Color adjustment method, color adjustment program, and information processor

Abstract

To adjust a color and a gradation of an image printed by a plurality of heads.MEANS FOR SOLVING THE PROBLEM: A color adjustment method includes: a formation step of relatively moving a plurality of heads arranged with nozzles discharging a liquid and a recording medium, and discharging a liquid from the plurality of heads arranged in a direction crossing the relative movement direction and forming an image for color adjustment on the recording medium; an acquisition step of acquiring a colorimetric value of the image for color adjustment; a determination step of determining whether or not to adjust the plurality of heads, using the colorimetric value; a generation step of generating a target indicating a target value for each gradation value common to the plurality of heads using the colorimetric value, when it has been determined that it is necessary to adjust the head; and a step of storing the adjustment values of the plurality of heads which have been changed on the basis of the target, in a storage part.SELECTED DRAWING: Figure 11

Description

[Technical field]

[0001] The present invention relates to a color adjustment method, a color adjustment program, and an information processing device. [Background technology]

[0002] Conventionally, there is known a technique for forming a test image on a sheet to generate a test chart, and performing calibration to adjust image forming conditions using the test image. As an example, conventionally, there is known an image forming apparatus in which, if the test chart is formed of a first type of sheet, the test image is read while being conveyed using an ADF unit, and, if the test chart is formed of a second type of sheet, the sheet is fixed to a platen glass and the test image is read, and calibration is performed based on the result of reading the test image. Summary of the Invention [Problem to be solved by the invention]

[0003] The above-mentioned conventional technology relates to an electrophotographic image forming apparatus, and does not disclose adjustment (calibration) of color and gradation of an image printed by multiple heads in an inkjet device in which multiple heads are arranged in the main scanning direction.

[0004] The disclosed technology has been made in consideration of the above circumstances, and aims to adjust the color and gradation of images printed by multiple heads. [Means for solving the problem]

[0005] The disclosed technology is a color adjustment method including a formation step of relatively moving a recording medium and a plurality of heads each having nozzles that eject liquid, and ejecting liquid from the plurality of heads arranged in a direction intersecting the direction of the relative movement to form an image for color adjustment on the recording medium, an acquisition step of acquiring colorimetric values ​​of the image for color adjustment, a determination step of using the colorimetric values ​​to determine whether adjustment of the plurality of heads is necessary, a generation step of using the colorimetric values ​​to generate a target indicating a target value for each gradation value common to the plurality of heads when it is determined that adjustment of the heads is necessary, and a step of storing the adjustment values ​​of the plurality of heads changed based on the target in a memory unit. Effect of the Invention

[0006] It is possible to adjust the color and tone of images printed with multiple heads. [Brief description of the drawings]

[0007] [Figure 1] 1A and 1B are diagrams illustrating color measurement and color adjustment of a color adjustment image on a recording medium formed by a printing system. [Diagram 2] FIG. 1 is a diagram showing an overall outline of a printing system. [Diagram 3] FIG. 2 is a bottom view showing an example in which recording heads according to an embodiment of the present invention are arranged in a line head configuration. [Figure 4] FIG. 2 is a hardware block diagram of an information processing device 3. [Diagram 5] FIG. 2 is a functional block diagram of an information processing device. [Figure 6] FIG. 1 is a diagram showing a schematic flow of an application of a color adjustment determination method including a color measurement step of the present invention. [Figure 7] 11 is an explanatory diagram of a color adjustment image in which a plurality of gradations are set for obtaining color information; FIG. [Figure 8] FIG. 11 is a first sequence diagram showing the operation of the color adjustment system. [Figure 9]13 is a diagram showing a color measurement value acquisition table for a plurality of sections (positions) of the head displayed on the information processing device when the color adjustment target is a primary color. FIG. [Figure 10] 11 is a diagram illustrating a primary color adjustment value calculation table displayed on the information processing device. FIG. [Figure 11] 6 is a flowchart showing a process for setting manual adjustment values ​​of primary colors in the information processing apparatus according to the first embodiment. [Figure 12] 4 is a diagram illustrating a functional configuration of a primary color target generation unit. FIG. [Figure 13] 13 is a flowchart illustrating a process of a first target generation unit. [Figure 14] 11A and 11B are diagrams illustrating a process of generating a new target in the information processing device. [Figure 15] 11 is a diagram illustrating a boundary at which a method for generating a new target is switched. FIG. [Figure 16] FIG. 11 is a diagram for explaining a process of creating a γ table. [Figure 17] FIG. 13 is a conceptual diagram of adjustment using a hue angle in a secondary color. [Figure 18] FIG. 13 is a second sequence diagram showing the operation of the color adjustment system. [Figure 19] 13 is a diagram showing an example of a color measurement value acquisition table for a plurality of sections of a head displayed on an information processing device when a secondary color is to be adjusted; FIG. [Figure 20] 11 is a diagram illustrating a secondary color adjustment value calculation table displayed on the information processing device. FIG. [Figure 21] 10 is a flowchart showing a process for setting manual adjustment values ​​of secondary colors in an information processing apparatus according to a second embodiment. [Figure 22] FIG. 11 is a diagram showing a schematic flow of a color adjustment method in a printing system in which a scanner has color measurement capabilities. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following drawings, the same components are denoted by the same reference numerals, and duplicated explanations may be omitted.

[0009] <Overall view> FIG. 1 is an overall explanatory diagram of a color adjustment system capable of realizing a color adjustment judgment method formed by a printing system of the present invention.

[0010] The color adjustment system 100 includes a printing system 1, a DFE (Digital Front End) 2, an information processing device 3, and a colorimeter 5. In Fig. 1, the printing system 1 forms a color adjustment image (an image for evaluation, an image for inspection) on a recording medium P based on a signal sent from the DFE 2. At this time, the printing system 1 forms the color adjustment image on the recording medium by ejecting ink droplets (droplets) of a predetermined color from multiple heads (see Fig. 3) of printing mechanisms (image forming units) 120, 160 (see Fig. 2), and outputs the recording medium P on which the color adjustment image has been formed.

[0011] Ink is an example of a liquid, and the liquid may be, for example, water-based or oil-based. It may also be a photocurable liquid that is cured by UV or the like. It may also contain a dye or a pigment.

[0012] An operator (operator, customer engineer, etc.) 6 measures (evaluates) the color of the image for color adjustment on the recording medium P using a colorimeter 5, and obtains color information. However, this does not apply when the automatic adjustment function is used. The color information is required for profile creation after calibration, etc.

[0013] The printing system 1 may also have an automatic colorimeter 7. The automatic colorimeter 7 obtains digital color space values ​​(RGB values) of the color adjustment image for each color on the recording medium P being printed, and converts them into color measurement values ​​(Lab values) and KCMY density information (solid density) as color information. The conversion may use a 1D-LUT (one-dimensional lookup table) that is one-to-one with the paper information, or an average 1D-LUT for multiple papers most commonly used in the printing machine. Also, the color information may be obtained by measuring the spectral reflectance without going through the RGB values, and obtaining the Lab values ​​(L*a*b*). This is also true for multi-colors such as orange, green, and violet.

[0014] The color information measured by the colorimeter 5 is transferred to the information processing device 3. Alternatively, the color information measured by the colorimeter 5 is manually input by an operator 6 to the information processing device 3. Note that in this embodiment, the color of the color adjustment image may be measured by either the colorimeter 5 or the automatic colorimeter 7. Also, while FIG. 1 illustrates the colorimeter 5 and the automatic colorimeter 7, this is not limiting. The printing system 1 of this embodiment may include either the colorimeter 5 or the automatic colorimeter 7.

[0015] The information processing device 3 calculates and displays adjustment values ​​for each head H1Y to head H7Y, etc. (see FIG. 3) for manually adjusting color unevenness and for head rows HC1 to HC7. The information processing device 3 is a terminal that can be confirmed and calculated by the operator 6, and is a personal computer, tablet, smartphone, other dedicated wireless terminal, etc.

[0016] At this time, a color adjustment judgment program capable of executing the color adjustment judgment method of the present invention is pre-installed in the information processing device 3. For example, this color adjustment judgment program may be made applicable by a CD-ROM 4 or the like, or may be distributed via a telecommunication line such as the Internet.

[0017] Then, the information processing device 3 transfers the calculated adjustment value to the input unit 201 of the DFE 2 or the input unit 101 of the printing system 1. Alternatively, the adjustment value displayed on the information processing device 3 may be manually input by the operator 6 to the input unit 201 or the input unit 101.

[0018] <Printing system> 2 is a diagram showing an overall outline of a printing system, in which an inkjet continuous feed press is shown as an example of a printing system 1 according to an embodiment of the present invention.

[0019] The printing system 1 includes a paper feed mechanism 110, a printing mechanism 120 (front side), a post-drying mechanism 130, an image inspection mechanism 140, a reversing mechanism 150, a printing mechanism 160 (rear side), a drying mechanism 170, an image inspection mechanism 180, and a winding device 190.

[0020] A recording medium P made of paper, film, or the like is unwound by an unwinder, which is a paper feed mechanism 110, and reaches a printing mechanism 120 where printing is performed on the front side (first side).

[0021] A mechanism for applying a treatment liquid (pre-treatment liquid) to the recording surface of the recording medium P, for example, for controlling the permeability of the ink, may be inserted before the printing mechanism 120.

[0022] The recording medium P that has passed through the printing mechanism 120 passes through a drying mechanism 130 that is a drying device on the front side, and then passes through an image inspection mechanism 140 .

[0023] In this embodiment, an example will be described in which the drying mechanism 130 is a heat drum 131 that performs contact heating from the rear surface of the recording medium P. The heating temperature in the heat drum 131 is set to about 50°C to 100°C, depending on the printing speed and the drying property of the ink. The drying mechanism 130 can also be replaced by other means such as hot air, infrared rays, pressure, ultraviolet rays, and high frequency waves, or a combination of these mechanisms. Furthermore, if the ink is a curable ink, a curing mechanism may be provided instead of the drying mechanism.

[0024] The image inspection mechanism (automatic inspection mechanism) 140, which is disposed after the drying mechanism 130, performs automatic inspection for adjusting color unevenness and stabilizing gradation. The image inspection mechanism 140 includes a mechanism for reading color information of an image such as a scanner, and a control mechanism for calculating the read color information. The scanner of the image inspection mechanism (color inspection mechanism) 140 reads color information of an image for color adjustment in order to automatically adjust color unevenness. The color information of the read image is calculated by either a control mechanism in the image inspection mechanism 140, a control unit in the printing system 1, or the DFE2, which is a connected computer. The image inspection mechanism 140 can be used inline, but may also be used offline. The image inspection mechanism 140 may also be the same mechanism as the automatic colorimeter 7.

[0025] Next, the recording medium P passes through an inversion mechanism 150 that inverts the recording medium P, a printing mechanism 160 that prints the back side (second side), a drying mechanism 170 that dries the back side, and an image inspection mechanism 180.

[0026] The color unevenness on the back side is adjusted by an image inspection mechanism 180 having the same function as the image inspection mechanism 140 described above.

[0027] Finally, the recording medium P is wound up by a winding device (rewinder) 190, which is an example of a post-processing device that processes the printed recording medium P. Depending on the content of the post-processing after printing, instead of the rewinder, a conveying step including a cutting operation to cut the paper using a cutter may be performed.

