We present a new two-image photometric stereo method that is capable of determining surface deformations when extended light sources are used and the imager and light sources are close to the surface. Surface reflectance is modeled using a linear combination of Lambertian, backscatter, and new extended-source Phong specular reflection component models. The ambiguity resulting from using only two light sources is resolved in the surface normal integration phase, in which the resulting surface is constrained to being a valid image-based triangular facet surface. The method has been tested on an application involving waste-storage drum inspection and yields good accuracy.
Albrecht E. Carver,
Robert J. Schalkoff,
"Deformation detection on composite reflectance surfaces using two-image photometric stereo," Optical Engineering 40(2), (1 February 2001). http://dx.doi.org/10.1117/1.1339200