JP2009194552A - Method of determining number of patches, calibration method and printer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To determine the proper number of patches of each of colors in a test chart used for color calibration. <P>SOLUTION: The method of determining the number of patches of each of colors in a test chart used for color calibration includes: a step of acquiring a colorimetric value in a color space corresponding to each tone value for each of a first color and a second color; and a step of finding the number of patches of the first color based on the colorimetric value of the first color and finding the number of patches of the second color based on the colorimetric value of the second color. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for determining the number of patches, a calibration method, and a printing apparatus.

Many color printers that can express a plurality of colors are used. In such a color printer, color calibration is performed in order to improve color reproducibility. When performing color calibration, a test chart for color calibration is printed. Then, the color of the chart is measured to obtain a color measurement value in the color space, and a color shift output from the printer is corrected based on the color measurement result.
JP 2006-237987 A

  As described above, the color shift is corrected based on the color measurement result of the test chart. Depending on the ink color used, a color in which a difference in gradation appears large in the above-described color space, and a color that appears relatively small. Exists. If the same number of patches are measured for each color under these circumstances, a colorimetric result with a short distance between colorimetric values in the color space can be obtained for colors that show a small difference in gradation. On the other hand, in the case of a color having a large gradation difference, a color measurement result having a long distance between color measurement values in the color space is obtained.

  If the distance between the colorimetric values in the color space between the gradations is different for each color, it may be desired to increase the number of patches in the case of a color in which the difference in the colorimetric values appears greatly. In addition, in the case of a color that shows a small difference in colorimetric values, the number of patches may be further reduced. When the number of patches is insufficient, the accuracy of calibration correction is low, and when the number of patches is large, the color measurement time becomes long. Therefore, it is desirable that the number of patches of each color used be an appropriate number of patches.

  SUMMARY An advantage of some aspects of the invention is that the number of patches of each color in a test chart used for color calibration is set to an appropriate number.

The main invention for achieving the above object is:
A method for determining the number of patches of each color in a test chart used for color calibration,
Obtaining a colorimetric value in a color space corresponding to each gradation value for each of the first color and the second color;
Obtaining the number of patches of the first color based on the colorimetric value of the first color, and obtaining the number of patches of the second color based on the colorimetric value of the second color;
This is a method for determining the number of patches including.

  Other features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

  At least the following matters will become clear from the description of the present specification and the accompanying drawings.

A method for determining the number of patches of each color in a test chart used for color calibration,
Obtaining a colorimetric value in a color space corresponding to each gradation value for each of the first color and the second color;
Obtaining the number of patches of the first color based on the colorimetric value of the first color, and obtaining the number of patches of the second color based on the colorimetric value of the second color;
How to determine the number of patches that contain
In this way, the number of patches of each color in the test chart used for color calibration can be set to an appropriate number of patches.

  In this method of determining the number of patches, it is preferable that the number of patches of the first color and the number of patches of the second color are different. Further, based on the length of the curve in the color space of the first color and the second color obtained from the acquired colorimetric value, the number of patches of the first color and the second color It is desirable to determine the number of patches. Further, it is desirable to assign a larger number of patches as the length of the curve in the color space is longer. Further, the length of the curve of the first color is obtained based on the sum of the distances between the colorimetric values in the color space corresponding to the gradation values of the first color, and the respective floors of the second color are obtained. It is desirable to obtain the length of the curve of the second color based on the sum of the distances between the colorimetric values in the color space corresponding to the tone value.

Further, the number of patches of the first color and the number of the first color so that the distance of the colorimetric value between the patches of the first color and the distance of the colorimetric value between the patches of the second color are equal. It is desirable to obtain the number of patches of two colors. Furthermore, the method further includes a step of acquiring a degree of variation in the color space in the medium for each of the first color and the second color, and the first color and the second color in the color space. The number of patches of the first color and the second color is obtained according to the length of the curve and the degree of variation in the colorimetric values of the color space of the first color and the second color on the medium. It is desirable. The color space is preferably a uniform color space. The color space is preferably a CIE L ^* a ^* b ^* color space.
In this way, the number of patches of each color in the test chart used for color calibration can be set to an appropriate number of patches.

Printing a test chart including a plurality of patches of a first color and a plurality of patches of a second color having a larger number of patches than the plurality of patches of the first color;
Performing color calibration of the first color by measuring the plurality of patches of the first color, and performing calibration of the second color by measuring the plurality of patches of the second color When,
Calibration method including:

In this calibration method, it is preferable that the distance in the color space between the first color patches and the distance in the color space between the second color patches are equal.
In this way, calibration can be performed with an appropriate number of patches for each color.

