JP7796726B2 - Image forming system, tone correction data generation method, and program - Google Patents

Description

The present invention relates to a gradation correction data generating device, a gradation correction data generating method, a program, and an image forming system.

Inkjet printing devices are known that use white ink to form the base of printed materials that use transparent substrates. For example, a color image is printed, and then a full-page image of white ink is printed over the color image. When a printed material printed in this way is viewed from the side opposite the printed surface of the substrate, the color image is visible on a white background.

Patent Document 1 describes a printing device that uses multiple colors of ink, including white ink, to print images that include color and white areas. The device described in this document mixes white ink with other color inks to fine-tune the white hue and form a toned white image. The white hue in the toned white image is measured using a white background and a black background.

Patent Document 2 describes a printing device that acquires an error in the amount of ink applied to a transparent substrate and corrects the amount of ink applied based on the error. The device described in this document prints white patches and process color patches such as cyan on the transparent substrate, measures the patches in Lab space, and performs color correction based on the colorimetric data.

Figure 17 of the same document illustrates colorimetry using a black and white background, with cyan, magenta, yellow, and black applied against a white background, and white applied against a black background.

JP 2014-97671 A JP 2011-73306 A

However, in printing using white ink, the correction of gradation values to achieve the target density value is performed manually by deriving a tone curve that represents the density value for each gradation value and modifying the tone curve. This requires trial and error and skill on the part of the worker. This issue is not limited to printing using ink, but can also exist in image formation using colorants such as toner.

Patent Document 1 describes adjusting the whiteness of a toned white image by mixing other color inks with white ink, but does not describe correcting the gradation density of the white ink. Similarly, Patent Document 2 also does not describe correcting the gradation density of the white ink.

The present invention has been made in consideration of these circumstances, and aims to provide a gradation correction data generation device, a gradation correction data generation method, a program, and an image forming system that can reduce trial and error on the part of the operator and enable the generation of gradation density conversion data to which a quantitative method is applied.

The gradation correction data generating device according to the present disclosure is a gradation correction data generating device that includes a processor and a storage device that stores a program executed by the processor. The processor executes instructions from the program to obtain first measurement data obtained by measuring a patch group formed on a substrate using a white colorant, the patch group including one or more patches to which dots of multiple sizes are applied, against a white background; obtain second measurement data obtained by measuring the patch group against a black background; derive an evaluation index value for the density value for each gradation value in the white colorant based on the first measurement data and the second measurement data; and generate gradation correction data that corrects the relationship between the density value and the gradation value in the white colorant based on the evaluation index value.

The gradation correction data generation device disclosed herein reduces the need for trial and error on the part of the operator, and can apply a quantitative method to generate gradation correction data that corrects the relationship between gradation values and density values in white colorants.

The colorant contains particles that produce the colors that make up the color image formed on the substrate. An example of a white colorant is white ink.

The patch may be a small image representing the density of each color. The patch shape may be a rectangle.

An example of tone correction data is tone correction data in lookup table format.

In another aspect of the gradation correction data generating device, the processor acquires, as first measurement data, measurement data of a first patch group including a plurality of first patches, and acquires, as second measurement data, measurement data of a second patch group including a plurality of second patches, each of which has the same gradation value as that of the plurality of first patches.

According to this aspect, first measurement data and second measurement data can be obtained for the same gradation value in a single measurement.

In another aspect of the gradation correction data generating device, the processor applies the concealment rate as the evaluation index value.

According to this aspect, whiteness can be evaluated by applying the hiding rate specified in existing standards.

In another aspect of the gradation correction data generating device, the processor derives an evaluation index value using first measurement data normalized using the density values of a white background and second measurement data normalized using the density values of a black background.

According to this aspect, the influence of the density of the white background on the first measurement data and the influence of the density of the black background on the second measurement data can be suppressed.

The gradation correction data generation method disclosed herein is a gradation correction data generation method in which a computer acquires first measurement data by measuring a patch group formed on a substrate using a white colorant, the patch group including multiple patches with different gradation values, and the patch group including one or more patches to which multiple sizes of dots are applied, against a white background; acquires second measurement data by measuring the patch group against a black background; derives an evaluation index value for the density value for each gradation value in the white colorant based on the first measurement data and the second measurement data; and generates gradation correction data that corrects the relationship between the density value and the gradation value in the white colorant based on the evaluation index value.

The gradation correction data generation method according to the present disclosure can achieve the same effects as the gradation correction data generation device according to the present disclosure. The constituent elements of the gradation correction data generation device according to other aspects can be applied to the constituent elements of the gradation correction data generation method according to other aspects.

The program disclosed herein is a program that causes a computer to perform the following functions: acquire first measurement data by measuring a patch group formed on a substrate using a white colorant, the patch group including multiple patches with different gradation values, and the patch group including one or more patches to which multiple sizes of dots are applied, while applying a white background; acquire second measurement data by measuring the patch group while applying a black background; derive an evaluation index value for the density value for each gradation value in the white colorant based on the first measurement data and the second measurement data; and generate gradation correction data that corrects the relationship between the density value and the gradation value in the white colorant based on the evaluation index value.

The program according to the present disclosure can achieve the same effects as the gradation correction data generation device according to the present disclosure. The constituent elements of the gradation correction data generation device according to other aspects can be applied to the constituent elements of the program according to other aspects.

The image forming system according to the present disclosure includes an image forming device having a head that ejects a white colorant toward a substrate; a measurement device that measures a group of patches formed on the substrate using the white colorant against a white background and also measures the group of patches against a black background; and a gradation correction data generation device that generates gradation correction data that corrects the relationship between the gradation value and the density value in the white colorant based on measurement data obtained from the measurement device. The image forming device includes a second processor and a second storage device that stores a second program executed by the second processor. The second processor generates a pattern including a plurality of patches with different gradation values formed using the white colorant ejected from the head. and forming a patch group including one or more patches to which dots of a plurality of sizes are applied, the gradation correction data generating device having a first processor and a first storage device in which a first program executed by the first processor is stored, the first processor executing instructions of the first program to obtain from the measuring device first measurement data to which a white background is applied and second measurement data to which a black background is applied, deriving an evaluation index value for the density value for each gradation value in the white colorant based on the first measurement data and the second measurement data, and generating gradation correction data that corrects the relationship between the density value and the gradation value in the white colorant based on the evaluation index value.

The image forming system according to the present disclosure can achieve the same effects as the gradation correction data generating device according to the present disclosure. The constituent elements of the gradation correction data generating device according to other aspects can be applied to the constituent elements of the image forming system according to other aspects.

An example of an image forming system is an inkjet printing system equipped with an inkjet printing device.

In another aspect of the image forming system, the second processor uses the head to form a patch group in which multiple patches are arranged along the relative transport direction between the head and the substrate.

According to this aspect, density unevenness in patches printed using the single-pass method can be suppressed, and the measurement accuracy of the first measurement data and the second measurement data can be improved.

An example of an image forming device that performs single-pass printing is one that includes a conveying device that conveys the head and substrate relatively in the substrate conveying direction, and a line head in which multiple recording elements are arranged over a length equal to or greater than the entire length of the substrate in the substrate width direction perpendicular to the substrate conveying direction.

In another aspect of the image forming system, the second processor forms a first patch group, to which a white background is applied when measured using a measuring device, at a position on the substrate corresponding to the white background, and forms a second patch group, to which a black background is applied when measured using a measuring device, at a position on the substrate corresponding to the black background, the second patch group including a plurality of second patches to which the same gradation values as each of the plurality of first patches constituting the first patch group are applied, at a position on the substrate corresponding to the black background; the measuring device includes a stage on which the white background and the black background are formed on the same plane, a third processor, and a third memory device in which a third program executed by the third processor is stored; and the third processor detects alignment between the white background and the first patch group.

This aspect makes it possible to grasp the positional misalignment between the white background and the first patch group. This reduces the reduction in accuracy of the first measurement data caused by the positional misalignment between the white background and the first patch group.

In another aspect of the image forming system, a third processor detects alignment between the black background and the second group of patches.

