I'm trying to achieve an 'erasing' effect. Basically, imagine a blue ball roling over a green background. Everywhere the blue ball has rolled to should permanently turn transparent.
Keying the blue ball is trivial. When setting out for this project, I expected to be able to 'export' the keylight data in some form onto a mask layer, presumably by using a, possibly compley, expression.
However, I fail to both see and successfuly google a way to get useful data from the keylight effect.