JP2003169219A - Method and apparatus for calibration - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a calibration apparatus that can correct an optional color in a way of not causing the correction effect to other colors. <P>SOLUTION: A gray gradation path output section 2 transfers gray gradation patch data produced by a gray gradation patch generating section 1 to a printer 3, which prints out a gray gradation patch print 4. A colorimetric unit 5 measures the color of the print 4, and a gray gradation colorimetric section 6 gives the result to a multi-dimensional LUT adjustment section 7. The multi- dimensional LUT adjustment section 7 first obtains a sensitivity characteristic matrix denoting a rate of a change in each element of a measurement value color space with respect to a change in each element in an output color space, then obtains a difference between measured data and base data in an initial state of the multi-dimensional LUT on the basis of a cross-reference between the gray gradation patch data and colorimetric data of the patch to obtain a change in the colorimetric value in the color space. The multi-dimensional LUT adjustment section 7 obtains grating point data in the output color space on the basis of the change amount and the sensitivity characteristic matrix to correct the multi-dimensional LUT. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a calibration device and a calibration method for correcting a color conversion parameter of a color conversion device that performs color conversion using a multi-dimensional lookup table in an output device such as a color printer. Is.

[0002]

2. Description of the Related Art In an output device such as a color printer, an input color space is generally different from an output color space used for print processing, and therefore a color conversion device for converting the color space is indispensable. For this color space conversion, a one-dimensional look-up table (especially if the final stage of color conversion is To
ne Representation Curve, which may also be referred to as TRC for short, is also used in the following description), a multi-dimensional lookup table having dimensions equal to the input color space (hereinafter abbreviated as multi-dimensional LUT), input value An algorithm such as a matrix operation that obtains an output value by multiplying by a first-order term, a higher-order term, a constant, or the like is used. In general, after performing multidimensional LUT processing or matrix operation, TR for each element of the output color space
The method of performing C processing is often used. Especially recently
Processing combining multidimensional LUT processing and TRC processing is becoming mainstream.

Generally, the color conversion parameters used in these processes are adjusted in accordance with the characteristics of each output device when the output device is manufactured, so that the correct color output can be obtained immediately after the manufacturing. However, if time has passed since the device was manufactured,
The characteristics of the output device change. Therefore, the color conversion parameter and the characteristics of the output device do not match, and correct color output cannot be obtained. In addition, depending on the output device, the characteristics of the output device may vary depending on the elapsed time after the power is turned on and the number of output sheets, which also causes the output of the correct color to not be obtained.

When colors are not output correctly, a particular problem is that the densities of color materials such as cyan, magenta, yellow, and black do not increase gently in proportion to the input value, but suddenly increase at certain points. There are problems that the change in that part looks like an outline, and that the color changes in a region such as gray where the color change is particularly noticeable. To solve this problem,
It is necessary to readjust the color conversion parameters before using the output device so that the color conversion parameters match the output characteristics during use. This process is called calibration.

As a specific method of calibration, first, a color pattern (generally called a patch) determined by an output device is output, and the color is measured by a colorimeter or a scanner whose conversion characteristic is known. Measure with an input device. Then, it is represented by a numerical value in a device-independent color space such as L ^* a ^* b ^* or L ^* u ^* v ^* , and the readjustment is performed by recalculating or correcting the color conversion parameter based on the numerical value. The method is taken.

Conventionally, such a calibration process has been performed by adjusting a color conversion parameter in the TRC process. For example, Japanese Patent No. 2738413
In the method described in the publication, in order to gradually increase the gradation of the color material, measured values of a plurality of density patches of a single color material are used to perform TRC processing for each channel. Had adjusted the color conversion parameters of. Further, in the methods described in JP-A-2-76760, JP-A-7-115556, and JP-A-2000-278545, measurement values of gray patches of a plurality of densities are used for each channel. Gray is corrected by adjusting the color conversion parameter in the TRC processing.

However, in both cases, since color correction is performed by adjusting the color conversion parameters during TRC processing, when it is attempted to perform grayscale correction and grayscale correction for a single color material at the same time, both The correction amounts affect each other, and it is difficult to achieve both the color material single-color gradation correction and the gray correction. That is, in the case of gray, in addition to black single color, other color materials are mixed to perform color reproduction, and when gradation correction of a certain single color is performed, gray is colored. On the contrary, when the gradation correction of each color is performed according to gray, the gradation of each single color changes, and the color reproducibility deteriorates. Therefore, it is difficult to achieve both the grayscale correction of a single color and the correction of gray only by adjusting the color conversion parameter in the TRC processing. Such a problem is not limited to gray, and is a problem similarly occurring when correction is performed for a certain color of secondary color or higher.

[0008]

[Patent Document 1] Japanese Patent No. 2738413

[Patent Document 2] Japanese Patent Application Laid-Open No. 2-76760

[Patent Document 3] JP-A-7-115556

[Patent Document 4] Japanese Patent Laid-Open No. 2000-278545

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and performs correction for an arbitrary color and correction so that the influence of the correction does not affect other colors. An object of the present invention is to provide a calibration device and a calibration method that can perform the calibration. For example, a calibration device that can perform a calibration so that a good output result can be obtained even when the gradation correction of a single color material and the correction of a specific color range of secondary colors such as gray are simultaneously performed. And to provide a calibration method.

[0010]

In the calibration apparatus and the calibration method according to the present invention, the color conversion parameters are corrected by adjusting the multidimensional LUT. According to the first configuration of the present invention, in the color conversion processing using the multidimensional LUT, the calibration patch output from the output device is subjected to colorimetry, and the multidimensional L is calculated based on the colorimetric value.
It is characterized by adjusting the UT. By adjusting the multi-dimensional LUT in this way, whether the color material is a single color or a color in the color range of secondary colors such as gray,
Partial adjustment is possible. For example, gray can be a tertiary color or a quaternary color, but when the TRC parameters are adjusted as in the conventional case, all the individual colors of each color material change. However, according to the present invention, since only the gray area in the multi-dimensional LUT is adjusted, there is little or no effect on other color ranges. Further, for example, even when the gradation correction of a single color material and the correction of a specific color range of secondary colors such as gray are simultaneously performed, good correction can be performed for each color range. Therefore, by performing calibration with the calibration device and the calibration method of the present invention, it is possible to always obtain an image in which accurate color reproduction is performed from the output device.

In the second configuration of the present invention, the multidimensional L
In the color conversion process combining UT process and TRC,
It is characterized in that gradation correction of a single color of a color material is performed by adjusting a TRC parameter, and correction of a color area of a secondary color such as gray is performed by adjusting a multidimensional LUT. In this case, when the gradation correction of a single color material and the correction of a color region of a secondary color such as gray are performed, the TRC parameters are adjusted first, and then the adjusted TRC parameters are used. It is advisable to adjust the multi-dimensional LUT for color regions of secondary colors and above. Also in this second configuration, since the color adjustment of the color range of secondary colors such as gray can be performed by the partial adjustment for the multidimensional LUT, is there any influence on other color ranges? Or small. Therefore, the color range to be adjusted can be satisfactorily corrected without affecting other colors, and an image whose color is reproduced accurately can be always obtained from the output device.

When adjusting a multi-dimensional LUT, first, which color is to be arranged in a patch is determined according to a parameter to be partially adjusted, and the patch is used for calibration. Therefore, the patch range can be limited to the color range to be adjusted, and the calibration can be performed with a small number of patches. After that, a new verification patch is created according to the adjusted parameter, and the verification accuracy is measured by measuring the verification patch. If sufficient calibration accuracy is not obtained, the data of the verification patch is also used as the data for calibration, and the calibration is performed again. This process can be configured to be repeated until sufficient calibration accuracy is obtained. As a result, sufficient accuracy can be obtained with the minimum required number of patches.

[0013]

FIG. 1 is a block diagram showing a first embodiment of the present invention. In the figure, 1 is a gray gradation patch generation unit, 2 is a gray gradation patch output unit, 3 is a printer, 4 is a gray gradation patch print, 5 is a colorimeter, 6 is a gray gradation patch color measurement unit, and 7 is a colorimeter. Is a multi-dimensional LUT adjustment unit. In the first embodiment, description will be made assuming that calibration is performed for gray. Of course, other colors can be similarly calibrated.

The gray gradation patch generator 1 is a multidimensional LU.
Gray tone patch data for calibrating T (gray tone patch data) is generated. This gray gradation patch is a size on the image obtained by converting the value of the input color included in the gray area to be adjusted among the items of the multidimensional LUT into the color material color space by the multidimensional LUT before correction. It is the image data arranged in this way. Here, the color material color space is assumed to be a C (cyan) M (magenta) Y (yellow) K (black) color space, and the gray gradation patch generation unit 1
Generates gray tone patch data in the CMYK color space. The gray gradation patch output unit 2 converts the gray gradation patch data generated by the gray gradation patch generation unit 1 into an image that becomes a gray gradation patch, and sends it to the output device (here, the printer 3).

The printer 3 is one of the output devices, and forms an image using, for example, color materials (ink, toner, etc.) of three colors of C, M, Y or four colors added with K. Usually, the printer 3 has a color conversion device that performs color conversion from the RGB color space or the L ^* a ^* b ^* color space to the CMY color space or the CMYK color space, which is the color material color space. It is assumed that the conversion device performs color conversion using a multidimensional LUT. For example, if the input image signal is a signal in the L ^* a ^* b ^* color space, a three-dimensional LUT is used. When performing calibration, the gray gradation patch image delivered from the gray gradation patch output unit 2 is printed by the multidimensional LUT without conversion, and the gray gradation patch print 4 is obtained.

The gray gradation patch colorimetric section 6 includes a printer 3
Gray gradation patch print 4 printed by
Numerical value measured by the colorimeter 5 and independent of the device, eg
If L ^*a^*b^*Multi-dimensional LU for colorimetric values expressed in color space
It is sent to the T adjustment unit 7.

The multi-dimensional LUT adjusting unit 7 determines the colorimetric value in the L ^* a ^* b ^* color space of the gray gradation patch print 4 sent from the gray gradation patch colorimetric unit 6 and the colorimetric value thereof. Color values in the corresponding color material color space (that is, gray gradation patch data generated by the gray gradation patch generation unit 1)
Find the correspondence with. Then, the adjustment amount of the multidimensional LUT is calculated from the correspondence relationship. For example, when the input color space of the multi-dimensional LUT is the L ^* a ^* b ^* color space, gray adjustment involves adjusting the output values of CMY or CMYK at grid points that satisfy the condition of a ^* = b ^* = 0. do it.