A controller for printing a test chart comprising a plurality of patches of a first color and a plurality of patches of a second color having a larger number of patches than the plurality of patches of the first color;
A first correction value obtained by calibration of the first color using the colorimetric results of the plurality of patches of the first color, and a second color using the colorimetry results of the plurality of patches of the second color. A memory for storing a second correction value by calibration of
A printing apparatus comprising:
In this way, calibration can be performed based on the appropriate number of patches for each color and printing can be performed.

=== First Embodiment ===
FIG. 1 is a diagram showing a configuration of a system for determining the number of patches of each ink color in a test chart. In the figure, a computer 100, a printer 1, and a color colorimeter 40 are shown.

<Colorimeter 40>
FIG. 2 is a diagram for explaining the structure of the color colorimeter 40. In the figure, an external view of the color measuring device 40 is shown. The color color measuring device 40 includes a color measuring table 41, a backing 42, a color measuring head 43, a color measuring device carriage 44, a rail 45, and a paper feed roller 46.

A backing 42 made of a white plate is fixed to the color measuring table 41. The color measuring head 43 performs color measurement by scanning the paper on the backing 42. The colorimeter carriage 44 includes a motor (not shown), moves on the rail 45, and moves the colorimeter head 43 in the main scanning direction. The paper feed roller 46 conveys a predetermined amount of paper in the sub-scanning direction every time color measurement in the main scanning direction is completed. The colorimeter 40 directs the colorimetric head 43 to the object to be colorimetrically to determine the colors of a plurality of color components L ^* , a ^* , b ^* based on the L ^* a ^* b ^* color space in the CIE (1076) standard The component amount is detected, and colorimetric values L ^* , a ^* , b ^* corresponding to the detected amount are generated. That is, when color measurement is performed for each point, a set of color measurement values including L ^* values, a ^* values, and b ^* values is obtained. Here, the CIE L ^* a ^* b ^* color space is a uniform color space independent of a device having a plurality of color components L ^* , a ^* , b ^* as color component amounts. Note that L ^* represents lightness, and a ^* and b ^* are color coordinates representing hue and saturation.

The color colorimeter 40 outputs the colorimetric values generated by the colorimetry to the computer 100. The color space of the colorimetric values to be output may be a CIE L ^* u ^* v ^* color space.

<Printer 1>
The printer 1 is a printer that forms an image by ejecting ink droplets onto a sheet. The printer 1 has a head mounted with a plurality of colors of ink, and ejects ink while moving the head in a direction orthogonal to the transport direction while intermittently transporting the paper in the transport direction of the paper. An image is formed by a collection of minute inks that have landed on the paper. The printer 1 used here can eject eight types of inks of cyan C, magenta M, yellow Y, black K, light cyan LC, light magenta LM, light black LK, and light light black LLK. .

  Here, the above-described eight colors of ink are used, but the type of color is not limited to this. Further, the ink to be used may be a pigment ink mixed with a color material made of pigment, or may be a dye ink mixed with a color material made of dye. Although an ink discharge type printer will be described here as an example, a color laser printer that forms an image on paper using a plurality of colors of toner may be used.

<Computer 100>
The computer 100 includes a processing device (not shown) and a storage device. The processing device is an arithmetic device such as a CPU. The storage device is a ROM, a RAM, a hard disk drive, a CD-ROM drive, or the like, and stores a program for executing a patch number determination method described later. The RAM and the hard disk drive are also used as areas for storing calculation results as needed when executing a program. The computer 100 is connected to the printer 1 and the color measuring device 40 via an interface. The computer 100 can cause the printer 1 to print a desired image by transmitting the print data to the printer 1. Further, the computer 100 can output a color measurement command to the color colorimeter 40 and acquire a color measurement result as described later.

<About color calibration>
Printers have slightly different color output characteristics between individuals. Color calibration is performed to correct this and improve the color reproducibility of the printer. The color calibration is performed by the following procedure, for example. First, the printer prints a test chart. Next, the printed test chart is fixed to the color colorimeter, and the color measurement of the test chart is performed. Next, based on the measured colorimetric value, a deviation amount of the printed color is obtained. Next, a conversion table for correcting this deviation amount is created. Then, by performing printing while correcting the shift amount using this conversion table, it is possible to perform printing with an appropriate color.

