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Intensity

In a Color plot, the intensity, or brightness, for each pixel is determined from the cosine of the angle A between the surface normal and the vector from the viewpoint to the surface. The intensity I is given by

I = [cos(A)]7/4	if cos(A) >= 0
I = |cos(A)|	if cos(A) < 0

If the light position is not at the viewpoint, Sabrina traces a ray from the surface to the light position. If the ray encounters an opaque object before it exits the geometry, the surface is shadowed from the light source and I = 0. Otherwise, I is as defined above.

The algorithm gives incorrect results when the light position is between opaque objects. The tracking should end at the light source position rather than the outside of the entire model. We will fix this discrepancy in the future.

The additional tracking will increase rendering time.