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View Full Version : is there a premult. operator in AE?

Redsand1080
05-20-2008, 03:08 PM
I am trying to do color correction on a foreground layer that has a straight alpha channel. I recently read that it was better to do color corrections on a straight alpha channel image because you are changing the values for the color component of an RGB image only...and not messing with the transparency of those RGB pixels. If the layer is premultiplyed, however, you change the transparency of those RGB pixels (because transparency is included when those RGB values are multiplyed by the background color) in addition to the color component...which is undesirable and can lead to artifacts.

I read about one technique that said you should color correct the image with a straight alpha...then once you are finished apply a 'premultiply operator' to the layer to premultiply the RGB values by the alpha. That way you end up with a premultiplyed image with accurate transparency in the RGB values AFTER you color correct the image.

I can't seem to find a filter or anything in AE to allow me to do this. Is this possible to accomplish in AE...or do i need to use Nuke, or Shake or Digital Fusion? Or is there some technique that differs slightly from what i am disscussing here...but will accomplish the same general principle of color correction without screwing with the 'transparency' of RGB pixels.


Any ideas would be great!


Thanks! :thumbsup:
Mylenium
05-21-2008, 06:23 AM
Shift Channels? Set Channels? Set Matte? Matte modes? CC Composite? There's a ton of tools you could use to re-introduce a matted Alpha. personally I very much like the WE Alpha Tool from Walker FX which combines all possible manipulations in on interface, but of course it doesn't come for free with AE.

Mylenium
Redsand1080
05-21-2008, 03:11 PM
Thanks a lot...i will look into those solutions very soon. Hopefully today actually.


Much obliged! :beer:
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05-21-2008, 03:11 PM
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