J. Chabrowski et Kw. Zhang, ON VARIATIONAL APPROACH TO PHOTOMETRIC STEREO, Annales de l Institut Henri Poincare. Analyse non lineaire, 10(4), 1993, pp. 363-375
In this article we discuss a variational aspect of a system of two equ
ations arising in photometric stereo. Assuming that this system has tw
o distinct solutions, we construct a minimizing sequence for any funct
ion lying on a segment joining these two solutions. In general, the sy
stem in question may have one, two, four or more than four solutions.