Otsu´s method for clip limiting histograms for contrast enhancement of digital mammograms

This paper presents a novel Otsu based clipping technique for Contrast — Limited Adaptive Histogram Equalization (OC-CLAHE) algorithm for enhancing the contrast of digital mammograms. The algorithm is proposed because the existing CLAHE technique limits the amplification of contrast by clipping the histogram at a predefined value. This clip-limit is crisp and invariant to image data. This causes all the pixels inside the window region of the image to be equally affected. The proposed Otsu based clipping algorithm automates the selection of clip-limit which makes it flexible and variant to image data. Measures of Contrast Improvement Index (CII) and Discrete Entropy (DE) are used to evaluate contrast enhancement. Experimental results show that the proposed OC-CLAHE algorithm produces better contrast enhancement than several state-of-art algorithms.