Research on Hue-Preserving Color Image Enhancement without Gamut Problem

Abstract

This paper gives theoretical analysis for the change of saturation of a RGB color vector under hue preserving transformation, and presents non-ideal performance of existing hue-Preserving image enhancing methods. Then it proposes a basic framework which is used to extend existing gray enhancement technologies to color images. By taking histogram equalization technology as example, a new hue preserving method for color image enhancement is studied. When the proposed method is applied to underexposed images, hue and saturation are preserved because underexposed images often have enough saturation; when it is applied to overexposed images, hue is preserved and saturation is raised. The method is simple but more effective. One of its novelties lies in its treatment of the maximum of RGB components, so that it does not generate gamut problem. The experimental results with many test images show that the method is superior to the other ones subjectively and objectively. Compared with the other methods, its better performance consists of three points: the first one is that saturation of the output images is high; the second one is that it brings less color levels merged and keeps more color levels; the last one is that the color levels kept have a more uniform distribution in the RGB cube. Moreover, the proposed method doesn’t need any color space conversion, so its computational complexity is less than ones of the methods based on HSI, YIQ, YCrCB etc.