Enhancement of MPEG/JPEG images based on histogram equalization without gamut problem

In the case of digital image/video processing, color images are represented in the YC_bC_r. The Y component is the luminance of the color. The other two components C_b,C_r represent the color-difference component. The bandwidth of C_b,C_r components are much smaller than that of luminance signal. Thus, this color space is suitable for image compression and adopted for JPEG and MPEG. The YC_bC_r color space is related with the HSI (hue, saturation, intensity) color space. The HSI color space is an ideal tool for developing image processing. In this paper, we propose a novel method which is combined the luminance enhancement and the saturation enhancement, in the YC_bC_r color space. The width and shape of (C_b,C_r) space is changed depending on the value of Y component. Since, the saturation enhancement method must be given limiting condition for the RGB color space, the constrained condition for the values of C_b,C_r are derived. Thus, the proposed method is free from gamut problem.