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

Abstract

To provide an inkjet printing device, which is configured to be able to suppress defect of a printed image when there is a nozzle which cannot properly discharges, more effectively than before.SOLUTION: An area corresponding to a width of each ink discharge head 251 is divided into K-comparison areas corresponding to K-temporary compensation coefficients which are different from each other (S100), and a plurality of temporary defective nozzles are set for each comparison area (S110), where K is two or more integers. K-sample image data are extracted from photographed images of a compensation coefficient calculation chart obtained by applying the K-temporary compensation coefficients to the K-comparison areas respectively to perform ink amount compensation processing (S180), and data that are influenced by a nozzle that cannot properly discharges ink are deleted from the K-sample image data (S190). A temporary compensation coefficient that is adopted as a compensation coefficient is determined, on the basis of K-comparison data obtained through the above steps (S200).SELECTED DRAWING: Figure 17

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 are widely known that perform printing by ejecting ink onto a printing medium such as printing paper. In an inkjet printing device, if the ejection interval becomes long, during the period in which printing is being performed, the ink may dry due to evaporation of the solvent near the nozzle, air bubbles may get mixed in the nozzle, dust may adhere to the nozzle, and so on. In other words, ejection problems may occur in the nozzle.

[0003] Nozzle ejection defects can be roughly classified into three types, which will be described with reference to Figs. 40 to 42. Figs. 40 to 42 show a part of a printed image obtained by printing a step-like regular pattern (test pattern), and the black shaded parts are the parts where ink is applied. In Fig. 40, the dotted line part with the reference number 91 has no ink applied to the part where ink should be applied. Hereinafter, such an ejection defect is referred to as "non-ejection". In Fig. 41, the dotted line part with the reference number 92 has a shape of the part where ink is applied 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 part where ink is applied spreads in the main scanning direction (the direction perpendicular to the conveyance direction of the printing paper). In Fig. 42, the dotted line part with the reference number 93 has ink applied to a part that is shifted in the main scanning direction from the part 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 contains 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. The variation in the amount of ink ejected causes uneven density in the printed image. Therefore, shading correction processing has been conventionally performed on the print data to compensate for such variation in the amount of ink ejected.

[0006] Regarding the above-mentioned alternative droplet ejection, Japanese Patent Application Laid-Open No. 2021-160200 discloses a technique for determining a distribution ratio (the ratio at which the correction value of a nozzle with a discharge defect is distributed to adjacent nozzles on both sides) using a dedicated chart (chart for obtaining a distribution ratio) (see embodiment 2). According to this technique, a distribution ratio obtaining chart is printed in which the gradation value of a nozzle is intentionally assigned "0" at regular intervals, and the gradation value is changed at four different distribution ratios in the nozzles on both sides of the nozzle (intentionally defective nozzle) to which the gradation value is assigned. Then, a distribution ratio according to the gradation value is determined based on a scanned image of the distribution ratio obtaining chart. At that time, a distribution ratio that provides the most uniform density when a known spatial filter is applied to the scanned image is selected for each gradation value. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent Publication No. 2021-160200 Summary of the Invention [Problem to be solved by the invention]

[0008] However, according to the technology disclosed in JP 2021-160200 A, it is assumed that when a nozzle with a defective discharge exists, the defective discharge state is eliminated by cleaning. Therefore, when a nozzle with a defective discharge exists whose defective discharge state cannot be eliminated by cleaning, the technology disclosed in JP 2021-160200 A cannot be applied. In addition, it is possible to correct the gradation values ​​at positions corresponding to the nozzles on both sides of the defective discharge nozzle using a coefficient predetermined according to the gradation value at the position corresponding to the defective discharge nozzle, but the suitable coefficient varies depending on the type of printing paper and printing conditions. Therefore, defects in the printed image cannot be effectively suppressed.

[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 more effectively suppressing the occurrence of defects in printed images when a faulty ejection nozzle is present 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 that is 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 dividing step of dividing a predetermined region in a direction perpendicular to the transport direction of the print medium into a plurality of divided regions including K comparison regions corresponding to K different provisional compensation coefficients, where K is an integer equal to or greater than 2; a provisional defective nozzle setting step of setting a plurality of provisional defective nozzles which are assumed to be in a defective discharge state from among two or more corresponding nozzles 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 provisional compensation coefficients to the K comparison areas respectively to predetermined image data having a constant density in a direction perpendicular to the transport direction of the print medium, 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 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 discharge failure detection chart imaging step of imaging the discharge failure detection chart printed in the discharge failure detection chart printing step; a compensation coefficient calculation chart imaging step of imaging the compensation coefficient calculation chart printed in the compensation coefficient calculation chart printing step; a discharge failure nozzle detection step of detecting a nozzle having a discharge failure based on first imaging data which is imaging data obtained in the discharge failure detection chart imaging step; a sample image data extraction step of extracting K sample image data corresponding to the K comparison regions from second imaging data which is imaging data obtained in the compensation coefficient calculation chart imaging step; a data deleting step of generating K pieces of comparison data by deleting data in a range corresponding to the position of the true defective nozzle, which is the nozzle detected in the ejection defective nozzle detection step, from the K pieces of sample image data; a coefficient determination step of determining one of the K provisional compensation coefficients as the compensation coefficient based on the K pieces of comparison data; The present invention is characterized by comprising:

[0011] The second invention is the first invention, the plurality of divided regions includes, in addition to the K comparison regions, a normal region that is not affected by the provisional defective nozzle, In the sample image data extraction step, normal area data corresponding to the normal area is further extracted from the second imaging data, In the coefficient determining step, the compensation coefficient is determined based on the K pieces of comparison data and the normal region data.

[0012] The third invention relates to the second invention, In the coefficient determination step, an average value for each of the K comparison data and an average value for the normal area data are calculated, and the average value for the normal area data is set as a target value, and a provisional compensation coefficient corresponding to the comparison area corresponding to the comparison data for which an average value closest to the target value is obtained among the K comparison data is determined as the compensation coefficient.

[0013] The fourth invention relates to the third invention, wherein N is an integer equal to or greater than 2, and each of the K comparison regions corresponds to N provisional defective nozzles; Each of the K sample image data includes N partial image data corresponding to the N provisional defective nozzles, In the data deleting step, for each of the K pieces of sample image data, partial image data corresponding to an area affected by the true defective nozzle is deleted from the N pieces of partial image data.

[0014] The fifth invention relates to the second invention, wherein N is an integer equal to or greater than 2, and each of the K comparison regions corresponds to N provisional defective nozzles; In the data deletion step, data of P positions influenced by the true faulty nozzle among the positions of the N tentative faulty nozzles is deleted for each of the K pieces of sample image data, where P is an integer equal to or greater than 1 and equal to or less than (N-1); In the coefficient determination step, for each of the K pieces of comparison data, a peak average value, which is the average value of the data for (NP) positions among the data for the positions of the N pieces of provisional defective nozzles excluding the data for the P positions deleted in the data deletion step, and an average value for the normal area data are calculated, and the average value for the normal area data is set as a target value, and a provisional compensation coefficient associated with the comparison area corresponding to the comparison data for which the peak average value closest to the target value was obtained among the K pieces of comparison data is determined as the compensation coefficient.

