Facsimile and static presentation processing – Natural color facsimile – Color correction
Reexamination Certificate
2000-01-13
2004-06-01
Williams, Kimberly (Department: 2626)
Facsimile and static presentation processing
Natural color facsimile
Color correction
C358S500000, C358S501000, C358S523000, C382S162000, C382S167000
Reexamination Certificate
active
06744544
ABSTRACT:
DETAILED DESCRIPTION OF THE INVENTION
1. Field of the Invention
This invention relates to a method and apparatus for forming and correcting a color image for correcting difference in color reproducibility between different color image processing devices so that the resulting corrected color reproducibility will be perceived to be psychologically more acceptable.
2. Related Art
With recent promulgation of color printing devices and large-capacity storage devices, electronic color image information is being utilized in increasing numbers, such as by storing an image of a color display in the form of a hard copy or preparing and storing a large quantity of color prints for later printing.
However, it is a frequent occurrence that the same color image information my be perceived to the human eye as being different color images due to difference in fidelity of an input device or an output device with respect to color reproduction.
For example, the color reproducibility of color printers of different manufacturers differs from one manufacturer to another. In addition, a significant difference has been felt in color reproducibilty between the image of a color display and that of a color printer depending on the difference in the color information volume.
FIG. 26
shows color reproduction gamuts of commonplace monitor and printer. In
FIG. 26
, luminosity L* is plotted against saturation C* as prescribed in L*a*b* color specification system of CIE 1976 (recommendation by Commission Internationale de Enluminure, referred to hereinafter CIE recommendations). Meanwhile, C* is given by the following equation:
Equation 1
As shown in this figure, a significant difference is observed between the color reproduction gamuts between the two devices.
FIG. 27
shows coordinates of the monitor and the printer in the L*a*b* color specification system. It is seen that the printer has a color reproduction gamut narrower than that of the monitor and undergoes position deviation in the color reproduction gamut.
In general, a color gamut that can be outputted differs from one output device to another. If color image data conversion is to be performed between output devices having different color reproduction gamuts, color gamut re-arrangement is done in some form or other.
If the partial color areas for which the human being feels a psychological meaning, such as the blue color recognized as the sky color or the yellow color recognized as the lemon color, are distributed as shown in
FIG. 28
, it is desirable that these colors after image data conversion be mapped within these ranges. However, as shown in
FIG. 29
or
30
, there are occasions wherein, if color information exchange is done only mechanically, the colors be mapped in areas other than the color area shown in FIG.
28
.
In color image data exchange from the monitor image information to the printer image information shown in
FIG. 29
, the color reproduction gamut of the printer information is narrow so that, after mapping part of the partial color area A′ is lost. In the color image data exchange in the opposite direction to that shown in
FIG. 29
, there is produced a deviation in a partial color area A″ after mapping, as shown in FIG.
30
.
If, in re-arranging the color information, the color reproduction gamut is not corrected sufficiently for position deviation or difference in the gamut for color reproduction, it invokes a psychologically alien feeling for the viewer.
There has been disclosed in the prior art a selective color hue adjustment system of a color image in the color perceptual space which consists in changing only a particular color for color hue adjustment of e.g., a color hard copy (Journal of Picture Electronic Association, vol.18, no. 15). In the prior-art technique, only a particular color is changed in color hue adjustment in order to avoid the color hue of the entire image being changed in addition to the area whose color is to be changed.
FIG. 31
is a block diagram showing the above-mentioned prior art. For specifying the color gamut to be processed and the direction and quantity of color hue adjustment, the H*ab, L*, C*ab coordinate systems of the polar coordinates in the L*a*b* space. As for the color gamut to be adjusted, color designation is made using the membership function, while the quantity of color hue adjustment is weighted using the membership function. The color gamut extraction is made in consideration of continuity of the color space.
A three-dimensional lookup table, in which selective color hue adjustment &PHgr; C and color correction &PHgr; M as to the representative lattice points of the color space are made in advance, is prepared, and color space lattice points are interpolated based upon this lookup table in order to prepare an image.
Problem to be Solved by the Invention
As discussed hereinabove; color reproducibility differs with machine types of the same apparatus, while the gamut for color reproduction, which is an extent of possible color reproduction, also differs with different image apparatus, such as color displays, color printers or color image scanners, such that color hue adjustment needs to be carried out in order to obtain desired color reproducibility.
In the above descried prior-art color hue adjustment, since arithmetic-logical operations are carried out using a lookup table processed in many ways, processing is time consuming, while it is difficult to reduce the time required for processing. The membership function is employed only for securing continuity if the color space of the color gamut which is to be adjusted, while there is no explicit reference to how the membership function is to be employed for color correction of the entire image.
The conventional practice in eliminating position deviation or difference in the gamut for color reproduction has been to cut off, curtail or compress the non-coincident portions of the gamut for color reproduction. However, this leads merely to deviation in saturation or chromaticity.
It is therefore an object of the present invention to provide a method and apparatus for forming and correcting a color image whereby the difference in color reproducibility in an image system or apparatus may be diminished for realizing proper color reproduction.
Means to Solve the Problem
For accomplishing the above object, the present invention provides many aspects.
In one aspect, the present invention provides a method for forming and correcting a color image having the steps of entering an information value representing a color gamut in a coordinate system of a perceptual color space, associating the information value with an information value representing an other color gamut determined by a pre-set color gamut with the aid of a first fuzzy processing from one color component to another for converting, by such association, the color gamut in the coordinate system of the perceptual color space into a converted color gamut which is a prescribed color gamut, and outputting an information value representing the converted color gamut in the coordinate system.
If the input signal is an image signal, the input image signal is converted into an information value representing a color gamut in a coordinate system of a perceptual color space with the aid of a second fuzzy processing, the information value is converted in accordance with the steps as defined in the first aspect, the converted information value is converted into and outputted as a image signal with the aid of a third fuzzy processing.
The conversion into the conversion color gamut is preferably carried out in the following manner.
That is, a pre-set reproduction color gamut of an input device and a pre-set reproduction color gamut of an output device are compared to each other for extracting a color gamut thereof, the color gamut is devided into plural partial color areas based upon plural pre-set memory colors from one color component to another, the reproduction color gamut of the input device or the reproduction color gamut of the output device, whichever is narrower, is devided i
Hatada Akinobu
Nagashima Mieko
Nagashima Toku
Carter Tia A.
Morrison & Foerster / LLP
Williams Kimberly
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