Magno Borgo:
Removal area/clean plate, regrained to match the background plate. It has an alpha channel, blurred to smooth transition. But when its composited Over the original plate (heavy grain), on the semi-transparent alpha region the grain is faint because of the blending.
This is a question that I have had asked to me many times. It's a very tricky question. I have heard lots of different ideas on how to solve the problem. Seeing that this question came from a nuke trainer, this is a problem for a lot of artist. Have a read.