Premultiply

A utility Matchbox shader for Autodesk Flame, Flame Assist, Flare, and Smoke that premultiplies or unpremultiplies a fill based on a matte. Handy for using right on the timeline as a Timeline FX prior to a 2D Transform to deal with unpremultiplied logos and things (typically PNGs.)

While Autodesk supplies a matchbox called 'PremultiplyOnBlack', it doesn't pass the matte through which makes it useless on the timeline (and creates messier schematics in Batch/BFX since you have to feed it the input matte for it to operate, but have to connect the original matte to anything downstream.)

Updated 15-Apr-2016: Added a clamping button for limiting output values to 0.0-1.0, useful for unpremultiply. Turned on by default.

Updated 11-Mar-2016: Fixed the input mapping for Front and Matte so it works on the timeline automatically without having to change them manually.

Updated 14-Aug-2015: Added user-selectable background color for premultiplying over or removing background colors other than black.

Grab Premultiply from the Logik Matchbook site.