OCIO and ACES in Pixotope

ACES

ACES, or the Academy Color Encoding System, is an open color management and interchange system developed by the Academy of Motion Picture Arts and Sciences (AMPAS) and industry partners. It:

• standardizes the color science used in projects of all types

• gives the industry a standardized color management system that encompasses:

  • production

  • post-production

  • presentation

  • archiving

In an industry with dozens of different camera systems, multiple encoding options, different display devices, etc The Academy saw a need for a system like ACES to manage color in a precise yet straightforward way, no matter the camera or display being used.

Many software developers have tackled color management in their own applications, but none of those solutions are industry-wide and open. ACES is an industry-standard color management solution that anyone can use to manage the color pipeline of any project.

To learn more about ACES, follow the links below:

• Helpful Explanation of Why use ACES:

  • Academy Color Encoding (ACES) by Chris Brejon as part of his CG Cinematography blog

• Reference:

  • Academy Color Encoding System (ACES)

  • ACES "working" Spaces

• Forums:

  • ACES Central

• Resources:

  • ACES configs: https://github.com/AcademySoftwareFoundation/OpenColorIO-Config-ACES/releases

Pixotope uses OCIO 2.5.0 with ACES 2.0. Pixotope's OCIO config is our own version, based on the ACES reference configuration.

Gamut compression in ACES 2.0

With ACES 2.0, out-of-gamut colors are no longer handled with a harsh clipping model. Instead, the Output Transforms (DRTs) are built around a perceptual color appearance model (Hellwig 2022 / JMH). Every time an Output Transform is processed - whether the target is Rec.709 SDR, P3-D65 or Rec.2020 HDR - the image data is routed through this volumetric perceptual space, and gamut compression is dynamically and automatically calculated based on the limitations of the target display.

In practice this means that colors which fall outside the target display's gamut are compressed towards it rather than clipped, preserving gradations in highly saturated areas instead of collapsing them into flat blocks of a single color. This happens automatically as part of every output conversion - no manual gamut handling is needed.

ACES working Color Spaces: ACEScg vs ACEScc vs ACES2065-1

Use this rule of thumb when thinking about an ACES pipeline for media production:

For live rendering: ACEScg

• Preferred working color space for Pixotope and live VP production.

• Good for intermediate exchange between DCCs in VFX or animation pipelines

• Using ACEScg in an internal pipeline reduces the color processing needed to work on shots in other DCCs

• Fine for archival purposes internally for vfx and animation studios if it is being used for production of the final shots

• Uses AP1 primaries

Optional for log based color grading: ACEScc or ACEScct

• Specifically developed to support legacy film grading workflows

• Makes color grading tools feel much more like they do when working in a log space that many colorists and some comp artists prefer.

• ACEScc is a pure log function, but ACEScct has a "toe" near black, to simulate the minimum density of photographic negative film, and the legacy DPX or Cineon log curve.

• Intended for internal use within a software package - not intended to store image data to disk with.

• Uses AP1 primaries

For interchange: ACES 2065-1

• Also known as ACES

• Highly recommended for interchange between facilities

• Good for archival purposes

• Colorists may choose to use ACEScct or even ACEScg or ACES2065-1, or perhaps even the camera encoding a project was shot on. Always exchanging ACES2065-1 guarantees consistency

• Uses AP0 primaries

OCIO

OpenColorIO (OCIO) is a complete color management solution geared towards television and motion picture production with an emphasis on visual effects and computer graphics. OCIO provides a straightforward and consistent user experience across all supporting applications while allowing for sophisticated back-end configuration options suitable for high-end production usage. OCIO is compatible with the Academy Color Encoding Specification (ACES) and is LUT-format agnostic, supporting many popular formats.

OCIO is fully user-configurable, and all color management knowledge resides in the color transforms and human-readable configuration files.

Pixotope currently uses the OCIO 2.5.0 implementation.