[0028] <Head configuration> 3 is a bottom view showing an example of a line head arrangement of recording heads according to an embodiment of the present invention. More specifically, it is a plan view showing a state in which a plurality of recording heads are arranged in a staggered manner in the printing mechanisms 120 and 160 shown in FIG. 2, as seen from below.

[0029] The recording medium P is transported to the printing mechanisms 120 and 160 by multiple rollers in the direction of the arrow shown in Fig. 2. Since the printing mechanisms 120 and 160 have almost the same configuration, the following description will use the printing mechanism 120. The printing mechanism 120 is equipped with a head unit 121 configured with a single-pass inkjet line head, as shown in Fig. 3.

[0030] This head unit 121 ejects ink droplets of basic colors, for example, black (K), cyan (C), magenta (M), and yellow (Y), to form an image on the recording medium P. The head unit 121 may further include a head that ejects droplets of specific colors (special colors) such as orange and violet, or an overcoat that imparts gloss or performs other processing.

[0031] Since head unit 121 needs to be larger than the width of the recording medium on which an image can be formed, it is composed of multiple connected inkjet recording heads, each of which has a row of nozzle holes (nozzles) 122 from which ink droplets are ejected. In Fig. 3, yellow head unit 121Y is composed of multiple heads (recording heads) H1Y to H7Y. Magenta head unit 121M, cyan head unit 121C, and black head unit 121K are each also composed of multiple heads.

[0032] The head unit 121 can be retracted (separated) from the path along which the recording medium P is transported, and in the retracted state, maintenance operations are performed to clean the nozzle surface and eject thickened ink.

[0033] In each head unit 121, multiple inkjet recording heads are arranged in a staggered pattern on a flat base frame 123 in two rows in a direction perpendicular to the transport direction of the recording medium P, for a total of seven heads, and both ends of each inkjet recording head 17 are fixed to the base frame 123 with screws 124a, 124b.

[0034] In addition, the position of each inkjet recording head in the main scanning direction (direction perpendicular to the recording medium transport direction) and sub-scanning direction (recording medium transport direction) is determined by three positioning surfaces 125a, 125b, and 125c (shown as black circles in this figure).

[0035] In this embodiment, as shown in FIG. 3, inkjet recording head units 121K, 121C, 121M, and 121Y of four different colors, for example K, C, M, and Y, are arranged along the transport direction of the recording medium P and fixed to a main body frame (not shown) with screws.

[0036] These multiple heads and nozzles have variations in ejection characteristics and other aspects, so the printed result will have color differences between the ejecting heads and within the heads. Therefore, color unevenness adjustment is required to correct color unevenness.

[0037] In addition, multiple heads (e.g., heads H1Y, H1M, H1C, and H1K) arranged in line in the transport direction can form secondary or tertiary colors on the recording medium by ejecting different inks. For convenience, these transport direction rows are referred to as head row HC1, head row HC2, head row HC3, head row HC4, head row HC5, head row HC6, and head row HC7.

[0038] <Information processing device> Fig. 4 is a hardware block diagram of the information processing device 3. As shown in Fig. 4, the information processing device 3 includes a CPU (Central Processing Unit) 31, an HDD (Harms Disk Drive) 32, a RAM (Ramdom Access Memory) 33, a ROM (Read Only Memory) 34, a display device 35, an input device 36, a CD-ROM driver 37, an external interface 38, and a communication interface 39, which are all interconnected via a bus 30.

[0039] The CD-ROM driver 37, which is an example of a drive device, is an interface with the CD-ROM 4, which is a removable recording medium. This allows the information processing device 3 to read and / or write data from a storage medium such as the CD-ROM 4 via the CD-ROM driver 37.

[0040] The color adjustment judgment program according to the embodiment of the present invention is stored in a storage medium such as the CD-ROM 4 or a USB storage device, and can be read by the information processing device 3 via the CD-ROM driver 37 or a USB driver. Alternatively, the color adjustment judgment program may be installed in the HDD 32.

[0041] The HDD 32 is a non-volatile storage device that stores various programs and data. The stored programs and data include, for example, an information processing system that controls the entire information processing device 3 (for example, an OS (Operating System) that is basic software such as "Windows (registered trademark)" or "UNIX (registered trademark)", and applications that provide various functions (for example, "document creation, table creation, and editing functions") on the information processing system.

[0042] For example, the color adjustment judgment program according to the embodiment of the present invention also uses part of the application of the table creation function and the calculation function. The HDD 32 manages the above-mentioned stored programs and data by a predetermined file system and / or DB (Data Base).

[0043] The input device 36 includes a keyboard, a mouse, and the like, and is used to input various operation signals to the information processing device 3.

[0044] The external interface 38 is an interface that connects to an external device by wired connection, and is, for example, a USB driver. In this embodiment, the external interface 38 can be connected to the colorimeter 5 via a wire (for example, a USB cable) 51. In this case, color information measured by the colorimeter 5 is transferred to the information processing device 3 via the wire 51. Note that, if the storage medium is a USB, the color adjustment judgment program may be executed via the external interface 38, which is a USB driver.

[0045] The display device 35 includes a display and displays the processing results (e.g., the "print result") by the information processing device 3, a GUI (Graphical User Interface) (e.g., a "setting screen for color conversion"), color information such as colorimetric values, values ​​being calculated (KCMY density, hue angle), adjustment values, etc.

[0046] The communication interface 39 is an interface that can be wirelessly connected to the printing system 1 or the DFE 2. Through the communication interface 39, the information processing device 3 transfers the results of calculation (the head to be adjusted and the adjustment values) calculated based on the acquired color information to the printing system 1 or the DFE 2.

[0047] The ROM 34 is a non-volatile semiconductor memory that can retain internal data even when the power is turned off. The ROM 34 stores data such as a BIOS (Basic Input / Output System) that is executed when the information processing device 3 is started, and system settings and network-related settings of the information processing device 3.

[0048] The RAM 33 is a volatile semiconductor memory (storage device) that temporarily stores the programs and data read from the various storage devices described above.

[0049] The CPU 31 executes the programs read onto the RAM 33 to realize overall control of the information processing device 3 and the operation of various installed functions.

[0050] In the information processing device 3, with the above hardware configuration, for example, a printer driver or a program related to an application read onto the RAM 33 from the HDD 32 is executed by the CPU 31, thereby enabling calculation and transmission of adjustment values ​​for color adjustment.

[0051] Fig. 5 is a functional block diagram of an information processing device, showing functions that can be executed by the hardware configuration of Fig. 4.

[0052] The information processing device 3 includes, as functional units, a colorimetric value acquisition unit 301, a color difference calculation unit 302, a primary color target color difference storage unit 303, a primary color color difference comparison unit 304, a secondary color target color difference storage unit 305, and a second color difference comparison unit 306. The primary color color difference comparison unit 304 and the secondary color color difference comparison unit 306 function as an adjustment presence / absence determination unit that determines whether or not color adjustment is necessary based on the comparison result.

[0053] The colorimetric value acquisition unit 301 acquires color information resulting from measuring the color of the color adjustment image using the colorimeter 5 or the automatic colorimeter 7. The colorimetric value acquisition unit 301 acquires the colorimetric values ​​(L*, a*, b*) and density values ​​(KCMY density) of each head KCMY of the multiple heads as color information. Note that the density values ​​(KCMY density) may not be acquired by the colorimetric value acquisition unit 301, but may be calculated from the colorimetric values.

[0054] A color difference calculation unit 302 calculates the color difference between the heads based on the color information acquired by the colorimetric value acquisition unit 301. The color difference between the heads is the color difference between images formed by a plurality of heads.

[0055] The primary color target color difference storage unit 303 stores the target color difference to be referenced when determining whether or not to adjust the head for the primary color. The target color difference is a threshold value of the color difference between heads used to determine whether or not to adjust the head.

[0056] In this embodiment, head adjustment means adjustment of the color and gradation of an image printed by multiple heads. A primary color difference comparison unit 304 compares the color difference between the heads calculated by the color difference calculation unit 302 with the target color difference stored in a primary color target color difference storage unit 303, and determines whether or not to adjust the heads.

[0057] The secondary color target color difference storage unit 305 stores target color differences that are referenced when adjusting secondary colors or tertiary colors. The concept of secondary color is not limited to a specific color, but refers to a color that is generated on a recording medium using two types of ink. The secondary color difference comparison unit 306 compares the color difference between the heads calculated by the color difference calculation unit 302 with the target color difference stored in the secondary color target color difference storage unit 305, and determines whether or not to adjust the heads. In other words, the primary color color difference comparison unit 304 and the secondary color color difference comparison unit 306 are determination units that determine whether or not to adjust the heads.

[0058] The information processing device 3 also includes a density value acquisition unit 311, a primary color target generation unit 312, and a primary color processing unit 313. The information processing device 3 further includes a hue angle calculation unit 321, a secondary color target generation unit 322, and a secondary color processing unit 323. The information processing device 3 also includes an output unit 331 and an adjustment value storage unit 332.

[0059] The density value acquisition unit 311 calculates the KCMY densities of all the heads from the color information acquired by the colorimetric value acquisition unit 301. The primary color target generation unit 312 generates a primary color target for adjusting the heads for the primary colors. The primary color target in this embodiment is a target value of the primary color for each gradation value that is common to all the heads. The primary color target generation unit 312 also creates a table for correcting the gradation values ​​using the primary color targets. The table generated by the primary color target generation unit 312 may be a γ table that is a TRC (Tone Reproduction Curve).

[0060] The primary color processing unit 313 sets adjustment values ​​for each head based on the table generated by the primary color target generation unit 312 .

[0061] The hue angle calculation unit 321 calculates the hue angle of the secondary color formed using ink of a plurality of colors for each head row.

[0062] The secondary color target generation unit 322 generates secondary color targets for adjusting the heads related to the secondary colors. In this embodiment, the secondary color targets are target values ​​of the primary colors for each gradation value common to all heads for each primary color included in the secondary colors. In addition, the secondary color target generation unit 322 uses the secondary color targets to create a table for correcting the gradation values ​​of each color for which the targets have been generated. The secondary color processing unit 323 sets adjustment values ​​for each head based on the table generated by the secondary color target generation unit 322.

[0063] In this embodiment, the primary color target generation unit 312 and the secondary color target generation unit 322 may have the same configuration. The primary color target generation unit 312 will be described in detail later.

[0064] The output unit 331 outputs data. Examples of output include at least display, and may further include transmission. When executing the color adjustment determination method, the output unit 331 is realized by the display device 35 and the communication interface 39 that performs data communication, as shown in FIG.

[0065] The adjustment value storage unit 332 stores the adjustment values ​​set by the primary color processing unit 313 and the secondary color processing unit 323 .

[0066] 5, a primary color target generation unit 312 and a primary color processing unit 313 are used to adjust primary colors related to the densities (solid densities) of K, C, M, and Y. Also, a hue angle calculation unit 321, a secondary color target generation unit 322, and a secondary color processing unit 323 are used to adjust secondary colors and tertiary colors. Note that the hue angle calculation unit 321, the secondary color target generation unit 322, and the secondary color processing unit 323 are also applicable to the adjustment of primary colors.

