Color image reproduction methods and systems known in the art capture images on image-receptive media, which can be stored in analog or digital form, and then output as a visual reproduction. For example, color images may be captured on negative film and then reproduced optically or electronically on photographic paper. Images can also be captured on positive photographic materials, known as transparencies, and then viewed directly by projection or back-illumination, or copied onto other transparencies, or printed onto photographic paper. In other cases, color images can be captured by electronic devices, such as video or still CCD cameras, and viewed on monitors or printed using dye sublimation thermal printers. In each case previously cited, these systems are subjected to customer satisfaction criteria and may or may not embody digital tone reproduction manipulation or some form of color enhancement. The systems mentioned above are just some examples of color image reproduction systems. The application of this invention is not limited to the above systems, but can be applied to any system for producing color reproductions, such as the reproduction of reflection original images encoded and stored on a KODAK PHOTO CD.TM. imaging system.
One of the important criteria for viewer satisfaction in photographic reproductions is the correspondence between the optical reflectances of objects in the original scene compared to those of the reproduction. Viewers prefer to have high quality images with pleasing tone reproduction and high colorfulness while maintaining good skin tone. Technological advances have been made over the years in photographic films by incorporating more chemical enhancement, and in photographic papers by increasing the paper contrast. Some current methods for making color reproductions produce fairly bright colors and offer reasonable skin tone reproduction; however, there have been limitations on the extent to which color enhancement can be employed. One common problem associated with higher color enhancement films is that the reproduced colors are more saturated while the skin tone reproduction is oversaturated. The resulting reproductions are judged to be inferior to less colorful prints. Moreover, it has not been fully appreciated that the preferred visual reproduction does not usually correspond to the most accurate rendition.
Conventional silver halide photographic systems are subject to limitations imposed by optically printing one chemically developed material onto another chemically developable material and do not reproduce the scenes in a way that is preferred to the viewer. More specifically, conventional systems have not produced images having preferred highly saturated colors without adversely affecting desired skin tones.
Aside from color enhancement, the quality of image reproductions is also affected by the tone scale or tone mapping employed to reproduce the density variations that make up an image. It has previously been discovered that the use of a preferential tone scale or mapping as described generally in U.S. Pat. No. 5,300,381 issued to J. Buhr and H. Franchino entitled "Color Image Reproduction of Scenes with Preferential Tone Mapping", which is incorporated herein by reference in its entirety, can be utilized to provide a reproduced image that is perceived by the viewer to be a reproduction of the original scene which is preferred to that previously obtainable. The prior improvement in tone mapping has provided a degree of preferred reproduction of color images but the use of tone mapping alone has not enabled the full extent of improvement desired by the viewer.
It is a problem to be solved to provide viewer preferred visual reproductions of scenes which exhibit both increased color saturation and pleasing skin tones.