Color in Computer Vision: Fundamentals and Applications

Chapter 3: Color Image Formation

The image formation process described in this chapter involves three processes (illumination, material reflection, and detection/observation) interacting to generate the final color image. The process starts with light, which illuminates the visual scene. Light is described as electromagnetic radiation of a certain intensity, consisting of particles (photons) containing energy of certain wavelengths, each photon traveling in a certain direction. When many of the photons travel in the same direction, the light is directed and forms a beam of light. When all photons travel in a random direction, the light is diffuse. Light is typically emitted by light sources. A light source can be characterized by the way the light bundle is directed and by the emitted spectra of photons over the wavelengths. When more photons of short wavelength are emitted relative to the long wavelengths, the color of the light source is bluish. When more photons of long wavelengths are emitted, the color is reddish. For candle light and halogen illumination, the emitted spectra follow that of a so-called black body radiator [25], for which the smooth emitted spectra can be uniquely characterized by a single number, being the temperature of the radiator. As many natural light sources emit spectra that are similar in color to such a black body radiator, the color of a light source is defined by the “correlated color temperature,” that is, the temperature of a black body radiator ...