JP2003289445A - Color adjustment method, program for executing color adjustment method, and recording medium having the program stored thereon - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color adjustment method for matching a gray color obtained by overlapping CMY and the color tone of the entire image to a reference gray or a reference overall color tone when a color image output apparatus provides outputs, and to provide a program for executing the color adjustment method and a recording medium having the program stored thereon. <P>SOLUTION: In the color adjustment method, gradation correction curves for respective C, M, Y are obtained on the basis of: outputs as to a plurality of combinations from a minimum value to a maximum value of three fundamental colors (CMY) in a color image output apparatus; and a plurality of gray outputs by the three fundamental colors (CMY) in a reference color image output apparatus. The image data of a color image outputted from the color image output apparatus are corrected by using the color correction curves. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color adjusting method for output by a color image output device, a program for executing the color adjusting method, and a recording medium storing the program.

[0002]

2. Description of the Related Art Conventionally, in a halftone dot type color printer, since the color of each color material of CMYK is close to the printing ink color, the difference in the dot thickening is corrected (dot gain curve correction).
Was performed based on the measurement result of the dot area ratio for each of CMYK, it was possible to match the color to the printing machine to some extent. The secondary colors of red R, green G, and blue B, the black of three colors of CMY, CMYK
Regarding the black of the four colors and the colors around them, the appearance of the colors was different from the printing machine, so it was difficult to perform exact color matching.
Therefore, a color management system based on a device color profile has been proposed, and it has become possible to more accurately match the color of the proof color printer to the color of the printing machine.

[0003]

However, when the printing conditions of the color printer for proofreading (color image output device), for example, the lot of the color material or the recording medium or the usage environment are different, the above dot gain curve correction is performed. Despite matching colors with the color management system or C
There are cases in which the gray in which MY is superimposed and the color tone of the entire image are output differently.

The present invention has been made in view of the above circumstances, and an object of the present invention is to maintain a constant gray tone of CMY superposed images and a color tone of the entire image when output by a color image output device. To provide a color adjusting method, a program for executing the color adjusting method, and a recording medium storing the program.

[0005]

In order to achieve the above-mentioned object, the invention according to claim 1 is such that the gray or the whole tone of a color image output by a color image output device is the standard gray or the whole tone. In a color adjusting method for adjusting to a color tone, the three basic colors (CM
Y) output for a plurality of combinations from the minimum value to the maximum value, and 3 in the color image output device as a reference.
And a step of correcting the image data of the color image output by the color image output device by obtaining the gradation correction curves for C, M, and Y based on the output of a plurality of gray colors of the basic colors (CMY). It is characterized by including.

According to a second aspect of the present invention, a plurality of gray outputs by a single black color (K) in the color image output device and a plurality of black outputs by a single black color (K) in the reference color image output device are provided. Further, a step of obtaining a K gradation correction curve so as to reproduce the lightness of the reference gray output based on the gray output and the image data of the color image output by the color image output device is further corrected. It is characterized by including.

According to the third aspect of the present invention, the output for a plurality of combinations of the minimum value to the maximum value of the three basic colors (CMY) is output as the three basic colors (CMY).
It is characterized in that each of a plurality of C, M, and Y obtained by equally dividing each of the plurality of values from the minimum value to the maximum value is obtained.

Further, the invention according to claim 4 is characterized in that the plurality of gray colors of the three basic colors (CMY) are output by the uniform three basic colors (CMY).

According to a fifth aspect of the invention, there is provided a program for causing a computer to execute the color adjusting method according to any one of the first to fourth aspects.

The invention according to claim 6 is a computer-readable recording medium in which the program according to claim 5 is stored.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 17 shows a color adjustment for adjusting the color tone of the output color of the calibration color printer 20 (color image output device) to the color tone of the printed matter of the printing machine, and the calibration method of the present invention for keeping the output color constant. 1 illustrates an example of a configuration to be implemented. As shown in FIG. 17, it comprises a personal computer 10 and a proof color printer 20. The personal computer 10 includes an arithmetic processing unit 11 which is a microprocessor, a first storage unit 12 which is a memory, a second storage unit 13 which is a hard disk, an interface 14 which is a communication means with the outside, a display unit 15 which is a display, and a keyboard. The operation unit 16 and the internal bus 17 that enables them to communicate. Also, PC 1
0 and the proof color printer 20 are connected by a bus 30 for enabling transfer of image information and the like.

Further, a gradation correction curve, which will be described later, is stored in the second storage unit 13, and when a color image is output by the calibrating color printer 20 using a printer driver, an image is output so as to have a target color tone. It acts to correct the data.

FIG. 1 is a flowchart showing each step of a color adjusting method including an example of a method of calibrating an output color of a calibrating color printer according to an embodiment of the present invention. This color adjusting method is executed so that the color of the printing machine is reproduced by the proofing color printer 20 with the printing machine (not shown) as a target for color matching. The step of making corrections for calibration is included.

First, each step of the color adjusting method according to the present embodiment will be schematically described with reference to FIG.

First, a color printer 2 for calibrating standard conditions
The color chart (CMY), gray patch (CMY), and gray patch (K) of the output product output at 0 are measured (S
11), a lookup table is created based on the color measurement result of the color chart (CMY) (S12). on the other hand,
The gray patches (CMY) and gray patches (K) of the printed matter output by the printing machine are colorimetrically measured (S13). Next, C, M, and Y reference tone correction curves are created from the gray patch (CMY) color measurement result of the printed matter and the look-up table created in step S12 of the calibration color printer 20 (S14). Further, a K reference gradation correction curve is created from the color measurement result of each gray patch (K) (S15).