  In the embodiment described below, the number of patches of each color in the test chart used in such calibration is determined.

<About CIE L ^* a ^* b ^* space>
The CIE L ^* a ^* b ^* color space is a uniform color space. The uniform color space is a color space in which equidistances in color space coordinates are perceptually equal differences.

FIG. 3 is an example when the CIE L ^* a ^* b ^* color space is viewed from L = 100 in the a ^* b ^* coordinate direction. FIG. 4 is an example when the CIE L ^* a ^* b ^* color space is viewed in the L ^* b ^* coordinate direction from a = 120. FIG. 5 is an example when the CIE L ^* a ^* b ^* color space is viewed in the L ^* a ^* coordinate direction from b = 120. FIG. 6 is an example when the CIE L ^* a ^* b ^* color space is viewed three-dimensionally. Here, CIE L ^* a ^* b ^* for each ink color (cyan C, magenta M, yellow Y, black K, light cyan LC, light magenta LM, light black LK, light light black LLK) installed in the printer 1 described above ^. The path obtained by plotting the colorimetric values in the color space is shown.

Referring to each figure, the path taken through the space differs depending on each ink color, and the lengths of these curves also differ. The CIE L ^* a ^* b ^* color space is a uniform color space as described above, and the distance in this space indicates a color difference. When the curve length is long, the color difference between gradations is large, and when the curve length is short, the color difference between gradations is small.

  For example, the length of the yellow Y curve shown in the figure is longer than the length of the light black LK curve. Then, the color difference between the yellow Y gradation values is larger than the color difference between the light black LK gradation values.

As described above, depending on the ink color used, there are ink colors in which a color difference between gradations appears large and ink colors that appear relatively small. In color calibration, the color shift is corrected based on the color measurement results. However, if the same number of patches are measured for each ink color under such circumstances, the color difference between gradations appears to be small. in the case of color, L ^* while a ^* b ^* distance between colorimetric value in the color space can be obtained short colorimetric result, if the color the color difference between the gradation appears large, L ^* a ^* B ^* Color measurement results are obtained in which the distance between the color measurement values is separated in the color space.

If the color difference between tones is different for each color, you may want to increase the number of patches for colors that show a large color difference, but you may want to reduce the number of patches for colors that show a small color difference. is there. When the number of patches is insufficient, the accuracy of calibration correction is low, and when the number of patches is large, the color measurement time becomes long. Therefore, it is desirable that the number of patches of each ink color used is an appropriate number of patches. In the flowchart of the first embodiment shown below, the number of patches is determined based on the length of the curve in the L ^* a ^* b ^* color space of each ink color.

<How to determine the number of patches>
FIG. 7 is a flowchart for explaining the first embodiment. Hereinafter, the method for determining the number of patches in the first embodiment will be described with reference to this flowchart.

  First, a test chart with 0 to 255 gradations is printed (S202). Here, eight types of inks of cyan C, magenta M, yellow Y, black K, light cyan LC, light magenta LM, light black LK, and light light black LLK are used. A patch having each gradation value of 255 gradations is printed on a sheet. Since the test chart printed here is for determining the number of patches of each ink color, the same number of patches are printed for all ink colors. In addition, since the accuracy of the ink color to be measured is required, it is desirable that the output is performed by a printer that has already been calibrated.

  FIG. 8 is a diagram for explaining a test chart having the same number of patches for all ink colors. In the figure, patches of yellow Y, black K, light cyan LC, light magenta LM, and light black LK are omitted due to space limitations, and examples of test charts for cyan M, magenta M, and light light black LLK are shown. . The numbers in the figure are gradation values for each ink color.

  Next, color measurement of the printed test chart is performed (S204). When colorimetry is performed, colorimetric values corresponding to the patches on the paper are obtained.

Next, a colorimetric value interpolated in the patch is obtained (S206). By the way, when the head of the printer 1 prints a patch of a test chart, the head characteristics may fluctuate when shifting to printing of a patch of a different gradation. Therefore, although it should originally have a constant colorimetric value within one patch, in practice there are slight variations in color. Therefore, here, polynomial interpolation is performed using each of the L ^* value, a ^* value, and b ^* value of a plurality of adjacent patches, and the colorimetric value of each patch is obtained. Here, the colorimetric values of each patch are obtained using polynomial interpolation, but the colorimetric values of each patch are obtained by calculating the moving average of the colorimetric values of a plurality of adjacent patches. Also good.