[0067] Here, a primary color is a single color generated on a recording medium using one type of ink, such as yellow (Y), magenta (M), cyan (C), and black (K). On the other hand, a secondary color is a color generated on a recording medium by ejecting two or more types of ink from two or more types of heads, such as R (red), G (green), and B (blue). Of course, if a device is equipped with inks of colors such as R (red), G (green), and B (blue), R (red), G (green), and B (blue) are also primary colors. A secondary color is not a concept limited to a specific color, but refers to a color generated on a recording medium using two types of ink.

[0068] Hereinafter, the functions of each internal component will be described in detail with reference to FIGS.

[0069] <Outline flow> Fig. 6 is a diagram showing a schematic flow of a color adjustment judgment method including a color measurement step of the present invention. In the color adjustment step, as shown in Fig. 6, an automatic adjustment is first performed in step S1, and then a manual adjustment is performed in step S2, and the color adjustment step is completed (step S3).

[0070] Here, the color difference between nozzles in the same head is relatively small, so it is often possible to adjust it by automatic adjustment. However, because the scanner's reading sensitivity to gradation is insufficient, even if the automatic adjustment shown in S1 is repeated, the color difference between heads, which tends to become larger, cannot be read sufficiently, and the adjustment value cannot be accurately predicted, making adjustment difficult. In the following explanation, the color difference between images formed by multiple heads is described as the color difference between heads.

[0071] Therefore, in order to adjust the color unevenness between the heads that remains after the automatic adjustment in S1, the color difference between the heads is adjusted by manual adjustment in S2. Note that manual adjustment places a heavy burden on the operator, so it is preferable to adjust the color difference manually after adjusting the unevenness within the heads by automatic adjustment.

[0072] In this way, automatic adjustment mainly performs color adjustment within the same head, while manual adjustment performs color adjustment between different heads.

[0073] In conventional manual adjustments, the worker visually judges whether or not to perform head color adjustment. Therefore, the accuracy of the adjustment depends on the worker's skill, and there were cases where the target inter-head color difference could not be achieved. Also, there were cases where it took a very long time to achieve the target inter-head color difference.

[0074] Therefore, in the color adjustment determination method according to one embodiment of the present invention, the information processing device 3 executes a process for determining whether or not to perform color adjustment on the head during the manual adjustment process shown in S2.

[0075] <Example of image for color adjustment> Here, a color adjustment image used in the process of acquiring color information in the automatic adjustment of S1 and the manual adjustment of S2 in FIG. 6 will be described.

[0076] FIG. 7 is an explanatory diagram of a color adjustment image in which a plurality of gradations are set for acquiring color information. In FIG. 7, (a) shows an example of a color adjustment image printed in the printing system 1. In this embodiment, the color adjustment image is a gradation image, and image data showing the color adjustment image is gradation data for color adjustment. (b) is a gradation image (gradation chart for color adjustment) for color adjustment on a recording medium printed based on the gradation data. (c) is a gradation image (gradation chart for color confirmation) for color confirmation on a recording medium after adjustment. The gradation image (gradation chart for color adjustment) is an example of an image for color adjustment. In addition, the gradation image (gradation chart for color confirmation) for color confirmation is an example of an image for color confirmation. In this embodiment, gradation data for printing the gradation image (gradation chart for color adjustment) for color adjustment may be stored in advance in the printing system 1 or the information processing device 3.

[0077] Note that while FIG. 3 shows an example in which seven heads H1 to H7 are arranged in each of the head units 121Y, 121M, 121C, and 121K, in this example, an example in which there are five heads H1 to H5 for each color will be described.

[0078] 7(a) to (c) show gradations using black (K), for example. The gradation data shown in Fig. 7(a) shows an example of filling in five levels (steps) of density, from the bottom up: 20%, 40%, 60%, 80%, and 100%.

[0079] Here, the KCMY density of a single primary color is also called CMYK density, Tone, solid density, film thickness, ink thickness, or component density value, and more specifically, it is the expression of color shading by the density of dots in the area filled with halftone dots. As mentioned above, the gradation data of the primary colors is not limited to the four colors of KCMY. If inks such as R (red), G (green), and B (blue) are installed, the gradation data of those colors is also used.

[0080] Then, based on the set 5-level gradation data, for example, the black recording heads H1K to H5K output a gradation image for color adjustment (a gradation chart for color adjustment). At this time, as shown in FIG. 7(b), the color (density) of the image output by each head may differ.

[0081] As shown in S2 of Fig. 6 above, color adjustment is performed by manual adjustment to reduce the variation between heads. In detail, the settings are changed in the printing system 1 so that the parts with low density in the color adjustment gradation chart (e.g., head H4K) are shifted to higher gradations, and the parts with low density (e.g., head H2K) are shifted to lower gradations, as shown in Fig. 7(b).

[0082] By changing the above settings, the output chart (tone chart for color confirmation) after adjustment will have almost the same colors as those in FIG. 7(a), as shown in FIG. 7(c).

[0083] Here, Figure 7(a) shows an example of output from black recording heads H1K to H5K, but a similar layout is used to output color adjustment gradation charts for C (cyan), M (magenta), and Y (yellow), which are single ink colors for checking primary colors.

[0084] When investigating a secondary color obtained by mixing two types of ink, a color adjustment gradation chart for R (red), G (green), and B (blue), for example, is output based on the gradation data shown in Fig. 7(a). As an example of an RGB chart, it is preferable that the pattern contains the same proportions of the primary colors that make up each color.

[0085] 7 shows an example with five gradation levels, but another example of the color adjustment gradation chart may be a chart output based on gradation data with gradation values ​​of 0% to 100% in increments of 10%. By outputting a color adjustment gradation chart for 10 gradations of 10%, 20%, . . . , 100%, and measuring the colors of all 10 levels, it is possible to adjust color unevenness with high precision.

[0086] Conversely, examples of gradation charts for color adjustment include those with an even smaller number of output gradations. For example, in many cases, in a certain gradation range, the change in color relative to gradation (gradation-density characteristics, etc.) is linear, so it is possible to select several representative gradation points and reflect the same adjustment value as the representative points for the rest. For example, by dividing into three groups, such as 10%-50%, 60%-80%, and 90%-100%, and using the adjustment values ​​obtained at 50%, 80%, and 100% as the adjustment values ​​for the same group, it is possible to reduce the number of color measurement points.

[0087] Alternatively, a chart with any number of gradation steps may be output as the image to be printed, and color information may be obtained. For example, any gradation to be adjusted can be matched to the control adjustment point of the DFE2 or the like, and adjustment can be made with the optimal number of steps for the hardware.

[0088] Furthermore, the gradation levels of the image to be printed may be set in units of gradation regions in which the gradation-color characteristics are linear.

[0089] Based on the gradation data with the regions set in this way (see FIG. 7(a)), the color adjustment gradation chart (see FIG. 7(b)) printed on the recording medium P is measured using a colorimeter 5 to obtain color information. At this time, for example, in the case of K (black), the colorimetric values ​​of the areas (head unit) formed by each of the multiple heads H1K, H2K, H3K, H4K, and H5K are obtained. Each of the horizontal rows in FIG. 7(b) is the area formed by the multiple heads H1K, H2K, H3K, H4K, and H5K that have the same gradation in FIG. 7(a).

[0090] As color information for calculating the adjustment value, the color information obtained when measuring the color with the colorimeter 5 includes at least the colorimetric value (Lab value) in the case of a primary color, and in order to further improve accuracy, it is preferable to also obtain various color information such as density and the XYZ color system.

[0091] On the other hand, in the case of secondary colors, colorimetric values ​​(Lab values) are sufficient as color information, and the hue angle is calculated from the colorimetric values ​​and used to calculate the adjustment value. The colorimetric values ​​may also be Lab values ​​or CIE XYZ values. Also, the hue angle may not be calculated from the colorimetric values, but may be calculated directly as color information using the hue angle hab (C Lab hue angle) or hu (CIE Luv hue angle).

[0092] Using the color information of the color adjustment image output onto the recording medium as described above, an adjustment value to be used during manual adjustment is calculated in the information processing device.

[0093] In addition, in Fig. 7, an example is given in which the measurement unit when acquiring color information is adjusted by head, but the adjustment unit can be any unit. Also, in order to reduce the influence of the variation in the measurement results due to the printing position, it is more preferable to measure the color at multiple points within the same head.

[0094] For example, it may be on a nozzle basis, or on a block basis (section basis) where the nozzles are divided into blocks. As an example of a section basis, since the characteristics differ at both ends and the center of the head, color measurement is performed on three points (three sections) at both ends and the center as shown in Figure 10 described later, and the average value is used to treat the head as one head for adjustment.

[0095] <Manual adjustment of primary colors> Fig. 8 shows the operation of the color adjustment system 100 when performing manual adjustment of a primary color according to the first embodiment. Fig. 8 is a first sequence diagram showing the operation of the color adjustment system.

[0096] In step S21, when an instruction to start adjustment is given by operator 6, printing system 1 prints (formation step) a color adjustment image (color adjustment gradation chart) based on gradation data such as that shown in FIG. 7(a) in order to grasp color information for each gradation and for each head for each head and nozzle.

[0097] In step S22, the automatic colorimeter 7 measures the color of the color adjustment image (color adjustment gradation chart) as shown in FIG. 7B, which was printed in step S21, and obtains color information. In step S22, the automatic colorimeter 7 transmits the color information to the information processing device 3.

[0098] In step S24, the information processing device 3 acquires the color information and sets an adjustment value for the head that needs adjustment based on the color information. Details of the method of setting the adjustment value will be described later with reference to Fig. 9. Note that the method of acquiring the color information by the information processing device 3 may be a method other than the method of receiving the color information from the automatic colorimeter 7.

[0099] In step S25, the information processing device 3 transfers the adjustment values ​​set in step S24 to the printing system 1 (or the DFE 2). Alternatively, the operator 6 manually inputs the adjustment values ​​displayed on the information processing device 3 to the input unit 101 or 201 of the printing system 1 (or the DFE 2).

[0100] In step S26, the printing system 1 (or DFE 2) changes the settings to reflect the head adjustment values ​​for the nozzle groups of the head. An example of the setting change is a method of controlling the dot diameter of ink droplets by changing the head drive voltage (the shape of the drive waveform applied to a piezoelectric element or the like, which is a drive member that drives the ink ejection operation in the head) of the head to be adjusted from the other head drive voltage. Alternatively, in order to control the dot diameter, the head may be moved up and down to change the flight distance when the ink droplets are ejected. Alternatively, the gradation may be set for each head by image processing. Furthermore, the gradation or density of the head may be adjusted by other adjustment methods.

[0101] Then, in step S27, the printing system 1 prints a color confirmation image (color confirmation gradation chart) in a setting state in which the adjustment values ​​are reflected, for grasping color information for each gradation.

[0102] In step S28, the automatic colorimeter 7 measures the color of the color confirmation gradation chart that reflects the adjustment for each head output in S27, and obtains color information. Then, in step S29, the automatic colorimeter 7 transmits the color information to the information processing device 3.

[0103] In step S30, the information processing device determines whether further adjustment is necessary. Specifically, if the color difference between the heads in the color confirmation image (color confirmation gradation chart) measured in S28 is smaller than the target color difference, the information processing device 3 ends the manual adjustment. In this way, the obtained adjustment value is reflected and it is determined from the adjusted image whether readjustment is necessary.

