ACES in practice (Maya/Arnold)

There are a few really good source/guide about ACES (Academy Color Encoding System).
To extend that information here’s a simple guide how to use ACES in Maya/Arnold.
This is a basic/general (not ideal) approach when you have the “non-ACES” sRGB textures for color maps, and also “non-ACES” sRGB based EXR and HDR images (hdr textures for lighting).

  • Download the OCIO (OpenColorIO) config files (this contains all ACES versions and other OCIO based configs and files)
  • Unzip it
  • In Maya go to Window -> Settings/Preferences -> Preferences -> Color Management
    • Load the latest version of the OCIO config file for ACES: OCIO Config Path (The current version is ACES_1.2)
  • Turn off the Use OCIO Input Color Space Rules (This way you can create your own.
    That’s necessary to get correct results.)
  • In Maya there is a simple way to create rules for different cases (texture inputs).
    You don’t have to convert the textures into ACES primaries.
    I recommend the following rules (this is a file extension and file name based system, so you have to be really careful about the used naming conventions – as always):
    • Default: Utility – sRGB – Texture
    • You can create new rules by clicking the Add button.
    • Guide: rule name: Image Extension, Image File Path Pattern, Input Color Space
      This is the actual order of creation. The order is important.
    • exr: exr, *, Utility -linear -sRGB
    • hdr: hdr, *, Utility -linear -sRGB
    • displacement: *, *isplacement*, Utility – Raw
    • bump: *, *ump*, Utility – Raw
    • metalness: *, *etalness*, Utility -Raw
    • roughness: *, *oughness*, Utility – Raw
    • mask: *, *mask*, Utility – Raw
    • opacity: *, *pacity*, Utility – Raw
    • normal: *, *ormal*, Utility – Raw
    • albedo: *, *lbedo*, Utility – sRGB – Texture
    • color: *, *olor*, Utility – sRGB – Texture
      Those last two is for safety reasons to make sure the color, basecolor, albedo textures get the correct settings.
    • The evaluation of the final list will be executed from bottom to top in Maya.
  • When the list is finished you can change the order by clicking the Up and Down buttons (above the list).
  • Of course you can add more rules if it’s necessary (IOR, Anisotropy etc.) and extend it for other naming conventions.
    The logic is where you have raw data (where there is no direct, visual interpretation of the values, “just math”) you have to use the Utility – Raw Input Color Space.
    Where you have sRGB color data, but you store that in a linear scale (for example Light source like IBL textures as such) use the Utility -linear -sRGB Input Color Space.
    For regular sRGB (non-linear) color textures use the Utility – sRGB – Texture Input Color Space (like albedo, diffuse, sheen color etc.).
  • The View Transform is automatically set to sRGB(ACES), that’s correct for most users.
  • Don’t forget to use an OCIO capable software to view and edit the rendered EXR files.
    I recommend Nuke.
    From there you can convert the results into standard sRGB images (or other outputs, it’s really depends on what’s your target device category is).
  • That’s it.

You can download the original version of the zombie character at here.

Cheers, D

Original res of the featured image:

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