JP2007174125A - Gray adjusting method and recording system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of performing a gray adjustment that is simpler and more accurate in a color printer. <P>SOLUTION: A user records an image for ascertaining the state of gray, subjects the image to colorimetrics processing, and acquires image data. Then, a point at which a gray adjustment is required is designated, a colormetrics adjustment target value for the designated point is calculated from data representing gray near to the shade of gray at the designated point resting on the basis of the obtained image data. Furthermore, image data representing gray modifying patches used for gray adjustments made for the designated point are formed on the basis of data representing the gray at the designated point, and the modifying patches are recorded. The gray patches are recorded and subjected to colorimetrics processing. Lastly, a patch close to the modifying target value is selected from the peripheral patches to adjust gray. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a gray adjustment method and a recording system, and more particularly to a gray adjustment method and a recording system for adjusting, for example, gray color shift in an ink jet recording apparatus.

  Recording devices such as ink-jet color printers include cyan (C), magenta (M), yellow (Y), and black (K) inks as well as light cyan (LC) and light magenta (LM). Some printers use light ink to form a color image. In many cases, the gray color of a color image recorded by this printer is recorded not only with K ink but also with a combination of a plurality of inks such as C, M, Y, LC, and LM.

  Therefore, the greater the number of inks that make up gray, the more likely it is that the ejection of each ink will change due to the effects of changes over time, differences in solids, etc. The possibility of occurrence is also increased. Since the characteristics of the human eye are very sensitive to colors in the vicinity of gray, in some cases, even if the ink ejection characteristics slightly change, gray color shakes and color shifts are recognized.

  Conventionally, several methods have been proposed for correcting gray color fluctuations and color shifts due to the effects of changes over time and differences in solids. For example, according to Patent Document 1, a patch (custom A pattern) for checking gray color shake or color shift is printed, and color shake or color shift is determined from the patch. Then, a gray patch (custom B pattern) for correction is printed, and the user selects an optimal gray patch, creates a color correction lookup table corresponding to the selection, and performs color correction.

For example, according to Patent Document 2, a color test pattern including a color patch representing a preferable halftone gray is printed, compared with a reference gray prepared in advance, and the user selects a color patch closest to gray. Then, a color conversion lookup table is created from the relationship between the selected patch and the reference gray, and color correction is performed.
Japanese Patent No. 3552874 (FIG. 24, page 23) US Pat. No. 6008907 (FIG. 3, page 4)

  However, the above conventional example has the following problems.

  In the case of the invention described in Patent Document 1, since there is no comparison-use gray chart, the user has to imagine the optimal color tone of the gray at the correction location from the gray color other than the correction location. Then, the patch that looks similar to the ideal gray you imagined must be selected from among the gray patches for correction that have slightly different colors (there are only a few color differences). There is a problem that it is very difficult to judge.

  In the case of the invention described in Patent Document 2, since there is a gray chart for comparison, selecting the optimum gray patch from the correction gray patches is the case of the invention described in Patent Document 1. It is relatively easy. However, the dynamic range of the comparison gray chart and the dynamic range of the combination of the recording apparatus to be adjusted and the recording medium are hardly the same. For this reason, it is necessary to select a correction gray patch while taking into account the difference in brightness between the correction gray patch and the corresponding reference gray patch, which is a very difficult task. In addition, this method has a problem that it is not possible to cope with a case where the user wants a desired gray color instead of a predetermined standard gray color.

  The present invention has been made in view of the above-described conventional example, and an object thereof is to provide a gray adjustment method and a recording system capable of performing gray adjustment in a color recording apparatus more easily and accurately.

  In order to achieve the above object, the gray adjustment method of the present invention comprises the following steps.

  That is, a gray adjustment method for a recording apparatus that records a color image based on color image data obtained by performing image processing including gamma conversion processing and color conversion processing on input color image data, the gamma conversion A first recording step of recording a gray state confirmation image from the recording device using a current conversion table used in the processing and color conversion processing; and a first colorimetric measurement of the confirmation image by a colorimeter Based on the colorimetry step, the designation step for specifying the location where gray adjustment is required in the confirmation image in man-machine interactive, and the image data obtained by the colorimetry in the first colorimetry step, A calculation step of calculating a colorimetric adjustment target value for the specified location from data representing gray close to the gray density of the specified location, and representing the gray of the specified location. A generation step of generating image data representing a plurality of patches for gray correction used for gray adjustment of the designated location based on the data to be processed, and from the recording device based on the image data generated in the generation step A second recording step of recording the plurality of correction patches; a second color measurement step of measuring the plurality of correction patches by the colorimeter; and the adjustment target value and each of the plurality of correction patches. A selection step of comparing and referring to the colorimetric data to be represented and selecting a patch that minimizes the color difference between the two, and the gamma conversion processing and the color conversion processing based on the data represented by the patch selected in the selection step A change process for changing the value of the conversion table used in any of the processes, and a confirmation image after gray adjustment using the conversion data changed in the change process. And having a third recording process of.

