Compensation coefficient determination method, printing method, printing device, and compensation coefficient determination program

Abstract

To enable an inkjet printing device to correct a defect of a printed image when there is a discharge-defect nozzle more precisely than before.SOLUTION: Temporary defect nozzles are respectively set for K comparison regions associated with K temporary compensation coefficients which are different from each other (S110). K pieces of sample image data are extracted from a photographed image of a compensation coefficient calculation chart obtained by applying the K temporary compensation coefficients to the K comparison regions respectively and by applying ink amount compensation processing to predetermined image data (S180). A function representing a correspondence relation between a brightness difference between a measured brightness value and a target brightness value and a coefficient value is generated based on the K pieces of sample image data (S200). A compensation coefficient that is actually applied to the ink amount compensation processing is calculated using the function (S210).SELECTED DRAWING: Figure 18

Description

[Technical field]

[0001] The present invention relates to an inkjet printing device, and more specifically to a technique for controlling the amount of ink ejected so as to prevent defects from occurring in a printed image even if a nozzle that is in a defective ejection state (hereinafter referred to as a "defective ejection nozzle") is present. [Background technology]

[0002] Inkjet printing devices that perform printing by ejecting ink onto a printing medium such as printing paper are widely known. Inkjet printing devices can cause problems such as drying of the ink due to evaporation of the solvent near the nozzle, inclusion of air bubbles inside the nozzle, and adhesion of dust to the nozzle. In other words, ejection problems from the nozzle can occur.

[0003] Nozzle ejection defects can be roughly classified into three types, which will be described with reference to Figs. 39 to 41. Figs. 39 to 41 show a part of a printed image obtained by printing a step-like regular pattern (test pattern), and the black shaded areas are the areas where ink is applied. In Fig. 39, the dotted line area with the reference number 91 shows that no ink is applied to the area where ink should be applied. Hereinafter, such an ejection defect is referred to as "non-ejection". In Fig. 40, the dotted line area with the reference number 92 shows that the shape of the area where ink is applied is different from the original shape. Hereinafter, such an ejection defect is referred to as "shape defect". Shape defects also include ejection defects in a state where the ink is smudged due to insufficient density and ejection defects in a state where the area where ink is applied spreads in the main scanning direction (the direction perpendicular to the conveyance direction of the printing paper). In Fig. 41, the dotted line area with the reference number 93 shows that ink is applied to an area that is shifted in the main scanning direction from the area where ink should be applied. Hereinafter, such an ejection defect is referred to as "sideways jump".

[0004] When ejection defects such as those described above occur in an inkjet printing device, defects in the printed image occur, such as white streaks and missing dots. Therefore, operations to restore the function of the ejection-defective nozzle (cleaning and flushing) and substitute droplet ejection, in which ink droplets that should be ejected by the ejection-defective nozzle are ejected by surrounding nozzles, have been conventionally performed.

[0005] Furthermore, since a print head includes many nozzles, even if the above-mentioned ejection failure does not occur, there is variation in the amount of ink ejected among the multiple nozzles. Furthermore, since the characteristics of each print head are different, there is also variation in the amount of ink ejected among the multiple print heads. The variation in the amount of ink ejected causes uneven density in the printed image. Therefore, shading correction processing has been conventionally performed on print data to compensate for such variation in the amount of ink ejected.

[0006] Note that the technology for controlling the amount of ink ejection by performing the above-mentioned alternative droplet ejection and shading correction processing is disclosed in, for example, JP 2022-136042 A. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2022-136042 A Summary of the Invention [Problem to be solved by the invention]

[0008] JP 2022-136042 A describes generating a uniformity-compensated transfer function (a function for performing shading correction processing), generating a defect-neighborhood-corrected transfer function (a function for performing alternative droplet ejection), and generating a defect-neighborhood transfer function based on the uniformity-compensated transfer function and the defect-neighborhood-corrected transfer function, but does not describe in detail how to obtain each transfer function. Therefore, according to the printing system described in JP 2022-136042 A, even if the effect of correcting the jet-out state (ejection failure state) in real time is obtained, if each transfer function is not appropriately determined, defects in the printed image will not be corrected with high accuracy when a nozzle with a discharge failure exists. In other words, a good printed product may not be obtained.

[0009] SUMMARY OF THE PRESENT DISCLOSURE In view of the above, an object of the present invention is to provide an inkjet printing apparatus capable of correcting defects in a printed image caused by the presence of a faulty ejection nozzle with greater accuracy than ever before. [Means for solving the problem]

[0010] A first aspect of the present invention is a compensation coefficient determination method for determining a compensation coefficient to be applied to an ink amount compensation process that compensates for the amount of ink ejected onto a printing medium when a nozzle in an ejection failure state is present in a printing device having a plurality of nozzles that eject ink onto a printing medium, the compensation coefficient being: a region setting step of setting a plurality of divided regions including K comparison regions corresponding to K mutually different provisional compensation coefficients, where K is an integer of 2 or more, and normal regions that are not influenced by provisionally defective nozzles that are assumed to be in a hypothetical discharge defective state; a tentative defective nozzle setting step of setting the tentative defective nozzle for each of the K comparison regions; a compensation coefficient calculation chart data generating step of generating compensation coefficient calculation chart data representing a compensation coefficient calculation chart for determining the compensation coefficients by applying the K temporary compensation coefficients to the K comparison areas for predetermined image data having a constant density, a compensation coefficient calculation chart printing step of printing the compensation coefficient calculation chart by ejecting ink from the plurality of nozzles based on the compensation coefficient calculation chart data; a compensation coefficient calculation chart imaging step of acquiring imaging data, which is brightness value data, by imaging the compensation coefficient calculation chart printed in the compensation coefficient calculation chart printing step; a data extraction step of extracting, from the imaging data obtained in the compensation coefficient calculation chart imaging step, K pieces of sample image data, each of which includes data of a luminance value of 1 or more, which is data corresponding to each of the K comparison areas and which corresponds to the positions of the provisional defective nozzles, and normal area data, which is data of a luminance value corresponding to the normal area; a function generating step of generating a function representing a correspondence relationship between a luminance difference between a luminance value in the sample image data and a luminance value in the normal area data, and a coefficient value including the K temporary compensation coefficients, based on the K sample image data and the normal area data; a compensation coefficient calculation step of calculating the compensation coefficient by using the function generated in the function generation step; The present invention is characterized by comprising:

[0011] The second invention is the first invention, The K is an integer of 3 or more, The function generated in the function generating step is a nonlinear function.

[0012] The third invention is the second invention, The compensation coefficient calculation step includes: calculating an approximation of a coefficient value that makes the luminance difference zero based on the nonlinear function; extracting Q sample image data corresponding to Q temporary compensation coefficients near the approximation value from the K sample image data, where Q is an integer equal to or greater than 2; generating a linear function representing a correspondence relationship between the luminance difference and the coefficient value based on the Q sample image data and the normal area data; calculating a coefficient value that makes the luminance difference 0 based on the linear function as the compensation coefficient; The present invention is characterized by comprising:

[0013] The fourth invention relates to the first invention, The K is an integer of 2 or more, The function generated in the function generating step is a linear function.

[0014] The fifth invention relates to the first invention, In the compensation coefficient calculation step, a coefficient value that makes the luminance difference zero is calculated as the compensation coefficient.

[0015] The sixth aspect of the present invention relates to the first aspect of the present invention, In the tentative defective nozzle setting step, N tentative defective nozzles are set for each of the K comparison regions, where N is an integer equal to or greater than 2; Each of the K pieces of sample image data includes data on N luminance values ​​corresponding to the positions of the N provisional defective nozzles.

[0016] The seventh aspect of the present invention is the first aspect of the present invention, the compensation coefficient calculation chart is configured with J sheets for each ink color, where J is an integer of 2 or more; Each of the K pieces of sample image data includes J pieces of luminance value data corresponding to each of the J sheets.

[0017] The eighth aspect of the present invention is the first aspect of the present invention, In the tentative defective nozzle setting step, N tentative defective nozzles are set for each of the K comparison regions, where N is an integer equal to or greater than 2; the compensation coefficient calculation chart is configured with J sheets for each ink color, where J is an integer of 2 or more; Each of the K pieces of sample image data includes (N×J) pieces of luminance value data corresponding to all combinations of the N provisional defective nozzles and the J sheets.

[0018] The ninth aspect of the present invention is the first aspect of the present invention, In the region setting step, the plurality of divided regions are set so that the K comparison regions are aligned in a direction perpendicular to the transport direction of the print medium.

[0019] A tenth aspect of the present invention relates to the first aspect of the present invention, In the region setting step, the plurality of divided regions are set so that the K comparison regions are aligned in a transport direction of the print medium.

[0020] The eleventh aspect of the present invention is the first aspect of the present invention, the compensation coefficient calculation chart is made up of M density regions corresponding to M different densities in a transport direction of the print medium, where M is an integer equal to or greater than 2; In the function generating step, a function is generated for each concentration, The compensation coefficient calculation step is characterized in that the compensation coefficient is calculated for each concentration using a corresponding function.

[0021] A twelfth aspect of the present invention is the method for producing the first aspect of the present invention, The compensation coefficient determination method includes: a discharge failure detection chart printing step of printing a discharge failure detection chart for detecting nozzles in a discharge failure state by discharging ink from the plurality of nozzles; a discharge failure detection chart imaging step of imaging the discharge failure detection chart printed in the discharge failure detection chart printing step; a discharge failure nozzle detection step of detecting a nozzle having a discharge failure based on the imaging data obtained in the discharge failure detection chart imaging step; a data deleting step of deleting brightness value data corresponding to the positions of true defective nozzles, which are nozzles detected in the ejection defective nozzle detection step, from the K pieces of sample image data extracted in the data extraction step; Further comprising: The function generating step is characterized in that K pieces of sample image data are used after the data of the luminance values ​​corresponding to the positions of the true defective nozzles have been deleted in the data deleting step.

[0022] A thirteenth aspect of the present invention is a printing method using a printing device having a plurality of nozzles that eject ink onto a printing medium, comprising: a shading data generating step of generating shading data used in a shading correction process that compensates for variations in the amount of ink ejected among the plurality of nozzles; a shading data correcting step of correcting the shading data by performing the ink amount compensation process on the shading data using a compensation coefficient determined by the compensation coefficient determination method of any one of the first to twelfth aspects of the present invention; a print data generating step of generating print data by performing a rasterization process on the input data; a shading correction step of correcting the print data by performing the shading correction process on the print data using the shading data corrected in the shading data correction step; a halftone processing step of generating halftone image data by performing halftone processing on the print data corrected in the shading correction step; an ink ejection step of ejecting ink from the plurality of nozzles based on the halftone image data; The present invention is characterized by comprising:

[0023] A fourteenth aspect of the present invention is a printing device comprising a plurality of nozzles which eject ink onto a printing medium, an imaging device which captures a print image, and a control unit which controls the ejection of ink from the plurality of nozzles and the imaging of the print image by the imaging device, and which performs, during printing, an ink amount compensation process which compensates for the amount of ink ejected onto the printing medium when a nozzle having an ejection defect is present, The control unit is an area setting process for setting a plurality of divided areas including K comparison areas corresponding to K different provisional compensation coefficients, where K is an integer of 2 or more, and normal areas that are not influenced by provisionally defective nozzles that are assumed to be in a discharge failure state; a tentative defective nozzle setting process for setting the tentative defective nozzle for each of the K comparison regions; a compensation coefficient calculation chart data generation process for generating compensation coefficient calculation chart data representing a compensation coefficient calculation chart for determining the compensation coefficients by performing the ink amount compensation process by applying the K temporary compensation coefficients to the K comparison areas for predetermined image data having a constant density; a compensation coefficient calculation chart printing process for controlling the ejection of ink from the plurality of nozzles based on the compensation coefficient calculation chart data so that the compensation coefficient calculation chart is printed; a compensation coefficient calculation chart imaging process for imaging the compensation coefficient calculation chart printed in the compensation coefficient calculation chart printing process by the imaging device; a data extraction process for extracting, from the imaging data obtained in the compensation coefficient calculation chart imaging process, K pieces of sample image data, each of which includes data with a luminance value of 1 or more, which is data corresponding to each of the K comparison areas and which corresponds to the positions of the provisional defective nozzles, and normal area data, which is data with a luminance value corresponding to the normal area; a function generation process for generating a function representing a correspondence relationship between a luminance difference between a luminance value in the sample image data and a luminance value in the normal area data, and a coefficient value including the K temporary compensation coefficients, based on the K sample image data and the normal area data; a compensation coefficient calculation process for calculating the compensation coefficient by using the function generated in the function generation process; The present invention is characterized by carrying out the following steps.

