Gamma, in rough terms, allows the player to adjust the brightness of the game. A more detailed article about Gamma correction can be found on Wikipedia.

Disabling animated tiles causes the creation of a "background surface" that we use for caching the background layer of tiles (aka the ground). We only do this for the tiles that are visible on screen, so that few millisecond pause you're seeing happens when we update this surface. Perhaps it would be better render the background surface for the entire map. This would use more memory, but would remove the stuttering.