[0104] The target color difference in this embodiment is the maximum value that is allowable as the color difference between heads, and may be set in advance.

[0105] In step S30, if any inter-head color difference is greater than the target color difference and readjustment is necessary, the process returns to the step of setting the adjustment value (step S24), and the adjustment is further repeated until it is determined in step S30 that adjustment is not necessary.

[0106] In the above description, the information processing device 3 determines whether to repeat the adjustment based on a specific target color difference in step S30, but the determination is not limited to this. In the present embodiment, for example, the operator 6 may visually determine whether to repeat the adjustment by comparing the printed adjusted color confirmation image (color confirmation gradation chart) with the color adjustment image (color adjustment gradation chart) before adjustment.

[0107] Also, although an example of outputting a color confirmation gradation chart again has been described here, if all inter-head color differences are smaller than the target color differences in step S34 of FIG. 11 described later, the process may end without setting new adjustment values ​​in the manual adjustment value setting step of S24 of FIG. 8.

[0108] <Calculation of primary color adjustment values ​​by information processing device> Hereinafter, manual adjustment value setting of the primary colors in the information processing device 3 will be described with reference to FIGS.

[0109] Fig. 9 is a diagram showing a color measurement value acquisition table for a plurality of sections (positions) of a head when the color adjustment target is a primary color, displayed on the information processing device 3. Fig. 10 is a diagram for explaining a primary color adjustment value calculation table displayed on the information processing device 3, in which (a) shows the color difference between the heads, (b) shows the difference between the target values ​​of the KCMY densities of all heads and the KCMY densities of each head, and (c) shows the adjustment values ​​of the KCMY densities set for the heads.

[0110] Here, the colorimetric values ​​(Lab values) reflect the apparent darkness in the L value (density), and the difference in hue in the a and b values. The primary colors K, C, M, and Y, which are generated using one type of ink, have the same hue (a* value, b* value) if the same ink is used, so it is sufficient to adjust the density.

[0111] Therefore, when determining which head to adjust for each of the primary colors KCMY, it is efficient to use color measurement values ​​(Lab values) to determine whether adjustment is necessary and to calculate adjustment values ​​using KCMY densities. However, since there is a tendency for densities to saturate near solid gradations and for density differences between heads to become smaller, Lab values ​​can also be used for these adjustment values.

[0112] In this embodiment, the colorimetric value acquisition unit 301 of the information processing device 3 may acquire colorimetric values ​​measured by the automatic colorimeter 7 in the form of a colorimetric value acquisition table 91, as shown in Fig. 9. In the colorimetric value acquisition table 91 shown in Fig. 9, color information for each gradation is acquired for each section of an image formed by each head for each head of each color included in each head row.

[0113] In FIG. 10, the adjustment values ​​are set using primary color targets generated by a primary color target generation unit 312, which will be described later.

[0114] Fig. 11 shows a detailed flow of setting manual adjustment values ​​of primary colors in the information processing device 3, which is executed in step S24 in the above-mentioned Fig. 8. Fig. 11 is a flow chart showing processing of setting manual adjustment values ​​of primary colors in the information processing device according to the first embodiment.

[0115] In FIG. 11, a primary color target generator 312 generates a primary color target, and adjusts the KCMY densities of each head so as to approach the density characteristics indicated by the primary color target.

[0116] In step S31, the information processing device 3 of this embodiment requests the printing system 1 to adjust the engine.

[0117] When the printing system 1 receives a request for engine adjustment, it performs engine adjustment. The engine adjustment is preferably, for example, adjustment of the nozzle discharge amount. The adjustment of the nozzle discharge amount may be, for example, cleaning of the nozzles themselves, or, when there is color unevenness for each nozzle in the head, adjustment so that the discharge amount of the other nozzle rows is matched to the nozzle row with the lightest color.

[0118] As will be described later, the request for engine adjustment from the information processing device 3 to the printing system 1 is repeated if the target color difference is equal to or greater than the threshold value, but a limit may be placed on the number of times this request is made.

[0119] In step S32, the colorimetric value acquisition unit 301 (see FIG. 5) of the information processing device 3 acquires color information detected by the automatic colorimeter 7 for each gradation (colorimetric value acquisition step, density acquisition step). When the information processing device 3 acquires color information, it is preferable that values ​​detected by the automatic colorimeter 7 of the output color adjustment gradation chart are transferred and automatically imported into the information processing device 3. Alternatively, the operator 6 may manually input the measurement results of the colorimeter 5. Here, in S32, the colorimetric values ​​(Lab values) and densities (KCMY densities) of each of the multiple heads KCMY are acquired as color information. Note that the densities (KCMY densities) may be calculated from the colorimetric values ​​without acquiring the densities (KCMY densities) as described above.

[0120] For example, in the information processing device 3, the colorimetric values ​​of each color (K, C, M, Y) acquired by the colorimetric value acquisition unit 301 are displayed in a colorimetric value acquisition table 91 as shown in FIG.

[0121] In step S33, the color difference calculation unit 302 of the information processing device 3 calculates the color difference between adjacent heads (pair, between two locations) from the colorimetric values ​​(color difference calculation step). Adjacent heads here are heads lined up in a direction perpendicular to the conveying direction of the recording medium, such as head H1Y and head H2Y in FIG. 3. For example, in the information processing device 3, the calculated color difference between the heads is displayed in a table as shown in FIG. 10(a). Here, for example, the color difference when the gradation shown in FIG. 9 is 60% is displayed.

[0122] In this embodiment, the color difference ΔE, which indicates the difference in color, is expressed as the distance between two points (Lab distance) in the Lab value color space. The color difference is expressed as ΔE (ΔE=[(ΔL*)2+(Δa*)2+(Δb*)2]1 / 2).

[0123] In this embodiment, the color difference ΔE is described as ΔE*ab based on the Lab value, but ΔE may also be ΔE*uv (ΔE*uv=[(ΔL*)²+(Δu*)²+(Δv*)²]² consisting of Luv values ​​(L*u*v).

[0124] In step S34, the primary color difference comparison unit 304 of the information processing device 3 compares the color difference between the heads with the target color difference. For example, the target color difference stored in the primary color target color difference storage unit 303 of the information processing device 3 is set to 1.5. At this time, in the color differences between the heads shown in the table of FIG. 10(a), the color difference between the heads H1Y and H2Y in Yellow (Y) and the color difference between the heads H4C and H5C in Cyan (C) shown in the underlined parts exceed the target color difference. Therefore, these head pairs (heads H1Y and H2Y in Y, and heads H4C and H5C in C) become adjustment candidate head pairs for manual adjustment (two heads determined to require adjustment), and the subsequent manual adjustment process is performed.

[0125] This step S34 is a judgment step for judging whether head adjustment is necessary using the color difference. If at least one of the calculated color differences between the heads is greater than, for example, the color difference that is the color value of the solid target set for each paper (Yes in step S34), the process proceeds to step S35.

[0126] On the other hand, if the color differences between the heads are all smaller than the target color differences (No in step S34), the information processing device 3 does not perform any further manual adjustments and returns to step S31. Note that the number of times that the engine adjustment request is made to the printing system 1 in step S31 may be limited. Then, when the determined inter-head color differences are all smaller than the target color differences and the number of times that the engine adjustment request has been made to the printing system 1 reaches a predetermined number, the information processing device returns to step S3 in FIG. 6 and ends the process. This makes it possible to shorten the adjustment time. Also, it is possible to prevent over-adjustment.

[0127] In step S35, the information processing device 3 calculates the KCMY densities of all the heads from the KCMY densities resulting from measuring the color adjustment image (color adjustment gradation chart) created by the multiple heads by the density value acquisition unit 311. In other words, the density value acquisition unit 311 of this embodiment is an example of a gradation characteristic acquisition unit that acquires the gradation characteristics of the multiple heads based on the color adjustment image.

[0128] In addition, in this flow, if L*a*b* is used as the target in the following steps, the color difference with respect to paper white is calculated as the color value. In any case, any color value that can explain the gradational change of color with respect to the gradation value in a one-to-one correspondence is acceptable.

[0129] In step S36, the information processing device 3 creates a primary color target by the primary color target generation unit 312. The primary color target may be a target that has excellent gradation characteristics and is suitable for profile creation in a later stage. Furthermore, the primary color target generation unit 312 may generate a target such that the maximum density of the head that outputs the lowest density among all heads becomes the target value. In other words, the target generation process by the primary color target generation unit 312 of this embodiment may include a process of selecting the head that outputs the lowest color value. Details of the process by the primary color target generation unit 312 will be described later.

[0130] In this embodiment, by generating targets in this manner, sufficient color adjustment can be performed even for heads that cannot express darker colors.

[0131] In step S37, the primary color processing unit 313 of the information processing device 3 adjusts the color value of each head to the primary color target created in step S36. In other words, the color value of the head may be the color value of an image formed by the ink ejected from the head.

[0132] The means for matching is not limited, but for example, adjustment may be performed so that the color value of the density for each gradation value and the density of the target of the primary color are minimized. Furthermore, after color adjustment, the primary color processing unit 313 may create a table that allows the adjustment results to be applied to each head.

[0133] 10(b), for Yellow (Y), comparing the values ​​of head H1Y and head H2Y, head H2Y is further from the target value, and for Cyan (C), comparing the values ​​of head H4C and head H5C, head H5C is further from the target value. Therefore, head H1Y for Yellow (Y) and head H5C for Cyan (C), which are underlined, are adjusted.

[0134] Then, in step S38, the information processing device 3 causes the output unit 331 to display the adjustment values ​​on the display device 35 so that the head to be adjusted, the color to be adjusted, and the adjustment direction can be seen in the table, as shown in Fig. 10(c). Here, the output unit 331 may output the set adjustment values ​​directly to the printing system 1 or the DFE 2. In other words, the output unit 331 changes the settings of the adjustment values ​​for the heads of the printing system 1.

[0135] In step S39, the information processing device 3 stores the head adjustment values ​​(KCMY densities) in the adjustment value storage unit 332, and ends the process.

[0136] In this manner, in this embodiment, the color difference between the heads is compared with the target color difference, and if the color difference between the heads is smaller than the target color difference, the adjustment ends, but if it is larger, the adjustment value is recalculated and the readjustment process is repeated.

[0137] Furthermore, in the flow chart shown in FIG. 11, an example has been given in which adjustment is performed in units of heads, but the adjustment unit can be any desired one.

[0138] For example, when the average colorimetric value of a plurality of sections is used as the colorimetric value used to determine adjustment, when selecting a section to be adjusted, if the color difference is greater than an arbitrary target color difference, only that section is adjusted.

[0139] Here, in the examples of Figures 9 and 10, we have explained a case where KCMY densities are used as the target color (desired color) during adjustment. With this control, even if there is a color that is extremely far from the target color, it is possible to prevent the occurrence of an unadjustable section by adjusting the KCMY densities toward the target value.

[0140] However, the KCMY density colors calculated from the maximum or minimum color measurement value (the brightest point or the darkest point) of the entire print area may be used as the target color when adjusting color unevenness. This makes it possible to prevent the image from becoming too light or too dark when using lightness or density.