Further, the following steps are steps for correcting the output color of the calibration color printer 20 for calibration. First, a color chart (CMY) and a gray patch (K) are newly output by the proof color printer 20 for color measurement (S16). Next, a lookup table is created based on the color measurement result of the color chart (CMY) (S17). Next, C, M, and Y calibration gradation correction curves are created from the gray patch (CMY) colorimetric result of the reference condition of step S11 and the newly created look-up table (S18). Further, a calibration gradation correction curve for K is created from the color measurement results of the gray patch (K) in steps S11 and S16 (S1).
9). The reference gradation correction curve of step S14 and the calibration gradation correction curve of step S18 are combined to create a new gradation correction curve for CMY (S20).
Reference tone correction curve of step S15 and step S19
A new gradation correction curve for K is created by combining the calibration gradation correction curves of (S21). Then, for each pixel of the image data, CMYK is calculated in steps S20 and S.
The gradation correction curve obtained in step 21 is used for correction, and the CMYK values to be output to the calibration color printer 20 are obtained and output from the calibration color printer 20 (S22).

Each step will be described in more detail below. Two LUTs of CMY → L * a * b * LUT L * a * b * → CMY LUT are used for the look-up table (hereinafter, referred to as “LUT”) of the above-described calibration color printer 20. CMY → L * a * b * L
The UT converts the CMY color value into the color system value L * a * b *, and the L * a * b * → CMY LUT is the color system value L.
* A * b * is converted into CMY color values.

(Steps S11, S12) First, with respect to the calibration color printer 20 of the reference conditions, CMY → L *
CMY → L * a obtained by obtaining a * b * LUT
L * a * b * → CMY LU based on * b * LUT
Find T.

The CMY → L * a * b * LUT is, for example, as shown in FIG. 2, and is a three-dimensional input / three-dimensional output in which the L * a * b * value is input to the CMY LUT input point. Specifically, color patches are colorimetrically measured for a large number of combinations of all color spaces of CMY, and L * a * b * values of each color patch are obtained and made into an LUT. For example, the following method You can decide with.

First, the minimum values 0 to 255 of C, M, and Y are divided into four, and 0, 64, 128, 191, and 2 are divided.
55 levels, C × M × Y: 5 × 5 × 5 = 125
A color chart as shown in FIG. 3 in which color patches are arranged for a combination of points is printed by the calibration color printer 20, and 5 * 5 * 5 = 125 points of each patch are color-measured to obtain L * a.
Determine the * b * value.

Also, when measuring the color of this color chart, CM
Y equivalent 0, 12, 25, 38, 51, 64, 76, 8
9, 102, 115, 128, 140, 153, 16
6, 178, 191, 204, 217, 229, 24
A total of 21,255 gray patches including white and black of 2,255 are output, and the L * a * b * value is obtained by measuring the color with a colorimeter.
Furthermore, K single color (0, 32, 64, 96, 128,
159, 191, 223, 255) and outputs the gray patch to obtain the L * value. The output of these two gray patches serves as a reference for calibration of the output color of the calibration color printer 20.

Further, a three-dimensional input / three-dimensional output LUT
Is 5 × 5 × 5 for points between 9 × 9 × 9 grid points.
= 125 points of each patch are interpolated and converted into 9x9x9 patches. As shown in FIG. 4, if black circles ● are grid points (sample points) and triangles and triangles are points to be interpolated, respectively, there are two grid points before and after the triangle, as in the case of triangle. Different interpolation formulas are used when there are one point and three points before and after as shown by a mark.

Here, the color system of the points to be interpolated is Lm * am
* Bm * and the color system of each sample point is Li * ai * b
When i * (i = 1 to 4), in the former case (marked with Δ), the following interpolation formula is used: Lm * =-(1/16) L1 ** + (9/16) L2 **
(9/16) L3 *-(1/16) L4 * am * =-(1/16) a1 * + (9/16) a2 **
(9/16) a3 *-(1/16) a4 * bm * =-(1/16) b1 * + (9/16) b2 ** +
It is interpolated as (9/16) b3 *-(1/16) b4 *.

In the latter case (marked with X), the following interpolation formula is used: Lm * = (5/16) L1 ** + (15/16) L2 *-
(5/16) L3 *-(1/16) L4 * am * = (5/16) a1 ** + (15/16) a2 *-
(5/16) a3 *-(1/16) a4 * bm * = (5/16) b1 ** + (15/16) b2 *-
It is interpolated as (95/16) b3 *-(1/16) b4 *.

FIG. 5 shows an example of the order of interpolation processing for three-dimensional CMY. The CMY5 × 5 × 5 is interpolated into 9 × 9 × 9 by performing the interpolation process in the order shown in FIG. 5 (corresponding to Roman numerals in FIG. 5). As a result, the L * a * b * value is calculated for the CMY combination by expanding to 9 × 9 × 9 = 729 points even though only 5 × 5 × 5 = 125 patches are actually measured. You can

On the other hand, the L * a * b * → CMY LUT is
As shown in FIG. 6, it is a three-dimensional input / three-dimensional output LUT, and the points between the 33 × 33 × 33 grid points are interpolated and converted.

