Printing device and printing method

Abstract

To provide an inkjet printing device that can appropriately suppress deterioration in a printing quality due to dot omission and density fluctuation in a print image.SOLUTION: An area which should be corrected to suppress occurrence of image defect due to a defective nozzle or the like is determined on a print image that should be formed on a substrate. When the area is a single-color / high-density area which should be formed by discharging single-color ink thereto and when the area is a mixed color / high-density area which should be formed with two or more color ink and a ratio of quantities of ink of ink color of the defective nozzle to quantities of total ink is high, printing data are corrected so that white ink (when the substrate is white) or transparent ink (when the substrate is other than white) is discharged to the area and then the color ink is discharged. The print image is formed on the substrate on the basis of the corrected printing data, which can suppress occurrence of image defect due to the defective nozzle or the like.SELECTED DRAWING: Figure 21

Description

[Technical Field]

[0001] The present invention relates to a printing device having an ink ejection head (print head) provided with a large number of nozzles that eject ink, and a printing method using the same. [Background technology]

[0002] Inkjet printing devices (hereinafter simply referred to as "inkjet printing devices") that perform printing by ejecting ink onto a printing medium such as printing paper have been known for some time. Inkjet printing devices generally use aqueous ink for printing. However, in recent years, there has been progress in the development of inkjet printing devices that print using UV ink (ultraviolet-curable ink), for example, label printing. In inkjet printing devices that use UV ink, UV light (ultraviolet rays) is irradiated onto the UV ink ejected from the ink ejection head to fix the UV ink onto a substrate as the printing medium.

[0003] Inkjet printing devices use nozzles in inkjet heads that vary in density. Therefore, even when ink is ejected from multiple nozzles in an inkjet head based on the same drive signal, variations in the amount of ink ejected from those multiple nozzles occur. Printing performed under these conditions results in poor quality printouts. Therefore, density uniformity correction is performed to correct the density of print data so that ink is ejected uniformly from all nozzles.

[0004] Furthermore, inkjet printing devices may experience ink ejection defects due to factors such as ink solidification caused by long periods of non-use. When ink ejection defects occur, dots corresponding to nozzles with ejection defects (hereinafter referred to as "defective nozzles") are missing from the printed image, resulting in dot omissions. Therefore, nozzle dropout correction is performed to correct the density of print data so that ink that should be ejected from the defective nozzle is instead ejected from other nozzles (typically, nozzles adjacent to the defective nozzle). An example of nozzle dropout correction is disclosed in Japanese Patent Application Laid-Open No. 2014-188785.

[0005] With reference to FIG. 37, density uniformization correction and nozzle dropout correction will be further explained. Here, we focus on five pixel areas 9(1) to 9(5) corresponding to five nozzles. It is assumed that monochrome printing is performed on the five pixel areas 9(1) to 9(5) using the same color ink ejected from the five nozzles. It is also assumed that the density (halftone %) of all five pixel areas 9(1) to 9(5) is 50, as shown in the portion labeled 91 in the print data generated by RIP processing. By density uniformization correction, the density of the five pixel areas 9(1) to 9(5) is corrected, for example, as shown in the portion labeled 92. In this example, the nozzle corresponding to pixel area 9(1) ejects 5 / 4 times as much ink as the nozzle corresponding to pixel area 9(2) based on the same drive signal, so the density of pixel area 9(1) is corrected to 40, which is 4 / 5 of 50. Furthermore, based on the same drive signal, the nozzle corresponding to pixel portion 9(4) ejects (5 / 6) times as much ink as the nozzle corresponding to pixel portion 9(2), so the density of pixel portion 9(4) is corrected to 60, which is (6 / 5) times 50. In this example, of the five nozzles, the nozzle corresponding to pixel portion 9(3) is the defective nozzle. Therefore, nozzle defect correction is performed on the data indicated by the portion labeled 92. As a result, the densities of the five pixel portions 9(1) to 9(5) are corrected as indicated by the portion labeled 93. In this regard, because the density of pixel portion 9(3) before nozzle defect correction was 40, 20 is added to the density of pixel portion 9(2), and 20 is also added to the density of pixel portion 9(4). In other words, the density of pixel portion 9(2) is corrected to 70, and the density of pixel portion 9(4) is corrected to 80.