A grid point is a point corresponding to one item of a multidimensional LUT when each item of the multidimensional LUT is considered as a point in a space having the same number of dimensions. This space can be regarded as the input color space. On the other hand, multidimensional L
The value of each item of UT can be regarded as the value of the output color space. Therefore, one item of the multidimensional LUT, that is, a grid point is one point in the input color space, and at the same time, it can be regarded as a mapping from the input color space to the output color space.

The multidimensional LU in the multidimensional LUT adjusting section 7
When calculating the adjustment amount of T, first the parameters of the multidimensional LUT
Color material at the time of creating the data (herein called the initial state)
Color space and L^*a^*b^*It is necessary to seek the correspondence of the color space
It Therefore, I used it when I created a multi-dimensional LUT,
Color material color space and L^*a^*b^*Data showing the correspondence of the color space
I have to get it. Multidimensional LU in the initial state
The patch data used when the parameters of T were created
If there is, it is the colorant color space and L in the initial state.^*a
^*b^*Color material color space because it shows the correspondence of color space
And L^*a^*b^*It can be used as data showing the correspondence of color spaces
Wear. In addition, the input of the multi-dimensional LUT is device-independent.
If it is a color space, the color space and L^*a^*b
^*It is thought that it indicates the correspondence of the color space, so before adjustment
L using the multidimensional LUT of^*a^*b ^*Value in colorant color space
By converting the color material color space and L^*a^*b^*Color sky
It is possible to create data indicating the correspondence between the two.

However, the color data of the gray gradation patch is actually
Data is not always included in this correspondence data
Therefore, in that case, least squares method or neural network
The initial state of gray gradation patch data
It is necessary to predict the correspondence relationship in. Like this
The color space and L in the initial state and at the time of correction.^*a ^*
b^*Since the correspondence of the color space is obtained, L at both time points^*
a^*b^*By taking the difference between the values, the initial state and the
L the color change^*a^*b^*Can be calculated as color difference
it can.

To correct the multi-dimensional lookup table
In addition, the same L
^*a^*b^*In the color space where the color value is obtained
The amount of change must be calculated. So, the first time
Color material color space and L^*a ^*b^*From the correspondence of the color space,
L^*a^*b^*Ratio of change in color material color space to change in color value
Calculate the sum. This proportion is given in matrix form, but the color
Since the type of material is the same, there are
It is considered to be an amount that does not change at all. So this
L calculated from the matrix first^*a^*b^*Multiply with color difference
The amount of change in the color material color space can be calculated by
It Finally, using this variation, the multidimensional LUT parameters
It is possible to correct the gray gradation by correcting
it can.

2 and 3 are flow charts showing a first example of the operation according to the first embodiment of the present invention.
Here, the case where the printer 3 uses three colors of C, M, and Y as color materials will be described. First, in S21, base data is obtained. The base data is the actual data in the above-mentioned initial state, and is C after correction in S25 described later.
It is data required when predicting the MY value. In this example, the base data is the CMY value and the corresponding L ^* a.
^Represented as a list of ^* b ^* value pairs. Here, it is assumed that the patch values measured when the parameters of the multidimensional LUT are first created are used as the base data.

In S22, the gray gradation patch generation unit 1 generates gray gradation patch data. The gradation patch data is an array of CMY output data corresponding to the gray area to be corrected in the multidimensional LUT, that is, the grid points of a ^* = b ^* = 0.

In S23, the gray gradation patch output unit 2 generates a patch image from the gray gradation patch data generated by the gray gradation patch generation unit 1 in S22. The patch image is one in which the colors of patch data are regularly arranged in the image with a fixed size. Then, the generated patch image is printed on the printer 3 to obtain a gray gradation patch print 4.

In step S24, the data measured by the user on the gray tone patch print 4 with the colorimeter 5 is read by the gray tone patch colorimetric unit 6. This data is L ^* a ^* b
^* Measured in color space.

In step S25, the multidimensional LUT adjustment unit 7
Is the L ^* a ^* b read by the gray gradation patch color measurement unit 6.
^* Data and CM generated by the gray gradation patch generator 1
The corrected CMY value is obtained for each grid point from the Y gray gradation patch data. By setting the obtained corrected CMY values at each grid point of the multidimensional LUT,
Calibration in gray can be done. Thereafter, the printer 3 uses the corrected multidimensional LUT in the color conversion device to convert the C from the L ^* a ^* b ^* color space.
If color conversion processing to the MY color space is performed, accurate color conversion can be performed.

Next, a method of calculating the corrected CMY values in S25 will be described with reference to the flowchart of FIG. In S31, the grayscale patch data C
The L ^* a ^* b ^* value is calculated from the MY value using the base data to obtain the initial L ^* a ^* b ^* value (L ^* o, a ^* o, b ^* o). This calculation can be performed, for example, by the color transfer characteristic prediction method described in Japanese Patent Laid-Open No. 10-262157.

In step S32, the base data is used to detect
Degree characteristics (L for changes in CMY values ^*a^*b^*Change in value
Quantity). Therefore, the sensitivity characteristic takes the form of a matrix. this
Sensitivity characteristics are also disclosed in, for example, Japanese Patent Laid-Open No. 10-262157.
It can be determined by the method described.

Since the value of the sensitivity characteristic differs depending on the value of the L ^* a ^* b ^* / CMY coordinates, it is necessary to determine at which coordinate the sensitivity characteristic is calculated. For example, L ^* a ^* b ^* values (L ^* o, a ^* o, b) in the initial state obtained in S31
^* o), L ^* a measured from gray gradation patch print 4
^The sensitivity characteristic can be calculated at the ^* b ^* measured value (L ^* p, a ^* p, b ^* p), or the midpoint between the two.

The sensitivity characteristic thus obtained has the following matrix form.

[Equation 1]

In S33, the corrected CMY value is obtained using the sensitivity characteristic matrix obtained in S32.

[Equation 2] Here, (Co, Mo, Yo) is the CMY value of the corrected multidimensional table, and (L ^* p, a ^* p, b ^* p) is L ^* a ^* measured from the gray gradation patch print 4 ^. b ^* measured value,
(Cp, Mp, Yp) is the CMY value of the gray gradation patch.

Here, the inverse matrix of the sensitivity characteristic matrix is used to obtain the CMY values from the L ^* a ^* b ^* values, but in some cases, the inverse matrix is not obtained and (Co, Mo, Yo) is changed. A method may be used in which the value on the left side of the following equation is searched for, or the absolute value of the vector on the left side is regarded as an error and a value that minimizes this is searched for.

[Equation 3]

The CMY values after correction can be calculated by performing the above processing for all grid points that need correction. By replacing the CMY values at the grid points with the CMY values, the multidimensional LUT can be corrected. After the correction processing of the multidimensional LUT is performed in this manner, the smoothing processing may be performed again on the whole or a part of the multidimensional LUT to suppress the abrupt change of the color conversion parameter.

In order to perform the gray correction in a wider area, the grid points for generating the gray gradation patch data in S22 are not limited to the area where a ^* = b ^* = 0 but the surrounding area, that is, a. Both ^* and b ^* may be extended to a region close to 0.

Further, in this example, the patch values measured when the parameters of the multidimensional LUT were first created were used as the base data, but a list of arbitrary L ^* a ^* b ^* values is used before the correction. Converted by LUT and L ^* a ^* b ^* value and C
The base data may be obtained by finding a pair of MY values. Furthermore, a value obtained by newly generating, printing, and measuring another patch may be used as the base data. However, when another patch is newly generated as the base data, this can be used for the calculation of the sensitivity characteristic, but it is unsuitable for use in the calculation of the L ^* a ^* b ^* value in the initial state. . In this case, in order to calculate the initial L ^* a ^* b ^* value, the patch value measured when the parameters of the multidimensional LUT were first created or the list of arbitrary L ^* a ^* b ^* values was corrected. The value obtained by conversion with the previous multi-dimensional LUT must be used as base data.

When a new patch is generated as the base data, the patch can be dynamically generated in accordance with the color region related to the parameter to be adjusted in the multidimensional LUT. As a result, the number of patches can be greatly reduced as compared with the case where patches are created over the entire color region of the output device. It is also possible to obtain sufficient accuracy with the minimum required number of patches by repeating the method of performing calibration with a small number of patches at the beginning and adding patches when sufficient accuracy is not obtained. it can.

Further, in order to eliminate the influence of variations in the output color due to the print position, the patches arranged on the paper may be rearranged appropriately.

Further, the color area to be corrected using the multidimensional LUT is not necessarily limited to the gray area, and various colors such as skin color can be corrected.

Further, the input color space and the output color space need not be limited to the L ^* a ^* b ^* color space and the CMY color space, respectively.
It is possible to use color spaces such as Y, XYZ, L ^* u ^* v ^* , and YCbCr, and RGB as the output color space.
It is also possible to use a color space such as or YCbCr. However, when using another input color space, it is necessary to know which region in the color space corresponds to gray (or a color to be adjusted by the multidimensional LUT). When the input color space is RGB, R is generally
Since the region where = B = G can be regarded as a gray region, the correction may be performed at those grid points or the peripheral region thereof.

FIG. 4 is a flowchart showing a second example of the operation according to the first embodiment of the present invention. In addition,
FIG. 4 shows the processing in S25 of FIG. 2, and here FIG. 2 is shared with the above-mentioned first example.
The drawing corresponding to is omitted. In this second example, a case where the printer 3 uses four colors of C, M, Y, and K as color materials will be described. Therefore, in the correction of the gray area, it is necessary to correct not only CMY but also the K component.

In S21 of FIG. 2, first, base data is obtained. The base data is the actual data in the above-mentioned initial state, and is the data required when predicting the corrected CMYK values in S25 described later. In this example, the base data is CMYK values and the corresponding L ^* a ^* b ^*.
Expressed as a list of value pairs. Here, it is assumed that the patch values measured when the parameters of the multidimensional LUT are first created are used as the base data.

In S22, the gray gradation patch generator 1 generates gray gradation patch data. This gradation patch data is an array of CMYK output data corresponding to a gray area to be corrected in the multidimensional LUT, that is, a grid point of a ^* = b ^* = 0.

In S23, the gray gradation patch output unit 2 generates a patch image from the gray gradation patch data generated by the gray gradation patch generation unit 1 in S22. The patch image is one in which the colors of patch data are regularly arranged in the image with a fixed size. Then, the generated patch image is printed on the printer 3 to obtain a gray gradation patch print 4.

In step S24, the gray gradation patch color measuring unit 6 reads the data measured by the user on the gray gradation patch print 4 with the colorimeter 5. This data is L ^* a ^* b
^* Measured in color space.

