Variational Uncalibrated Photometric Stereo under General Lighting
This addresses the limitation of photometric stereo techniques that require controlled laboratory setups, making it more applicable to real-world scenarios with general lighting.
The paper tackles the problem of photometric stereo under general lighting without calibration by proposing a variational approach that jointly recovers shape, reflectance, and illumination, reducing mean angular error by a factor of 2-3 compared to state-of-the-art methods.
Photometric stereo (PS) techniques nowadays remain constrained to an ideal laboratory setup where modeling and calibration of lighting is amenable. To eliminate such restrictions, we propose an efficient principled variational approach to uncalibrated PS under general illumination. To this end, the Lambertian reflectance model is approximated through a spherical harmonic expansion, which preserves the spatial invariance of the lighting. The joint recovery of shape, reflectance and illumination is then formulated as a single variational problem. There the shape estimation is carried out directly in terms of the underlying perspective depth map, thus implicitly ensuring integrability and bypassing the need for a subsequent normal integration. To tackle the resulting nonconvex problem numerically, we undertake a two-phase procedure to initialize a balloon-like perspective depth map, followed by a "lagged" block coordinate descent scheme. The experiments validate efficiency and robustness of this approach. Across a variety of evaluations, we are able to reduce the mean angular error consistently by a factor of 2-3 compared to the state-of-the-art.