Color image contrast enhacement method based on differential intensity/saturation gray-levels histograms

Histogram equalization (HE) is a simple and effective method for contrast enhancement as it can automatically define the gray-levels transformation function based on the distribution of gray-levels included in the image. HE fails to produce satisfactory results for a broad variety of low-contrast images because the HE does not use a spatial feature included in the input image. The differential gray-levels histogram which is contained edge information of the input image, were defined. Furthermore, the differential gray-levels histogram equalization (DHE) has been proposed. The DHE shows better enhancement results compared to the HE results for many kinds of images. In this paper, we propose a DHE method for color images. In the case of color images, two differential gray-level histograms can be defined. One is intensity gray-levels histogram, the other is saturation gray-levels histogram. The differential histogram for color image is defined in combination with two gray-levels histograms. The DHE method is extended to the color image processing by using the differential gray-levels histogram for color image. The proposed method has one parameter and the emphasis property of color images can be controlled by the parameter. The guideline for decision of the parameter which is agreed in a human sense is shown.