A method of obtaining the three-dimensional input / three-dimensional output LUT of FIG. 6 will be described. For simplicity, the basic colors are C and M, 2
Described as a color. In addition, C, M, and Y are all 0 to 2
It shall take the value of 55. First, the above-mentioned CMY → L *
C * M * Y of a * b * LUT: L * a * b *-> CMY LUT is calculated using the three-dimensional data of 9 * 9 * 9. FIG. 8 is a plot of L * on the vertical axis and a * on the horizontal axis for a two-dimensional 9 × 9 combination of M and C in CMY (Y = 0). Although it is actually three-dimensional, it is shown in two dimensions for simplicity.

For this CMY distribution, the target point [L * (0-100) a * (-127-
128) b * (-127 to 128): 33 × 33 × 33
= 35937 each LUT input point], L * a * b * is given as a target value T ′. When the target value T'is in the region surrounded by the grid points a'to d'as shown in FIG. 8, the MC combination (target value T) in the MC coordinate system is the grid points a to d'as shown in FIG. It is presumed to be within the area surrounded by d. Then, the location of the target value T in the area formed by the grid points a to d is obtained by performing a convergence calculation process while associating the color system of FIG. 8 with the coordinate system of FIG. Although the conversion from the coordinate system of FIG. 9 to the color system of FIG. 8 is known, the reverse conversion is very complicated and a good conversion formula is known. This is because it has not been done.

Next, the area So formed by the grid points a to d in FIG. 10 is equally divided into four areas S1 to S4. 5
The individual division points e to i are calculated by weighted averaging using the already obtained surrounding grid points. Then, the values obtained by converting the values corresponding to the division points e to i into the L * a * b * color system are plotted in the color system of FIG. 11, and the plotted division points e ′ to i ′ are used. Four areas S formed
Which region of 1'-S4 'has the target value T'is determined. As shown in FIG. 11, when in the area S2 ',
As shown in FIG. 10, the target value T is S corresponding to the area S2 ′.
It is presumed to be in 2.

Next, the estimated region S2 is equally divided into S5 to S8. The five division points j to n are calculated by weighted averaging using the lattice points or the division points around which the division points have already been obtained. Then, the value corresponding to the division points j to n is set to L * a.
The values converted to the * b * color system are plotted in the color system of FIG. 11, and in which of the four areas S5 ′ to S8 ′ formed by the plotted dividing points j ′ to n ′. Determine if there is a target value T '. Area S as shown in FIG.
When it is 8 ', the target value T is estimated to be in the area S8 corresponding to the area S8' as shown in FIG.

Next, the estimated area S8 is equally divided into four areas S9 to S12. The five division points o to s are calculated by weighted averaging using the surrounding grid points or division points that have already been obtained. Then, the values obtained by converting the values corresponding to the division points o to s into the L * a * b * color system are plotted in the color system of FIG. 11, and the plotted division points o ′
~ S 'four regions S9'-S12' formed by
In which of the areas the target value T'is located is determined. Figure 11
When the target value T is in the region S10 'as shown in FIG.
Presumed to be in.

By repeating the division of the regions as described above, the lattice gradually becomes smaller and finally converges. Then, the target value T is obtained by averaging the four lattice points or the division points forming the converged area, and thus the combination of the basic colors indicating the output colors to be obtained can be obtained.

Further, in the present embodiment, the method based on the convergence calculation as described above is described.
An interpolation method as described in the specification of 895086 may be used.

By the way, when the target value T'is outside the color reproduction range formed by the vertices W ', C', M ', B'of the L * a * b * color system as shown in FIG. It is necessary to move this target value T'to the color reproduction range. In this case, the target value T ′ is moved in the achromatic color direction, and the coordinates of the intersection with the boundary of the color reproduction range in the achromatic color direction is set as the target value, as shown in FIG. A target value T to be calculated is calculated.

The target value T'does not necessarily have to be moved to the boundary, but may be moved within the color reproduction range. Also, here, for the sake of explanation, the example of the two-dimensional C × M is shown, but actually, the three-dimensional C × M × Y is used.
It is necessary to calculate the values of C, M, and Y one by one with each LUT input point of 33 * 33 * 33 points of L * a * b * as a target value T '.

As described above, L * a * b * → CMY
The LUT is required.

(Step S13) On the other hand, 0, 12, 25, 38, 51, 64, 7 of CMY equivalents in the printing machine.
6, 89, 102, 115, 128, 140, 153,
166, 178, 191, 204, 217, 229, 2
A gray patch of 21 steps including 42 and 255 of white and black is output, and the color is measured by a colorimeter to obtain the L * a * b * value. In addition, K single color (0, 32, 64, 96, 128, 159,
191, 223, 255) is output and the L * value is obtained.

(Step S14) Next, from the values of the L * a * b * color system obtained from the gray patches of the printing machine, the CMY LUT of the proofing color printer 20 is used to calculate CMY. Then, a reference gradation correction curve for each of CMY is created.

