I think the best thing to do is just submit a patch that breaks that function into two methods, with one adding the un-pre-multiplication. I looked into doing it, but I'm not very close to a test case, so I'd be afraid I wouldn't know if it was right.
Jay 2011/4/23 Stephan Houben <steph...@planet.nl>: > Hi list, > > Today I noticed that the bitmap's get-argb-pixels method returns > un-premultiplied alpha, even though it internally uses Cairo > which uses pre-multiplied alpha. > > Looking at the code, it goes out of its way to convert > pre-multipled alpha to un-premultiplied alpha. > I then need to go out of my way again to convert it back to > premultiplied alpha. Which is inefficient and silly. > > Could we have a method to get at the premultiplied alpha directly? > The Cairo folks chose it for a reason; if you want to interpolate between > two pixel values then only premultiplied alpha will give the correct result. > > (See http://www.gimp.org/docs/plug-in/appendix-alpha.html for some > discussion on this). > > I would therefore assume that it might be of wider interest than just me. > > Thanks, > > Stephan > _________________________________________________ > For list-related administrative tasks: > http://lists.racket-lang.org/listinfo/users > -- Jay McCarthy <j...@cs.byu.edu> Assistant Professor / Brigham Young University http://faculty.cs.byu.edu/~jay "The glory of God is Intelligence" - D&C 93 _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users
