Distinct from gray-scale image enhancement, color image enhancement has two additional requirements. One is to preserve the natural color of the original image, and the other is to effectively present the information contained in the luminance and color components. We show that the color difference map and the luminance map represent different aspects of a color image. An enhancement scheme for color images is proposed based on this observation. In this method, an adaptive luminance masking function is generated from the local luminance contrast and color contrast. Overenhancement distortion, which is caused by the constraint of the display range, is also analyzed. A refinement algorithm is developed to solve this problem.