Posted by Steve on 01/13/07 01:46

"Koncept" <user@unknown.invalid> wrote in message
news:120120071815543076%user@unknown.invalid...
| I came across this: http://www.gimp.org/docs/plug-in/appendix-alpha.html
|
| Premultiplied alpha is just a different way of representing alphified
| pixels. If the separate alpha pixel is (r, g, b, a), then the
| premultiplied alpha pixel is (ar, ag, ab, a).
|
| The reason why it's interesting is that linear combinations of pixels
| (i.e. a1p1 + a2p2) work better in premultiplied alpha space than in
| separate alpha space.
|
| For example, taking the 50/50 blend of white and transparent works like
| this: White is (1, 1, 1, 1) and transparent is (0, 0, 0, 0) in both
| spaces. So the 50/50 blend is (0.5, 0.5, 0.5, 0.5). In separated space,
| that's half-transparent gray, but in premultiplied space, that's
| half-transparent white, which is what you expect.
|
| --
| Koncept <<
| "The snake that cannot shed its skin perishes. So do the spirits who are
| prevented from changing their opinions; they cease to be a
pirit." -Nietzsche

hey koncept.

that explains it, however he really didn't want an answer so much as he
wanted an excuse to cuss. were he as bright as his arrogance proclaims, he'd
have crossed this explanation before in his course of study on computer
graphics.

cheers.

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