Shape from shading with a generalized reflectance map model

Most conventional SFS (shape from shading) algorithms have been developed under three basic assumptions on surface properties and imaging geometry to simplify the problem, namely, a Lambertian surface, a distant point light source and orthographic projection. In this research, we derive a physics-based generalized reflectance map model which includes diffuse and specular reflection effects, a nearby point light source and perspective projection, and then we develop a new direct shape recovery algorithm from shaded images. The basic idea of our solution method is to discretize the image irradiance equation with a finite triangular element surface model, to express the resulting nonlinear system of equations in terms of depth variables only and to recover the object shape by linearizing the nonlinear equations and minimizing a quadratic cost functional. We perform numerical experiments with one or multiple photometric stereo images to demonstrate the performance of the derived physics-based reflectance map model and the proposed SFS algorithm. (C) 1997 Academic Press.