Image forming system, tone correction data generation method, and program

Abstract

Provided are a tone correction data generation device, a tone correction data generation method, a program, and an image formation system that suppress trial and error by workers and enable generation of tone concentration conversion data to which a quantitative method is applied. The present invention: acquires first measurement data that is obtained by applying a white background and measuring a patch group that includes a plurality of patches that are formed on a substrate using a white colorant and that have different tone values, the patch group including at least one patch to which dots of a plurality of sizes are applied; acquires second measurement data that is obtained by applying a black background and measuring the patch group; derives a concentration value evaluation index value for each tone value in the white colorant on the basis of the first measurement data and the second measurement data; and generates tone correction data for correcting the relationship of concentration values to tone values in the white colorant on the basis of the evaluation index values.

Description

[Technical Field]

[0001] The present invention relates to a tone correction data generating device, a tone correction data generating method, a program, and an image forming system. [Background technology]

[0002] Inkjet printing devices are known that use white ink to form the base of a printed material that uses a transparent substrate. For example, a color image is printed, and then a full-surface image of white ink is printed over the color image. When a printed material printed in this manner is viewed from the side opposite the printed surface of the substrate, the color image is visible on a white background.

[0003] Patent Document 1 describes a printing device that uses multiple color inks, including white ink, to print an image that includes color and white areas. The device described in this document mixes white ink with other color inks to finely adjust the white color to form a toned white image. The white color in the toned white image is measured using a white background and a black background.

[0004] 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 a white patch and a patch of a process color such as cyan on the transparent substrate, measures the color of the patch in Lab space, and performs color correction based on the colorimetric data.

[0005] FIG. 17 of the same document illustrates colorimetry in which a black and white background is used, with cyan, magenta, yellow and black being applied to the white background, and white being applied to the black background. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-97671 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-73306 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in printing using white ink, the correction of gradation values ​​to achieve a target density value is performed manually by deriving a tone curve that represents density values ​​for gradation values ​​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.

[0008] Patent Document 1 describes the adjustment of the whiteness of a toned white image by mixing other color inks with white ink, but does not describe the correction of the gradation density of the white ink.Similarly, Patent Document 2 also does not describe the correction of the gradation density of the white ink.

[0009] The present invention has been made in consideration of the above 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. [Means for solving the problem]

[0010] A gradation correction data generating device according to the present disclosure is a gradation correction data generating device including a processor and a storage device storing a program executed by the processor, wherein the processor executes instructions of the program to acquire 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, and to acquire second measurement data obtained by measuring the patch group against a black background; 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.

[0011] The gradation correction data generating device according to the present disclosure can reduce 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 a white colorant.

[0012] 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.

[0013] The patch may be a small image representing the density of each color, and the shape of the patch may be a rectangle.

[0014] An example of the tone correction data is tone correction data in a look-up table format.

[0015] In another aspect of the gradation correction data generating device, a 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 to which the same gradation values ​​as each of the plurality of first patches are applied.

[0016] According to this aspect, the first measurement data and the second measurement data can be obtained for the same gradation value in one measurement.

[0017] In the tone correction data generating device according to another aspect, the processor applies a hiding ratio as the evaluation index value.

[0018] According to this aspect, the white color can be evaluated by applying the hiding ratio defined in the existing standard.

[0019] In another aspect of the gradation correction data generating device, a processor derives an evaluation index value using first measurement data normalized using density values ​​of a white background and second measurement data normalized using density values ​​of a black background.

[0020] According to this aspect, it is possible to suppress 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.

[0021] The gradation correction data generation method according to the present disclosure is a gradation correction data generation method in which a computer acquires first measurement data by measuring a patch group that is formed on a base material using a white colorant and includes a plurality of patches with different gradation values, the patch group including one or more patches to which dots of a plurality of sizes 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.

[0022] The gradation correction data generating method 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 gradation correction data generating method according to other aspects.

[0023] The program according to the present disclosure is a program that causes a computer to realize the following functions: a function to acquire first measurement data obtained by measuring a patch group that is formed on a substrate using a white colorant and includes a plurality of patches with different gradation values, the patch group including one or more patches to which dots of a plurality of sizes are applied, while applying a white background; a function to acquire second measurement data obtained by measuring the patch group while applying a black background; a function to 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 a function to 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.

[0024] The program according to the present disclosure can achieve the same effects as the gradation correction data generating device according to the present disclosure. The components of the gradation correction data generating device according to other aspects can be applied to the components of the program according to other aspects.

[0025] An 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 by applying a white background and also measures the group of patches by applying a black background, and a gradation correction data generation device that generates gradation correction data that corrects the relationship between gradation values ​​and density values ​​in the white colorant based on measurement data acquired from the measurement device, wherein the image forming device includes a second processor and a second storage device that stores a second program that is executed by the second processor, and the second processor processes a group of patches formed using the white colorant ejected from the head and including a plurality of patches with different gradation values. 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.