This aspect makes it possible to grasp the positional misalignment between the black background and the second patch group. This reduces the reduction in accuracy of the second measurement data caused by the positional misalignment between the black background and the second patch group.

In another aspect of the image forming system, the second processor forms an alignment mark representing the boundary between the first patch group and the second patch group.

According to this aspect, alignment between the stage and the substrate can be performed using alignment marks formed on the substrate.

The alignment mark may include a first mark that is the same color as the black background or a color similar to the black background.The alignment mark may include a first mark that is the same color as the white background or a color similar to the white background.

In another aspect of the image forming system, the third processor acquires the density of the white background, and if the density of the white background is below a specified threshold, issues a warning indicating that the density of the white background is below a specified threshold.

This aspect makes it possible to grasp the decrease in density of the white background. This makes it possible to suppress a decrease in the measurement accuracy of the first measurement data due to the decrease in density of the white background.

In another aspect of the image forming system, the third processor acquires the density of the black background and, if the density of the black background is below a specified threshold, issues a warning indicating that the density of the black background is below a specified threshold.

This aspect makes it possible to grasp the decrease in density of the black background. This makes it possible to suppress a decrease in the measurement accuracy of the second measurement data due to the decrease in density of the black background.

The present invention reduces the need for trial and error on the part of the operator, and enables the application of quantitative methods to generate gradation correction data that corrects the relationship between gradation values and density values in white colorants.

FIG. 1 is a functional block diagram of a tone correction data generating device. FIG. 2 is a functional block diagram of the correction processing unit shown in FIG. FIG. 3 is a flowchart showing the procedure of the tone correction LUT generation method. FIG. 4 is a schematic diagram of the tone correction LUT generation process. FIG. 5 is an explanatory diagram of a gradation correction chart. FIG. 6 is a plan view of the background showing an example of the background configuration. FIG. 7 is a schematic diagram showing the alignment of the tone correction chart and the background. FIG. 8 is an explanatory diagram showing an example of misalignment between the tone correction chart and the background. FIG. 9 is an explanatory diagram showing another example of misalignment between the tone correction chart and the background. FIG. 10 is an explanatory diagram of the driving voltages applied to printing the gradation correction chart. FIG. 11 is a diagram showing the overall configuration of an inkjet printing system according to an embodiment. FIG. 12 is a functional block diagram showing the electrical configuration of the inkjet printing system shown in FIG. FIG. 13 is a block diagram showing the hardware configuration of a control device applied to the inkjet printing system shown in FIG.

A preferred embodiment of the present invention will now be described in detail with reference to the accompanying drawings. In this specification, identical components will be designated by the same reference symbols, and duplicate explanations will be omitted where appropriate.

[Configuration example of a tone correction data generating device according to an embodiment]
1 is a functional block diagram of a tone correction data generating apparatus 10. The tone correction data generating apparatus 10 shown in the figure has a measuring instrument 12, a printer 14, and a display device 16 connected thereto.

The gradation correction data generating device 10 generates gradation correction data that is applied to correct the nonlinearity between gradation values and density values for image data printed using the printer 14. The printer 14 performs printing based on the image data to which gradation values corrected by applying the gradation correction data are applied. Hereinafter, the printer 14 will be described as an inkjet printing device equipped with an inkjet head.

The gradation correction data generating device 10 includes an image data storage unit 20. The image data storage unit 20 stores gradation correction chart data representing a gradation correction chart to be printed on a substrate. The image data storage unit 20 can also store data representing target values for density for each gradation value to be reproduced when the gradation correction chart is printed. Note that "storing" refers to saving data in memory, and is synonymous with "memorizing," "recording," and "retaining."

The gradation correction data generating device 10 includes a printer control unit 22. The printer control unit 22 reads gradation correction chart data from the image data storage unit 20 and generates an ejection control signal based on the gradation correction chart data. The printer 14 prints the gradation correction chart based on the ejection control signal.

The printer control unit 22 displays various information related to the printer 14 on the display device 16. The display device 16 is a touch panel type and displays the printer operation screen 16A. The user can operate the printer operation screen 16A to send various information to the printer 14.

The measuring instrument 12 measures the density values of the patches that make up the gradation correction chart printed on the substrate. The measuring instrument 12 may be a spectroscopic optical densitometer. The measuring instrument 12 transmits the measurement results to the gradation correction LUT generation unit 26.

The gradation correction data generating device 10 includes a measuring instrument control unit 24. The measuring instrument control unit 24 sets measurement conditions for the measuring instrument 12 and controls the measurement of the gradation correction chart using the measuring instrument 12.

The gradation correction data generating device 10 includes a gradation correction LUT generating unit 26 and an LUT storage unit 28. The gradation correction LUT generating unit 26 generates a gradation correction LUT that defines the conversion relationship between gradation values and density values. Note that LUT is an abbreviation for lookup table.

Specifically, the measurement data of the patches for each tone value of the tone correction chart is compared with the target density value for each tone value, the tone value that achieves the target density value is derived, and a tone correction LUT that represents the conversion relationship between tone values and density values is generated.

The gradation correction LUT generation unit 26 generates a gradation correction LUT for each color. The gradation correction LUT generation unit 26 generates a gradation correction LUT for each of various conditions, such as ink type, substrate type, and printer settings. Generating a gradation correction LUT here may include updating an existing gradation correction LUT.

The LUT storage unit 28 stores the gradation correction LUT generated using the gradation correction LUT generation unit 26. The LUT storage unit 28 stores the gradation correction LUT for each color and for each type of condition.

The gradation correction data generating device 10 includes a correction processing unit 30. The correction processing unit 30 includes a gradation correction processing unit 31. The correction processing unit 30 may also include various correction processing units that are applied to the gradation correction chart data, such as an in-plane unevenness correction processing unit and a non-ejecting nozzle correction processing unit. Note that various correction processing units, such as the in-plane unevenness correction processing unit, are not shown in Figure 1.

The gradation correction processing unit 31 corrects the gradation values for each color by referencing the gradation correction LUT. The printer control unit 22 generates an ejection control signal based on the gradation correction chart data with corrected gradation values, and sends the ejection control signal to the printer 14. The printer 14 prints the gradation correction chart based on the ejection control signal.

[Configuration example of correction processing unit]
Fig. 2 is a functional block diagram of the correction processing unit shown in Fig. 1. The correction processing unit 30 shown in Fig. 2 may be a computer equipped with one or more processors and one or more memories. The processor executes programs stored in the memory to realize various functions of the correction processing unit 30. Fig. 2 illustrates a personal computer as an example of the computer.

The correction processing unit 30 includes a gradation correction processing unit 31, an in-plane unevenness correction processing unit 52, and a non-ejection correction processing unit 54. The gradation correction processing unit 31 reads gradation correction chart data from the gradation correction chart data storage unit 20.

The gradation correction processing unit 31 separates the gradation correction chart data into gradation correction chart data for each color: cyan, magenta, yellow-black, and white. The gradation correction processing unit 31 corrects the gradation values for each color using the gradation correction chart data for each color, by referencing the gradation correction LUT for each color stored in the LUT storage unit 28. Figure 2 shows a tone curve representing the relationship between gradation values and density values as an example of a gradation correction LUT.

The in-plane unevenness correction processing unit 52 corrects in-plane unevenness in the patches that make up the gradation correction chart. Specifically, the in-plane unevenness correction processing unit 52 corrects the ejection amount for each nozzle in accordance with the ejection characteristics of each nozzle of the inkjet head provided in the printer 14 shown in Figure 1.

The non-ejection correction processing unit 54 corrects non-ejection nozzles. Specifically, the non-ejection correction processing unit 54 masks the non-ejection nozzles and performs substitute ejection for the non-ejection nozzles using nozzles near the non-ejection nozzles.

By performing in-plane unevenness correction and non-ejecting nozzle correction, the printer 14 can print a gradation correction chart that includes patches that suppress in-plane unevenness and streaks caused by non-ejecting nozzles.

The gradation correction chart data corrected using the correction processing unit 30 is sent to the printer control unit 22. The printer control unit 22 generates an ejection control signal based on the received gradation correction chart data and sends the ejection control signal to the printer 14. The printer 14 prints the gradation correction chart based on the ejection control signal.

