http://www-viz.tamu.edu/students/bmoyer/617/ambocc/
“At SIGGRAPH 2002, technical directors from Industrial Light and Magic presented a technique they call ambient occlusion. Simple, but highly effective, ambient occlusion’s been used for years at studios like BlueSky and ILM to achieve grounded realism, without the cost of full global illumination.Fancy name aside, ambient occlusion is simply a ratio of how much ambient light a surface point would be likely to receive. It simulates a huge dome light surrounding the entire scene. If a a surface point is under a foot or table, it will end up much darker than the top of someone’s head or the tabletop. This can then be multiplied by various other surface attributes to achieve a subtle, but very powerful, lighting effect.”
