Introduction

Color images are formed by optical imaging systems from physical scenes that are composed of three-dimensional matter interacting with light. Light radiated from light sources is reflected, refracted, scattered, or diffracted by matter. As a result of all these light–matter interactions, light is redistributed spatially and temporally to create the physical scenes that we see and take pictures of. The study of color imaging science, thus, should begin with the light-field formation process of the physical scenes. This is what we mean by scene physics. The necessity for studying such a subject arises not simply to generate realistic color images by computer graphics. It is also driven by our need to understand and model the scene physics to develop computational algorithms that can adjust the color balance and tone scale of color images automatically so that optimal reproduction and display can be achieved.

General description of light reflection

Our discussion of reflection (Fresnel equations) in Section 5.4.1 assumes that the object surface is perfectly smooth, flat, and isotropic. However, the surfaces of real objects are almost never like that. In order to characterize light reflection and scattering from surfaces, we need a more general way to describe the optical property of surface reflection.

Although surface reflection is a well-studied subject, the terms used in the literature have not yet been standardized. Difficulties arise not only with the definitions, but also with the underlying concept of measurement and the models of the assumed physical processes. Let us start by treating light as rays (geometric optics) and see what can happen as light interacts with a rough surface.