As mentioned in Chapter 1, image enhancement refers to any digital processing by which the image quality is improved. By image quality we mean such image features as contrast, sharpness, edges, boundaries, etc. There are situations where the originally acquired images lack contrast due to poor lighting conditions. In such cases, simple contrast stretching could rectify the problem. Lack of sharpness in images is another instance that could be corrected by linear filtering. When images are acquired through optical means, nonlinear filtering might be required in order to increase the contrast or image sharpness. Since enhancement is aimed at improving the visual quality of images, it is rather difficult ...