Image Contrast Enhancement Based on Block-Wise Intensity-Pair Distribution with Two Expansion Forces
In this paper, we present a block overlapped intensity-pair distribution based image enhancement algorithm. Instead of using the intensity-pair distribution of the whole image, this proposed algorithm takes the intensity-pair distribution block-wise and maps the intensity of the center pixel according to an expansion function. Analyzing the intensity difference of the intensity-pair, two different expansion force sets are generated for contrast stretch: one for soft edges, another for strong edges. In addition, a set of anti-expansion force is generated for smooth regions to avoid noticeable change. The contrast stretch and over-enhancement are controlled with a linear magnitude mapping function instead of a non-linear one. This linear mapping preserves the relative contrast enhancement ratio between the gray levels. The local information from blocks easily facilitates the contrast enhancement, brings out subtle edge information, and removes noises from the image.
KeywordsAnti-expansion force expansion force intensity pair
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