PHOTOMETRIC STEREO PROJECT
Compute the normal map for part of a sphere with Phong reflectance model from 4-light source photometric stereo (use a=0.3, b=0.7, n=3.0).
Need to compute each surface normal from 3-light sources that mutually illuminate a surface point with primarily diffuse reflection.
Arrange 4-light sources so as to maximally cover as much of the sphere as possible with mutual illuminaton (WARNING: Placing light sources too close together produces measurement errors).
Integrate the normal map to produce a depth map.