[0006] The density uniformity correction and nozzle dropout correction described above suppress the occurrence of image defects (such as streaky density reductions due to missing dots) caused by individual differences between nozzles or defective nozzles. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-188785 Summary of the Invention [Problem to be solved by the invention]

[0008] However, when a defective nozzle occurs, even if the amount of ink that should have been ejected from the defective nozzle is ejected from other nozzles through nozzle defect correction, it may not be possible to obtain a printed product in which the defect is properly resolved. In particular, when a defect occurs in a nozzle corresponding to an area where high-density monochrome printing is performed, the dot size of the ink ejected from the other nozzles is likely to be insufficient to eliminate the image defect caused by the missing dot. As such, depending on the image to be printed, conventional nozzle defect correction cannot produce a printed product of sufficient quality.

[0009] In addition, ink ejection heads generally contain multiple head modules, and density and color unevenness can occur in areas where the area where ink is ejected by one head module overlaps with the area where ink is ejected by an adjacent head module.

[0010] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an inkjet printing apparatus that can effectively prevent degradation of print quality due to missing dots, unevenness, and the like in printed images. [Means for solving the problem]

[0011] A first aspect of the present invention is a printing device that forms a print image on a print medium by ejecting ink onto the print medium based on print data, comprising: a conveying unit that conveys the print medium; a first ink ejection head including a plurality of ink ejection ports that ejects a first ink onto the printing medium transported by the transport unit; a second ink ejection head including a plurality of ink ejection ports that ejects a second ink onto the printing medium transported by the transport unit; a third ink ejection head that is disposed upstream of the first ink ejection head and the second ink ejection head in the direction in which the print medium is transported by the transport unit, and that includes a plurality of ink ejection ports and ejects a third ink onto the print medium being transported by the transport unit; an ejection control unit that controls ejection of the first ink by the first ink ejection head, ejection of the second ink by the second ink ejection head, and ejection of the third ink by the third ink ejection head; a correction area determination unit that determines a correction area to be corrected using the third ink in the print image formed on the print medium, a wetting and spreading range of the first ink on the printing medium is larger when the first ink is ejected onto the third ink ejected onto the printing medium than when the first ink is ejected directly onto the printing medium; a wetting and spreading range of the second ink on the printing medium is larger when the third ink is ejected onto the third ink that has been ejected onto the printing medium than when the second ink is ejected directly onto the printing medium; a wetting and spreading range of the first ink and the second ink on the printing medium when the first ink and the second ink are ejected so as to mix is larger when the first ink and the second ink are ejected onto the third ink ejected onto the printing medium than when the first ink and the second ink are ejected directly onto the printing medium; The ejection control unit controls the first ink ejection head, the second ink ejection head, and the third ink ejection head so that the third ink is ejected into the correction area before the first ink is ejected into the correction area to form the print image, and so that the third ink is ejected into the correction area before the second ink is ejected into the correction area to form the print image.

[0012] A second aspect of the present invention is the method according to the first aspect of the present invention, The correction area determination unit determines the correction area based on the position of a defective orifice, which is an ink ejection orifice having an ejection defect, among a plurality of ink ejection orifices included in the first ink ejection head or the second ink ejection head.

[0013] A third aspect of the present invention is the method according to the second aspect of the present invention, The correction area determination unit determines the correction area so that the correction area includes an area where the third ink is ejected from an ink ejection port corresponding to an ink ejection port adjacent to the defective ejection port and included in the third ink ejection head.

[0014] A fourth aspect of the present invention is the method according to the second aspect of the present invention, The correction area determination unit if the correction area is a monochromatic area onto which only one of the first ink and the second ink is ejected, determining the correction area based on the print data so that only an area onto which the amount of the one ink is ejected that is greater than a predetermined first reference value is included in the correction area; If the correction area is an area where both the first ink and the second ink are ejected and is a mixed color area where the color of the first ink and the color of the second ink are mixed, the correction area is determined based on the print data so that only areas where the total ink amount is greater than a predetermined second judgment reference value and the ratio of the ink amount of the ink color of the ink ejection head including the defective ejection port among the first ink ejection head and the second ink ejection head to the total ink amount is greater than a predetermined third judgment reference value are included in the correction area.