[Procedure for generating a tone correction LUT]
3 is a flowchart showing the steps of the method for generating a tone correction LUT. In a printing condition setting step S10, the printer control unit 22 shown in FIG. 1 sets printing conditions for the tone correction chart for the printer 14. Examples of printing conditions include the type of ink and the type of base material.

In the gradation correction chart printing process S12, the printer control unit 22 prints the gradation correction chart based on the gradation correction chart data that has been subjected to various correction processes such as gradation correction processing.

In the gradation correction chart measurement process S14, the measuring device 12 shown in FIG. 1 is used to measure the gradation correction chart printed in the gradation correction chart printing process S12. The measurement of the gradation correction chart may be performed automatically or manually.

In automatic measurement, a substrate on which a gradation correction chart output from the printer 14 is printed is transported to the measuring instrument 12 between the printer 14 and the measuring instrument 12, the substrate is set in the measuring instrument 12, and the gradation correction chart is measured.

In manual measurement, the substrate on which the gradation correction chart is printed from the printer 14 is manually set into the measuring instrument 12, and the gradation correction chart is measured. Details of the measurement of the gradation correction chart will be described later.

In the gradation correction LUT generation process S16, the gradation correction LUT generation unit 26 acquires measurement data of the gradation correction chart from the measuring instrument 12 and generates a gradation correction LUT based on the acquired measurement data of the gradation correction chart.

Specifically, in the tone correction LUT generation process S16, the tone correction LUT generation unit 26 generates a tone correction LUT that corrects the correspondence between tone values and density values. An example of a tone curve in which the relationship between tone values and density values for each color has been corrected is shown in Figure 2.

Figure 4 is a schematic diagram of the tone correction LUT generation process. Figure 4 uses four types of graph-format schematic diagrams to illustrate the processing of each step in the tone correction LUT generation process S16. Here, we will explain how to correct an existing tone correction LUT.

Line 60 shows the relationship between the input signal value and the output signal value of an existing gradation correction LUT. In an existing gradation correction LUT, the input signal value and the output signal value are the same. If the input signal value is X and the output signal value is Y, the output signal value Y is expressed as Y = X. The existing gradation correction LUT here refers to the gradation correction LUT applied to printing the gradation correction chart.

Curve 62 schematically represents the relationship between the signal value applied to printing each patch of the gradation correction chart and the target density value. The target density value corresponds to the density value of curve 62. A table representing the relationship between the signal value applied to printing each patch of the gradation correction chart and the target density value is stored in the image data storage unit 20 shown in Figure 1, etc.

Curve 64 shows a schematic diagram of the relationship between the signal value applied to printing each patch of the gradation correction chart and the measurement data of each patch obtained in the gradation correction chart measurement process S14. The measurement data of each patch corresponds to the density value of curve 64.

Ideally, the measurement data for each patch on the gradation correction chart should match the target density value, but due to variations in the ejection characteristics of the inkjet head, the measurement data for each patch differs from the target density value.

Curve 66 schematically shows a gradation correction LUT in which the output signal value is a signal value that reproduces the target density value, and the input signal value is a gradation value derived based on image data.

The tone correction LUT is generated by applying the following steps: First, the signal value corresponding to the target density value is derived from a table showing the relationship between the signal value applied to printing each patch of the tone correction chart represented as curve 62 and the target density value.

Next, a signal value that reproduces the target density value is derived using the relationship between the signal value applied to printing each patch of the gradation correction chart, represented as curve 64, and the measurement data for each patch. The signal value that reproduces the target density value derived from curve 64 is assigned to the input signal value that is applied to the target density value.

This derives the relationship between the pre-correction signal values already assigned to each patch and the post-correction signal values that reproduce the target density value, and generates a gradation correction LUT that uses the pre-correction signal values as input and the post-correction signal values as output.

In the gradation correction LUT storage step S18, the gradation correction LUT generation unit 26 stores the gradation correction LUT in the LUT storage unit 28. The printer 14 reads the gradation correction LUT stored in the LUT storage unit 28 and applies the gradation correction LUT to the processing of image data. Note that the gradation correction LUT generation method described in the embodiment is an example of a gradation correction data generation method.

[White image density management]
An example of a white image printed using white ink is the background of a color image printed on a transparent substrate. It is important that the white image applied to the background of a color image is opaque. Generally, the degree of transparency of a white image can be evaluated using the opacity ratio as an index. The opacity ratio is calculated by applying a white background and a black background, measuring the density values of multiple white patches with different signal values representing gradation values, and applying a calculation method defined in the standard.

For example, for a white patch, the hiding power can be calculated by applying Method B specified in Japanese Industrial Standard JIS K 5600-4-1 Hiding Power. JIS K 5600-4-1 Hiding Power is a Japanese Industrial Standard that was created by translating ISO/FDIS 6504-3, published in 1998, without changing the technical content or format of the standard. JIS is an abbreviation for Japanese Industrial Standards. ISO is an abbreviation for International Organization for Standardization.

The white in white images and white ink is not limited to the strict definition of white, which reflects 100% of all wavelengths of visible light, but includes the broader definition of white that is generally recognized as white. White ink refers to ink sold under names such as white ink and white ink. An example of white ink is ink containing a white pigment such as titanium oxide particles. Note that white is synonymous with white and white color, and these terms can be used interchangeably. The white ink described in the embodiments is an example of a white colorant.

In this embodiment, a white patch is measured using two different background colors, and a gradation correction LUT is created by associating the signal value applied when printing the white patch with the hiding rate that controls the white ink, making it possible to directly control the density of the white ink using the signal value applied to printing.

[Specific examples of tone correction charts]
FIG. 5 is an explanatory diagram of a gradation correction chart. FIG. 5 illustrates a gradation correction chart 102 printed on a substrate 100. The substrate 100 is a transparent sheet-like medium, and a non-permeable medium is used. Examples of materials for the substrate 100 include ONY (Oriented Nylon), OPP (Oriented Polypropylene), and PET (PolyEthylene Terephthalate).

"Non-permeable" means that the material is non-permeable to the water-based inks described below. "Transparent" means that the visible light transmittance is between 30% and 100%, preferably between 70% and 100%.

The gradation correction chart 102 includes a process color patch group 112 composed of multiple patches 110 printed using process color inks. The process color patch group 112 includes a cyan patch group 112C, a magenta patch group 112M, a yellow patch group 112Y, and a black patch group 112K.

The cyan patch group 112C has multiple cyan patches 110C as its components. The magenta patch group 112M has multiple magenta patches 110M as its components. The yellow patch group 112Y has multiple yellow patches 110Y as its components. The black patch group 112K has multiple black patches 110K as its components.

The gradation correction chart 102 includes a spot color patch group 116, which is composed of multiple spot color patches 114 printed using spot color ink. The spot color patch group 116 includes an orange patch group 116O, a green patch group 116G, and a violet patch group 116V.

The orange patch group 116O has multiple orange patches 114O as its component elements. The green patch group 116G has multiple green patches 114G as its component elements. The violet patch group 116V has multiple violet patches 114V as its component elements.

The gradation correction chart 102 includes a first white patch group 120 and a second white patch group 122. The first white patch group 120 includes a plurality of first white patches 124. The second white patch group 122 includes a plurality of second white patches 126.

The gradation values of the multiple first white patches 124 that make up the first white patch group 120 increase from downstream to upstream in the substrate transport direction. The minimum gradation value is applied to the first white patch 124 at the downstream end in the substrate transport direction. The maximum gradation value is applied to the first white patch 124 at the upstream end in the substrate transport direction. Note that the substrate transport direction described in the embodiment is an example of a relative transport direction.

The first white patch group 120 shown in Figure 5 is composed of 16 first white patches 124. For example, if the gradation values are expressed as numbers from 0 to 255, the gradation values of the 16 first white patches 124 have a minimum gradation value of 0, a maximum gradation value of 255, and increase in gradation value in increments of 17.

The multiple first white patches 124 that make up the second white patch group 122 are applied with the same gradation value as the second white patch 126. In other words, the same gradation value is applied to the first white patch 124 and the second white patch 126 that are located at the same position in the substrate transport direction.

