This paper proposes a new method for making automatic improvements in digital color image quality. With this method, images obtained either with a video camera or by scanning photographs are automatically enhanced on a display, and no prior knowledge is required with regard to the image data distortions introduced by optical scanners, cameras, or transmission systems. In this paper, the feature values of three important factors for color image quality -- image sharpness, contrast, and saturation -- are defined based on human visual perception, and algorithms used for image enhancement are introduced. The method has been experimentally applied with excellent results to the enhancement of images obtained by scanning photographs: quality improvements achieved automatically were 70% of those achieved manually by human subjects. This simple, effective method appears to hold great promise for application to a variety of imaging devices.