Restoration of scene information reflected from a non-specular surface

A recently published experiment called "dual photography" exploits Helmholtz reciprocity by illuminating a scene with a pixilated light source and imaging other parts of that scene with a camera so that light transport between every pair of source-to-camera pixels is measured. The positions of the source and camera are then computationally interchanged to generate a "dual image" of the scene from the viewpoint of the source illuminated from the position of the camera. Although information from parts of the scene normally hidden from the camera are made available, this technique is rather contrived and therefore limited in practical applications since it requires access to the path from the source to the scene for the pixilated illumination. We propose this limitation may be relieved and additional scene information may be recovered if the scattering properties of media in the scene are known. To this end, we have shown through simulation and experimentation that information not directly visible to either the camera or the source, but illuminated by a source scattered off another part of the scene, may be recovered in limited initial cases. This paper discusses the technique of using the bidirectional reflectance distribution function (BRDF) of a non-specular medium to allow a camera collocated with a laser source and scattered off that medium to recover scene information not directly visible to the camera.