View Full Version : Unpremultiply (divide by alpha) in AE

11 November 2008, 09:13 PM
OK so after having used the Nuke and Fusion demos, and falling in love with them (mainly Nuke), I'm trying to recreate my comps for multipass compositing in AE. Well we know this isn't going to be easy.

Main problem (aside from very complicated project structures with many comps) is that there is no straightforward divide operation in the standard AE package. How hard is it to write custom plug-ins for AE? Right now to do a divide by the alpha:

1) Comp with alpha shifted to RGB and inverted, alpha set to full

2) That gets piped into another compound arithmetic with the original image (alpha set to full again), set to multiply RGB.

3) Pipe the result of that into another comp and set to add on top of original image and voila, I have divided (multiply by inverse) by the alpha.

What a pain in the a$$! Now Genarts Sapphire MathOps has a divide in there but thats is a $600 single lic plugin. Shouldn't there be an easier way?


11 November 2008, 06:59 PM
Well I caved and pulled the demo of Sapphire, rather than messing with writing an AE plugin. It is possible to achieve the same workflow in AE as in Nuke and Fusion for multipass compositing with MathOps, but man is it ugly.


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11 November 2008, 06:59 PM
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