The first white patch group 120 and the second white patch group 122 are arranged at different positions in the substrate width direction, which is perpendicular to the substrate transport direction. Note that "perpendicular" here means that the angle between the two directions is less than or greater than 90 degrees, but can also include essentially perpendicular positions that provide the same effect as when the angle between the two directions is 90 degrees.

The process color patch group 112 and the special color patch group 116 are applied with the same gradation values as the first white patch group 120. The process color patch group 112 and the special color patch group 116 are arranged at different positions in the width direction of the substrate.

Each of the patch groups of each color that make up the process color patch group 112 is arranged at a different position in the width direction of the substrate. Furthermore, each of the patch groups of each color that make up the special color patch group 116 is arranged at a different position in the width direction of the substrate.

The gradation correction chart 102 has patches of each color arranged along the substrate transport direction in order of gradation value, and patches of different colors arranged along the substrate width direction have the same gradation value.

The substrate 100 on which the gradation correction chart 102 is printed is printed with a first background alignment mark 104 and a second background alignment mark 105. The first background alignment mark 104 is printed using black ink. The second background alignment mark 105 is printed using white ink. The first background alignment mark 104 and the second background alignment mark 105 are formed at both ends of the substrate in the transport direction.

The first background alignment mark 104 and the second background alignment mark 105 are applied as triangles. The first background alignment mark 104 and the second background alignment mark 105 are arranged so that the vertex 104A of the first background alignment mark 104 and the vertex 105A of the second background alignment mark 105 face each other.

The first background alignment mark 104 and the second background alignment mark 105 are used to align the background with the gradation correction chart 102. The background is illustrated in Figure 6 with the reference numeral 200.

The shape, color, and position of the first background alignment mark 104 and the second background alignment mark 105 are not limited to the example shown in Figure 5, and the shape, color, and position can be specified as appropriate.

The gradation correction chart 102 is printed with a first measurement start position mark 106 and a second measurement start position mark 108. The first measurement start position mark 106 is printed using black ink. The second measurement start position mark 108 is printed using white ink.

The first measurement start position mark 106 indicates the measurement start position of the process color patch group 112, the special color patch 114, and the first white patch group 120 on the gradation correction chart 102. The second measurement start position mark 108 indicates the measurement start position of the second white patch group 122.

[Example of background configuration applied to measuring the gradation correction chart]
Fig. 6 is a plan view of a background showing an example of the configuration of the background. The background 200 shown in Fig. 6 is applied to the measuring instrument 12 shown in Fig. 1. When measuring the gradation correction chart 102 printed on the substrate 100 shown in Fig. 5, the substrate 100 is supported using a stage 201.

The background 200 is formed on the substrate support surface 201A that supports the substrate 100 of the stage 201. For example, the background 200 can be formed on the substrate support surface 201A by attaching a sheet on which the background 200 is printed to the substrate support surface 201A. The background 200 can also be formed on the substrate support surface 201A by applying a surface treatment such as painting. Note that the substrate support surface 201A described in the embodiment is an example of the same surface on which the white background and the black background are formed.

The background 200 comprises a white background 202 and a black background 204. The boundary 205 between the white background 202 and the black background 204 is located between the first white patch group 120 and the second white patch group 122 when the stage 201 and the gradation correction chart 102 shown in Figure 5 are correctly aligned.

[Alignment of the gradation correction chart and background]
7 is a schematic diagram of the alignment of the gradation correction chart and the background. The figure shows a state in which the gradation correction chart 102 is aligned with the background 200 formed on the stage 201. Note that in the figure, some of the reference numerals shown in FIGS. 5 and 6 are omitted. The same applies to FIGS. 8 and 9.

When the gradation correction chart 102 is aligned to the correct position relative to the background 200, the first white patch group 120 is superimposed on the white background 202, and the second white patch group 122 is superimposed on the black background 204.

When the gradation correction chart 102 is aligned to the correct position relative to the background 200, the first background alignment mark 104 and the white background 202 are separated, and the second background alignment mark 105 and the black background 204 are separated.

That is, when the first background alignment mark 104, to which black is applied, is located on top of the white background 202, the first background alignment mark 104 is visible.

Furthermore, when the second background alignment mark 105, to which white is applied, is located on top of the black background 204, the second background alignment mark 105 is visible.

Figure 8 is an explanatory diagram showing an example of misalignment between the gradation correction chart and the background. If the position of the gradation correction chart 102 is shifted toward the black background 204, the color of the first background alignment mark 104 will be similar to that of the black background 204, making it impossible to distinguish between the first background alignment mark 104 and the white background 202.

Figure 9 is an explanatory diagram showing another example of misalignment between the gradation correction chart and the background. When the position of the gradation correction chart 102 is shifted toward the white background 202, the color of the second background alignment mark 105 becomes similar to the color of the white background 202, making it impossible to distinguish between the second background alignment mark 105 and the black background 204.

In other words, if the gradation correction chart 102 is shifted toward the black background 204, some or all of the first background alignment mark 104 will not be visible. Figure 8 shows a case where none of the first background alignment mark 104 is visible.

Similarly, if the gradation correction chart 102 is shifted toward the white background 202, some or all of the second background alignment mark 105 will not be visible. Figure 8 shows a case where none of the second background alignment mark 105 is visible.

In other words, when the gradation correction chart 102 is placed on the background 200, the appropriateness of the alignment between the background 200 and the gradation correction chart 102 can be automatically detected depending on whether the first background alignment mark 104 and the second background alignment mark 105 are visible.

Note that the first chart alignment mark 206 and the second chart alignment mark 208 described in the embodiment are examples of boundary marks.

[Measurement of Gradation Correction Chart and Calculation of Gradation Correction Data]
The gradation correction chart 102 is aligned to the correct position with respect to the background 200, and the gradation correction chart 102 is measured. Specifically, the Y value of the CIEXYZ color system is obtained for each of the multiple first white patches 124 that make up the first white patch group 120. Similarly, the Y value of the CIEXYZ color system is obtained for each of the multiple second white patches 126 that make up the second white patch group 122.

The measurement values of the first white patch 124 are affected by the density of the white background 202. Similarly, the measurement values of the second white patch 126 are affected by the density of the black background 204. In order to avoid the influence of the white background 202 on the measurement values of the first white patch 124 and the influence of the black background 204 on the second white patch 126, the measurement values of the first white patch 124 and the measurement values of the second white patch 126 are normalized using the density values of the white background 202 and the black background 204.

If the Y value of the observation light source is _YL , the Y value of the black background 204 is _Ybk , and the measurement value acquired using the black background 204 as the background is _Ymk , the normalized Y value _Ynb is expressed as _Ynb = ( _Ymk - _Ybk )/( _YL - _Ybk ). In other words, the measurement value _Ymb , which is an absolute value, is converted into a Y value _Ynb , which is a relative value using the black background 204 as the reference.

When a white background 202 is used, the Y value of the white background 202 is _Ywh , and the measurement value obtained using the white background 202 as the background is _Ymw , and the normalized Y value _Ynw is expressed as _Ynw = ( _Ymw - _Ywh )/( _YL - _Ywh ). The Y value _Ywh of the white background 202 can be the Y value obtained by measuring the area on the substrate 100 where the tone correction chart 102 is not formed. The same applies to the Y value _Ybk of the black background 204.

Using the Y value _Ynw based on the measurement data of the first white patch 124 and the Y value _Ynb based on the measurement data of the second white patch 126, the hiding ratio _Ynb / _Ynw for each gradation value in white is calculated.

The target hiding ratio for each gradation value in white ink is obtained, and the target hiding ratio representing the target white ink density is compared with the hiding ratio calculated from the measurement data of each patch, and the difference between the calculated hiding ratio and the target hiding ratio is calculated. A gradation correction LUT to be applied to the white ink is generated based on the calculated hiding ratio difference.

Specifically, density values are converted to hiding rates and a gradation correction LUT to be applied to white ink is generated in accordance with the procedure of the gradation correction LUT generation process S16 in Figure 3, which is explained using Figure 4. The gradation correction LUT is stored in the LUT storage unit 28 shown in Figure 1.