In S25, the multidimensional LUT adjustment unit 7
Is the L ^* a ^* b read by the gray gradation patch color measurement unit 6.
^* Data and CM generated by the gray gradation patch generator 1
Corrected CMYK from YK gray gradation patch data
Find the value for each grid point. CMYK after correction calculated
Calibration in gray can be done by setting a value at each grid point of the multi-dimensional LUT. After that, in the printer 3, if the color conversion apparatus performs color conversion processing from the L ^* a ^* b ^* color space to the CMYK color space using the corrected multi-dimensional LUT, accurate color conversion can be performed.

Next, in S25, the corrected CMYK values are
For the calculation method, refer to the flowchart shown in FIG.
It demonstrates using. In S41, the gray gradation patch
L from the CMYK values of the data using the base data^*a^*b
^*Calculate the value, L in the initial state ^*a^*b^*Value (L^*o, a
^*o, b^*o) get. This calculation is performed, for example, in Japanese Patent Laid-Open No. 10-2
Color transfer characteristic prediction method described in Japanese Patent No. 62157
Can be done by

In step S42, the sensitivity characteristic (the amount of change in L ^* a ^* b ^* value with respect to the change in CMYK value) is obtained using the base data. Therefore, the sensitivity characteristic takes the form of a matrix. This sensitivity characteristic can also be obtained by the method described in, for example, Japanese Patent Laid-Open No. 10-262157.

Since the value of the sensitivity characteristic differs depending on the value of the L ^* a ^* b ^* / CMYK coordinates, it is necessary to determine at which coordinate the sensitivity characteristic is calculated. For example, the L ^* a ^* b ^* value (L ^* o, a ^* o, in the initial state obtained in S41)
b ^* o), L ^* measured from gray gradation patch print 4
The sensitivity characteristic can be calculated at the a ^* b ^* measured value (L ^* p, a ^* p, b ^* p) or the midpoint between the two. The sensitivity characteristic thus obtained has the form of the following matrix.

[Equation 4]

In S43, the corrected K value is calculated as follows using the amount of change in the L ^* value with respect to the K value in the sensitivity characteristic.

[Equation 5] Here, Ko is the K value of the corrected multidimensional table,
Kp is the K value of the gray gradation patch data, L ^* o is the L ^* value in the initial state, and L ^* p is the L ^* measurement value measured from the gray gradation patch print 4.

In step S44, the corrected CMY value is obtained as follows using the sensitivity characteristic.

[Equation 6] Here, (Co, Mo, Yo) is the CMY value of the corrected multidimensional table, (Cp, Mp, Yp) is the CMY value of the gray gradation patch data, and (L ^* o, a ^* o, b ^*). o) is the L ^* a ^* b ^* value in the initial state, and (L ^* p, a ^* p, b ^* p) is the L ^* a ^* b ^* measurement value measured from the gray gradation patch print 4.

Instead of calculating the inverse matrix here,
Similar to the first operation example in the above-described first embodiment, a method of searching for (Co, Mo, Yo) that satisfies the above expression or minimizes the error may be adopted. .

By performing the above processing for all the grid points that need to be corrected, the corrected CMYK values can be calculated. This CMYK value is the grid point C
By replacing the MYK values, it is possible to correct the multidimensional LUT. After the correction processing of the multidimensional LUT is performed in this manner, the smoothing processing may be performed again on the whole or a part of the multidimensional LUT to suppress the abrupt change of the color conversion parameter.

In order to perform the gray correction in a wider area, the grid points for generating the gray gradation patch data in S22 are not limited to the area where a ^* = b ^* = 0 but the surrounding area, that is, a ^*. Both b and b ^* may be extended to a region close to 0.

Further, in this operation example, the patch values measured when the parameters of the multidimensional LUT are first created are used as the base data, but a list of arbitrary L ^* a ^* b ^* values is used as a base data before correction. It is also possible to obtain a pair of L ^* a ^* b ^* value and CMYK value by converting with the dimension LUT and use as the base data.
Furthermore, another patch is newly generated as base data,
A value obtained by printing and measuring may be used. However, when another patch is newly generated as base data,
This can be used for calculation of the sensitivity characteristic, but it is unsuitable for calculation of the L ^* a ^* b ^* value in the initial state. In this case, in order to calculate the initial L ^* a ^* b ^* value, the patch value measured when the parameters of the multidimensional LUT were first created or the list of arbitrary L ^* a ^* b ^* values was corrected. The value obtained by conversion with the previous multi-dimensional LUT must be used as base data.

When a patch is newly generated as the base data, the patch can be dynamically generated in accordance with the color area related to the parameter to be adjusted in the multidimensional LUT. As a result, the number of patches can be greatly reduced as compared with the case where patches are created over the entire color region of the output device. It is also possible to obtain sufficient accuracy with the minimum required number of patches by repeating the method of performing calibration with a small number of patches at the beginning and adding patches when sufficient accuracy is not obtained. it can.

Further, in order to eliminate the influence of the variation of the output color due to the print position, the patches may be rearranged appropriately to form one patch image. Furthermore, a multidimensional LUT
The color area to be corrected using is not necessarily limited to the gray area, and it is possible to correct any color area such as a skin color.

Also, regarding the input color space, L ^* a ^* b ^*
The color space is not limited to RGB, CMY, XYZ, L ^* u ^* v ^* , YCbC as an input color space.
It is also possible to use a color space such as r. However,
When using another input color space, it is necessary to know which region in the color space corresponds to gray (or a color to be adjusted by the multidimensional LUT). When the input color space is RGB, generally R = B =
Since the G region can be regarded as a gray region, the correction may be performed at those grid points or the peripheral region thereof.

FIG. 5 is a block diagram showing a second embodiment of the present invention. The same parts as those in FIG. 1 are denoted by the same reference numerals, and redundant description may be omitted. Reference numeral 8 is a pure color gradation patch generation unit, 9 is a pure color gradation patch output unit, 10 is a pure color gradation patch print, 11 is a pure color gradation patch color measurement unit, 1
2 is a TRC adjustment unit. In this second embodiment,
The printer 3 serves as a color conversion device together with the multi-dimensional LUT.
An example is shown in which color conversion is performed using RC, TRC adjustment is performed for pure colors, and multidimensional LUT adjustment is performed for secondary or higher colors.

The pure color gradation patch generator 8 generates gradation patch data (pure color gradation patch data) of a single color material for TRC adjustment. This pure color gradation patch has color values of a plurality of densities, for example, C (cyan), M (magenta), Y (yellow), and K (black) of a color material used in the printer 3, on the image. The image data is arranged in a size. The pure color gradation patch output unit 9 converts the pure color gradation patch data generated by the pure color gradation patch generation unit 8 into an image that becomes a pure color gradation patch, and outputs the output device (here, the printer 3).
Send to.

The printer 3 is one of the output devices, and forms an image using, for example, color materials (ink, toner, etc.) of three colors of C, M, Y or four colors added with K. In the second embodiment, the printer 3 is assumed to perform color conversion from the L ^* a ^* b ^* color space to the CMY color space of the printer as a color conversion device, and for that purpose, one three-dimensional LUT is used.
(Hereinafter, referred to as a multidimensional LUT) and an independent TRC for each color of CMY or CMYK to be processed thereafter. When performing the calibration, the pure color gradation patch image and the gray gradation patch image transferred from the pure color gradation patch output unit 9 and the gray gradation patch output unit 2 are not converted by the multidimensional LUT. Print to obtain a pure color gradation patch print 10 and a gray gradation patch print 4.

The pure color gradation patch colorimetric section 11 includes the printer 3
Pure color gradation patch print 10 printed by
Numerical value measured by the colorimeter 5 and independent of the device, eg
If L ^*a^*b^*TRC adjustment of colorimetric values by expressing in color space
Send to department 12.

The TRC adjusting unit 12 corresponds to the colorimetric value in the L ^* a ^* b ^* color space of the pure color gradation patch print 10 sent from the pure color gradation patch colorimetric unit 11 and the colorimetric value. The correspondence with the color value in the color material color space (that is, the pure color gradation patch data generated by the pure color gradation patch generation unit 8) is obtained. Then, the TRC parameters are calculated from the correspondence.

The gray gradation patch generation unit 1, the gray gradation patch output unit 2, and the gray gradation patch color measurement unit 6 are the same as those in the first embodiment. That is, the gray gradation patch generation unit 1 generates gray gradation patch data for multidimensional LUT adjustment. Then, in the gray gradation patch output unit 2, the gray gradation patch data is imaged and sent to the printer 3, and the printer 3 outputs the gray gradation patch print 4. The gray gradation patch is a multi-dimensional LUT and a T before the correction of the input color value included in the gray area to be adjusted among the items of the multi-dimensional LUT.
The image data is converted into a color material color space by RC and arranged in a certain size on the image. Gray gradation patch color measurement unit 6
Is a multi-dimensional colorimetric value obtained by measuring the grayscale patch print 4 printed by the printer 3 with a colorimeter 5 and expressing it in a device-independent numerical value, for example, L ^* a ^* b ^* color space. It is sent to the LUT adjusting unit 7.

The multi-dimensional LUT adjusting unit 7 determines the colorimetric value in the L ^* a ^* b ^* color space of the gray gradation patch print 4 sent from the gray gradation patch colorimetric unit 6 and the colorimetric value thereof. Color values in the corresponding color material color space (that is, gray gradation patch data generated by the gray gradation patch generation unit 1)
Find the correspondence with. Then, the adjustment amount of the multidimensional LUT is calculated from the correspondence relationship.

Multidimensional LU in multidimensional LUT adjusting unit 7
When calculating the adjustment amount of T, it is necessary to find the correspondence between the color material color space and the L ^* a ^* b ^* color space in the initial state, as in the first embodiment described above. Similar to the first embodiment, if there is patch data used when creating the color conversion parameters of the multidimensional LUT, it can be used,
If the input of the multi-dimensional LUT is a device-independent color space, L ^* a ^* b is calculated using the LUT and TRC before correction.
^By converting the ^* value into the color material color space, it is possible to create data indicating the correspondence between the color material color space and the L ^* a ^* b ^* color space.

As in the first embodiment, the difference between the values in the L ^* a ^* b ^* color space in the initial state and at the time of correction is also obtained. As a result, the change in color between the initial state and the time of correction can be obtained as the L ^* a ^* b ^* color difference.