[0015] The sixth aspect of the present invention relates to the first aspect of the present invention, In the coefficient determination step, a provisional compensation coefficient associated with a comparison area corresponding to the comparison data having the smallest difference between the maximum value and the minimum value among the K comparison data is determined as the compensation coefficient.

[0016] The seventh aspect of the present invention is the first aspect of the present invention, the printing device includes a plurality of print heads, each print head including a portion of the plurality of nozzles; The K comparison regions are provided for each print head, the K temporary compensation coefficients corresponding to the K comparison regions are common among the plurality of print heads; The sample image data extraction step is characterized in that one sample image data is extracted by extracting data of multiple comparison areas corresponding to the same provisional compensation coefficient among the multiple print heads from the second imaging data.

[0017] The eighth aspect of the present invention is the first aspect of the present invention, The compensation coefficient calculation chart is characterized in that it is made up of a plurality of sheets, one for each ink color.

[0018] A ninth aspect of the present invention relates to the eighth aspect of the present invention, In the tentative defective nozzle setting step, a different nozzle is set as the tentative defective nozzle for each of the K comparison regions for each sheet.

[0019] A tenth aspect of the present invention relates to 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; The compensation coefficient is determined for each concentration in the coefficient determination step.

[0020] An eleventh 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 tenth 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:

[0021] A twelfth aspect of the present invention relates to the eleventh aspect of the present invention, The nozzle adjacent to the true faulty nozzle is defined as an adjacent nozzle, the compensation coefficient is represented by C, which is a value between 0 and 1, the position value corresponding to the true faulty nozzle in the shading data before the shading data correction step is executed is represented by Vf, the position value corresponding to the adjacent nozzle in the shading data before the shading data correction step is executed is represented by Vn, and the position value corresponding to the adjacent nozzle in the shading data after the shading data correction step is executed is represented by V, where V is expressed by the following formula. V = Vn + Vf × C

[0022] A thirteenth aspect of the present invention relates to the twelfth aspect of the present invention, The value of a position in the shading data corresponding to the truly defective nozzle after the shading data correction step is executed is characterized by being 0.

[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 in an ejection failure state is present, The control unit is an area division process for dividing a predetermined area in a direction perpendicular to the transport direction of the print medium into a plurality of divided areas including K comparison areas corresponding to K different provisional compensation coefficients, where K is an integer equal to or greater than 2; a provisional defective nozzle setting process for setting a plurality of provisional defective nozzles which are assumed to be in a defective discharge state from among two or more corresponding nozzles for each of the K comparison regions; a compensation coefficient calculation chart data generation process that generates 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 in a direction perpendicular to the transport direction of the print medium; a discharge failure detection chart printing process for controlling the ejection of ink from the plurality of nozzles so as to print a discharge failure detection chart for detecting nozzles in a discharge failure state; 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 discharge failure detection chart imaging process for imaging the discharge failure detection chart printed in the discharge failure detection chart printing step with the imaging device; a compensation coefficient calculation chart imaging process for imaging the compensation coefficient calculation chart printed in the compensation coefficient calculation chart printing step with the imaging device; a defective nozzle detection process for detecting a nozzle having a defective discharge state based on first imaging data, which is imaging data obtained in the defective discharge detection chart imaging step; a sample image data extraction process for extracting K sample image data corresponding to the K comparison regions from second imaging data, which is imaging data obtained in the compensation coefficient calculation chart imaging step; a data deletion process for generating K pieces of comparison data by deleting data in a range corresponding to the position of a true defective nozzle, which is a nozzle detected in the ejection defective nozzle detection process, from the K pieces of sample image data; a coefficient determination process for determining one of the K provisional compensation coefficients as the compensation coefficient based on the K pieces of comparison data; 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 dividing step of dividing a predetermined region in a direction perpendicular to the transport direction of the print medium into a plurality of divided regions including K comparison regions corresponding to K different provisional compensation coefficients, where K is an integer equal to or greater than 2; a provisional defective nozzle setting step of setting a plurality of provisional defective nozzles which are assumed to be in a defective discharge state from among two or more corresponding nozzles 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 provisional compensation coefficients to the K comparison areas respectively to predetermined image data having a constant density in a direction perpendicular to the transport direction of the print medium, a discharge failure detection chart printing step of controlling the discharge of ink from the plurality of nozzles so as to print a discharge failure detection chart for detecting nozzles in a discharge failure state; 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 discharge failure detection chart imaging step of imaging the discharge failure detection chart printed in the discharge failure detection chart printing step with the imaging device; 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 discharge failure nozzle detection step of detecting a nozzle having a discharge failure based on first imaging data which is imaging data obtained in the discharge failure detection chart imaging step; a sample image data extraction step of extracting K sample image data corresponding to the K comparison regions from second imaging data which is imaging data obtained in the compensation coefficient calculation chart imaging step; a data deleting step of generating K pieces of comparison data by deleting data in a range corresponding to the position of the true defective nozzle, which is the nozzle detected in the ejection defective nozzle detection step, from the K pieces of sample image data; a coefficient determination step of determining one of the K provisional compensation coefficients as the compensation coefficient based on the K pieces of comparison data; The present invention is characterized in that the above-mentioned is executed.

