What does Post Processing do?

[DeadJukez | TTV]

I turned Post Processing down from epic to medium, and I got an extra 20 frames. What exactly does it do though?

[Jaeden]

Reduces your frame rate primarily.

Post Processing are things done after the texture has been rendered by the game, such as specific shading or lighting to make textures look more realistic in the environment.
For some reason Arks post processing has less affect and more penalty than any other game i've played. I've got my settings on epic/high but post processing on low.