I believe what they are doing is taking the framebuffer (either from the previous frame, or the current) scaling it down to a lower resolution texture and applying a contrast filter to it - Then overlaying it back over the screen. They also increase the feedback and dampen down the contrast when the camera moves quicky it seems, to give a motion blur effect - it's all very nice :)
I've seen the effect on the PS2 version, so it can be done without a pixel shader however, although on the PS2 it is possible to apply a contrast filter when you copy back from the backbuffer (which you can't really do on PC). Also, the PS2 has alot of fill-rate, so the fullscreen overlays aren't a problem.
It's a really nice effect and can be emulated in blitz, but it means copying back from the frame buffer so its going to be slow. I did a mock up of the effect not so long back in blitz, it looked nice but it was just too slow (it really needs RenderToTexture to avoid the copy back) :(
I've seen the effect on the PS2 version, so it can be done without a pixel shader however, although on the PS2 it is possible to apply a contrast filter when you copy back from the backbuffer (which you can't really do on PC). Also, the PS2 has alot of fill-rate, so the fullscreen overlays aren't a problem.
It's a really nice effect and can be emulated in blitz, but it means copying back from the frame buffer so its going to be slow. I did a mock up of the effect not so long back in blitz, it looked nice but it was just too slow (it really needs RenderToTexture to avoid the copy back) :(