METHOD OF ENHANCING A DIGITAL IMAGE BY GRAY-LEVEL GROUPING

Methods for enhancing the quality of an electronic image, including automated methods for contrast enhancement and image noise reduction. In many embodiments the method provides for grouping the histogram components of a low-contrast image into the proper number of bins according to a criterion, then redistributing these bins uniformly over the grayscale, and finally ungrouping the previously grouped gray-levels. The technique is named gray-level grouping (GLG). An extension of GLG called Selective Gray-Level Grouping (SGLG), and various variations thereof are also provided. SGLG selectively groups and ungroups histogram components to achieve specific application purposes, such as eliminating background noise, enhancing a specific segment of the histogram, and so on. GLG techniques may be applied to both monochromatic grayscale images and to color images. Several preprocessing or postprocessing methods for image noise reduction are provided for use independently or for use with GLG techniques to both reduce or eliminate background noise and enhance the image contrast in noisy low-contrast images.