Recorders – Record receiver deforming
Patent
1991-07-12
1994-10-11
Evans, Arthur G.
Recorders
Record receiver deforming
346157, G06F 1500
Patent
active
053554400
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
Technical Field
This invention relates to a color image processing method and apparatus therefor, in which dot area ratio is decided by a color scanner when color printing is performed using inks of the four colors yellow (Y), magenta (M), cyan (C) and black (K).
Background Art
In color printing, in principle most colors can be printed by the superimposed printing of inks of the three colors Y, M, C.
However, the following problems are encountered with such three colors superimposed printing:
3 three ink colors need to be superimposed at the same location for black reproduction, which is uneconomical because a large amount of ink is used; and
In general, therefore, attempts have been made to solve these problems by performing color printing using four colors, in which black (K) ink is added to the Y, M, C inks.
However, in a case where color printing is carried out with four colors inclusive of the color black, certain problems arise. Specifically, it is difficult to decide the dot area ratio of each color for the purpose of reproducing a target color, and excellent color reproduction cannot always be obtained even if printing is performed at the dot area ratios decided by the conventional method.
By way of example, one method of deciding dot area ratio according to the prior art is to obtain the ratio by inserting the R, G, B signals of the colors to be reproduced into the following masking equation: ##EQU1##
Here [a.sub.ij ] (i,j=1, 2, 3) is a parameter referred to as a "masking coefficient". The dot area ratio of each of the three colors Y, M, C is obtained by appropriately deciding this parameter.
In the case of the four colors, Y, M, C, K, tentative dot area ratios for Y, M, and C are determined as set forth above; then the dot area ratio for K is obtained by multiplying the minimum value among those for Y, M and C with a certain black ratio. Then, the final area ratios for Y, M, and C are determined by subtracting the area ratio for K from their tentative ratio values. removal) for those skilled in the color printing, and has been widely implemented in various printers as is referred to in U.S. Pat. No. 5,057,914 to Ricoh Co. which is best applied to subtractive color mixing system as color photography. It is well known that desirable color reproduction cannot be achieved by directly applying this approach to color printing that is based on dot area modulation and that involves in part additive color mixing. 5,121,196 to Konica as follows:
The Konica patent proposes a solution for these disadvantages of the UCR method; it consists of preparing a series of color patches with color inks to be used, and determining the YMCK data of a target color form the original and measured data for the color patches by interpolation. However, the Konica method is accompanied with the following drawbacks; collection and patch preparation are highly time consuming. be large enough: in order to, for example, double the accuracy along each axis of YMCK, then one must increase the number of patches by the factor of 2.sup.4 =16. a non-linear relationship, the accuracy of interpolation depends on the site in the color space. In particular, the accuracy becomes poor at the boundaries between reproducible and unreproducible regions where color patch data for interpolation are inevitably scarce. which deals with the statistical dot overlap in color printing in a vigorous colorimetric manner. However, in the Neugebauer approach, three equations hold for tristimulus values X, Y and Z, which are insufficient for the four unknowns YMCK. Neugebauer equation but after an almost unpractically lengthy calculation. We have judged that the Neugebauer approach is the most appropriate for a faithful color reproduction by area modulation, being capable of solving the problem of black addition. Based on such judgment, we have tried to solve the various drawbacks described above accompanying the Neugebauer approach.
The present invention has been devised in view of the foregoing points and its object is to provide a color
REFERENCES:
patent: 5057914 (1991-10-01), Tsuji et al.
patent: 5121146 (1992-06-01), Hung et al.
Nakamura Chiho
Sayanagi Kazuo
Evans Arthur G.
Shaken Co., Ltd.
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