Contrast Enhancement by Multiscale and Nonlinear Operators 7.1 Introduction

Image enhancement techniques have been widely used in elds such as radiology , where the subjective quality of images is important for human interpretation (diagnosis). Contrast is an important factor in any subjective evaluation of image quality. Many algorithms for accomplishing contrast enhancement have been developed and applied to problems in medical imaging. A comprehensive survey of existing methods can be found in 1]. Among them, histogram modiication and edge enhancement techniques have been most commonly used along with traditional methods of image processing. Histogram modiication techniques 2, 3] are attractive due to their simplicity and speed, and have achieved acceptable results for some applications. In general, a transformation function is derived from a desired histogram and the histogram of an input image. In general, the transformation function is almost always nonlinear. For continuous functions, a 1