Piecewise histogram equalization（Piecewise HE） was proposed

which combines the benefits of contrast stretching and existing histogram equalization.The swallow of saturation and brightness is avoided in the enhanced image by a piecewise linear mapping function

which combines with the mean and standard deviation of the histogram

and the parameters selection of Piecewise HE is explored when over-enhancement existed.The experimental results have demonstrated that the proposed method can enhance the images effectively

which avoids the swallow and over-enhancement problems of the existing histogram equalization methods.The proposed method not only preserves the original details

but also has a more natural visual effect in the enhanced image.