OCIO 2.1 Release


OpenColorIO 2.1 was delivered in August 2021 and is in the VFX Reference Platform for calendar year 2022.

New Feature Guide

ACES 1.3 Gamut Compression

ACES 1.3 introduced a scene-referred gamut compression algorithm that compresses colors captured by a camera into the AP1 gamut. This avoids artifacts that may occur downstream (such as in the ACES Output Transforms) for scene elements such as colored lights. This supersedes the earlier “Blue Light Artifact Fix” LMT.

ACES RGC User Guide

ACES RGC Implementation Guide

The implementation includes a BuiltinTransform for the ACES Reference Gamut Compression. Here’s what that looks like in Config YAML:

!<BuiltinTransform> {style: ACES-LMT - ACES 1.3 Reference Gamut Compression}

There is also a FixedFunctionTransform for the underlying gamut compression algorithm. As described in the links above, it takes seven parameter values:

[ Limit_Cyan, Limit_Magenta, Limit_Yellow, Threshold_Cyan, Threshold_Magenta, Threshold_Yellow, Roll-off ].

Here is how that looks in Config YAML with the parameters set for the ACES 1.3 Reference Gamut Compression:

!<FixedFunctionTransform> {style: ACES_GamutComp13, params: [1.147, 1.264, 1.312, 0.815, 0.803, 0.88, 1.2]}

And here’s how it looks in a CTF file:

<FixedFunction inBitDepth="32f" outBitDepth="32f" style="GamutComp13Fwd" params="1.147 1.264 1.312 0.815 0.803 0.88 1.2" />

Config authors: These new transforms may be used in configs with version 2.1 or higher and CTF files with version 2.1 or higher.

OpenFX OCIO plug-ins

A framework to support OpenFX plug-ins has been added and example source code may be found in the vendor/openfx directory. The initial set consists of two plug-ins, one for applying a ColorSpaceTransform and another for applying a DisplayViewTransform.

Some screenshots of the UI may be found in PR #1371.

End users: There are currently no pre-built executables available, so you will need to compile these yourself.

Developers: Set the CMake variable -D OCIO_BUILD_OPENFX=ON to build the plug-ins.

Support for PyPI (pip install)

Python wheel generation has been added and support for the Python Package Index (PyPI). This allows you to easily install the OCIO Python bindings without needing to build from source or use one of the OS-specific package managers. The command is simply:

pip install opencolorio

Support for emitting Open Shading Language (OSL)

The OCIO GPU Renderer may now emit shaders in Open Shading Language format. There is a new GpuLanguage enum: LANGUAGE_OSL_1.

Note that the OCIO library does not need to be compiled against the OSL library but running the OSL unit tests does require OSL and OIIO. These will be built automatically if CMake is able to find them or you set -D OSL_ROOT to indicate the installed location.

Currently, Lut1D and Lut3D Transforms are not supported and will throw an exception if used. All other transforms are supported. However, dynamic properties are currently locked to their initial values and may not be adjusted.

Support for Apple Metal Shading Language and OpenGL ES

The OCIO GPU Renderer may now emit shaders in these other new languages. The new GpuLanguage enums are:




Test suite for the Academy/ASC Common LUT Format (CLF)

The set of CLF test files was expanded and a set of Python scripts was added under share/clf which were developed by the ACES Common LUT Format Implementation Working Group. The scripts allow use of the OpenColorIO renderers to process a sample image through each CLF file in the test suite and then compare the reference images to a set of corresponding images from another CLF implementation to see if the differences are within the tolerance allowed by the CLF Implementation Guide.

Imath 3 support

OCIO and its CI system now support Imath 3 for the Half data type dependency.

Noteworthy API updates


Config::getColorSpaceFromFilepath() is now the proper way to extract a color space from a file path, regardless of whether the config is version 1, or version 2 or higher. It works regardless of whether the config has FileRules defined. Therefore, the older Config::parseColorSpaceFromString() method (which does not work with FileRules) is officially deprecated.

Note that Config::getColorSpaceFromFilepath() always returns a color space, regardless of whether the config’s strictparsing attribute is true or false. This was a request from app developers that always need a default (which is a common scenario). Please see Issue #1398 for more details on how to take special action if strictparsing is true.


There is a new Config::getDefaultView(display, colorspaceName) method that takes advantage of the ViewingRules feature that was introduced in OCIO 2.0. It returns the default view that is most appropriate for a given color space. If the color space is known, developers should call this rather than Config::getDefaultView(display).

The motivation is that the best view transform to use varies with the color space. For example, a scene-referred color space typically wants some kind of tone-map such as an ACES Output Transform. However, a display-referred color space will look wrong with such a view transform since it has already been tone-mapped.

One scenario where this new method is ideal is when an application needs to generate thumbnails for a large number of images that are in a variety of color spaces. Note that the config must have the Viewing Rules set in order to return different views, but if the rules are not set, it will still return the same result as Config::getDefaultView(display), so it may be used with either v1 or v2 configs.

Release Notes

For more detail, please see the GitHub release pages:

OCIO 2.1.0

OCIO 2.1.1

OCIO 2.1.2

OCIO 2.1.3