I have a question concerning alpha channels in after effects. I'm doing a intro to a television series and I want to incorporate shadow elements that will be practically shot against a vellum screen (like this video here http://www.blind.com/work/directors/chris-do/gap-sound-of-color/) but how would I key the white out and still maintain the soft edges? is it as simple as adding an alpha channel? any suggestions would be appreciated, cheers.
If it's just dark shadows on white the easiest way is to just switch the blending mode to multiply, which will drop out all of the white while keeping the soft edges. Dave's suggestion would be best if you need to use the shadows as a matte for another layer.