[0026] 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 components of the gradation correction data generating device according to other aspects can be applied to the components of the image forming system according to other aspects.

[0027] An example of an image forming system is an inkjet printing system that includes an inkjet printing device.

[0028] In an image forming system according to another aspect, the second processor uses the head to form a patch group in which a plurality of patches are arranged along the relative transport direction between the head and the substrate.

[0029] 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.

[0030] 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.

[0031] In another aspect of the image forming system, a 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 a second patch group, to which a black background is applied when measured using a measuring 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; 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.

[0032] According to this aspect, it is possible to grasp the positional misalignment between the white background and the first patch group, thereby suppressing a decrease in accuracy of the first measurement data due to the positional misalignment between the white background and the first patch group.

[0033] In another aspect of the image forming system, the third processor detects alignment between the black background and the second group of patches.

[0034] According to this aspect, it is possible to grasp the positional misalignment between the black background and the second patch group, thereby suppressing a decrease in the accuracy of the second measurement data due to the positional misalignment between the black background and the second patch group.

[0035] In an image forming system according to another aspect, the second processor forms an alignment mark that indicates a boundary between the first patch group and the second patch group.

[0036] According to this aspect, the alignment marks formed on the substrate can be used to align the stage and the substrate.

[0037] 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.

[0038] 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 equal to or less than a specified threshold, issues a warning indicating that the density of the white background is equal to or less than the specified threshold.

[0039] According to this aspect, it is possible to grasp the density decrease of the white background, thereby suppressing a decrease in the measurement accuracy of the first measurement data due to the density decrease of the white background.

[0040] 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 the specified threshold.

[0041] According to this aspect, it is possible to grasp the density decrease of the black background, thereby suppressing a decrease in the measurement accuracy of the second measurement data due to the density decrease of the black background. [Effects of the Invention]

[0042] According to the present invention, trial and error by an operator is suppressed, and a quantitative method can be applied to generate tone correction data that corrects the relationship between tone values ​​and density values ​​in a white colorant. [Brief explanation of the drawings]

[0043] [Figure 1]FIG. 1 is a functional block diagram of a tone correction data generating device. [Figure 2] FIG. 2 is a functional block diagram of the correction processing unit shown in FIG. [Figure 3] FIG. 3 is a flowchart showing the steps of the tone correction LUT generation method. [Figure 4] FIG. 4 is a schematic diagram of the tone correction LUT generation process. [Figure 5] FIG. 5 is an explanatory diagram of a gradation correction chart. [Figure 6] FIG. 6 is a plan view of the background showing an example of the background configuration. [Figure 7] FIG. 7 is a schematic diagram showing the alignment of the tone correction chart and the background. [Figure 8] FIG. 8 is an explanatory diagram showing an example of positional deviation between the gradation correction chart and the background. [Figure 9] FIG. 9 is an explanatory diagram showing another example of the positional deviation between the gradation correction chart and the background. [Figure 10] FIG. 10 is an explanatory diagram of the driving voltages applied to printing the gradation correction chart. [Figure 11] FIG. 11 is a diagram showing the overall configuration of an inkjet printing system according to an embodiment. [Figure 12] FIG. 12 is a functional block diagram showing the electrical configuration of the inkjet printing system shown in FIG. [Figure 13] FIG. 13 is a block diagram showing the hardware configuration of a control device applied to the inkjet printing system shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0044] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. In this specification, the same components are designated by the same reference numerals, and redundant explanations will be omitted where appropriate.

[0045] [Configuration Example of Tone Correction Data Generating Device According to the Embodiment] 1 is a functional block diagram of a tone correction data generating device 10. The tone correction data generating device 10 shown in the figure is connected to a measuring instrument 12, a printer 14, and a display device 16.

[0046] The gradation correction data generating device 10 generates gradation correction data that is applied to correct nonlinearity between gradation values ​​and density values ​​for image data to be printed using a 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.

[0047] 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 ​​of 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."

[0048] 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 a discharge control signal based on the gradation correction chart data. The printer 14 prints the gradation correction chart based on the discharge control signal.

[0049] Printer control unit 22 displays various types of information related to printer 14 on display device 16. Display device 16 is a touch panel type and displays printer operation screen 16A. The user can operate printer operation screen 16A to send various types of information to printer 14.

[0050] The measuring device 12 measures the density values ​​of the patches that make up the tone correction chart printed on the substrate. A spectroscopic optical densitometer may be used as the measuring device 12. The measuring device 12 sends the measurement results to the tone correction LUT generation unit 26.

[0051] The gradation correction data generating device 10 includes a measuring device control unit 24. The measuring device control unit 24 sets measurement conditions for the measuring device 12 and controls the measurement of the gradation correction chart using the measuring device 12.

[0052] 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.

[0053] 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 realizes the target density value is derived, and a tone correction LUT that represents the conversion relationship between the tone value and the density value is generated.

[0054] 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, printer settings, etc. The generation of a gradation correction LUT here can include updating an existing gradation correction LUT.