The gradation correction LUT applied to white ink represents the relationship between the signal value representing the gradation value and the opacity, which is the evaluation index value for the white patch. For white ink, a signal value that achieves the target opacity is derived, enabling printing that reproduces the target density value. It also makes it possible to adjust the density value of white ink to correspond to the target opacity when the density value is changed.

For example, when printing a white image in which the white ink coverage rate is set to 53 percent, if the white ink coverage rate is changed to 51 percent in order to reduce the cost of white ink, the white gradation correction LUT can be referenced to obtain a signal value representing the gradation value at which the coverage rate is 51 percent.

In this way, when the white ink coverage rate is changed, it is not necessary to derive a signal value representing the gradation value corresponding to the changed white ink coverage rate based on printing and measuring the gradation correction chart 102.

For process color inks such as cyan and spot color inks such as orange, the LUTs for each color stored in the LUT storage unit 28 shown in Figure 1 are corrected based on the Y value of the CIEXYZ color system of each patch 110 for each color obtained in measuring the gradation correction chart 102.

For colors other than white, such as cyan, the Y value _Yn obtained by normalizing the Y value _YL of the observation illuminant and the Y value _Ywh of the white background 202 is also applied in the LUT correction. Note that normalization of measurement values using the density of the background 200 is not limited to the above example. Methods other than those described above can be applied as long as absolute measurement values can be converted to relative values using the background color as a reference.

When converting absolute measurement values to relative values, the higher the density contrast between the patch 110 and the background 200, the more likely it is that the LUT correction accuracy will improve. Therefore, it is preferable to measure the density of the background 200 and issue a warning if the measured density value is below a specified threshold.

An example of a warning is to display text information indicating the content of the warning on the display device 16 shown in Figure 1, and to prompt the user to replace the background 200, etc. The Y value of the background 200 may be the Y value obtained by measuring the non-formed area of the gradation correction chart 102 on the substrate 100.

When single-pass printing is applied to the printer 14, it is preferable that the arrangement direction of multiple patches 110 of the same color be parallel to the substrate transport direction. When multiple patches 110 of the same color are arranged parallel to the substrate transport direction, the in-plane density uniformity of each patch 110 is relatively improved, and the correction accuracy of the LUT can be relatively improved. Note that while the term "parallel" here strictly refers to intersecting, it can also include essentially parallel, which provides the same effect as parallel.

When the tone correction chart 102 is measured, if the in-plane density uniformity of the background 200 is relatively high, the correction accuracy of the LUT can be relatively improved. Therefore, it is preferable to measure the in-plane density unevenness of the background 200 and issue a warning if the measured density unevenness is equal to or greater than a specified threshold. The warning can be in the form exemplified above. A user who sees the warning can replace or clean the background 200, thereby suppressing the in-plane density unevenness of the background 200.

Note that the first white patch 124 described in the embodiment is an example of a plurality of first patches. The first white patch group 120 described in the embodiment is an example of a first patch group. The second white patch 126 described in the embodiment is an example of a plurality of second patches. The second white patch group 122 described in the embodiment is an example of a second patch group.

Furthermore, the measurement values of the first white patch 124 described in the embodiment are an example of first measurement data. The measurement values of the second white patch 126 described in the embodiment are an example of second measurement data.

[Driving voltage applied to printing the gradation correction chart]
Fig. 10 is an explanatory diagram of the driving voltage applied to printing the gradation correction chart, which is a graph showing one ejection cycle of the driving voltage supplied to the piezoelectric ejection type inkjet head provided in the printer 14 shown in Fig. 1.

The horizontal axis of the graph shown in Figure 10 represents time, measured in microseconds. The vertical axis of the graph shown in the same figure represents voltage, measured in volts. Note that the values shown in Figure 10 are examples and can be defined as appropriate depending on the printing conditions and the specifications of the piezoelectric element installed in the inkjet head.

The inkjet head uses a continuous firing drive method, and one or more ejection drive pulses corresponding to the ejection volume are supplied from among the multiple ejection drive pulses that make up the drive waveform 300 shown in Figure 10. This allows the inkjet head to eject large, medium, and small droplets, each with a different volume.

For example, when ejecting a small droplet, ejection drive pulse 312 is applied. When ejecting a medium droplet, ejection drive pulse 306, ejection drive pulse 308, ejection drive pulse 310, and ejection drive pulse 312 are applied.

When ejecting large droplets, ejection drive pulse 302, ejection drive pulse 304, ejection drive pulse 306, ejection drive pulse 308, ejection drive pulse 310 and ejection drive pulse 312 are applied.

The drive waveform element following the ejection drive pulse 312 is a reverberation suppression waveform element 314. The reverberation suppression waveform element 314 can be added to all cases of large, medium, and small droplets in order to suppress ink vibration immediately after the ink droplet is ejected.

The printing of the gradation correction chart 102 shown in Figure 5 is performed under the same printing conditions as normal printing. That is, of the patches that make up the patch group that makes up the gradation correction chart 102, at least one patch for each color is printed using a combination of dots of multiple sizes.

For example, for a patch 110 with a relatively small gradation value, only small dots corresponding to small droplets are applied, and for a patch 110 with a relatively small gradation value, small dots and medium dots corresponding to medium droplets are applied.

Note that the patch group constituting the gradation correction chart 102 described in the embodiment is an example of a patch group that includes one or more patches to which dots of multiple sizes are applied.

[Configuration example of inkjet printing system according to the embodiment]
11 is a diagram showing the overall configuration of an inkjet printing system according to an embodiment. The inkjet printing system 400 includes a digital printing device 406 that prints a color image on a transparent substrate 401 using single-pass printing.

In this embodiment, flexible packaging such as a plastic film is exemplified as the substrate 401. The substrate 401 may be a single layer, or may be made up of multiple overlapping layers. The substrate 401 may be in a continuous roll-to-roll form, or in the form of sheets cut to a specified length. The substrate 401 may also be referred to as a medium, media, sheet, film, substrate, etc. The substrate 401 shown in Figure 11 corresponds to the substrate 100 shown in Figure 5.

The inkjet printing system 400 comprises a substrate supply device 402, a first intermediate conveying device 404, a printing device 406, a second intermediate conveying device 408, a measuring device 410, a drying device 412, and an accumulation device 414. Each part will be described in detail below.

[Base material supply device]
When the substrate 401 is in a continuous form, the substrate supply device 402 includes a roll storage unit that stores a roll of the substrate 401. When the substrate 401 is in a sheet form, the substrate supply device 402 includes a tray that stores the substrate 401. The substrate supply device 402 supplies the substrate 401 to the first intermediate conveying device 404 in response to printing control of the printing device 406. The substrate supply device 402 may include a correction mechanism that corrects the attitude of the substrate 401.

[First intermediate conveying device]
The first intermediate conveying device 404 transfers the substrate 401 supplied from the substrate supplying device 402 to the printing device 406. The first intermediate conveying device 404 may have a known configuration depending on the shape of the substrate 401. The arrow line pointing from the substrate supplying device 402 to the first intermediate conveying device 404 indicates the substrate conveyance direction.

[Printing device]
The printing device 406 includes an inkjet head 420C, an inkjet head 420M, an inkjet head 420Y, an inkjet head 420K, and an inkjet head 420W.

Inkjet head 420C, inkjet head 420M, inkjet head 420Y, inkjet head 420K and inkjet head 420W are arranged in the order described above from the upstream side along the substrate transport direction.

Inkjet head 420C ejects cyan ink. Inkjet head 420M ejects magenta ink. Inkjet head 420Y ejects yellow ink. Inkjet head 420K ejects black ink. Inkjet head 420W ejects white ink.

The inkjet head 420C, etc. may be a line head in which multiple nozzles are arranged across a length equal to or greater than the entire length of the substrate 401 in the width direction of the substrate. The multiple nozzles provided in the inkjet head 420C, etc. may be arranged two-dimensionally, such as in a matrix.

The inkjet head 420C and the like may employ a piezoelectric ejection method that uses a piezoelectric element as the ejection pressure element that generates the ejection pressure. The inkjet head 420C and the like may employ a thermal method that ejects ink by utilizing the film boiling phenomenon of ink.