[0024] A fifteenth aspect of the present invention is a compensation coefficient determination program for determining a compensation coefficient to be applied to an ink amount compensation process that compensates for the amount of ink ejected onto a printing medium when a nozzle in an ejection failure state is present in a printing device having a plurality of nozzles that eject ink onto a printing medium and an imaging device that captures a print image, the compensation coefficient determination program comprising: A computer included in the printing device, a region setting step of setting a plurality of divided regions including K comparison regions corresponding to K mutually different provisional compensation coefficients, where K is an integer of 2 or more, and normal regions that are not influenced by provisionally defective nozzles that are assumed to be in a hypothetical discharge defective state; a tentative defective nozzle setting step of setting the tentative defective nozzle for each of the K comparison regions; a compensation coefficient calculation chart data generating step of generating compensation coefficient calculation chart data representing a compensation coefficient calculation chart for determining the compensation coefficients by applying the K temporary compensation coefficients to the K comparison areas for predetermined image data having a constant density, a compensation coefficient calculation chart printing step of controlling the ejection of ink from the plurality of nozzles based on the compensation coefficient calculation chart data so that the compensation coefficient calculation chart is printed; a compensation coefficient calculation chart imaging step of imaging the compensation coefficient calculation chart printed in the compensation coefficient calculation chart printing step with the imaging device; a data extraction step of extracting, from the imaging data obtained in the compensation coefficient calculation chart imaging step, K pieces of sample image data, each of which includes data of a luminance value of 1 or more, which is data corresponding to each of the K comparison areas and which corresponds to the positions of the provisional defective nozzles, and normal area data, which is data of a luminance value corresponding to the normal area; a function generating step of generating a function representing a correspondence relationship between a luminance difference between a luminance value in the sample image data and a luminance value in the normal area data, and a coefficient value including the K temporary compensation coefficients, based on the K sample image data and the normal area data; a compensation coefficient calculation step of calculating the compensation coefficient by using the function generated in the function generation step; The present invention is characterized in that the above-mentioned is executed.

[0025] A sixteenth aspect of the present invention is a compensation coefficient determination method for determining a compensation coefficient to be applied to an ink amount compensation process for compensating for an amount of ink ejected onto a printing medium when a nozzle in an ejection failure state exists in a printing device having a plurality of nozzles that eject ink onto a printing medium, the method comprising: a compensation coefficient calculation chart printing step of printing a compensation coefficient calculation chart for determining the compensation coefficients by ejecting ink from the plurality of nozzles based on compensation coefficient calculation chart data obtained by applying the K temporary compensation coefficients to predetermined image data having a constant density and performing the ink amount compensation process in a state in which K comparison areas corresponding to K different temporary compensation coefficients, where K is an integer equal to or greater than 2, and a plurality of divided areas including K comparison areas each corresponding to a temporary defective nozzle set to a hypothetical ejection defective state, and a normal area not affected by the temporary defective nozzle are set; a compensation coefficient calculation chart imaging step of acquiring imaging data, which is brightness value data, by imaging the compensation coefficient calculation chart printed in the compensation coefficient calculation chart printing step; a data extraction step of extracting, from the imaging data obtained in the compensation coefficient calculation chart imaging step, K pieces of sample image data, each of which includes data of a luminance value of 1 or more, which is data corresponding to each of the K comparison areas and which corresponds to the positions of the provisional defective nozzles, and normal area data, which is data of a luminance value corresponding to the normal area; a function generating step of generating a function representing a correspondence relationship between a luminance difference between a luminance value in the sample image data and a luminance value in the normal area data, and a coefficient value including the K temporary compensation coefficients, based on the K sample image data and the normal area data; a compensation coefficient calculation step of calculating the compensation coefficient by using the function generated in the function generation step; The present invention is characterized by comprising:

[0026] A seventeenth aspect of the present invention is a printing device comprising a plurality of nozzles which eject ink onto a printing medium, an imaging device which captures a print image, and a control unit which controls the ejection of ink from the plurality of nozzles and the imaging of the print image by the imaging device, and which performs, during printing, an ink amount compensation process which compensates for the amount of ink ejected onto the printing medium when a nozzle having an ejection defect is present, The control unit is a compensation coefficient calculation chart printing process for controlling the ejection of ink from the plurality of nozzles based on compensation coefficient calculation chart data obtained by applying the ink amount compensation process to predetermined image data having a constant density by applying the K provisional compensation coefficients to the K comparison areas in a state in which a plurality of divided areas are set, the K comparison areas corresponding to K different provisional compensation coefficients, where K is an integer of 2 or greater, and each comparison area corresponding to a provisional defective nozzle that is virtually set to be in an ejection defective state, and normal areas that are not affected by the provisional defective nozzles, so that a compensation coefficient calculation chart for determining the compensation coefficients is printed; a compensation coefficient calculation chart imaging process for imaging the compensation coefficient calculation chart printed in the compensation coefficient calculation chart printing process by the imaging device; a data extraction process for extracting, from the imaging data obtained in the compensation coefficient calculation chart imaging process, K pieces of sample image data, each of which includes data with a luminance value of 1 or more, which is data corresponding to each of the K comparison areas and which corresponds to the positions of the provisional defective nozzles, and normal area data, which is data with a luminance value corresponding to the normal area; a function generation process for generating a function representing a correspondence relationship between a luminance difference between a luminance value in the sample image data and a luminance value in the normal area data, and a coefficient value including the K temporary compensation coefficients, based on the K sample image data and the normal area data; a compensation coefficient calculation process for calculating the compensation coefficient by using the function generated in the function generation process; The present invention is characterized by carrying out the following steps.

[0027] An eighteenth aspect of the present invention is a compensation coefficient determination program for determining a compensation coefficient to be applied to an ink amount compensation process that compensates for the amount of ink ejected onto a printing medium when a nozzle in an ejection failure state is present in a printing device having a plurality of nozzles that eject ink onto a printing medium and an imaging device that captures a print image, the compensation coefficient determination program comprising: A computer included in the printing device, a compensation coefficient calculation chart printing step of controlling the ejection of ink from the plurality of nozzles based on compensation coefficient calculation chart data obtained by applying the ink amount compensation process to predetermined image data having a constant density, in a state in which K comparison areas corresponding to K different provisional compensation coefficients, where K is an integer equal to or greater than 2, and a plurality of divided areas including K comparison areas each corresponding to a provisional defective nozzle that is virtually set to be in an ejection defective state, and normal areas not affected by the provisional defective nozzles, are set so that a compensation coefficient calculation chart for determining the compensation coefficients is printed, where K is an integer equal to or greater than 2; a compensation coefficient calculation chart imaging step of imaging the compensation coefficient calculation chart printed in the compensation coefficient calculation chart printing step with the imaging device; a data extraction step of extracting, from the imaging data obtained in the compensation coefficient calculation chart imaging step, K pieces of sample image data, each of which includes data of a luminance value of 1 or more, which is data corresponding to each of the K comparison areas and which corresponds to the positions of the provisional defective nozzles, and normal area data, which is data of a luminance value corresponding to the normal area; a function generating step of generating a function representing a correspondence relationship between a luminance difference between a luminance value in the sample image data and a luminance value in the normal area data, and a coefficient value including the K temporary compensation coefficients, based on the K sample image data and the normal area data; a compensation coefficient calculation step of calculating the compensation coefficient by using the function generated in the function generation step; The present invention is characterized in that the above-mentioned is executed. Effect of the Invention

[0028] According to the first invention, a function expressing a correspondence relationship between the luminance difference between the measured luminance value (luminance value in the sample image data) and the target luminance value (luminance value in the normal area data) and the coefficient value including the K provisional compensation coefficients is obtained based on data obtained by applying K provisional compensation coefficients (K is an integer of 2 or more) to the ink amount compensation process. Then, the compensation coefficient actually applied to the ink amount compensation process is obtained using the function. In this way, the compensation coefficient actually applied to the ink amount compensation process is determined using a function based on data obtained by applying the provisional compensation coefficients to the ink amount compensation process. Therefore, a suitable compensation coefficient is obtained. As described above, for a printing device that performs printing by ejecting ink from a nozzle, defects in a printed image when there is a nozzle with an ejection defect are corrected more accurately than before. In addition, the need for reprinting is reduced by accurately correcting defects in a printed image. This reduces wasteful consumption of ink and printing media, which can contribute to the achievement of the SDGs (Sustainable Development Goals).

[0029] According to the second aspect of the present invention, a nonlinear function is used to calculate the compensation coefficient. Since the optical dot gain differs between an area where the provisional compensation coefficient value is small and white streaks appear and an area where the provisional compensation coefficient value is large and black streaks appear, the use of the nonlinear function in this way makes it possible to accurately find an appropriate compensation coefficient.

[0030] According to the third aspect of the present invention, a suitable compensation coefficient can be determined with high accuracy in a short time.

[0031] According to the fourth aspect of the present invention, it is possible to determine the compensation coefficient in a significantly shorter time than when a nonlinear function is used to calculate the compensation coefficient.

[0032] According to the fifth aspect of the invention, the same effects as those of the first aspect of the invention can be obtained.

[0033] According to the sixth aspect of the present invention, the larger the value of N, the more data is used to generate a function that represents the correspondence between the luminance difference and the coefficient value. This improves the accuracy of the function approximation of the correspondence between the luminance difference and the coefficient value, and as a result, a more accurate and suitable compensation coefficient is obtained.

[0034] According to the seventh aspect of the present invention, by increasing the value of J, a more accurate and suitable compensation coefficient can be obtained, as in the sixth aspect of the present invention.

[0035] According to the eighth aspect of the present invention, by increasing the values ​​of N and J, a more accurate and suitable compensation coefficient can be obtained, as in the sixth aspect of the present invention.

[0036] According to the ninth aspect of the present invention, it is possible to shorten the printing length of the printing medium required to print the compensation coefficient calculation chart.

[0037] According to the tenth aspect of the present invention, it is possible to reduce the number of nozzles that are set as provisionally defective nozzles.

[0038] According to the eleventh aspect of the present invention, a compensation coefficient is determined for each of a plurality of densities, so that defects in the printed image can be corrected more accurately than ever before, regardless of the density of the printed image in the area corresponding to the ejection-failed nozzle.

[0039] According to the twelfth aspect of the present invention, even if a discharge-failed nozzle (true faulty nozzle) is present at a position corresponding to the tentative faulty nozzle, the brightness value data corresponding to the position of the discharge-failed nozzle is deleted. Therefore, the compensation coefficient to be applied to the ink volume compensation process can be suitably determined without being affected by the discharge-failed nozzle.

[0040] According to the thirteenth aspect of the present invention, ink volume compensation processing is applied to the shading data, and by correcting the print data using the corrected shading data, it is possible to suppress not only the occurrence of defects in the printed image caused by the presence of nozzles with poor ejection capabilities, but also the occurrence of uneven density caused by variations in the amount of ink ejected among multiple nozzles.

[0041] According to the fourteenth aspect of the present invention, the same effects as those of the first aspect of the present invention can be obtained.

[0042] According to the fifteenth aspect of the present invention, the same effects as those of the first aspect of the present invention can be obtained.

[0043] According to the sixteenth aspect of the present invention, the same effects as those of the first aspect of the present invention can be obtained.

[0044] According to the seventeenth aspect of the present invention, the same effects as those of the first aspect of the present invention can be obtained.

