Facsimile and static presentation processing – Natural color facsimile – Image reproduction
Patent
1991-11-27
1994-06-07
Powell, Mark R.
Facsimile and static presentation processing
Natural color facsimile
Image reproduction
358519, 358522, 358523, 358518, H04N 146
Patent
active
053194730
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the performance of color gamut compressions in an apparatus such as a color printer device. More particularly, the present Invention relates to a color printer device wherein a color Image to be printed is analyzed at the same time it is being stored, and the color gamut of the image is compressed at the same time it is being removed from storage for printing, so that the color image can be analyzed and compressed in real time.
2. Discussion of the Related Art
Color printers that can be used for producing color reproductions of original and color images are known. Methods and apparatus relating to color image reproduction are described in, for example, U.S. Pat. Nos. 4,670,780, 4,707,727, 4,731,662, and 4,873,570, all of which are expressly incorporated herein by reference. The following articles, which relate to color image reproductions, are also expressly incorporated herein by reference: Stone et al., "Color Gamut Mapping and the Printing of Digital Color Images," ACM Transactions on Graphics, Vol. 7, No. 4, pp. 249-292 (October 1988); Stone et al., "Color Gamut Mapping and the Printing of Digital Color Images," Xerox Report EDL-88-1 [P88-00021], pp. 1-52 (April 1988); and Gordon et al., "On the Rendition of Unprintable Colors," Proceedings of the Technical Association of the Graphic Arts, pp. 186-195 (1987).
A color printer is limited in the range of colors it can reproduce. Thus, a source image (i.e., an original image) to be printed by the color printer may include colors that the printer is not able to reproduce. This in particularly true of color images created for a CRT (cathode-ray tube) monitor because the color gamut available to a CRT is typically much larger than the color gamut of a color printer. Consequently, it is often the case that the colors of the source image gamut must be mapped into the colors of the printer gamut (i.e., the colors which the printer is capable of producing) before any printing can be carried out. This process is called "gamut compression," because it involves compressing the color gamut of the source image until it fits within the color gamut of the printer.
A method of mapping the colors of a source image into the producible colors of a printer gamut (i.e., a method of compressing the source image gamut) is disclosed in U.S. Pat. No, 4,758,885, which is expressly incorporated herein by reference. In the '885 patent, the source image gamut of a monitor is shrunk so that it will fit within the printer gamut. However, in the '885 patent, the gamut of every source image is shrunk or compressed in the same way. Even if the source image only contains colors that the printer is capable of printing, the colors in the source image gamut are still mapped (i.e., the source image gamut is still compressed) before the source image is reproduced. Thus, in the '895 patent, unnecessary distortions and changes are introduced to the source image in situations where the original source image gamut does not need to be compressed in order to fit within the printer gamut.
Rather than compressing each source image in the same way, it is preferable to determine a different mapping or compression scheme for each source image so that unnecessary distortion of the source image can be kept to a minimum. For example, if all of the colors of a source image gamut are within the printer gamut, then the source image should not be mapped (i.e., the color gamut of the source image should not be compressed). This approach is suggested in the Stone et al. articles incorporated by reference above. Nevertheless, the methods described in the Stone et al. articles require sophisticated human analysis of the source image and printer gamuts.
The need for sophisticated human analysis can be eliminated by carrying out the gamut compression automatically, as described in the following articles by P. Laihanen, both of which are expressly incorporated herein by reference: "Optimization of Digital Color Reproduction on the B
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Grant, III Jerome
Powell Mark R.
Xerox Corporation
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