[0055] The LUT storage unit 28 stores the tone correction LUT generated by the tone correction LUT generation unit 26. The LUT storage unit 28 stores the tone correction LUT for each color and for each of various conditions.

[0056] 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-ejection nozzle correction processing unit. Note that various correction processing units, such as the in-plane unevenness correction processing unit, are not shown in FIG. 1.

[0057] The gradation correction processing unit 31 corrects the gradation values ​​for each color by referring to the gradation correction LUT. The printer control unit 22 generates a discharge control signal based on the gradation correction chart data with the corrected gradation values, and transmits the discharge control signal to the printer 14. The printer 14 prints the gradation correction chart based on the discharge control signal.

[0058] [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 the figure 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.

[0059] The correction processing unit 30 includes a gradation correction processing unit 31, an in-plane unevenness correction processing unit 52, and a discharge failure correction processing unit 54. The gradation correction processing unit 31 reads out gradation correction chart data from the gradation correction chart data storage unit 20.

[0060] 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 value of each color for 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 illustrates a tone curve representing the relationship between gradation value and density value as an example of the gradation correction LUT.

[0061] The in-plane unevenness correction processor 52 corrects in-plane unevenness in the patches that make up the gradation correction chart. Specifically, the in-plane unevenness correction processor 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 FIG.

[0062] The non-discharge correction processing unit 54 corrects the non-discharge nozzles. Specifically, the non-discharge correction processing unit 54 masks the non-discharge nozzles and performs substitute discharge for the non-discharge nozzles using nozzles in the vicinity of the non-discharge nozzles.

[0063] By performing in-plane unevenness correction and non-discharge nozzle correction, the printer 14 can print a tone correction chart that includes patches in which in-plane unevenness is suppressed and streaks caused by non-discharge nozzles are suppressed.

[0064] 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 a discharge control signal based on the received gradation correction chart data and sends the discharge control signal to the printer 14. The printer 14 prints the gradation correction chart based on the discharge control signal.

[0065] [Procedure for generating a tone correction LUT] Fig. 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.

[0066] In the tone correction chart printing step S12, the printer control unit 22 prints a tone correction chart based on the tone correction chart data that has been subjected to various correction processes such as tone correction.

[0067] In the gradation correction chart measurement step S14, the gradation correction chart printed in the gradation correction chart printing step S12 is measured using the measuring instrument 12 shown in Fig. 1. The measurement of the gradation correction chart may be performed automatically or manually.

[0068] 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.

[0069] In manual measurement, the substrate on which the gradation correction chart is printed and output from the printer 14 is manually set in the measuring instrument 12, and the gradation correction chart is measured. Details of the measurement of the gradation correction chart will be described later.

[0070] In the tone correction LUT generation step S16, the tone correction LUT generation unit 26 acquires measurement data of the tone correction chart from the measuring instrument 12, and generates a tone correction LUT based on the acquired measurement data of the tone correction chart.

[0071] Specifically, in the tone correction LUT generation step 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 FIG.

[0072] Fig. 4 is a schematic diagram of the tone correction LUT generation process. Fig. 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.

[0073] A straight line 60 shows the relationship between the input signal value and the output signal value of an existing tone correction LUT. In an existing tone 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 tone correction LUT here refers to a tone correction LUT that is applied to printing a tone correction chart.

[0074] 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 FIG. 1 or the like.

[0075] Curve 64 schematically shows the relationship between the signal value applied to printing each patch of the gradation correction chart and the measurement data of each patch acquired in the gradation correction chart measurement step S14. The measurement data of each patch corresponds to the density value of curve 64.

[0076] The measurement data of each patch of the gradation correction chart should ideally match the target density value, but due to variations in the ejection characteristics of the inkjet head, the measurement data of each patch differs from the target density value.

[0077] A curve 66 schematically shows a tone correction LUT in which the signal value that reproduces the target density value is the output signal value, and the tone value derived based on the image data is the input signal value.

[0078] The tone correction LUT is generated by applying the following steps: First, a signal value associated with a 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.

[0079] 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 and the measurement data of each patch, which is represented as curve 64. 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.

[0080] 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 tone correction LUT that uses the pre-correction signal values ​​as input and the post-correction signal values ​​as output.

[0081] 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.

[0082] [White image density control] 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.

[0083] For example, for a white patch, the hiding rate 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.

[0084] The white in white images and white inks 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 inks sold under names such as white ink and white ink. An example of a white ink is an 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 interpreted interchangeably. The white ink described in the embodiments is an example of a white colorant.

[0085] In this embodiment, a white patch is measured using two different background colors, and a tone correction LUT is created by relating the signal value applied when printing the white patch to 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.

[0086] [Example of a tone correction chart] 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).

[0087] "Non-permeable" means that the material is non-permeable to aqueous inks, which will be described later. "Transparent" means that the visible light transmittance is 30% or more and 100% or less, and preferably 70% or more and 100% or less.

[0088] The gradation correction chart 102 includes a process color patch group 112 composed of a plurality of 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.

