Processing Color Images, Brightness and Color Conversion

The use of color in image processing is due to two main reasons. Firstly, color is an important feature that often facilitates recognition and selection of an object in an image. Secondly, a person is able to distinguish between thousands of different shades of color and only about two dozen shades of gray. The second circumstance is especially important when visual (that is, performed directly by man) image analysis.Processing of color images can divided into two main areas: image processing in natural colors and image processing in pseudo-colors. In the first case, the images in question are usually formed by color image recording devices, such as a color television camera or a color scanner. In the second case, the task is to assign colors to some intensity values of a monochrome signal or to some ranges of changes in its intensity. Until relatively recently, digital processing of color images was carried out mostly at the level of pseudo colors. Over the past decade, however, color input devices and color image processing hardware have become quite affordable. As a result, natural image processing technology currently used in a wide range of applications, including publishing systems, visualization systems, and the Internet. It will be clear from the subsequent discussions that some halftone processing techniques developed in previous chapters are directly applicable to color images. Other methods should be reformulated and consistent with the properties of the color space, which constructed later in this chapter. The methods described in this chapter are far from exhaustive; they illustrate a variety of techniques applicable to color image processing.