No reference measurement of contrast distortion and optimal contrast enhancement

In this paper, a novel histogram-based model for contrast enhancement is proposed. Based on our analysis about the relationships of histogram with contrast, we establish a model which 1) achieves contrast enhancement by an optimal transform of histogram, 2) gives two metrics called contrast gain and nonlinear-ity of transform to measure the strength of enhancement and the seriousness of distortion caused by enhancement respectively. The ratio of the two proposed metrics not only gives a guidance for the configuration of parameter in the algorithm, but also provides a useful measurement for contrast distortion, which can be a potential solution to judge whether the contrast of an image is optimal. Experimental results show the superior performances of the proposed algorithm in image enhancement.