Photometric stereo applied to diffuse surfaces that violate Lambert's law.

This paper investigates the use of photometric stereo (PS) with reflectance functions that are diffuse but not Lambertian. We show that, for the special case where light sources are arranged at 90° intervals around the optical axis, standard PS is not limited to Lambertian surfaces, and we define criteria for its use. A series of rough test surfaces are used as models for surface microstructure-we found that the Oren Nayar (ON) reflectance model accurately predicted the surfaces' reflectance functions. The ON model does not meet our theoretical criteria for using PS, but PS performs well in simulations if the microroughness is moderate (rms slope <0.3). When PS was applied to real surfaces, the estimated and actual slopes were highly correlated, but there were significant errors in the slope estimates for the rougher samples.