Shape Reconstruction in Photometric Stereo Compensating for Inter-reflection and Directional Diffuse Reflection

In photometric stereo one of the common problems may be inter-reflections occurring in concave surface parts of the object. They may locally blur the images in shade, resulting in a locally distorted shape. The effects may be more significant with increasing curvature of the concavity. Another problem may be non-Lambertian reflection, in which case shape reconstruction based on the Lambertian reflection may give non-local distortions. A combination of the diffuse and specular reflections called directional diffuse reflection may be typical of the nonLambertian reflections. In this paper, we present image processing methods of reducing the effects of the two problems. They are described mathematically, and experimental results are given to examine the two methods.