Reflections on the generalized bas-relief ambiguity

Prior work has argued that when a Lambertian surface in fixed pose is observed in multiple images under varying distant illumination, there is an equivalence class of surfaces given by the generalized bas-relief (GBR) ambiguity that could have produced these images. In contrast, this paper shows that for general nonconvex surfaces, interreflections completely resolve the GBR ambiguity. In turn, the full Euclidean geometry can be recovered from uncalibrated photometric stereo for which the light source directions and strengths are unknown. Further, we show that surfaces with a translational symmetry do not lend enough constraints to be disambiguated by inter reflections.