I've created a green screen key using Primatte in one comp, and I want to use that same key in another comp, but where the background has since been replaced and rendered out with an effect I want to keep on the foreground subject. I bet it's something simple...
Actually I bet that explanantion's confusing.
Subject X is against green in a video in comp A.
X was extracted using a key and rendered with an effect and a new background to creat video B.
I want to extract subject X from B (and keep the new effect) using the alpha channel created in comp A.
So how do I copy and paste the alpha channel from comp A to a new comp with video B in it?
Pre-compose, use as a matte layer.