  It is desirable that the confirmation image recorded in the first recording step includes an image in which gray shades change continuously and a plurality of patches in which gray shades change discretely.

  It is preferable that the data expressing the gray and the colorimetric data are expressed by an L * a * b * space.

  In this case, in the calculation of the adjustment target value, the lightness representing the L * component is the same value as the data represented by the designated portion, and the chromaticity representing the a * component and the b * component is the colorimetric data. It is desirable to calculate by interpolation calculation.

  Further, in the generating step, L * a * b * data is calculated by regarding the RGB data representing the gray of the designated portion as a theoretical value of sRGB data, and the calculated L * a * b * data is calculated. It is desirable to generate image data representing a plurality of patches for gray correction by calculating L * a * b * data in which saturation and hue are changed by a plurality of values as the center.

  The input color image data is multi-value RGB data, and it is desirable to use a one-dimensional lookup table for the gamma conversion process and a three-dimensional lookup table for the color conversion process.

  In this case, in the changing step, when changing the conversion table of the color conversion process, it is preferable to change the gray axis table data of the three-dimensional lookup table, or to change the conversion table of the gamma conversion process. In this case, it is better to change the one-dimensional lookup table.

  In the selection step, the colorimetric data representing each of the plurality of correction patches is interpolated to increase the number of the plurality of correction patches, and the colorimetry representing each of the plurality of correction patches increased. It is preferable to compare and refer to the data and the adjustment target value and select a patch that minimizes the color difference between the two.

  According to another aspect of the invention, there is provided a recording system to which the gray adjustment method having the above configuration is applied, the recording system being recorded by a recording device, a host device that supplies image data to the recording device, and the recording device. A recording system including a colorimeter that performs colorimetry of an image.

  According to the present invention, in gray adjustment, instead of visually selecting the optimum gray from patches around the adjustment location designated by the user, data representing the designated location and surrounding patches is recorded and measured. Select by calculation based on colored data.

  In the conventional visual selection, it has been very difficult to select a desired optimal gray from gray patches around the adjustment point, which is slightly different in color. However, according to the present invention, the target value of the correction point is calculated and the target value is calculated. It is possible to automatically select a patch that is colorimetrically close to the value. Thereby, there is an effect that gray can be finely adjusted more easily.

  Further, since the target value is automatically calculated without using the reference gray chart, there is an effect that the optimum gray can be selected with high accuracy.

  In addition, the color correction patches are not recorded and colorimetrically measured in the entire gray range, but patches are recorded and colorimetrically measured only at user-specified locations, reducing time and labor when adjusting gray. There is also an advantage of being able to.

  Also, when creating a normal color conversion table, color patches are recorded and colorimetry is performed to create a color conversion table. Since there are few patches around the gray included in this color patch, gray is adjusted with sufficient accuracy. I can't say that. On the other hand, according to the present invention, the patches around the designated adjustment location are adjusted, for example, by obtaining a large number of patches by finely changing the saturation and hue, and adjusting the gray using the data recorded and measured. , More accurate gray can be adjusted.

  Hereinafter, preferred embodiments of the present invention will be described more specifically and in detail with reference to the accompanying drawings.

  In this embodiment, a gray adjustment method in an ink jet recording apparatus (hereinafter referred to as a recording apparatus) that inputs RGB image data and records a color image will be described.

  This recording apparatus uses, for example, a recording head that ejects four colors of ink of cyan (C), magenta (M), yellow (Y), and black (K), and uses, for example, large formats such as A3, A2, and A1. The recording apparatus records a color image on the recording medium. Of course, it goes without saying that the recording apparatus to which the present invention is applied is applied to a recording apparatus that records on a relatively small recording medium such as A3 or smaller, for example, B4, A4, B5 size.

  FIG. 1 is a diagram showing a flow of image processing executed by the recording apparatus until actual recording.

