Contrast Enhancement Using Weighted Coupled Histogram Equalization with Laplace Transform

Histogram equalization is a traditional algorithm improving the image contrast, but it comes at the cost of mean brightness shift and details loss. In order to solve these problems, a novel approach to processing foreground pixels and background pixels independently is proposed and investigated. Since details are mainly contained in the foreground, the weighted coupling of histogram equalization and Laplace transform were adopted to balance contrast enhancement and details preservation. The weighting factors of image foreground and background were determined by the amount of their respective information. The proposed method was conducted to images acquired from CVG-UGR and US-SIPI image databases and then compared with other methods such as clipping histogram spikes, histogram addition, and non-linear transformation to verify its validity. Results show that the proposed algorithm can effectively enhance the contrast without introducing distortions, and preserve the mean brightness and details well at the same time.