[0089] The cyan patch group 112C includes a plurality of cyan patches 110C as its constituent elements. The magenta patch group 112M includes a plurality of magenta patches 110M as its constituent elements. The yellow patch group 112Y includes a plurality of yellow patches 110Y as its constituent elements. The black patch group 112K includes a plurality of black patches 110K as its constituent elements.

[0090] The gradation correction chart 102 includes a spot color patch group 116, which is composed of a plurality of spot color patches 114 printed using spot color inks. The spot color patch group 116 includes an orange patch group 116O, a green patch group 116G, and a violet patch group 116V.

[0091] The orange patch group 116O includes a plurality of orange patches 114O as constituent elements, the green patch group 116G includes a plurality of green patches 114G as constituent elements, and the violet patch group 116V includes a plurality of violet patches 114V as constituent elements.

[0092] 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.

[0093] The gradation values ​​of the multiple first white patches 124 constituting the first white patch group 120 increase from the downstream side to the upstream side in the substrate transport direction. The minimum gradation value is applied to the first white patch 124 at the end on the downstream side in the substrate transport direction. The maximum gradation value is applied to the first white patch 124 at the end on the upstream side in the substrate transport direction. The substrate transport direction described in the embodiment is an example of a relative transport direction.

[0094] 5 is made up of 16 first white patches 124. For example, when the gradation values ​​are expressed as numbers from 0 to 255, the gradation values ​​of the 16 first white patches 124 are incremented by 17, with the minimum gradation value being 0 and the maximum gradation value being 255.

[0095] The same gradation value is applied to the multiple first white patches 124 that make up the second white patch group 122 as to the second white patches 126. In other words, the same gradation value is applied to the first white patches 124 and the second white patches 126 that are located at the same position in the substrate transport direction.

[0096] 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 conveyance direction. Note that the term "perpendicular" here means that the angle between the two directions is less than 90 degrees or more than 90 degrees, but it can also include being substantially perpendicular, which provides the same effect as when the angle between the two directions is 90 degrees.

[0097] 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.

[0098] The patch groups of each color that make up the process color patch group 112 are arranged at different positions in the width direction of the substrate, and the patch groups of each color that make up the spot color patch group 116 are arranged at different positions in the width direction of the substrate.

[0099] In the gradation correction chart 102, patches of each color are 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.

[0100] A first background alignment mark 104 and a second background alignment mark 105 are printed on the substrate 100 on which the gradation correction chart 102 is printed. 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 on both ends of the substrate in the transport direction.

[0101] A triangle is applied to the first background alignment mark 104 and the second background alignment mark 105. The first background alignment mark 104 and the second background alignment mark 105 are arranged such that a vertex 104A of the first background alignment mark 104 and a vertex 105A of the second background alignment mark 105 face each other.

[0102] 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 shown in FIG.

[0103] The shapes, colors, and positions of the first background alignment mark 104 and the second background alignment mark 105 are not limited to the example shown in FIG. 5, and the shapes, colors, and positions can be defined as appropriate.

[0104] A first measurement start position mark 106 and a second measurement start position mark 108 are printed on the gradation correction chart 102. The first measurement start position mark 106 is printed using black ink. The second measurement start position mark 108 is printed using white ink.

[0105] 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 tone correction chart 102. The second measurement start position mark 108 indicates the measurement start position of the second white patch group 122.

[0106] [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 the figure 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.

[0107] 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. 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.

[0108] The background 200 includes a white background 202 and a black background 204. A 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 FIG.

[0109] [Alignment of the gradation correction chart with the background] Fig. 7 is a schematic diagram of the alignment of the gradation correction chart and the background. This figure shows the state in which the gradation correction chart 102 is aligned with the background 200 formed on the stage 201. Note that in this figure, some of the reference numerals shown in Figs. 5 and 6 are omitted. The same applies to Figs. 8 and 9.

[0110] When the tone 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 .

[0111] When the gradation correction chart 102 is aligned to the correct position with respect 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.

[0112] That is, when the first background alignment mark 104, to which black is applied, is located on the white background 202, the first background alignment mark 104 is visible.

[0113] Furthermore, when the second background alignment mark 105, to which white is applied, is located on the black background 204, the second background alignment mark 105 is visible.

[0114] 8 is an explanatory diagram showing an example of misalignment between the gradation correction chart and the background. When the position of the gradation correction chart 102 is shifted toward the black background 204, the color of the first background alignment mark 104 becomes 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.

[0115] 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.

[0116] In other words, when the gradation correction chart 102 is shifted toward the black background 204, part or all of the first background alignment mark 104 is not visible. Figure 8 shows a case where the first background alignment mark 104 is not visible at all.

[0117] Similarly, when the gradation correction chart 102 is shifted toward the white background 202, the second background alignment mark 105 is partially or completely invisible. Figure 8 shows a case where the second background alignment mark 105 is completely invisible.

[0118] 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 or not.

[0119] The first chart alignment mark 206 and the second chart alignment mark 208 described in the embodiment are examples of boundary marks.

