Here is the problem: CG and VFX are done in OCIO/ACES, but the colorist uses a different picture formation (like OpenDRT, JP2499, Genesis, etc.). How to ensure that VFX artists can preview their work correctly, and bake the showlut into Rec.709 previews?
Using LUTs in Nuke is not very straightforward. For instance, if the colorist is working in DaVinci Wide Gamut/Intermediate, and exports a LUT with a baked-in display transform for Nuke, how to apply it correctly? Should we switch the Viewer to RAW and create the Input Process of 2 nodes, first OCIOColorspace converting ACEScg files into DWG log, second OCIOFileTransform loading the LUT?
The description of the OCIOFileTransform node is very confusing, like for the working space field: “Sets the color space in which the file is applied. The input is transformed from scene linear to the specified working space, the file color transform is applied, and then the result is transformed back to scene linear.” But the intended output is Rec.709 display, not scene linear.
Or, do we need a custom OCIO config? Would appreciate any help in clarifying the matter, as we were not able to find any clear information online.
The file transform mechanism doesn’t allow to redefine the output as a new space but rather expects the file to only do something in a particular space and output it’s result in that same space. Think showLUTs created in ACEScct for example that can be loaded before the ACES output transform and toggled on and off without breaking the rest of the image pipe. In such a case you would set the node’s working space to ACEScct and it would do a conversion from the configs defined scene-linear color space to the chosen space and back to scene-linear after applying the file.
I think to tackle your problem you sort of have two options.
Stay with a ‘native’ Nuke ACES OCIO config and set up a custom viewer process.
Customize, or use a customized OCIO config that incorporates one or more other image formation pipelines, like those linked by Daniel.
I’d personally opt for nr 2 as it’s a bit easier to access, read, customize and share. Especially in the context that a project may not have anything to do with ACES at all it wouldn’t make much sense to force an ACES config. Jed Smith’s OpenDRT for example comes with it’s own OCIO config ready to use.
Many thanks for the explanation! I did suspect OCIOFileTransform was intended for loading scene-referred LUTs.
We do need ACES for file exchange as our 3D artists use it. We are now testing OpenDRT OCIO config in Nuke and it is working nicely, I especially like the selection of linear working spaces, including DaVinci Wide Gamut. I am only having trouble with customization - for instance, if trying to add a custom display based on a showlut, there is an error that the config is invalid.
If there’s an error it should show which code lines are problematic. If the error pop up doesn’t tell anything it may be visible in the console window of Nuke.
Perhaps if you show the altered/added code snippets here users can have a look at it and point out possible issues.