Can someone tell me what exactly maxed post processing setting enables?

I have everything on ultra/max, vsync off and when I set post processing on max, my framerate drops to about 20-25 fps. When I go one down in the post processing settings my frame rate goes all the way to 80-90 fps.



Now, I can't really see any difference so it's no big deal but I'm just curious what causes this massive drop.



Spec:

AMD FX6350, R9 390x, 16GB ram.

Not that I can answer the question but that 390x should eat just about anything you throw at it !

Well, whatever it is, it's hammering my system without any visual improvements. And yeah, 390x should eat it alive but...it's not :/