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Re: unpremultiply in combustion?

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Mayec RRe: unpremultiply in combustion?
by on Jan 29, 2007 at 11:56:01 pm

Thanks for your reply Rayk.

The file does not have alpha embedded, but, believe me, it is premultiplied. Premultiplied is the same as what you mean by "rendered against a bg color". If saved as premultiplied, the pixels that do not have a full (white) alpha value are partly mixed with the black background, and thus are darkened, resulting in the ugly dark fringe we all know, when they are *again* multiplied by the alpha in the compositing process (in the "set matte" step in this case).

If it were not premultiplied, the render would look very ugly, with strange white-ish aliased borders, but it would composite perfectly with a separate alpha pass and I would have no problems

Check in your 3D application: save TGAs with premultiplied alpha and without (both without embedded alpha) and see the difference.

Rerendering would be the best option right now, but it's not an option anymore (big slow Vray renders, tight deadline). I'll look at the sapphire plug-ins you mention...

Mayec


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