A17: Photometric Stereo

There will be cases when 3D reconstruction of surfaces is needed. One common 3D reconstruction method is photometric stereo. In this technique the surface has to be illuminated by a source at different locations approximately at infinity. The assumption that the point light source is at infinity allows us to assume that a plane wave approaches the surface. This allows us to write the intentsity of light reflected by the surface as , which is a simple dot product.

In this activity, we were to reconstruct a spherical surface using photometric stereo. The synthetic surface was illuminated by a far away point source at from four different known locations (Figure 1). There are areas in the images or intensity distributions taken that are zero, which would result to division by zero errors in calculating for n. We simply add a very small value to avoid this.

Figure 1.

Figure 2 shows the reconstructed surface. Note that there are depressions along interfaces between the black and white parts of the surface. Since the system was not fed with information on the color of the object, the change in color was reconstructed as a depression on the object's surface.

Figure 2.

Figure 3.

I give myself a grade of 9 because the surface was reconstructed correctly.

I would like to thank Ms. Irene Crisologo for helping me in using plot3D. :)