Next, assuming that the same L ^* a ^* b ^* color value is obtained in the initial state and at the time of correction, the amount of change in the color material color space is obtained. In the second embodiment, Since there is a TRC after the multidimensional LUT, the multidimensional LU
The correction amount of T must be a value before conversion by TRC. Therefore, in the correspondence data of the color material color space in the initial state and the L ^* a ^* b ^* color space, the TR after adjusting the color material color space data by the TRC adjustment unit 12 is performed.
The inverse conversion by C is performed to convert the color value before conversion by TRC. Then, from this correspondence data, L ^* a ^*
b ^* Calculate a matrix that represents the ratio of the change in the color material color space to the change in the color value. The calculation method is the same as in the first embodiment described above. Finally, the amount of change in the color material color space can be obtained by multiplying this matrix by the L ^* a ^* b ^* color difference described above. Then, the multi-dimensional LUT parameter may be corrected using the calculated change amount.

6 to 8 show a second embodiment of the present invention.
6 is a flowchart showing a first operation example in the embodiment.
It Here, the printer 3 is cyan, magenta, and yellow.
An image is formed using the three color materials. Well
In addition, here, by adjusting the TRC, gradation compensation of a single color material can be performed.
Of the multi-dimensional LUT in the gray area, that is,
a ^*= B^*CMY output of grid points satisfying the condition of = 0
Explains the case of correcting gray by adjusting the value
Reveal

First, in S51 of FIG. 6, base data is obtained. The base data is TRC in S55 and S59.
And actual data required when calculating a correction value of a multidimensional LUT, and is represented as a list of pairs of CMY values and corresponding L ^* a ^* b ^* values. Here, the value of the patch measured when the multidimensional LUT parameter is first created is used as the base data.

In S52, the pure color gradation patch generation unit 8
Generates pure color gradation patch data for each color of CMY. This gradation patch data is composed of a plurality of CMY pure colors having different predetermined densities.

In S53, the pure color gradation patch output unit 9
Generates a patch image from the pure color gradation patch data generated by the pure color gradation patch generation unit 8. The patch image is one in which the colors of patch data are regularly arranged in the image with a fixed size. Then, the pure color gradation patch output unit 9 sends the patch image to the printer 3, and the printer 3 prints the patch image on paper to obtain a pure color gradation patch print 10.

In S54, the pure color gradation patch colorimetry unit 11 reads the data measured by the user on the pure color gradation patch print 10 with the colorimeter 5. This data is L ^* a ^* b
^* Measured in color space.

In S55, the TRC adjusting section 12 sets L ^* a ^{* of the} data read by the pure color gradation patch color measuring section 11 ^.
The TRC parameter is recalculated from the b ^* value and the CMY pure color gradation patch data generated by the pure color gradation patch generation unit 8. As will be described later in detail, pure color gradation patch print 1
Color material color of each patch of 0 (cyan, magenta, yellow)
From the correspondence between the value of L and the value of L ^* a ^* b ^* , the relationship between the value of the color material color and the density of the color actually output is obtained in the form of a table.

In S56, the gray gradation patch generation unit 1 generates gray gradation patch data. The gradation patch data is an array of CMY output data corresponding to the gray area to be corrected in the multidimensional LUT, that is, the grid points of a ^* = b ^* = 0.

In step S57, the gray gradation patch output unit 2 generates a patch image from the gray gradation patch data generated by the gray gradation patch generation unit 1. The patch image is one in which the colors of patch data are regularly arranged in the image with a fixed size. Then, the gray gradation patch output unit 2 sends the patch image to the printer 3, and the printer 3 prints the patch image on paper and prints the gray gradation patch 4
To get

In step S58, the gray gradation patch color measuring unit 6 reads the data obtained by the user measuring the gray gradation patch with the colorimeter 5. This data is measured in the L ^* a ^* b ^* color space.

In S59, the multidimensional LUT adjusting unit 7
Is the L ^* a ^* b read by the gray gradation patch color measurement unit 6.
^* Data and CM generated by the gray gradation patch generator 1
Y gray gradation patch data, and TRC adjustment unit 12
From the TRC calculated by, the corrected CM as described later
The Y value is calculated for each grid point of the multidimensional LUT.

Next, a method of calculating the corrected TRC in S55 will be described with reference to the flowchart shown in FIG. In S61, the CMY of the pure color gradation patch
From the value, the L ^* a ^* b ^* value is calculated using the base data, and the L ^* a ^* b ^* value (L ^* o, a ^* o, b ^* o) in the initial state is obtained. This calculation can be performed, for example, by the color transfer characteristic prediction method described in Japanese Patent Laid-Open No. 10-262157.

In S62, the sensitivity characteristic (the amount of change in L ^* a ^* b ^* with respect to the change in CMY) is calculated using the base data.
Ask for. This sensitivity characteristic is also described in, for example, Japanese Patent Laid-Open No. 10-262.
It can be determined by the method described in Japanese Patent No. 157 or the like. The value of the sensitivity characteristic differs depending on the value of the L ^* a ^* b ^* / CMY coordinates, but here, the value is the L ^* a ^* b ^* value (L ^* o, a ^* o, b ^* o) in the initial state obtained in S61. , The sensitivity characteristic calculated from the data in which all the values of the elements other than the element converted by the TRC in the pure color gradation patch data are 0.

Now, as an example, when the sensitivity characteristic for performing the TRC correction of cyan is calculated, the following vector form is obtained.

[Equation 7] Sensitivity characteristics are calculated in the same manner for magenta and yellow.

In S63, the corrected value is calculated using the vector of the sensitivity characteristic obtained as described above.
However, taking the case of cyan as an example, the following three formulas appear.

[Equation 8] Here, Co is the corrected C value of TRC, and Cp is the pure color gradation parameter.
Data C value, (L ^*o, a^*o, b^*o) is the initial state
L^*a^*b^*Value, (L^*p, a^*p, b^*p) is a pure color gradation
L measured from Chiprint 10^*a^*b^*Measured value
It From these three formulas, for example, the least squares method is used.
Value that minimizes the sum of squares of the differences between the elements on both sides.
It may be Co. The same applies to magenta and yellow.
The corrected value can be obtained by the method.

Finally, in S64, if the values calculated from all the patches are smoothly complemented, the corrected TRC is obtained.
Is obtained.

Next, the CM after correction in S59 of FIG.
For the method of calculating the Y value, use the flowchart shown in FIG.
And explain. In S71, the gray gradation patch day
L from the CMY value of the data using the base data^*a^*b^*value
To calculate L in the initial state^*a ^*b^*Value (L^*o, a^*o, b
^*o) get. This calculation is performed, for example, in Japanese Patent Laid-Open No. 10-2621.
In the color transfer characteristic prediction method described in Japanese Patent No. 57
Therefore, it can be performed.

In S72, the CMY value of the base data is converted by applying the TRC obtained in S55 in reverse.

In S73, the CMY values of the gray gradation patch data are converted by applying the TRC obtained in S55 in reverse. This value is (Cp, Mp, Yp).

At S74, the sense is made using the base data.
Degree characteristics (L for changes in CMY values ^*a^*b^*Change in value
Quantity). Therefore, the sensitivity characteristic takes the form of a matrix. this
Sensitivity characteristics are also disclosed in, for example, Japanese Patent Laid-Open No. 10-262157.
It can be determined by the method described.
However, the CMY values of the base data were obtained in S73.
It is a value after the TRC reverse conversion.

Since the value of the sensitivity characteristic differs depending on the value of the L ^* a ^* b ^* / CMY coordinates, it is necessary to determine at which coordinate the sensitivity characteristic is calculated. For example, the initial L ^* a ^* b ^* value (L ^* o, a ^* o, b ^* o) obtained in S71,
L ^* a ^* b ^* measured from gray gradation patch print 4
Sensitivity characteristics can be calculated at the measured values (L ^* p, a ^* p, b ^* p) or the midpoint between the two.

The sensitivity characteristic thus obtained has the following matrix form.

[Equation 9]

At S75, the corrected CMY value is obtained using the sensitivity characteristic matrix obtained as described above.

[Equation 10] Here, (Co, Mo, Yo) is the CMY value of the corrected multidimensional table, and (L ^* p, a ^* p, b ^* p) is L ^* a ^* measured from the gray gradation patch print 4 ^. b ^* Measured value. Note that instead of calculating the inverse matrix here, the above equation is satisfied or the error is minimized (Co,
It is similar to the above-described first embodiment that another method such as a method of searching for (Mo, Yo) may be used.

By performing the above processing for all grid points that need to be corrected, the corrected CMY value can be calculated. This CMY value is the CMY of the grid point
By replacing the values, it is possible to correct the multidimensional LUT. After the correction processing of the multidimensional LUT is performed in this manner, the smoothing processing may be performed again on the whole or a part of the multidimensional LUT to suppress the abrupt change of the color conversion parameter.

By the above method, the gradation of the color material single color can be corrected by adjusting the TRC, and the gray can be corrected by adjusting the multidimensional LUT. In this embodiment, the pure color gradation patch and the gray gradation patch are separately output and measured, but not limited to this, for example, the pure color gradation patch generation unit 8, the gray gradation patch generation unit 1, and the pure color gradation patch. The output unit 9 and the gray gradation patch output unit 2, the pure color gradation patch colorimetric unit 11 and the gray gradation patch colorimetric unit 6 are respectively integrated into one, and the pure color gradation patch and the gray gradation patch are simultaneously generated and output. The measurement may be performed. Further, in order to eliminate the influence of variations in the output color due to the print position, the pure color gradation patches or the gray gradation patches may be rearranged appropriately.

FIG. 9 is a flow chart showing a second example of the operation according to the second embodiment of the present invention. In addition,
FIG. 9 shows the processing in S59 of FIG. 6, and here, FIGS. 6 and 7 are shared with the above-described first example, and the drawings corresponding to FIGS. 6 and 7 are omitted. In this second example, the printer 3 uses C, M, Y, and K as color materials.
The case of using the four colors will be described. Further, here, the TRC is adjusted to correct the gradation of a single color material, and in the multi-dimensional LUT, a gray area, that is, a ^* = b ^* =
A case will be described in which gray correction is performed by adjusting the CMYK output values of grid points that satisfy the condition of 0. Since K color is used as the color material together with 3 colors of CMY,
In the correction of the gray area, it is necessary to correct not only CMY but also the K component.

First, in S51 of FIG. 6, base data is obtained. The base data is TRC in S55 and S59.
And actual data necessary for calculating the correction value of the multidimensional LUT, and in the second operation example, it is represented as a list of CMYK values and corresponding L ^* a ^* b ^* values.
Here, the patch values measured when the parameters of the multidimensional LUT are first created are used as the base data.

