Adaptive contrast enhancement methods with brightness preserving

Brightness preserving methods are very high demand to the consumer electronic products. Numerous histogram equalization (HE)-based brightness preserving methods tend to produce unwanted artifacts. Thus, we propose two methods to overcome the drawbacks. The first proposed method divides the histogram based on the median, and iteratively divides into the lower and upper sub-histograms, to produce a totally four sub-histograms. The separating points in the lower and upper sub-histograms are assigned to a new dynamic range and clipping process is implemented to each sub-histogram. Finally, the conventional HE is implemented. The second method is the extension of the bi-histogram equalization plateau limit (BHEPL). This method segments the histogram of input image based on its mean value. Then, clipping process is implemented to each sub-histogram based on their median value. The proposed methods are compared with several conventional methods. The experiment results show that, both of the proposed methods outperform those conventional methods by producing clearer enhanced image with brightness and details preserving ability^.