proper diffuse colour pass for denoising
If a material has sheen, metallic, or transmission, then whatever is plugged into the diffuse (base) colour input is lost from the diffuse colour pass.
The diffuse texture needs to be accessible in the compositor in order to use the denoiser correctly, (so texture detail isn't lost).
I propose a new 'denoising diffuse colour pass', which has just the base colour information without lighting, metallic, sheen, or transmission information.
2 Comments
I might be wrong, but isn't that what we already have when we check the "denoising data" option in the render passes (which isn't a pass but actually a group of passes for denoising).
That seems more like a bug than a need for a new feature (maybe it's because of the way Principled BSDF works- you could use a Principled with black for diffuse and then use add-shader to add it to the diffuse of your choosing, may not be %100 physically accurate, though). Anyways, in 2.82 there will be custom AOVs which allow you do to just about anything in the compositor.