In S52, the pure color gradation patch generation unit 8
Generates pure color gradation patch data for each color of CMYK. The gradation patch data is composed of a plurality of CMYK pure colors having different predetermined densities.

In S53, the pure color gradation patch output unit 9
Generates a patch image from the pure color gradation patch data generated by the pure color gradation patch generation unit 8. The patch image is one in which the colors of the patch data are regularly arranged in the image with a fixed size. Then, the pure color gradation patch output unit 9 sends the patch image to the printer 3, and the printer 3 prints the patch image on paper to obtain a pure color gradation patch print 10.

In step S54, the pure color gradation patch color measuring unit 11 reads the data measured by the user on the pure color gradation patch print 10 with the colorimeter 5. This data is L ^* a ^* b
^* Measured in color space.

In step S55, the TRC adjusting unit 12 calculates the TRC from the L ^* a ^* b ^* data read by the pure color gradation patch colorimetric unit 11 and the CMYK pure color gradation patch data generated by the pure color gradation patch generating unit 8. To recalculate. Specifically, based on the correspondence between the color material values (cyan, magenta, yellow, black) of each patch and the L ^* a ^* b ^* values, the relationship between the color material value and the density of the color actually output is shown in the form of a table. Ask in.

In S56, the gray gradation patch generator 1 generates gray gradation patch data. This gray gradation patch data is an array of CMYK output data corresponding to the gray area to be corrected in the multidimensional LUT, that is, the grid points of a ^* = b ^* = 0.

In S57, the gray gradation patch output unit 2 generates a patch image from the gray gradation patch data generated by the gray gradation patch generation unit 1. The patch image is one in which the colors of the patch data are regularly arranged in the image with a fixed size. Then, the gray gradation patch output unit 2 sends the patch image to the printer 3, and the printer 3 prints the patch image on paper to obtain a gray gradation patch print 4.

In S58, the data measured by the user on the gray tone patch print 4 with the colorimeter 5 is read by the gray tone patch colorimetric unit 6. This data is L ^* a ^* b
^* Measured in color space.

In S59, the multidimensional LUT adjusting unit 7
Is the L ^* a ^* b read by the gray gradation patch color measurement unit 6.
^* Data and CM generated by the gray gradation patch generator 1
YK gray gradation patch data, and TRC adjustment unit 1
The corrected CMYK values are calculated for each grid point from the TRC calculated by 2.

The method of calculating the corrected TRC in S55 is the same as the method of the first operation example in the second embodiment described with reference to FIG. However, this second
In the operation example of, black TRC is calculated in addition to cyan, magenta, and yellow.

Next, in S59 of FIG. 6, the corrected CMY is corrected.
The method for calculating the K value is shown in the flowchart shown in FIG.
It demonstrates using. In S81, the gray gradation patch
L from the CMYK values of the data using the base data^*a^*b
^*Calculate the value, L in the initial state ^*a^*b^*Value (L^*o, a
^*o, b^*o) get. This calculation is performed, for example, in Japanese Patent Laid-Open No. 10-2
Color transfer characteristic prediction method described in Japanese Patent No. 62157
And so on.

In S82, CMYK of the base data
The value is converted by applying the TRC obtained in S55 in reverse.

In S83, the CMYK values of the gray gradation patch data are converted by applying the TRC obtained in S55 in reverse. This value is (Cp, Mp, Yp, Kp).

In S84, the sensitivity characteristic (the amount of change in the L ^* a ^* b ^* value with respect to the change in the CMYK value) is obtained using the base data. Therefore, the sensitivity characteristic takes the form of a matrix. This sensitivity characteristic can also be obtained, for example, by the method described in Japanese Patent Laid-Open No. 10-262157. However, the CMYK values of the base data are the values after the inverse TRC conversion obtained in S82.

Since the value of the sensitivity characteristic differs depending on the value of the L ^* a ^* b ^* / CMYK coordinates, it is necessary to determine at which coordinate the sensitivity characteristic is calculated. For example, the initial state L ^* a ^* b ^* value (L ^* o, a ^* o, b ^* o) obtained in S81 and the L ^* a ^* b ^* measurement value ((( ^* The sensitivity characteristic can be calculated at L ^* p, a ^* p, b ^* p), or the middle point between them.

The sensitivity characteristic thus obtained has the form of the following matrix.

[Equation 11]

At S85, the corrected K value is calculated as follows using the amount of change in the L ^* value with respect to the K value in the sensitivity characteristic.

[Equation 12] However, here, Ko is the K value of the corrected multidimensional LUT, K
p is the K value obtained by performing inverse TRC conversion on the gray gradation patch data in S83, L ^* o is the L ^* value in the initial state obtained in S81, and L ^*
p is an L ^* measurement value obtained by measuring the color of the gray gradation patch print 4.

At S86, the corrected CMY values are obtained as follows using the sensitivity characteristics.

[Equation 13] Here, (Co, Mo, Yo) is the CMY value of the corrected multidimensional table, (Cp, Mp, Yp) is the CMY value of the gray gradation patch data that has been subjected to the inverse TRC conversion in S83,
(L ^* o, a ^* o, b ^* o) is L in the initial state obtained in S81.
^* a ^* b ^* value, (L ^* p, a ^* p, b ^* p) is the L ^* a ^* b ^* measurement value obtained by measuring the color of the gray gradation patch print 4. Here, instead of calculating the inverse matrix, the above equation is satisfied, or the error is minimized (Co, Mo, Y
It is similar to the above-described first example and first embodiment that other methods such as a method of searching o) may be used.

The CMYK values after correction can be calculated by performing the above processing for all grid points that need correction. This CMYK value is the grid point C
By replacing the MYK values, it is possible to correct the multidimensional LUT. After the correction processing of the multidimensional LUT is performed in this manner, the smoothing processing may be performed again on the whole or a part of the multidimensional LUT to suppress the abrupt change of the color conversion parameter.

As described above, it is possible to correct the gradation of the color material single color by adjusting the TRC and to correct the gray by adjusting the multidimensional LUT.

Also in this second operation example, the pure color gradation patch and the gray gradation patch are separately output and measured, but the generation and output of the pure color and gray patches are performed as in the first operation example described above. Alternatively, the means for performing the measurement may be integrated into one, and the output and the measurement may be performed at the same time. Further, in order to eliminate the influence of variations in the output color due to the print position, the pure color gradation patches or the gray gradation patches may be rearranged appropriately.

In each of the two operation examples in the above-described first and second embodiments, the printer 3 is L ^*.
The description has been made assuming that a color conversion device that receives an image signal in the a ^* b ^* color space and performs conversion into the CMY color space or the CMYK color space is provided. In addition to this, for example, from the CMYK color space different from that of the printer 3, the CMYK of the printer 3
There may be a case where a color conversion device that performs color conversion is included in the color space.
In this case, the color conversion apparatus uses one 4D lookup table, or one 4D lookup table and a TRC that is independent for each CMYK color in the subsequent stage.
Can consist of: CM different from printer 3
As the YK color space, for example, SOWP or Japan C
Printing CMYK defined as a standard such as color
Color space is conceivable. In this case, the difference from each operation example in each of the above-described embodiments is that a patch is created for a grid point where C = M = Y when a gray gradation patch is generated, and this grid point is used in the subsequent steps. Is to calculate a correction value for. As a result, the multidimensional LUT or the multidimensional LUT and TRC can be obtained in the same manner as described above.
Can be calibrated.

In addition to grid points where C = M = Y, patches are created for grid points within a certain range with three differences of C, M, and Y, and correction values for grid points near gray are obtained. May be asked. Of course, the same calibration can be performed for any color other than gray.

It is also possible to save the data when the calibration is performed as described above and use it as the base data for the next calibration.

FIG. 10 is a block diagram showing a third embodiment of the present invention. The same parts as those in FIGS. 1 and 5 are designated by the same reference numerals, and the duplicated description may be omitted. Thirteen
Is a gray gradation verification patch generation unit, 14 is a gray gradation verification patch output unit, 15 is a gray gradation verification patch print,
Reference numeral 16 is a gray gradation verification patch colorimetric unit, and 17 is an accuracy determination unit. Here, the configuration based on the above-described first embodiment is shown.

The gray gradation verification patch generation unit 13 uses the multidimensional LUT adjusted by the multidimensional LUT adjustment unit 7 to generate a patch for accuracy verification. This accuracy verification patch contains some adjusted grays. Further, other colors (for example, chromatic colors around gray) can be included as necessary. The gray gradation verification patch output unit 14 prints the accuracy verification patch generated by the gray gradation verification patch generation unit 13 from the printer 3 to obtain a gray gradation verification patch print 15. In addition,
The gray gradation verification patch print may include the gray gradation patch generated by the gray gradation patch generation unit 1 in addition to the accuracy verification patch newly generated by the gray gradation verification patch generation unit 13. it can.

The gray gradation verification patch colorimetric unit 16 measures the color of the gray gradation verification patch print 15 printed by the printer 3 by the colorimeter 5 to obtain a colorimetric value.
The color value in this case is, for example, device-independent L ^* a ^* b
^* Good to get as a value in the color space.

The accuracy determining section 17 determines that the conversion accuracy of the adjusted multidimensional LUT reaches the target value based on the colorimetric values obtained by the gray gradation verification patch colorimetric section 16 and that sufficient accuracy is obtained. Judge whether or not. When it is determined that the conversion accuracy does not reach the target value and sufficient accuracy is not obtained, the colorimetric value obtained by the gray tone verification patch colorimetric unit 16 and the gray tone verification patch are obtained. The pair of patch data generated by the generation unit 13 is given to the multidimensional LUT adjustment unit 7 to readjust the multidimensional LUT. When the conversion accuracy reaches the target value, the adjusted multidimensional LUT becomes the calibrated multidimensional LUT. The conversion accuracy can be determined by the amount of change (color difference) between the target value and the colorimetric value in the colorimetric color space. At this time,
For example, it is also possible to obtain the amount of change for all the parameters for correcting the multi-dimensional LUT and use a statistical amount such as the maximum value, average value, or intermediate value of the amounts of change to determine whether or not the target value has been reached. .

FIG. 11 is a flow chart showing a first example of the operation in the third embodiment of the invention. Here, it is assumed that the printer 3 forms an image using three color materials of C, M, and Y. First, in step S91, initial base data is obtained. Here, first the multi-dimensional LUT
The value of the patch measured when the parameter of was created is used as the base data. If no such patch value remains, it is also possible to generate base data from a multidimensional LUT, as described in the first embodiment.

