Difference sphere: An approach to near light source estimation

We present a novel approach for estimating light sources from a single image of a scene that is illuminated by major near point light sources, a few directional light sources and ambient light. We propose to employ a pair of reference spheres as light probes and introduce the difference sphere that we acquire by differencing the intensities of two image regions of the reference spheres. Because the effect by directional light sources and ambient light is eliminated by differencing, the key advantage of considering the difference sphere is that it enables us to identify near point light sources including their radiant intensities. We also show that analysis of gray level contours on spherical surfaces facilitates separate identification of multiple combined light sources and is well suited to the difference sphere. We demonstrate the effectiveness of the entire algorithm with experimental results while also investigating the applicability to an open scanner in indoor scene.