   Simulating Photoshop layer blend modes in OGL - possible?
  I was wondering if it's possible to use the glBlendFunc parameters to simulate the different types of layer blends you get in photoshop (eg Multiply, dodge, burn, etc).I've been playing around with them and I don't think it can be done using the blend functions, but maybe I'm wrong?  Assuming it can't be done with blendfuncs, is there any way in OGL to simulate such behaviour without having to do a per pixel calculation on the cpu?   
  The solution these days is to do the blending yourself inside of a GPU shader. GPU Gems 1 or 2 has a chapter on colour correction. This gives source for things like Levels and Curves too.   