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q concerning premultiplied footage
is a matte operator the only way to extract the image from a premultiplied/pre-matted scene? i.e., say I import a bouncing ball shot against a blue screen. its been keyed, exported out (premultiplied, animation, mill of colors+, etc.).
So then if were I bring it back in to some compositing program, it will have a black or whatever color background representative of the alpha channel’s transparency, right? Is their any way to make that representation actually transparent without adding some kind of operator? Or if that were my intent, should I just always render straight?
I’m just curious, because I seem to remember once bringing in premultiplied footage and it already being transparent. But I’m perfectly willing to blame it on my bad memory upon further advice. Thanks!
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2 Replies
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Hi,
If you are bringing the keyed footage back into AE, it shouldn’t matter if it is straight or premultiplied. AE should deal with it just fine so long as you set the footage interpretation correctly. You may want to make sure that AE is interpreting it right – select the footage and hit Command-F or Crtl-F and then make sure it is set to Pre-multiplied or Straight.
If you rendered the footage with a matte and it’s coming in without one, it is possible that you rendered to a codec that does not support matte channels. I know 10 and 8 Bit Uncompressed codecs will not preserve the matte. Animation will, so you can use that if you need a lossless codec.
I hope this helps,
Lars
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if you have an alpha channel you will have transparency regardless if the rgb portion was rendered premultiplied or straight.
the only difference is the premultiplied version may have a black (or what ever the bg color was set to) fringe around it, while the ‘straight’ version will not. some software, like ae, can be set to remove the fringe either by setting that footage as being premultiplied in the interpret footage settings or by adding the remove background color effect.
if you are having trouble under standing these settings, check out this tutorial, straight vs premult, aharon does a nice job of explaining it.
Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW
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