The general technique for brightness, contrast, etc. is: Instead of rendering things directly to the screen, you draw them onto a separate texture (a “render target”), then you use a flat quad model with that texture applied to it, and you can give it a custom shader to do whatever per-pixel effects you want.
Check you the thread on 2D lighting for more info: Simple 2D Lighting
For a tilt-shift that depends on actual depth, I’m not so sure. I think it would be about the same, but you would need to use the depth buffer as well.