[0025] A sixteenth aspect of the present invention is a compensation coefficient 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 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 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 the K comparison areas to predetermined image data having a constant density in the direction perpendicular to the transport direction of the printing medium, in a state in which a predetermined area is divided into a plurality of divided areas including K comparison areas each associated with a plurality of temporarily defective nozzles that are virtually set to a defective ejection state, where K is an integer of 2 or more; a discharge failure detection chart imaging step of imaging the discharge failure detection chart printed in the discharge failure detection chart printing step; a compensation coefficient calculation chart imaging step of imaging the compensation coefficient calculation chart printed in the compensation coefficient calculation chart printing step; a discharge failure nozzle detection step of detecting a nozzle having a discharge failure based on first imaging data which is imaging data obtained in the discharge failure detection chart imaging step; a sample image data extraction step of extracting K sample image data corresponding to the K comparison regions from second imaging data which is imaging data obtained in the compensation coefficient calculation chart imaging step; a data deleting step of generating K pieces of comparison data by deleting data in a range corresponding to the position of the true defective nozzle, which is the nozzle detected in the ejection defective nozzle detection step, from the K pieces of sample image data; a coefficient determination step of determining one of the K provisional compensation coefficients as the compensation coefficient based on the K pieces of comparison data; 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 in an ejection failure state is present, The control unit is a discharge failure detection chart printing process for controlling the ejection of ink from the plurality of nozzles so as to print a discharge failure detection chart for detecting nozzles in a discharge failure state; 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 K provisional compensation coefficients to the K comparison areas for predetermined image data having a constant density in the direction perpendicular to the transport direction of the printing medium, in a state in which a predetermined area is divided into a plurality of divided areas including K comparison areas corresponding to K different provisional compensation coefficients, the K comparison areas corresponding to a plurality of provisional defective nozzles that are virtually set to a defective ejection state, where K is an integer equal to or greater than 2, so that a compensation coefficient calculation chart for determining the compensation coefficients is printed; a discharge failure detection chart imaging process for imaging the discharge failure detection chart printed in the discharge failure detection chart printing process by the imaging device; 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 discharge failure nozzle detection process for detecting a nozzle having a discharge failure based on first imaging data, which is imaging data obtained in the discharge failure detection chart imaging process; a sample image data extraction process for extracting K sample image data corresponding to the K comparison regions from second imaging data, which is imaging data obtained in the compensation coefficient calculation chart imaging process; a data deletion process for generating K pieces of comparison data by deleting data in a range corresponding to the position of a true defective nozzle, which is a nozzle detected in the ejection defective nozzle detection process, from the K pieces of sample image data; a coefficient determination process for determining one of the K provisional compensation coefficients as the compensation coefficient based on the K pieces of comparison data; 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 discharge failure detection chart printing step of controlling the discharge of ink from the plurality of nozzles so as to print a discharge failure detection chart for detecting nozzles in a discharge failure state; 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 K provisional compensation coefficients to the K comparison areas for predetermined image data having a constant density in the direction orthogonal to the transport direction of the printing medium, in a state in which a predetermined area is divided into a plurality of divided areas including K comparison areas corresponding to K different provisional compensation coefficients, the K comparison areas corresponding to a plurality of provisional defective nozzles that are virtually set to a defective ejection state, where K is an integer equal to or greater than 2, so that a compensation coefficient calculation chart for determining the compensation coefficients is printed; a discharge failure detection chart imaging step of imaging the discharge failure detection chart printed in the discharge failure detection chart printing step with the imaging device; 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 discharge failure nozzle detection step of detecting a nozzle having a discharge failure based on first imaging data which is imaging data obtained in the discharge failure detection chart imaging step; a sample image data extraction step of extracting K sample image data corresponding to the K comparison regions from second imaging data which is imaging data obtained in the compensation coefficient calculation chart imaging step; a data deleting step of generating K pieces of comparison data by deleting data in a range corresponding to the position of the true defective nozzle, which is the nozzle detected in the ejection defective nozzle detection step, from the K pieces of sample image data; a coefficient determination step of determining one of the K provisional compensation coefficients as the compensation coefficient based on the K pieces of comparison data; The present invention is characterized in that the above-mentioned is executed. Effect of the Invention

[0028] According to the first aspect of the present invention, a provisional compensation coefficient to be actually applied as a compensation coefficient to the ink amount compensation process is determined from among the provisional compensation coefficients based on data obtained by applying a plurality of provisional compensation coefficients to the ink amount compensation process (a process for compensating for the amount of ink discharged to a printing medium when a discharge-faulty nozzle is present). In this way, the compensation coefficient is determined based on data obtained by actually performing the ink amount compensation process. In addition, prior to the final determination of the compensation coefficient, data of the area affected by the discharge-faulty nozzle is deleted. As a result, a suitable compensation coefficient is determined with high accuracy, and the occurrence of defects in a printed image when a discharge-faulty nozzle is present is more effectively suppressed than in the past. In addition, wasteful consumption of ink and printing media is reduced, which can contribute to the achievement of the SDGs (Sustainable Development Goals).

[0029] According to the second aspect of the present invention, it is possible to determine the compensation coefficient taking into consideration the density obtained in an area where there are no ejection-failed nozzles.

[0030] According to the third aspect of the present invention, even if there is a discharge-fault nozzle, it is possible to output a print image having a density approximately equal to that when there is no discharge-fault nozzle.

[0031] According to the fourth aspect of the invention, the same effects as those of the third aspect of the invention can be obtained.

[0032] According to the fifth aspect of the present invention, the compensation coefficient is finally determined based on a relatively small number of data, thereby reducing the processing load.

[0033] According to the sixth aspect of the present invention, the compensation coefficient to be actually applied to the ink amount compensation process is determined without comparing a plurality of comparison data with data in the normal region.

[0034] According to the seventh aspect of the present invention, it is possible to determine the compensation coefficient to be actually applied to the ink amount compensation process so as to eliminate the effects of variations in characteristics between a plurality of print heads.

[0035] According to the eighth aspect of the invention, the same effects as those of the first aspect of the invention can be obtained.

[0036] According to the ninth aspect of the present invention, a different nozzle is set as the provisional defective nozzle for each sheet, so that the influence of variations in the ink ejection amount among a plurality of nozzles is more effectively suppressed.

[0037] According to the tenth aspect of the present invention, a compensation coefficient is determined for each of a plurality of densities, so that the occurrence of defects in the printed image is suppressed more effectively than in the past, regardless of the density of the printed image in the area corresponding to the ejection-failed nozzle.

[0038] According to the eleventh 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.

[0039] According to the twelfth aspect of the present invention, the ink that should be ejected from the ejection-failed nozzle is instead ejected from a nozzle adjacent to the ejection-failed nozzle, so that it is possible to more reliably prevent defects from occurring in the printed image.

[0040] According to the thirteenth aspect of the present invention, the same effects as those of the twelfth aspect of the present invention can be obtained.

[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] 8A to 8C 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] 11 is a graph showing an example of the relationship between a provisional compensation coefficient and an average luminance value in the embodiment. [Figure 17] 10 is a flowchart showing a processing procedure for determining a compensation coefficient in the embodiment. [Figure 18]10A and 10B are diagrams for explaining setting of a provisionally defective nozzle in the embodiment. [Figure 19] FIG. 4 is a schematic diagram illustrating an entire compensation coefficient calculation chart in the embodiment. [Figure 20] FIG. 2 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 21] 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 22] FIG. 11 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. [Diagram 23] FIG. 11 is a diagram for explaining a case where different nozzles are set as provisional defective nozzles for each sheet in the embodiment. [Figure 24] 5 is a schematic diagram illustrating an entire discharge defect detection chart in the embodiment. FIG. [Diagram 25] FIG. 4 is a schematic diagram showing a discharge failure detection chart for one color in the embodiment. [Figure 26] 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 27] 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 28] 10A to 10C are diagrams for explaining sample image data in the embodiment. [Figure 29] FIG. 13 is a diagram for explaining a case in which the position of a true defective nozzle is included in the area of ​​one of the four partial image data in the embodiment. [Diagram 30] 10A and 10B are schematic diagrams illustrating an example of comparison data obtained when the position of a truly defective nozzle is included in the region of partial image data 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] 11A and 11B are diagrams for explaining calculation of an average luminance value in the case where there are no truly defective nozzles in the embodiment. [Diagram 33] 13A and 13B are diagrams for explaining calculation of an average luminance value when a truly defective nozzle is present in the embodiment. [Diagram 34] FIG. 11 is a diagram illustrating sample image data in a first modified example. [Diagram 35] FIG. 13 is a diagram for explaining deletion of data from sample image data when a truly defective nozzle is present in the first modified example. [Diagram 36] FIG. 13 is a diagram for explaining deletion of data from sample image data when a truly defective nozzle is present in the first modified example. [Figure 37] FIG. 11 is a diagram for explaining the concept of a method for determining a compensation coefficient in a second modified example. [Figure 38] FIG. 13 is a diagram for explaining the concept of a method for determining a compensation coefficient in a third modified example. [Figure 39] 13 is a flowchart showing a procedure for determining a compensation coefficient in a fourth modified example. [Diagram 40] FIG. 11 is a diagram for explaining non-ejection. [Diagram 41] FIG. 13 is a diagram for explaining a shape defect. [Diagram 42] 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. In this case, 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 way, a larger amount of ink is ejected from the nozzle adjacent to the defective nozzle than would be the case otherwise. This makes defects in the printed image caused by the defective nozzle not ejecting ink normally less noticeable. In other words, the occurrence of defects in the printed image is suppressed.

