Extracting Shape and Reflectance of Lambertian, Specular, and Hybrid Surfaces

All existing shape extraction techniques that are based on photometric measurements rely on assumed surface reflection properties. We propose a method for determining the shape of surfaces whose reflectance properties may 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 the relative strengths of the Lambertian and specular reflection components. The proposed method has been named "photometric sampling" as it uses samples of a photometric function that relates image intensity to surface orientation, reflectance, and light source characteristics, that describes the reflectance model and orientation of a surface point. Experiments were conducted on Lambertian surfaces, specular surfaces, and hybrid surfaces whose reflectance model is composed of both Lambertian and specular components. The results show high accuracy in measured orientations and estimated reflectance parameters.