Question about IIF config

Marie Fétiveau <m...@...>

Hello all !

I'm having a look at IIF config.ocio and I was wondering how you build the aceslg2_to_Rec709.cube LUT for the rrt_odt_r709 colorspace.

I'm asking because when I compare an OCIOColorspace node (in : aces, out : rrt_odt_r709) and two TuttleCTL nodes (one with the RRT 2.2.1 and another with the REC701 softproof ODT), there are some differences :
- a small shift
- + some noise in yellows with OCIOColorspace node.

Here's a screenshot of my nuke scene and a jpg export with TuttleCTL nodes and an OpenColorIO Node.
For my tests, I'm using an XRite colorchart shot with a Red One and exported in EXR thanks to REDCineX (ACES option enabled).

am I mis-using the OCIOColorspace node ?

Anyway, I will be pleased to understand how the LUT was processed and configured in the ocio config file.
I don't fully understand the purpose of the AllocationTransform vars before the FileTransform :
- !<ColorSpace>
    name: rrt_odt_r709
    family: rrt_odt_r709
    bitdepth: 32f
    isdata: false
    allocation: uniform
    allocationvars: [0, 1]
    from_reference: !<GroupTransform>
        - !<AllocationTransform> {allocation: lg2, vars: [-10.4739, 5.52607]}
        - !<FileTransform> {src: aceslg2_to_Rec709.cube, interpolation: linear}

Thanks a lot !