I have a question about the latest changes about the WCS definitions that are proposed here: https://github.com/aforsythe/aces-dev/commit/b8497c0af1615ae037635b901df1818336e83d67
Generally limiting the definition of a working color space to the transforms that actually require it – namely the ASC-CDL node – seems like the right way to me in order to limit the use of WCS to necessary use cases, and to further substantiate the intended use of working color spaces in the context of LMTs. It also might help reduce maybe yet unforeseeable consequences for the future of “regular” LMTs, where now ACES 2065-1 (AP0) is always required in order to make them applicable as universally as possible.
I have one question about how to use that in a use case that we currently cover in our software:
In Livegrade (and I guess also in other applications) users have the option also to apply one or more 3D LUTs in the WCS (e.g. ACEScct) before or after the ASC-CDL.*
If we want to recreate such a pipeline (for instance IDT X -> ASC-CDL in WCS Y -> 3DLUT in WCS Y -> RRT -> ODT Z) in other systems, how would we encode that in the proposed AMF variant?
Maybe we are missing a second “legacy” transform node that also requires a WCS definition, namely a “LUT-based transform”. Again you could argue that it is necessary to specify a WCS for that (because applying LUTs in linear doesn’t make much practical sense the same ways as ACS-CDLs). So we might need to introduce a similar mechanism for 1D / 3D LUTs as for ASC-CDLs. Or is this already covered somehow else?
I feel we’re getting very close now, but didn’t nail yet the use cases with externally defined transforms in the role of “LMTs”. With this I mean transforms that are custom-created for certain scenes or productions, and thus need to be defined outside the AMF file (e.g. as the mentioned 3D LUT files, or maybe also as CLF files), and that yet need to be referenced from the AMF file somehow as look transforms in order to be able to recreate that pipeline.
Maybe @Alexander_Forsythe or @CClark can add some clarifying comments. Thank you!
(*) Allowing to apply 3D LUTs in the WCS together with the ASC-CDL has become necessary in order to allow “custom LMTs” (e.g. provided by a post house or dailies facility) to be transported and applied in the format of 3D LUTs – especially as long as we didn’t have CLF or other formats that allow to be applied meaningfully in the scene-linear encoding of ACES 2065-1. Thus providing such “LMTs” as 3D LUTs (to be applied in a certain working color space) has become a practicable way of encoding and applying custom LMTs in such available 3D LUT formats.