For example, L * a * obtained in step S13
The value of the b * color system is L * = 57,0, a * = 5.3, b *
= 3.6, L * a * b *: 33 × 33 × 33 →
The distance between the input point of L * a * b *: 33 × 33 × 33 and the input point of L * a * b * of the CMY LUT is L *: 57,0 / 100 × 32 = 18.2, , L *
The distance DL1 to the first points L1 and L1 of L1 and the distance DL2 to the second points L2 and L2 of L * are L1 = 18, DL
1 = 0.2, L2 = 19, DL2 = 0.8 a *: (5.3 + 127) /255×32=16.6, so the first point a1 of a * and the distance DL1 to a1 are:
The distance Da2 between the second point a2 of a * and a2 is a1 =
16, Da1 = 0.6, a2 = 17, Da2 = 0.4 b *: (3.6 + 127) /255×32=16.4, so the distance b1 between the first point b1 of b * and b1 When,
The distance Db2 between the second point b2 of b * and b2 is b1 =
16, Db1 = 0.4, b2 = 17, Db2 = 0.6.

L * a * b *: 33 × 33 × 33 → CMY
L * 2 points (L1, L2) x a * 2 points (a from the LUT
1, a2) × b * 2 points (b1, b2) = CMY values for 8 points are CL1a1b1, CL1a1b2, CL1a2b1, C
L1a2b2, CL2a1b1, CL2a1b2, CL2a2b1, C
L2a2b2, ML1a1b1, ML1a1b2, ML1a2b1, M
L1a2b2, ML2a1b1, ML2a1b2, ML2a2b1, M
L2a2b2, YL1a1b1, YL1a1b2, YL1a2b1, Y
L1a2b2, YL2a1b1, YL2a1b2, YL2a2b1, Y
If L2a2b2, then L * = 57,0, a * = 5.3, b * = 3.
The value of CMY for 6 is obtained by the following equation: C = DL2 × Da2 × Db2 × CL1a1b1 + DL2 × Da2 × Db1 × CL1a1b2 + DL2 × Da1 × Db2 × CL1a2b1 + DL2 × Da1 × Db1 × CL1a2b2 × D1 × D1 × D1 × D1 + DL1 × Da2 × Db1 × CL2a1b2 + DL1 × Da1 × Db2 × CL2a2b1 + DL1 × Da1 × Db1 × CL2a2b2 M = DL2 × Da2 × Db2 × ML1a1b1 × DL2a1 × 1 + DL2 × DL2 × 1d1 + DL1 × DL2 × DL2 × Db1 × DL2 × Db1 × DL2 × Db1 × DL2 × Db1 × DL2 × D2 ML1a2b2 + DL1 × Da2 × Db2 × ML2a1b1 + DL1 × Da2 × Db1 × ML2a1b2 + DL1 × Da1 × Db2 × ML2a2b1 + DL1 × Da1 × Db1 × ML2a2b 2 Y = DL2 × Da2 × Db2 × YL1a1b1 + DL2 × Da2 × Db1 × YL1a1b2 + DL2 × Da1 × Db2 × YL1a2b1 + DL2 × Da1 × Db1 × YL1a2b2 + DL1 × Da2 × Db2 × YL2a1b1 + DL1 × Da2 × Db1 × YL2a1b2 + DL1 × Da1 × Db2 XYL2a2b1 + DL1 x Da1 x Db1 x YL2a2b2.

As described above, 21 points of L * a * b * obtained from the gray patch of the printing machine were calculated,
The output value of each CMY color is obtained, and a reference tone correction curve for each CMY color as shown in FIG. 7 is created.

(Step S15) Next, a K reference gradation correction curve is created. First, K single color (0, 32,
64, 96, 128, 159, 191, 223, 25
5), L1, L2, Lin3, Lin4, Lin
5, Lin6, Lin7, Lin8, Lin9.

Next, K single color (0, 32, 64, 96, 1
28, 159, 191, 223, 255), L * values obtained by the calibrating color printer 20 under the reference conditions in step S11 are Lout1, Lout2, Lout3,
Lout4, Lout5, Lout6, Lout7, L
Let out8 and Lout9.

As shown in FIG. 15, the above-mentioned Lin1 to L
From in9 and Lout1 to Lout9, from the maximum density point of the K single color of the printed matter of the printing machine to 0, the K of the calibration color printer 20 is reproduced so as to reproduce the lightness data L * obtained from the values of the color system. By obtaining the value of, a K reference gradation correction curve as shown in FIG. 16 is created.

In this reference gradation correction curve, white L * may actually differ between the printed matter of the printing press and the calibration color printer 20, and white (0) is corrected by matching L *. Make a curve that does not exist. Further, when the minimum lightness of K of the printing machine is smaller than the minimum lightness of K of the calibration color printer 20, the lightness L * cannot be reproduced, so that it can be reproduced with the minimum lightness of K of the calibration color printer 20. Make a curve. Further, in this embodiment, the output value is 255 with respect to the input value 255 of the K gradation correction curve, but this is to improve the character reproduction by outputting the solid K image.

As described above, by using each of the CMYK reference gradation correction curves, a color having the target value of CMYK of the printed matter of the printing machine is output by the calibration color printer 20 under the reference condition. become.

Further, in the present embodiment, for example, when the output color or the like changes due to the color material lot or environmental changes, the above-described color matching state based on the color output of the proof color printer is used as a reference. The correction for calibration described below is further performed so that the output color is the same as the output color in. Although the above-mentioned numerical values and figures are used for explanation, it goes without saying that the shapes of the gradation correction curves and the like shown in FIG. 7 and FIG. 16 are different because the numerical values are different in the actual case.

