ABSTRACT

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 to quantify the performance of the different enhancement techniques. Any technique that results in improving the visual quality of an image is acceptable. The only factor that influences the choice of an enhancement algorithm is the complexity of the algorithm. Table 5-1 lists various processing options available for the enhancement of images. Depending on which aspect of the original image is to be improved, we could choose any one of the class of algorithms from the list as the candidate.