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RichH
03-20-2006, 12:06 PM
Hi All,

I've been using after effects for a while when it occured to me that i can color correct footage with seemingly no adverse effects like fringing etc. I'm importing single tga's with alpha (pre-multiply option).
I was wondering if anyone can put me straight as to how AE handles the whole pre-multiply thing? Does it magically work it all out for you as you change any rgb values? If anyone can explain it in terms of ((foreground x alpha) + (backround x inversealpha)) would be most helpful

Just curious

Many thanks, Rich
jussing
03-20-2006, 03:38 PM
Hmm no, it doesn't do any magic.

If all you want to do is import the footage and alpha composite it, After Effects will do fine, as long as you remember to check "interpret alpha as premultiplied".

But, if you want to do heavy color correction (like multiplying a texture pass with an ambient occlusion pass), you need to work on un-premultiplied material, without alphas entirely, and import the alpha as seperate footage, and apply it after all color correction has taken place.

Cheers,
- Jonas
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