(Steps S16 and S17) First,
About the proofing color printer 20, CMY → L * a *
b * LUT is calculated, and further CMY → L * a * is calculated.
L * a * b * → CMY LUT based on b * LUT
Ask for.

The CMY → L * a * b * LUT is, for example, as shown in FIG. 2, and is a three-dimensional input / three-dimensional output in which the L * a * b * value is input to the CMY LUT input point. Specifically, color patches are colorimetrically measured for a large number of combinations of all color spaces of CMY, and L * a * b * values of each color patch are obtained and made into an LUT. For example, the following method You can decide with.

First, the minimum values 0 to 255 of C, M, and Y are divided into four, and 0, 64, 128, 191, and 2 are divided.
55 levels, C × M × Y: 5 × 5 × 5 = 125
A color chart as shown in FIG. 3 in which color patches are arranged for combinations of points is printed by the proof color printer 20, and 5 * 5 * 5 = 125 points of each patch are sequentially measured to measure L * a * b *. Determine the value.

Further, K single color (0, 32, 64, 96, 1
28, 159, 191, 223, 255) and outputs L * value.

Further, a three-dimensional input / three-dimensional output LUT
Is 5 × 5 × 5 for points between 9 × 9 × 9 grid points.
= 125 points of each patch are interpolated and converted into 9x9x9 patches. As shown in FIG. 4, if black circles ● are grid points (sample points) and triangles and triangles are points to be interpolated, respectively, there are two grid points before and after the triangle, as in the case of triangle. Different interpolation formulas are used when there are one point and three points before and after as shown by a mark.

Here, the color system of the points to be interpolated is Lm * am
* Bm * and the color system of each sample point is Li * ai * b
When i * (i = 1 to 4), in the former case (marked with Δ), the following interpolation formula is used: Lm * =-(1/16) L1 ** + (9/16) L2 **
(9/16) L3 *-(1/16) L4 * am * =-(1/16) a1 * + (9/16) a2 **
(9/16) a3 *-(1/16) a4 * bm * =-(1/16) b1 * + (9/16) b2 ** +
It is interpolated as (9/16) b3 *-(1/16) b4 *.

In the latter case (marked with X), Lm * = (5/16) L1 ** + (15/16) L2 *-
(5/16) L3 *-(1/16) L4 * am * = (5/16) a1 ** + (15/16) a2 *-
(5/16) a3 *-(1/16) a4 * bm * = (5/16) b1 ** + (15/16) b2 *-
It is interpolated as (95/16) b3 *-(1/16) b4 *.

FIG. 5 shows an example of the order of interpolation processing for three-dimensional CMY. The CMY5 × 5 × 5 is interpolated into 9 × 9 × 9 by performing the interpolation process in the order shown in FIG. 5 (corresponding to Roman numerals in FIG. 5). As a result, the L * a * b * value is calculated for the CMY combination by expanding to 9 × 9 × 9 = 729 points even though only 5 × 5 × 5 = 125 patches are actually measured. You can

On the other hand, the L * a * b * → CMY LUT is
As shown in FIG. 6, it is a three-dimensional input / three-dimensional output LUT, and the points between the 33 × 33 × 33 grid points are interpolated and converted.

A method of obtaining the three-dimensional input / three-dimensional output LUT of FIG. 6 will be described. For simplicity, the basic colors are C and M, 2
Described as a color. In addition, C, M, and Y are all 0 to 2
It shall take the value of 55. First, the above-mentioned CMY → L *
C * M * Y of a * b * LUT: L * a * b *-> CMY LUT is calculated using the three-dimensional data of 9 * 9 * 9. FIG. 8 is a plot of L * on the vertical axis and a * on the horizontal axis for a two-dimensional 9 × 9 combination of M and C in CMY (Y = 0). Although it is actually three-dimensional, it is shown in two dimensions for simplicity.

For this CMY distribution, the target point [L * (0-100) a * (-127-
128) b * (-127 to 128): 33 × 33 × 33
= 35937 each LUT input point], L * a * b * is given as a target value T ′. When the target value T'is in the region surrounded by the grid points a'to d'as shown in FIG. 8, the MC combination (target value T) in the MC coordinate system is the grid points a to d'as shown in FIG. It is presumed to be within the area surrounded by d. Then, the location of the target value T in the area formed by the grid points a to d is obtained by performing a convergence calculation process while associating the color system of FIG. 8 with the coordinate system of FIG. Although the conversion from the coordinate system of FIG. 9 to the color system of FIG. 8 is known, the reverse conversion is very complicated and a good conversion formula is known. This is because it has not been done.

Next, the area So formed by the grid points a to d in FIG. 10 is equally divided into four areas S1 to S4. 5
The individual division points e to i are calculated by weighted averaging using the already obtained surrounding grid points. Then, the values obtained by converting the values corresponding to the division points e to i into the L * a * b * color system are plotted in the color system of FIG. 11, and the plotted division points e ′ to i ′ are used. Four areas S formed
Which region of 1'-S4 'has the target value T'is determined. As shown in FIG. 11, when in the area S2 ',
As shown in FIG. 10, the target value T is S corresponding to the area S2 ′.
It is presumed to be in 2.

