Photometric stereo with quasi-point light source

This paper presents a complete computational framework for the photometric stereo system composed of some LED lamps and a single web-camera. To describe the lighting condition accurately, the angular and distance attenuation factors, as well as the LED radiance property, are considered in the modeling of the light source. The calibration of the system's parameters is a critical step for our setup, and a two-step calibration procedure is proposed in this work. A multiple-sphere-based approach is first used to estimate the light source positions. Then, a reference-plane-based approach is applied to estimate the principal optical axis of each light source and its principal energy. For each surface point on the target, the direction and intensity of its incidental light ray can be precisely determined by the calibration parameters and the quasi-point light model. Based on the initial 3D reconstruction result, an iterative procedure is applied to optimize the model's parameters for each surface point with respect to its initial estimated depth. In the experiments, both regular and free-form surfaces including a real human face are used. The results show that accurate 3D reconstruction results can be obtained by the proposed approach based on the low-cost setup.