Nick Lamb wrote: > Pre-multiplying is a performance hack only, please don't let people > think of it as something that will cure "black fringes" -- it won't. > Perhaps that wasn't your intention, but in any case... Gimp should do premultiplied alpha. Not because it cures acne or extends human life expectancy by an astounding 3000 precent, but because people in the professional paint box community use images formatted to that convention on a regular basis, and Gimp could be helpful to that crowd if the dear little creature would only eat pre-multiplied alpha and composite with it. That, of course, gives rise to a rub. I don't believe this can happen transparently to the user, even if the Gimp had premultiplied capability. I believe you've commented on this in past premultiplied alpha go-rounds that it is touch-and-go whether a file's meta data hints about premultiplied alpha, even if the metadata chunk has a slot for an alpha premultiplied flag. And premultiplied pixels are otherwise indistinguishable from unmultiplied ones. So it is doubtful to me that any paint program any time soon can automagically determine which is which, so a human (or a self-aware equivalent) would have to do the determination for it. That means (a) education (including the distinction among types of alpha in standard Gimp documentation) (b) a clear statement that Gimp is an unmultiplied compositor (though certain tools and plug-ins necessarily have to internally play the premultiplied game - blur comes to mind) and (c) If you care about what you do, figure out how your image sources are doing their alpha. Perhaps a later Gimp will know how to consume premultiplied alpha (you'll have to throw some switches) the 1.x Gimps of the next two years or so won't know how to do it. Be good, be well Garry
