Fake Global Illumination

Abstract

Global illumination computation is inherently costly since all other points may affect the illumination of a particular point. The inherent complexity can be reduced if the physically plausible model is replaced by another model that is simpler to solve but provides somehow similarly looking results. The dependence of the radiance of a point on all other points can be eliminated if we recognize that the illumination influence of a unit area surface diminishes with the square of the distance (refer to the geometry factor in equation (1.9)), thus it is worth considering only the local neighborhood of each point during shading and replacing the rest by some average. A point is said to be “open” in directions where the local neighborhood is not visible from it. In open directions, a constant or direction-dependent ambient illumination is assumed, which represents the “rest”. In not open directions, the ambient light is assumed to be blocked.