[0015] A fifth aspect of the present invention is a printing method using a printing device that includes a transport unit that transports a print medium, a first ink ejection head that ejects a first ink onto the print medium transported by the transport unit, a second ink ejection head that ejects a second ink onto the print medium transported by the transport unit, and a third ink ejection head that ejects a third ink onto the print medium transported by the transport unit, and that forms a print image on the print medium based on print data, the method comprising: ejecting the first ink from the first ink ejection head to form the print image; ejecting the second ink from the second ink ejection head to form the print image; determining a correction area to be corrected using the third ink in the printed image formed on the printing medium; ejecting the third ink from the third ink ejection head onto the correction area before the first ink is ejected onto the correction area to form the print image; ejecting the third ink from the third ink ejection head onto the correction area before the second ink is ejected onto the correction area to form the print image; Equipped with a wetting and spreading range of the first ink on the printing medium is larger when the first ink is ejected onto the third ink ejected onto the printing medium than when the first ink is ejected directly onto the printing medium; a wetting and spreading range of the second ink on the printing medium is larger when the third ink is ejected onto the third ink that has been ejected onto the printing medium than when the second ink is ejected directly onto the printing medium; When the first ink and the second ink are ejected so as to mix, the wetting and spreading range of the first ink and the second ink on the printing medium is larger when the first ink and the second ink are ejected onto the third ink ejected onto the printing medium than when the first ink and the second ink are ejected directly onto the printing medium.

[0016] Other aspects of the present invention will be apparent from the above aspects of the present invention and the following description of the embodiments and their modifications, and therefore will not be described here. [Effects of the Invention]

[0017] According to a first aspect of the present invention, a printing device is provided with a third ink ejection head that ejects a third ink, located upstream of a first ink ejection head that ejects a first ink and a second ink ejection head that ejects a second ink for forming a print image on the print medium, in relation to a direction in which the print medium is transported by a transport unit, and a correction area determination unit determines a correction area to be corrected using the third ink in the print image to be formed on the print medium. The third ink is ejected into the correction area before the first ink is ejected into the correction area to form the print image, and the third ink is ejected into the correction area before the second ink is ejected into the correction area to form the print image. The wet spreading range of the first ink on the print medium is larger when the first ink is ejected onto the third ink ejected onto the print medium than when the first ink is ejected directly onto the print medium, and the same is true for the wet spreading range of the second ink on the print medium. Furthermore, when the first ink and the second ink are ejected so that they mix, the wet spread range of the first ink and the second ink on the printing medium is larger when the first ink and the second ink are ejected onto the third ink ejected onto the printing medium than when the first ink and the second ink are ejected directly onto the printing medium. Therefore, not only when only one of the first ink and the second ink is ejected into the correction area, but also when the first ink and the second ink are ejected so that they mix, the dot size of the first ink and the dot size of the second ink are larger than they should be. As a result, by defining the correction area as, for example, an area corresponding to a defective nozzle or an area where an area ejected by one ink ejection head overlaps with an area ejected by an adjacent ink ejection head, it is possible to improve print quality compared to conventional methods.

[0018] According to a second aspect of the present invention, when a defective orifice (defective nozzle) is detected in the first ink ejection head or the second ink ejection head, the correction area is determined taking into account the position of the defective orifice, thereby making it possible to suppress unevenness caused by the presence of the defective orifice.

[0019] According to the third aspect of the invention, the occurrence of image defects in printed images due to the presence of defective ejection ports is effectively suppressed.

[0020] According to a fourth aspect of the present invention, when a correction area where missing nozzle correction should be performed to suppress the occurrence of image defects due to defective ejection orifices is a monochromatic area where only one of the first ink or the second ink is ejected, only areas where the amount of the one ink is greater than a predetermined first reference value are included in the correction area. Also, when the correction area where missing nozzle correction should be performed is an area where both the first ink and the second ink are ejected and a mixed-color area where the color of the first ink is mixed with the color of the second ink, only areas where the total ink amount is greater than a predetermined second reference value and where the ratio of the ink amount of the ink color of the ink ejection head that includes the defective ejection orifice to the total ink amount is greater than a predetermined third reference value are included in the correction area. In this way, in both single-color and mixed-color regions, when nozzle defect correction is to be performed to suppress the occurrence of image defects caused by defective ejection ports, whether nozzle defect correction using the third ink or normal nozzle defect correction without using the third ink should be performed is determined based on a predetermined judgment reference value, allowing nozzle defect correction to be performed more appropriately and effectively than before.

