:O. Well... math is pretty much free on GPUs these days right? Yeah I was wondering the same thing... seems like a much cheaper approximation would be good enough since using data from the last frame is already an approximation. Anything to get it closer to the final tone mapped space. Note also that if any post-processing or color grading is done on the final image that should ideally be taken into account during the resolve as well, although there's no guarantee that those operators are even invertable.