In S92, the gray gradation patch generation unit 1 adjusts the base data in the initial state and the multidimensional LU.
Gray tone patch data is generated from the values of the grid points of T. Specifically, the CMY value of the gray gradation patch necessary for the calculation of the adjustment amount is obtained from the CMY value of the area to be adjusted among the lattice points of the multidimensional LUT.

In S93, L is calculated by using the CMY values of the gray gradation patch obtained in S92 and the base data in the initial state.
Calculate the ^* a ^* b ^* values. This value is the calibration target value. This calculation is performed, for example, in JP-A-10-26.
The color transfer characteristic prediction method described in Japanese Patent No. 2157 can be used.

In S94, the gray gradation patch output unit 2 generates a patch image from the gray gradation patch data generated by the gray gradation patch generation unit 1 in S91. The patch image is one in which the colors of patch data are regularly arranged in the image with a fixed size. Then, the generated patch image is printed on the printer 3 to obtain a gray gradation patch print 4.

In S95, the data measured by the user on the gray tone patch print 4 with the colorimeter 5 is read by the gray tone patch colorimetric unit 6. This data is L ^* a ^* b
^* Measured in color space.

In S96, the multidimensional LUT adjustment unit 7
Is the L ^* a ^* b read by the gray gradation patch color measurement unit 6.
^* Data and CM generated by the gray gradation patch generator 1
From the value obtained by converting the target value obtained in S93 into CMY by regarding the Y gray gradation patch data as the base data,
The corrected CMY value is calculated for each grid point of the multidimensional LUT. This calculation can also be performed by the color transfer characteristic prediction method described above.

In S97, the gray gradation verification patch generator 13 uses the corrected CMY values obtained in S96 to generate gray value gradation patch data for accuracy verification. Then, a patch image is generated by the gray gradation verification patch output unit 14 from the generated gradation patch data and printed by the printer 3, and a gray gradation verification patch print 15 is obtained.

In S98, the user verifies the gray gradation.
Data obtained by measuring the patch print 15 with the colorimeter 5 is
The ray gradation verification patch colorimetric unit 16 reads it. This data
Is L ^*a^*b^*Measured in color space.

In S99, the calibration target value generated in S93 is compared with the data measured in S98 to obtain the color difference in the L ^* a ^* b ^* color space of each patch. If the color difference is within a certain range, it is determined that the calibration accuracy is sufficient. As the criterion, a patch color difference average value or maximum value, or other appropriate statistic can be used. Also, L ^*
It is also possible to use the distance from the gray axis (the square root of the sum of squares of a ^* and b ^* ) instead of the color difference in the a ^* b ^* color space and pay attention only to the saturation of the patch.

If the calibration accuracy is sufficient,
In S100, the multidimensional LUT is corrected using the corrected CMY values obtained in S96, and the process ends.

If the accuracy is not sufficient, in S101, the data of the gray gradation verification patch generated in S97 is added to the data of the gray gradation patch generated in S92, and again in S96, the multidimensional LUT adjusting unit 7 is added. Calculate the correction amount by. The processes of S96 to 99 and S101 are repeated until sufficient accuracy is obtained in this way. Since the number of gray gradation patch data increases each time the repetition is performed, the accuracy of the correction value can be improved.

By performing the above processing, the multidimensional L
The UT can be corrected with high accuracy. After the correction processing of the multi-dimensional LUT is performed in this manner, the multi-dimensional LU is again processed.
A smoothing process may be performed on all or part of T to suppress an abrupt change in the color conversion parameter. Also,
In S93, L ^* a is calculated using the base data in the initial state.
Instead of calculating the ^* b ^* value, a predetermined target value may be used. If the calibration accuracy does not fall within the fixed range no matter how many times the correction value is calculated in S99, the repetition may be terminated at an appropriate number.

FIG. 12 is a flow chart showing a second example of the operation in the third embodiment of the invention. In this second example, the printer 3 uses C, M, Y, and K as color materials.
The case of using the four colors will be described. Therefore, in the correction of the gray area, it is necessary to correct not only CMY but also the K component.

First, in S111, initial base data is obtained. Here, it is assumed that the patch values measured when the parameters of the multidimensional LUT are first created are used as the base data. If no such patch value remains, it is also possible to generate base data from a multidimensional LUT, as described in the first embodiment.

In S112, the gray tone patch generation unit 1 performs multidimensional L adjustment with the base data in the initial state.
Gray tone patch data is generated from the values of the grid points of the UT. Specifically, among the lattice points of the multidimensional LUT, the CMY values of the gray gradation patch necessary for the calculation of the adjustment amount are obtained from the CMYK values of the area to be adjusted.

In S113, the L ^* a ^* b ^* values are calculated using the CMYK values of the gray gradation patch obtained in S112 and the base data in the initial state. This value is the calibration target value. This calculation is performed, for example, in Japanese Patent Laid-Open No.
It can be performed by the color transfer characteristic prediction method described in Japanese Patent Laid-Open No. 262157.

In S114, the gray gradation patch output unit 2 generates a patch image from the gray gradation patch data generated by the gray gradation patch generation unit 1 in S112.
The patch image is one in which the colors of patch data are regularly arranged in the image with a fixed size. Then, the generated patch image is printed on the printer 3 to obtain a gray gradation patch print 4.

In S115, the gray gradation patch colorimetry unit 6 reads the data measured by the user on the gray gradation patch print 4 with the colorimeter 5. This data is L ^* a ^*
b ^* Measured in color space.

In step S116, the sensitivity characteristic (the amount of change in the L ^* a ^* b ^* value with respect to the change in the CMYK value) is obtained using the base data. Therefore, the sensitivity characteristic takes the form of a matrix.
This sensitivity characteristic can also be obtained, for example, by the method described in JP-A-10-262157. The sensitivity characteristic matrix is as follows, as in the first embodiment, and its value differs depending on the value of the L ^* a ^* b ^* / CMYK coordinates.

[Equation 14]

In step S117, the K value after correction is first calculated using the change amount of the L ^* value with respect to the K value in the sensitivity characteristic.
Calculation is performed using the following equations as in the case of the above embodiment.

[Equation 15] Here, Ko is the K value of the corrected multidimensional table,
Kp is the K value of the gray gradation patch data, L ^* o is the L ^* value in the initial state, and L ^* p is the L ^* measurement value measured from the gray gradation patch print 4.

In S118, the multidimensional LUT adjustment unit 7
Is the L ^* a ^* b read by the gray gradation patch color measurement unit 6.
^* Data and CM generated by the gray gradation patch generator 1
By considering the Y gray gradation patch data as base data, the CMY value is calculated from the target value obtained in S113 and the corrected K value obtained in S117, and the corrected CMY value is calculated as the grid point of the multidimensional LUT. Ask for each. This calculation can also be performed by the above-described color transfer characteristic prediction method or the like.

In S119, the gray gradation verification patch generation unit 13 uses the corrected CMYK values obtained in S117 and S118 to generate gray value gradation patch data for accuracy verification. Then, the gray gradation verification patch output unit 14 generates a patch image from the gradation patch data, causes the printer 3 to print the patch image, and obtains a gray gradation verification patch print 15.

In S120, the data obtained by the user measuring the gray gradation verification patch print 15 with the colorimeter 5 is
The gray gradation verification patch colorimetric unit 16 reads it. This data is measured in the L ^* a ^* b ^* color space.

In S121, the calibration target value generated in S113 and the data measured in S120 are compared to obtain the color difference in the L ^* a ^* b ^* color space of each patch. If the color difference is within a certain range,
Judge that the calibration accuracy is sufficient. As the criterion, a patch color difference average value or maximum value, or other appropriate statistic can be used. It is also possible to use the distance from the gray axis (the square root of the sum of squares of a ^* and b ^* ) instead of the color difference in the L ^* a ^* b ^* color space to correct only the saturation of the patch. it can.

If the calibration accuracy is sufficient,
In S122, the multidimensional LUT is corrected using the corrected CMYK values obtained in S117 and S118,
The process ends.

If the accuracy is not sufficient, in S123, the data of the gray gradation verification patch generated in S119 is added to the data of the gray gradation patch generated in S112, and the correction amount is corrected again in the processing of S116 to S118. Calculate. Until sufficient accuracy is obtained in this way, S
The processes of 116 to S121 and S123 are repeated. Since the number of gray gradation patch data increases each time the repetition is performed, the accuracy of the correction value can be improved.

By performing the above processing, the multidimensional L
The UT can be corrected with high accuracy. After the correction processing of the multi-dimensional LUT is performed in this manner, the multi-dimensional LU is again processed.
A smoothing process may be performed on all or part of T to suppress an abrupt change in the color conversion parameter. Also,
Instead of calculating the L ^* a ^* b ^* value using the base data in the initial state as the target value in S113, a predetermined target value may be used. If the calibration accuracy does not fall within the fixed range no matter how many times the correction value is calculated in S121, the repetition may be terminated at an appropriate number.

In the third embodiment, the CMY values after correction are not obtained after the sensitivity characteristic matrix is obtained as in the first embodiment described above, but the calibration target values are used. Based on the L ^* a ^* b ^* value, the L ^* a ^* b ^* data read by the gray gradation patch colorimetric unit 6 and the CMY gray gradation patch data generated by the gray gradation patch generation unit 1 are used as bases. The corrected CMY values are obtained by considering the data and applying it to perform color conversion. However, the method of obtaining the sensitivity characteristic matrix as in the first embodiment can be used. In that case, a new patch is generated as the base data in the first embodiment, and sufficient accuracy cannot be obtained. When the patch is added, the processing is the same as when the patch is added.

Further, also in the third embodiment, the TRC correction can be combined as in the second embodiment. In that case, as shown by the broken line in FIG. 10, the corrected T in the multidimensional LUT adjustment unit 7
Using RC, as described in the second embodiment, the inverse conversion calculation using TRC may be performed for the value in the color material color space.

[0150]

As is apparent from the above description, according to the present invention, the color conversion parameters are corrected by adjusting the multi-dimensional LUT and the reproduction color is calibrated. Adjustments can be made without affecting the color of the. For example, even if the gradation correction of a single color material used in the printer and the correction of the gray axis that is the tertiary color are performed at the same time, the adjustments can be performed without affecting each other. Therefore, even when a color change occurs in the output device, there is an effect that the color adjustment can be performed almost accurately and a good output result can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a flowchart showing a first example of an operation according to the first exemplary embodiment of the present invention.

FIG. 3 is a flowchart showing a first example (multidimensional LUT correction processing) of the operation according to the first embodiment of the present invention.

FIG. 4 is a flowchart showing a second example (multidimensional LUT correction process) of the operation according to the first embodiment of the present invention.

FIG. 5 is a block diagram showing a second embodiment of the present invention.

