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ACES Color Workflow Deep Dive

· 5 min read
Andrea Rosado
Andrea Rosado
Junior VFX Coordinator

What is ACES?​

Academy Color Encoding System is a color management system created by the Academy of Motion Picture Arts and Sciences. It is designed to improve the exchange of files in production between on-set look development all the way through final color correction, allowing everyone in the production to see the same image. ACES is meant to be a standardized color space aiming to universally facilitate workflows without so much color space conversion that sacrifices color accuracy, allowing long-term archiving as well.

ACES can encode all colors part of the HVS (Human Visual System) and beyond the spectral locus to create pixels on screen. All values visible to humans are part of the spectrum locus in the chromaticity diagram, however the values outside of this spectral locus, even though they are not visible to humans, are useful for color transforms and math computations. This wider range of colors captures more accurately the colors and tones of the real world.

ACES reverse-engineers the camera color system that is baked within and transforms it back into the pure linear light info without any camera alteration. “ACES is often described as scene-referred or scene-linear. Abstracting away the camera’s bias allows us to get closer to the actual real-world scene that the camera records.” Other than color, ACES displays a wider range of brightness levels handling (HDR) High Dynamic Ranges better than traditional linear color spaces.

Difference between ACES and Linear Encoding​

Linear encoding without ACES, the default color encoding from Nuke (such as SRGB or Rec709) has a different and more specific purpose compared to ACES. Linear encoding like SRGB’s main purpose is for general display instead of color manipulation since it is the standard color space for most monitors, websites and general digital content (great for intermediate steps in a workflow). Linear encoding has a more limited Gamut of color and doesn’t expand beyond the spectral locus. When manipulating and displaying the image, some of the issues that may arise are the way pixels are being calculated when over-exposed, showing artifacts and information that would not be “camera-correct”. By having a standard dynamic range (SDR), the linear encoding compresses the image and can lead to clipping, making the image lose detail in highlights and shadows. Even though ACES also clips down the values of an image, it does not provide artifacting, it gives a more balanced/ softer look in the composition.

Improvements in ACES 2.0 (A look to the future)​

Quoting the following article: Getting your VFX head around ACES 2.0

Key design goals of ACES 2.0:

  • Improve consistency of tone scale and provide an easy to use parameter to allow for outputs between preset dynamic ranges
  • Minimize hue skews across exposure range in a region of same hue
  • Unify for structural consistency across transform type
  • Easy to use parameters to create outputs other than the presets
  • Robust gamut mapping to improve harsh clipping artifacts
  • Fill extents of output code value cube (where appropriate and expected)
  • Invertible – not necessarily reversible, but Output > ACES > Output round-trip should be possible
  • Accomplish all of the above while maintaining an acceptable “out-of-the box” rendering

“Alex Fry: The two main things that are better are, better visual and perceptual matches between the SDR and HDR renderings of the transforms, and better behavior for extreme colors at the edge of gamut, or extreme colors that are heavily overexposed. Both of those areas are much improved.”

How can this be beneficial at Baked?​

By learning about the advantages of ACES color space workflow, the approach can be integrated during production making it the standard production color space. This way it can facilitate communication between different departments within and outside of Baked. Allowing everyone to be on the same “visual page” since this color encoding system is more reliable, expanding higher-quality renders with the widest possible color gamut. Other than this, ACES facilitates archives as well, allowing production to jump back to older projects that used the same workflow to implement it in newer ones without problems.

Practical Artist Workflow at Baked:​

In daily use, an artist working in Nuke simply sets their OCIO config to ACES (at baked this looks like baked_fn-nuke_studio-config-v1.0.0_aces-v1.3_ocio-v2.1.ocio) and then, for each Read node, assigns the camera’s input color space via the OCIOLookTransform node (e.g. ARRI Alexa Log C → ACEScg). The OCIOLookTransform node applies an additional gamut compression method for handling negative pixels in ACES 2065-1 Interchange input color spaces. All compositing is then done in this unified, scene‑linear ACEScg space, ensuring that blending, keying, and grading behave predictably across different source formats. If a classic log to lin conversion is required, an OCIOLogConvert node may be used. When interfacing with legacy footage or external clients still on Rec.709 or sRGB, artists use additional OCIONamedTransform nodes or baked-in Look transforms in the config to convert those inputs cleanly using ACES. This small discipline—assign early, work linear, output transform late—keeps the whole pipeline “color‑correct” from start to finish and preserves maximum headroom for HDR finishing or archival.