  In FIG. 1, input multi-value RGB image data 10 is converted into R′G′B ′ data by an input gamma processing unit 11. The input gamma processing unit 10 performs gamma conversion using a one-dimensional lookup table for color adjustment processing by the user in the printer driver, for example, adjustment of brightness, color balance, contrast, and the like.

  The R'G'B 'data after the input gamma processing is then converted into R "G" B "data by the color conversion processing unit 12. This color conversion processing is performed from the RGB space data of the input image. This is a process using a three-dimensional lookup table for mapping to device RGB space data specific to the recording apparatus to be actually recorded.Normally, the color of the recording apparatus is created by this color conversion process. .

  Next, the R "G" B "data after the color conversion process is converted into density data corresponding to the CMYK ink color by the ink color separation processing unit 13. This ink color separation process is performed on the target recording apparatus. The inherent device RGB space data is performed by a three-dimensional lookup table in which ink is separated so as to maximize the color gamut in the recording apparatus.The CMYK data after ink color separation processing is output gamma processing section. 14 is converted into C′M′Y′K ′ data in step 14. The output gamma processing unit performs processing for adjusting the output characteristics of each ink. 'Data is converted into N-valued C "M" Y "K" data by the halftone processing unit 15, and recording is performed in the recording apparatus using this data.

  FIG. 2 is a block diagram showing a system configuration for realizing the gray adjustment method.

  As shown in FIG. 2, this system includes an ink jet recording apparatus (hereinafter referred to as a recording apparatus) 100 on which the above-described recording head is mounted, a colorimeter 110, and a host PC 120. The host PC 120 is connected to the recording apparatus 100 via a USB interface or the like, and supplies image data to the recording apparatus 100.

  The host PC 120 is operated by an operating system (OS) 121 such as WINDOWS (registered trademark) and executes an application (APPL) 122. The image data generated by the application 122 is converted into image data that can be processed by the recording apparatus 100 by the printer driver 123 and transferred to the recording apparatus 100 via the communication interface (I / F) 124.

  FIG. 3 is a diagram illustrating a schematic configuration of the recording apparatus 100.

  In FIG. 3, reference numeral 601 denotes a head cartridge. This is composed of four independent recording heads respectively corresponding to ink tanks filled with four color inks of black (K), cyan (C), magenta (M) and yellow (Y). Each recording head has 1280 nozzles. Reference numeral 602 denotes a carriage that supports the head cartridge 601 and moves them together with recording. The carriage 602 is at the home position (HP) shown in the drawing during standby such as a non-recording state. Reference numeral 603 denotes a conveyance roller, which rotates while holding the recording paper 605 together with an auxiliary roller (not shown), and conveys the recording paper 605 in the Y direction as needed. Reference numeral 604 denotes a paper feed roller that feeds the recording paper 605 and plays a role of suppressing the recording paper 605 in the same manner as the transport roller 603 and the auxiliary roller.

  Each of the four recording heads has 1280 nozzles arranged in the transport direction.

  A basic bidirectional recording operation in the above configuration will be described with reference to FIG.

  During standby, the carriage 602 at the home position (HP) performs recording by ejecting ink onto the recording paper 605 according to the recording data by a plurality of nozzles of the recording head while moving in the X direction by a recording start command. This carriage movement direction is called the main scanning direction. When the recording is completed to the end of the recording paper 605, the recording paper 605 is conveyed by a predetermined width in the Y direction by the rotation of the conveying roller 604. This recording paper conveyance direction is referred to as the sub-scanning direction. Subsequently, the carriage 602 performs recording by discharging ink while moving the X direction in the reverse direction, and the carriage 602 returns to the home position (HP). Image recording is realized by repeating the carriage scanning operation and the recording paper transport operation.

  Four pl ink droplets are ejected by one ejection operation from four recording heads each having 1280 nozzles used in the recording apparatus of this embodiment. Further, 1280 nozzle rows are arranged in order as nozzle rows for ejecting K, C, M, and Y inks in the main scanning direction. Further, the nozzle resolution of the recording head is 1200 dpi.

  Note that the image processing shown in FIG. 1 is realized by the following three basic processing configurations by load distribution between the host PC and the recording apparatus. The first configuration is a configuration in which all image processing is executed by the printer driver 123 shown in FIG. The second configuration is a configuration in which the recording apparatus 100 inputs multi-value RGB image data, and the image processing is executed by an image processing unit configured by an MPU, an ASIC, or a system LSI provided in the recording apparatus. The third configuration is a configuration in which the recording apparatus takes charge of part of the image processing shown in FIG. 1 and the host PC takes charge of the rest.

