Recovering surface normal of specular object by Hough transform method

In order to recover surface normal and albedo of specular objects under the condition of large shadows and highlights by photometric stereo, a novel robust method utilising Hough transform is proposed. The photometric image sequence is taken by a fixed camera when the light source is rotated around the optical axis of the camera. Since the bidirectional reflectance distribution function of many surfaces can be approximated as a combination of a diffuse component and a specular component, the diffuse part of the intensity at a fixed point on the surface obeys a sine curve when the light source rotates. The surface normal and albedo information are hidden in the sine curve and can be revealed by means of Hough transform. The bilateral symmetry of the sine curve is used to narrow the searching range of the initial phase and to speed up the Hough transform. Experiments performed on synthetic and real objects with large shadows and strong specular reflectance show the better performance of the proposed method.