A one-source photometric method for N-order specular surfaces

In a previous paper, we proposed a photometric method for the first order specular surfaces. In the present paper, we propose a photometric method for n-order specular surfaces (where n describes the sharpness of the specular property of the surface), when the incident light intensity and direction are unknown. The image is considered as a perspective projection and the Image-Surface Orientation Equation (ISEO) is proposed. One can calculate the surface normal from the ISEO. The constraint is that the surface is rather planar in a small region. Our algorithm is implemented and tested for artificial data created by computer and the results, which are given in the paper, are encouraging.