
4.4. Lighting and shading 117
Figure 4.18: Diffuse illumination. (a) T h e b r ig htest illumination occurs when the
incident light direction is at right a n g les to the surface. (b) The illumination tends to
zero as the direction of the incident light becomes parallel to the surface.
the camera and the action; this is illustr ated in figure 4.17. In the following
expressions we will assume that p is th e point to be illuminated on the v is ib le
polygon which has a surface normal ˆn at p. We will now proceed to consider
models for the components:
1. Ambient reflection (I
a
)
When there are no lights in a scene the picture will b