[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, a known method such as an error diffusion method or a dither method can be adopted.

[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, and a coefficient determination unit 524.

[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 deletion unit 523 deletes data within a range 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, thereby generating a plurality of comparison data 66 corresponding to the plurality of sample image data 64. Note that the plurality of comparison data 66 correspond to a plurality of provisional compensation coefficients prepared for the purpose of determining the compensation coefficient 62 to be actually applied to the ink amount compensation process.

[0088] The coefficient determination unit 524 determines one of the multiple provisional compensation coefficients as the compensation coefficient 62 to be actually applied to the ink amount compensation process, based on the results of comparing each of the multiple comparison data 66 with the normal area data 65. Note that the determination of the compensation coefficient 62 will be described in detail later.

[0089] <6.2 How to determine the compensation coefficient> <6.2.1 Concept> With reference to Figures 14 to 16, 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 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 Figure 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.

[0091] In this embodiment, various compensation coefficients are prepared as provisional compensation coefficients, and the provisional compensation coefficient that obtains an average brightness value that is closest to the normal case (the case where there are no faulty ejection nozzles) when ink volume compensation processing is performed using these provisional compensation coefficients is adopted as the compensation coefficient 62 to be applied to the ink volume compensation processing when printing is performed based on an actual print job.

[0092] More specifically, in this embodiment, 21 provisional compensation coefficients (0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%) are prepared. In addition, for each ink ejection head 251, the area in the main scanning direction is divided into 21 comparison areas corresponding to the above 21 provisional compensation coefficients and a normal area corresponding to the above normal case. Furthermore, for each of the 21 comparison areas, four provisional defective nozzles that are assumed to be in a hypothetical ejection defective state are set from among the corresponding multiple nozzles. Then, based on the second imaging data 55 obtained by imaging the compensation coefficient calculation chart including images corresponding to the 21 comparison areas and the normal area, the compensation coefficient 62 to be actually applied to the ink amount compensation process is determined from among the 21 provisional compensation coefficients.

[0093] FIG. 15 shows an example of the distribution (spatial change) of the luminance 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 reference numeral 77 corresponds to the position of the provisional defective nozzle. Based on such a distribution of luminance values, an average luminance value is obtained for each comparison region. FIG. 16 shows a graph showing an example of the relationship between the provisional compensation coefficient and the average luminance value. Note that the average luminance value in the normal region is set to 0. In FIG. 16, the relationship between the provisional compensation coefficient and the average luminance value is shown by a thick dotted line marked with reference numeral 78. The smaller the provisional compensation coefficient, the smaller the amount of ink ejected in the corresponding region, so the higher the average luminance value, and the larger the provisional compensation coefficient, the larger the amount of ink ejected in the corresponding region, so the lower the average luminance value. From the portion marked with reference numeral 79 in FIG. 16, it can be seen that in this example, when the provisional compensation coefficient is 45%, the average luminance value closest to the average luminance value in the normal region is obtained. Therefore, in this example, the compensation coefficient 62 actually applied to the ink amount compensation process is determined to be 45%.

[0094] <6.2.2 Procedure for 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. 17. First, for each ink ejection head 251, the area in the main scanning direction (the direction perpendicular to the transport direction of the print paper 5) is divided into 21 comparison areas corresponding to the 21 mutually different temporary compensation coefficients and one normal area (step S100). In this embodiment, the 21 comparison areas and one normal area correspond to a plurality of divided areas. Note that the number of temporary compensation coefficients to be prepared is not limited to 21. Also, it is not necessary to provide a normal area for each ink ejection head 251. That is, it is sufficient that the area corresponding to the width of the ink ejection head 251 in the main scanning direction is divided into a plurality of divided areas including K comparison areas corresponding to K mutually different temporary compensation coefficients, where K is an integer of 2 or more.

[0095] Incidentally, when five ink ejection heads 251 are provided for one ink color, the areas corresponding to the five ink ejection heads 251 are divided into 21 comparison areas and one normal area. 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.

[0096] 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 21 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 21 comparison regions 76(1) to 76(21), as shown in schematic form in FIG.

[0097] Next, compensation coefficient calculation chart data 53 representing a compensation coefficient calculation chart for determining the compensation coefficient 62 is generated (step S120). FIG. 19 is a schematic diagram showing the entire compensation coefficient calculation chart 69. As shown in FIG. 19, 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.

[0098] FIG. 20 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. 20, 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). 20, the compensation coefficient calculation chart 69 includes a portion corresponding to each of the 21 comparison regions 76(1) to 76(21) and a portion corresponding to the normal region 81. As shown in FIG. 21, the portion corresponding to one comparison region 76 for one density includes a portion 694 corresponding to four provisional defective nozzles. Note that 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.

[0099] In step S120, compensation coefficient calculation chart data 53 representing the compensation coefficient calculation chart 69 as described above is generated by performing ink amount compensation processing by applying 21 provisional compensation coefficients to 21 comparison areas 76(1) to 76(21) respectively for image data having a constant density in the main scanning direction.

[0100] 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. 22. 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. 23. Note that, in FIG. 22 and FIG. 23, 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. 23), the influence of the variation in the ink ejection amount among a plurality of nozzles can be more effectively suppressed.

[0101] 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. 24 is a schematic diagram showing the entire discharge failure detection chart 68. As shown in FIG. 24, 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. 25 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.

[0102] 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. 26. The image of the portion shown in FIG. 26 includes images corresponding to the 21 comparison regions 76(1) to 76(21) and an image corresponding to a normal region 81.

[0103] 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.

[0104] 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. 25. 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. 27. In the example shown in FIG. 27, 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."

[0105] Next, the sample image data extraction unit 522 extracts, for each ink color, 21 sample image data 64 corresponding to the 21 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.

[0106] In this embodiment, as shown in FIG. 28, each of the 21 sample image data 64 includes four partial image data 640(1) to 640(4) corresponding to the four provisionally defective nozzles 80 (see FIG. 18).

