<title>Three-dimensional stereo using photometric ratios</title>

Abstract

We present a novel robust methodology for corresponding a dense set of points on an object surface from photometric values, for 3-D stereo computation of depth. The methodology utilizes multiple stereo pairs of images, each stereo pair taken of exactly the same scene but under different illumination. With just 2 stereo pairs of images taken respectively for 2 different illumination conditions, a stereo pair of ratio images can be produced; one for the ratio of left images, and one for the ratio of right images. We demonstrate how the photometric ratios composing these images can be used for accurate correspondence of object points. Object points having the same photometric ratio with respect to 2 different illumination conditions comprise a well-defined equivalence class of physical constraints defined by local surface orientation relative to illumination conditions. We formally show that for diffuse reflection the photometric ratio is invariant to varying camera characteristics, surface albedo, and viewpoint and that therefore the same photometric ratio in both images of a stereo pair implies the same equivalence class of physical constraints.