[0141] Furthermore, it is possible to specify a specific color as the target color for adjustment when adjusting color unevenness. For example, if it is assumed that a specific color will be printed continuously, such as in a national flag, a company name, or a catchphrase, adjusting the KCMY densities to approximate that specific color will make it easier to adjust the colors more efficiently when printing an actual image. In this case, the color is stored in advance, and, for example, in S34, the KCMY densities of that specific color, which is the target color, are called up, and in S35, the differences between the KCMY densities of that specific color and the KCMY densities of each head are calculated.

[0142] In the case of a primary color, it is preferable to use relative density when approaching the density, the brightest maximum density, or the darkest minimum density indicated by a target, and to use absolute density when approaching a specific color.

[0143] 10, adjustment is performed for a specific gradation, but it is preferable to determine whether head adjustment is necessary for each of multiple gradations. Also, instead of a gradation chart that includes images of multiple gradations, an image of only a specific gradation may be output, and the necessity for adjustment may be determined using this as an image for color adjustment.

[0144] Next, generation of the primary color targets in this embodiment will be described below. Fig. 12 is a diagram illustrating the functional configuration of a primary color target generation unit.

[0145] The primary color target generation unit 312 of this embodiment has an acquisition unit 352, a conversion unit 353, a first target generation unit 354 (first generation unit), a judgment unit 355, a second target generation unit 356 (second generation unit), a target determination unit 357 (determination unit), and a table generation unit 358.

[0146] The acquisition unit 352 acquires the maximum gradation value input by the operator 6 (manager) based on the color adjustment image.

[0147] In this embodiment, a setting screen for setting the maximum gradation value may be displayed on the display device 35 of the information processing device 3, etc., and the maximum gradation value of each process color (monochrome) may be input by the operator 6 (administrator) on the setting screen.

[0148] In addition, the gradation value that is considered to be the maximum in the color adjustment image differs depending on the type of recording medium P on which the color adjustment image is formed. For this reason, the operator 6 inputs the maximum gradation value corresponding to each paper. This allows adjustment with Lab values ​​(Lab values) corresponding to any maximum gradation value or tristimulus values ​​XYZ (CIE XYZ) described later, improving the ability to respond to each paper. For example, when the operator 6 judges that there is almost no difference in density between 95 and 100[%] in the gradation of C (cyan), he inputs 95[%] as the maximum gradation value of C (cyan). In addition, by inputting a gradation value that is considered to have the maximum density, rather than 100[%] as the maximum gradation value, it is possible to suppress over-application of ink and the resulting distortion of the paper when printing with a gradation value of 100[%], and also to reduce costs by suppressing the use of excess ink. Note that if the maximum value of density can be set as the maximum gradation value, the density or Lab value may be input.

[0149] A conversion unit 353 converts the color measurement value, the maximum gradation value acquired by the acquisition unit 352, and the color specification value of the existing target (first target) into Lab distances, which will be described later, in order to use them in generating the target.

[0150] Here, the existing target indicates an ideal density characteristic for a gradation value, and is stored in advance in an auxiliary storage device. The existing target may be, for example, a characteristic of color values ​​such as Lab values ​​for gradation values, tristimulus values ​​XYZ, or values ​​converted from these. The existing target may be determined from a printing standard specification or profile, or may be determined artificially as master data. The existing target may be stored in advance in the HDD 32 or ROM 34 as table-format data at the time of product shipment.

[0151] Furthermore, the conversion unit 353 converts the above-mentioned colorimetric values, maximum gradation values, and colorimetric values ​​in the existing targets into relative Lab values ​​based on paper white. The relative Lab values ​​are not absolute Lab values, which are Lab values ​​when the CIE standard light source D50 is applied, but Lab values ​​based on paper white in order to prevent ink from being applied to the gradation value 0[%] (paper white). Here, the absolute Lab values ​​are L_abs, a_abs, and b_abs, the absolute Lab values ​​of paper white are L_0, a_0, and b_0, and the relative Lab values ​​are L_ref, a_ref, and b_ref. In this case, if the values ​​converted from the CIE1976(L*,a*,b*) color space to the tristimulus values ​​XYZ of the CIE1931XYZ color space are X_abs, Y_abs, Z_abs, X_0, Y_0, Z_0, X_ref, Y_ref, Z_ref, X_ref, Y_ref, Z_ref are calculated by the following formula (1).

[0152] X_ref=(X_D50 / X_0)×X_abs ···(1) Y_ref=(Y_D50 / Y_0)×Y_abs Z_ref = (Z_D50 / Z_0) × Z_abs

[0153] Here, X_D50, Y_D50, and Z_D50 are expressed by the following equation (2).

[0154] X_D50≒0.9642 (2) Y_D50≒1 Z_D50 ≒ 0.8249

[0155] Here, the tristimulus values ​​X_D50, Y_D50, and Z_D50 in the above formula (2) are the white point of a D50 light source. By converting to Lab values ​​using the tristimulus values ​​X_ref, Y_ref, and Z_ref obtained in the above formula (1), it is possible to calculate L_ref, a_ref, and b_ref, which are relative Lab values ​​from paper white. In this way, the conversion unit 353 converts the above-mentioned colorimetric values ​​(Lab values), maximum gradation values, and color specification values ​​in existing targets into relative Lab values ​​based on paper white.

[0156] Furthermore, the conversion unit 353 converts the relative Lab values ​​into Lab distances in order to treat the relative Lab values ​​with paper white as the reference (origin) as one-dimensional indices for gradation values. For data having Lab values ​​for gradation values, the Lab distance can be expressed as in the following formula (3) by defining the Lab values ​​of paper white as L_white, a_white, and b_white, and the i-th Lab value for gradation values ​​other than paper white as L_i, a_i, and b_i.

[0157] Lab distance (i)=√{(L_i-L_white)2+(a_i-a_white)2+(b_i-b_white)2} ···(3)

[0158] The conversion unit 353 converts the relative Lab values ​​of the color measurement value, the maximum gradation value, and the color specification value in the existing target into Lab distances using the above formula (3).

[0159] In addition, when calculating the Lab distance, the conversion unit 353 may perform linear interpolation to interpolate between the Lab distances of the discrete chart or the Lab distances of the existing target, and may perform a process to remove outliers caused by color measurement errors or the like by moving average processing or threshold judgment. For example, in the case of performing interpolation, the conversion unit 353 may perform spline linear interpolation so that Y=f(X) holds, where X is the gradation value of the patch of the color adjustment image and Y is the Lab distance for the gradation value X. In addition, although the conversion unit 353 converts the color measurement value, the maximum gradation value, and the color specification value of the existing target into the Lab distance, the conversion unit 353 is not limited to the Lab distance, and may convert color values ​​related to a predetermined color system other than the Lab distance.

[0160] The first target generation unit 354 generates a first target based on the maximum gradation value converted by the conversion unit 353 and the existing A provisional target F'(x) (third target) is generated from the Lab distance of the target. Here, x is a gradation value, and F'(x) is the Lab distance calculated from the gradation value x. For example, if the existing target is E(x), the Lab distance corresponding to the maximum gradation value is IL, and the gradation value of the connection point is C, the first target generation unit 354 generates a provisional target F'(x) expressed by the following formulas (4) and (5).

[0161] F′(x)=E(x)+(IL-E(100){(xC) / (100-C)}2 (x>C) (4) F′(x)=E(x) (for x≦C) (5)

[0162] Here, the connection point is a point that moves on the existing target E(x) as shown in Fig. 14 described later, and is a point that connects the graph of the part of the graph of the provisional target F'(x) expressed by the above formula (4) with the graph of the part expressed by formula (5). Therefore, the provisional target F'(x) is a function that passes through the Lab distance to the maximum gradation value for each color set based on the color adjustment image and the connection point, and is a graph where the graph of the part expressed by the above formula (4) and the graph of the part expressed by formula (5) are continuously connected at the connection point.

[0163] It is desirable for the temporary target F'(x) generated by the first target generation unit 354 to match the existing target E(x) as closely as possible, but as described above, since the maximum gradation value is set by the user and the Lab distance corresponding to the maximum gradation value is predetermined, it is not possible to generate the temporary target F'(x) so as to strictly match the existing target E(x). Therefore, the first target generation unit 354 searches for a temporary target F'(x) on the existing target E(x) that satisfies the following (Condition 1) and (Condition 2).

[0164] (Condition 1) The tentative target F'(x) has a part that follows the existing target E(x) (an example of the first condition). (Condition 2) The portion of the tentative target F'(x) that does not follow the existing target E(x) has gradation (an example of the second condition).

[0165] Here, the term "gradation" refers to the property that the Lab distance increases continuously and monotonically as the gradation value increases, and is a concept that includes a state in which the Lab distance (an example of a color value) is saturated. More specifically, in the gradation in this embodiment, it is desirable that the Lab distance does not change sharply or saturate excessively with increasing gradation value. For example, when 256 patches with gradation values ​​from 0 to 100 are prepared, it is desirable that the color difference (e.g., ΔE76) between adjacent patches is less than 0.1, and if the Lab distance is represented by the distance in the Lab space from the paper white, the gradation (continuity) for this color value is that the Lab distance increases with increasing gradation value. However, there is a limit to the increase per unit gradation value, for example, 0.1 per 1%. When the provisional target F'(x) is generated by the above formula (4) and formula (5), there will be a part that follows the existing target E(x) according to formula (5), so in this case (condition 1) will always be satisfied. Note that (Condition 1) may be that the portion of the tentative target F'(x) that follows the existing target E(x) exists within a predetermined gradation range or more. In this case, depending on the position of the connection point, there may be cases where (Condition 1) is not satisfied.

[0166] The determination unit 355 determines whether or not the tentative target F'(x) satisfies both (Condition 1) and (Condition 2) when the above-mentioned connection point is moved on the existing target E(x).

[0167] When the judgment unit 355 judges that (Condition 1) and (Condition 2) are not satisfied even if the connection point is moved on the existing target E(x), the second target generation unit 356 generates G(x) (fourth target) represented by the following equation (6) as a new target.

[0168] G(x)=F″(x) / F″(100)×IL ···(6)

[0169] Here, F"(x) is the target when the connection point in the temporary target F'(x) is near the gradation value x=0. Therefore, the new target G(x) is generated based on the ratio of the targets F"(x), and is obtained by normalizing the target F"(x) and multiplying it by a variable. As described above, the target F"(x) is the temporary target F'(x) when the connection point is near the gradation value x=0, but it is preferable that it satisfies (condition 2), that is, that it monotonically increases. Furthermore, the target F"(x) may be calculated in any manner, but it can be calculated in advance, for example, by iterating the Lab distance IL to find out up to which Lab distance IL the temporary target F'(x) can be expressed.

[0170] The target determination unit 357 determines a new target (second target) based on the result of the determination by the determination unit 355. Specifically, when a tentative target F'(x) determined by the determination unit 355 to satisfy both (Condition 1) and (Condition 2) is found, the target determination unit 357 determines the tentative target F'(x) as the new target F(x). On the other hand, when a tentative target F'(x) determined by the determination unit 355 to satisfy both (Condition 1) and (Condition 2) is not found, the target determination unit 357 determines the target G(x) generated by the second target generation unit 356 as the new target.

[0171] A table creating unit 358 uses the new target determined by the target determining unit 357 to create a γ table, which is a TRC (Tone Reproduction Curve) for correcting the gradation value.