[0045] According to the eighteenth aspect of the present invention, the same effects as those of the first aspect of the present invention can be obtained. [Brief description of the drawings]

[0046] [Figure 1] 1 is a diagram illustrating the overall configuration of a printing system according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram showing a configuration example of an inkjet printing apparatus in the embodiment. [Diagram 3] FIG. 4 is a plan view showing one configuration example of a recording unit in the embodiment. [Figure 4] 5A to 5C are diagrams for explaining the arrangement of nozzles in an ink ejection head in the embodiment. [Diagram 5] FIG. 2 is a block diagram showing a hardware configuration of the print control device in the embodiment. [Figure 6] 10A to 10C are diagrams for explaining shading correction processing in the embodiment. [Figure 7]10A to 10C are diagrams for explaining the ink amount compensation process in the embodiment. [Figure 8] 5 is a flowchart showing a procedure for print output in the printing system according to the embodiment. [Figure 9] 10 is a flowchart showing a detailed procedure of a shading data generating process in the embodiment. [Figure 10] FIG. 11 is a diagram showing an example of a shading chart in the embodiment. [Figure 11] 3 is a block diagram showing a functional configuration of a control unit realized by execution of a print control program in the print control device in the embodiment. FIG. [Figure 12] 4 is a block diagram showing a detailed configuration of a correction coefficient calculation unit in the embodiment. FIG. [Figure 13] 4 is a block diagram showing a detailed configuration of a compensation coefficient calculation unit in the embodiment. FIG. [Figure 14] 11 is a diagram for explaining the concept of a method for determining a compensation coefficient in the embodiment. FIG. [Figure 15] FIG. 11 is a diagram showing an example of the distribution (spatial change) of luminance values ​​obtained by the ink amount compensation process for two comparison regions corresponding to two given provisional compensation coefficients in the embodiment. [Figure 16] 13 is an example of a graph obtained when luminance difference data obtained for 14 provisional compensation coefficients are plotted on a plane in the embodiment. [Figure 17] FIG. 4 is a diagram showing an example of a curve representing a quadratic function obtained based on luminance difference data in the embodiment. [Figure 18] 10 is a flowchart showing a processing procedure for determining a compensation coefficient in the embodiment. [Figure 19] 10A and 10B are diagrams for explaining setting of a provisionally defective nozzle in the embodiment. [Figure 20] FIG. 4 is a schematic diagram illustrating an entire compensation coefficient calculation chart in the embodiment. [Figure 21]FIG. 11 is a schematic diagram illustrating a compensation coefficient calculation chart for one color and one sheet for an area corresponding to one ink ejection head in the embodiment. [Figure 22] FIG. 11 is a schematic diagram showing a portion of the compensation coefficient calculation chart corresponding to one comparison region for one concentration in the embodiment. [Figure 23] FIG. 13 is a diagram for explaining a case where the same nozzle is set as the tentative defective nozzle for all five sheets in the embodiment. [Figure 24] FIG. 11 is a diagram for explaining a case where different nozzles are set as provisional defective nozzles for each sheet in the embodiment. [Diagram 25] 5 is a schematic diagram illustrating an entire discharge defect detection chart in the embodiment. FIG. [Figure 26] FIG. 4 is a schematic diagram showing a discharge defect detection chart for one color in the embodiment. [Figure 27] FIG. 11 is a schematic diagram showing a portion of the printed compensation coefficient calculation chart corresponding to one ink ejection head 251 and one density in the embodiment. [Figure 28] FIG. 11 is a diagram showing an example of an image represented by first imaging data in a case where a discharge-fault nozzle is present in the embodiment. [Figure 29] 10A to 10C are diagrams for explaining sample image data in the embodiment. [Diagram 30] 10A and 10B are diagrams for explaining sample image data after data deletion in the embodiment. [Diagram 31] 10A and 10B are diagrams for explaining a case in which the position of the ejection-failure nozzle is close to an area of ​​partial image data in the embodiment. [Diagram 32] FIG. 11 is a diagram showing an example of a straight line representing a linear function obtained based on luminance difference data in the first modified example of the embodiment. [Diagram 33] 13 is a flowchart showing a detailed procedure of a process for calculating a compensation coefficient to be adopted in a second modified example of the embodiment. [Diagram 34]FIG. 13 is a diagram for explaining extraction of sample image data corresponding to a provisional compensation coefficient near a provisional compensation coefficient in the second modified example. [Diagram 35] FIG. 11 is a diagram for explaining generation of a linear function that represents a correspondence relationship between a luminance difference and a coefficient value in the second modified example. [Diagram 36] FIG. 13 is a diagram for explaining setting of a plurality of comparison regions in the third modified example of the embodiment. [Figure 37] FIG. 13 is a diagram illustrating a printed image of a compensation coefficient calculation chart in the third modified example. [Figure 38] 13 is a flowchart showing a procedure for determining a compensation coefficient in the fourth modified example of the embodiment. [Figure 39] FIG. 11 is a diagram for explaining non-ejection. [Diagram 40] FIG. 13 is a diagram for explaining a shape defect. [Diagram 41] FIG. 13 is a diagram for explaining a sideways jump. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0047] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0048] <1. Overall configuration of the printing system> FIG. 1 is an overall configuration diagram of a printing system according to an embodiment of the present invention. This printing system is composed of an inkjet printing device 10 and a print data generating device 30. The inkjet printing device 10 and the print data generating device 30 are connected to each other by a LAN 4. The print data generating device 30 generates print data by performing rasterization processing or the like on input data such as a PDF file. This print data is data that has not been subjected to halftone processing, and halftone processing is performed by a print control device 100 in the inkjet printing device 10 as described later. The print data generated by the print data generating device 30 is transmitted to the inkjet printing device 10 via the LAN 4. The inkjet printing device 10 is composed of a printing machine main body 200 and a print control device 100 that controls the operation of the printing machine main body 200. The inkjet printing device 10 outputs a print image on printing paper as a printing medium based on the print data transmitted from the print data generating device 30 without using a printing plate. The present invention can also be applied to a case where a printing medium other than printing paper (for example, a film) is used.

[0049] <2. Configuration of the printer body of the inkjet printing device> 2 is a schematic diagram showing an example of the configuration of the inkjet printing apparatus 10. As described above, the inkjet printing apparatus 10 is made up of the print control device 100 and the printing machine main body 200.

[0050] The printing machine main body 200 includes a paper feed section 202 that supplies printing paper (in this example, rolled printing paper) 5 to the printing mechanism 201, the printing mechanism 201 that prints on the printing paper 5, and a paper winding section 208 that winds up the printing paper 5 into a roll after printing.

[0051] The printing mechanism 201 includes a first driving roller 203 for transporting the printing paper 5 to the inside, a plurality of support rollers 204 for transporting the printing paper 5 inside the printing mechanism 201, a recording unit 205 for recording a print image on the printing paper 5, a drying mechanism 206 for drying the printing paper 5 on which the print image has been recorded, and a second driving roller 207 for outputting the printing paper 5 from inside the printing mechanism 201. The recording unit 205 is composed of a K head unit 25K for ejecting K (black) ink, a C head unit 25C for ejecting C (cyan) ink, an M head unit 25M for ejecting M (magenta) ink, and a Y head unit 25Y for ejecting Y (yellow) ink. The printing mechanism 201 also includes an inline scanner 40 as an imaging device for capturing an image of the printing image recorded on the printing paper 5 by the recording unit 205. The imaging data obtained by the in-line scanner 40 capturing an image of a print image is sent to the print control device 100. In the following description, when there is no need to distinguish between the colors of ink ejected from the head units, the head units will be denoted by the reference symbol 25.

[0052] FIG. 3 is a plan view showing an example of the configuration of the recording unit 205. As shown in FIG. 3, the recording unit 205 is composed of a K-color head unit 25K, a C-color head unit 25C, an M-color head unit 25M, and a Y-color head unit 25Y, which are arranged in a row in the transport direction (sub-scanning direction) of the print paper 5. Each head unit 25 is composed of a plurality of ink ejection heads (print heads) 251 arranged in a staggered pattern. Each ink ejection head 251 includes a large number of nozzles (not shown in FIG. 3) that eject ink. Each nozzle of the ink ejection head 251 included in the K-color head unit 25K ejects K-color ink, each nozzle of the ink ejection head 251 included in the C-color head unit 25C ejects C-color ink, each nozzle of the ink ejection head 251 included in the M-color head unit 25M ejects M-color ink, and each nozzle of the ink ejection head 251 included in the Y-color head unit 25Y ejects Y-color ink.

[0053] FIG. 4 is a diagram for explaining an example of the arrangement of nozzles in the ink ejection head 251. Typically, the ink ejection head 251 includes multiple rows of nozzle groups each consisting of multiple nozzles arranged in a main scanning direction (a direction perpendicular to the transport direction of the print paper 5). In the example shown in FIG. 4, the ink ejection head 251 includes four rows of nozzle groups. The portion marked with reference numeral 41 in FIG. 4 shows a schematic diagram of the landing position of ink ejected from each nozzle on the print paper 5. The multiple nozzles in the ink ejection head 251 are arranged such that the landing position of ink ejected from the nozzles included in the first row of nozzle groups, the landing position of ink ejected from the nozzles included in the second row of nozzle groups, the landing position of ink ejected from the nozzles included in the third row of nozzle groups, and the landing position of ink ejected from the nozzles included in the fourth row of nozzle groups are different from each other. For example, the landing position of ink ejected from each nozzle included in the first row of nozzles is a position between the landing position of ink ejected from nozzles included in the third row of nozzles and the landing position of ink ejected from nozzles included in the fourth row of nozzles. In the example shown in Fig. 4, the landing position 42 of ink ejected from a nozzle labeled 252(p) is a position between the landing position 43 of ink ejected from a nozzle labeled 252(q) and the landing position 44 of ink ejected from a nozzle labeled 252(r). Therefore, the adjacent nozzles (nozzles on both sides) of the nozzle labeled 252(p) are the nozzle labeled 252(q) and the nozzle labeled 252(r).

[0054] <3. Hardware configuration of print control device> FIG. 5 is a block diagram showing a hardware configuration of the print control device 100. As shown in FIG. 5, the print control device 100 includes a main body 110, an auxiliary storage device 121, an optical disk drive 122, a display unit 123, a keyboard 124, and a mouse 125. The main body 110 includes a CPU 111, a memory 112, a first disk interface unit 113, a second disk interface unit 114, a display control unit 115, an input interface unit 116, and a communication interface unit 117. The CPU 111, the memory 112, the first disk interface unit 113, the second disk interface unit 114, the display control unit 115, the input interface unit 116, and the communication interface unit 117 are connected to each other via a system bus. The auxiliary storage device 121 is connected to the first disk interface unit 113. The optical disk drive 122 is connected to the second disk interface unit 114. The display unit (display device) 123 is connected to the display control unit 115. A keyboard 124 and a mouse 125 are connected to the input interface unit 116. The printing machine main body 200 is connected to the communication interface unit 117 via a communication cable. The communication interface unit 117 is also connected to the LAN 4. The auxiliary storage device 121 is a magnetic disk device or the like. An optical disk 19 serving as a computer-readable recording medium such as a CD-ROM or DVD-ROM is inserted into the optical disk drive 122. The display unit 123 is a liquid crystal display or the like. The display unit 123 is used to display information desired by the operator. The keyboard 124 and the mouse 125 are used by the operator to input instructions to this print control device 100.

[0055] The auxiliary storage device 121 stores a print control program (program for controlling the execution of print processing by the printer main body 200) 13. The print control program 13 in this embodiment includes, as a subprogram, a compensation coefficient determination program for determining a coefficient (hereinafter referred to as a "compensation coefficient") to be applied to an ink amount compensation process that compensates for the amount of ink ejected onto the print paper 5 when an ejection failure nozzle is present. The CPU 111 realizes various functions of the print control device 100 by reading the print control program 13 stored in the auxiliary storage device 121 into the memory 112 and executing it. The memory 112 includes a RAM (Random Access Memory) and a ROM (Read Only Memory). The memory 112 functions as a work area for the CPU 111 to execute the print control program 13 stored in the auxiliary storage device 121. The print control program 13 is provided by being stored in the computer-readable recording medium (non-transient recording medium). That is, the user purchases, for example, the optical disk 19 as a recording medium for the print control program 13 , inserts it into the optical disk drive 122 , reads out the print control program 13 from the optical disk 19 , and installs it in the auxiliary storage device 121 .

[0056] <4. Overview of correction process> In the inkjet printing device 10 according to this embodiment, a correction process is performed to suppress the occurrence of density unevenness caused by the variation in the amount of ink ejected among a plurality of nozzles and the occurrence of defects in the printed image caused by the presence of a defective nozzle (for example, white streaks and missing dots). Specifically, the correction process includes a shading correction process that compensates for the variation in the amount of ink ejected among a plurality of nozzles, and an ink amount compensation process that compensates for the amount of ink ejected onto the printing paper 5 when a defective nozzle is present. The ink amount compensation process is a process for realizing the above-mentioned substitute droplet ejection. Hereinafter, the shading correction process and the ink amount compensation process will be described with reference to FIG. 6 and FIG. 7. Here, attention will be paid to five pixel portions 7(1) to 7(5) corresponding to five nozzles. It is assumed that a single color is printed in the five pixel portions 7(1) to 7(5) using the same color ink ejected from the above five nozzles. Note that, with respect to FIG. 6 and FIG. 7, the numerical values ​​inside the rectangles corresponding to the pixel portions 7(1) to 7(5) respectively represent density values ​​in the data.