The printing device 406 forms a color image on the transparent substrate 401 using color inks such as cyan ink, and then forms a white image that serves as a background image by overlaying the color image using white ink. When the printed material produced using the substrate 401 is viewed from the non-printed side of the substrate 401, the color image can be seen.

Note that the inkjet head 420W described in the embodiment is an example of a head that ejects white colorant toward a substrate. The nozzles and ejection pressure elements described in the embodiment are examples of components of multiple recording elements.

The printing device 406 is equipped with a printing drum 422. The printing drum 422 has a cylindrical shape. The printing drum 422 is equipped with a substrate support area on its circumferential surface that supports the substrate 401. The substrate support area is not shown in the figure.

The rotation shaft of the printing drum 422 is connected to a motor (not shown) via a drive mechanism (not shown). When the motor is rotated, the printing drum 422 rotates in the direction indicated by the arrow. When the printing drum 422 is rotated, the substrate 401 supported on the circumferential surface of the printing drum 422 is transported along the rotation direction of the printing drum 422.

The substrate support area has multiple suction holes formed. The multiple suction holes are arranged based on a specified pattern. The multiple suction holes are connected to a suction flow path (not shown). The suction flow path is connected to a suction pump (not shown). By operating the suction pump to generate negative pressure in the multiple suction holes, the substrate 401 is suction-supported on the circumferential surface of the printing drum 422.

The transport form of the substrate 401 in the printing device 406 is not limited to a transport form using a printing drum 422. For example, a transport form using a transport belt or a transport form using multiple rollers can be applied.

[Second intermediate conveying device]
The second intermediate conveying device 408 delivers the substrate 401 delivered from the printing drum 422 to the measuring device 410. The second intermediate conveying device 408 may have a similar configuration to the first intermediate conveying device 404. The arrow line shown on the second intermediate conveying device 408 indicates the substrate conveying direction in the second intermediate conveying device 408.

[Measuring equipment]
The measuring device 410 includes a concentration measuring device 430, a plurality of reading and conveying rollers 432, and a stage 434. The measuring device 410 also includes an illumination device. The illumination device is not shown. The concentration measuring device 430 shown in Fig. 11 corresponds to the measuring device 12 shown in Fig. 1. The stage 434 shown in Fig. 11 corresponds to the stage 201 provided in the measuring device 12 shown in Fig. 1.

The density measuring device 430 shown in Figure 11 can measure the gradation correction chart printed on the substrate 401, similar to the measuring device 12 shown in Figure 1. The inkjet printing system 400 can generate gradation correction data for each color based on the measurement data of the gradation correction chart, and can generate a gradation correction LUT for each color based on the gradation correction data for each color.

Figure 11 illustrates a roller conveying method as an example of a method for conveying the substrate 401 in the measuring device 410, but other methods such as a belt conveying method and a drum conveying method can also be applied as a method for conveying the substrate 401 in the measuring device 410.

The measuring device 410 may be equipped with an imaging device that captures an image of the test pattern printed on the substrate 401. The inkjet printing system 400 can detect ejection abnormalities in the inkjet head 420C, etc. based on the image data of the test pattern.

[Drying equipment]
The drying device 412 performs a drying process on the printed substrate 401. The drying device 412 may be equipped with a heater and a fan, and may be configured to blow warm air onto the printed substrate 401. The drying device 412 includes a drying conveying unit that conveys the printed substrate 401. As a conveying form for the printed substrate 401, a known conveying form such as a drum conveying, a belt conveying, or a roller conveying may be applied. The arrow shown on the drying device 412 indicates the substrate conveying direction from the drying device 412.

[Stacking device]
The accumulation device 414 stores the substrate 401 delivered from the drying device 412. When the substrate 401 is in a continuous form, the accumulation device 414 includes a roll storage section that stores a roll on which the substrate 401 is wound. When the substrate 401 is in a sheet form, the accumulation device 414 includes a tray that stores the substrate 401.

[Electrical configuration of inkjet printing system]
Fig. 12 is a functional block diagram showing the electrical configuration of the inkjet printing system shown in Fig. 11. The inkjet printing system 400 includes a system control unit 460, a transport control unit 462, a print control unit 466, a measurement control unit 468, a drying control unit 470, and an information acquisition unit 472.

The system control unit 460 comprehensively controls the overall operation of the inkjet printing system 400. The system control unit 460 sends command signals to various control units. The system control unit 460 functions as a memory controller that controls the storage of data in memory 474 and the reading of data from memory 474.

The system control unit 460 acquires the sensor signal transmitted from the sensor 476 and transmits a command signal based on the sensor signal to various control units. The sensor 476 includes a position detection sensor and a temperature sensor provided in each part of the inkjet printing system 400.

The conveying control unit 462 sets conveying conditions based on command signals sent from the system control unit 460 and controls the operation of the conveying device 464 based on the set conveying conditions. The conveying device 464 shown in FIG. 12 includes the first intermediate conveying device 404, printing drum 422, reading conveying roller 432, and drying conveying device provided in the drying device 412 shown in FIG. 11. The conveying device 464 may also include the substrate supply device 402 and the accumulation device 414.

The print control unit 466 sets print conditions based on command signals sent from the system control unit 460 and controls the operation of the printing device 406 based on the set print conditions. The print control unit 466 shown in Figure 12 has the functions of the printer control unit 22 shown in Figure 1.

The print control unit 466 has an image processing unit that performs color separation processing, color conversion processing, correction processing for each process, and halftone processing on the print data to generate halftone data for each color.

The print control unit 466 includes a drive voltage generation unit that generates a drive voltage to be supplied to the inkjet head 420C, etc. based on halftone data for each color. The print control unit 466 includes a drive voltage output unit that supplies a drive voltage to the inkjet head 420C.

The printing control unit 466 can use an inkjet head 420C shown in Figure 11 or the like to print a gradation correction chart including a group of cyan, magenta, yellow, black, and white patches based on the image data of the gradation correction chart.

When generating a halftone image of the gradation correction chart, the printing control unit 466 generates a multi-value halftone image and, based on the multi-value halftone image, combines multiple types of dots of different sizes to print the gradation correction chart.

When printing the gradation correction chart, the print control unit 466 arranges multiple patches that make up the patch group for each color along the substrate transport direction.

The printing control unit 466 may have the functions of the gradation correction LUT generation unit 26 and correction processing unit 30 shown in Figure 1. The inkjet printing system 400 shown in Figure 12 may have, in addition to the printing control unit 466, a gradation correction data generation unit having functions similar to those of the gradation correction data generation device 10 shown in Figure 1.

Of the printing control unit 466 shown in Figure 12, the processing unit corresponding to the gradation correction data generating device 10 shown in Figure 1 acquires measurement data of the gradation correction chart from the measurement control unit 468 and generates a gradation correction LUT based on the measurement data of the gradation correction chart.

The measurement control unit 468 sets measurement conditions based on command signals sent from the system control unit 460 and controls the operation of the measurement device 410 based on the set measurement conditions. The measurement control unit 468 shown in Figure 12 may have the functions of the measurement instrument control unit 24 shown in Figure 1.

The measurement control unit 468 may issue a warning if the density value of the background formed on the stage 434 is below a specified threshold. The measurement control unit 468 may also issue a warning if the in-plane density unevenness in the background formed on the stage 434 is above a specified threshold.

The drying control unit 470 sets the processing conditions for the main drying process based on the command signal sent from the system control unit 460 and controls the operation of the drying device 412 based on the set processing conditions.

The information acquisition unit 472 acquires various information that is applied to the control of the inkjet printing system 400. The system control unit 460 transmits command signals to various control units based on the various information acquired using the information acquisition unit 472.

Memory 474 can store various data, parameters, and programs applied to the inkjet printing system 400. Memory 474 can function as the LUT storage unit 28 shown in Figure 1.

Figure 13 is a block diagram showing the hardware configuration of a control device applied to the inkjet printing system shown in Figure 11. The control device 500 provided in the inkjet printing system 400 includes a processor 502, a non-transitory tangible computer-readable medium 504, a communication interface 506, and an input/output interface 508.

