Application of Computer Algebra to Photometric Stereo with Two Light Sources

This paper addresses the problem of reconstructing the shape of an unknown Lambertian surface from its two photometric images obtained by successive illumination of the surface with two different remote light sources. Using computer algebra methods, we investigate the conditions of existence and uniqueness of a solution to a system of algebraic equations that determine the gradient of a function of two variables given by the equation u(x, y) − z = 0. We also analyze necessary and sufficient conditions for unique determination of a second-order algebraic surface from its two images in the general case. Correctness of the theoretical results obtained is confirmed by simulating photometric images of various surfaces.