[0021] The effects of other aspects of the present invention are clear from the explanation of the effects of the above aspects of the present invention and the effects of the following embodiment and its modifications, and therefore will not be explained here. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a diagram illustrating the overall configuration of a printing system according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing an example of the configuration of an inkjet printing apparatus according to the first embodiment. [Figure 3] FIG. 2 is a plan view schematically showing the configuration of a recording section in the first embodiment. [Figure 4] FIG. 2 is a plan view showing an example of the configuration of an ink ejection surface of one ink ejection head in the first embodiment. [Figure 5] FIG. 2 is a diagram for explaining an arrangement of nozzles in a head module in the first embodiment. [Figure 6] FIG. 2 is a block diagram showing a hardware configuration of a print control device in the first embodiment. [Figure 7] FIG. 2 is a diagram for explaining an overview of white correction in the first embodiment. [Figure 8] FIG. 1A is a diagram for explaining ink ejection when white correction is performed on a single-color area in the first embodiment, and FIG. 1B is a diagram for explaining ink ejection when white correction is performed on a mixed-color area. [Figure 9] FIG. 10 is a diagram showing an example of the results of an experiment on the wetting and spreading of color ink on a film substrate. [Figure 10] 10A and 10B are diagrams for explaining how to obtain a determination reference value for determining whether or not white correction is necessary when eliminating an image defect caused by a defective nozzle in a single-color area in the first embodiment. [Figure 11] 10A, 10B, and 10C are diagrams for explaining how to obtain a determination reference value for determining whether or not white correction is necessary when eliminating an image defect caused by a defective nozzle in a color mixing region in the first embodiment. [Figure 12] FIG. 2 is a diagram for explaining an overview of transparency correction in the first embodiment. [Figure 13] FIG. 10A is a diagram for explaining ink ejection when transparency correction is performed on a single-color area in the first embodiment, and FIG. 10B is a diagram for explaining ink ejection when transparency correction is performed on a mixed-color area. [Figure 14] FIG. 2 is a block diagram showing a detailed functional configuration of a density correction processing unit in the first embodiment. [Figure 15]FIG. 2 is a diagram showing an example of a template for white correction in the first embodiment. [Figure 16] FIG. 4 is a diagram for explaining creation of a correction pattern in the first embodiment. [Figure 17] FIG. 4 is a diagram for explaining creation of a correction pattern in the first embodiment. [Figure 18] FIG. 2 is a diagram showing an example of a template for white correction in the first embodiment. [Figure 19] FIG. 2 is a diagram showing an example of a template for white correction in the first embodiment. [Figure 20] FIG. 2 is a diagram showing an example of a template for white correction in the first embodiment. [Figure 21] 10 is a flowchart for explaining a procedure of density correction in the first embodiment. [Figure 22] FIG. 4 is a diagram for explaining an example of determining whether or not white correction needs to be performed in the first embodiment. [Figure 23] 23 is a diagram for explaining the effect of determining whether or not white correction is necessary for the region R3 shown in FIG. 22. FIG. [Figure 24] 23 is a diagram for explaining the effect of determining whether or not white correction is necessary for the region R4 shown in FIG. 22. FIG. [Figure 25] 23 is a diagram for explaining the effect of determining whether or not white correction is necessary for the region R5 shown in FIG. 22. FIG. [Figure 26] 23 is a diagram for explaining the effect of determining whether or not white correction is necessary for the region R6 shown in FIG. 22. FIG. [Figure 27] FIG. 10 is a block diagram showing a detailed functional configuration of a density correction processing unit in a first modified example of the first embodiment. [Figure 28] 10 is a flowchart illustrating a procedure for density correction in a first modified example of the first embodiment. [Figure 29]FIG. 10 is a block diagram showing a detailed functional configuration of a density correction processing unit in a second modified example of the first embodiment. [Figure 30] 10 is a flowchart illustrating a procedure for density correction in a second modified example of the first embodiment. [Figure 31] FIG. 10 is a diagram for explaining an outline of yellow correction in the third modified example of the first embodiment. [Figure 32] FIG. 10 is a diagram for explaining ink ejection in a region where yellow correction has been performed in the third modified example of the first embodiment. [Figure 33] FIG. 10 is a diagram illustrating an outline of a second embodiment of the present invention. [Figure 34] FIG. 11 is a block diagram showing a detailed functional configuration of a density correction processing unit in the second embodiment. [Figure 35] FIG. 11 is a diagram showing an example of a template for white correction in the second embodiment. [Figure 36] 10 is a flowchart for explaining a procedure of density correction in the second embodiment. [Figure 37] 10A and 10B are diagrams for explaining density uniformization correction and nozzle missing correction in a conventional example. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0024] <1. First embodiment> <1.1 Overall configuration of the printing system> FIG. 1 is a diagram illustrating the overall configuration of a printing system according to a first embodiment of the present invention. This printing system comprises 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 via a communication line 4. The print data generating device 30 generates print data by performing RIP processing and other processes on input data such as a PDF file. The print data comprises density data for each of multiple ink colors. The print data generated by the print data generating device 30 is transmitted to the inkjet printing device 10 via the communication line 4. The inkjet printing device 10 prints by ejecting ink onto a substrate, such as a printing medium like film or printing paper, based on the print data transmitted from the print data generating device 30, without using printing plates. In this embodiment, UV ink (ultraviolet-curable ink) is used for printing. The inkjet printing device 10 comprises a printing machine main body 100 and a print control device 200 that controls the operation of the printing machine main body 100.

