflection print scanner

3

digital camera
"Exif:SceneType" : int

Set to 1, if a directly-photographed image, otherwise it should not be present.

"Exif:CustomRendered" : int

Set to 0 for a normal process, 1 if some custom processing has been performed on the image data.

"Exif:ExposureMode" : int

The exposure mode:

0

auto

1

manual

2

auto-bracket
"Exif:WhiteBalance" : int

Set to 0 for auto white balance, 1 for manual white balance.

"Exif:DigitalZoomRatio" : float

The digital zoom ratio used when the image was shot.

"Exif:FocalLengthIn35mmFilm" : int

The equivalent focal length of a 35mm camera, in mm.

"Exif:SceneCaptureType" : int

The type of scene that was shot:

0

standard

1

landscape

2

portrait

3

night scene
"Exif:GainControl" : float

The degree of overall gain adjustment:

0

none

1

low gain up

2

high gain up

3

low gain down

4

high gain down
"Exif:Contrast" : int

The direction of contrast processing applied by the camera:

0

normal

1

soft

2

hard
"Exif:Saturation" : int

The direction of saturation processing applied by the camera:

0

normal

1

low saturation

2

high saturation
"Exif:Sharpness" : int

The direction of sharpness processing applied by the camera:

0

normal

1

soft

2

hard
"Exif:SubjectDistanceRange" : int

The distance to the subject:

0

unknown

1

macro

2

close

3

distant
"Exif:ImageUniqueID" : string

A unique identifier for the image, as 16 ASCII hexidecimal digits representing a 128-bit number.

GPS Exif metadata

The following GPS-related Exif metadata tags correspond to items in the “standard” set of metadata.

"GPS:LatitudeRef" : string

Whether the GPS:Latitude tag refers to north or south: N or S.

"GPS:Latitude" : float[3]

The degrees, minutes, and seconds of latitude (see also GPS:LatitudeRef).

"GPS:LongitudeRef" : string

Whether the GPS:Longitude tag refers to east or west: E or a W.

"GPS:Longitude" : float[3]

The degrees, minutes, and seconds of longitude (see also GPS:LongitudeRef).

"GPS:AltitudeRef" : string

A value of 0 indicates that the altitude is above sea level, 1 indicates below sea level.

"GPS:Altitude" : float

Absolute value of the altitude, in meters, relative to sea level (see GPS:AltitudeRef for whether it’s above or below sea level).

"GPS:TimeStamp" : float[3]

Gives the hours, minutes, and seconds, in UTC.

"GPS:Satellites" : string

Information about what satellites were visible.

"GPS:Status" : string

A indicates a measurement in progress, V indicates measurement interoperability.

"GPS:MeasureMode" : string

2 indicates a 2D measurement, 3 indicates a 3D measurement.

"GPS:DOP" : float

Data degree of precision.

"GPS:SpeedRef" : string

Indicates the units of the related GPS:Speed tag: K for km/h, M for miles/h, N for knots.

"GPS:Speed" : float

Speed of the GPS receiver (see GPS:SpeedRef for the units).

"GPS:TrackRef" : string

Describes the meaning of the GPS:Track field: T for true direction, M for magnetic direction.

"GPS:Track" : float

Direction of the GPS receiver movement (from 0–359.99). The related GPS:TrackRef indicate whether it’s true or magnetic.

"GPS:ImgDirectionRef" : string

Describes the meaning of the GPS:ImgDirection field: T for true direction, M for magnetic direction.

"GPS:ImgDirection" : float

Direction of the image when captured (from 0–359.99). The related GPS:ImgDirectionRef indicate whether it’s true or magnetic.

"GPS:MapDatum" : string

The geodetic survey data used by the GPS receiver.

"GPS:DestLatitudeRef" : string

Whether the GPS:DestLatitude tag refers to north or south: N or S.

"GPS:DestLatitude" : float[3]

The degrees, minutes, and seconds of latitude of the destination (see also GPS:DestLatitudeRef).

"GPS:DestLongitudeRef" : string

Whether the GPS:DestLongitude tag refers to east or west: E or W.

"GPS:DestLongitude" : float[3]

The degrees, minutes, and seconds of longitude of the destination (see also GPS:DestLongitudeRef).

"GPS:DestBearingRef" : string

Describes the meaning of the GPS:DestBearing field: T for true direction, M for magnetic direction.

"GPS:DestBearing" : float

Bearing to the destination point (from 0–359.99). The related GPS:DestBearingRef indicate whether it’s true or magnetic.

"GPS:DestDistanceRef" : string

Indicates the units of the related GPS:DestDistance tag: K for km, M for miles, N for knots.

"GPS:DestDistance" : float

Distance to the destination (see GPS:DestDistanceRef for the units).

"GPS:ProcessingMethod" : string

Processing method information.

"GPS:AreaInformation" : string

Name of the GPS area.

"GPS:DateStamp" : string

Date according to the GPS device, in format YYYY:MM:DD.

"GPS:Differential" : int

If 1, indicates that differential correction was applied.

"GPS:HPositioningError" : float

Positioning error.

IPTC metadata

The IPTC (International Press Telecommunications Council) publishes conventions for storing image metadata, and this standard is growing in popularity and is commonly used in photo-browsing programs to record captions and keywords.

The following IPTC metadata items correspond exactly to metadata in the OpenImageIO conventions, so it is recommended that you use the standards and that plugins supporting IPTC metadata respond likewise:

IPTC tag

OpenImageIO metadata convention

Caption

"ImageDescription"

Keyword

IPTC keywords should be concatenated, separated by semicolons (;), and stored as the Keywords attribute.