[0120] [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, a Y value in 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, a Y value in the CIEXYZ color system is obtained for each of the multiple second white patches 126 that make up the second white patch group 122.

[0121] 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.

[0122] The Y value of the observation light source is L The Y value of the black background 204 is set to Y bk and the measurements taken against a black background 204 are Y mk Then, the normalized Y value Y nb is Y nb =(Y mk -Y bk ) / (Y L -Y bk ) In other words, the absolute value of the measured value Y mb is the Y value Y relative to the black background 204 nb is converted to

[0123] When the white background 202 is used, the Y value of the white background 202 is set to Ywh and the measurement value obtained against a white background 202 is Y mw and the normalized Y value Y nw is Y nw =(Y mw -Y wh ) / (Y L -Y wh ) The Y value Y of the white background 202 wh The Y value obtained by measuring the area of ​​the base material 100 where the gradation correction chart 102 is not formed can be applied to the Y value Y of the black background 204. bk The same is true for .

[0124] Y value based on measurement data of the first white patch 124 nw and the Y value Y based on the measurement data of the second white patch 126 nb Using this, the hiding rate Y for each tone value in white nb / Y nw is calculated.

[0125] A target hiding ratio for each gradation value of the white ink is acquired, the target hiding ratio representing the target density of the white ink is compared with the hiding ratio calculated from the measurement data of each patch, and a 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.

[0126] Specifically, density values ​​are converted into hiding rates and a tone correction LUT to be applied to white ink is generated in accordance with the procedure of the tone correction LUT generation step S16 in Fig. 3, which will be explained using Fig. 4. The tone correction LUT is stored in the LUT storage unit 28 shown in Fig. 1.

[0127] The tone correction LUT applied to white ink represents the relationship between the signal value representing the tone value and the opacity, which is the evaluation index value for the white patch. For white ink, the 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.

[0128] 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.

[0129] In this way, when the white ink covering ratio is changed, it is not necessary to derive a signal value representing the gradation value corresponding to the changed white ink covering ratio based on printing and measuring the gradation correction chart 102.

[0130] 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.

[0131] For colors other than white, such as cyan, the Y value of the observation light source is also used for LUT correction. L and the Y value of the white background 202 is Y wh The normalized Y value Y n Note that normalization of the measurement value using the density of the background 200 is not limited to the above example. Methods other than the above may be applied as long as the absolute measurement value can be converted to a relative value using the background color as a reference.

[0132] When converting absolute measurement values ​​into relative values, the correction accuracy of the LUT can be improved as the density contrast between the patch 110 and the background 200 becomes relatively higher. Therefore, a preferred mode is one in which the density of the background 200 is measured and a warning is issued when the measured density value is equal to or less than a specified threshold value.

[0133] 1, text information indicating the content of the warning is displayed on the display device 16, urging the user to replace the background 200. The Y value of the background 200 may be a Y value obtained by measuring an area on the base material 100 where the tone correction chart 102 is not formed.

[0134] When single-pass printing is applied to the printer 14, the arrangement direction of multiple patches 110 of the same color is preferably 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, although the term "parallel" used here strictly means intersecting, it can also include substantially parallel, which provides the same effect as parallel.

[0135] 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 if the measured density unevenness is equal to or greater than a specified threshold, to issue a warning. The warning can be in any of the modes 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.

[0136] 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.

[0137] Furthermore, the measurement values ​​of the first white patch 124 described in the embodiment are an example of first measurement data, and the measurement values ​​of the second white patch 126 described in the embodiment are an example of second measurement data.

[0138] [Drive voltage applied to printing the gradation correction chart] Fig. 10 is an explanatory diagram of the drive voltage applied to printing the gradation correction chart. Fig. 10 graphically illustrates one ejection cycle of the drive voltage supplied to the piezoelectric ejection type inkjet head provided in the printer 14 shown in Fig. 1.

[0139] The horizontal axis of the graph shown in Figure 10 represents time in microseconds. The vertical axis of the graph shown in the same figure represents voltage in volts. Note that the values ​​shown in Figure 10 are just an example and can be defined appropriately depending on the printing conditions and the specifications of the piezoelectric element provided in the inkjet head.

[0140] The inkjet head is driven by a continuous firing 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 Fig. 10. This allows the inkjet head to eject large, medium, and small droplets, each with a different volume.

[0141] For example, when a small droplet is ejected, the ejection drive pulse 312 is applied. When a medium droplet is ejected, the ejection drive pulse 306, the ejection drive pulse 308, the ejection drive pulse 310, and the ejection drive pulse 312 are applied.

[0142] When ejecting a large droplet, an ejection drive pulse 302, an ejection drive pulse 304, an ejection drive pulse 306, an ejection drive pulse 308, an ejection drive pulse 310, and an ejection drive pulse 312 are applied.

[0143] 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 of the cases of large, medium, and small droplets, with the aim of suppressing vibration of the ink immediately after the ink droplet is ejected.