[0172] Next, the processing of the primary color target generation unit 312 will be described with reference to Figs. 13 to 16. Fig. 13 is a flowchart explaining the processing of the first target generation unit. Fig. 13 shows details of the processing of step S36 in Fig. 11. Fig. 14 is a diagram explaining the generation processing of a new target of the information processing device. Fig. 15 is a diagram explaining the boundary at which the method of generating a new target switches. Fig. 16 is a diagram explaining the creation processing of a γ table. Note that the processing shown in Fig. 13 is performed for each color of the process colors.

[0173] In step S131, the primary color target generation unit 312 acquires the colorimetric values ​​acquired by the colorimetric value acquisition unit 301. In addition, the acquisition unit 352 acquires the maximum gradation value of each input color.

[0174] Following step S131, in step S132, the conversion unit 353 of the primary color target generation unit 312 converts the colorimetric value, the maximum gradation value acquired by the acquisition unit 352, and the color specification value in the existing target into relative Lab values ​​based on paper white, and further converts the relative Lab values ​​into Lab distances so that they can be treated as one-dimensional indexes for the gradation values.

[0175] Following step 132, in step S133, the first target generation unit 354 determines the initial value of the connection point moving on the existing target E(x). In the example shown in FIG. 14(a), the first target generation unit 354 sets the initial value of the connection point on the existing target E(x) to a gradation value C=100[%]. Note that the initial value of the connection point is not limited to the gradation value C=100[%], and other points may be set as the initial value. Also, in the example shown in FIG. 14(a), the Lab distance of the maximum gradation value is set below the Lab distance at the gradation value C=100[%] of the existing target E(x), but this is not limited thereto, and it may be set above, and even in this case, the same processing as the subsequent processing can be performed.

[0176] Following step S133, in step S134, the first target generation unit 354 generates a tentative target F'(x) by the above-mentioned equations (4) and (5).

[0177] Following step S134, in step S135, the determination unit 355 of the primary color target generation unit 312 determines whether the temporary target F'(x) generated by the first target generation unit 354 satisfies both (Condition 1) and (Condition 2).

[0178] For example, in step S139, when the connection point shifts toward the gradation value x of 0 and becomes the position shown in Fig. 14(b), the graph of the portion of the provisional target F'(x) where x>C (dotted line portion) has no gradation because the Lab distance decreases as the gradation value x increases, and (Condition 2) is satisfied. In addition, in determining whether or not (Condition 2) is satisfied, the determination unit 355 may, for example, obtain a slope S(x)=dF'(x) / dx (e.g., dx ≈ 0.01) for the graph of the portion where x>C, and if the slope S(x) for the gradation value x in the graph of that portion is a non-negative value and is equal to or greater than a threshold value (e.g., 0.1), determine that gradation is maintained and that (Condition 2) is satisfied.

[0179] Also, for example, in step S139, when the connection point is shifted in the direction opposite to the gradation value x of 0 to become the position shown in Figure 14 (c), the graph of the part x>C (dotted line part) of the provisional target F'(x) will show a monotonically increasing tonality because the Lab distance increases as the gradation value x increases, thereby satisfying (Condition 1).

[0180] In step S135, if the temporary target F'(x) satisfies both (Condition 1) and (Condition 2), the primary color target generation unit 312 proceeds to step S136. In addition, in step S135, if the temporary target F'(x) does not satisfy at least one of (Condition 1) and (Condition 2), the primary color target generation unit 312 proceeds to step S137.

[0181] In step S136, the target determination unit 357 of the primary color target generation unit 312 determines the tentative target F'(x) as a new target F(x).

[0182] In step S137, the determination unit 355 determines whether or not the gradation value C of the connection point in the existing target E(x) is near x = 0. Specifically, when the determination unit 355 determines that the gradation value C of the connection point is near x = 0, it determines that the connection point cannot be moved any further toward x = 0.

[0183] If it is determined in step S137 that the gradation value C of the connection point is near x=0, the primary color target generation unit 312 proceeds to step S138. If it is determined in step S137 that the gradation value C of the connection point is not near x=0 (i.e., the connection point can still be moved toward x=0), the primary color target generation unit 312 proceeds to step S139.

[0184] In step S138, the second target generation unit 356 of the primary color target generation unit 312 determines that a new target cannot be generated from the provisional target F'(x), and generates a target G(x) by the above-mentioned formula (6). Then, the target determination unit 357 determines the target G(x) generated by the second target generation unit 356 as the new target, and proceeds to step S140 described later.

[0185] 15(a) shows the position of the connection point when the new target F(x) is determined in the case where the maximum gradation value is set so that the Lab distance is equal to or greater than the predetermined Lab distance y1. In this state, it is shown that there is still room to move the connection point toward x=0.

[0186] 15(b) shows the position of the connection point when the new target F(x) is determined when the maximum gradation value is set so that the Lab distance is the same as the predetermined Lab distance y1. In this state, the connection point is located near x=0 and cannot be moved any further toward 0, and the predetermined Lab distance y1 indicates the limit of the Lab distance when the provisional target F'(x) is determined as the new target F(x).

[0187] FIG. 15(c) shows a case where, when the maximum gradation value is set so that the Lab distance is less than the predetermined Lab distance y1, a new target cannot be determined by the provisional target F′(x), and a new target is determined by the target G(x) generated based on the ratio of the target F″(x) using the above-mentioned equation (6).

[0188] In step S139, the first target generation unit 354 moves the connection point on the existing target E(x) toward the x=0 side by a predetermined amount, and the process returns to step S134.

[0189] Next, in step S140, the table creation unit 358 creates a γ table, which is a TRC for correcting gradation values, using a graph (a graph of interpolated gradation characteristics before adjustment) obtained by interpolating the Lab distance for the colorimetric value of the color adjustment image converted by the conversion unit 353, and a new target determined by the target determination unit 357. Note that the new target is F(x) in Fig. 16(a). That is, the table creation unit 358 creates a γ table (an example of correction information) by taking the gradation value corresponding to the colorimetric value of the color adjustment image as the input gradation value (in, first gradation value) and determining the output gradation value (out, second gradation value) for the input gradation value.

[0190] Specifically, as shown in Fig. 16(a), since the Lab distance of point P1 on the graph of the interpolated gradation characteristics corresponding to the input gradation value (in) corresponding to the colorimetric value of the color adjustment image differs from the Lab distance of point P2 on F(x) as a new target, the table creation unit 358 obtains point P3 on the graph of the interpolated gradation characteristics that is the same as the Lab distance of point P2. Then, the table creation unit 358 sets the gradation value of point P3 as the output gradation value (out) for the input gradation value (in) and performs this correspondence over the entire gradation value range of 0 to 100[%], thereby creating a graph that associates input gradation values ​​with output gradation values ​​as shown in Fig. 16(b), that is, a γ table as a TRC for correcting gradation values.

[0191] If the process shown in FIG. 13 described above is the first time, the color measurement values ​​and the new target can be stored in the HDD 32 or the like, and can be referenced thereafter when the user outputs an image with the same color tone.

[0192] In addition, since the process shown in FIG. 13 uses Lab values ​​and not density, it can also be applied to colors other than process colors such as orange and green, which have no density specification other than the conventional CMYK process colors.

[0193] As described above, in the information processing device 3 of this embodiment, the acquisition unit 352 acquires a maximum gradation value preset according to the paper, the conversion unit 353 converts the colorimetric value acquired by the colorimetric value acquisition unit 301, the maximum gradation value, and the colorimetric value of the existing target, which is the characteristic of the ideal colorimetric value for the gradation value, into Lab distances, respectively, and the target determination unit 357 determines, as a new target, a target (F(x) or G(x)) that passes through a point determined by the Lab distance corresponding to the maximum gradation value, generated based on the existing target converted into Lab distance. As a result, in this embodiment, a new target is generated using a maximum gradation value determined according to the paper, and it is possible to improve the ability to respond to each paper having different printing characteristics while ensuring gradation reproducibility (gradation).

[0194] Furthermore, in the information processing device 3, the first target generation unit 354 generates a provisional target that passes through a point determined by the Lab value corresponding to the maximum gradation value based on the existing target converted into Lab distance, the judgment unit 355 judges whether or not the provisional target satisfies each of the following conditions: that there is a part of the provisional target that follows the existing target (condition 1), and that the part of the provisional target other than the part that follows has gradation (condition 2). If the judgment unit 355 judges that the provisional target satisfies both (condition 1) and (condition 2), the target determination unit 357 determines the provisional target as a new target. As a result, the target is generated in a form that follows the existing target as much as possible, and gradation in the highlight area can be ensured by using an appropriate existing target.

[0195] The above explains the case of primary colors, but in the case of secondary colors, adjustments in density or brightness are not possible, so adjustments by automatic inspection using a scanner alone are even more difficult, and there is a strong need to rely on manual adjustments to correctly adjust the color tone.

[0196] In addition, since it is necessary to determine which of the constituent colors should be adjusted and to what extent, the difficulty of manual adjustment is even higher than in the case of primary colors. Therefore, the following color adjustment of secondary colors is performed.

[0197] <Secondary Color Adjustment (Second Embodiment)> FIG. 17 is a conceptual diagram of adjustment using the hue angle in a secondary color.

[0198] In the Lab value color space, the L* axis is the lightness axis that represents brightness, with values ​​closer to 0 indicating black and values ​​closer to 100 indicating white. The a* axis represents green to red, with negative values ​​indicating green and positive values ​​indicating red. The b* axis represents blue to yellow, with negative values ​​indicating blue and positive values ​​indicating yellow. The higher the values ​​on both the a* and b* axes, the stronger the color (higher saturation).

[0199] As described above, the color difference ΔE, which indicates the difference in color, is expressed as the distance between two points on a uniform color space such as the Lab value color space.

[0200] In the color adjustment of this embodiment, since it is premised on a secondary color that does not use black, the lightness L is assumed to be equal and adjustment is performed using the hue angle difference ΔH.

[0201] For example, in the case of CIE Lab, the hue angle is calculated as follows: hue angle hab = atan(b* / a*) [degrees]. The hue angle hab is the angle from the +a* axis of CIE Lab.

[0202] In the case of CIE Luv, the hue angle is calculated as huv = hab = atan(u* / v*) [degrees]. The hue angle huv is the angle from the +u* axis of CIE Luv.

[0203] Using this difference in hue angle, for example in CIE Lab, the balance between the two colors of ink ejected onto the recording medium P, which affects the a* and b* values, is adjusted. The following description will be given based on the hue angle in CIE Lab.

[0204] <Secondary color manual adjustment flow> Fig. 18 shows the operation of the color adjustment system 100 when performing manual adjustment of the secondary color according to the second embodiment. Fig. 18 is a second sequence diagram showing the operation of the color adjustment system.

[0205] In this embodiment, the difference is that the color adjustment image (color adjustment gradation chart) that is the subject of adjustment judgment is a secondary color (RGB) rather than a primary color (KCMY). Therefore, the sequence in Fig. 18 differs from the primary color sequence in Fig. 8 in that an image reflecting two types of adjustment value candidates is printed in step S1807, and the adjustment value that results in the smaller difference from the target value is selected in step S1810. The differences will be described in detail with reference to Fig. 19.