ExposureTime

ExposureTime

CopyrightNotice

Copyright

Creator

Artist

The remainder of IPTC metadata fields should use the following names, prefixed with IPTC: to avoid conflicts with other plugins or standards.

"IPTC:ObjecTypeReference" : string

Object type reference.

"IPTC:ObjectAttributeReference" : string

Object attribute reference.

"IPTC:ObjectName" : string

The name of the object in the picture.

"IPTC:EditStatus" : string

Edit status.

"IPTC:SubjectReference" : string

Subject reference.

"IPTC:Category" : string

Category.

"IPTC:ContentLocationCode" : string

Code for content location.

"IPTC:ContentLocationName" : string

Name of content location.

"IPTC:ReleaseDate" : string
"IPTC:ReleaseTime" : string

Release date and time.

"IPTC:ExpirationDate" : string
"IPTC:ExpirationTime" : string

Expiration date and time.

"IPTC:Instructions" : string

Special instructions for handling the image.

"IPTC:ReferenceService" : string
"IPTC:ReferenceDate" : string
"IPTC:ReferenceNumber" : string

Reference date, service, and number.

"IPTC:DateCreated" : string
"IPTC:TimeCreated" : string

Date and time that the image was created.

"IPTC:DigitalCreationDate" : string
"IPTC:DigitalCreationTime" : string

Date and time that the image was digitized.

"IPTC:ProgramVersion" : string

The version number of the creation software.

"IPTC:AuthorsPosition" : string

The job title or position of the creator of the image.

"IPTC:City" : string
"IPTC:Sublocation" : string
"IPTC:State" : string
"IPTC:Country" : string
"IPTC:CountryCode" : string

The city, sublocation within the city, state, country, and country code of the location of the image.

"IPTC:Headline" : string

Any headline that is meant to accompany the image.

"IPTC:Provider" : string

The provider of the image, or credit line.

"IPTC:Source" : string

The source of the image.

"IPTC:Contact" : string

The contact information for the image (possibly including name, address, email, etc.).

"IPTC:CaptionWriter" : string

The name of the person who wrote the caption or description of the image.

"IPTC:JobID" : string
"IPTC:MasterDocumentID" : string
"IPTC:ShortDocumentID" : string
"IPTC:UniqueDocumentID" : string
"IPTC:OwnerID" : string

Various identification tags.

"IPTC:Prefs" : string
"IPTC:ClassifyState" : string
"IPTC:SimilarityIndex" : string

Who knows what the heck these are?

"IPTC:DocumentNotes" : string

Notes about the image or document.

"IPTC:DocumentHistory" : string

The history of the image or document.

SMPTE metadata

"smpte:TimeCode" : int[2]

SMPTE time code, encoded as an array of 2 32-bit integers (as a TypeDesc, it will be tagged with vecsemantics TIMECODE).

"smpte:KeyCode" : int[7]

SMPTE key code, encoded as an array of 7 32-bit integers (as a TypeDesc, it will be tagged with vecsemantics KEYCODE).

Extension conventions

To avoid conflicts with other plugins, or with any additional standard metadata names that may be added in future verions of OpenImageIO, it is strongly advised that writers of new plugins should prefix their metadata with the name of the format, much like the "Exif:" and "IPTC:" metadata.

Glossary

Channel

One of several data values persent in each pixel. Examples include red, green, blue, alpha, etc. The data in one channel of a pixel may be represented by a single number, whereas the pixel as a whole requires one number for each channel.

Client

A client (as in “client application”) is a program or library that uses OpenImageIO or any of its constituent libraries.

Data format

The representation used to store a piece of data. Examples include 8-bit unsigned integers, 32-bit floating-point numbers, etc.

Image File Format

The specification and data layout of an image on disk. For example, TIFF, JPEG/JFIF, OpenEXR, etc.

Image Format Plugin

A DSO/DLL that implements the ImageInput and ImageOutput classes for a particular image file format.

Format Plugin

See image format plugin.

Metadata

Data about data. As used in OpenImageIO, this means Information about an image, beyond describing the values of the pixels themselves. Examples include the name of the artist that created the image, the date that an image was scanned, the camera settings used when a photograph was taken, etc.

Multi-part image / multi-part file

This is what OpenEXR calls a file containing multiple subimages.

Native data format

The data format used in the disk file representing an image. Note that with OpenImageIO, this may be different than the data format used by an application to store the image in the computer’s RAM.

Pixel

One pixel element of an image, consisting of one number describing each channel of data at a particular location in an image.

Plugin

See image format plugin.

Scanline

A single horizontal row of pixels of an image. See also tile.

Scanline Image

An image whose data layout on disk is organized by breaking the image up into horizontal scanlines, typically with the ability to read or write an entire scanline at once. See also tiled image.

Subimage

Some image file formats allow the storage of multiple images in each file. These are called subimages in OpenImageIO. Note that in OpenEXR, these are called multi-part files.

Thumbnail

A small, lower-resolution preview image that is stored in an image file, in addition to the main image that the file represents. Not all image file formats support thumbnails.

Tile

A rectangular region of pixels of an image. A rectangular tile is more spatially coherent than a scanline that stretches across the entire image — that is, a pixel’s neighbors are most likely in the same tile, whereas a pixel in a scanline image will typically have most of its immediate neighbors on different scanlines (requiring additional scanline reads in order to access them).

Tiled Image

An image whose data layout on disk is organized by breaking the image up into rectangular regions of pixels called tiles. All the pixels in a tile can be read or written at once, and individual tiles may be read or written separately from other tiles.

Volume Image

A 3-D set of pixels that has not only horizontal and vertical dimensions, but also a “depth” dimension.