OCIO 2.5 Release

Timeline

OpenColorIO 2.5 was delivered in September 2025 and is in the VFX Reference Platform for calendar year 2026.

Breaking Changes

Please be aware of the following changes when upgrading to OCIO 2.5.

For Users

  • OCIOZ archive files created on Windows in prior releases should be regenerated due to an issue in a third-party library. Please see below for more details.

  • For applications that use the categories attribute of color spaces to filter the color space menus shown to users, the filtering will now include color spaces that do not have any category set. (Though applications may use a new API call to override this behavior.)

For Developers

  • Applications that use the OCIO GPU renderer may need to make small adjustments to their code due to changes that were required in order to support the Khronos Vulkan graphics API.

  • The Python functions getActiveDisplays and getActiveViews now return iterators, please see below for details.

  • Please see the section below about version updates to required third-party dependencies.

New Feature Guide

Config Merging (PREVIEW RELEASE)

Config files may now be merged. This was a long-standing feature request and it opens up interesting new possibilities for how configs are created, managed, and deployed. Because the workflow ramifications of this feature are far-reaching, this is being labelled a Preview Release and therefore the API and behavior may change as a result of more feedback and testing.

Five different merge strategy options are provided, along with an extensive set of parameters to customize the process. The new feature handles the complexities inherent in the very flexible OCIO config format such as:

  • Handling name or alias conflicts.

  • Handling differences in reference connection spaces by adding compensating color space conversions to transforms.

  • Avoiding adding duplicate color spaces (even if they are named are differently). This allows applications to avoid adding color spaces that may already be present in the user’s config.

  • Providing a mechanism to group added color spaces under a separate menu hierarchy.

For Users

End-users may use the new ociomergeconfigs command-line tool to merge configs. A new OCIOM file format is provided to set the parameters that control how the merge is done. For example, you may merge a specific set of color spaces or displays and views that are needed for a given project into a general-purpose base config.

For Developers

Developers may use the new API to merge a set of color spaces that an application requires into the user’s config. (This is typically done on the fly, in memory, to avoid modifying any config files on disk.) Applications may then publish their required color spaces as a config file which makes the process transparent to color scientists or pipeline experts at a facility who may use ociomergeconfigs to merge the application color spaces into their own configs and validate everything works as intended.

Built-in ACES 2.0 Configs

The ACES 2.0 library support was finalized in the OCIO 2.4.2 release. In the 2.5.0 release, built-in ACES 2.0 versions of the Studio and CG config are now provided. This allows use of the ACES 2.0 Output Transforms as OCIO views.

This ASWF Open Source Days presentation from ILM’s Alex Fry provides a great overview of the benefits of the new configs.

In addition, the new configs make expanded use of OCIO v2 features such as File Rules and Viewing Rules and add a virtual display to support use with ICC monitor profiles.

Please take note that the display color spaces in the new configs pass through negative values rather than clamping them (by mirroring the transfer function around the origin). This provides better support for video workflows that require values below reference black to be passed through.

Finally, there are a few other color space additions including a Gamma 2.2 Rec.709 display color space and a color space for DJI Log.

For Users

The following URI strings may be provided anywhere you would normally provide a file path to a config (e.g. as the OCIO environment variable):

To use the updated OCIO CG Config for ACES, use this string for the config path:

ocio://cg-config-v4.0.0_aces-v2.0_ocio-v2.5

To use the updated OCIO Studio Config for ACES, use this string for the config path:

ocio://studio-config-v4.0.0_aces-v2.0_ocio-v2.5

This string will give you the current default config, which is the latest ACES 2 CG Config:

ocio://default

This string now points to this latest ACES 2 CG config:

ocio://cg-config-latest

This string now points to this latest ACES 2 Studio config:

ocio://studio-config-latest

Hue Curve Transform

A new GradingHueCurveTransform is added to allow a type of selective color correction often available in grading tools. A set of eight spline-based curve adjustments are provided:

  • Hue-Hue: Map input hue to output hue (where a diagonal line is the identity).

  • Hue-Sat: Adjust saturation as a function of hue (a value of 1.0 is the identity).

  • Hue-Lum: Adjust luma as a function of hue (a value of 1.0 is the identity).

  • Lum-Sat: Adjust saturation as a function of luma (a value of 1.0 is the identity).

  • Sat-Sat: Adjust saturation as a function of saturation (a diagonal is the identity).

  • Lum-Lum: Adjust luma as a function of luma, maintaining hue & sat (diagonal is identity).

  • Sat-Lum: Adjust luma as a function of saturation (a value of 1.0 is the identity).

  • Hue-FX : Map input hue to delta output hue (a value of 0.0 is the identity).

Unlike the typical implementation of tools of this type, this transform is invertible and has been developed to work well on video, log, and scene-linear color encodings.

The parameters may be adjusted via OCIO’s dynamic parameter mechanism which allows adjustments to be made without having to recreate a Processor object. This facilitates real-time adjustment in applications.

Vulkan Support

For Developers

Support has been added for the Khronos Vulkan graphics API standard. The OCIO GPU renderer may now be used within applications that use Vulkan to get the most out of the latest GPUs.

This has required a small modification to the existing GPU API. Developers that use the GPU interface may need to modify their code when updating to OCIO 2.5. The API for the following functions have been modified: addUniform, addTexture, add3DTexture, and createShaderText. The addToDeclareShaderCode function has been replaced by the more specific addToParameterDeclareShaderCode and addToTextureDeclareShaderCode. In addition new functions have been added to get the descriptor set and texture binding indices. The GPU_LANGUAGE_GLSL_VK_4_6 option is now available for the GpuLanguage enum.

