What it's All About
In the real world, when two objects "meet", as when a chair sits on the floor, there is almost always a small shadowed gap between the parts. The one object (the chair) obstructs all but the most direct light from reaching the other. That is, it obstructs the ambient light. However, most rendering algorithms fail to produce the necessary shading.
During the ray-tracing of the scene, a hemispherical sampling can be taken at each point to establish the proximity of other surfaces. Should near-by surfaces be detected, the pixel in question is shaded more darkly, depending on the amount of obstruction encountered in the sample.
Without Ambient Occlusion
With Ambient Occlusion
Last updated: April, 2014