Then, the calculated colorimetric value distance Delta] E _rt between 1 gradations, the sum _{E rt} of colorimetric value distance Delta] E _rt for each ink color is determined (S208). When the gradation value is k, the L ^* value is L _k ^* , the a ^* value is a _k ^* , and the b ^* value is b _k ^* . At this time, ΔE _rt between one gradation is
ΔE _rt = {(L _{k + 1} ^* −L _k ^* ) ² + ( _{ak 1} ^* −a _k ^* ) ² + (b _{k + 1} ^* −b _k ^* ) ² } ^1/2
Is calculated as This colorimetric value distance ΔE _rt is also a color difference between one gradation.

Next, the total value E _rt (the length of the color measurement value curve) of the color measurement value distance ΔE _rt for each ink color is obtained. In this way, the curve length E _rt in the L ^* a ^* b ^* color space of each ink color can be obtained.

Here, a test chart for eight types of ink is printed on one sheet of paper, and all ink colors are measured at once. However, one color patch of one ink color is printed on one sheet. Printing may be performed and color measurement may be performed for each ink color. In this case, the length E _rt of the curve in the L ^* a ^* b ^* color space of each ink color is obtained by performing the above-described calculations in steps S202 to S208 for each ink color.

FIG. 9 is an example of calculation of the number of patches when a test chart is printed on matte paper. In the drawing, the ink color and the length E _rt of the curve in the L ^* a ^* b ^* color space corresponding to each ink color are shown. For example, it is shown that 110.9995 is obtained as the length of the curve in the L ^* a ^* b ^* color space of the colorimetric value for cyan C. In the figure, the number of patches for each ink color is shown, which will be described later.

Next, the total length of the curves in the L ^* a ^* b ^* color space of the colorimetric values of all eight ink colors is obtained (S210). That is, the sum of the lengths of the curves in the L ^* a ^* b ^* color space of cyan C, magenta M, yellow Y, black K, light cyan LC, light magenta LM, light black LK, and light light black LLK is obtained. In FIG. 9, the result is shown as “Total” and 678.3068.

Next, the number of patches allocated for each ink color is calculated (S212). Here, a case where the total number of patches is determined in advance will be described. The number of patches allocated for each ink color can be obtained by the following equation.
Number of patches = (total number of patches−number of ink colors) × (E _{rt of the} corresponding ink color) / (total of E _rt of all ink colors) +1

For example, when obtaining the number of patches on calculated for cyan C, the total number of patches and 300, the number of ink colors and 8, the corresponding ink color of the _{E rt} and 110.7995, all ink colors _{E rt} 678.3068 Is substituted into the above equation. Then, the calculated number of patches for cyan C is 48.69739 as shown in the figure. In this way, the calculated number of patches for each ink color is obtained.

  However, the number of patches must be a natural number. Therefore, the number of patches in the above calculation result is rounded off to a natural number. For example, the number of cyan C patches is rounded to 49. The number of patches of each ink color obtained in this way is indicated as “number of patches”.

  Next, it is determined whether or not the total number of obtained patches matches the predetermined total number of patches (S214). This is because, as a result of the above rounding, the total number of patches of all ink colors may be larger or smaller than a predetermined number of patches (300 in the drawing). As a result of the determination, when the total number of obtained patches matches the predetermined number of patches (here, 300), this flow ends.

  On the other hand, if the total number of obtained patches and the predetermined number of patches do not match, the number of patches of the ink color with the largest number of patches is increased or decreased to match the predetermined number of patches ( S216). For example, if the total number of patches for each color obtained is large, the number of cyan C patches with the largest number of calculated patches is reduced and the total number of patches is adjusted to 300. Then, this flow ends.

  A patch of each ink color is created with the number of patches thus obtained. At that time, the patches are allocated so that the gradation value intervals are equal. By doing so, the patches can be allocated so that the distances between the colorimetric values between the patches in the color space are substantially equal over all ink colors. Then, uniform color calibration can be performed in the color space over all ink colors.

In particular, the L ^* a ^* b ^* color space is a uniform color space, and is a color space in which equidistances in color space coordinates are perceptually equal differences. Therefore, color calibration can be performed based on a patch having a perceptually uniform color difference over all ink colors. In addition, the color patches can be efficiently arranged on one sheet.

FIG. 10 is an example of calculation of the number of patches when a test chart is printed on glossy paper. In the figure, as in FIG. 9, the ink color and the length of the curve in the L ^* a ^* b ^* color space of each ink color are shown as the total E _rt . The number of patches is also shown for each ink color.