  In the case of the first configuration, the gray adjustment table obtained by the gray adjustment method described below is reflected in the printer driver. In the case of the second configuration, the gray adjustment table is transferred from the host PC to the recording apparatus, and the MPU, ASIC, or system LSI lookup table is changed. In the case of the third configuration, the gray adjustment table is reflected in the printer driver or the recording apparatus.

  FIG. 4 is a flowchart showing the work procedure of the gray adjustment method. Here, a method for adjusting the gray recorded by the recording apparatus 100 will be described.

  First, in step S201, a confirmation image for confirming the gray state recorded by the recording apparatus 100 is recorded. Then, this confirmation image is measured by a colorimeter to generate image data.

  FIG. 5 is a diagram showing an example of a gray confirmation image.

  The portion (a) of the confirmation image shown in FIG. 5 has a gradation from white to black, the density of which continuously changes, and the shake of gray tone can be easily confirmed. On the other hand, the part (b) records a patch whose density changes stepwise based on the data of the grid point position of the gray axis in the three-dimensional lookup table of the color conversion processing unit 12. In addition, numbers (1 to 16) are assigned to the patches in the portion (b) so that the patches can be easily identified. Further, (a) and (b) are arranged so that the positions of the respective gradations are substantially the same position. The recording apparatus 100 is set by selecting a recording mode and a recording medium that are actually used.

  In the next step S202, the user visually confirms the recorded confirmation image, and designates a location where a color tone fluctuation has occurred. For this designation, the corresponding image is displayed on the display (not shown) of the host PC 120 by the data used for recording the confirmation image, and the display screen is clicked using a pointing device and a keyboard (not shown). Do. Alternatively, it is possible to visually determine a portion having a tone fluctuation from the gradation of (a) and the patch portion of (b) of the recorded confirmation image, and specify the patch number of (b) by inputting with a keyboard. In this way, one or more locations that need correction may be designated.

  In step S203, gray correction patch image data is generated. Here, a patch image is created by combining the gray patch around the correction location designated in step S202 and the gray patch of FIG. 5B. For the gray patch around the designated location, for example, data is created by the following method.

  L * a * b * data is calculated by regarding the RGB of the gray patch gradation value at the designated location as the theoretical value of the sRGB data. The theoretical L * a * b * value of the surrounding gray with the saturation and hue centered on the calculated L * a * b * data is calculated, and the theoretical formula is calculated from the relational expression of L * a * b * -sRGB. A theoretical RGB value corresponding to the L * a * b * value is calculated. For example, assuming that the saturation is changed in three steps and the hue is changed in increments of 20 °, 3 × (360 ÷ 20) = 54 peripheral patches are output for each correction portion.

  In step S204, a patch image is recorded using the gray correction patch image data created in step S203. The same setting as the setting for recording the confirmation image in step S201 is performed and recorded by the recording apparatus 100.

  In step S205, the recorded patch image for gray correction is measured with a colorimeter. This color measurement uses a colorimeter so that L * a * b * data can be measured. Save the measured data as a file. This color measurement data file is stored in a hard disk (not shown) of the host PC 120.

  In step S206, a gray adjustment table is created. Here, a gray adjustment table is created by inputting the correction part number designated in step S202 and the colorimetric data file obtained in step S205. The gray adjustment table created in this embodiment is obtained by correcting the gray axis table data of the three-dimensional lookup table of the color conversion processing unit 12 shown in FIG. A method for creating the gray adjustment table will be described in detail later.

  In step S207, the adjusted confirmation image is recorded. Here, the three-dimensional lookup table of the color conversion process 12 is replaced with the gray adjustment table created in step S206, and the same confirmation image as in step S201 is recorded.

  Finally, in step S208, the confirmation image recorded in step S207 is visually confirmed. When the gray color tone is not lost, the gray adjustment is terminated. When the color tone is still lost, the process returns to step S202. Continue to fix.

  Here, details of the gray adjustment table creation method performed in step S206 will be described.

  FIG. 6 is a flowchart showing a procedure for creating a gray adjustment table.

  In step S401, the number of the correction portion designated in step S202 is acquired, and the gray gradation value to be corrected corresponding to the number is acquired.

  In step S402, the color measurement data is acquired from the color measurement data file acquired in step S205, and the color measurement data of the current gray patch and the gray patch around the correction portion are acquired.

