Abstract: To preserve brightness better,one efficient method for contrast enhancement is proposed based on histogram equalization.First,the cumulative distribution function is used to calculate critical points which play an important role in preserving brightness.Then,the histogram is separated into several sub-histograms by critical points and equalization is applied for each sub-histogram.Finally,the enhanced images are obtained by merging the sub-images for each sub-histogram.The experimental results show that the proposed method can preserve the brightness better and enhance the contrast more efficiently than most other histogram equalization based methods.