The length of the curve at each ink color of L ^* a ^* b ^* color space at the time of printing a test chart on glossy paper, the ink color of L ^* a ^* b ^* color space at the time of printing a test chart on matte paper The lengths of the curves at are different. This is because the reflected color differs depending on the degree of ink absorption on the paper, and the colorimetric values differ between the papers.

If the length of the curve in the L ^* a ^* b ^* color space of each ink color differs between sheets, the number of patches of each color determined based on the length of the curve also differs between sheets. Therefore, the number of test chart patches corresponding to each sheet may be obtained by performing the above-described embodiment for each different sheet.

  FIG. 11 is a flowchart of a method for determining the number of patches for each ink color when the total number of patches is variable. In the method for determining the number of patches when the total number of patches is variable, steps S202 to S210 of the method for determining the number of patches are performed in the same manner. Then, step S212 'described below is performed. Therefore, the description from step S202 to step S210 is omitted, and step S212 'will be described.

In step S212 ′, the number of patches for each ink color is calculated using the basic distance. The basic distance is a distance in an L ^* a ^* b ^* color space between patches arbitrarily set when creating a test chart. The number of patches of each color is obtained by the following formula.
Number of patches = (E _{rt of the} corresponding ink color / basic distance) +1

For example, _{E rt} of cyan C in the matte paper described above was 110.7995. Then, if the basic distance is determined as 2.5 and the number of patches is obtained by the above formula, 45.31981 is obtained. Since the number of patches must be a natural number, the number of patches on the matte paper is 45 when the decimal part is rounded off. Similarly, the number of patches of other ink colors can be obtained. FIG. 9 shows the number of patches of each color on the mat paper when the number of patches is obtained as variable. FIG. 10 shows the number of patches of each color on glossy paper when the number of patches is determined as variable.

=== Second Embodiment ===
FIG. 12 is a diagram for explaining the degree of color variation that occurs in the plane of the sheet when printing is performed on the sheet.

  In the figure, the paper feed direction is the paper feed direction in the printer. In the figure, the moving direction of the head of the printer is shown. The home side in the moving direction of the head is the home side on which the printer head stands by, and the opposite side is shown as the anti-home side. The vertical direction of the plane formed by the axis in the paper feeding direction and the axis in the head moving direction indicates the degree of color variation occurring in the plane of the paper.

The figure shows the degree of color variation depending on the position of a sheet when a color of a certain gradation value for a certain ink color is printed on one sheet. The degree of variation is represented by a deviation from the average value of the colorimetric values. If the average values of L ^* , a ^* , and b ^* are L ^* _ave , a ^* _ave , and b ^* _ave , respectively, the deviation at this time is obtained by the following equation.
Deviation = {(L ^* _ave− L ^* ) ² + (a ^* _ave− a ^* ) ² + (b ^* _ave− b ^* ) ² } ^1/2
Here, in the L ^* a ^* b ^* color space, L ^* _ave is 88.0, a ^* _ave value is −8.8, and b ^* _ave value is 58.9.

  According to this, it can be seen that periodic color variations occur in the paper feed direction. This is because the roller for feeding the paper of the printer 1 is not a perfect circle, so that a periodic difference occurs in the conveyance amount, and this causes periodic color variations. it is conceivable that.

  The color variation that occurs on the paper is recognized in any ink color, but the degree of variation varies depending on the ink color. That is, there are ink colors that tend to vary and ink colors that do not. For ink colors that tend to cause color variations in this way, it is desirable to perform calibration using a larger number of patches, and for ink colors that are less likely to vary, calibration should be performed with a smaller number of patches. it can. In this way, patches of each color can be efficiently arranged on a sheet by changing the number of patches according to the ease of color variation in the surface for each ink color.

  In the second embodiment, in consideration of this point, the number of patches of each ink color is adjusted by further considering the degree of variation for each ink color occurring in the plane of the paper.

<How to determine the number of patches>
FIG. 13 is a flowchart for explaining the second embodiment. Hereinafter, a method for determining the number of patches in the second embodiment will be described with reference to this flowchart. In the second embodiment, the number of patches is obtained in consideration of the length of the curve in the L ^* a ^* b ^* color space of each color and the degree of variation in ink color that occurs in the plane of the paper.

  First, a plurality of (here, 10) charts having 0 to 255 gradations are printed (S202). The test chart to be printed is the same as the test chart shown in FIG. Here, a plurality of charts are printed in order to obtain the degree of color variation occurring in the plane.

