Under Woodham's original assumptions — Lambertian reflectance, known point-like distant light sources, and uniform albedo — the problem can be solved by inverting the linear equation , where is a (known) vector of observed intensities, is the (unknown) surface normal, and is a (known) matrix of normalized light directions.
Photometric stereo has since been generalized to many other situations, including non-uniform albedo, extended light sources, and non-Lambertian surface finishes. Current research aims to make the method work in the presence of projected shadows, highlights, and non-uniform lighting. Surface normals define the local metric, using this observation Bronstein et al.  defined a 3D face recognition system based on the reconstructed metric without integrating the surface. The metric of the facial surface is known to be robust to expressions.
- Woodham, R.J. 1980. Photometric method for determining surface orientation from multiple images. Optical Engineerings 19, I, 139-144.
- B. K. P. Horn, 1989. Obtaining shape from shading information. In B. K. P. Horn and M. J. Brooks, eds., Shape from Shading, pages 121–171. MIT Press.
- "A Photometric Stereo Approach to Face Recognition". University of the West of England. Retrieved 2011-03-27.
- A.M. Bronstein, M.M. Bronstein, A. Spira, R. Kimmel. "Face recognition from facial surface metric". European Conf. Computer Vision-ECCV 2004. Retrieved 2004.
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