[0107] After step S180 is completed, the data deletion unit 523 deletes data in a range corresponding to the position of the true defective nozzle (the ejection defective nozzle detected in step S170) from the 21 sample image data 64, thereby generating 21 comparison data 66 (step S190). In this regard, in this embodiment, for example, if the position 641 of the true defective nozzle is included in the area of ​​partial image data 640(3) among the four partial image data 640(1) to 640(4) constituting one sample image data 64 as shown in FIG. 29, the data obtained by deleting the partial image data 640(3) from the four partial image data 640(1) to 640(4) is used as the comparison data 66. Therefore, in this example, the comparison data 66 is composed of partial image data 660(1) corresponding to the partial image data 640(1), partial image data 660(2) corresponding to the partial image data 640(2), and partial image data 660(4) corresponding to the partial image data 640(4), as shown in FIG. 30.

[0108] Note that even if the position of the discharge-failed nozzle is not included in the region of the partial image data constituting the sample image data 64, if the presence of the discharge-failed nozzle affects the average value of the partial image data, the corresponding partial image data is deleted when generating the comparison data 66. For example, as shown in FIG. 31, if the position 642 of the discharge-failed nozzle is not included in 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 average value of partial image data 640(3). Therefore, even in such a case, the data obtained by deleting partial image data 640(3) from the four partial image data 640(1) to 640(4) is used as the comparison data 66.

[0109] As described above, in this embodiment, in step S190, for each of the 21 sample image data 64, partial image data corresponding to the area affected by the true defective nozzle is deleted from the four partial image data 640(1) to 640(4).

[0110] After step S190 is completed, the coefficient determination unit 524 determines one of the 21 provisional compensation coefficients as the compensation coefficient 62 to be actually applied to the ink amount compensation process based on the 21 pieces of comparison data 66 and the normal area data 65 (step S200). The compensation coefficient 62 is determined for each density of the images constituting the compensation coefficient calculation chart 69 (for each of 11 levels of density in this embodiment). The compensation coefficient 62 corresponding to a density between a certain level of density and the density of an adjacent level can be found, for example, by using linear interpolation. For example, the compensation coefficient 62 for a density of 62% is found by linear interpolation using the compensation coefficient 62 for a density of 60% and the compensation coefficient 62 for a density of 70%.

[0111] In step S200, first, the average value for each of the 21 pieces of comparison data 66 and the average value for the normal area data 65 are calculated. The comparison data 66 and the normal area data 65 are luminance value data. Therefore, the average luminance value for each of the 21 pieces of comparison data 66 and the average luminance value for the normal area data 65 are calculated.

[0112] Here, we will explain how to obtain the average brightness value for each comparison data 66. Note that, again, for the sake of convenience, we will focus on only one ink ejection head 251 and an area corresponding to one sheet of the compensation coefficient calculation chart data 53. Also, the average value of each partial image data constituting the comparison data 66 (average brightness value in the area of ​​each partial image data) is referred to as the "partial average value."

[0113] When there are no truly faulty nozzles, the comparison data 66 is made up of four partial image data 660(1)-660(4), as shown in Fig. 32. If the partial average values ​​of the partial image data 660(1)-660(4) are represented as V1-V4, respectively, the average brightness value Vave of the comparison data is calculated using the following equation (2). Vave=(V1+V2+V3+V4) / 4 ···(2)

[0114] When a truly defective nozzle is present in a position that affects the average luminance value of partial image data 640(3) as shown in Figures 29 and 31, comparison data 66 is made up of three partial image data 660(1), 660(2), and 660(4), as shown in Figure 33. If the partial average values ​​of partial image data 660(1), 660(2), and 660(4) are represented as V1, V2, and V4, respectively, the average luminance value Vave of the comparison data is calculated using the following equation (3). Vave = (V1 + V2 + V4) / 3 (3)

[0115] In this manner, an average luminance value is calculated for each of the 21 pieces of comparison data 66. Then, the average luminance value for the normal area data 65 is set as a target value, and the target value is compared with the average luminance value for each of the 21 pieces of comparison data 66. As a result, the provisional compensation coefficient associated with the comparison area 76 corresponding to the comparison data for which an average luminance value closest to the target value was obtained among the 21 pieces of comparison data 66 is determined as the compensation coefficient 62 to be actually applied to the ink amount compensation process.

[0116] In this embodiment, step S100 realizes the area division step, step S110 realizes the temporary faulty nozzle setting step, step S120 realizes the compensation coefficient calculation chart data generation step, step S130 realizes the discharge failure detection chart printing step, step S140 realizes the compensation coefficient calculation chart printing step, step S150 realizes the discharge failure detection chart imaging step, step S160 realizes the compensation coefficient calculation chart imaging step, step S170 realizes the discharge failure nozzle detection step, step S180 realizes the sample image data extraction step, step S190 realizes the data deletion step, and step S200 realizes the coefficient determination step.

[0117] <7. Effects> According to this embodiment, 21 provisional compensation coefficients are prepared as various compensation coefficients, and a provisional compensation coefficient to be actually applied as the compensation coefficient 62 in the ink amount compensation process is determined from the 21 provisional compensation coefficients based on data obtained by using the 21 provisional compensation coefficients in the ink amount compensation process. In this way, the compensation coefficient 62 is determined based on data obtained by actually performing the ink amount compensation process. In addition, prior to the final determination of the compensation coefficient 62, data in the area affected by the nozzle with poor ejection is deleted. As described above, since a suitable compensation coefficient 62 can be determined with high accuracy, the occurrence of defects in the printed image when a nozzle with poor ejection is present in the inkjet printing device 10 is more effectively suppressed than in the past. In addition, since the wasteful consumption of ink and printing paper 5 is reduced, it is possible to contribute to the achievement of the SDGs (Sustainable Development Goals).

[0118] <8. Variations> Below, a modification of the above embodiment will be described.

[0119] <8.1 First modified example> In the above embodiment, each sample image data 64 is made up of four partial image data 640(1)-640(4) (see FIG. 28), and when generating the comparison data 66, the partial image data 640 affected by the defective ejection nozzle is deleted. In contrast, in this modified example, as shown in FIG. 34, the data of the entire comparison region 76 is used as the sample image data 64. Below, the points that differ from the above embodiment regarding the processing procedure for determining the compensation coefficient 62 will be described.

[0120] In step S180 in FIG. 17, as shown in FIG. 34, data of the entire comparison region 76 is extracted as sample image data 64. In step S190 in FIG. 17, a predetermined range of data is deleted from each sample image data 64 based on the position of the true defective nozzle. In this regard, when the position marked with reference numeral 82 in FIG. 35 corresponds to the position of the true defective nozzle, for example, data in the range indicated by the arrow marked with reference numeral 85 in FIG. 36 is deleted from the sample image data 64. As a result, the comparison data 66 is composed of data in the range indicated by the arrow marked with reference numeral 83 in FIG. 36 and data in the range indicated by the arrow marked with reference numeral 84 in FIG. 36. Then, in the example shown in FIG. 36, in step S200 in FIG. 17, an average luminance value is calculated based on data in the range indicated by the arrow marked with reference numeral 83 in FIG. 36 and data in the range indicated by the arrow marked with reference numeral 84 in FIG. 36.