[0144] The same printing conditions as for normal printing are applied to printing the gradation correction chart 102 shown in Fig. 5. 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.

[0145] For example, only small dots corresponding to small droplets are applied to patches 110 with relatively small gradation values, and small dots and medium dots corresponding to medium droplets are applied to patches 110 with relatively small gradation values.

[0146] The patch group constituting the tone correction chart 102 described in the embodiment is an example of a patch group including one or more patches to which dots of multiple sizes are applied.

[0147] [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.

[0148] In this embodiment, the substrate 401 is exemplified by a flexible packaging such as a plastic film. The substrate 401 may be a single layer, or may be a laminate of multiple layers. The substrate 401 may be in a continuous roll-to-roll form, or may be in the form of a sheet cut to a specified length. The substrate 401 may also be called a medium, media, sheet, film, substrate, or the like. The substrate 401 shown in FIG. 11 corresponds to the substrate 100 shown in FIG. 5.

[0149] The inkjet printing system 400 includes 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 a stacking device 414. Each of these devices will be described in detail below.

[0150] [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 around which the substrate 401 is wound. 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.

[0151] [First intermediate conveying device] The first intermediate conveying device 404 delivers 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.

[0152] [Printing device] Printing device 406 includes inkjet head 420C, inkjet head 420M, inkjet head 420Y, inkjet head 420K, and inkjet head 420W.

[0153] Inkjet head 420C, inkjet head 420M, inkjet head 420Y, inkjet head 420K, and inkjet head 420W are arranged in the above-described order from the upstream side along the substrate transport direction.

[0154] Inkjet head 420C ejects cyan ink, inkjet head 420M ejects magenta ink, inkjet head 420Y ejects yellow ink, inkjet head 420K ejects black ink, and inkjet head 420W ejects white ink.

[0155] The inkjet head 420C etc. may be a line head in which a plurality of nozzles are arranged across a length in the width direction of the substrate that is equal to or greater than the entire length of the substrate 401. The plurality of nozzles provided in the inkjet head 420C etc. may be arranged two-dimensionally, such as in a matrix.

[0156] The inkjet head 420C may employ a piezoelectric ejection method that uses a piezoelectric element as an ejection pressure element to generate ejection pressure, or a thermal method that uses film boiling of ink to eject ink.

[0157] The printing device 406 forms a color image on the transparent substrate 401 using color inks such as cyan ink, and forms a white image as a background image by overlaying the color image using white ink. When the printed matter produced using the substrate 401 is viewed from the non-printed side of the substrate 401, the color image can be seen.

[0158] The inkjet head 420W and the like described in the embodiment are examples of heads that eject a white colorant toward a substrate. The nozzles and ejection pressure elements described in the embodiment are examples of components of a plurality of recording elements.

[0159] The printing device 406 includes a printing drum 422. The printing drum 422 has a cylindrical shape. The printing drum 422 includes a substrate support area on its circumferential surface that supports the substrate 401. The substrate support area is not shown in the figure.

[0160] The rotation shaft of the print drum 422 is connected to a motor (not shown) via a drive mechanism (not shown). When the motor is rotated, the print drum 422 rotates in the direction indicated by the arrow. When the print drum 422 is rotated, the substrate 401 supported on the circumferential surface of the print drum 422 is transported in the direction of rotation of the print drum 422.

[0161] The substrate support area has a plurality of suction holes formed therein. The plurality of suction holes are arranged based on a specified pattern. The plurality of suction holes communicate with 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 plurality of suction holes, the substrate 401 is suction-supported on the circumferential surface of the print drum 422.

[0162] The conveyance form of the substrate 401 in the printing device 406 is not limited to a conveyance form using the print drum 422. For example, a conveyance form using a conveyor belt or a conveyance form using a plurality of rollers can be applied.

[0163] [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.

[0164] [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.

[0165] 1, the concentration measuring instrument 430 shown in Fig. 11 can measure the gradation correction chart printed on the substrate 401, similar to the measuring instrument 12 shown in Fig. 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.

[0166] Although FIG. 11 illustrates a roller conveyance method as an example of a method for conveying the substrate 401 in the measuring device 410, other methods such as a belt conveyance method and a drum conveyance method may also be used as a method for conveying the substrate 401 in the measuring device 410.

[0167] The measuring device 410 may include an imaging device that captures an image of the test pattern printed on the substrate 401. The inkjet printing system 400 may detect ejection abnormalities in the inkjet head 420C or the like based on the image data of the test pattern.

[0168] [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 is equipped with 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.

[0169] [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.

[0170] [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.

[0171] 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 the memory 474 and the reading of data from the memory 474.

[0172] The system control unit 460 acquires a 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.

[0173] The conveyance control unit 462 sets conveyance conditions based on command signals sent from the system control unit 460, and controls the operation of the conveyance device 464 based on the set conveyance conditions. The conveyance device 464 shown in Fig. 12 includes the first intermediate conveyance device 404, the print drum 422, the reading conveyance roller 432, and the drying conveyance device provided in the drying device 412 shown in Fig. 11. The conveyance device 464 may also include the base material supply device 402 and the accumulation device 414.

