Illumination for Computer Generated Pictures
The quality of computer generated images of
three-dimensional scenes depends on the shading 
technique used to paint the objects on the cathode-ray
tube screen.  The shading algorithm itself depends 
in part on the method for modeling the object, which
also determines the hidden surface algorithm.  The 
various methods of object modeling, shading, and hidden
surface removal are thus strongly interconnected. 
 Several shading techniques corresponding to different
methods of object modeling and the related hidden 
surface algorithms are presented here.  Human visual
perception and the fundamental laws of optics are 
considered in the development of a shading rule that
provides better quality and increased realism in 
generated images.
CACM June, 1975
Phong, B. T.