[0025] <1.2 Configuration of inkjet printing device> FIG. 2 is a schematic diagram showing an example configuration of an inkjet printing device 10. As described above, the inkjet printing device 10 is composed of a printing press main body 100 and a printing control device 200. The printing press main body 100 includes a substrate delivery unit 11 that supplies the substrate 12, a first drive roller 13 that transports the substrate 12 into the printing mechanism, a plurality of support rollers 14 that transport the substrate 12 within the printing mechanism, a recording unit 15 that records an image on the substrate 12 by ejecting ink onto the substrate 12 and curing the ink ejected onto the substrate 12, an imaging unit 16 that captures an image of the printed image (the substrate 12 after printing), a second drive roller 17 that outputs the substrate 12 from the printing mechanism, and a substrate winding unit 18 that winds up the substrate 12 after printing. As described below, the recording unit 15 includes an ink ejection head that ejects ink and a UV-LED (ultraviolet light-emitting diode) that cures the ink. The print control device 200 controls the operation of the printer main body 100 configured as described above. The first drive roller 13, the plurality of support rollers 14, and the second drive roller 17 constitute a transport unit.

[0026] In this embodiment, before printing to obtain a desired printed matter, an inspection chart is printed to inspect the state of the nozzles in the ink ejection head. The printed image obtained by printing the inspection chart is captured by the imaging unit 16, and the captured image data is sent to the print control device 200. The print control device 200 then performs density correction, which will be described later, based on the captured image data.

[0027] FIG. 3 is a plan view schematically showing the configuration of the recording unit 15 in this embodiment. The recording unit 15 includes a plurality of ink ejection heads 150 that eject ink, and a plurality of UV-LEDs 159 that cure the ink ejected onto the substrate 12 by irradiating it with ultraviolet light. More specifically, the recording unit 15 includes an ink ejection head 150(W) that ejects white ink, a UV-LED 159(b) that cures the white ink ejected onto the substrate 12 by irradiating it with ultraviolet light, an ink ejection head 150(B) that ejects blue ink, an ink ejection head 150(O) that ejects orange ink, an ink ejection head 150(C) that ejects cyan ink, an ink ejection head 150(M) that ejects magenta ink, and an ink ejection head 150( The ink ejection head 150(W) for white ink and the ink ejection head 150(E) for transparent ink are disposed upstream of the ink ejection heads 150(B), 150(O), 150(C), 150(M), 150(Y), and 150(K) for black ink. The ink ejection head 150(W) for white ink and the ink ejection head 150(E) for transparent ink are disposed upstream of the ink ejection heads 150(B), 150(O), 150(C), 150(M), 150(Y), and 150(K) for color inks ...

[0028] In this embodiment, the ink ejection head 150(E) for transparent ink and the ink ejection head 150(W) for white ink are selectively used depending on the type of substrate 12 used for printing (white substrate 12 or substrate 12 other than a white substrate). That is, when a white substrate 12 is used for printing, white ink is ejected from the ink ejection head 150(W) onto the substrate 12. In this case, transparent ink is not ejected from the ink ejection head 150(E) onto the substrate 12. On the other hand, when a substrate 12 other than a white substrate is used for printing, transparent ink is ejected from the ink ejection head 150(E) onto the substrate 12. In this case, white ink is not ejected from the ink ejection head 150(W) onto the substrate 12.

[0029] The substrate 12, which serves as a printing medium, is transported from bottom to top in FIG. 3. First, transparent ink or white ink is ejected onto the substrate 12. Then, the transparent ink or white ink is cured by the UV-LED 159(a) corresponding to the transparent ink or the UV-LED 159(b) corresponding to the white ink. Next, blue ink, orange ink, cyan ink, magenta ink, yellow ink, and black ink are ejected onto the substrate 12 in this order, and the blue ink, orange ink, cyan ink, magenta ink, yellow ink, and black ink are cured by the UV-LED 159(c). However, if white ink is ejected onto the substrate 12 by performing white correction (described below), the white ink is not cured by the UV-LED 159(b). Therefore, if white correction is performed, color inks are ejected onto uncured white ink. Furthermore, if transparent ink is ejected onto the substrate 12 by performing transparency correction (described below), the transparent ink is not cured by the UV-LED 159(a). Therefore, even when transparency correction is performed, color ink is ejected onto the uncured transparent ink.

