 | | | premultiplied alpha | premultiplied alpha 2004-03-09 - By Andy Hayes
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i guess the only way is to generate the desired over is to make the additive
mix nodes in the rendertree - ie the 'over' composite equivalents:
a premultiplied 'over' would be equal to Argb + (( 1 - Aa) * Brgb)
and a normal 'over' would be equal to (Argb * Aa) + (( 1 - Aa ) * Brgb)
where A and B are the images for the 'A over B' configuration and 'rgba' the
color channels.
You can knock up the tree fairly easily in the rendertree.
also, to remove the 'premultiplied' notion from an image simply divide its
rgb values by the alpha, and use a straight forward additive mix
a bit ot but may be useful?
Andy
-- --Original Message-- --
From: owner-xsi@(protected) [mailto:owner-xsi@(protected)]On Behalf
Of kim aldis
Sent: 09 March 2004 16:24
To: XSI@(protected)
Subject: RE: premultiplied alpha
Strictly speaking, un-premultiply. I've never found one. Try feeding the
alpha into a mix2nodes, put the image into one node and make the other a
lighter colour. Something approaching the colour of your image. Not ideal, I
know but that's about the best I've found so far.
> -- --Original Message-- --
> From: owner-xsi@(protected)
> [mailto:owner-xsi@(protected)] On Behalf Of Jamination@(protected)
> Sent: 09 March 2004 15:58
> To: XSI@(protected)
> Subject: premultiplied alpha
>
> when i apply maps with alphas to objects (as decals) i'm
> getting some black halos around the image. is there a
> premultiplied option anywhere to help me remove this effects,
> i'm struggling to find anything.
>
> thanks
> phil harbath
> jamination
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