Non-Line-of-Sight Estimation of Fast Human Motion with Slow Scanning Imagers

Non-line-of-sight (NLoS) reconstruction, i.e., the task of imaging scenes beyond the camera's field of view, is often implemented using source-and-sensor systems that scan the visible region and analyze secondary reflections of light that has interacted with the hidden static scene. Estimating human activity around the corner will be a task of major interest for emerging NLoS applications, and some attempts have been reported in the recent literature. However, due to the long exposure times and comprehensive scans needed for NLoS sensing, the reconstruction of continuous movement remains prone to artifacts and is unreliable. In this paper, we analyze the interplay between dynamic scenes and scanning hardware to identify possible failure cases for filtering and data-driven approaches. Our studies indicate that existing reconstruction methods are prone to systematic error due to the space-time skew introduced by scanning setups. To alleviate this issue, we propose an image formation model for dynamic scenes that explicitly integrates motion skew. Using this model, we construct a baseline method for human pose estimation that achieves high accuracy, even at very slow scan rates.