Intensity/saturation enhancement based on differential gray-levels histogram equalization

The differential gray-levels histogram equalization (DHE) which was an expanded version of the histogram equalization (HE) is a simple and effective contrast enhancement method since the differential gray-levels histogram contains spatial features of the input image. The DHE for color images (DHEfC) is also proposed. In DHEfC, the intensity component is enhanced by using intensity/saturation differential gray-levels histograms. The DHEfC shows good results for the color image enhancement from the contrast and colorfulness points of view. However, the DHEfC cannot enhance saturation. In this paper, first, we introduce the saturation enhancement method by using the intensity/saturation differential gray-levels histograms. Then, we propose the combining method called the combining DHEfC (CDHEfC). The CDHEfC has the ability to enhance both intensity and saturation at the same time. The colorfulness of enhancement results of CDHEfC is superior to those of DHEfC. Furthermore, the colorfulness degree of enhancement images of CDHEfC can be controlled by one parameter while keeping the contrast degree. The effectiveness of CDHfC is shown by experimental results.