I'm no graphics expert, but I'm pretty sure premul is not just an optimization technique -- it's a fundamentally different approach at alpha blending, and it ma

I'm no graphics expert, but I'm pretty sure premul is not just an optimization technique -- it's a fundamentally different approach at alpha blending, and it makes some new things possible and some behavior more correct. See http://blogs.msdn.com/b/shawnhar/archive/2009/11/06/premultiplied-alpha.aspx http://blogs.msdn.com/b/shawnhar/archive/2009/11/06/premulti... . Sure, if you don't need the extra features premul provides (like the built-in ability for additive blending), then you can do some clever computations like IE apparently does to get the same result, but it's much simpler just to do things with premul.