Shape and reflectance from two-bounce light transients

Computer vision and image-based inference have predominantly focused on extracting scene information by assuming that the camera measures direct light transport (i.e., single-bounce light paths). As a consequence, strong multi-bounce effects are treated typically as sources of noise and, in many scenarios, the presence of such effects can result in gross errors in the estimates of shape and reflectance. This paper provides the theoretical and algorithmic foundations for shape and reflectance estimation from two-bounce light transients, i.e., scenarios where photons from a light source interact with the scene exactly twice before reaching the sensor We derive sufficient conditions for exact recovery of shape and reflectance given lengths and intensities associated with two-bounce light paths. We also develop algorithms for recovery of shape and reflectance, and validate these on a range of simulated scenes.