Next, the estimated area S2 is equally divided into S5 to S8. The five division points j to n are calculated by weighted averaging using the lattice points or the division points around which the division points have already been obtained. Then, the value corresponding to the division points j to n is set to L * a.
The values converted to the * b * color system are plotted in the color system of FIG. 11, and in which of the four areas S5 ′ to S8 ′ formed by the plotted dividing points j ′ to n ′. Determine if there is a target value T '. Area S as shown in FIG.
When it is 8 ', the target value T is estimated to be in the area S8 corresponding to the area S8' as shown in FIG.

Next, the estimated area S8 is equally divided into four areas S9 to S12. The five division points o to s are calculated by weighted averaging using the surrounding grid points or division points that have already been obtained. Then, the values obtained by converting the values corresponding to the division points o to s into the L * a * b * color system are plotted in the color system of FIG. 11, and the plotted division points o ′
~ S 'four regions S9'-S12' formed by
In which of the areas the target value T'is located is determined. Figure 11
When the target value T is in the region S10 'as shown in FIG.
Presumed to be in.

By repeating the division of the region as described above, the lattice gradually becomes smaller and finally converges. Then, the target value T is obtained by averaging the four lattice points or the division points forming the converged area, and thus the combination of the basic colors indicating the output colors to be obtained can be obtained.

In the present embodiment, the method based on the convergence calculation as described above is described.
An interpolation method as described in the specification of 895086 may be used.

By the way, when the target value T'is outside the color reproduction range formed by the vertices W ', C', M ', B'of the L * a * b * color system as shown in FIG. It is necessary to move this target value T'to the color reproduction range. In this case, the target value T ′ is moved in the achromatic color direction, and the coordinates of the intersection with the boundary of the color reproduction range in the achromatic color direction is set as the target value, as shown in FIG. A target value T to be calculated is calculated.

The target value T'does not have to be moved to the boundary, but may be moved within the color reproduction range. Also, here, for the sake of explanation, the example of the two-dimensional C × M is shown, but actually, the three-dimensional C × M × Y is used.
It is necessary to calculate the values of C, M, and Y one by one with each LUT input point of 33 * 33 * 33 points of L * a * b * as a target value T '.

As described above, L * a * b * → CMY
The LUT is required.

(Step S18) Next, step S11
L * a of the CMY equivalent gray patch of the standard condition obtained in
Using the L * a * b * → CMY LUT of the calibrating color printer 20 for which the value of the * b * color system has been obtained in step S17, CMY is obtained, and calibration gradation correction curves for each of CMY are created. .

For example, the value of the L * a * b * color system of the reference condition obtained in step S11 is L * = 57,0, a * =
5.3 and b * = 3.6, L * a * b *: 33 ×
33 × 33 → L * a * b * of CMY LUT: 33 × 3
The distance between the 3 × 33 input point and each L * a * b * input point is L *: 57,0 / 100 × 32 = 18.2, so L *
The distance DL1 to the first points L1 and L1 of L1 and the distance DL2 to the second points L2 and L2 of L * are L1 = 18, DL
1 = 0.2, L2 = 19, DL2 = 0.8 a *: (5.3 + 127) /255×32=16.6, so the first point a1 of a * and the distance DL1 to a1 are:
The distance Da2 between the second point a2 of a * and a2 is a1 =
16, Da1 = 0.6, a2 = 17, Da2 = 0.4 b *: (3.6 + 127) /255×32=16.4, so the distance b1 between the first point b1 of b * and b1 When,
The distance Db2 between the second point b2 of b * and b2 is b1 =
16, Db1 = 0.4, b2 = 17, Db2 = 0.6.

L * a * b *: 33 × 33 × 33 → CMY
L * 2 points (L1, L2) x a * 2 points (a from the LUT
1, a2) × b * 2 points (b1, b2) = CMY values for 8 points are CL1a1b1, CL1a1b2, CL1a2b1, C
L1a2b2, CL2a1b1, CL2a1b2, CL2a2b1, C
L2a2b2, ML1a1b1, ML1a1b2, ML1a2b1, M
L1a2b2, ML2a1b1, ML2a1b2, ML2a2b1, M
L2a2b2, YL1a1b1, YL1a1b2, YL1a2b1, Y
L1a2b2, YL2a1b1, YL2a1b2, YL2a2b1, Y
If L2a2b2, then L * = 57,0, a * = 5.3, b * = 3.
The value of CMY for 6 is obtained by the following equation: C = DL2 × Da2 × Db2 × CL1a1b1 + DL2 × Da2 × Db1 × CL1a1b2 + DL2 × Da1 × Db2 × CL1a2b1 + DL2 × Da1 × Db1 × CL1a2b2 × D1 × D1 × D1 × D1 + DL1 × Da2 × Db1 × CL2a1b2 + DL1 × Da1 × Db2 × CL2a2b1 + DL1 × Da1 × Db1 × CL2a2b2 M = DL2 × Da2 × Db2 × ML1a1b1 × DL2a1 × 1 + DL2 × DL2 × 1d1 + DL1 × DL2 × DL2 × Db1 × DL2 × Db1 × DL2 × Db1 × DL2 × Db1 × DL2 × D2 ML1a2b2 + DL1 × Da2 × Db2 × ML2a1b1 + DL1 × Da2 × Db1 × ML2a1b2 + DL1 × Da1 × Db2 × ML2a2b1 + DL1 × Da1 × Db1 × ML2a2b 2 Y = DL2 × Da2 × Db2 × YL1a1b1 + DL2 × Da2 × Db1 × YL1a1b2 + DL2 × Da1 × Db2 × YL1a2b1 + DL2 × Da1 × Db1 × YL1a2b2 + DL1 × Da2 × Db2 × YL2a1b1 + DL1 × Da2 × Db1 × YL2a1b2 + DL1 × Da1 × Db2 XYL2a2b1 + DL1 x Da1 x Db1 x YL2a2b2.