[0174] 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 FIG. 12 has the functions of the printer control unit 22 shown in FIG.

[0175] The print control unit 466 includes an image processing unit that performs color separation processing, color conversion processing, correction processing for each processing, and halftone processing on the print data to generate halftone data for each color.

[0176] The print control unit 466 includes a drive voltage generation unit that generates drive voltages to be supplied to the inkjet head 420C, etc. based on halftone data for each color. The print control unit 466 also includes a drive voltage output unit that supplies drive voltages to the inkjet head 420C.

[0177] The print control unit 466 can use the inkjet head 420C shown in FIG. 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.

[0178] When generating a halftone image of the gradation correction chart, the print control unit 466 generates a multi-value halftone image and prints the gradation correction chart by combining multiple types of dots of different sizes based on the multi-value halftone image.

[0179] When printing the tone correction chart, the print control unit 466 arranges a plurality of patches that make up the patch group of each color along the substrate transport direction.

[0180] The print control unit 466 may have the functions of the gradation correction LUT generation unit 26 and the correction processing unit 30 shown in Fig. 1. The inkjet printing system 400 shown in Fig. 12 may have, in addition to the print control unit 466, a gradation correction data generation unit having the same functions as the gradation correction data generation device 10 shown in Fig. 1.

[0181] 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.

[0182] Measurement control unit 468 sets measurement conditions based on command signals sent from system control unit 460, and controls the operation of measurement device 410 based on the set measurement conditions. Measurement control unit 468 shown in FIG. 12 may have the functions of measurement instrument control unit 24 shown in FIG.

[0183] The measurement control unit 468 can issue a warning when the density value of the background formed on the stage 434 is equal to or less than a specified threshold. The measurement control unit 468 can also issue a warning when the in-plane density unevenness in the background formed on the stage 434 is equal to or greater than a specified threshold.

[0184] The drying control unit 470 sets processing conditions for the main drying process based on a command signal sent from the system control unit 460, and controls the operation of the drying device 412 based on the set processing conditions.

[0185] The information acquisition unit 472 acquires various pieces of information that are 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 pieces of information acquired using the information acquisition unit 472.

[0186] The memory 474 can store various data, parameters, and programs applied to the inkjet printing system 400. The memory 474 can function as the LUT storage unit 28 shown in FIG.

[0187] Fig. 13 is a block diagram showing the hardware configuration of a control device applied to the inkjet printing system shown in Fig. 11. The control device 500 provided in the inkjet printing system 400 includes a processor 502, a computer-readable medium 504 which is a non-transitory tangible entity, a communication interface 506, and an input / output interface 508.

[0188] A computer is applied to the control device 500. The computer may be in the form of a server, a personal computer, a workstation, a tablet terminal, or the like.

[0189] The processor 502 includes a central processing unit (CPU). The processor 502 may include a graphics processing unit (GPU). 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.

[0190] The processor 502 can function as a first processor that performs processing related to generation of tone correction data, a second processor that performs processing related to image formation, and a third processor that performs processing related to measurement.

[0191] The computer-readable medium 504 includes a memory serving as a primary storage device and a storage serving as an auxiliary 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.

[0192] A hard disk drive may be referred to as an HDD, which is an abbreviation of the English term Hard Disk Drive, and a solid state drive may be referred to as an SSD, which is an abbreviation of the English term Solid State Drive.

[0193] The control device 500 is connected to a network via a communication interface 506, and is communicably connected to an external device. The network may be a local area network (LAN), etc. The network is not shown in the figure.

[0194] The computer-readable medium 504 stores a transport control program 520 , a print control program 522 , a measurement control program 524 , a drying control program 526 , and a tone correction data generation program 528 .

[0195] 12. The print control program 522 corresponds to the print control applied to the print device 406. The measurement control program 524 corresponds to the measurement control applied to the measurement 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.

[0196] The various programs stored in the computer-readable medium 504 include one or more instructions. Various data, various parameters, etc. are stored in the computer-readable medium 504. Note that the memory 474 shown in FIG. 12 is included in the computer-readable medium 504 shown in FIG. 13.

[0197] 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.

[0198] The gradation correction data generation program 528 described in the embodiment is an example of a first program. The transport control program 520, print 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.

[0199] In the inkjet printing system 400, a processor 502 executes various programs stored in a 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."

[0200] The control device 500 performs data communication with an external device via a communication interface 506. The communication interface 506 may be compliant with various standards such as USB (Universal Serial Bus). The communication form of the communication interface 506 may be either wired communication or wireless communication.

[0201] 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 implemented by input devices such as a keyboard and a mouse. The display device 514 displays various information applied to the control device 500.

[0202] The display device 514 may be a liquid crystal display, an organic EL display, a projector, or the like. Any combination of multiple devices may be used for the display device 514. Note that the "EL" in organic EL display is an abbreviation for Electro-Luminescence. The display device 514 shown in FIG. 13 corresponds to the display device 16 shown in FIG. 1.