  In step S403, the target L * a * b * of the correction location designated in step S202 is calculated. In this embodiment, the L * value representing brightness is left unchanged as the original L * value. On the other hand, with respect to the a * and b * values that are chromaticity data, the a * and b * values are calculated by interpolation based on the a * and b * values of the gray patches of the normal color tone that are adjacent to the corrected portion.

  For example, when linear interpolation is used, the target L * a * b * of the corrected portion is calculated as follows.

  First, the colorimetric values (L *, a *, b *) of normal gray patches on both sides are set to (L1, a1, b1) and (L2, a2, b2), respectively. On the other hand, the colorimetric values (L *, a *, b *) of the designated correction location are set to (L0, a0, b0), and the target values (L *, a *, b *) of the correction location are set to (Lt, at , Bt), Lt, at, bt are as follows.

That is,
Lt = L0,
at = (L2-L0) / (L2-L1) × a0 +
(L0-L1) / (L2-L1) × a1,
bt = (L2-L0) / (L2-L1) × b0 +
(L0-L1) / (L2-L1) × b1
It is.

  In step S404, a gray patch that is colorimetrically close to the target (L * a * b *) value of the correction portion calculated in step S403 is searched from the peripheral patches. Here, the color difference ΔE between the gray patch around the designated correction portion and the target (L * a * b * value) is calculated, and the gray patch with the smallest color difference ΔE is searched. The RGB value of the searched gray patch is replaced with the table value of the correction part, and the table is corrected.

  Therefore, according to the embodiment described above, gray adjustment can be easily performed with high accuracy in a man-machine interactive manner.

<Other embodiments>
The method of creating the gray adjustment table shown in FIG. 6 is not limited to this. For example, it is possible to create a gray adjustment table by the procedure shown in FIG. In FIG. 7, the same processing steps as those described in FIG. 6 are denoted by the same step reference numerals, and the description thereof is omitted.

  Only the characteristic part of the processing of FIG. 7 will be described below.

  In step S403a, virtual data existing between patches is generated by calculation from the colorimetric data of the gray patch around the specified correction portion, and the number of data is increased.

  For example, in the same way as described in connection with step S203, for example, assuming that the saturation is shaken in three stages and the hue is changed in increments of 20 °, 3 × (360 ÷ 20) = 54 surroundings per correction point A gray patch is obtained.

  At this time, first, the number of data is increased by interpolation calculation using two data adjacent in the saturation direction. As a result, it is possible to create data of steps in five steps in the saturation direction, and it is possible to increase the data from 54 data to 5 × (360 ÷ 20) = 90. Next, intermediate data in the hue direction at each saturation is created. In the same saturation data, when intermediate data between adjacent data is created by interpolation calculation, the hue can be obtained in increments of 10 °. Thereby, the data can be increased from 90 data to 5 × (360 ÷ 10) = 180. In this way, the data of the gray patch around the corrected portion is increased and a database is created.

  In the last step S404a, a gray patch colorimetrically close to the target (L * a * b *) value of the correction portion calculated in step S403 is searched from the peripheral patch database created in step S403a. Here, the color difference ΔE between the gray patch of the database and the target (L * a * b *) value is calculated, and the gray patch with the smallest color difference ΔE is searched. Then, the RGB value of the searched gray patch is replaced with the table value of the corrected portion, and the table is corrected.

<Another Example>
In step S206 of FIG. 4, the example of creating the gray adjustment table for correcting the gray axis table data of the three-dimensional lookup table of the color conversion processing unit 12 shown in FIG. 1 has been described. It is not limited.

  For example, the one-dimensional lookup table of the input gamma processing unit 11 shown in FIG. 1 may be modified by changing the processing in step S404 in FIG.

  FIG. 8 is a flowchart illustrating a procedure for adjusting gray by changing the one-dimensional lookup table of the input gamma processing unit 11.

  First, in step S601, the input gamma table before correction is sampled, and the table value of the input gamma table located at the gray patch gradation value shown in FIG. 5B is stored.

  Next, in step S602, the optimum gray for the corrected portion is searched. In this embodiment, the color difference ΔE between the target (L * a * b *) value of the correction location and the peripheral gray patch is calculated, and a gray patch having the smallest color difference ΔE is searched for, and this is set as the optimum gray. .

  Further, in step S603, the sampling data corresponding to the corrected portion acquired in step S601 is replaced with the optimum gray searched in step S602.