As described above, 21 points of L * a * b * obtained from the CMY uniform gray patches of the reference conditions are calculated, output values of each CMY color are obtained, and each CMY color shown in FIG. 7 is obtained. Create a gradation correction curve for calibration.

(Step S19) Next, a calibration gradation correction curve for K is created. First, K single color (0, 3
2, 64, 96, 128, 159, 191, 223, 2
55), which is the reference L * obtained in step S11.
Values are Lin1, Lin2, Lin3, Lin4, Lin
5, Lin6, Lin7, Lin8, Lin9.

Next, K single color (0, 32, 64, 96, 1
28, 159, 191, 223, 255), the L * value newly obtained in step S16 is set to Lout1, Lo.
ut2, Lout3, Lout4, Lout5, Lou
Let t6, Lout7, Lout8, and Lout9.

As shown in FIG. 15, the above Lin1 to L
The value of K of the calibration color printer 20 is reproduced from in9 and Lout1 to Lout9 so as to reproduce the lightness data L * obtained from the value of the color system from the maximum density point of the reference K single color to 0. Is calculated from the L * value newly obtained in step S16 to obtain K as shown in FIG.
Create a gradation correction curve for calibration.

This gradation correction curve is actually a white L
* May be different between the standard condition and the newly measured condition, and white (0) should be a curve that is not corrected to match L *. If the minimum brightness of the reference K is smaller than the newly measured minimum brightness of K, the brightness L *
Since it cannot be reproduced, a curve that can be reproduced with the newly calculated minimum brightness of K is used. Further, in this embodiment, the output value is 255 with respect to the input value 255 of the K gradation correction curve, but this is to improve the character reproduction by outputting the solid K image.

As described above, by using the calibration gradation correction curves for each of CMYK, the same output color as the output color in the state of color matching with the output color of the calibration color printer as a reference is output. be able to.

(Steps 20 and 21) Further, the CMYK reference gradation correction curves obtained in steps S14 and S15 are corrected, and C obtained in steps S18 and S19.
A gradation correction curve for each of CMYK for simultaneously performing the correction by the gradation correction curve for each of MYK is created.

For each of CMYK, 0, 12, 25,
38, 51, 64, 76, 89, 102, 115, 12
8, 140, 153, 166, 178, 191, 20
For the 21 input values 4, 217, 229, 242, 255, the output value by the reference gradation correction curve is calculated, and the output value when the output value is input to the calibration gradation correction curve is calculated. Results 0, 12, 25, 38, 5
1, 64, 76, 89, 102, 115, 128, 14
0, 153, 166, 178, 191, 204, 21
A gradation correction curve for simultaneously performing these two corrections is created by obtaining a curve that is an output value for 21 input values of 7, 229, 242, 255.

(Step S22) CMYK as described above
By using each gradation correction curve, the amount of each of CMYK of the image data is corrected by the gradation correction curve and output from the calibration color printer 20.

In the above embodiment, step S2.
0, one gradation correction curve is obtained from the reference gradation correction curve for performing color matching with the printing machine in S21 and the calibration gradation correction curve for making the output color of the reference condition equivalent,
Although it has been explained that the calibration color printer uses the gradation correction curve to output, the standard gradation correction curve for color matching the printing image data of the printing machine with the printing machine is not combined into one. It is also possible to perform the correction and then the correction using the calibration gradation correction curve for making the output color equivalent to the reference condition. However, the processing speed becomes faster with the correction by the gradation correction curve that is put together.

Further, the method of creating the reference gradation correction curve for performing color matching with the printing machine and the calibration gradation correction curve for making the output color of the reference condition equivalent are explained with the same method. The reference gradation correction curve for performing color matching with the machine may be obtained by another method. However,
When the same method is used, each gradation correction curve can be created by the same work, so the operator does not get confused at the time of creation, and since only one program is required, it is easy to provide as a color adjustment method. Yes, the capacity is small when stored in a recording medium such as a hard disk.

Although the gradation correction curve is used to perform color matching with the printing machine, conversion using a CMYK → CMYK four-dimensional LUT or the like obtained from the device color profile used in the color management system has been described. Alternatively, the correction may be performed by the conversion using the four-dimensional LUT of CMYK → CMYK, and then the correction using the calibration gradation correction curve for making the output color equal to the reference condition. good.

In the above description, the method of correcting the difference from the reference condition for one calibration color printer has been described. However, a plurality of calibration color printers are adjusted to one reference calibration color printer. The correction for the correction may be performed by the method using the calibration gradation correction curve of this embodiment.

In addition to the proof color printer,
The printing press may be calibrated in the same manner, or if there are a plurality of printing presses, the correction for adjusting to one reference printing press may be performed by the calibration gradation correction curve of this embodiment. .

