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.)

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