Hi. I have rendered some animation in cinema 4d and have an alpha channel in the passes. I want to use that alpha to create a track matte. I can do that for the image itself but I can't figure out how to use it to constrain an effect to a specific area. So say I have a ball and an alpha channel for it, and I want to adjust the levels on the ball but leave the background as it is. Thanks for the help.
Duplicate the layer that gets the effect. Apply the effect to the uppermost instance of the layer. Use the c4d layer as either an Alpha or Alpha Inverted matte for the uppermost layer. Done.
Ah, ok. Thats what I had done in the past but thought it seemed like a bit of a messy way around it. If thats the way its done then cool. Thanks for the answer.