  Finally, in step S604, intermediate data is created by interpolation calculation so as to smoothly connect the replaced sampling data, and a one-dimensional lookup table is created, and the created one-dimensional lookup table is used as an input gamma table.

It is a figure which shows the flow of the image process which a recording device performs by actual recording. It is a block diagram which shows the structure of the system which implement | achieves the adjustment method of gray. 1 is a diagram illustrating a schematic configuration of a recording apparatus 100. FIG. It is a flowchart which shows the operation | movement procedure of a gray adjustment method. It is a figure which shows the example of the image for gray confirmation. It is a flowchart which shows the procedure of table preparation for gray adjustment. It is a flowchart which shows the gray adjustment table preparation procedure according to another Example. 4 is a flowchart showing a procedure for adjusting gray by changing a one-dimensional lookup table of an input gamma processing unit 11.

Explanation of symbols

10 Input RGB Image Data 11 Input Gamma Processing Unit 12 Color Conversion Processing Unit 13 Ink Color Separation Processing Unit 14 Output Gamma Processing Unit 15 Halftone Processing Unit

Claims (11)

A gray adjustment method for a recording apparatus for recording a color image based on color image data obtained by performing image processing including gamma conversion processing and color conversion processing on input color image data,
A first recording step of recording a gray state confirmation image from the recording device using a current conversion table used in the gamma conversion processing and color conversion processing;
A first colorimetry step for measuring the confirmation image with a colorimeter;
A designation process for designating a place where gray adjustment is required in the confirmation image in man-machine interactive;
Based on the image data obtained by the colorimetry in the first colorimetry step, a colorimetric adjustment target value for the designated location is obtained from data representing gray close to the gray density of the designated location. A calculation step of calculating
Based on the data representing the gray of the designated location, a generation step of generating image data representing a plurality of gray correction patches used for gray adjustment of the designated location;
A second recording step of recording the plurality of correction patches from the recording device based on the image data generated in the generation step;
A second color measurement step of measuring the plurality of correction patches with the colorimeter;
A selection step of comparing and referring to the adjustment target value and the colorimetric data representing each of the plurality of correction patches to select a patch that minimizes the color difference between the two;
A change step of changing a value of a conversion table used for any of the gamma conversion processing and the color conversion processing based on data represented by the patch selected in the selection step;
And a third recording step of recording a confirmation image after gray adjustment using the conversion data changed in the changing step.   2. The gray according to claim 1, wherein the confirmation image recorded in the first recording step includes an image in which gray shades change continuously and a plurality of patches in which gray shades change discretely. Adjustment method.   The gray adjustment method according to claim 1 or 2, wherein the data representing the gray and the colorimetric data are represented by an L * a * b * space.   In the calculation of the adjustment target value in the calculation step, the brightness representing the L * component is the value of the data represented by the designated location, and the chromaticity representing the a * component and the b * component is the colorimetric data. The gray adjustment method according to claim 3, wherein the gray adjustment method is calculated by interpolation calculation.   In the generating step, L * a * b * data is calculated by regarding the RGB data representing gray of the designated portion as a theoretical value of sRGB data, and the calculated L * a * b * data is the center. 5. The image data representing a plurality of gray correction patches is generated by calculating L * a * b * data in which saturation and hue are changed by a plurality of values, respectively. Gray adjustment method. The input color image data is multi-value RGB data,
A one-dimensional lookup table is used for the gamma conversion process,
6. The gray adjustment method according to claim 5, wherein a three-dimensional lookup table is used for the color conversion processing.   The gray adjustment method according to claim 6, wherein in the changing step, table data of the gray axis of the three-dimensional lookup table is changed.   The gray adjustment method according to claim 6, wherein in the changing step, the one-dimensional lookup table is changed.   The selecting step increases the number of the plurality of correction patches by interpolating calorimetric data representing each of the plurality of correction patches, and the color measurement representing each of the plurality of correction patches having the increased number. 2. The gray adjustment method according to claim 1, wherein a patch having a minimum color difference is selected by comparing and referring to the data and the adjustment target value. A recording system to which the gray adjustment method according to claim 1 is applied,
The recording system includes: a recording apparatus; a host apparatus that supplies image data to the recording apparatus; and a colorimeter that performs colorimetry of an image recorded by the recording apparatus. The recording apparatus includes an inkjet recording head that performs color recording by discharging a plurality of colors of ink,
The recording system according to claim 10, wherein gray is expressed by a combination of the plurality of color inks.