Writing an OCIO Look color space in Nuke

Discussions - Using ACES VFX
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What is the proper way to implement an LMT in OCIO v1?

I originally had this which gives me the look in the display, but not as an output for a Write node:

displays:
  sRGB Monitor:
    - !<View> {name: Filmic - Medium Contrast, colorspace: Output - sRGB, look: +LMT_neutral_tonemap}
...
looks:
  - !<Look>
    name: LMT_neutral_tonemap
    process_space: ACEScct
    transform: !<FileTransform> {src: LMT_neutralTonemap.cc}

This gives me the look in my display in Nuke correctly, but it does not appear in the color space for a Write node in Nuke. Following this discussion I did the following in order to get both the look in the display and as an output:

displays:
  sRGB Monitor:
    - !<View> {name: Filmic - Medium Contrast, colorspace: Output - sRGB - LMT medium contrast}

  - !<ColorSpace>
    name: Output - sRGB - LMT medium contrast
    family: Output
    equalitygroup: ""
    bitdepth: 32f
    description: ACES 1.0 Output - sRGB Transform with LMT
    isdata: false
    allocation: uniform
    allocationvars: [0, 1]
    to_reference: !<GroupTransform>
      children:
        - !<FileTransform> {src: InvRRT.sRGB.Log2_48_nits_Shaper.spi3d, interpolation: tetrahedral}
        - !<FileTransform> {src: Log2_48_nits_Shaper_to_linear.spi1d, interpolation: linear}
        - !<ColorSpaceTransform> {src: ACES - ACES2065-1, dst: ACES - ACES2065-1, looks: LMT_neutral_tonemap, direction: inverse}
    from_reference: !<GroupTransform>
      children:
        - !<ColorSpaceTransform> {src: ACES - ACES2065-1, dst: ACES - ACES2065-1, looks: LMT_neutral_tonemap}
        - !<FileTransform> {src: Log2_48_nits_Shaper_to_linear.spi1d, interpolation: linear, direction: inverse}
        - !<FileTransform> {src: Log2_48_nits_Shaper.RRT.sRGB.spi3d, interpolation: tetrahedral}

This look color space however has no effect, neither in the display or when writing the color space, and I just get the Output - sRGB result.

As a workaround I can just bypass Looks all together and do this:

      children:
        - !<FileTransform> {src: Log2_48_nits_Shaper_to_linear.spi1d, interpolation: linear, direction: inverse}
        - !<FileTransform> {src: LMT_neutralTonemap_low.cc}
        - !<FileTransform> {src: Log2_48_nits_Shaper.RRT.sRGB.spi3d, interpolation: tetrahedral}

However I’d like to understand how to properly use Looks (i.e. an LMT) in an OCIO config. Thanks!

2

Found the problem! Needed to use a LookTransform not a ColorspaceTransform. Like this:

    to_reference: !<GroupTransform>
      children:
        - !<FileTransform> {src: InvRRT.sRGB.Log2_48_nits_Shaper.spi3d, interpolation: tetrahedral}
        - !<FileTransform> {src: Log2_48_nits_Shaper_to_linear.spi1d, interpolation: linear}
        - !<LookTransform> {src: ACES - ACES2065-1, dst: ACES - ACES2065-1, looks: LMT_neutral_tonemap, direction: inverse}
    from_reference: !<GroupTransform>
      children:
        - !<LookTransform> {src: ACES - ACES2065-1, dst: ACES - ACES2065-1, looks: LMT_neutral_tonemap}
        - !<FileTransform> {src: Log2_48_nits_Shaper_to_linear.spi1d, interpolation: linear, direction: inverse}
        - !<FileTransform> {src: Log2_48_nits_Shaper.RRT.sRGB.spi3d, interpolation: tetrahedral}
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