The light transport matrix (LTM) is an instrumental tool in line-of-sight
(LOS) imaging, describing how light interacts with the scene and enabling
applications such as relighting or separation of illumination components. We
introduce a framework to estimate the LTM of non-line-of-sight (NLOS)
scenarios, coupling recent virtual forward light propagation models for NLOS
imaging with the LOS light transport equation. We design computational
projector-camera setups, and use these virtual imaging systems to estimate the
transport matrix of hidden scenes. We introduce the specific illumination
functions to compute the different elements of the matrix, overcoming the
challenging wide-aperture conditions of NLOS setups. Our NLOS light transport
matrix allows us to (re)illuminate specific locations of a hidden scene, and
separate direct, first-order indirect, and higher-order indirect illumination
of complex cluttered hidden scenes, similar to existing LOS techniques.

该论文提出了一种新的框架，使用虚拟成像系统来估算非直视成像场景下的光传输矩阵（Light transport matrix），克服了非直视成像装置的开口角限制，并且通过该光传输矩阵可以实现对隐蔽场景中某些特定位置（indirect illumination）的再照明以及直接、一阶和更高阶间接光照明（illumination）的分离，类似于现有的直视成像技术。