[0057] First, the shading correction process will be described with reference to FIG. 6. Here, it is assumed that when printing is performed at a constant density (50%) without executing the shading correction process, the amount of ink ejected onto pixel portion 7(1) and pixel portion 7(3) is (5 / 4) times that of pixel portion 7(2), the amount of ink ejected onto pixel portion 7(4) is (5 / 6) times that of pixel portion 7(2), and the amount of ink ejected onto pixel portion 7(5) is (5 / 3) times that of pixel portion 7(2). At this time, the density value shown in the portion labeled with reference numeral 71 is corrected by the shading correction process to the density value shown in the portion labeled with reference numeral 72. By correcting the density data in this manner, the variation in the amount of ink ejected among the multiple nozzles is reduced, and the occurrence of uneven density is suppressed.

[0058] Next, the ink amount compensation process will be described with reference to FIG. 7. Here, it is assumed that the nozzle corresponding to the pixel portion 7(3) is a defective nozzle. At this time, for example, the density value shown in the portion marked with the reference symbol 73 is corrected to the density value shown in the portion marked with the reference symbol 74 by the ink amount compensation process. The density value for the pixel portion 7(3) is corrected from 50 to 0, and the density value for the pixel portion 7(2) and the pixel portion 7(4) is corrected from 50 to 70. By correcting the density data in this manner, a larger amount of ink is ejected from the nozzle adjacent to the defective nozzle than would be the case otherwise. As a result, defects in the printed image caused by the defective nozzle not ejecting ink normally are not noticeable. In other words, the occurrence of defects in the printed image is suppressed. In this embodiment, the ink amount compensation process is applied to the shading data described later.

[0059] <5. Print output procedure> The procedure for print output in this printing system will be described with reference to the flowchart shown in Fig. 8. Here, it is assumed that the compensation coefficients used in the ink amount compensation process have already been determined.

[0060] First, in the inkjet printing device 10, a process for generating shading data that is used when performing shading correction processing on print data (shading data generation process) is performed (step S10). The shading data generation process will be described in detail later.

[0061] Next, the shading data generated in step S10 is subjected to an ink amount compensation process using a compensation coefficient determined as described below, thereby correcting the shading data (step S20). If the compensation coefficient used in the ink amount compensation process is represented by C, which is a value between 0 and 1, the position value corresponding to the discharge-failed nozzle (the true faulty nozzle described below) in the shading data before the process of step S20 is executed is represented by Vf, the position value corresponding to the nozzle adjacent to the discharge-failed nozzle in the shading data before the process of step S20 is executed is represented by Vn, and the position value corresponding to the nozzle adjacent to the discharge-failed nozzle in the shading data after the process of step S20 is executed is represented by V, then V can be expressed by the following equation (1). V = Vn + Vf × C (1)

[0062] It should be noted that after the processing of step S20 has been executed, the value of the position in the shading data corresponding to the discharge-failed nozzle is 0.

[0063] As described above, in this embodiment, the shading data is corrected by the ink amount compensation process. Note that in step S50, which will be described later, the print data is corrected using the corrected shading data. Therefore, hereinafter, this corrected shading data is also referred to as the "correction coefficient."

[0064] After the shading data is corrected, the print data generating device 30 performs a rasterization process on the input data such as a PDF file to generate print data (step S30). Then, the print data is transferred from the print data generating device 30 to the print control device 100 in the inkjet printing device 10 (step S40).

[0065] Thereafter, in the print control device 100, the shading correction process is performed on the print data using the correction coefficient obtained in step S20 (i.e., the shading data corrected in step S20), thereby correcting the print data (step S50).

[0066] After the shading correction process is completed, the print control device 100 performs halftone processing on the print data corrected in step S50, thereby generating halftone image data (step S60).

[0067] Finally, printing is performed by the recording unit 205 based on the halftone image data generated in step S60 (step S70). That is, an image is formed on the printing paper 5 by controlling the ejection of ink from the multiple nozzles included in each ink ejection head 251 constituting the recording unit 205 based on the halftone image data.

[0068] Note that the processes of steps S10 and S20 do not necessarily have to be performed for each print job. In other words, after the processes of steps S10 and S20 are performed once, the processes of steps S30 to S70 can be repeatedly performed for multiple print jobs.

[0069] In this embodiment, a shading data generation step is realized by step S10, a shading data correction step is realized by step S20, a print data generation step is realized by step S30, a shading correction step is realized by step S50, a halftone processing step is realized by step S60, and an ink ejection step is realized by step S70.

[0070] FIG. 9 is a flowchart showing a detailed procedure of the shading data generation process (the process of step S10 in FIG. 8). After the shading data generation process starts, a shading chart such as that shown in FIG. 10 is printed (step S12). The shading chart data representing the shading chart is stored in advance in the auxiliary storage device 121 in the print control device 100. The shading chart is an image whose density changes stepwise in the conveying direction (sub-scanning direction) of the print paper 5. For example, in the shading chart shown in FIG. 10, the density value of the portion marked with the reference symbol 75(1) is 5%, the density value of the portion marked with the reference symbol 75(2) is 10%, the density value of the portion marked with the reference symbol 75(3) is 30%, the density value of the portion marked with the reference symbol 75(4) is 50%, the density value of the portion marked with the reference symbol 75(5) is 80%, and the density value of the portion marked with the reference symbol 75(6) is 100%.

[0071] After printing the shading chart, the shading chart is imaged by the in-line scanner 40 (step S14). Then, based on the image data obtained in step S14, a density correction amount is calculated by a known method (step S16). The data representing the density correction amount is shading data. When the process of step S16 ends, the shading data generation process ends.

[0072] <6. Details of correction process> The correction process will be described in detail below.

[0073] <6.1 Functional configuration of the control section> 11 is a block diagram showing the functional configuration of a control unit 150 that is realized by executing the print control program 13 in the print control device 100. The control unit 150 includes a transport control unit 151, an ink ejection control unit 152, a drying control unit 153, an imaging control unit 154, a compensation coefficient calculation chart data generation processing unit 155, a correction coefficient calculation unit 156, a print data correction unit 157, and a halftone processing unit 158.

[0074] The conveyance control unit 151 controls the speed (conveyance speed) at which the conveyance mechanism 29 conveys the print paper 5. The conveyance mechanism 29 is realized by a paper delivery unit 202, a first drive roller 203, a plurality of support rollers 204, a second drive roller 207, and a paper winding unit 208 (see FIG. 2). The drying control unit 153 controls the temperature (drying temperature) at which the drying mechanism 206 dries the print paper 5 after printing. The imaging control unit 154 controls the timing at which the inline scanner 40 captures the print image.

[0075] The compensation coefficient calculation chart data generation processing unit 155 generates compensation coefficient calculation chart data 53 that represents a compensation coefficient calculation chart for determining compensation coefficients used in the ink amount compensation process. The generation of the compensation coefficient calculation chart data 53 will be described in detail later.

[0076] The correction coefficient calculation unit 156 calculates a correction coefficient 57 for correcting the print data 50 generated by the print data generation device 30, based on first captured data 54 obtained by the in-line scanner 40 capturing an ejection failure detection chart for detecting ejection failure nozzles, second captured data 55 obtained by the in-line scanner 40 capturing an image of a compensation coefficient calculation chart, and third captured data 56 obtained by the in-line scanner 40 capturing an image of a shading chart as shown in Fig. 10. The correction coefficient calculation unit 156 will be described in detail later.

[0077] The print data correction unit 157 corrects the print data 50 generated by the print data generating device 30 using the correction coefficient 57 calculated by the correction coefficient calculation unit 156. In other words, the print data correction unit 157 performs shading correction processing on the print data 50 generated by the print data generating device 30 using the correction coefficient 57 calculated by the correction coefficient calculation unit 156. The print data correction unit 157 outputs the corrected print data 58.

[0078] The halftone processing unit 158 ​​performs halftone processing on the data to be printed, thereby generating halftone image data 59 including information indicating the ink dot size corresponding to each pixel. For example, three sizes (L size, M size, and S size) are prepared as the ink dot size. In this embodiment, the halftone processing is performed on the print data 58 corrected by the print data correction unit 157, the shading chart data 51 representing the shading chart, the discharge failure detection chart data 52 representing the discharge failure detection chart, and the compensation coefficient calculation chart data 53 generated by the compensation coefficient calculation chart data generation processing unit 155. Note that the specific method of the halftone processing is not particularly limited, and for example, known methods such as the error diffusion method and the dither method can be adopted. In addition, a part of the discharge failure detection chart data 52 (for example, the data of the part corresponding to the part 681 representing the step-like pattern described later with reference to FIG. 26) does not need to be subjected to the halftone processing.

[0079] The ink ejection control unit 152 controls the amount of ink ejected from each nozzle included in each ink ejection head 251 that constitutes the recording unit 205 based on halftone image data 59 generated by the halftone processing unit 158.

[0080] 12 is a block diagram showing a detailed configuration of the correction coefficient calculation unit 156. The correction coefficient calculation unit 156 includes a shading data generation unit 510, a compensation coefficient calculation unit 520, and a shading data correction unit 530.

[0081] The shading data generating unit 510 generates shading data (data representing the amount of density correction) 61 based on the third captured data 56 obtained by the in-line scanner 40 capturing an image of a shading chart as shown in FIG.

[0082] The compensation coefficient calculation unit 520 determines a compensation coefficient 62 to be used in the ink amount compensation process, based on first captured data 54 obtained by the in-line scanner 40 capturing an image of the discharge defect detection chart, and second captured data 55 obtained by the in-line scanner 40 capturing an image of the compensation coefficient calculation chart. Details of the compensation coefficient calculation unit 520 will be described later.

[0083] The shading data correction unit 530 performs ink amount compensation processing on the shading data 61 generated by the shading data generation unit 510, using the compensation coefficient 62 calculated by the compensation coefficient calculation unit 520. As a result, a correction coefficient 57 for correcting the print data 50 is calculated.

[0084] 13 is a block diagram showing a detailed configuration of the compensation coefficient calculation unit 520. The compensation coefficient calculation unit 520 includes a discharge-failed nozzle detection unit 521, a sample image data extraction unit 522, a data deletion unit 523, a function generation unit 524, and a coefficient calculation unit 525.

[0085] The discharge-faulty nozzle detection unit 521 detects the discharge-faulty nozzle 63 based on the first imaging data 54. There are no particular limitations on the specific method for detecting the discharge-faulty nozzle 63, but for example, the discharge-faulty nozzle 63 can be detected by a method using machine learning.

[0086] The sample image data extraction unit 522 extracts a plurality of sample image data 64 corresponding to a plurality of comparison areas set to determine the compensation coefficient 62 to be applied to the ink amount compensation process from the second captured data 55. The sample image data extraction unit 522 further extracts normal area data 65 corresponding to the normal area from the second captured data 55. The comparison area and normal area will be described later.

[0087] The data deleting unit 523 deletes data corresponding to the position of the nozzle (failed nozzle) 63 detected by the failed nozzle detection unit 521 from the plurality of sample image data 64. As a result, a plurality of sample image data 66 from which the data corresponding to the position of the failed nozzle 63 has been deleted is output from the data deleting unit 523. Note that these plurality of sample image data 66 are associated with a plurality of provisional compensation coefficients prepared for the sake of convenience in order to determine the compensation coefficient 62 to be actually applied to the ink amount compensation process.

[0088] The function generation unit 524 generates a function 67 that expresses the correspondence between the luminance difference between the luminance value in the sample image data 66 and the luminance value in the normal area data 65, and coefficient values ​​including a plurality of temporary compensation coefficients, based on the plurality of sample image data 66 and the normal area data 65. The coefficient calculation unit 525 uses the function 67 generated by the function generation unit 524 to calculate a compensation coefficient 62 to be actually applied to the ink amount compensation process. Note that the generation of the function 67 by the function generation unit 524 and the calculation of the compensation coefficient 62 by the coefficient calculation unit 525 will be described in detail later.

[0089] <6.2 How to determine the compensation coefficient> <6.2.1 Concept> With reference to Figs. 14 to 17, the concept of how to determine the compensation coefficient 62 will be described. The compensation coefficient 62 is a coefficient used in the ink amount compensation process, and as described above, in the ink amount compensation process, the density data (shading data in this embodiment) of the pixel portion corresponding to the discharge-failed nozzle and the pixel portion corresponding to the adjacent nozzles of the discharge-failed nozzle (nozzles on both sides of the discharge-failed nozzle) are corrected (see Fig. 7). At that time, the value obtained by multiplying the original density value of the pixel portion corresponding to the discharge-failed nozzle by the compensation coefficient 62 is added to the original density value of the pixel portion of the nozzle adjacent to the discharge-failed nozzle. The suitable compensation coefficient 62 changes depending on the type of printing paper 5 and the printing conditions.

