Reflectance modeling for a textured object under uncontrolled illumination from high dynamic range maps

Abstract

During the past several years, considerable work has been presented on the methods for measuring and modeling the observed reflectance properties of materials. However, most of these works have been done under controlled lighting configurations, and require a constant bidirectional reflectance distribution function (BRDF), which is a measure of the amount of light scattered by a medium from one direction into another, or a homogeneous material over the object regions. This paper discusses a method to estimate the reflectance properties of a textured object under uncontrolled illumination. Assuming that the object has a constant specular reflectance property over its surface, the BRDF can be approximated as a constant specular component and a spatially varying diffuse component. The proposed method will first approximate the illumination distribution of a scene from a set of high dynamic range (HDR) radiance maps of a light probe. Next, a patch on the surface of an object is selected; several HDR intensity maps of the patch taken under different viewing conditions are used to estimate the average specular reflectance parameters of this patch. With the separation of the specular component and the diffuse component of each sample, and using the separated diffuse component, the diffuse reflectance parameters for each point over the surface are next estimated. The test results show that the method is effective for textured objects with constant specular reflectance properties. The method can also be directly applied to objects with piecewise-smooth material, which means that although the surface of an object does not have a constant specular reflectance property; when sub-divided into many smaller meshes, the specular parameter of each mesh can be regarded as uniform.