[0203] Examples of the hardware structure of the processor 502 include a CPU, a GPU, a PLD (Programmable Logic Device), and an 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.

[0204] 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 task.

[0205] A processing unit may be configured with one of these various processors, or may be configured with two or more processors of the same or different types. Examples of combinations of various processors include a combination of one or more FPGAs and one or more CPUs, and a combination of one or more FPGAs and one or more GPUs. Another example of a combination of various processors is a combination of one or more CPUs and one or more GPUs.

[0206] A single processor may be used to configure multiple functional units. An example of using a single processor to configure multiple functional units is a configuration in which a single processor is configured by applying a combination of one or more CPUs and software, such as an SoC (System On a Chip), which is typified by a computer such as a client or server, and this processor operates as multiple functional units.

[0207] Another example of using one processor to configure multiple functional units is to use a processor that uses one IC chip to realize the functions of an entire system including multiple functional units. Note that IC is an abbreviation for Integrated Circuit.

[0208] In this way, the various functional units are configured as hardware structures using one or more of the various processors described above.More specifically, the hardware structures of the various processors described above are electric circuits (circuitry) that combine circuit elements such as semiconductor elements.

[0209] The computer-readable medium 504 may include semiconductor devices such as read-only memory (ROM) and random access memory (RAM). The computer-readable medium 504 may include a magnetic storage medium such as a hard disk. The computer-readable medium 504 may comprise multiple types of storage media.

[0210] [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.

[0211] [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.

[0212] 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. Correction data is generated to correct a gradation correction LUT that indicates the relationship between gradation values ​​and density values ​​in white ink, based on the density measurement values ​​of the first white patch group 120 and the density measurement values ​​of the second white patch group 122. This makes it possible to obtain gradation values ​​that correspond to target density values ​​in white ink based on a quantitative method, without trial and error.

[0213] [2] The concealment ratio 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.

[0214] [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.

[0215] [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.

[0216] [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 patches 110 and can improve correction accuracy.

[0217] [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 can prevent a decrease in correction accuracy due to a decrease in density of the white background 202.

[0218] [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 can prevent a decrease in correction accuracy due to a decrease in the density of the black background 204.

[0219] [8] A warning is issued when the density unevenness within the surface of 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.

[0220] [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.

[0221] [Example of application to image forming systems] 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.

[0222] [About the image] 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.

[0223] [Print image] Printing an image may include concepts such as image formation, recording, printing, drawing, and printing.

[0224] The above-described embodiments of the present invention may be modified, added, or deleted as appropriate within the scope of the spirit of the present invention. The present invention is not limited to the above-described embodiments, and many modifications are possible within the technical concept of the present invention by those skilled in the art. [Explanation of symbols]

[0225] 10 Gradation correction data generator 12 Measuring instruments 14 Printers 16 Display device 16A Printer operation screen 20 Image data storage unit 22 Printer control unit 24 Measuring instrument control section 26 Tone correction LUT generation section 28 LUT storage section 30 Correction processing section 31 Gradation correction processing section 52 In-plane unevenness correction processing section 54 Non-discharge correction processing section 60 straight line 62 curve 64 curve 66 curve 100 Base material 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 patches 112C Cyan Patch Group 112K Black Patch Group 112M Magenta Patch Group 112Y Yellow Patch Group 114 Special 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 backgrounds Stage 201 201A Base material 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 Base material 402 Base material supply device 404 First intermediate transport device 406 Printing device 408 Second intermediate transport device 410 Measuring Equipment 412 Drying equipment 414 Accumulation Device 420C inkjet head 420K inkjet head 420M inkjet head 420W inkjet head 420Y inkjet head 422 Printing drum 430 Concentration measuring device 432 Reading conveyance roller 434 Stage 460 System Control Unit 462 Transport control unit 464 Transport Equipment 466 Printing control unit 468 Measurement control section 470 Drying control unit 472 Information Acquisition Department 474 memory 476 Sensors 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 Printing Control Program 524 Measurement Control Program 526 Drying Control Program 528 Gradation Correction Data Generation Program S10~S18 Steps of the tone correction LUT generation method

Claims

1. A gradation 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.

2. 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. 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.

4. 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.

5. 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.

6. 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.

7. 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.

8. The image forming system according to claim 7 , wherein the first processor applies a concealment rate as the evaluation index value.

9. 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.

10. A gradation correction data generation method applicable to an image forming system including a gradation correction data generation device, an image forming device having a head that emits a white colorant toward a substrate, and a measuring device having a stage on which a white background and a black background are formed on the same surface, 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.

11. A program applicable to an image forming system including a gradation correction data generating device, an image forming device having a head that emits a white colorant toward a substrate, and a measuring device having a stage on which a white background and a black background are formed on the same surface, 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.

12. A non-transitory computer-readable recording medium on which the program according to claim 11 is recorded.

Images