The control device 500 is implemented as a computer. The computer may be in the form of a server, a personal computer, a workstation, a tablet terminal, or the like.

The processor 502 includes a CPU (Central Processing Unit). The processor 502 may also include a GPU (Graphics Processing Unit). The processor 502 is connected to a computer-readable medium 504, a communication interface 506, and an input/output interface 508 via a bus 510. An input device 512 and a display device 514 are connected to the bus 510 via the input/output interface 508.

Processor 502 can function as a first processor that performs processing related to the generation of gradation correction data, a second processor that performs processing related to image formation, and a third processor that performs processing related to measurement.

The computer-readable medium 504 includes memory, which is a primary storage device, and storage, which is a secondary storage device. The computer-readable medium 504 may be a semiconductor memory, a hard disk drive, a solid-state drive, or the like. The computer-readable medium 504 may be any combination of multiple devices.

Note that a hard disk device may be referred to as an HDD, which is an abbreviation for Hard Disk Drive in English. A solid state drive device may be referred to as an SSD, which is an abbreviation for Solid State Drive in English.

The control device 500 is connected to a network via the communication interface 506 and is communicatively connected to external devices. The network may be a LAN (Local Area Network) or the like. The network is not shown in the figure.

The computer-readable medium 504 stores a conveying control program 520, a printing control program 522, a measurement control program 524, a drying control program 526, and a gradation correction data generation program 528.

The transport control program 520 corresponds to the transport control applied to the transport device 464 shown in FIG. 12. The printing control program 522 corresponds to the printing control applied to the printing device 406. The measurement control program 524 corresponds to the measurement control applied to the measuring device 410. The drying control program 526 corresponds to the drying control applied to the drying device 412. The gradation correction data generation program 528 corresponds to the generation of correction data applied to the gradation correction process and the gradation correction process.

The various programs stored on the computer-readable medium 504 include one or more instructions. The computer-readable medium 504 stores various data, various parameters, etc. Note that the memory 474 shown in FIG. 12 is included in the computer-readable medium 504 shown in FIG. 13.

The computer-readable medium 504 can function as a first storage device in which a gradation correction data generation program 528 is stored. The computer-readable medium 504 can function as a second storage device in which a transport control program 520, a printing control program 522, and a drying control program 526 are stored. The computer-readable medium 504 can function as a third storage device in which a measurement control program 524 is stored.

Note that the gradation correction data generation program 528 described in the embodiment is an example of a first program. The transport control program 520, printing control program 522, and drying control program 526 described in the embodiment are examples of components of a second program. The measurement control program 524 described in the embodiment is an example of a third program.

In the inkjet printing system 400, the processor 502 executes various programs stored in the computer-readable medium 504 to realize various functions of the inkjet printing system 400. Note that the term program is synonymous with the term software.

The control device 500 performs data communication with external devices via the communication interface 506. The communication interface 506 may use various standards, such as USB (Universal Serial Bus). The communication form of the communication interface 506 may be either wired communication or wireless communication.

The control device 500 is connected to an input device 512 and a display device 514 via an input/output interface 508. The input device 512 is an input device such as a keyboard and a mouse. The display device 514 displays various information applied to the control device 500.

The display device 514 may be a liquid crystal display, an organic EL display, a projector, or the like. The display device 514 may be any combination of multiple devices. Note that the "EL" in organic EL display is an abbreviation for Electro-Luminescence. The display device 514 shown in Figure 13 corresponds to the display device 16 shown in Figure 1.

Here, examples of the hardware structure of the processor 502 include a CPU, GPU, PLD (Programmable Logic Device), and ASIC (Application Specific Integrated Circuit). A CPU is a general-purpose processor that executes programs and functions as various functional units. A GPU is a processor specialized for image processing.

A PLD is a processor whose electrical circuit configuration can be changed after the device is manufactured. An example of a PLD is an FPGA (Field Programmable Gate Array). An ASIC is a processor with dedicated electrical circuitry designed specifically to perform a specific process.

A single processing unit may be composed of one of these various processors, or two or more processors of the same or different types. Examples of combinations of various processors include a combination of one or more FPGAs with one or more CPUs, and a combination of one or more FPGAs with one or more GPUs. Another example of a combination of various processors is a combination of one or more CPUs with one or more GPUs.

A single processor may be used to configure multiple functional units. An example of using a single processor to configure multiple functional units is to configure a single processor by applying a combination of one or more CPUs and software, such as in a SoC (System On a Chip) computer, which is typically used in a client or server computer, and have this processor operate as multiple functional units.

Another example of using a single processor to configure multiple functional units is to use a processor that uses a single IC chip to realize the functions of an entire system including multiple functional units. Note that IC is an abbreviation for Integrated Circuit.

In this way, the various functional units are configured as a hardware structure using one or more of the various processors described above. Furthermore, the hardware structure of the various processors described above is, more specifically, an electrical circuit (circuitry) that combines circuit elements such as semiconductor elements.

The computer-readable medium 504 may include semiconductor elements such as read-only memory (ROM) and random access memory (RAM). The computer-readable medium 504 may include magnetic storage media such as a hard disk. The computer-readable medium 504 may comprise multiple types of storage media.

[Effects of the embodiment]
The tone correction data generating device, tone correction LUT generating method, program, and inkjet printing device according to the embodiments can achieve the following advantageous effects.

[1]
The gradation correction chart 102 includes a first white patch group 120 and a second white patch group 122. The first white patch group 120 includes a plurality of first white patches 124 having different signal values corresponding to gradation values. The second white patch group 122 includes a plurality of second white patches 126 to which the same signal values as those of the plurality of first white patches 124 are applied.

The density values of the first white patch group 120 are measured using a white background 202. The density values of the second white patch group 122 are measured using a black background 204. Based on the density measurement values of the first white patch group 120 and the second white patch group 122, correction data is generated to correct the gradation correction LUT, which shows the relationship between gradation values and density values in white ink. This makes it possible to obtain gradation values corresponding to target density values in white ink based on a quantitative method without trial and error.

[2]
The concealment rate is applied to the evaluation index value of the density of the white ink calculated based on the measurement data of the first white patch group 120 and the measurement data of the second white patch group 122. This makes it possible to evaluate the density of the white ink based on the prescribed standard.

[3]
The measurement data of the first white patch group 120 is normalized using the density value of the white background 202. This reduces the influence of the density of the white background 202 on the measurement data of the first white patch group 120.

[4]
The measurement data of the second white patch group 122 is normalized using the density value of the black background 204. This reduces the influence of the density of the black background 204 on the measurement data of the second white patch group 122.

[5]
In a single-pass printing device, the patches 110 for each color that make up the tone correction chart 102 are arranged in a direction parallel to the substrate transport direction, which improves the uniformity of density within the surface of the patch 110 and can improve correction accuracy.

[6]
A warning is issued when the density value of the white background 202 is equal to or less than a specified threshold value. This makes it possible to suppress a decrease in correction accuracy due to a decrease in density of the white background 202.

[7]
A warning is issued when the density value of the black background 204 is equal to or less than a specified threshold value. This makes it possible to suppress a decrease in correction accuracy due to a decrease in the density of the black background 204.

[8]
A warning is issued when the density unevenness within the white background 202 is equal to or greater than a specified threshold value. This makes it possible to suppress a decrease in correction accuracy due to the occurrence of density unevenness in the white background 202.

[9]
A warning is issued when the density unevenness within the black background 204 is equal to or greater than a specified threshold value. This makes it possible to suppress a decrease in correction accuracy due to the occurrence of density unevenness in the black background 204.

[Example of application to an image forming system]
In this embodiment, an inkjet printing system 400 equipped with an inkjet printing device 406 is exemplified as an example of an image forming system, but the gradation correction data according to the embodiment can also be applied to image forming methods other than the inkjet method, such as an image forming system equipped with an electrophotographic image forming device.

[About the images]
The term "image" is to be interpreted in a broad sense and may include color images, black and white images, single color images, gradation images, uniform density images, solid images, etc. The term "image" is used as a comprehensive term that includes not only photographic images but also designs, characters, symbols, line drawings, mosaic patterns, color-coded patterns, and various other patterns. The term "image" may include any combination of the above.