[0206] The color adjustment image (color adjustment gradation chart) used in this embodiment has the same layout as that shown in FIG. 7(a), and outputs a chart of three colors, R (red), G (green), and B (blue), as an example of secondary colors. Assume that this RGB is a pattern in which the primary colors that compose each are contained in the same proportions. Even in the case of secondary colors, the horizontal rows in FIG. 7(b) have the same gradation information of the original image data. Also, the vertical columns in FIG. 7(b) are formed by the respective head rows HC, and the areas formed by the head rows HC1, HC2, HC3, HC4, and HC5 are lined up in the horizontal direction.

[0207] Here, an overview of the calculation of the two types of adjustment values ​​to be output will be explained by returning to Fig. 17. Which of the adjustment values ​​of the first color and the second color that make up the secondary color should be set to + can be found from the relationship between the hue angle before adjustment and the target hue angle.

[0208] 17, an example will be described in which red is a secondary color that is generated on a recording medium by inks of the primary colors yellow and magenta. For example, suppose that the hue of red before adjustment is closer to yellow than the target hue. In other words, suppose that the hue angle is larger than the target hue angle.

[0209] In this case, since we want to make the adjusted hue closer to magenta, when adjusting the adjustment value, we output a color confirmation gradation chart with magenta set to + (plus) (increased) and a color confirmation gradation chart with Yellow set to - (minus) (decreased).

[0210] When using secondary colors, even if the direction in which the angle should be changed can be calculated, it is often difficult to determine which of the two colors should be adjusted. Therefore, if you want to get closer to a specific color, you can find a more accurate adjustment value by trying both the value obtained by adjusting that color to + (plus) and the value obtained by adjusting the other color to - (minus).

[0211] In addition, which of the adjustment values ​​of the first color and the second color that make up the secondary color should be set to + may be determined by storing information on the hue angle of the single color ink, and setting the ratio of the ink whose target hue angle is closer than the hue angle before adjustment to a higher value. However, for example, when the color to be adjusted is red, it is known in advance that if the hue angle is larger than the target value, it should be closer to magenta, so the change in the ink ratio may be determined without using information on the hue angle of the single color ink.

[0212] <Calculation of secondary color adjustment values ​​by information processing device> Hereinafter, the manual adjustment value setting of the secondary color in the information processing device 3 will be described with reference to FIGS.

[0213] Fig. 19 shows an example of a color measurement value acquisition table for multiple sections of a head displayed on an information processing device when the color adjustment target is a secondary color. Fig. 20 is a diagram for explaining a secondary color adjustment value calculation table displayed on an information processing device, in which (a) shows the difference in hue angle between head rows, (b) shows the difference between the hue angle of all head rows and the target value, and (c) shows the head row and the set adjustment value.

[0214] As shown in Fig. 19, in the step of acquiring color measurement values, color information for each gradation is acquired for each of multiple sections of an image formed by each head row. As an example, as shown in Fig. 20, an example is shown in which an adjustment value is set for a specific gradation using a target value for each head row in each section.

[0215] Fig. 21 shows a detailed flow of setting manual adjustment values ​​of secondary colors in the information processing device 3, which is executed in step S1804 in the above-mentioned Fig. 18. Fig. 21 is a flow chart showing processing of setting manual adjustment values ​​of secondary colors in the information processing device according to the second embodiment.

[0216] In step S40 in FIG. 21, the information processing device 3 of this embodiment requests the printing system 1 to adjust the engine.

[0217] Next, in step S41, the colorimetric value acquisition unit 301 (see FIG. 5) of the information processing device 3 acquires colorimetric values ​​(Lab values) as color information detected by the colorimeter 5 (acquisition step). For example, in the information processing device 3, the colorimetric values ​​(Lab values) and KCMY densities, which are acquired values ​​of each secondary color (R, G, B) that have been transferred or manually entered, are displayed in a table as shown in FIG.

[0218] In step S42, the color difference calculation unit 302 of the information processing device 3 calculates the color difference between adjacent head arrays (between two locations) (color difference calculation step). Adjacent head arrays here refer to head arrays aligned in a direction perpendicular to the conveying direction of the recording medium, such as head array HC1 and head array HC2 in Fig. 3. For example, in the information processing device 3, the color difference ΔE between the head arrays in the secondary color in the printing system 1 equipped with five head arrays HC1 to HC5 is displayed in a table as shown in Fig. 20(a).

[0219] The secondary color is formed by ejection from multiple heads arranged in a row in the transport direction. Therefore, when making a judgment on adjustment based on the secondary color, the color difference used for the judgment is the color difference between the images formed by the head rows. The color difference between the images formed by multiple head rows is described as the color difference between head rows.

[0220] In step S43, the secondary color difference comparator 306 of the information processing device 3 compares the color difference between the head rows with the target color difference.

[0221] 20(a), for example, the target color difference between head arrays in secondary colors stored in secondary color target color difference storage unit 305 is set to ΔE<2.5. In this case, the underlined parts are head array combinations (two "two head arrays") in which the color difference between head arrays HC3 and HC4 and the color difference between head arrays HC4 and HC5 are greater than the target ΔE. These head array pairs (head array HC3 and head array HC4, and head array HC4 and head array HC5) are adjustment candidate head array pairs for manual adjustment.

[0222] This step S43 is a judgment step for judging whether or not head row adjustment is necessary using color difference. If at least one of the calculated inter-head row color differences is greater than the target (YES in step S43), that is, if there is a pair of head rows that is the target of manual adjustment, the process proceeds to step S44.

[0223] On the other hand, if the color difference between the head rows is smaller than the target color difference (No in step S43), the entire color adjustment process is terminated without carrying out subsequent manual color adjustment.

[0224] If the answer is Yes in step S43, in step S44, the hue angle calculation unit 321 of the information processing device 3 calculates the hue angle of the secondary color formed using multiple colors of ink for each of the head rows HC1 to HC5 (hue angle acquisition step), and the process proceeds to step S45.

[0225] In step S45, the secondary color target generation unit 322 generates a first color target and a second color target included in the secondary color. The method of generating targets by the secondary color target generation unit 322 is similar to that of the primary color target generation unit 312.

[0226] In step S46, the secondary color target generator 322 generates a table corresponding to each target from the first color target and the second color target.

[0227] In step S47, based on the generated table, the secondary color processing unit 323 sets a color confirmation gradation chart in which the adjustment value of the head ejecting the first color of ink that constitutes the secondary color is set to + (plus), and a color confirmation gradation chart in which the adjustment value of the head ejecting the second color of ink is set to - (minus), and in step S48, stores the adjustment values ​​in the adjustment value memory unit 332.

[0228] For example, to increase (+) the hue angle of the secondary color Green formed by the head row HC4 as shown in Fig. 20(c), the adjustment value of the Cyan ink is set to + (plus) or the adjustment value of the Yellow ink is set to - (minus) as shown in Fig. 17. For example, for a hue angle corresponding to a target color (Green (target)) and a hue angle before adjustment (Green (before adjustment)), the head (first head) that ejects ink closer to the hue angle corresponding to the target color is set to head H4C of the first color (Cyan), and the head (second head) that ejects ink closer to the hue angle corresponding to the color before adjustment is set to head H4Y of the second color (Yellow).

[0229] At this time, as color confirmation images, both an image in which the ejection volume of the head H4C for the first color (cyan) is increased (first color confirmation image) and an image in which the ejection volume of the head H4Y for the second color (yellow) is decreased (second color confirmation image) are output. For this purpose, a setting in which the adjustment value of the head for the first color is set to + (plus) and a setting in which the adjustment value of the head for the second color is set to - (minus) are output. The extent of the change to be made to the heads ejecting ink of each color is arbitrary, but it is preferable to make the change based on the magnitude of the difference. It is also possible to make the change by the smallest amount of change.

[0230] Then, the information processing device 3 returns to S1805 in FIG. 18, transfers or inputs the adjustment values ​​of the two types of color confirmation gradation charts to the printing system, changes the settings in S1806 to adjust to match the two types of candidates, and prints the two types of color confirmation gradation charts in S1807 (color confirmation image formation step).

[0231] Then, in step S1808, the two types of color confirmation gradation charts are measured by the colorimeter 5, and in step S1809, the colorimeter 5 transmits the colorimetric measurement results to the information processing device 3.

[0232] Next, in step S1810, the information processing device 3 selects the candidate with the smaller inter-head row color difference (the one with the better balance). Note that the selection of the candidate may be performed by the operator 6.

[0233] Then, in step S1811, the information processing device 3 compares the color difference between the head rows with the target color difference between the head rows using the second color difference comparing unit 306, and ends the adjustment if the color difference between the head rows is smaller than the target color difference. Step S1811 in Fig. 18 is a secondary color adjustment head determination step that determines which of the first head (cyan head H4C in Fig. 18) or the second head (yellow head H4Y in Fig. 18) in a given head row is to be adjusted.

[0234] In this way, the color difference between the head rows is compared with the target color difference between the head rows, and if it is smaller than the target color difference, the adjustment ends, but if it is larger, the adjustment value is recalculated and the readjustment process is repeated.

[0235] In this way, when it is difficult to determine which color should be adjusted for which head, a more accurate adjustment value can be found by printing and trying both adjustment values. Also, in the case of secondary colors, a more visually uniform image can be obtained by determining the adjustment value based on the hue angle.

[0236] If the settings were those of the color confirmation gradation chart printed the first time, which had a better balance, then in step S1812 of FIG. 18, the adjustment value settings in the printing system 1 are returned to the first settings, and the process ends.

[0237] In this way, in the case of secondary colors, it is difficult to accurately grasp the difference in density, so it is preferable to use the hue angle. The adjustment amount for adjusting to the target color may be obtained from a calibration curve obtained by linearly interpolating the color characteristics for each gradation, or adjustment may be made at any gradation step.

[0238] In this way, when adjusting the secondary color, by using the hue angle as color information, it becomes possible to adjust the color tone that cannot be adjusted by density or brightness.

[0239] Moreover, instead of the hue angle difference, adjustment may be performed using the distance between two points on the a*b* plane or the u*v* plane.

[0240] Although the case of adjusting secondary colors is taken as an example here, adjustment of primary and tertiary colors is also possible using a method that uses the hue angle.

[0241] <Tertiary color adjustment> Furthermore, any hue angle can be used as a color target for adjustment when adjusting a tertiary color that is a mixture of three ink colors. The adjustment judgment method shown in the second embodiment can also be applied when adjusting a tertiary color (for example, composite black). Composite black can be adjusted by L* or density, but an adjustment value can also be calculated and set by the hue angle in the same way as with secondary colors.

[0242] This makes it possible to adjust tertiary or higher colors while adjusting the gray balance.

[0243] <Incorporating a colorimeter into a printing system> The above describes how to calculate adjustment values ​​for manual adjustment, but if a colorimeter capable of measuring color values ​​(Lab values) and monochrome densities can be installed within the printing system, it is also possible to calculate adjustment values ​​within the printing system during automatic adjustment and reflect color adjustments with a high degree of accuracy.

[0244] <Utilization of multi-stage scanners in printing systems> As shown in the flow in Figure 6 above, in the color information acquisition process for automatic adjustment in step S1, when adjusting color unevenness, scanning must be done on a nozzle or block basis to detect density unevenness and missing nozzles within the head, and scanning must be done at high resolution.