[0090] Part A of FIG. 14 shows the density values ​​of five pixels in a normal case where there is no defective nozzle, and the density values ​​of five pixels in four cases where ink amount compensation processing is performed using four types of compensation coefficients when a defective nozzle is present. In part B of FIG. 14, the target luminance value is shown by a dotted line with a reference number 41, the distribution (spatial change) of the luminance value in the five pixel parts for each case is shown by a solid line with a reference number 42, and the average value (average luminance value) of the luminance values ​​for each case other than the normal case is shown by a thick solid line with a reference number 43. For example, in the case of a "compensation coefficient of 20%", the amount of ink discharged to the corresponding area is small, so the average luminance value in the corresponding area is higher than the target luminance value. In the case of a "compensation coefficient of 60%", the amount of ink discharged to the corresponding area is large, so the average luminance value in the corresponding area is lower than the target luminance value. In the example shown in FIG. 14, in the case of a "compensation coefficient of 40%", the average luminance value in the corresponding area is close to the target luminance value. 14, it is assumed that a target luminance value 41 is set, and the compensation coefficient that provides a luminance value distribution 42 in which the difference between the target luminance value 41 and an average luminance value 43 is the smallest is determined as the final compensation coefficient. However, the target luminance value 41 is not necessarily required. For example, the maximum and minimum luminance values ​​on the luminance value distribution 42 and the difference between them can be obtained, and the compensation coefficient that provides the smallest difference can be determined as the final compensation coefficient.

[0091] In this embodiment, various compensation coefficients are prepared as provisional compensation coefficients, and ink amount compensation processing is performed using these provisional compensation coefficients. Using the captured image data of the print image based on the data obtained thereby, a function is obtained that represents the correspondence relationship between the luminance difference between the luminance value obtained by the ink amount compensation processing and the target luminance value, and the coefficient value (value of the compensation coefficient). More specifically, in this embodiment, 14 provisional compensation coefficients (1.0, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6, 1.65) are prepared. In addition, for each ink ejection head 251, the area in the main scanning direction is divided into 14 comparison areas corresponding to the above 14 provisional compensation coefficients and a normal area (an area not affected by the provisional defective nozzle described later) corresponding to the above normal case. Furthermore, for each of the 14 comparison areas, four provisional defective nozzles that are virtually considered to be in a defective ejection state are set from among the corresponding multiple nozzles. The position of the provisionally faulty nozzle is not particularly limited, but it is desirable to select as the provisionally faulty nozzle a nozzle where ejection defects are likely to be noticeable (for example, a nozzle that ejects ink before other nozzles. As an example, a nozzle belonging to the nozzle groups in the first and second rows in FIG. 4). The same provisional compensation coefficient is applied to these four provisionally faulty nozzles. Then, the above-mentioned function is calculated based on second imaging data 55 obtained by imaging a compensation coefficient calculation chart including images corresponding to the 14 comparison areas and normal areas.

[0092] Here, an example of using 14 provisional compensation coefficients in increments of 0.05 is described, but the present invention is not limited to this. For example, there may be missing values, multiple provisional compensation coefficients in increments of 0.1 may be used, and the increments may not be uniform. The number of provisional faulty nozzles set in each comparison area may be one or more, and is not limited to four. If the number of provisional faulty nozzles set in each comparison area is multiple, data can be obtained from the comparison area even if the provisional faulty nozzle coincides with a true faulty nozzle described later, which has the advantage of improving robustness.

[0093] FIG. 15 shows an example of the distribution (spatial change) of brightness values ​​obtained by the ink amount compensation process for two comparison regions 76 corresponding to two provisional compensation coefficients. The position of the portion marked with the reference symbol 77 corresponds to the position of the provisional defective nozzle. From such data of the distribution of brightness values, data corresponding to the position of the provisional defective nozzle is extracted as sample image data. In the example shown in FIG. 15, each sample image data contains data of four brightness values. However, in reality, the printing and imaging of the compensation coefficient calculation chart is repeated multiple times, so that the sample image data corresponding to one provisional compensation coefficient contains data of many brightness values. In addition, from the data of the distribution of brightness values, data corresponding to the normal region (not shown in FIG. 15) is extracted as normal region data. As a result, data of the brightness difference between the brightness value in the sample image data and the brightness value in the normal region data is obtained. For example, if the sample image data corresponding to each provisional compensation coefficient contains data of 40 brightness values, data of 40 brightness differences is obtained for each provisional compensation coefficient.

[0094] If the luminance difference data obtained for the above 14 provisional compensation coefficients are plotted on a plane with the horizontal axis representing the coefficient value and the vertical axis representing the luminance difference, a graph such as that shown in Figure 16 is obtained. If a function that best fits this luminance difference data is found and a coefficient value that makes the luminance difference zero based on this function is calculated, this coefficient value is considered to be the optimum value for the compensation coefficient 62 to be applied in the ink amount compensation process.

[0095] Therefore, in this embodiment, a nonlinear function that fits (fits) the luminance difference data obtained for the 14 provisional compensation coefficients is obtained. In other words, a multiple regression analysis is performed with the coefficient values ​​as explanatory variables and the luminance difference as the objective variable (explained line). The nonlinear function is not particularly limited, but for example, a quadratic function expressed by the following formula (2) or an exponential function expressed by the following formula (3) can be adopted. Y=aX 2 +bX+c ···(2) Y = a(1-exp(-bX)) + c (3) Here, X represents the coefficient value (value of the compensation coefficient), Y represents the luminance difference, and a, b, and c represent coefficients in the nonlinear function. Also, exp() is a function that returns the Zth power of e (the base of natural logarithms) when the value in the parentheses is represented as Z.

[0096] The coefficients a, b, and c in the above formula (2) and formula (3) can be determined using a known method such as the least squares method.

[0097] Here, it is assumed that a quadratic function represented by the curve labeled 82 in Figure 17 has been obtained based on the luminance difference data obtained for the 14 provisional compensation coefficients. In this case, the coefficient value on curve 82 representing this quadratic function where the luminance difference is 0 is the value of the black dot labeled 83 in Figure 17. Therefore, in this case, the value (coefficient value) of this black dot is determined as the compensation coefficient 62 to be actually applied to the ink amount compensation process.

[0098] In this embodiment, 14 provisional compensation coefficients are prepared to generate a nonlinear function that represents the correspondence between the luminance difference and the coefficient value, but it is preferable to prepare at least three provisional compensation coefficients to generate a nonlinear function.

[0099] <6.2.2 Compensation coefficient determination procedure (method of determining compensation coefficient)> The procedure of the process for determining the compensation coefficient 62 will be described with reference to the flowchart shown in FIG. 18. First, for each ink ejection head 251, 15 divided regions including 14 comparison regions corresponding to the 14 different provisional compensation coefficients and one normal region (region not affected by the provisional defective nozzle) are set (step S100). In this regard, in this embodiment, the 15 divided regions are set so that the 14 comparison regions are aligned in the main scanning direction (direction perpendicular to the transport direction of the print paper 5). The number of provisional compensation coefficients prepared is not limited to 14. Also, it is not necessary to provide a normal region for each ink ejection head 251.

[0100] Incidentally, when five ink ejection heads 251 are provided for one ink color, 14 comparison areas and one normal area are set for each of the five ink ejection heads 251. As will be described later, the compensation coefficient calculation chart is composed of five sheets of images for each color in the sub-scanning direction. As described above, there are 25 (=5×5) comparison areas corresponding to each provisional compensation coefficient. In this regard, 25 comparison areas corresponding to the same provisional compensation coefficient are treated as one comparison area. However, for ease of explanation, in the following, attention will be focused on one comparison area out of the 25 comparison areas corresponding to one provisional compensation coefficient.

[0101] After step S100 is completed, a number of provisionally defective nozzles that are assumed to be in a discharge failure state are set for each of the 14 comparison regions from among the corresponding nozzles (step S110). As described above, in this embodiment, four provisionally defective nozzles are set for each comparison region. That is, for each ink discharge head 251, four provisionally defective nozzles 80 are set for each of the 14 comparison regions 76(1) to 76(14), as shown in schematic form in FIG.

[0102] Next, compensation coefficient calculation chart data 53 representing a compensation coefficient calculation chart for determining the compensation coefficient 62 is generated (step S120). FIG. 20 is a schematic diagram showing the entire compensation coefficient calculation chart 69. As shown in FIG. 20, the compensation coefficient calculation chart 69 is composed of a portion 690(K) corresponding to K color, a portion 690(C) corresponding to C color, a portion 690(M) corresponding to M color, and a portion 690(Y) corresponding to Y color. However, the following description focuses on one color. The portion corresponding to each color includes images for multiple sheets. In this regard, in this embodiment, the portion corresponding to each color includes images for five sheets.

[0103] FIG. 21 is a schematic diagram showing a compensation coefficient calculation chart 69 for one color and one sheet for an area corresponding to one ink ejection head 251. The compensation coefficient calculation chart 69 is an image in which the density changes stepwise in the transport direction (sub-scanning direction) of the print paper 5. In this embodiment, it is assumed that the density changes in 11 steps. Specifically, in FIG. 21, the density of the portion marked with reference numeral 691(1) is 5%, the density of the portion marked with reference numeral 691(2) is 10%, the density of the portion marked with reference numeral 691(10) is 90%, and the density of the portion marked with reference numeral 691(11) is 100%. The density changes in 10% increments between the portion marked with reference numeral 691(2) and the portion marked with reference numeral 691(10). 21, the compensation coefficient calculation chart 69 includes a portion corresponding to each of the 14 comparison regions 76(1) to 76(14) and a portion corresponding to the normal region 81. The portion corresponding to one comparison region 76 for one density includes a portion 694 corresponding to four provisional defective nozzles, as shown in FIG. 22. The change in density on the compensation coefficient calculation chart 69 is not limited to 11 steps. It is sufficient that the compensation coefficient calculation chart 69 includes M density regions corresponding to M different densities in the transport direction of the printing paper 5, where M is an integer of 2 or greater.

[0104] In step S120, compensation coefficient calculation chart data 53 representing the compensation coefficient calculation chart 69 described above is generated by performing ink amount compensation processing by applying 14 provisional compensation coefficients to each of the 14 comparison areas 76(1) to 76(14) for image data having a constant density in the main scanning direction.

[0105] Incidentally, for each combination of the ink ejection head 251 and the density, the same nozzle may be set as the provisionally defective nozzle for all of the five sheets, or a different nozzle may be set as the provisionally defective nozzle for each sheet. When the same nozzle is set as the provisionally defective nozzle for all of the five sheets, the region (comparison region) corresponding to a certain provisional compensation coefficient for the maximum density in the entire region of the compensation coefficient calculation chart 69 is shaded as shown in FIG. 23. On the other hand, when a different nozzle is set as the provisionally defective nozzle for each sheet, the region (comparison region) corresponding to a certain provisional compensation coefficient for the maximum density in the entire region of the compensation coefficient calculation chart 69 is shaded as shown in FIG. 24. Note that, in FIG. 23 and FIG. 24, the regions marked with reference numerals 695(1) to 695(5) respectively represent the regions corresponding to the first to fifth sheets, and the regions marked with reference numerals 696(1) to 696(5) respectively represent the regions corresponding to the first to fifth ink ejection heads 251. When a different nozzle is set as the provisional defective nozzle for each sheet (see FIG. 24), the influence of the variation in the ink ejection amount among a plurality of nozzles can be more effectively suppressed.

[0106] After the compensation coefficient calculation chart data 53 is generated, a discharge failure detection chart for detecting discharge failure nozzles is printed (step S130). FIG. 25 is a schematic diagram showing the entire discharge failure detection chart 68. As shown in FIG. 25, the discharge failure detection chart 68 is composed of a portion 680 (K) corresponding to the K color, a portion 680 (C) corresponding to the C color, a portion 680 (M) corresponding to the M color, and a portion 680 (Y) corresponding to the Y color. FIG. 26 is a schematic diagram showing the discharge failure detection chart 68 for one color. The discharge failure detection chart 68 is composed of a portion 681 representing a staircase pattern to be formed by ejecting ink from all the nozzles in one head unit 25, and a portion 682 representing a tint pattern of a constant density as a whole to be formed by ejecting ink from all the nozzles in one head unit 25. In step S130, the above-described discharge failure detection chart 68 is printed by controlling the ink discharge from each nozzle included in each ink discharge head 251 constituting the recording unit 205 based on the discharge failure detection chart data 52. The discharge failure detection chart data 52 is stored in advance in the auxiliary storage device 121 in the print control device 100.

