Refining Outdoor Photometric Stereo Based on Sky Model

We propose an outdoor photometric stereo method, which considers environmental lighting for improving the performance of surface normal estimation. In the previous methods, the sky illumination effect has been either assumed to be constant throughout the scene, or to be removed by pre-processing. This paper exploits a sky model which can derive the entire sky luminance from a sky zenith image; then, sky illumination effect on a surface can be correctly calculated by iteratively refining its normal direction. This paper also extends a two-source photometric stereo method by introducing RANSAC, so that the input images of this method can be taken in a day. Experimental results with real outdoor objects show the effectiveness of the method.