Image-based lighting
Environment maps are images of the surrounding environment for a scene. Embedded within the environment map is information about the lighting environment. For example, an environment map may contain an interior scene with several windows, each of which are lit with a bright source from outside. It would substantially enhance the realism of the scene if the objects could be shaded in such a way as to represent these light sources.
The technique of using an environment image as a source of lighting information is referred to as image-based lighting. This technique was pioneered by Paul Debevec, who has published many papers on the subject (see debevec.org).
The basic idea here is to encode information about the lighting environment into a cube map texture. We pre-process the original environment map in such a way as to encode information about the lighting provided by the environment map into a second cube map. Then when rendering, we simply look up the appropriate location...