[0107] After printing the discharge failure detection chart 68, the ink discharge from each nozzle included in each ink discharge head 251 constituting the recording unit 205 is controlled based on the compensation coefficient calculation chart data 53 generated in step S120, thereby printing the compensation coefficient calculation chart 69 (step S140). A portion of the compensation coefficient calculation chart 69 printed in step S140 corresponding to one ink discharge head 251 and one density is, for example, as shown in FIG. 27. The image of the portion shown in FIG. 27 includes images corresponding to the 14 comparison regions 76(1) to 76(14) and an image corresponding to a normal region 81.

[0108] After printing the compensation coefficient calculation chart 69, the ejection defect detection chart 68 printed on the printing paper 5 in step S130 is imaged by the in-line scanner 40 (step S150), and further, the compensation coefficient calculation chart 69 printed on the printing paper 5 in step S140 is imaged by the in-line scanner 40 (step S160). First image data 54 is obtained in step S150, and second image data 55 is obtained in step S160.

[0109] Thereafter, the discharge-fault nozzle detection unit 521 detects discharge-fault nozzles that are causing non-discharge, shape defects, and sideways jumps, based on the first imaging data 54 obtained in step S150 (step S170). Incidentally, if there is no discharge-fault nozzle, the image represented by the first imaging data 54 will be an image as shown in FIG. 26. On the other hand, if there is a discharge-fault nozzle, the image represented by the first imaging data 54 will be, for example, an image as shown in FIG. 28. In the example shown in FIG. 28, the line pattern is not printed properly in the portion marked with the reference numeral 541 (non-discharge occurs). Also, the tint pattern is not printed properly in the portion marked with the reference numeral 542 corresponding to the discharge failure in the portion marked with the reference numeral 541. In this way, if there is a discharge-fault nozzle, the tint pattern is not printed properly in the portion corresponding to the discharge-fault nozzle. As described above, in step S170, the discharge-fault nozzle is detected based on the first imaging data 54. In the following, the discharge-fault nozzle detected in step S170 is referred to as a "true faulty nozzle."

[0110] Next, the sample image data extraction unit 522 extracts, for each ink color, 14 sample image data 64 corresponding to the 14 comparison regions 76 set for determining the compensation coefficient 62 from the second captured data 55 obtained in step S160 (step S180). In this embodiment, in step S180, the sample image data extraction unit 522 further extracts, for each ink color, normal region data 65 corresponding to the normal region 81 from the second captured data 55.

[0111] In this embodiment, each of the 14 sample image data 64 includes four partial image data 640(1) to 640(4) corresponding to the four provisionally defective nozzles 80 (see FIG. 19), as shown in FIG 29. In other words, each of the 14 sample image data 64 includes data of four brightness values.

[0112] After step S180 is completed, the data deletion unit 523 deletes data (luminance value data) corresponding to the position of the true defective nozzle (the ejection defective nozzle detected in step S170) from the 14 pieces of sample image data 64 (step S190). In this regard, in the present embodiment, for example, if the area of ​​partial image data 640(3) among the four pieces of partial image data 640(1) to 640(4) constituting one piece of sample image data 64 corresponds to the position of the true defective nozzle, partial image data 640(3) is deleted from the four pieces of partial image data 640(1) to 640(4). Therefore, in this example, the sample image data 66 after step S190 is completed is composed of partial image data 640(1), partial image data 640(2), and partial image data 640(4), as shown in FIG.

[0113] Note that even if the position of the discharge-failed nozzle does not correspond to the region of partial image data constituting sample image data 64, if the presence of the discharge-failed nozzle affects the brightness value of the partial image data, the corresponding partial image data is deleted in step S190. For example, as shown in FIG. 31, if position 642 of the discharge-failed nozzle does not correspond to the region of partial image data 640(3) but is close to the region of partial image data 640(3), the presence of the discharge-failed nozzle affects the brightness value of partial image data 640(3). Therefore, even in such a case, partial image data 640(3) is deleted from the four partial image data 640(1) to 640(4) in step S190.

[0114] As described above, in this embodiment, for each of the 14 sample image data 64, in step S190, the partial image data affected by the truly defective nozzle is deleted from the four partial image data 640(1) to 640(4).

[0115] After step S190, the function generating unit 524 generates a function representing the correspondence between the luminance difference between the measured luminance value (luminance value in the sample image data 66) and the target luminance value (luminance value in the normal area data 65) and the coefficient values ​​including the 14 provisional compensation coefficients based on the 14 sample image data 66 and the normal area data 65 (step S200). In this embodiment, in step S200, as a function representing the correspondence between the luminance difference and the coefficient values, a nonlinear function such as a quadratic function or an exponential function is generated as described above. That is, in step S200, for example, the values ​​of the coefficients a, b, and c in the above formula (2) or (3) are determined.

[0116] Finally, the coefficient calculation unit 525 uses the function (nonlinear function) generated in step S200 to calculate the compensation coefficient 62 to be actually applied to the ink amount compensation process (step S210). Specifically, for the above formula (2) or (3) in which the values ​​of coefficients a, b, and c are fixed, the value of X when Y is 0 is calculated. In this regard, if it is difficult to analytically determine the value of X, an approximation of X may be obtained using, for example, Newton's method, and the approximation may be used as the compensation coefficient 62.

[0117] Incidentally, in step S200, a function (nonlinear function) is generated for each density of the images constituting the compensation coefficient calculation chart 69 (for each of 11 levels of density in this embodiment). Then, in step S210, a compensation coefficient 62 is calculated for each density of the images constituting the compensation coefficient calculation chart 69 using a corresponding function. The compensation coefficient 62 corresponding to a density between a certain level of density and an adjacent level of density can be obtained, for example, by linear interpolation. For example, the compensation coefficient 62 for a density of 62% is obtained by linear interpolation using the compensation coefficient 62 for a density of 60% and the compensation coefficient 62 for a density of 70%.

[0118] In this embodiment, step S100 implements an area setting step, step S110 implements a temporary faulty nozzle setting step, step S120 implements a compensation coefficient calculation chart data generation step, step S130 implements a discharge failure detection chart printing step, step S140 implements a compensation coefficient calculation chart printing step, step S150 implements a discharge failure detection chart imaging step, step S160 implements a compensation coefficient calculation chart imaging step, step S170 implements a discharge failure nozzle detection step, step S180 implements a data extraction step, step S190 implements a data deletion step, step S200 implements a function generation step, and step S210 implements a compensation coefficient calculation step.

[0119] <7. Effects> According to this embodiment, 14 provisional compensation coefficients are prepared as various compensation coefficients, and a function is obtained based on data obtained by applying the 14 provisional compensation coefficients to the ink amount compensation process, which represents the correspondence between the luminance difference between the measured luminance value (the luminance value in the sample image data 66) and the target luminance value (the luminance value in the normal area data 65) and the coefficient value including the 14 provisional compensation coefficients. Then, based on the function, a coefficient value that makes the luminance difference zero is calculated as the compensation coefficient 62 to be applied to the ink amount compensation process. In this way, the compensation coefficient 62 to be actually applied to the ink amount compensation process is determined using a function based on data obtained by applying the provisional compensation coefficients to the ink amount compensation process. Therefore, a suitable compensation coefficient 62 is obtained. As described above, according to this embodiment, defects in a printed image when a nozzle with a discharge defect exists in the inkjet printing device 10 are corrected more accurately than in the past. However, the optical dot gain is different between an area where a white streak appears because the provisional compensation coefficient value is small and an area where a black streak appears because the provisional compensation coefficient value is large, so that a suitable compensation coefficient 62 can be obtained with high accuracy by using a nonlinear function as in this embodiment. In addition, by accurately correcting defects in printed images, the need for reprinting is reduced, which reduces the waste of ink and printing paper 5 and contributes to the achievement of the SDGs (Sustainable Development Goals).

[0120] <8. Variations> Below, a modification of the above embodiment will be described.

[0121] <8.1 Modifications regarding the calculation of compensation coefficient> In the above embodiment, a nonlinear function is generated using the imaging data of the compensation coefficient calculation chart 69, and a coefficient value that makes the luminance difference (the difference between the measured luminance value and the target luminance value) zero based on the nonlinear function is calculated as the compensation coefficient 62 to be applied to the ink amount compensation process. However, the present invention is not limited to this. Therefore, modified examples (first modified example and second modified example) related to the calculation of the compensation coefficient will be described below.

[0122] <8.1.1 First modified example> In this modified example, a linear function is used as the function for calculating the compensation coefficient 62. In general, the time required for processing based on a linear function is shorter than the time required for processing based on a nonlinear function. Therefore, for example, when shortening the processing time is given priority over the accuracy of correcting defects in a printed image, a linear function may be used as the function for calculating the compensation coefficient 62, as in this modified example. More specifically, a linear function expressed by the following formula (4) may be used. Y = aX + b (4) Here, X represents a coefficient value (the value of the compensation coefficient), Y represents a luminance difference, and a and b represent coefficients in the linear function.

[0123] When the graph shown in Fig. 16 is obtained by plotting the luminance difference data obtained for the above-mentioned 14 provisional compensation coefficients on a plane with the horizontal axis representing the coefficient value and the vertical axis representing the luminance difference, according to this modification, in step S200 in Fig. 18, a linear function represented by the straight line labeled 84 in Fig. 32, for example, is generated. Then, in step S210 in Fig. 18, a coefficient value that results in a luminance difference of 0 is found based on the linear function. In the example shown in Fig. 32, the coefficient value that results in a luminance difference of 0 is the value of the black dot portion labeled 85. Therefore, in this case, the value (coefficient value) of the black dot portion is set as the compensation coefficient 62 to be actually applied to the ink amount compensation process.

[0124] When a linear function is used to calculate the compensation coefficient 62 as in this modified example, it is preferable to prepare at least two provisional compensation coefficients.

[0125] <8.1.2 Second modified example> In the above embodiment, there is a risk that the time required for the process of calculating the compensation coefficient 62 actually applied to the ink amount compensation process using a nonlinear function (the process of step S210 in FIG. 18) will be significantly long. Therefore, in this modified example, a nonlinear function and a linear function are used so that a suitable compensation coefficient 62 can be found with high accuracy in a short time. This will be explained in detail below.

[0126] Fig. 33 is a flowchart showing the detailed procedure of the process (the process of step S210 in Fig. 18) for calculating the compensation coefficient 62 to be adopted. In step S200 in Fig. 18, a nonlinear function is generated in the same manner as in the above embodiment.

[0127] First, an approximation value of the coefficient value that makes the luminance difference 0 is calculated based on the nonlinear function generated in step S200 (step S212). Then, the approximation value calculated in step S212 is treated as a temporary compensation coefficient. Note that, for example, the Newton method can be used to calculate the approximation value.

[0128] Next, Q sample image data 66 corresponding to Q provisional compensation coefficients near the provisional compensation coefficient (the approximate value calculated in step S212) are extracted from the 14 sample image data 66 after the completion of step S190 in FIG. 18 (step S214), where Q is an integer of 2 or more. Here, it is assumed that two sample image data 66 are extracted in step S214. At this time, if the position of the part marked with reference numeral 86 in FIG. 34 corresponds to the position of the provisional compensation coefficient, sample image data 66 corresponding to "provisional compensation coefficient: 1.4" and sample image data 66 corresponding to "provisional compensation coefficient: 1.45" are extracted from the 14 sample image data 66. In this way, sample image data 66 corresponding to the maximum provisional compensation coefficient among the provisional compensation coefficients less than the provisional compensation coefficient, and sample image data 66 corresponding to the minimum provisional compensation coefficient among the provisional compensation coefficients greater than the provisional compensation coefficient are extracted.

[0129] Thereafter, a linear function expressing the correspondence between the luminance difference (the difference between the luminance value in the sample image data and the luminance value in the normal area data) and the coefficient value is generated (step S216) based on the Q sample image data 66 extracted in step S214 and the normal area data 65. In the above example, a linear function represented by a straight line indicated by reference numeral 87 in FIG. 35 is generated based on the sample image data 66 corresponding to "provisional compensation coefficient: 1.4" and the sample image data 66 corresponding to "provisional compensation coefficient: 1.45" and the normal area data 65.

[0130] Finally, a coefficient value that makes the luminance difference 0 based on the linear function generated in step S216 is calculated as the compensation coefficient 62 to be actually applied to the ink amount compensation process (step S218). In the example shown in Fig. 35, the coefficient value at the position of the portion marked with reference numeral 88 is the coefficient value that makes the luminance difference 0. Therefore, in this case, the coefficient value at the position of the portion marked with reference numeral 88 is determined as the compensation coefficient 62 to be actually applied to the ink amount compensation process.