  The description in FIG. 12 is an example in which printing of the same gradation is performed with one color in order to make it easy to understand the phenomenon of color variation in printing. In step S202, 10 charts with the same color and the same gradation can be obtained by printing 10 charts of 0 to 255 gradations, and color variations in printing are similarly obtained. Can do.

  Next, color measurement of the printed test chart is performed (S304). Here, color measurement is performed on the ten test charts described above. Thereby, the colorimetric value corresponding to each patch is obtained for each sheet.

Next, a colorimetric value interpolated between patches is obtained for the first chart of the 10 charts (S306). As described above, even in one patch having one gradation value, there is a slight color variation. Therefore, polynomial interpolation is performed using each of the L ^* value, a ^* value, and b ^* value of a plurality of adjacent patches to obtain a colorimetric value for each patch.

  Here, the interpolated colorimetric values are obtained only for the first chart, but this is because the other nine test charts are printed in order to obtain the degree of color variation occurring in the plane of the paper. This is because the chart is made.

Next, the first sheet of chart, is computed colorimetric values distance Delta] E _rt between 1 gradations, the sum _{E rt} of colorimetric value distance Delta] E _rt for each ink color is determined (S308). When the gradation value is k, the L ^* value is L _k ^* , the a ^* value is a _k ^* , and the b ^* value is b _k ^* . At this time, ΔE _rt between one gradation is
ΔE _rt = {(L _{k + 1} ^* −L _k ^* ) ² + ( _{ak 1} ^* −a _k ^* ) ² + (b _{k + 1} ^* −b _k ^* ) ² } ^1/2
Is calculated as This colorimetric value distance ΔE _rt is also a color difference between one gradation.

Next, the total value E _rt (the length of the color measurement value curve) of the color measurement value distance ΔE _rt for each ink color is obtained. In this way, the length E _rt of the curve in each ink color L ^* a ^* b ^* color space can be obtained.

FIG. 14 is an example of the calculation of the number of patches in the second embodiment. In the drawing, the ink color and the length E _rt of the curve in the L ^* a ^* b ^* color space corresponding to each ink color are shown. For example, it is shown that 119.618 is obtained as the length of the curve in the L ^* a ^* b ^* color space of the colorimetric value for cyan C. In the figure, the number of patches for each ink color is shown, which will be described later.

Next, standard deviations σ of L ^* , a ^* , and b ^* for each patch of the test chart are obtained from the color measurement results of the plurality of test charts (S310). Specifically, the standard deviation of the L ^* value, a ^* value, and b ^* value of the patch at the same position obtained over a plurality of sheets is obtained. Here, in order to obtain the degree of color variation, the colorimetric value obtained by interpolation is not used, but the calculation is performed using the colorimetric value before interpolation.

The standard deviation of L ^* is σ _L , the standard deviation of a ^* is σ _a, and the standard deviation of b ^* is σ _b . The standard deviation for the L ^* values of N patches at the same position can be obtained by the following equation.

In the present embodiment, since the colorimetric values can be obtained from 10 sheets, N is 10. Further, σ _a and σ _b of each patch can be obtained by using an equation for obtaining a standard deviation similar to the above equation.

Next, from the standard deviations σ _L , σ _a , and σ _b for each color patch in the test chart, E _vr for each ink color patch is obtained using the following formula (S312). E _vr can be obtained by the following equation.
E _vr = (σ _L ² + σ _a ² + σ _b ² ) ^1/2
Then, _{E vr - ave} is calculated the average value of _{E vr} of all patches for each ink color (S314).

FIG. 15 is a diagram illustrating an example of E _{vr_ave} for each ink color. In the figure, _{Evr_ave} of each ink color is shown, and the ratio of each ink color _{Evr_ave} to all ink colors described later is shown next to the _{Evr_ave} .

Next, the sum of the lengths E _rt of the curves in the L ^* a ^* b ^* color space of the colorimetric values of all eight ink colors is obtained (S316). That is, the sum of the lengths of the curves in the L ^* a ^* b ^* color space of cyan C, magenta M, yellow Y, black K, light cyan LC, light magenta LM, light black LK, and light light black LLK is obtained. In FIG. 14, this result is shown as “Total”, and 740.1767 is shown.