FIG. 6 is a flowchart showing a first operation example according to the second exemplary embodiment of the present invention.

FIG. 7 is a flowchart showing a first example (TRC correction processing) of the operation according to the second embodiment of the present invention.

FIG. 8 is a flowchart showing a first example (multidimensional LUT correction process) of the operation according to the second embodiment of the present invention.

FIG. 9 is a flowchart showing a second example (multidimensional LUT correction process) of the operation according to the second embodiment of the present invention.

FIG. 10 is a block diagram showing a third embodiment of the present invention.

FIG. 11 is a flowchart showing a first example of operation in the third exemplary embodiment of the present invention.

FIG. 12 is a flowchart showing a second example of operation in the third exemplary embodiment of the present invention.

[Explanation of symbols]

1 ... Gray gradation patch generation unit, 2 ... Gray gradation patch output unit, 3 ... Printer, 4 ... Gray gradation patch print,
5 ... Colorimeter, 6 ... Gray gradation patch color measurement section, 7 ... Multi-dimensional LUT adjustment section, 8 ... Pure color gradation patch generation section, 9 ... Pure color gradation patch output section, 10 ... Pure color gradation patch print, 11
... Pure color gradation patch colorimetry section, 12 ... TRC adjustment section, 13 ...
Gray gradation verification patch generation unit, 14 ... Gray gradation verification patch output unit, 15 ... Gray gradation verification patch print, 1
6 ... Gray gradation verification patch color measurement unit, 17 ... Accuracy determination unit.

Continued front page    (72) Inventor Hitoshi Ogatsu             430 Green, Sakai, Nakai-cho, Ashigaragami-gun, Kanagawa Prefecture             Inside of Fuji Xerox Co., Ltd. F-term (reference) 2C262 AB11 AB13 BA01 BA09 BA19                       BC13 BC17 BC19 CA07 FA12                       FA13 GA02                 5B057 AA11 BA02 CA01 CA08 CA12                       CA16 CB01 CB08 CB12 CB16                       CE17 CE18 CH07                 5C077 LL01 MP08 PP32 PP33 PP36                       PP37 PQ12 PQ23                 5C079 HB01 HB03 HB08 HB12 LB02                       MA04 MA11 NA03 NA29 PA03

Claims (60)