[0131] In the above example, two pieces of sample image data 66 are extracted from the Q pieces of sample image data 66 in step S214 in FIG. 33. That is, two pieces of data near the provisional compensation coefficient are extracted in order to obtain a linear function to be used in the final determination of the compensation coefficient 62. However, in order to obtain the linear function, three pieces of data near the provisional compensation coefficient may be extracted, or four or more pieces of data near the provisional compensation coefficient may be extracted. In this regard, when extracting three pieces of data near the provisional compensation coefficient, sample image data 66 corresponding to the maximum provisional compensation coefficient among the provisional compensation coefficients less than the provisional compensation coefficient, sample image data 66 corresponding to the minimum provisional compensation coefficient among the provisional compensation coefficients greater than the provisional compensation coefficient, and sample image data 66 corresponding to the second maximum provisional compensation coefficient among the provisional compensation coefficients less than the provisional compensation coefficient and the second minimum provisional compensation coefficient among the provisional compensation coefficients greater than the provisional compensation coefficient, which is close to the provisional compensation coefficient, are extracted (however, it is assumed that the provisional compensation coefficient does not match any of the provisional compensation coefficients). For example, if the provisional compensation coefficient is 1.43, sample image data 66 corresponding to "provisional compensation coefficient: 1.4", sample image data 66 corresponding to "provisional compensation coefficient: 1.45", and sample image data 66 corresponding to "provisional compensation coefficient: 1.5" are extracted; if the provisional compensation coefficient is 1.42, sample image data 66 corresponding to "provisional compensation coefficient: 1.4", sample image data 66 corresponding to "provisional compensation coefficient: 1.45", and sample image data 66 corresponding to "provisional compensation coefficient: 1.35" are extracted. When extracting four points of data near the provisional compensation coefficient, sample image data 66 corresponding to the maximum provisional compensation coefficient among the provisional compensation coefficients less than the provisional compensation coefficient, sample image data 66 corresponding to the second maximum provisional compensation coefficient among the provisional compensation coefficients less than the provisional compensation coefficient, sample image data 66 corresponding to the minimum provisional compensation coefficient among the provisional compensation coefficients greater than the provisional compensation coefficient, and sample image data 66 corresponding to the second minimum provisional compensation coefficient among the provisional compensation coefficients greater than the provisional compensation coefficient are extracted (however, it is assumed that the provisional compensation coefficient does not match any of the provisional compensation coefficients).When extracting five or more points of data near the provisional compensation coefficient, the sample image data 66 to be extracted can be determined in the same manner as when extracting three points of data near the provisional compensation coefficient or when extracting four points of data near the provisional compensation coefficient.

[0132] Although the type of function generated in step S200 in Fig. 18 is not particularly limited, from the viewpoint of accurately correcting defects in a printed image, a nonlinear function is more preferable than a linear function. Similarly, the type of function generated in step S216 in Fig. 33 is not particularly limited, but from the viewpoint of shortening processing time, a linear function is more preferable than a nonlinear function.

[0133] <8.2 Modifications regarding area setting (third modification)> In the above embodiment, the areas are set so that the 14 comparison areas 76 corresponding to the 14 temporary compensation coefficients are aligned in the main scanning direction (the direction perpendicular to the transport direction of the print paper 5) (see FIGS. 19 and 21). However, the direction in which the multiple comparison areas 76 are aligned is not limited to the main scanning direction, and the multiple comparison areas 76 may be aligned in the transport direction of the print paper 5.

[0134] In this modified example, for example, as shown in Fig. 36, the areas are set so that 14 comparison areas 76(1) to 76(14) corresponding to "provisional compensation coefficient: 1.0" to "provisional compensation coefficient: 1.65" are aligned in the transport direction of the print paper 5. In this case, the print image of the corresponding portion of the compensation coefficient calculation chart 69 will be as shown in schematic form in Fig. 37.

[0135] In the above embodiment, luminance value data corresponding to only one provisional compensation coefficient is obtained for one provisional faulty nozzle based on the imaging data (second imaging data 55) of the compensation coefficient calculation chart 69, but in this modified example, luminance value data corresponding to each of 14 provisional compensation coefficients is obtained for one provisional faulty nozzle based on the imaging data (second imaging data 55) of the compensation coefficient calculation chart 69. Therefore, according to this modified example, it is possible to reduce the number of nozzles set as provisional faulty nozzles compared to the above embodiment.

[0136] <8.3 Modifications regarding a series of processing procedures (fourth modification)> In the above embodiment, it was assumed that the series of processes (see FIG. 18) for determining the compensation coefficient 62, from the process of setting 14 comparison areas and one normal area for each ink ejection head 251 to the final process of calculating the compensation coefficient 62, would all be performed within one printing system (i.e., performed by the user of the inkjet printing apparatus 10). However, this is not limited to this. It is also possible to adopt an operation in which the manufacturer of the inkjet printing apparatus 10 performs the processes up to the generation of the compensation coefficient calculation chart data 53 (i.e., the processes up to step S120 in FIG. 18) and the processes subsequent to the process of printing the ejection defect detection chart 68 (the processes from step S130 onward in FIG. 18) are performed by the user of the inkjet printing apparatus 10.

[0137] FIG. 38 is a flowchart showing the procedure of the process for determining the compensation coefficient 62 in this modified example. First, the discharge failure detection chart 68 is printed (step S300). Next, the ink discharge from each nozzle included in each ink discharge head 251 constituting the recording unit 205 is controlled based on the compensation coefficient calculation chart data 53, thereby printing the compensation coefficient calculation chart 69 (step S310). In this regard, unlike the above embodiment, in this modified example, the compensation coefficient calculation chart data 53 representing the compensation coefficient calculation chart 69 is stored in advance in the auxiliary storage device 121 in the print control device 100. The compensation coefficient calculation chart data 53 is generated by the manufacturer of the inkjet printing device 10 by performing the processes of steps S100 to S120 in FIG. 18. That is, at the manufacturer of the inkjet printing device 10, 14 comparison regions 76 (each comparison region 76 corresponds to a provisional defective nozzle 80) associated with 14 mutually different provisional compensation coefficients and one normal region 81 are set for each ink ejection head 251, and the 14 provisional compensation coefficients are applied to the 14 comparison regions 76 respectively for predetermined image data having a constant density in the main scanning direction to perform ink amount compensation processing, thereby generating the compensation coefficient calculation chart data 53. After the compensation coefficient calculation chart data 53 is generated, processing similar to the processing of steps S150 to S210 in Fig. 18 (processing of steps S320 to S380 in Fig. 38) is performed.

[0138] In this modified example, step S310 realizes a compensation coefficient calculation chart printing step, step S330 realizes a compensation coefficient calculation chart imaging step, step S350 realizes a data extraction step, step S370 realizes a function generation step, and step S380 realizes a compensation coefficient calculation step.

[0139] <9. Supplementary Information> In the above embodiment, the effect of the discharge failure is mitigated by correcting the density values ​​of the nozzles on both sides of the nozzle with the discharge failure (for example, if the nozzle with the reference number 252(p) in FIG. 4 is the nozzle with the discharge failure, the density values ​​of the nozzles with the reference numbers 252(q) and 252(r) in the same figure are corrected). However, the nozzle whose density value is corrected may be a nozzle in the vicinity of the nozzle with the discharge failure in the main scanning direction, and does not necessarily have to be adjacent to the nozzle with the discharge failure. For example, the density value of a nozzle located 2 to 3 nozzles away from the nozzle with the discharge failure in the main scanning direction may be corrected. In addition, the nozzle whose density value is corrected does not have to be one nozzle on one side of the main scanning direction, but may be two or more nozzles. Furthermore, when correcting the density values ​​of two or more nozzles on one side of the main scanning direction, a nozzle whose density value is reduced may be included in those nozzles.

[0140] In the above embodiment, the CPU 111 as a processor executes the print control program 13 including the compensation coefficient determination program as a subprogram, thereby realizing various functions of the print control device 100. However, the present invention is not limited to the configuration using only one CPU 111 as shown in FIG. 5. A configuration using multiple processors, such as a configuration using multiple CPUs, can also be adopted. As a processor, in addition to a CPU, an MPU (Micro Processing Unit), a GPU (Graphics Processing Unit), a DSP (Digital Signal Processor), etc. can also be adopted. In addition, a combination of multiple types of processors can also be used. For example, with respect to the components shown in FIG. 11, some components and the remaining components can be realized by different processors. Furthermore, a configuration including an FPGA (Field-Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit) can also be adopted.

[0141] <10.Other> In the above embodiment (including the modified example), the inkjet printing device 10 performs color printing. However, the present invention is not limited to this, and an inkjet printing device that performs monochrome printing may also be used.

[0142] In addition, in the above embodiment (including the modified example), the inkjet printing device 10 using water-based ink is adopted. However, the present invention is not limited to this, and an inkjet printing device using UV ink (ultraviolet-curable ink) such as an inkjet printing device for label printing may be adopted. In this case, an ultraviolet irradiation mechanism for curing the UV ink on the printing paper 5 by irradiating ultraviolet light is provided inside the printing mechanism 201 (see FIG. 2) instead of the drying mechanism 206. In addition, the printing medium is not limited to a paper-based medium (printing paper), and films such as OPP (Oriented Polypropylene) or PET (Poly Ethylene Terephthalate) can also be used. In addition, in the above embodiment (including the modified example), a function representing the curve shown in FIG. 17 and the like is created based on the imaging data (luminance value data) obtained from the in-line scanner 40. However, the unit system of the function representing the curve shown in FIG. 17 and the like does not necessarily have to be the luminance value. For example, the luminance value may be converted into a density value, and a function representing the curve shown in FIG. 17 and the like may be created based on the density value. [Explanation of symbols]

[0143] 10...Inkjet printing device 40…Inline scanner 64,66...Sample image data 65…Normal area data 68…Discharge failure detection chart 69...Compensation coefficient calculation chart 76…Comparison area 80...Temporary defective nozzle 81…normal area 100...Print control device 155...Compensation coefficient calculation chart data generation processing unit 156...Correction coefficient calculation unit 157...Print data correction unit 200…Printing machine body 201...Printing mechanism 205…Recording section 251...Ink ejection head 510...Shading data generation unit 520...Compensation coefficient calculation unit 522...Sample image data extraction unit 524...Function generator 525...Coefficient calculation section 530...Shading data correction unit

Claims

1. 1. A method for determining a compensation coefficient to be applied to an ink amount compensation process for compensating for an amount of ink ejected onto a printing medium when a nozzle in an ejection failure state exists in a printing device having a plurality of nozzles that eject ink onto a printing medium, comprising: a region setting step of setting a plurality of divided regions including K comparison regions corresponding to K mutually different provisional compensation coefficients, where K is an integer of 2 or more, and normal regions that are not influenced by provisional defective nozzles that are assumed to be in a hypothetical discharge defective state; a tentative defective nozzle setting step of setting the tentative defective nozzle for each of the K comparison regions; a compensation coefficient calculation chart data generating step of generating compensation coefficient calculation chart data representing a compensation coefficient calculation chart for determining the compensation coefficients by applying the K temporary compensation coefficients to the K comparison areas for predetermined image data having a constant density, a compensation coefficient calculation chart printing step of printing the compensation coefficient calculation chart by ejecting ink from the plurality of nozzles based on the compensation coefficient calculation chart data; a compensation coefficient calculation chart imaging step of acquiring imaging data, which is brightness value data, by imaging the compensation coefficient calculation chart printed in the compensation coefficient calculation chart printing step; a data extraction step of extracting, from the imaging data obtained in the compensation coefficient calculation chart imaging step, K sample image data pieces each including one or more luminance value data, which are data corresponding to each of the K comparison areas and correspond to the positions of the provisional defective nozzles, and normal area data which is luminance value data corresponding to the normal area; a function generating step of generating a function representing a correspondence relationship between a luminance difference between a luminance value in the sample image data and a luminance value in the normal area data, and a coefficient value including the K provisional compensation coefficients, based on the K sample image data and the normal area data; a compensation coefficient calculation step of calculating the compensation coefficient by using the function generated in the function generation step; A compensation coefficient determination method comprising:

2. The K is an integer of 3 or more, 2. The compensation coefficient determining method according to claim 1, wherein the function generated in said function generating step is a nonlinear function.

3. The compensation coefficient calculation step includes: calculating an approximation of a coefficient value that makes the luminance difference zero based on the nonlinear function; extracting Q sample image data corresponding to Q provisional compensation coefficients near the approximate value from the K sample image data, where Q is an integer equal to or greater than 2; generating a linear function representing a correspondence relationship between the luminance difference and the coefficient value based on the Q sample image data and the normal area data; calculating a coefficient value that makes the luminance difference zero based on the linear function as the compensation coefficient; The method of claim 2 , further comprising:

4. The K is an integer of 2 or more, 2. The compensation coefficient determining method according to claim 1, wherein the function generated in said function generating step is a linear function.