[0030] In this embodiment, the first ink ejection head and the second ink ejection head are realized by two or more of ink ejection head 150(C), ink ejection head 150(M), ink ejection head 150(Y), ink ejection head 150(K), ink ejection head 150(O), and ink ejection head 150(B), which are ink heads that eject ink other than white ink and transparent ink (process color ink or special color ink); the third ink ejection head is realized by either ink ejection head 150(W) or ink ejection head 150(E); the first ultraviolet irradiation unit is realized by UV-LED 159(c); and the second ultraviolet irradiation unit is realized by either UV-LED 159(b) or UV-LED 159(a).

[0031] 3 is merely an example, and the present invention is not limited to this. For example, it is also possible to employ a recording unit 15 that is not provided with an ink ejection head 150(B) that ejects blue ink or an ink ejection head 150(O) that ejects orange ink.

[0032] FIG. 4 is a plan view showing an example of the configuration of the ink ejection surface of one ink ejection head 150. The ink ejection head 150 is composed of one rectangular head module 151. The head module 151 has a large number of nozzles 152 as ink ejection orifices. In the example shown in FIG. 4, the shape of the head module 151 is a single rectangle, but this is not limited to this and various configurations can be adopted, such as being composed of multiple parallelogram head modules or multiple trapezoidal head modules. Note that the nozzles correspond to the ink ejection orifices, and the above-mentioned defective nozzles correspond to the defective ejection orifices.

[0033] FIG. 5 is a diagram for explaining the arrangement of nozzles 152 in the head module 151. Typically, the head module 151 includes multiple rows of nozzle groups, each consisting of multiple nozzles aligned in the main scanning direction. In the example shown in FIG. 5, the head module 151 includes four rows of nozzle groups. The portion marked with reference numeral 41 in FIG. 5 schematically shows the landing positions on the substrate 12 of ink ejected from each nozzle 152. The multiple nozzles 152 in the head module 151 are arranged so that the landing positions of ink ejected from the nozzles 152 included in the first row of nozzle groups, the landing positions of ink ejected from the nozzles 152 included in the second row of nozzle groups, the landing positions of ink ejected from the nozzles 152 included in the third row of nozzle groups, and the landing positions of ink ejected from the nozzles 152 included in the fourth row of nozzle groups are all different from one another. For example, the landing position of ink ejected from each nozzle 152 included in the first row of nozzles is located between the landing position of ink ejected from the nozzles 152 included in the third row of nozzles and the landing position of ink ejected from the nozzles 152 included in the fourth row of nozzles.

[0034] In the example shown in Figure 5, the landing position 42 of ink ejected from the nozzle denoted by reference numeral 152(p) and the landing position 43 of ink ejected from the nozzle denoted by reference numeral 152(q) are adjacent to each other. In this specification, two nozzles whose ink landing positions are adjacent to each other are treated as "neighboring nozzles." In the above example, the nozzle denoted by reference numeral 152(p) and the nozzle denoted by reference numeral 152(q) are treated as neighboring nozzles.

[0035] In the following, if the name of any color is "Z," the nozzles that eject Z ink (nozzles included in the ink ejection head 150 for Z ink) may be referred to as "Z ink ejection nozzles." For example, the nozzles that eject cyan ink (nozzles included in the ink ejection head 150(C) for cyan ink) may be referred to as "cyan ink ejection nozzles."

[0036] <1.3 Hardware configuration of print control device> FIG. 6 is a block diagram showing the hardware configuration of the print control device 200. As shown in FIG. 6, the print control device 200 includes a main body 210, an auxiliary storage device 221, an optical disk drive 222, a display unit 223, a keyboard 224, and a mouse 225. The main body 210 includes a CPU (processor) 211, a memory 212, a first disk interface unit 213, a second disk interface unit 214, a display control unit 215, an input interface unit 216, and a communication interface unit 217. The CPU 211, the memory 212, the first disk interface unit 213, the second disk interface unit 214, the display control unit 215, the input interface unit 216, and the communication interface unit 217 are connected to one another via a system bus. The auxiliary storage device 221 is connected to the first disk interface unit 213. The optical disk drive 222 is connected to the second disk interface unit 214. The display control unit 215 is connected to a display unit (display device) 223. A keyboard 224 and a mouse 225 are connected to the input interface unit 216. The printing machine main body 100 is connected to the communication interface unit 217 via a communication cable. The communication interface unit 217 is also connected to the communication line 4. The auxiliary storage device 221 is a magnetic disk device or the like. An optical disk 29, which is a computer-readable recording medium such as a CD-ROM or DVD-ROM, is inserted into the optical disk drive 222. The display unit 223 is a liquid crystal display or the like. The display unit 223 is used to display information desired by the operator. The keyboard 224 and mouse 225 are used by the operator to input instructions to this printing control device 200.