As described above, according to the present embodiment, the CMY gray patches that are the reference of the image output device and the CMY color patches that are used for calibration in the image output device are corrected for calibration gradation correction for each CMY color. A curve is created, a K calibration gray level correction curve is obtained from the reference K gray patch and the K gray patch used for calibration, and each CMYK calibration gray level correction curve is used. Is converted and output from the proof color printer 20, it is possible to keep the gray of CMY superimposed and the color tone of the entire image constant.

Note that program software is created so that the computer executes the steps of the color adjusting method according to the present embodiment shown in FIG. 1, and the program software is stored in a computer-readable recording medium. be able to.

[0086]

As described above, according to the color adjusting method of the present invention, the calibration is performed and the image output device outputs, and C
It is possible to provide a color adjusting method capable of keeping the gray of MY superimposed and the color tone of the entire image constant, a program for executing the color adjusting method, and a recording medium storing the program.

[Brief description of drawings]

FIG. 1 is a flowchart showing a procedure of a color adjusting method including an example of an output color calibrating method of a calibrating color printer according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of an LUT that converts CMY color values into color system values L * a * b * in the present embodiment.

FIG. 3 is a diagram showing an example of a color patch image for measuring the CMY color values in the present embodiment.

FIG. 4 is a diagram showing a distribution of points to be interpolated with sample points on a locus according to CMY color values and color system values in the present embodiment.

FIG. 5 is a diagram showing the order of interpolation processing when converting a CMY color combination into a color system value in the present embodiment.

FIG. 6 shows color system values L * a * b * in the present embodiment.
FIG. 3 is an explanatory diagram of an LUT for converting CMY to CMY color values.

7 (a), (b), and (c) are diagrams showing gradation correction curves of respective colors which are output values for respective input values of Y, M, and C in the present embodiment.

FIG. 8 is a coordinate diagram showing a target value T ′ in coordinates of C and M color systems in the present embodiment.

FIG. 9 is a coordinate diagram showing a target value T at coordinates of a combination of C and M colors in the present embodiment.

FIG. 10 is a coordinate diagram of a convergence calculation process for estimating a target value T at coordinates of a combination of C and M colors in the present embodiment.

FIG. 11 is a coordinate diagram of a convergence calculation process for estimating a target value T ′ in the coordinates of the C and M color systems in the present embodiment.

FIG. 12 is a diagram showing the target value T ′ in the coordinates of the color systems of C and M when the target value T ′ is outside the color reproduction range in the present embodiment.

FIG. 13 is a coordinate diagram showing the target value T ′ in the coordinates of the color systems of C and M when the target value T ′ is outside the color reproduction range in the present embodiment. It is a coordinate diagram which shows having moved to within the range.

FIG. 14 shows C and M when a target value T ′ outside the color reproduction range is moved into the color reproduction range in the present embodiment.
It is a figure which shows the target value T in the coordinate of the color combination of.

FIG. 15 is a diagram showing 9-level L * of K single color of the printing machine and 9-level L * of K single color of the calibration color printer at the K gradation level in the present embodiment.

FIG. 16 is a diagram showing a K gradation correction curve which is an output value for each input value of K in the present embodiment.

FIG. 17 is a diagram showing an example of the configuration of the device according to the embodiment of the present invention.

[Explanation of symbols]

10 PC 11 Arithmetic processing unit 12 First memory 13 Second memory 14 Interface 15 Display 16 Operation part 17 Internal bus 20 Color printer for calibration 30 bus

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04N 1/46 B41J 3/00 BF term (reference) 2C262 AA29 AB11 BA09 BA16 BA20 BB03 BC09 BC10 BC19 5B057 AA11 BA02 CA01 CA08 CA12 CA16 CB01 CB08 CB12 CB16 CC01 CE17 CE18 CH07 CH08 5C077 LL04 LL19 MM27 MP08 PP15 PP33 PP36 PP37 PP43 PQ12 PQ23 TT02 5C079 HB02 HB03 HB08 LA03 LA12 LA21 LA28 LB01 MA04 MA10 MA11 NA03 PA03

Claims (6)

[Claims] 1. A color adjusting method for adjusting a gray or overall color tone of a color image output by a color image output device to a reference gray or overall color tone, wherein the three basic colors of the color image output device are used. C, M based on outputs of a plurality of combinations of (CMY) from the minimum value to the maximum value and a plurality of gray colors of three basic colors (CMY) in the color image output device serving as a reference. , Y for each gradation correction curve and correcting the image data of the color image output by the color image output device. 2. Based on a plurality of gray outputs of a single black color (K) in the color image output device and a plurality of gray outputs of a single black color (K) in the reference color image output device. The color according to claim 1, further comprising a step of obtaining a K gradation correction curve so as to reproduce the lightness of the reference gray output, and correcting the image data of the color image output by the color image output device. Adjustment method. 3. The output for a plurality of combinations of the minimum value to the maximum value of the three basic colors (CMY) is performed by a plurality of combinations from the minimum value to the maximum value of the three basic colors (CMY). The color adjusting method according to claim 1, wherein all the combinations of C, M, and Y obtained by dividing and equally dividing are obtained. 4. The output of a plurality of grays by the three basic colors (CMY) is a uniform output of the three basic colors (CMY).
The color adjustment method according to claim 1 or 3, according to. 5. A program for causing a computer to execute the color adjusting method according to any one of claims 1 to 4. 6. A computer-readable recording medium that stores the program according to claim 5.