Novel depth cues from uncalibrated near-field lighting

Distant lighting is widely assumed in computer vision. However, many scenes are illuminated by near light sources. An advantage of near lighting is that the intensity fall-off from the light source encodes scene depth. A drawback is that exact estimation of this depth requires the 3D position of the light source. In this paper, we analyze what kinds of depth cues are possible under uncalibrated near point lighting. A stationary scene is illuminated by a point source that is moved approximately along a line or in a plane. We observe the brightness profile at each pixel and demonstrate how to obtain three novel cues: plane-scene intersections, depth ordering and mirror symmetries. These cues are defined with respect to the line/plane in which the light source moves, and not the camera viewpoint. Plane-Scene Intersections are detected by finding those scene points that are closest to the light source path at some time instance. Depth Ordering for scenes with homogeneous BRDF is obtained by sorting pixels according to their shortest distances from a plane containing the light source. Mirror Symmetry pairs for scenes with homogeneous BRDFs are detected by reflecting scene points across a plane in which the light source moves. We show analytic results for Lambertian objects and demonstrate empirical evidence for a variety of other BRDFs. Read More…

Novel depth cues from uncalibrated near-field lighting