Active photometric stereo

An active vision technique for determining the absolute depth of surfaces is described. The algorithm assumes a very general model for the reflectance properties of the surface, and is valid for most of the shading models commonly used in computer vision work. The algorithm relies on the controlled motion of a point light source, which is not at infinity but relatively close to the surface and to the camera. The sensitivity of the computed depth values to errors in the measured quantities is derived, allowing a confidence measure for the depth to be determined. The confidence measure can aid in the estimation of accurate depth values from multiple image measurements taken over time. A method based on robust estimation that permits an unbiased estimate of the depth values to be obtained is presented. The results of experiments on synthetic and real-world imagery are reported, illustrating the efficacy of the active photometric stereo algorithm.>