[0121] As described above, each sample image data 64 does not have to be composed of a plurality of partial image data 640 .

[0122] <8.2 Second modified example> With reference to FIG. 37, a method for determining the compensation coefficient 62 in the second modified example of the above embodiment will be described. It is considered that, with respect to the above-mentioned comparison data 66, the more favorable the corresponding provisional compensation coefficient, the closer the data value (brightness value) corresponding to the position of the provisional defective nozzle will be to the average value (average brightness value) for the above-mentioned normal area data 65. Therefore, in this modified example, the average value (hereinafter referred to as the "peak average value") of the data values ​​corresponding to the position of the provisional defective nozzle is calculated for each of the above-mentioned 21 pieces of comparison data 66. Furthermore, before calculating the peak average value, in step S190 of FIG. 17, data for positions influenced by the true defective nozzle is deleted from the positions of the four provisional defective nozzles corresponding to each comparison area 76.

[0123] From the above, for example, if the distribution (spatial change) of data values ​​for the second captured data 55 corresponding to a certain comparison region 76 is as shown by the solid line labeled with reference numeral 86 in Fig. 37, there is no truly defective nozzle, and the four positions labeled with reference numerals 87(1) to 87(4) correspond to the four provisionally defective nozzles, then the average of the data values ​​at the four positions labeled with reference numerals 87(1) to 87(4) is found as the peak average of the comparison data 66 corresponding to that certain comparison region 76. Also, if the distribution of data values ​​for the second captured data 55 corresponding to a certain comparison region 76 is as shown by the solid line labeled with reference numeral 86 in Fig. 37, and there is a truly defective nozzle that affects the data value at the position labeled with reference numeral 87(1), then the average of the data values ​​at the three positions labeled with reference numerals 87(2) to 87(4) is found as the peak average of the comparison data 66 corresponding to that certain comparison region 76.

[0124] After the peak average value is determined for each of the 21 comparison data 66 in the manner described above, the provisional compensation coefficient corresponding to the comparison data 66 for which the peak average value closest to the average value for the normal area data 65 is obtained is determined as the compensation coefficient 62 to be actually applied to the ink amount compensation process.

[0125] As described above, in this modified example, in step S190 of Fig. 17, data for P positions affected by the true faulty nozzle among the positions of the four provisional faulty nozzles is deleted for each of the 21 sample image data, where P is an integer between 1 and 3. This generates 21 comparison data 66. Then, in step S200 of Fig. 17, for each of the 21 comparison data 66, a peak average value, which is the average value of the data for the (4-P) positions excluding the data for the P positions deleted in step S190 among the data for the positions of the four provisional faulty nozzles, and an average value for the normal area data 65 are obtained, and the average value for the normal area data 65 is set as a target value, and the provisional compensation coefficient associated with the comparison area 76 corresponding to the comparison data 66 for which the peak average value closest to the target value has been obtained among the 21 comparison data 66 is determined as the compensation coefficient 62 to be actually applied to the ink amount compensation process.

[0126] <8.3 Third modified example> With reference to Fig. 38, a method for determining the compensation coefficient 62 in the third modified example of the above embodiment will be described. It is considered that the more suitable the corresponding provisional compensation coefficient is for the above-mentioned comparison data 66, the smaller the variation in data value (brightness value). Therefore, in this modified example, the difference between the maximum and minimum data values ​​(brightness value) is found for each of the above-mentioned 21 pieces of comparison data 66. Furthermore, before finding the difference between the maximum and minimum data values, in step S190 of Fig. 17, a predetermined range of data is deleted based on the position of the true defective nozzle.

[0127] For example, if the distribution (spatial change) of data values ​​for the second captured data 55 corresponding to a certain comparison region 76 is as shown by the solid line labeled with reference symbol 88 in Fig. 38 and no truly defective nozzles are present, then the difference between the maximum and minimum data values ​​for the comparison data 66 corresponding to that certain comparison region 76 is represented by the length of the arrow labeled with reference symbol 89a in Fig. 38. Also, if the distribution of data values ​​for the second captured data 55 corresponding to a certain comparison region 76 is as shown by the solid line labeled with reference symbol 88 in Fig. 38, and a truly defective nozzle is present and data within the range of the arrow labeled with reference symbol 90 is deleted in step S190 of Fig. 17, then the difference between the maximum and minimum data values ​​for the comparison data 66 corresponding to that certain comparison region 76 is represented by the length of the arrow labeled with reference symbol 89b in Fig. 38.

[0128] After the difference between the maximum and minimum data values ​​for each of the 21 comparison data 66 is calculated, the provisional compensation coefficient corresponding to the comparison data 66 for which the smallest difference was obtained is determined as the compensation coefficient 62 to be actually applied to the ink amount compensation process.

[0129] As described above, in this modified example, in step S190 of Fig. 17, a predetermined range of data is deleted based on the position of the true faulty nozzle. This generates 21 pieces of comparison data 66. Then, in step S200 of Fig. 17, the provisional compensation coefficient associated with the comparison region 76 corresponding to the comparison data 66 with the smallest difference between the maximum and minimum values ​​among the 21 pieces of comparison data 66 is determined as the compensation coefficient 62 to be actually applied to the ink amount compensation process.

[0130] <8.4 Fourth Variation> In the above embodiment, it was assumed that the series of processes (see FIG. 17) for determining the compensation coefficient 62, from the process of dividing the area corresponding to the width of the ink ejection head 251 into a plurality of divided areas to the final process of determining 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. 17) and the processes subsequent to the process of printing the ejection defect detection chart 68 (the processes from step S130 onward in FIG. 17) are performed by the user of the inkjet printing apparatus 10.

[0131] FIG. 39 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, in this modified example, unlike the above embodiment, 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. 17. That is, at the manufacturer of the inkjet printing device 10, the area of ​​each ink ejection head 251 in the main scanning direction (the direction perpendicular to the transport direction of the printing paper 5) is divided into 21 comparison areas 76 (each comparison area 76 corresponds to a plurality of provisionally defective nozzles 80) associated with 21 different provisional compensation coefficients and one normal area 81, and the compensation coefficient calculation chart data 53 is generated by applying the 21 provisional compensation coefficients to the 21 comparison areas 76 for predetermined image data having a constant density in the main scanning direction to perform ink amount compensation processing. After the compensation coefficient calculation chart data 53 is generated, processing similar to the processing of steps S150 to S200 in Fig. 17 (processing of steps S320 to S370 in Fig. 39) is performed.

[0132] In this embodiment, step S300 realizes the step of printing a defective discharge detection chart, step S310 realizes the step of printing a compensation coefficient calculation chart, step S320 realizes the step of capturing an image of a defective discharge detection chart, step S330 realizes the step of capturing an image of a compensation coefficient calculation chart, step S340 realizes the step of detecting a defective discharge nozzle, step S350 realizes the step of extracting sample image data, step S360 realizes the step of deleting data, and step S370 realizes the step of determining a coefficient.