Next, the number of patches allocated for each ink color is calculated (S318). Here, a case where the total number of patches is determined in advance will be described. Based on the length of the curve in the L ^* a _* b ^* color space of each color, the number of patches assigned to each ink color can be obtained by the following equation.
Number of patches = (total number of patches−number of ink colors) × (E _{rt of the} corresponding ink color) / (total of E _rt of all ink colors) +1

The calculation result obtained by substituting each numerical value for each ink color into the above equation is shown in the “Calculation” item of “Fixed total number of patches” of “Number of patches obtained from E _rt ”. For example, 48.18935 is shown as the calculation result for cyan C. In this way, the calculated number of patches obtained from the _{Ert of} each ink color is obtained.

Next, the sum of E _{vr — ave} for all ink colors is obtained (S320). FIG. 15 shows _{6.6367 as} the total value of the average values E _{vr_ave} for all ink colors. Further, in the figure, there is shown the ratio of the time divided by 6.6367 of total values for each ink color of _{E vr - ave.}

E _{vr — ave} indicates the degree of color variation in the paper of each ink color. Therefore, the larger these numerical values, the greater the degree of color variation that occurs on the paper. _{Referring to} the ratio of _{Evr_ave,} the ratio of black K is 0.1857, which is the largest. Therefore, among the inks used in this embodiment, the degree of color variation on the black K paper is the largest. On the other hand, here, the ratio of light light black LLK is 0.0676, which is the smallest. Therefore, among the inks used in this embodiment, the degree of color variation in the light / light black LLK paper is the smallest.

Next, the number of patches of each ink color is obtained from the degree of variation E _{vr_ave} of each ink color (S318). To obtain the number of patches of each ink color from E _{vt_ave} , the following equation is used.
Number of patches = (total number of patches−number of ink colors) × ( _{Evr_ave of the} corresponding ink color) / (total of _{Evr_ave} of all ink colors) +1

For example, when calculating the number of patches for cyan C, the total number of patches is 300, the number of ink colors is 8, _{Evr_ave of the} corresponding ink color is 0.8918, and the total of _{Evr_ave} of all ink colors is 6 .6367 is substituted into the above equation. Then, the number of patches for the calculation of cyan C is 40.31192 as shown in the figure. In this way, the number of patches for calculation of each color is obtained.

Next, the number of patches is determined in consideration of the length of the curve in the L ^* a ^* b ^* color space and the degree of color variation in the paper (S324). Here, the number of patches is obtained by taking a weighted average of the number of patches calculated from E _rt and the number of patches calculated from E _vr . In order to simplify the description, here, it is assumed that an average of the number of patches calculated from E _rt and the number of patches calculated from E _vr is obtained.

For example, the number of patches calculated from _{E rt} in cyan C was 48.18935. In Cyan C, the number of patches calculated from E _vr was 40.31192. The average of these is 44.25064. In this way, the number of patches for calculation of each color is obtained.

  By the way, the number of patches must be a natural number. Therefore, the number of patches in the above calculation result is rounded off to a natural number. For example, the number of cyan C patches is 44 when rounded off. In this way, the number of patches (natural number) of each ink color is obtained.

  Next, it is determined whether or not the total number of obtained patches matches the predetermined number of patches (S326). This is because, in the above calculation result, the total number of patches of each ink color may be larger or smaller than a predetermined number of patches (300 in the figure). As a result of the determination, when the total number of obtained patches matches the predetermined number of patches, this flow ends.

  On the other hand, if the total number of patches obtained does not match the predetermined number of patches, the number of ink colors with a large number of patches is increased or decreased to match the predetermined number of patches (S328). ). In FIG. 14, the number of patches for calculation of magenta M is 48.73036, which is 49 when rounded off. At this time, the total number of obtained patches of each ink color is 299. However, this does not match the predetermined number of patches of 300. Therefore, 1 is added to the number of patches of magenta M having the ink color with the largest number of patches, and the number of patches is set to 50. In this way, the number of patches is adjusted to match the predetermined number of patches.

  By doing so, it is possible to determine the number of patches of each ink color by further considering the degree of color variation occurring in the plane of the paper.

In the second embodiment, the number of patches obtained from E _rt may be calculated using the basic distance. For example, _{E rt} cyan C was 119.618. Then, when the basic distance is determined as 2.5 and the number of patches is obtained, it is 48.84721. In this way, the variable total number of patches is obtained from _Ert .

Next, an average of the number of patches obtained as a result of _{obtaining the} variable total number of patches _Ert and the number of patches calculated from _Evr is obtained. For example, the number of patches calculated from _{E rt} in cyan was 48.84721. The number of patches calculated from E _vr in cyan was 40.31192. The average of these is 44.57957. Then, the number of patches of 45 is obtained by rounding off the decimal part of the calculation result to a natural number.

