I love how screen subtraction works on the PIK node and am trying to recreate it so that I can use it outside of PIK. So the question is, how do you write an expression (SeExpr/SeExprSimple) that will subtract a screen the way PIK does? How then, do you premult the result?
I've surmised (1-a)*color1[0...2], where color1 are the RGB values of the screen sample area. I'm a bit confused by the results. How do I bring it home?
Any help would be appreciated.