Slide 15 & 16 of 52

In computer graphics, we shade models based on the orientation of the surface to a light. If we use diffuse shading with a white object and no ambient component as seen in this first image, we couldn't add edge lines because they would get lost in the dark regions and highlights would be lost in the light regions.

Another option, as shown in the second slide, is to make the shading neutral so that it won't interfere with the edge lines and highlights.

This is a good but we can do better.