=== Other Embodiments ===
The above-described embodiments are for facilitating the understanding of the present invention, and are not intended to limit the present invention. The present invention can be changed and improved without departing from the gist thereof, and it is needless to say that the present invention includes equivalents thereof.

It is a figure which shows the structure of the determination system of the number of patches of each ink color in a test chart. It is a figure for demonstrating the structure of a color measuring device. This is an example when the CIE L ^* a ^* b ^* color space is viewed in the a ^* b ^* coordinate direction from L * = 100. This is an example when the CIE L ^* a ^* b ^* color space is viewed in the L ^* b ^* coordinate direction from a ^* = 120. This is an example when the CIE L ^* a ^* b ^* color space is viewed in the L ^* a ^* coordinate direction from b ^* = 120. This is an example when the CIE L ^* a ^* b ^* color space is viewed three-dimensionally. It is a flowchart for demonstrating 1st Embodiment. It is a figure for demonstrating the test chart which has the same number of patches about all the ink colors. It is an example of calculation of the number of patches when a test chart is printed on mat paper. It is an example of calculation of the number of patches when a test chart is printed on glossy paper. It is a flowchart about the determination method of the number of patches of each ink color when the total number of patches is variable. FIG. 6 is a diagram for explaining the degree of color variation that occurs in the surface of a sheet when printing is performed on the sheet. It is a flowchart for demonstrating 2nd Embodiment. It is an example of calculation of the number of patches in the second embodiment. It is a figure which shows an example of _{Evr_ave} of each ink color.

Explanation of symbols

1 printer,
40 color measuring device, 41 color measuring table, 42 backing,
43 Color measuring head, 44 Color measuring device carriage, 45 rail,
46 paper feed rollers, 100 computers

Claims (12)

A method for determining the number of patches of each color in a test chart used for color calibration,
Obtaining a colorimetric value in a color space corresponding to each gradation value for each of the first color and the second color;
Obtaining the number of patches of the first color based on the colorimetric value of the first color, and obtaining the number of patches of the second color based on the colorimetric value of the second color;
How to determine the number of patches that contain   The method for determining the number of patches according to claim 1, wherein the number of patches of the first color is different from the number of patches of the second color.   The number of patches of the first color and the number of patches of the second color based on the length of the curve in the color space of the first color and the second color obtained from the acquired colorimetric value The method for determining the number of patches according to claim 1 or 2, wherein:   The method for determining the number of patches according to claim 3, wherein a larger number of patches are assigned as the length of the curve in the color space is longer.   A length of the curve of the first color is obtained based on a sum of distances between colorimetric values in a color space corresponding to the gradation values of the first color, and the gradation values of the second color are obtained. 5. The method for determining the number of patches according to claim 3, wherein a length of the curve of the second color is obtained based on a sum of distances between colorimetric values in a color space corresponding to.   The number of patches of the first color and the second color so that the distance between the colorimetric values between the patches of the first color and the distance of the colorimetric values between the patches of the second color are equal. The method for determining the number of patches according to claim 1, wherein the number of patches of color is obtained. Further, for each of the first color and the second color, including a step of obtaining a variation degree of the color space in the medium,
According to the length of the curve in the color space of the first color and the second color, and the degree of variation in the colorimetric values of the color space of the first color and the second color in the medium, The method for determining the number of patches according to claim 1, wherein the number of patches of the first color and the second color is obtained.   The method for determining the number of patches according to claim 1, wherein the color space is a uniform color space. The method according to claim 1, wherein the color space is a CIE L ^* a ^* b ^* color space. Printing a test chart including a plurality of patches of a first color and a plurality of patches of a second color having a larger number of patches than the plurality of patches of the first color;
Steps of measuring the plurality of patches of the first color to calibrate the first color, and measuring the plurality of patches of the second color to calibrate the second color. When,
Calibration method including:   The calibration method according to claim 8, wherein a distance in a color space between the first color patches is equal to a distance in a color space between the second color patches. A controller for printing a test chart comprising a plurality of patches of a first color and a plurality of patches of a second color having a larger number of patches than the plurality of patches of the first color;
A first correction value obtained by calibration of the first color using the colorimetric results of the plurality of patches of the first color, and a second color using the colorimetry results of the plurality of patches of the second color. A memory for storing a second correction value by calibration of
A printing apparatus comprising:

Images