Federico Mena Quintero wrote: > And yes, the blend tool should do the right thing with alpha values, > i.e. premultiply them before compositing them in. I'll submit a patch > for it in the afternoon. > <rant_and_rave> I don't think this episode uncovered an alpha-related bug, so what needs to be fixed? Mr. Turner's example (unwittingly, perhaps) specified two different gradients (in the unmultiplied color space). And two different results were obtained. What went wrong? *Should* the gradient tool work in the premultiplied space, while GIMP mostly functions in the unmultiplied one? Won't this give users different alpha characteristics in different places? Won't they be better served with a consistent alpha channel behavior of the unmultiplied space in *most* places? Especially since - for better or worse - the rendering pipeline functions with unmultiplied alpha only? The gaussean blur HAS to pull premultiplied tricks. No surprises there either, for just as Mr. Lamb observed with premultiplied alpha, the unmultiplied space is no cure for the blues either. They happen to be two (mutually exclusive) conventions that can be applied to the alpha channel, and one has a Real Slick compositing algorithm associated with it, blessed by the Computer Graphics Gurus. In light of this, then, I think we should be very careful in preserving a consistent behavior when it come to how the alpha channel behaves, and warn users when inconsistencies (invariably) arise. </rant_and_rave> Be good, be well. Garry
