In the production of computer generated pictures of three dimensional objects, one stage of the calculation is the determination of the intensity of a given object once its visibility has been established. This is typically done by modelling the surface as a perfect diffuser, sometimes with a specular component added for the simulation of hilights. This paper presents a more accurate function for the generation of hilights which is based on some experimental measurements of how light reflects from real surfaces. It differs from previous models in that the intensity of the hilight changes with the direction of the light source. Also the position and shape of the hilights is somewhat different from that generated by simpler models. Finally, the hilight function generates different results when simulating metallic vs. nonmetallic surfaces. Many of the effects so generated are somewhat subtle and are apparent only during movie sequences. Some representative still frames from such movies are included.
J.F. Blinn (1977) studied this question.