[0133] <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.

[0134] 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.

[0135] <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.

[0136] In addition, in the above embodiment (including the modified example), an inkjet printing apparatus 10 using aqueous ink is used. However, the present invention is not limited to this, and an inkjet printing apparatus using UV ink (ultraviolet light curable ink) such as an inkjet printing apparatus for label printing may be used. In this case, an ultraviolet light irradiation mechanism that cures the UV ink on the printing paper 5 by irradiating it with ultraviolet light is provided inside the printing mechanism 201 (see FIG. 2) instead of the drying mechanism 206. [Explanation of symbols]

[0137] 10...Inkjet printing device 40…Inline scanner 64...Sample image data 65…Normal area data 66…Comparative data 68…Discharge failure detection chart 69...Compensation coefficient calculation chart 76…Comparison area 80...Temporary defective nozzle 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 521...Discharge failure nozzle detection unit 522...Sample image data extraction unit 523…Data Deletion Department 524...Coefficient determination unit 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 dividing step of dividing a predetermined region in a direction perpendicular to a transport direction of the print medium into a plurality of divided regions including K comparison regions corresponding to K different provisional compensation coefficients, where K is an integer equal to or greater than 2; a provisional defective nozzle setting step of setting a plurality of provisional defective nozzles which are assumed to be in a state of virtually defective ejection from among two or more corresponding nozzles 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 provisional compensation coefficients to the K comparison areas, respectively, for predetermined image data having a constant density in a direction perpendicular to the transport direction of the print medium, and performing the ink amount compensation process; 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 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 discharge failure detection chart imaging step of imaging the discharge failure detection chart printed in the discharge failure detection chart printing step; a compensation coefficient calculation chart imaging step of imaging the compensation coefficient calculation chart printed in the compensation coefficient calculation chart printing step; a discharge failure nozzle detection step of detecting a nozzle having a discharge failure based on first imaging data which is imaging data obtained in the discharge failure detection chart imaging step; a sample image data extracting step of extracting K sample image data corresponding to the K comparison regions from second imaging data which is imaging data obtained in the compensation coefficient calculation chart imaging step; a data deleting step for generating K pieces of comparison data by deleting data in a range corresponding to the position of the true defective nozzle, which is the nozzle detected in the ejection defective nozzle detection step, from the K pieces of sample image data; a coefficient determination step of determining one of the K provisional compensation coefficients as the compensation coefficient based on the K comparison data; A compensation coefficient determination method comprising:

2. the plurality of divided regions includes, in addition to the K comparison regions, a normal region that is not affected by the provisional defective nozzle, In the sample image data extraction step, normal area data corresponding to the normal area is further extracted from the second imaging data, 2. The compensation coefficient determination method according to claim 1, wherein in said coefficient determination step, said compensation coefficient is determined based on said K pieces of comparison data and said normal region data.

3. 3. The compensation coefficient determination method according to claim 2, characterized in that, in the coefficient determination step, an average value for each of the K comparison data and an average value for the normal area data are calculated, and the average value for the normal area data is set as a target value, and a provisional compensation coefficient associated with a comparison area corresponding to the comparison data for which an average value closest to the target value is obtained among the K comparison data is determined as the compensation coefficient.

4. wherein N is an integer equal to or greater than 2, and each of the K comparison regions corresponds to N provisional defective nozzles; Each of the K sample image data includes N partial image data corresponding to the N provisional defective nozzles, 4. The compensation coefficient determination method according to claim 3, characterized in that in the data deletion step, for each of the K pieces of sample image data, partial image data corresponding to an area affected by the true defective nozzle is deleted from the N pieces of partial image data.

5. wherein N is an integer equal to or greater than 2, and each of the K comparison regions corresponds to N provisional defective nozzles; In the data deletion step, data of P positions influenced by the true faulty nozzle among the positions of the N tentative faulty nozzles is deleted for each of the K pieces of sample image data, where P is an integer equal to or greater than 1 and equal to or less than (N-1); 3. The compensation coefficient determination method according to claim 2, characterized in that in the coefficient determination step, for each of the K pieces of comparison data, a peak average value, which is the average value of the data for (N-P) positions among the data for the positions of the N pieces of provisional defective nozzles excluding the data for the P positions deleted in the data deletion step, and an average value for the normal area data are calculated, and the average value for the normal area data is set as a target value, and a provisional compensation coefficient associated with a comparison area corresponding to the comparison data for which a peak average value closest to the target value has been obtained among the K pieces of comparison data is determined as the compensation coefficient.

6. 2. The compensation coefficient determination method according to claim 1, wherein in the coefficient determination step, a provisional compensation coefficient associated with a comparison region corresponding to the comparison data having a smallest difference between a maximum value and a minimum value among the K comparison data is determined as the compensation coefficient.

7. the printing device includes a plurality of print heads, each print head including a portion of the plurality of nozzles; The K comparison regions are provided for each print head, the K temporary compensation coefficients corresponding to the K comparison regions are common among the plurality of print heads, 2. The compensation coefficient determination method according to claim 1, wherein in the sample image data extraction step, one sample image data is extracted by extracting data of a plurality of comparison areas corresponding to the same provisional compensation coefficient among the plurality of print heads from the second imaging data.

8. 2. The compensation coefficient determination method according to claim 1, wherein the compensation coefficient calculation chart is made up of a plurality of sheets for each ink color.

9. 9. The compensation coefficient determination method according to claim 8, wherein in the tentative defective nozzle setting step, a different nozzle is set as the tentative defective nozzle for each of the K comparison regions for each sheet.

10. 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; 2. The compensation coefficient determining method according to claim 1, wherein in said coefficient determining step, said compensation coefficient is determined for each concentration.

11. 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 10; 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:

12. 12. The printing method of claim 11, wherein a nozzle adjacent to the true faulty nozzle is defined as an adjacent nozzle, the compensation coefficient is represented by C, which is a value between 0 and 1, a position value corresponding to the true faulty nozzle in the shading data before the shading data correction step is executed is represented by Vf, a position value corresponding to the adjacent nozzle in the shading data before the shading data correction step is executed is represented by Vn, and a position value corresponding to the adjacent nozzle in the shading data after the shading data correction step is executed is represented by V, where V is expressed by the following formula: V = Vn + Vf × C

13. 13. The printing method according to claim 12, wherein the value of a position in the shading data corresponding to the true faulty nozzle after the shading data correction step is executed is 0.

