Final gathering is an optional, additional step used to improve global illumination (GI). It increases the number of rays used to calculate GI to smooth out and eliminate adverse lighting artifacts.
Because global illumination is calculated from a photon map, rendering artifacts such as dark corners and low-frequency variations in the lighting may occur.
By activating final gathering, you increase the number of rays used to calculate global illumination, which reduces or eliminates these artifacts.
There is a catch when deciding to use final gathering. Final gathering can greatly increase rendering time. It is most useful for scenes with overall diffuse lighting.
You activate and adjust final gathering in the Advanced Render Settings palette.