[0037] The auxiliary storage device 221 stores a print control program P (a program for controlling the execution of print processing by the printing press main body 100). The CPU 211 reads the print control program P stored in the auxiliary storage device 221 into the memory 212 and executes it, thereby realizing various functions of the print control device 200. The memory 212 includes RAM and ROM. The memory 212 functions as a work area for the CPU 211 to execute the print control program P stored in the auxiliary storage device 221. The print control program P is provided by being stored in the computer-readable recording medium (non-transitory recording medium). That is, a user, for example, purchases an optical disc 29 as a recording medium for the print control program P, inserts it into the optical disc drive 222, reads the print control program P from the optical disc 29, and installs it in the auxiliary storage device 221.

[0038] <1.4 White Compensation> In this embodiment, when the substrate used as the print medium for printing is a white substrate, when the above-described nozzle chipping correction is performed, a process is performed to correct the density data included in the print data so that white ink is ejected from the white ink ejection nozzle corresponding to the nozzle adjacent to the defective nozzle (hereinafter referred to as the "defective-adjacent nozzle" for convenience). Hereinafter, this process will be referred to as "white correction."

[0039] FIG. 7 is a diagram illustrating an overview of white correction. For ease of explanation, FIG. 7 shows multiple nozzles arranged in a row in each ink ejection head 150. The UV-LED 159 is also omitted from FIG. 7. Assume that the nozzle labeled 51 among the multiple nozzles included in the cyan ink ink ejection head 150(C) is a defective nozzle. In this case, by performing the above-described nozzle dropout correction, a larger amount of cyan ink is ejected from the nozzles adjacent to the defective nozzle (the nozzles labeled 52 and 53). Furthermore, by performing white correction, white ink is ejected from the nozzles corresponding to the defective nozzles (the nozzles labeled 54 and 55). In this example, the cyan ink corresponds to the first ink or the second ink, and the white ink corresponds to the third ink.

[0040] In this embodiment, white correction is performed on a high-density monochromatic area that is to be printed with the monochromatic ink ejected from a defective nozzle, among areas where printing is performed with a monochromatic ink (hereinafter referred to as a "monochromatic area"). If the ink ejection head 150(C) for cyan ink includes a defective nozzle as described above, white correction is performed on an area where high-density cyan monochromatic printing, for example, with a density of 80% or more, is performed. Details of the judgment criteria for determining the area where white correction should be performed (hereinafter referred to as a "white correction area" (or simply a "correction area")) will be described later.

[0041] In this embodiment, white correction is also performed on areas (hereinafter referred to as "mixed color areas") where mixed printing is performed using two or more inks of colors other than white ink and clear ink (process color inks or spot color inks): cyan (C), magenta (M), yellow (Y), black (K), blue (B), and orange (O). For example, in a mixed color area of cyan and magenta ink, if the ink ejection head 150(C) for cyan ink contains a defective nozzle as described above, white correction is performed on areas where the sum of the print density of the cyan ink and the print density of the magenta ink is 90% or more and the print density of the ink ejected from the ink ejection head containing the defective nozzle, i.e., the cyan ink, is 70%. In this example, in addition to nozzles 52 and 53 in the ink ejection head 150(C) for cyan ink, nozzles 49 and 50 in the ink ejection head 150(M) for magenta ink are also defective adjacent nozzles (see FIG. 7), with one of the cyan ink and the magenta ink corresponding to the first ink and the other corresponding to the second ink, respectively, and white ink corresponding to the third ink. Details of the judgment reference value for determining the area within the color mixture area where white correction should be performed (white correction area) will be described later.

[0042] In the above example where white correction is performed on a single-color region, when the white correction is performed, during printing, white ink is first ejected onto the substrate 12 from the white ink ejection nozzles 54 and 55 corresponding to the defective adjacent nozzles. Then, cyan ink is ejected from the defective adjacent nozzles 52 and 53 in the cyan ink ink ejection head 150(C). That is, in the region where white correction has been performed, cyan ink is ejected on top of the white ink ejected onto the substrate 12, as shown schematically in FIG. 8(A).