[Print Image]
Printing an image may include concepts such as image formation, recording, printing, drawing, and printing.

The embodiments of the present invention described above may have their constituent elements modified, added, or deleted as appropriate, without departing from the spirit of the present invention. The present invention is not limited to the embodiments described above, and many modifications are possible within the technical spirit of the present invention by those with ordinary skill in the art.

10 Gradation correction data generating device 12 Measuring instrument 14 Printer 16 Display device 16A Printer operation screen 20 Image data storage unit 22 Printer control unit 24 Measuring instrument control unit 26 Gradation correction LUT generating unit 28 LUT storage unit 30 Correction processing unit 31 Gradation correction processing unit 52 In-plane unevenness correction processing unit 54 Discharge failure correction processing unit 60 Straight line 62 Curve 64 Curve 66 Curve 100 Substrate 102 Gradation correction chart 104 First background alignment mark 104A Vertex 105 Second background alignment mark 105A Vertex 106 First measurement start position mark 108 Second measurement start position mark 110 Patch 110C Cyan patch 110K Black patch 110M Magenta patch 110Y Yellow patch 112 Process color patch group 112C Cyan patch group 112K Black patch group 112M Magenta patch group 112Y Yellow patch group 114, special color patch 114G, green patch 114O, orange patch 114V, violet patch 120, first white patch group 122, second white patch group 124, first white patch 126, second white patch 200, background 201, stage 201A, substrate support surface 202, white background 204, black background 205, boundary 300, drive waveform 302, ejection drive pulse 304, ejection drive pulse 306, ejection drive pulse 308, ejection drive pulse 310, ejection drive pulse 312, ejection drive pulse 314, reverberation suppression waveform element 400, inkjet printing system 401, substrate 402, substrate supply device 404, first intermediate conveyance device 406, printing device 408, second intermediate conveyance device 410, measuring device 412, drying device 414, accumulation device 420C, inkjet head 420K, inkjet head 420M, inkjet head 420W, inkjet head 420Y Inkjet head 422, printing drum 430, density measuring device 432, reading transport roller 434, stage 460, system control unit 462, transport control unit 464, transport device 466, printing control unit 468, measurement control unit 470, drying control unit 472, information acquisition unit 474, memory 476, sensor 500, control device 502, processor 504, computer readable medium 506, communication interface 508, input/output interface 510, bus 512, input device 514, display device 520, transport control program 522, print control program 524, measurement control program 526, drying control program 528, gradation correction data generation program S10 to S18, steps of gradation correction LUT generation method

Claims (12)

a tone correction data generating device including a first processor and a first storage device that stores a first program executed by the first processor;
an image forming apparatus including a head that ejects a white colorant toward a substrate , the image forming apparatus including a second processor and a second storage device that stores a second program that is executed by the second processor ;
a measuring device including a stage on which a white background and a black background are formed on the same surface, the measuring device including a third processor and a third storage device in which a third program executed by the third processor is stored ;
An image forming system comprising:
The second processor executes instructions of the second program,
a first patch group, which is formed using the white colorant emitted from the head and includes a plurality of patches with different gradation values, and which includes one or more patches to which dots of a plurality of sizes are applied, to which the white background is applied when measured using the measurement device, is formed at a position on the substrate corresponding to the white background; and a second patch group, which is formed using the measurement device and includes a plurality of second patches to which the black background is applied when measured using the measurement device, and which includes a plurality of second patches to which the same gradation values as each of the plurality of first patches constituting the first patch group are applied, is formed at a position on the substrate corresponding to the black background;
The third processor executes instructions of the third program,
Detecting alignment between the white background and the first set of patches;
The first processor executes instructions of the first program,
acquiring first measurement data to which the white background is applied from the measurement device;
acquiring second measurement data from the measurement device to which the black background is applied;
deriving an evaluation index value for a density value for each gradation value of the white colorant based on the first measurement data and the second measurement data;
The image forming system generates tone correction data for correcting the relationship between tone values and density values in the white colorant based on the evaluation index value. The image forming system according to claim 1 , wherein the second processor uses the head to form the patch group in which the plurality of patches are arranged along a relative transport direction between the head and the substrate. 3. The image forming system according to claim 1 , wherein the third processor detects alignment between the black background and the second set of patches. The image forming system according to claim 1 , wherein the second processor forms an alignment mark that indicates a boundary between the first patch group and the second patch group. The third processor:
obtaining the density of the white background;
5. The image forming system according to claim 1 , wherein, when the density of the white background is equal to or less than a specified threshold, a warning indicating that the density of the white background is equal to or less than a specified threshold is issued. The third processor:
Obtaining the density of the black background;
The image forming system according to claim 1 , wherein, when the density of the black background is equal to or less than a specified threshold, a warning indicating that the density of the black background is equal to or less than a specified threshold is issued. The first processor:
Acquire measurement data of the first patch group as the first measurement data;
The image forming system according to claim 1 , wherein measurement data of the second patch group is acquired as the second measurement data. The image forming system according to claim 7 , wherein the first processor applies a concealment rate as the evaluation index value. The first processor:
9. The image forming system according to claim 1, wherein the evaluation index value is derived using the first measurement data normalized using the density value of the white background and the second measurement data normalized using the density value of the black background. A gradation correction data generation method applicable to an image forming system including a gradation correction data generation device, an image forming device including a head that emits a white colorant toward a substrate, and a measurement device including a stage on which a white background and a black background are formed on the same surface, the method comprising:
a computer that functions as the image forming apparatus,
a first patch group, which is formed using the white colorant emitted from the head and includes a plurality of patches with different gradation values, and which includes one or more patches to which dots of a plurality of sizes are applied, to which the white background is applied when measured using the measurement device, is formed at a position on the substrate corresponding to the white background; and a second patch group, which is formed using the measurement device and includes a plurality of second patches to which the black background is applied when measured using the measurement device, and which includes a plurality of second patches to which the same gradation values as each of the plurality of first patches constituting the first patch group are applied, is formed at a position on the substrate corresponding to the black background;
a computer that functions as the measurement device,
Detecting alignment between the white background and the first set of patches;
a computer that functions as the gradation correction data generating device,
acquiring first measurement data to which the white background is applied from the measurement device;
acquiring second measurement data from the measurement device to which the black background is applied;
deriving an evaluation index value for a density value for each gradation value of the white colorant based on the first measurement data and the second measurement data;
generating gradation correction data for correcting the relationship between the gradation value and the density value of the white colorant based on the evaluation index value;
A method for generating tone correction data . A program applied to an image forming system including a gradation correction data generating device, an image forming device including a head that emits a white colorant toward a substrate, and a measuring device including a stage on which a white background and a black background are formed on the same surface, the program comprising:
A computer that functions as the image forming apparatus includes:
a first patch group, which is formed using the white colorant emitted from the head and includes a plurality of patches with different gradation values, and which includes one or more patches to which dots of a plurality of sizes are applied, to which the white background is applied when measured using the measurement device, at a position on the substrate corresponding to the white background; and a second patch group, which is formed using the measurement device and includes a plurality of second patches to which the black background is applied when measured using the measurement device, and which includes a plurality of second patches to which the same gradation values as each of the plurality of first patches constituting the first patch group are applied, at a position on the substrate corresponding to the black background;
A computer functioning as the measuring device
detecting alignment of the white background with the first set of patches; and
a function of measuring the group of patches formed on the substrate using the white colorant against the white background to generate first measurement data, and a function of measuring the group of patches against the black background to generate second measurement data;
A computer functioning as the gradation correction data generating device includes:
a function of acquiring first measurement data to which the white background is applied from the measurement device;
a function of acquiring second measurement data from the measurement device to which the black background is applied;
a function of deriving an evaluation index value of a density value for each gradation value of the white colorant based on the first measurement data and the second measurement data; and
realizing a function of generating gradation correction data for correcting the relationship between the gradation value and the density value of the white colorant based on the evaluation index value;
program . A non-transitory computer-readable recording medium having the program according to claim 11 recorded thereon.