[Claims] 1. A calibration device for calibrating the multi-dimensional lookup table in an output device having a color conversion device for performing color conversion using a multi-dimensional lookup table having an order equal to the number of elements in an input color space. In the first colorimetric means for measuring the color of the first patch for calibration output from the output device, and the measured value obtained by the colorimetric measurement by the first colorimetric means. A calibration apparatus comprising: a first adjusting unit that corrects a part of a color conversion parameter of a multi-dimensional lookup table. 2. An output having a color conversion device for performing color conversion using a multi-dimensional lookup table having an order equal to the number of elements of an input color space and a number of one-dimensional lookup tables equal to the number of elements of an output color space. A calibration device for calibrating the multi-dimensional look-up table and the one-dimensional look-up table in a device, comprising: a first calibration color composed of a plurality of color materials output from the output device.
A part of the color conversion parameters of the multidimensional lookup table is corrected by using a first colorimetric means for measuring the color of the patch and a measurement value obtained by the colorimetric measurement by the first colorimetric means. The first adjusting unit, the second color measuring unit for measuring the color of the second patch for calibration composed of the gradation of the single color material output from the output device, and the second color measuring unit. A calibration apparatus comprising: a second adjusting unit that corrects a color conversion parameter of the one-dimensional lookup table using a measurement value obtained by color measurement. 3. The first adjusting means utilizes a color conversion parameter of the one-dimensional look-up table adjusted by the second adjusting means to part of a color conversion parameter of the multi-dimensional look-up table. The calibration device according to claim 2, wherein the calibration device corrects 4. The second patch is one in which the one-dimensional lookup table for correction outputs the colors of elements for which color conversion is performed at a plurality of densities by the output device. Alternatively, the calibration device according to claim 3. 5. When the second adjusting means corrects the color conversion parameter of the one-dimensional lookup table by using the measurement value obtained by measuring the color of the second patch, first, the output color space of the output color space is adjusted. A vector indicating the rate of change of each element of the colorimetric color space with respect to the change of each colorant element is obtained, and then an estimate is made in the colorimetric color space when creating the one-dimensional lookup table corresponding to each colorant element of the second patch. The amount of change is further calculated by calculating the difference between the estimated value and the measured value of the second patch, and finally, from the vector indicating the amount of change in the colorimetric color space and the ratio of the change. A change amount of the color material element in the output color space is obtained, and the color conversion parameter of the one-dimensional lookup table is corrected using the change amount of the color material element. The calibration device according to any one of claims 2 to 4. 6. The first patch has an output color space in which one or more color coordinate values in a region requiring correction of the color conversion parameter in the input color space are output using the color conversion parameter before correction. 6. The calibration device according to claim 1, wherein the calibration device converts the color coordinate value into a color value and outputs the converted color coordinate value by the output device. 7. The area requiring correction of the color conversion parameter is an achromatic area.
The calibration device described in. 8. The calibration device according to claim 6, wherein the region requiring correction of the color conversion parameter is a region in which a color distance from an achromatic region is within a certain range. 9. The method according to claim 7, wherein the input color space is an L ^* a ^* b ^* color space, and the achromatic color area is an area satisfying a ^* = b ^* = 0. The calibration device described in. 10. The calibration device according to claim 7, wherein the input color space is an RGB color space, and the achromatic color region is a region that satisfies R = G = B. 11. The input color space is a CMYK color space or a CMY color space, and the achromatic color region is C = M = Y.
The calibration device according to claim 7, wherein the calibration device is a region that satisfies the above condition. 12. The first patch is one in which one or more color coordinate values in an area in the output color space that requires correction of the color conversion parameter are output by the output device. The calibration device according to any one of claims 1 to 5. 13. The calibration device according to claim 12, wherein the area requiring correction of the color conversion parameter is an achromatic area. 14. The calibration device according to claim 12, wherein the region requiring correction of the color conversion parameter is a region in which the color distance from the achromatic region is within a certain range. 15. The calibration device according to claim 13, wherein the output color space is an RGB color space, and the achromatic color region is a region that satisfies R = G = B. 16. The output color space is a CMYK color space or a CMY color space, and the achromatic color region is C = M = Y.
The calibration device according to claim 13 or 14, wherein the calibration device is a region that satisfies the above condition. 17. The first adjusting means first corrects a part of the color conversion parameters of the multi-dimensional lookup table by using a measurement value obtained by measuring the color of the first patch. A matrix indicating the rate of change of each element in the colorimetric color space with respect to the change of each element in the output color space is obtained, and then the colorimetric color when creating the multidimensional lookup table corresponding to the value in the output color space of the first patch The estimated value in the space is obtained, and the change amount in the colorimetric color space is obtained by further calculating the difference between the estimated value and the measurement value of the first patch, and finally, the change amount in the measured value color space and the rate of the change are calculated. Find the amount of change in the output color space from the matrix
17. The method according to claim 1, wherein a part of the color conversion parameter of the multi-dimensional lookup table is corrected using the amount of change in the output color space.
The calibration device according to the item. 18. The output color space is a CMYK color space, and the first adjusting means uses the measurement values obtained by measuring the color of the first patch to determine the color of the multi-dimensional lookup table. When correcting a part of the conversion parameters, first, a matrix showing the ratio of the change of each element in the colorimetric color space to the change of each element in the output color space is obtained, and then the matrix corresponding to the value in the output color space of the first patch The estimated value in the colorimetric color space at the time of creating the multidimensional lookup table is calculated, and the difference in the colorimetric color space is calculated by calculating the difference between the estimated value and the measured value of the first patch, and then the black value is calculated. The change amount of black in the output color space is calculated from the ratio of the change in the coordinate value indicating the brightness in the color measurement color space to the change in and the change amount of the brightness in the color measurement color space. The amount of change of the remaining elements in the output color space is obtained from the amount of change in the colorimetric color space and the matrix indicating the rate of change, and one of the color conversion parameters of the multidimensional lookup table is calculated using the amount of change in the output color space. The calibration device according to any one of claims 1 to 14 or claim 16, which corrects a part. 19. The first adjusting means is a matrix showing a ratio of change of each element in the output color space with respect to change of each element in the input color space and estimation in the colorimetric color space when the multidimensional lookup table is created. When you ask for a value,
19. The calibration apparatus according to claim 17, wherein the colorimetric data of the output device used when creating the multidimensional lookup table is used. 20. The first adjusting means is a matrix showing a rate of change of each element in the output color space with respect to a change of each element in the input color space, and an estimation in the colorimetric color space when the multidimensional lookup table is created. When you ask for a value,
The calibration device according to claim 17 or 18, wherein the color conversion parameters of the multi-dimensional lookup table are used as they are. 21. The first adjusting means is a matrix showing a rate of change of each element in the output color space with respect to a change of each element in the input color space, and an estimation in the colorimetric color space when the multidimensional lookup table is created. When you ask for a value,
19. The calibration device according to claim 17, wherein the newly measured colorimetric data of the output device is used. 22. The first patch is a patch including a color of a parameter for correction of the color conversion parameters of the multidimensional lookup table and a color of a region in the vicinity thereof, and the first adjusting means 6. The method according to claim 1, wherein a part of the color conversion parameter of the multidimensional lookup table is corrected to a predetermined target value by using the measurement value measured by the first colorimetric means. The calibration device according to any one of 1. 23. The first patch is a patch composed of a color of a parameter to be corrected among the color conversion parameters of the multidimensional lookup table and a color of a region in the vicinity thereof, and the first adjusting means is , A matrix showing the rate of change of each element in the colorimetric color space with respect to the change of each element in the output color space is obtained using the measurement values measured by the first colorimetric means, and a target value for correction in the colorimetric color space is obtained. The amount of change in the colorimetric color space is obtained by calculating the difference between the measurement values of the first patches, and the amount of change in the black component of the output color space is obtained from the matrix showing the amount of change in the colorimetric color space and the rate of change. Corrects the black component of some of the color conversion parameters of the multi-dimensional lookup table,
2. The remaining component of a part of the color conversion parameters of the multi-dimensional lookup table is corrected by using the measurement value measured by the first color measuring unit and the correction value of the black component. The calibration device according to claim 5. 24. The first adjusting unit corrects a part of the color conversion parameters of the multi-dimensional lookup table, generates a verification patch using the corrected multi-dimensional lookup table, and performs the verification. 24. The calibration device according to claim 1, wherein a part of the color conversion parameters of the multi-dimensional lookup table is corrected using a patch. 25. The calibration device according to claim 24, wherein the first adjusting unit uses the generated measurement value of the verification patch in addition to the first patch. 26. The first adjusting means determines the conversion accuracy of the multidimensional lookup table by the verification patch, and the multidimensional lookup using the verification patch until the conversion accuracy reaches a target value. 25. The correction of the color conversion parameter of the table is repeated.
Alternatively, the calibration device according to claim 25. 27. The calibration device according to claim 26, wherein the first adjusting unit determines the conversion accuracy based on an amount of change in the colorimetric color space. 28. The first adjusting means obtains the amount of change in the colorimetric color space for all parameters for correcting the multi-dimensional lookup table, and obtains the maximum value, average value, and intermediate value of the amount of change. 28. It is determined whether or not a statistical amount such as has reached the target value.
The calibration device described in. 29. When the first patch or the first patch and the second patch are output from the output device, the order of patches of each color is randomly rearranged. The calibration device according to any one of claims 1 to 28. 30. The first adjusting means performs a correction process on the multi-dimensional lookup table and then performs a smoothing process on the whole or a part of the multi-dimensional lookup table again to rapidly change the color conversion parameters. 30. The calibration device according to any one of claims 1 to 29, which suppresses such changes. 31. A calibration method for calibrating the multi-dimensional lookup table in an output device having a color conversion device that performs color conversion using a multi-dimensional lookup table having an order equal to the number of elements in an input color space. In, the color of the first patch for calibration output from the output device is measured, and a part of the color conversion parameters of the multidimensional lookup table is corrected using the measurement value obtained by the color measurement. A calibration method characterized by the above. 32. An output having a color conversion device for performing color conversion using a multi-dimensional lookup table having an order equal to the number of elements of an input color space and a number of one-dimensional lookup tables equal to the number of elements of an output color space. In a calibration method for calibrating the multi-dimensional lookup table and the one-dimensional lookup table in a device, a first patch for calibration composed of a color obtained by combining a plurality of color materials output from the output device Is measured, and a part of the color conversion parameters of the multi-dimensional lookup table is corrected using the measurement values obtained by the color measurement, and from the gradation of the single color material output from the output device. The second patch for calibration is measured and the one-dimensional lookup table is obtained using the measured values obtained by measuring the color. A calibration method characterized by correcting the color conversion parameters of the bull. 33. After the color conversion parameter of the one-dimensional lookup table is corrected by using the measurement value obtained by the color measurement of the second patch, the color of the one-dimensional lookup table after the correction is corrected. 33. The calibration method according to claim 32, wherein a part of the color conversion parameters of the multidimensional lookup table is corrected by using the conversion parameters and the measurement values obtained by the colorimetry of the first patch. . 34. The second patch is characterized in that the one-dimensional lookup table for correction outputs the colors of the elements for which color conversion is performed in a plurality of densities by the output device. Alternatively, the calibration method according to claim 33. 35. When correcting the color conversion parameter of the one-dimensional lookup table using the measurement value obtained by measuring the color of the second patch, first, the color measurement color with respect to the change of each color material element in the output color space is measured. A vector indicating the rate of change of each element of the space is obtained, and then an estimated value in the colorimetric color space at the time of creating the one-dimensional lookup table corresponding to each color material element of the second patch is obtained. And the second
Change amount in the colorimetric color space is calculated by calculating the difference between the patch measurement values, and finally, the change amount in the color material element in the output color space is calculated from the vector indicating the change amount in the colorimetric color space and the rate of change 35. The calibration method according to claim 32, wherein the color conversion parameter of the one-dimensional lookup table is corrected using the amount of change in the color material element. 36. The first patch has an output color space in which one or more color coordinate values in an area in the input color space that requires correction of the color conversion parameter are output using the color conversion parameter before correction. 36. The calibration method according to claim 31, wherein the color coordinate values after conversion are output by the output device. 37. The calibration method according to claim 36, wherein the area requiring correction of the color conversion parameter is an achromatic area. 38. The calibration method according to claim 36, wherein the region requiring correction of the color conversion parameter is a region in which a color distance from an achromatic region is within a certain range. 39. The input color space is an L ^* a ^* b ^* color space, and the achromatic color region is a region satisfying a ^* = b ^* = 0. Calibration method described in. 40. The calibration method according to claim 37 or 38, wherein the input color space is an RGB color space, and the achromatic color region is a region satisfying R = G = B. 41. The input color space is a CMYK color space or a CMY color space, and the achromatic color region is C = M = Y.
39. The calibration method according to claim 37 or 38, wherein the calibration method is a region that satisfies the above condition. 42. The first patch is one in which one or more color coordinate values in an area in the output color space that requires correction of the color conversion parameter are output by the output device. Claim 31 to Claim 35
The calibration method according to any one of 1. 43. The calibration method according to claim 42, wherein the area requiring correction of the color conversion parameter is an achromatic area. 44. The calibration method according to claim 42, wherein the region requiring correction of the color conversion parameter is a region in which a color distance from an achromatic region is within a certain range. 45. The calibration method according to claim 43 or 44, wherein the output color space is an RGB color space, and the achromatic color region is a region that satisfies R = G = B. 46. The output color space is a CMYK color space or a CMY color space, and the achromatic color region is C = M = Y.
The calibration method according to claim 43 or claim 44, wherein the calibration method is a region that satisfies the above condition. 47. When correcting a part of the color conversion parameters of the multi-dimensional lookup table using the measurement values obtained by measuring the color of the first patch, first, a change of each element in the output color space is performed. To obtain a matrix showing the rate of change of each element in the colorimetric color space, and then to find an estimated value in the colorimetric color space when creating the multidimensional lookup table corresponding to the value in the output color space of the first patch, and The amount of change in the colorimetric color space is obtained by calculating the difference between the estimated value and the measurement value of the first patch, and finally, the change in the output color space is calculated from the matrix indicating the amount of change in the measurement value color space and the ratio of the change. The amount is obtained, and a part of the color conversion parameter of the multidimensional lookup table is corrected using the amount of change in the output color space.
47. The calibration method according to claim 46. 48. The output color space is a CMYK color space, and a part of color conversion parameters of the multidimensional lookup table is corrected using a measurement value obtained by measuring the color of the first patch. At this time, first, a matrix showing the rate of change of each element in the colorimetric color space with respect to the change of each element in the output color space is obtained, and then when a multidimensional lookup table corresponding to the value in the output color space of the first patch is created. Is calculated in the colorimetric color space, the difference in the colorimetric color space is calculated by calculating the difference between the estimated value and the measurement value of the first patch, and then the brightness in the colorimetric color space with respect to the change in the black value is calculated. The change amount of black in the output color space is calculated from the change rate of the coordinate value indicating the brightness and the change amount of brightness in the color measurement color space, and finally, the change amount of black and the change in the color measurement color space. Amount, the amount of change of the remaining elements in the output color space is obtained from the matrix indicating the change ratio, and a part of the color conversion parameters of the multidimensional lookup table is corrected using the amount of change in the output color space. The calibration method according to any one of claims 31 to 44 or claim 46, wherein: 49. A matrix showing a ratio of change of each element in the output color space to a change of each element in the input color space and a multidimensional look when an estimated value in the colorimetric color space at the time of creating the multidimensional look-up table is calculated. The colorimetric data of the output device used when creating the up table is used.
Calibration method described in. 50. The matrix showing the ratio of change of each element in the output color space to the change of each element in the input color space, and the multidimensional when the estimated value in the colorimetric color space when the multidimensional lookup table is created are obtained. 49. The calibration method according to claim 47 or 48, wherein the color conversion parameters of the look-up table are used as they are. 51. When a matrix showing a ratio of change of each element in the output color space with respect to change of each element in the input color space and an estimated value in the colorimetric color space at the time of creating the multi-dimensional lookup table are obtained, new measurement is performed. The colorimetric data of the output device that has been used is used.
Alternatively, the calibration method according to claim 48. 52. The first patch is a patch composed of a color of a parameter to be corrected among the color conversion parameters of the multi-dimensional lookup table and a color of a region in the vicinity thereof, and the first patch is subjected to colorimetry. The calibration according to any one of claims 31 to 35, wherein a part of the color conversion parameters of the multi-dimensional lookup table is corrected to a predetermined target value by using the measured value. Method. 53. The first patch is a patch including a color of a parameter for correction of the color conversion parameters of the multi-dimensional lookup table and a color of a region in the vicinity thereof, and the first patch is measured. When correcting some of the color conversion parameters of the multi-dimensional lookup table using the measurement values obtained by color, each element in the colorimetric color space with respect to a change in each element in the output color space is corrected using the measurement value. Of the measured value of the first patch is calculated by calculating the difference between the correction target value in the colorimetric color space and the measured value of the first patch, The amount of change in the black component of the output color space is calculated from the matrix indicating the rate of change, and the black component is corrected among some of the color conversion parameters of the multidimensional lookup table, The remaining component of a part of the color conversion parameters of the multi-dimensional lookup table is corrected using the measured value and the correction value of the black component. Calibration method described in. 54. After correcting a part of the color conversion parameters of the multi-dimensional lookup table, a verification patch is created using the color conversion parameters of the corrected multi-dimensional lookup table, and the verification patch is used. The calibration method according to any one of claims 31 to 53, wherein the color conversion parameters of the corrected multi-dimensional lookup table are re-corrected. 55. The color conversion parameter of the corrected multi-dimensional lookup table is recorrected by using the measurement value of the verification patch additionally used in the first patch. The calibration method described. 56. The conversion accuracy of the corrected multi-dimensional lookup table is determined by the verification patch, and the correction multi-dimensional lookup table using the verification patch is determined until the conversion accuracy reaches a target value. The calibration method according to claim 54 or 55, wherein re-correction of the color conversion parameter is repeated. 57. The determination of the conversion accuracy is performed based on the amount of change in the colorimetric color space.
The calibration method according to item 6. 58. The amount of change in the colorimetric color space is calculated for all parameters for correcting the multi-dimensional lookup table, and the statistic such as the maximum value, average value, or intermediate value of the amount of change is the target value. 58. The calibration method according to claim 57, wherein it is determined whether or not the value has reached. 59. When the first patch or the first patch and the second patch are output from the output device, the order of the patches of each color is randomly rearranged. The calibration method according to any one of claims 31 to 58. 60. After the correction processing of the multi-dimensional lookup table, the whole or a part of the multi-dimensional lookup table is smoothed again to suppress an abrupt change of the color conversion parameter. The calibration method according to any one of claims 31 to 59, wherein: