When scenery is hidden from view, light from the hidden region may be cast onto visible diffusely reflecting surfaces forming shadows called ‘penumbrae.’ If one is able to determine the proportions of penumbra light arriving from different directions, it is possible to form estimates of hidden scenery. This is what we refer to as non-line-of-sight (NLOS) imaging. NLOS imaging provides value in a variety of circumstances such as monitoring of hazardous environments, navigation, detecting hidden adversaries, and in collision avoidance for automated vehicles.
Many NLOS imaging systems rely on the fact that photon travel time is proportional to distance, and thus require expensive, ultra-fast optical systems. Instead, we develop passive imaging techniques using inexpensive, ubiquitous sensors, such as typical digital cameras, to make inferences without requiring time-varying or controlled illumination of the hidden scene.