Mammograms enhancement using wavelet transform and piecewise linear and nonlinear coefficient mapping

In this paper a multi-scale image enhancement strategy using wavelets as applied to digital mammograms is presented. For multiresolution wavelet analysis redundant dyadic discrete wavelet transform is utilized to allow translation invariance and low resolution enhancement capability. Two alternative nonlinear gain adjustments, piecewise linear and Gaussian form of gain adjustment are used for coefficient modification for the enhancement of subtle details such as microcalcification and low resolution edges of different lesion types. The results of comparing these methods of gain adjustment are presented. This comparing has done by defining new parameters for measuring quality of image based on the extent of sharpening of image segments. Utility of the proposed image enhancement algorithm in mammographic applications is illustrated by an improved visual quality and increase in contrast enhancement measure as applied to different types of abnormalities.