Facsimile and static presentation processing – Static presentation processing – Attribute control
Reexamination Certificate
1999-07-21
2003-07-01
Grant, II, Jerome (Department: 2624)
Facsimile and static presentation processing
Static presentation processing
Attribute control
C358S525000
Reexamination Certificate
active
06587223
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a color signal conversion method and color signal converter for color image printing.
2. Description of the Related Art
In the field of color image printing and color hard copy, color signal conversion from the three primary colors of light (RGB) to the three primary colors of color (CMY) has been indispensable when reproducing color by a printer.
In regard to the actual ink, however, there has been the problem that color conversion cannot be carried out simply because other colors are mixed in the ink. A three-dimensional interpolation using various color conversion tables has been proposed as a way of quickly and easily converting color signals.
The three-dimensional interpolation is a method of carrying out color conversion in color space in which three-dimensional color space is divided equally into n units in each direction of RGB so as to subdivide one RGB color space into n×n×n units. By subdividing color space in this way, color can be handled as a linear form in color space, thereby shortening the amount of time necessary for calculation compared with the case in which color does not change linearly and simplifying the calculation itself.
As shown in
FIGS. 1
a
-
1
d,
each interpolation calculation is carried out in 4-point, 5-point, 6-point,and 8-point interpolations using data of four to eight apices, respectively.
FIGS. 1
a
-
1
d
each show only one unit of a cube that has been cut into a number of units in each interpolation, each interpolation actually cutting a cube into four to eight unit cubes.
Three-dimensional interpolation calculation thus finds the current pixel data through linear interpolation using the four to eight points of apex data of the subdivided color space that contains the points currently being sought.
These interpolations divide three-dimensional color space represented by three primary colors into a plurality of color cube units, and within the color cube units, linear interpolation is carried out with color assumed to change linearly, thereby enabling fast and easy conversion of color signals.
A color signal converter of the prior art is disclosed in Japanese Patent Laid-open No. 99587/95. As shown in
FIG. 2
a,
this converter comprises picture element input section
100
, comparator
102
, adder
101
, addrress generator
103
, color conversion table memory
105
, selector
107
, weitht generator
103
, oblique triangular column determination section
104
, and oblique triangular column interpolation calculator
109
.
Picture element input section
100
inputs and divides RGB color image signals into higher-order bits(RH,GH,BH) and lower-order bits(RL,GL,BL). Comparator
102
compares the lower-order bits with themselves and outputs the compared results. Adder
101
adds the output of comparator
102
to that of picture element section
100
. Address generator
103
generates from the outputs of both picture element input section
100
and comparator
102
. Color conversion table memory
105
stores color conversion data for converting RGB to CMYK. Selector
107
selects the output of the color conversion table memory
105
. Weight generator
108
generates, from the lower-order bits, weight coefficients for interpolation points. Oblique triangular column determination section
104
determines the size of the weight coefficients and selects oblique triangular column made up of apices of each unit cubes which are obtained by dividing three primary color spaces into a plurality of unit cubes. Oblique triangular column interpolation calculator
109
interpolates output values read from color conversion table memory
105
using the weight coefficients.
In this way, the color signal converter of the prior art effects color conversion by linear interpolation in a state free of ripple (a phenomenon in which false contours are generated by interpolation) in all color space.
FIG. 2
b
is a simplified block diagram of
FIG. 2
a.
As shown in
FIG. 2
b,
when RGB signals are received in pixel input section
100
, the section
100
separates an RGBH signal for selecting color conversion table memory
105
and an RGBL signal for controlling oblique triangular column interpolation calculator
109
. Address generator
103
generates from the RGBH signals memory address signals for selecting a memory address in color conversion table memory
105
. Color conversion data that are specified by the addresses of the memory address signals are outputted from color conversion table memory
105
. Upon receipt of color conversion data signals and RGBL signals, oblique triangular column interpolation calculator
109
carries out an interpolation calculation of color conversion data signals and outputs interpolation calculation data signals, which are the calculation results of interpolating the color conversion data signals.
Another color signal converter of the prior art is disclosed in Japanese Patent Laid-open No. 288706/95. As shown in
FIG. 3
, this converter comprises first color reproduction area table
150
, second color reproduction area table
124
, color reproduction area conversion section
121
, entire corresponding color decision section
122
, optimum color reproduction area selecting section
123
, target color reproduction area by k-ink amount table
126
, color area reproduction area dividing section by k-ink amount
125
, entire corresponding ink amount storage memory
127
, candidate selection section
128
, interpolation calculation section
129
. First color reproduction area table
120
stores RGB values. Second color reproduction area table
124
stores CMYK values. Color reproduction area conversion section
121
performs conversion of source representative color signals (RGB values) while varying the RGB values outputted from first color reproduction area table
120
. Entire corresponding color decision section
122
searches target color reproduction area by K-ink amount table
126
and finds a set of CMYK ink amounts corresponding to the converted color signals. Optimum color reproduction area conversion selecting section
123
finds the optimum values of RGB values in color reproduction area conversion section
121
. Target color reproduction area by K-ink amount table
126
stores data obtained by colorimetring color samples of a plurality of colors obtained by adjusting CMY ink amounts for a plurality of different K-ink amounts. Color reproduction area dividing section by k-ink amount
125
divides color reproduction area table by K-ink amount
126
into independent color reproduction area tables for each K-ink amount. Entire corresponding ink amount storage memory
127
stores one or more sets of CMYK ink amounts obtained by the optimum conversion RGB values. Candidate selecting section
128
selects one or two sets of CMYK ink amounts in accordance with K-ink amount adjustment coefficient. Interpolation calculation section
129
carries out interpolation calculation with K-ink amount adjustment coefficients as an internal division ratio to calculate CMYK ink amounts.
Thus, in the color signal converter of the prior art, CMYK ink amounts corresponding to any color of a color image display device are determined based on actual measurement data; and K-ink amounts are selected based on K-ink amount adjustment coefficients. Moreover, the CMYK ink amounts are selected with K-ink amount adjustment coefficients, and the CMYK ink amount in each K-ink amount is determined.
In the converter disclosed in Japanese Patent Laid-open No. 99587/95 has the following problems. These color conversion data are produced under a certain condition, so that color conversion data corresponding to the external temperature conditions are compelled to be rewritten to color conversion table memory
105
in the event of a change in the external temperature.
Furthermore, because especially in an ink-jet printer, ink spray conditions change according to the temperature of the ink or the amount of time the printer is used, and hence color reproducibility is decreas
Choate Hall & Stewart
Grant II Jerome
NEC Corporation
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