CGTalk - pre multiplied

svenip

11-14-2002, 09:13 AM

hi,

we have a problem with multiplied images. first we take the 3D Footage into AE over the filmed plate. then we color grade the 3D Footage. everything looks ok in AE, no edges (well known from pre-multiplied image). but after that we render out only the 3D Layer and take it into shake to do tracking etc. then the error occurs and we get the edges. also if we re-import the images into AE it's visible.

so normally in shake i do an mdiv before any color correction and after that mmult. is there a way to do this in AE too. or how does AE handles pre-multiplied. the help files won't give me any specific answer to this topic.

Mauritius

11-15-2002, 01:29 AM

AfterEffects handles unmultiplication and re(pre)multiplication implictly. There is no way and no need to do this explicitly, as in Shake.

I'm not sure what your exact problem is -- dark edges due to double-premultiplication or false color edges due to a color correction in AE w/o prior automatic division by alpha (which is -- in theory -- impossible, as AE takes care of it).

In either case I suggest that you render out the footage unmultiplied from AE, hence saving the MDiv operation neccessary in Shake before any further color correction.

I extrapolate that you render 3D Layers with camera data imported from e.g. Maya and then continue compositing in Shake? I recently did the very same on a project and it worked w/o any problem, all color corrections took place in Shake though.

Cheers,

Moritz

--

"Ich wünsche ein sachliches Design."
-- durchschnittlicher deutscher Kunde

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