14. A printing device comprising a plurality of nozzles which eject ink onto a printing medium, an imaging device which captures an image of a print, 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, the printing device performing an ink amount compensation process during printing to compensate for the amount of ink ejected onto the printing medium when a nozzle in an ejection failure state exists, The control unit is an area division process for dividing a predetermined area in a direction perpendicular to the transport direction of the print medium into a plurality of divided areas including K comparison areas corresponding to K different provisional compensation coefficients, where K is an integer equal to or greater than 2; a provisional defective nozzle setting process for setting a plurality of provisional defective nozzles which are assumed to be in a defective discharge state from among two or more corresponding nozzles for each of the K comparison regions; a compensation coefficient calculation chart data generation process that generates 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 provisional compensation coefficients to the K comparison areas for predetermined image data having a constant density in a direction perpendicular to the transport direction of the print medium; a discharge failure detection chart printing process for controlling the ejection of ink from the plurality of nozzles so as to print a discharge failure detection chart for detecting nozzles in a discharge failure state; 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 discharge failure detection chart imaging process for imaging the discharge failure detection chart printed in the discharge failure detection chart printing step with the imaging device; a compensation coefficient calculation chart imaging process for imaging the compensation coefficient calculation chart printed in the compensation coefficient calculation chart printing step with the imaging device; a defective nozzle detection process for detecting a nozzle having a defective discharge state based on first imaging data, which is imaging data obtained in the defective discharge detection chart imaging step; a sample image data extraction process for extracting K sample image data corresponding to the K comparison regions from second imaging data, which is imaging data obtained in the compensation coefficient calculation chart imaging step; a data deletion process for generating K pieces of comparison data by deleting data in a range corresponding to the position of a true defective nozzle, which is a nozzle detected in the ejection defective nozzle detection process, from the K pieces of sample image data; a coefficient determination process for determining one of the K provisional compensation coefficients as the compensation coefficient based on the K pieces of comparison data; 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 dividing step of dividing a predetermined region in a direction perpendicular to a transport direction of the print medium into a plurality of divided regions including K comparison regions corresponding to K different provisional compensation coefficients, where K is an integer equal to or greater than 2; a provisional defective nozzle setting step of setting a plurality of provisional defective nozzles which are assumed to be in a state of virtually defective ejection from among two or more corresponding nozzles 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 provisional compensation coefficients to the K comparison areas, respectively, for predetermined image data having a constant density in a direction perpendicular to the transport direction of the print medium, and performing the ink amount compensation process; a discharge failure detection chart printing step of controlling the discharge of ink from the plurality of nozzles so as to print a discharge failure detection chart for detecting nozzles in a discharge failure state; 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 discharge failure detection chart imaging step of imaging the discharge failure detection chart printed in the discharge failure detection chart printing step with the imaging device; 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 discharge failure nozzle detection step of detecting a nozzle having a discharge failure based on first imaging data which is imaging data obtained in the discharge failure detection chart imaging step; a sample image data extracting step of extracting K sample image data corresponding to the K comparison regions from second imaging data which is imaging data obtained in the compensation coefficient calculation chart imaging step; a data deleting step for generating K pieces of comparison data by deleting data in a range corresponding to the position of the true defective nozzle, which is the nozzle detected in the ejection defective nozzle detection step, from the K pieces of sample image data; a coefficient determination step of determining one of the K provisional compensation coefficients as the compensation coefficient based on the K comparison data; A compensation coefficient determination program for executing the above.

16. 1. A compensation coefficient 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 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 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 the K comparison areas to predetermined image data having a constant density in the direction perpendicular to the transport direction of the printing medium, in a state in which a predetermined area is divided into a plurality of divided areas including K comparison areas each associated with a plurality of temporarily defective nozzles that are virtually set to be in a defective discharge state, where K is an integer of 2 or more; a discharge failure detection chart imaging step of imaging the discharge failure detection chart printed in the discharge failure detection chart printing step; a compensation coefficient calculation chart imaging step of imaging the compensation coefficient calculation chart printed in the compensation coefficient calculation chart printing step; a discharge failure nozzle detection step of detecting a nozzle having a discharge failure based on first imaging data which is imaging data obtained in the discharge failure detection chart imaging step; a sample image data extracting step of extracting K sample image data corresponding to the K comparison regions from second imaging data which is imaging data obtained in the compensation coefficient calculation chart imaging step; a data deleting step for generating K pieces of comparison data by deleting data in a range corresponding to the position of the true defective nozzle, which is the nozzle detected in the ejection defective nozzle detection step, from the K pieces of sample image data; a coefficient determination step of determining one of the K provisional compensation coefficients as the compensation coefficient based on the K comparison data; 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 an image of a print, 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, the printing device performing an ink amount compensation process during printing to compensate for the amount of ink ejected onto the printing medium when a nozzle in an ejection failure state exists, The control unit is a discharge failure detection chart printing process for controlling the ejection of ink from the plurality of nozzles so as to print a discharge failure detection chart for detecting nozzles in a discharge failure state; 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 in the direction orthogonal to the transport direction of the printing medium, in a state in which a predetermined region is divided into a plurality of divided regions including K comparison regions corresponding to K different provisional compensation coefficients, the K comparison regions corresponding to a plurality of provisional defective nozzles that are virtually set to a defective ejection state, where K is an integer of 2 or greater, so that a compensation coefficient calculation chart for determining the compensation coefficients is printed; a discharge failure detection chart imaging process for imaging the discharge failure detection chart printed in the discharge failure detection chart printing process by the imaging device; 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 defective nozzle detection process for detecting a nozzle having a defective discharge state based on first imaging data, which is imaging data obtained in the defective discharge detection chart imaging process; a sample image data extraction process for extracting K sample image data corresponding to the K comparison regions from second imaging data, which is imaging data obtained in the compensation coefficient calculation chart imaging process; a data deletion process for generating K pieces of comparison data by deleting data in a range corresponding to the position of a true defective nozzle, which is a nozzle detected in the ejection defective nozzle detection process, from the K pieces of sample image data; a coefficient determination process for determining one of the K provisional compensation coefficients as the compensation coefficient based on the K pieces of comparison data; 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 discharge failure detection chart printing step of controlling the discharge of ink from the plurality of nozzles so as to print a discharge failure detection chart for detecting nozzles in a discharge failure state; 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 K provisional compensation coefficients to the K comparison areas for predetermined image data having a constant density in the direction orthogonal to the transport direction of the printing medium, in a state in which a predetermined area is divided into a plurality of divided areas including K comparison areas corresponding to K different provisional compensation coefficients, the K comparison areas corresponding to a plurality of provisional defective nozzles that are virtually set to a defective ejection state, where K is an integer of 2 or more, so that a compensation coefficient calculation chart for determining the compensation coefficients is printed; a discharge failure detection chart imaging step of imaging the discharge failure detection chart printed in the discharge failure detection chart printing step with the imaging device; 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 discharge failure nozzle detection step of detecting a nozzle having a discharge failure based on first imaging data which is imaging data obtained in the discharge failure detection chart imaging step; a sample image data extracting step of extracting K sample image data corresponding to the K comparison regions from second imaging data which is imaging data obtained in the compensation coefficient calculation chart imaging step; a data deleting step for generating K pieces of comparison data by deleting data in a range corresponding to the position of the true defective nozzle, which is the nozzle detected in the ejection defective nozzle detection step, from the K pieces of sample image data; a coefficient determination step of determining one of the K provisional compensation coefficients as the compensation coefficient based on the K comparison data; A compensation coefficient determination program for executing the above.

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