New Color Space Attributes

For Config Authors

New attributes are provided to allow OCIO to better interoperate with other color standards. OCIO now supports the Color Interop ID developed by the Color Interop Forum. This allows config authors to set an ID on the color spaces in a config to unambiguously identify them as conforming to the recommendations of the ASWF Color Interop Forum. These IDs may then be used in file formats including OpenEXR and OpenUSD. (Please note that the IDs are for use in file formats but the color space’s name attribute is still what should be used in a UI.)

The new attributes are:

  • interop_id: Holds an ID string intended to be used across configs and file formats.

  • icc_profile_name: Holds the name of an associated ICC profile.

  • amf_transform_ids: Holds the ID strings associated with the ACES Metadata Format (AMF).

Please note that the drafts of various Color Interop Forum recommendations on this topic are currently being finalized and should be published on GitHub over the next few months.

New “edr-video” Encoding

For Config Authors

Color spaces currently have an encoding attribute that is used to give applications a general sense of how colors are distributed within the numerical encoding. There are currently two encodings that are recommended for use with video: sdr-video and hdr-video, where the latter is intended for color spaces such as Rec.2100-PQ and Rec.2100-HLG. However, there are increasingly a set of color spaces (such as “Display P3 HDR” in the built-in configs) that use what is essentially an SDR encoding that is extended so that it may be used in cases where there is a mix of both HDR and SDR content. For these color spaces, a new encoding is being introduced: edr-video.

Version Updates

The latest versions of all third-party dependencies have been reviewed for compatibility. In some cases, support for older versions has been dropped.

For Users

  • Support for minizip-ng 3.x has been dropped. Due to a bug in previous versions of that library, any OCIOZ files created on Windows would not have been cross-platform, are not fully supported in OCIO 2.5, and should be regenerated. You may use standard Zip decompressors to expand the .ocioz files on Windows and use the ocioarchive command-line tool to recompress them. The new files will be cross-platform and will be compatible with both OCIO 2.5 and previous releases.

For Developers

  • Support for CMake 4 has been added.

  • Support for more recent versions of all dependences has been added.

  • Support for C++ 11 and 14 has been dropped. OCIO now requires at least a C++ 17 compiler.

  • Support for Python 3.8 has been dropped.

  • Support for Expat prior to 2.6.0 has been dropped.

  • Support for OpenEXR prior to 3.2.0 has been dropped.

  • Support for Yaml-cpp prior to 0.8.0 has been dropped.

  • Continuous Integration testing has added VFX Platform 2025 and dropped 2021.

  • Miscellaneous other modifications and improvements have been made.

API Enhancements

For Developers

The previous “frozen docs” system for generating Python API documentation for ReadTheDocs has been replaced. This reduces the burden on developers when adding new API functions and simplifies the maintenance of the project.

The previous API for the active display and view lists returned one long string that developers would need to manually parse into tokens, which could be error-prone (as commas are both separators and may be used in display and view names). A new set of API calls has been provided to get and set active displays and views individually. In the case of Python, the getActiveDisplays and getActiveViews functions now return iterators, which is the only change that requires a modification to existing code.

In addition, here are some other new API functions:

  • The setDisplayTemporary function may be used to serialize displays created using an ICC profile and a config’s virtual display. This is helpful if a host application needs to serialize a config that includes those displays for use by plug-ins such as OpenFX.

  • The setTreatNoCategoryAsAny function may be used on the ColorSpaceMenuParameters class to control the menu filtering behavior for color spaces that do not have the categories attribute set. The default is to include those color spaces when doing category filtering since this is the least surprising behavior for end-users that are editing their own configs.

  • The following convenience methods have been added to the Config class for working with various types of views: isViewShared, clearSharedViews, AreViewsEqual, hasView, hasVirtualView, isVirtualViewShared, AreVirtualViewsEqual.

  • The setStringVar function is now available on the Context class in Python.

  • A removeNamedTransform function is now available.

  • The previously deprecated function getDefaultBuiltinConfigName has now been removed. Please use ResolveConfigPath("ocio://default") instead.

New Fixed Function Transforms

For Config Authors

The following new styles are available for use with FixedFunctionTransforms in config files with ocio_profile_version set to 2.5 or higher. They implement a conversion from an RGB color space encoding to a hue, saturation, and luma space that is used by the new hue curve transform. Three conversions are provided that are optimized for scene-linear, logarithmic, and video color spaces:

  • FIXED_FUNCTION_RGB_TO_HSY_LIN

  • FIXED_FUNCTION_RGB_TO_HSY_LOG

  • FIXED_FUNCTION_RGB_TO_HSY_VID

New Built-in Transforms

For Config Authors

In config files with ocio_profile_version set to 2.5 or higher, config authors may take advantage of the following new BuiltinTransform styles that mirror the transfer function around the origin to pass negative values rather than clamp them:

  • DISPLAY - CIE-XYZ-D65_to_REC.1886-REC.709 - MIRROR NEGS

  • DISPLAY - CIE-XYZ-D65_to_REC.1886-REC.2020 - MIRROR NEGS

  • DISPLAY - CIE-XYZ-D65_to_G2.2-REC.709 - MIRROR NEGS

  • DISPLAY - CIE-XYZ-D65_to_sRGB - MIRROR NEGS

  • DISPLAY - CIE-XYZ-D65_to_G2.6-P3-D65 - MIRROR NEGS

Release Notes

For additional details, please see the GitHub release page:

OCIO 2.5.0