thank you for looking into this and the detailed write-up. The workaround works fine. It also worked by assigning the mask to each layer but that's not very efficient. So thanks for the workaround!
I'm fairly new to Affinity and all the OCIO and ACES workflow. I'm working in Cinema 4D with Octane and I usually produce more animations than stills, which worked pretty good so far with linear. Stills however are different because of the ICC system.
Regarding the object layer color: it can be expensive to render out straight alphas for animations but I also got to say that I don't use the object color layer workaround “correct” here, but so far it always worked in PS. If you're interested in this workaround, there is a talk from Drew Nelson who explains this workflow [at 10:10]:
For stills however it's absolutely manageable to render out clean alphas and I will just do this now or probably switch to cryptomatte in general.
With the exr stills I want to completely finish my frame in Affinity so the output will be 8/16 bit. I usually work with the ICC display transform turned on. I quickly rebuild the image in an extra Affinity file as I didn't save the history before, so I probably just didn't pay attention to this. But thanks for the explanation and the procedural texture solution!
My workflow with this rendering was using the OCIO with source color: ACES — ACEScg, output — sRGB and the LUT is used to convert the image from linear to ICC srgb, so I can assign the sRGB IEC61966-2.1 (Linear) ICC Profile and get a correct export. But as I'm said, I'm new to this so its totally possible that I'm also making a mistake here. So far, the final export looked like it should. 🤔
Thanks for all the help!