5. 2. The compensation coefficient determination method according to claim 1, wherein in said compensation coefficient calculation step, a coefficient value that makes said luminance difference zero is calculated as said compensation coefficient.

6. In the tentative defective nozzle setting step, N tentative defective nozzles are set for each of the K comparison regions, where N is an integer equal to or greater than 2; 2. The compensation coefficient determination method according to claim 1, wherein each of the K sample image data includes data on N luminance values ​​corresponding to the positions of the N provisional defective nozzles.

7. the compensation coefficient calculation chart is configured with J sheets for each ink color, where J is an integer equal to or greater than 2; 2. The compensation coefficient determination method according to claim 1, wherein each of said K sample image data includes data of J luminance values ​​corresponding to each of said J sheets.

8. In the tentative defective nozzle setting step, N tentative defective nozzles are set for each of the K comparison regions, where N is an integer equal to or greater than 2; the compensation coefficient calculation chart is configured with J sheets for each ink color, where J is an integer equal to or greater than 2; 2. The compensation coefficient determination method according to claim 1, wherein each of the K sample image data includes (N x J) pieces of brightness value data corresponding to all combinations of the N provisional defective nozzles and the J sheets.

9. 2. The compensation coefficient determination method according to claim 1, wherein in the region setting step, the plurality of divided regions are set so that the K comparison regions are aligned in a direction perpendicular to a transport direction of the printing medium.

10. 2. The compensation coefficient determination method according to claim 1, wherein in said region setting step, said plurality of divided regions are set so that said K comparison regions are aligned in a transport direction of said printing medium.

11. the compensation coefficient calculation chart is made up of M density regions corresponding to M different densities in a transport direction of the print medium, where M is an integer equal to or greater than 2; In the function generating step, a function is generated for each concentration, 2. The compensation coefficient determination method according to claim 1, wherein in said compensation coefficient calculation step, said compensation coefficient is calculated for each concentration by using a corresponding function.

12. a discharge failure detection chart printing step of printing a discharge failure detection chart for detecting nozzles in a discharge failure state by discharging ink from the plurality of nozzles; a discharge failure detection chart imaging step of imaging the discharge failure detection chart printed in the discharge failure detection chart printing step; a discharge failure nozzle detection step of detecting a nozzle having a discharge failure based on the imaging data obtained in the discharge failure detection chart imaging step; a data deleting step of deleting brightness value data corresponding to the positions of true defective nozzles, which are nozzles detected in the ejection defective nozzle detection step, from the K pieces of sample image data extracted in the data extraction step; Further comprising:

2. The compensation coefficient determination method according to claim 1, wherein the function generation step uses K pieces of sample image data after the data of brightness values ​​corresponding to the positions of the true faulty nozzles have been deleted by the data deletion step.

13. A printing method using a printing device having a plurality of nozzles that eject ink onto a printing medium, comprising: a shading data generating step of generating shading data used in a shading correction process that compensates for variations in the amount of ink ejected among the plurality of nozzles; a shading data correcting step of correcting the shading data by performing the ink amount compensation process on the shading data using a compensation coefficient determined by the compensation coefficient determination method according to any one of claims 1 to 12; a print data generating step of generating print data by performing a rasterization process on the input data; a shading correction step of correcting the print data by performing the shading correction process on the print data using the shading data corrected in the shading data correction step; a halftone processing step of generating halftone image data by performing halftone processing on the print data corrected in the shading correction step; an ink ejection step of ejecting ink from the plurality of nozzles based on the halftone image data; A printing method comprising:

14. A printing device comprising a plurality of nozzles which eject ink onto a printing medium, an imaging device which captures a print image, and a control unit which controls the ejection of ink from the plurality of nozzles and the capturing of the print image by the imaging device, the printing device performing an ink amount compensation process during printing which compensates for the amount of ink ejected onto the printing medium when a nozzle having an ejection defect is present, The control unit is an area setting process for setting a plurality of divided areas including K comparison areas corresponding to K different provisional compensation coefficients, where K is an integer of 2 or more, and normal areas that are not affected by provisional defective nozzles that are assumed to be in a hypothetical discharge defective state; a tentative defective nozzle setting process for setting the tentative defective nozzle for each of the K comparison regions; a compensation coefficient calculation chart data generation process for generating compensation coefficient calculation chart data representing a compensation coefficient calculation chart for determining the compensation coefficients by performing the ink amount compensation process by applying the K temporary compensation coefficients to the K comparison areas for predetermined image data having a constant density; a compensation coefficient calculation chart printing process for controlling the ejection of ink from the plurality of nozzles based on the compensation coefficient calculation chart data so that the compensation coefficient calculation chart is printed; a compensation coefficient calculation chart imaging process for imaging the compensation coefficient calculation chart printed in the compensation coefficient calculation chart printing process by the imaging device; a data extraction process for extracting, from the imaging data obtained in the compensation coefficient calculation chart imaging process, K pieces of sample image data, each of which includes one or more pieces of luminance value data, which is data corresponding to each of the K comparison areas and corresponds to the positions of the provisional defective nozzles, and normal area data, which is data of luminance values ​​corresponding to the normal areas; a function generating process for generating a function representing a correspondence relationship between a luminance difference between a luminance value in the sample image data and a luminance value in the normal area data, and a coefficient value including the K provisional compensation coefficients, based on the K sample image data and the normal area data; a compensation coefficient calculation process for calculating the compensation coefficient by using the function generated in the function generation process; A printing device that executes the above.

15. 1. A compensation coefficient determination program for determining a compensation coefficient to be applied to an ink amount compensation process for compensating for an amount of ink ejected onto a printing medium when a nozzle in an ejection failure state is present in a printing device having a plurality of nozzles that eject ink onto a printing medium and an imaging device that images a print image, the compensation coefficient determination program comprising: A computer included in the printing device, a region setting step of setting a plurality of divided regions including K comparison regions corresponding to K mutually different provisional compensation coefficients, where K is an integer of 2 or more, and normal regions that are not influenced by provisional defective nozzles that are assumed to be in a hypothetical discharge defective state; a tentative defective nozzle setting step of setting the tentative defective nozzle for each of the K comparison regions; a compensation coefficient calculation chart data generating step of generating compensation coefficient calculation chart data representing a compensation coefficient calculation chart for determining the compensation coefficients by applying the K temporary compensation coefficients to the K comparison areas for predetermined image data having a constant density, a compensation coefficient calculation chart printing step of controlling the ejection of ink from the plurality of nozzles based on the compensation coefficient calculation chart data so that the compensation coefficient calculation chart is printed; a compensation coefficient calculation chart imaging step of imaging the compensation coefficient calculation chart printed in the compensation coefficient calculation chart printing step with the imaging device; a data extraction step of extracting, from the imaging data obtained in the compensation coefficient calculation chart imaging step, K sample image data pieces each including one or more luminance value data, which are data corresponding to each of the K comparison areas and correspond to the positions of the provisional defective nozzles, and normal area data which is luminance value data corresponding to the normal area; a function generating step of generating a function representing a correspondence relationship between a luminance difference between a luminance value in the sample image data and a luminance value in the normal area data, and a coefficient value including the K provisional compensation coefficients, based on the K sample image data and the normal area data; a compensation coefficient calculation step of calculating the compensation coefficient by using the function generated in the function generation step; A compensation coefficient determination program for executing the above.

16. 1. A method for determining a compensation coefficient to be applied to an ink amount compensation process for compensating for an amount of ink ejected onto a printing medium when a nozzle in an ejection failure state exists in a printing device having a plurality of nozzles that eject ink onto a printing medium, comprising: a compensation coefficient calculation chart printing step of printing a compensation coefficient calculation chart for determining the compensation coefficients by ejecting ink from the plurality of nozzles based on compensation coefficient calculation chart data obtained by applying the K temporary compensation coefficients to predetermined image data having a constant density, in a state in which K comparison regions corresponding to K different temporary compensation coefficients, where K is an integer of 2 or greater, and each comparison region corresponding to a temporary defective nozzle that is virtually set to be in an ejection defective state, and a normal region that is not affected by the temporary defective nozzle are set; a compensation coefficient calculation chart imaging step of acquiring imaging data, which is brightness value data, by imaging the compensation coefficient calculation chart printed in the compensation coefficient calculation chart printing step; a data extraction step of extracting, from the imaging data obtained in the compensation coefficient calculation chart imaging step, K sample image data pieces each including one or more luminance value data, which are data corresponding to each of the K comparison areas and correspond to the positions of the provisional defective nozzles, and normal area data which is luminance value data corresponding to the normal area; a function generating step of generating a function representing a correspondence relationship between a luminance difference between a luminance value in the sample image data and a luminance value in the normal area data, and a coefficient value including the K provisional compensation coefficients, based on the K sample image data and the normal area data; a compensation coefficient calculation step of calculating the compensation coefficient by using the function generated in the function generation step; A compensation coefficient determination method comprising:

17. A printing device comprising a plurality of nozzles which eject ink onto a printing medium, an imaging device which captures a print image, and a control unit which controls the ejection of ink from the plurality of nozzles and the capturing of the print image by the imaging device, the printing device performing an ink amount compensation process during printing which compensates for the amount of ink ejected onto the printing medium when a nozzle having an ejection defect is present, The control unit is a compensation coefficient calculation chart printing process for controlling the ejection of ink from the plurality of nozzles based on compensation coefficient calculation chart data obtained by applying the ink amount compensation process to predetermined image data having a constant density by applying the K provisional compensation coefficients to the K comparison areas in a state in which a plurality of divided areas are set, the K comparison areas corresponding to K different provisional compensation coefficients, where K is an integer of 2 or greater, and each comparison area corresponding to a provisional defective nozzle that is virtually set to be in an ejection defective state, and normal areas that are not affected by the provisional defective nozzles, so that a compensation coefficient calculation chart for determining the compensation coefficients is printed; a compensation coefficient calculation chart imaging process for imaging the compensation coefficient calculation chart printed in the compensation coefficient calculation chart printing process by the imaging device; a data extraction process for extracting, from the imaging data obtained in the compensation coefficient calculation chart imaging process, K pieces of sample image data, each of which includes one or more pieces of luminance value data, which is data corresponding to each of the K comparison areas and corresponds to the positions of the provisional defective nozzles, and normal area data, which is data of luminance values ​​corresponding to the normal areas; a function generating process for generating a function representing a correspondence relationship between a luminance difference between a luminance value in the sample image data and a luminance value in the normal area data, and a coefficient value including the K provisional compensation coefficients, based on the K sample image data and the normal area data; a compensation coefficient calculation process for calculating the compensation coefficient by using the function generated in the function generation process; A printing device that executes the above.

18. 1. A compensation coefficient determination program for determining a compensation coefficient to be applied to an ink amount compensation process for compensating for an amount of ink ejected onto a printing medium when a nozzle in an ejection failure state is present in a printing device having a plurality of nozzles that eject ink onto a printing medium and an imaging device that images a print image, the compensation coefficient determination program comprising: A computer included in the printing device, a compensation coefficient calculation chart printing step of controlling the ejection of ink from the plurality of nozzles based on compensation coefficient calculation chart data obtained by applying the ink amount compensation process to predetermined image data having a constant density by applying the K provisional compensation coefficients to the K comparison areas in a state in which a plurality of divided areas are set, the K comparison areas corresponding to K different provisional compensation coefficients, where K is an integer of 2 or greater, and each comparison area corresponding to a provisional defective nozzle that is virtually set to be in an ejection defective state, and normal areas that are not affected by the provisional defective nozzles, so that a compensation coefficient calculation chart for determining the compensation coefficients is printed; a compensation coefficient calculation chart imaging step of imaging the compensation coefficient calculation chart printed in the compensation coefficient calculation chart printing step with the imaging device; a data extraction step of extracting, from the imaging data obtained in the compensation coefficient calculation chart imaging step, K sample image data pieces each including one or more luminance value data, which are data corresponding to each of the K comparison areas and correspond to the positions of the provisional defective nozzles, and normal area data which is luminance value data corresponding to the normal area; a function generating step of generating a function representing a correspondence relationship between a luminance difference between a luminance value in the sample image data and a luminance value in the normal area data, and a coefficient value including the K provisional compensation coefficients, based on the K sample image data and the normal area data; a compensation coefficient calculation step of calculating the compensation coefficient by using the function generated in the function generation step; A compensation coefficient determination program for executing the above.

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