[0245] Therefore, since the color difference between the heads is large, manual adjustment has been necessary. However, instead of the above manual adjustment, the hue angle may be obtained by the scanner itself included in the image inspection mechanism 140, 180 (see FIG. 2), and color adjustment between the heads may be performed by the control unit of the printing system 1 or the DFE 2.

[0246] In this case, if one were to simultaneously perform the automatic adjustment shown in S1 of FIG. 6 and the manual adjustment shown in S2, a very large amount of memory would be required to simultaneously satisfy the requirements for two scanned images and to process the entire width of the printing area.

[0247] Therefore, by changing the settings in two stages on a single scanner capable of color measurement, making high resolution / low bit adjustments such as for nozzle dropout, and then making low resolution / multiple bit adjustments such as for color, it becomes possible to make adjustments including the color tint of secondary colors even on the scanner.

[0248] FIG. 22 is a diagram showing a schematic flow of a color adjustment method in a printing system in which the scanner has color measurement capabilities.

[0249] In step S81, high resolution, low bit adjustments such as missing nozzles in the head are performed first. In other words, when adjusting color unevenness in a small section (adjusting streaks), color information is read at high resolution. The high resolution adjustment in S81 is performed in the same way as the conventional automatic color unevenness adjustment, and adjustments are made mainly for missing nozzles in the head.

[0250] In step S82, in order to adjust the color (e.g., secondary color), a low-resolution, multi-bit adjustment is performed to calculate an adjustment value for adjusting the color between heads or between head rows. This multi-bit adjustment is performed in the same manner as in Figures 16 to 18 for the above-mentioned secondary color using a colorimeter, and the adjustment is centered on the color.

[0251] In this way, by adjusting the color tone using a scanner with changed settings, it is possible to make adjustments that take color tone into account even with a scanner that is less expensive than a colorimeter.

[0252] <Other Modifications 1> The color difference calculation unit 302, the primary color difference comparison unit 304, and the secondary color difference comparison unit 306 (adjustment presence / absence determination unit) of this embodiment may be configured by a neural network generated by machine learning. In this case, when the information processing device 3 acquires colorimetric values ​​from the automatic colorimeter 7, the information processing device 3 may input the colorimetric values ​​to the neural network. The neural network may calculate the color difference between the heads based on the input colorimetric values ​​and the target color difference, and output a determination result as to whether or not to adjust the heads. In this way, it becomes unnecessary for the operator 6 to manually measure the color of the color adjustment image, and the adjustment procedure can be simplified.

[0253] <Other Modifications 2> In this embodiment, a line head inkjet device is described in which a recording medium is transported and multiple heads are arranged in a direction perpendicular to the transport direction, but the present invention can also be applied to a serial inkjet device in which the head moves relative to the recording medium, as long as multiple heads are arranged in a direction perpendicular to the head movement direction. In other words, the present invention can be applied to any form in which multiple heads are arranged in a direction perpendicular to the relative movement direction of the recording medium and the head.

[0254] Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and changes are possible within the scope of the gist of the embodiments of the present invention described in the claims. For example, aspects of the present invention are as follows. <1> a forming step of relatively moving a plurality of heads, each having nozzles for ejecting liquid, and a recording medium, and ejecting liquid from the plurality of heads arranged in a direction intersecting the direction of the relative movement, to form a color adjustment image on the recording medium; acquiring colorimetric values ​​of the color adjustment image; a determining step of determining whether or not adjustment of the plurality of heads is necessary using the color measurement values; a generation step of generating a target indicating a target value for each gradation value common to the plurality of heads using the color measurement value when it is determined that adjustment of the head is necessary; and storing the adjustment values ​​of the plurality of heads, which have been changed based on the target, in a storage unit. <2> The target is generated using the color measurement value, an existing target stored in advance in a storage device, and a maximum gradation value. <1> Color adjustment method described. <3> displaying a screen for inputting the maximum gradation value on a display device; <2> Color adjustment method described. <4> the increase tendency of the target value for each gradation value in the target is a monotonically increasing tendency, except when the gradation value is in a range including a minimum value and near the minimum value, and when the gradation value is in a range including a maximum value and near the maximum value; <1> ~ <3> 13. The color adjusting method according to claim 12 . <5> an adjustment step of adjusting the ejection amount of the nozzle when it is determined in the determination step that adjustment of the head is not required; <1> ~ <4> 13. The color adjusting method according to claim 12 . <6> an acquisition step of acquiring color measurement values ​​of portions of the color adjustment image formed by each of a plurality of heads arranged at different positions in the intersecting direction; and a color difference calculation step of calculating a color difference between at least two points from the color measurement value for each of the points, the determining step determines whether or not adjustment of the plurality of heads is necessary based on the color difference; <1> ~ <5> 13. The color adjusting method according to claim 12 . <7> obtaining a hue angle of the color adjustment image; a hue angle difference calculation step of calculating a hue angle difference which is a difference between a hue angle corresponding to a desired target color and a hue angle of a portion of the color adjustment image formed by a plurality of heads included in each of the two head arrays, The determining step includes: determining whether adjustment of the plurality of heads is necessary based on the hue angle difference; <1> ~ <6> 13. The color adjusting method according to claim 12 . <8> an image forming apparatus having the plurality of heads, moving the plurality of heads relative to the recording medium, and discharging liquid from the plurality of heads arranged in a direction intersecting a direction of the relative movement, Claim <1> ~ <7> 13. An image forming apparatus, wherein the plurality of heads are adjusted by the color adjustment method described in any one of claims 1 to 12. <9> a plurality of heads each having nozzles for ejecting liquid are moved relative to a recording medium, and liquid is ejected from the plurality of heads arranged in a direction intersecting the direction of the relative movement, thereby acquiring colorimetric values ​​of a color adjustment image formed on the recording medium; Using the color measurement values, determine whether adjustment of the plurality of heads is necessary; generating a target indicating a target value for each gradation value common to the plurality of heads using the color measurement value when it is determined that adjustment of the head is necessary; a color adjustment program that causes an information processing device to execute a process of storing, in a storage unit, the adjustment values ​​of the plurality of heads that have been changed based on the target; <10> a colorimetric value acquisition unit that relatively moves a recording medium and a plurality of heads each having nozzles for ejecting a liquid, and acquires colorimetric values ​​of a color adjustment image formed on the recording medium by ejecting liquid from the plurality of heads that are arranged in a direction intersecting the direction of the relative movement; an adjustment determination unit that determines whether or not adjustment of the plurality of heads is necessary using the color measurement values; a target generation unit that generates a target indicating a target value for each gradation value common to the plurality of heads, using the color measurement value, when it is determined that adjustment of the head is necessary; and a storage unit that stores adjustment values ​​of the plurality of heads that have been changed based on the target. <11> The adjustment determination unit uses a neural network generated by machine learning. <10> The information processing device described. [Explanation of symbols]

[0255] 1 Printing System 2 DFE 3. Information processing equipment 4 CD-ROM (storage medium) 5 Colorimeter 7 Automatic colorimeter 121 (121Y, 121M, 121C, 121K) Head Unit 122 Nozzle 301 Colorimetric value acquisition unit 302 Color difference calculation section 304 Primary color color difference comparison section (adjustment presence / absence judgment section) 306 Secondary color color difference comparison section (adjustment presence / absence judgment section) H1Y, H2Y, H3Y, H4Y, H5Y, H6Y, H7Y Recording head (head, yellow head) H1M recording head (head, magenta head) H1C, H4C, H5C recording head (head, cyan head) H1K, H2K, H3K, H4K, H5K recording head (head, black head) HC1,HC2,HC3,HC4,HC5,HC6,HC7 Head Row P Recording medium [Prior art documents] [Patent documents]

[0256] [Patent Document 1] Patent Publication No. 2021-044697

Claims

1. a forming step of relatively moving a plurality of heads, each having nozzles for ejecting liquid, and a recording medium, and ejecting liquid from the plurality of heads arranged in a direction intersecting the direction of the relative movement, to form a color adjustment image on the recording medium; acquiring colorimetric values ​​of the color adjustment image; a determining step of determining whether or not adjustment of the plurality of heads is necessary using the color measurement values; a generation step of generating a target indicating a target value for each gradation value common to the plurality of heads using the colorimetric value when it is determined that adjustment of the head is necessary; and storing the adjustment values ​​of the plurality of heads, which have been changed based on the target, in a storage unit.

2. 2. The color adjustment method according to claim 1, wherein the target is generated using the color measurement value, an existing target stored in advance in a storage device, and a maximum gradation value.

3. 3. The color adjustment method according to claim 2, further comprising the step of displaying on a display device a screen for inputting said maximum gradation value.

4. 2. The color adjustment method according to claim 1, wherein the tendency of increase in the target value for each gradation value in the target is a monotonically increasing tendency, except when the gradation value is in a range near the minimum value including a minimum value, and when the gradation value is in a range near the maximum value including a maximum value.

5. 2. The color adjustment method according to claim 1, further comprising an adjustment step of adjusting the ejection amount of the nozzles when it is determined in the determination step that adjustment of the head is not required.

6. an acquisition step of acquiring color measurement values ​​of portions of the color adjustment image formed by each of a plurality of heads arranged at different positions in the intersecting direction; and a color difference calculation step of calculating a color difference between at least two points from the color measurement value for each of the points, 2. The color adjustment method according to claim 1, wherein said determining step determines whether or not adjustment of said plurality of heads is necessary based on said color difference.

7. obtaining a hue angle of the color adjustment image; a hue angle difference calculation step of calculating a hue angle difference which is a difference between a hue angle corresponding to a desired target color and a hue angle of a portion of the color adjustment image formed by a plurality of heads included in each of the two head arrays, The determining step includes: The color adjustment method according to claim 1 , further comprising determining whether adjustment of the plurality of heads is necessary based on the hue angle difference.

8. an image forming apparatus having the plurality of heads, moving the plurality of heads relative to the recording medium, and discharging liquid from the plurality of heads arranged in a direction intersecting a direction of the relative movement, An image forming apparatus, wherein the plurality of heads are adjusted by the color adjustment method according to any one of claims 1 to 7.

9. a plurality of heads each having nozzles for ejecting a liquid are moved relative to a recording medium, and liquid is ejected from the plurality of heads arranged in a direction intersecting the direction of the relative movement to form a color adjustment image on the recording medium, and color measurement values ​​of the color adjustment image are acquired; Using the color measurement values, determine whether adjustment of the plurality of heads is necessary; generating a target indicating a target value for each gradation value common to the plurality of heads using the color measurement value when it is determined that adjustment of the head is necessary; a color adjustment program that causes an information processing device to execute a process of storing, in a storage unit, the adjustment values ​​of the plurality of heads that have been changed based on the target;

10. a colorimetric value acquisition unit that relatively moves a recording medium and a plurality of heads each having nozzles for ejecting a liquid, and acquires colorimetric values ​​of a color adjustment image formed on the recording medium by ejecting liquid from the plurality of heads that are arranged in a direction intersecting the direction of the relative movement; an adjustment determination unit that determines whether or not adjustment of the plurality of heads is necessary using the color measurement values; a target generation unit that generates a target indicating a target value for each gradation value common to the plurality of heads using the color measurement value when it is determined that adjustment of the head is necessary; and a storage unit that stores adjustment values ​​of the plurality of heads that have been changed based on the target.

11. The information processing device according to claim 10 , wherein the adjustment determination unit uses a neural network generated by machine learning.

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