Determining shape and reflectance of Lambertian, specular, and hybrid surfaces using extended sources

Abstract

A method is presented for determining the shape of surfaces whose reflectance properties can vary from Lambertian to specular, without prior knowledge of the relative strengths of the Lambertian and specular components of reflection. The object surface is illuminated using extended light sources and is viewed from a single direction. Surface illumination using extended sources makes it possible to ensure the detection of both Lambertian and specular reflections. Multiple source directions are used to obtain an image sequence of the object. An extraction algorithm uses the set of image intensity values measured at each surface point to compute orientation as well as relative strengths of the Lambertian and specular reflection components. The method, photometric sampling, uses samples of a photometric function that relates image intensity to surface orientation, reflectance, and light source characteristics. Experiments conducted on Lambertian surfaces, specular surfaces, and hybrid surfaces show high accuracy in measured orientations and estimated reflectance parameters.