Point Light Measurement and Calibration for Photometric Stereo

Accurate measurement and calibration of the light position or the lighting direction is essential for pixel-level 3-D reconstruction based on photometric stereo. Differing from previous methods using a Lambert ball or a mirror ball for measurement and calibration, we employ a standard block with a related shadow model for a more accurate estimation of light positions. In essence, we propose a new measurement and calibration method that calculates the point light position from the triangulation relations between the lighting direction and the shadow, while the standard block is placed on a white flat plane under a fixed light. In this way, we can calibrate the pose of the point light source from the shadow model in all lighting directions. In addition, the lighting direction from the far-point source is also analyzed and solved. In our experiments, we apply the proposed scheme to photometric stereo and multispectral photometric stereo. Experimental results not only validate the accuracy of our method, but also help us to further reveal the effects of slant and tilt angles of the lighting directions on 3-D reconstruction based on photometric stereo.