[Webkit-unassigned] [Bug 150940] Color interpolation for colors with alpha incorrect (gradients)

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Fri Nov 6 10:58:58 PST 2015


--- Comment #9 from Christian Schnorr <christian.schnorr at me.com> ---
> > Mh, I'm a little confused now as I'm not quite familiar with this
> > terminology. Is interpolation in premultiplied RGBA what we are seeing now
> > or what would be the correct thing to do?
> That's what you're seeing now. Transparent red in premultiplied color just
> becomes transparent, so any time you interpolate from it you end up with
> grayish intermediate values.

Sorry if this is really obvious and I am missing something, but that makes only little sense to me.

I am currently seeing this behavior in Safari:
[opaque black (0,0,0,1)] => [semitransparent dark red (128,0,0,0.5)] => [transparent red (255,0,0,0)] (all components interpolated linearly)

However, I think it should look like this: (and it does in Firefox)
[opaque black (0,0,0,1)] => [semitransparent black (0,0,0,0.5)] => [transparent black (0,0,0,0)] (color components weighted with alpha)

Your description ("so any time you interpolate from it you end up with grayish intermediate values") sounds like the latter is what you call interpolation in premultiplied RGBA, however you are also stating that what I am currently seeing is interpolation in premultiplied RGBA...

Could you please clear this up? Which of the two examples is interpolated in premultiplied RGBA? And how is the other method called?

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