MODIFIED CLAHE: AN ADAPTIVE ALGORITHM FOR CONTRAST ENHANCEMENT OF AERIAL, MEDICAL AND UNDERWATER IMAGES

Image enhancement has been an area of active research for decades. Most of the studies are aimed at improving the quality of image for better visualization. Contrast Limited Adaptive Histogram Equalization (CLAHE) is a technique to enhance the visibility of local details of an image by increasing the contrast of local regions. The algorithm is extensively used by various researches for applications in medical imagery. The drawback of CLAHE algorithm is the fact that it is not automatic and needs two input parameters viz., N size of the sub window and CL the clip limit for the method to work. Unfortunately none of the researchers have done the automatic selection of N and CL to make the algorithm suitable for any autonomous system. This paper proposes a novel extension of the conventional CLAHE algorithm, where N and CL are calculated automatically from the given image data itself thereby making the algorithm fully adaptive. Our proposed algorithm is used to study the enhancement of aerial, medical and underwater images. To demonstrate the effectiveness of our algorithm, a set of quality metric parameters are used. In the conventional CLAHE algorithm, we vary the value of N and CL and use the quality metric parameters to obtain the best output for a given combination of N and CL. It is observed that for a given set input images, the best results obtained using conventional CLAHE algorithm exactly matches with the results obtained using our algorithm, where N and CL are calculated automatically.