I've added an argument to `get-argb-pixels' and `set-argb-pixels' to make them work in premultiplied mode.
At Sat, 23 Apr 2011 22:54:47 +0200, Stephan Houben wrote: > 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
