ABSTRACT
Image enhancement techniques are employed to emphasize, sharpen and/or smooth image features for display and analysis. Application algorithms are often developed empirically to find a solution to an imaging problem. Enhancement is used as a preprocessing step in some applications to ease the vision task, for example, to enhance the details in an X-ray to allow better diagnostic capabilities or to enhance a satellite image of an airline runway to facilitate military reconnaissance. Image enhancement is used for postprocessing to generate a visually desirable image, so image enhancement is as much an art as it is a science. This chapter includes gray-scale modification by considering direct mapping equations and explores methods for histogram manipulation, including equalization and specification. We discuss specific adaptive contrast enhancement equations and methods, and application to color images. Major sections on image sharpening and image smoothing using both the spectral and spatial domains are included. A number of sharpening algorithms are discussed, such as directional difference filters, unsharp masking and homomorphic filtering. Along with the text are 60 illustrative figures and 193 associated monochrome and color images. The end of chapter exercises include problems and programming exercises.
