Analysis

Reconstructing the 3D point mesh of an object from 2D images is a difficult problem. The task is even more complicated when the object has arbitrary and unknown surface reflectance. Traditional reconstructing techniques make explicit or implicit assumptions about the bidirectional reflectance distribution function (BRDF), which represents the surface reflectance. A widely used assumption is that the surface is Lambertian, that is the light is reflected equally in each direction. Although it works in many cases, specular objects disobey Lambert’s law. In this paper we present an overview of a technique – termed Helmholtz stereopsis – which handles the problem of arbitrary and unknown BRDFs. The technique is based on Helmholtz reciprocity. It exploits the symmetry of surface reflectance by choosing those pairs of light source and camera positions that guarantee that the relationship between corresponding image points is independent of the BRDF. By applying this technique the problem of BRDFs can be eliminated. The operation of the method is illustrated by examples