I also went through that process with my app Picfx. Using OpenGL for filters is much quicker, the only downside I've found is being limited by the texture size,

I also went through that process with my app Picfx. Using OpenGL for filters is much quicker, the only downside I've found is being limited by the texture size, I did set up a way to process images in tiles but ultimately decided to just limit images to the texture size. Great info on the colour space, I'm sure it will be useful.