A critical step in the rendering of three-dimensioanl scenes is the final assignment of colors to pixels. The perspective projection process determines where a pixel is drawn on the screen. Visible surface computations determine which pixels are to be drawn. How the pixels are assigned colors is determined by the illumination models. The colors that we percieve on the surfaces of objects result from complex interations between light and matter.
Illumination models can be either empirical or physically based .
An emprical model results from the fitting of a function to observed data. Physically based models, on the other hand, attempt to simulate the interactions between light and various materials. The first Illumination models that we will discuss are largely empircal. Basically they are simplified formulas which generate results that fit both the underlying physics and our experiences. Light is the most important ingredent in any illumination model.