I have searched around and nothing was obvious to me if this has been discussed before. Apologies if it has.
The MultiMatteRenderElement looks great and appears to be the solution we have been waiting for for ages. However the anti-aliasing doesn’t seem to be exact It seems better than the standard VRay Element one (ie it has some), but not as smooth as the main render. I have tried to upload an example at rogepost.com but its vanished so cant right now. But has anyone noticed this?
If you do a direct comparison with it and a scanline self-illuminated material RGB render, do they look the same?
the Renderelements in general make their sampling decisions with the beauty pass. This means that if your beauty pass does not meet the thresholds (For example you are rendering everything black ) then the Renderelements don’t generate more samples.
There best solution for the multimatte elements is to use adaptive subdivison sampling and check the object outline checkbox.
This will force sampling along the object outlines.