[0043] The wet spread range of a color ink (cyan ink in the above example) on the substrate 12 is larger when the color ink is ejected onto white ink that has been ejected onto the substrate 12 than when the color ink is ejected directly onto the substrate 12. Here, the wet spread range refers to the area occupied by dots formed on the print medium by ejecting the ink. Therefore, the size of dots formed on the substrate 12 as a print medium by ejecting the color ink is larger when the color ink is ejected onto white ink that has been ejected onto the substrate 12 than when the color ink is ejected directly onto the substrate 12. An example of the results of an experiment related to this is shown in FIG. 9. The area marked with reference numeral 61 in FIG. 9 shows the dot size (of the ink) obtained when the color ink is ejected directly onto a certain film substrate, and the area marked with reference numeral 62 in FIG. 9 shows the dot size (of the ink) obtained when the color ink is ejected onto the certain substrate after ejecting white ink. It can be seen that for all color inks, the wet spread range is increased (the dot size of the color ink is artificially increased) by ejecting white ink onto the substrate beforehand. In view of the above, by ejecting white ink in advance to the position (position on the substrate 12) where color ink is ejected from the nozzle adjacent to the defective nozzle, the color ink ejected from the nozzle adjacent to the defective nozzle will spread sufficiently on the substrate 12, and the effect of nozzle missing correction (the effect of suppressing the occurrence of image defects caused by the defective nozzle and preventing a decline in print quality) will be enhanced.

[0044] Furthermore, although the white ink is normally cured by ultraviolet irradiation after being ejected, in this embodiment, when white ink is ejected onto a target area due to white correction, ultraviolet irradiation of the white ink by UV-LED 159(b) is stopped or the intensity of the ultraviolet irradiation is reduced. By stopping ultraviolet irradiation of the white ink in this way (meaning stopping ultraviolet irradiation or reducing the intensity of ultraviolet irradiation), the range over which the white ink wets and spreads is increased, and the range over which the color inks ejected onto the white ink wet and spread is also effectively increased.

[0045] In the above example where white correction is performed on the color mixture region, when the white correction is performed, during printing, white ink is first ejected onto the substrate 12 from the white ink ejection nozzles 54, 55 corresponding to the defective adjacent nozzles. Then, cyan ink is ejected from the defective adjacent nozzles 52, 53 in the cyan ink ink ejection head 150(C), and then magenta ink is ejected from the defective adjacent nozzles 49, 50 in the magenta ink ejection head 150(M) (see FIG. 7). That is, in the region where white correction has been performed, cyan ink is ejected onto the white ink ejected onto the substrate 12, and magenta ink is ejected onto the cyan ink, as shown schematically in FIG. 8(B).

[0046] <1.5 How to determine the white correction area> As described above, conventional nozzle missing correction (hereinafter also referred to as "normal nozzle missing correction") may not be able to fully resolve printed image defects (typically streaky density reductions due to missing dots) caused by poor ink ejection. In particular, when image defects caused by poor ejection occur in high-density monochromatic areas, the dot size of the ink ejected from the nozzle adjacent to the defective nozzle is insufficient to resolve the image defect. While white correction as described above can be performed to resolve such printed image defects, depending on the density of the image to be printed (or the corresponding ink amount per pixel), performing white correction may result in excessive correction or unnecessary consumption of white ink. For this reason, it is necessary to determine in advance an appropriate reference value (a reference value for determining whether white correction is appropriate) for determining whether white correction or normal nozzle missing correction should be performed when image defects caused by poor ejection occur in monochromatic areas. Furthermore, when image defects caused by poor ejection occur in multicolor areas, whether white correction is appropriate depends on the total ink amount (TAC (Total Area Coverage) value), which is the sum of the ink amounts per pixel of multiple colors of ink ejected in the multicolor area. Furthermore, even if the total ink volume is the same, whether or not it is appropriate to perform white correction depends on the proportion of the ink volume per pixel that should be ejected from the defective nozzle into the color-mixed area to the total ink volume (hereinafter referred to as the "defective nozzle ink volume proportion").

[0047] Therefore, in this embodiment, when an image defect due to poor ejection occurs in a single-color area, the maximum total ink amount that can sufficiently eliminate the image defect with normal nozzle missing correction is determined as the first judgment reference value. Also, when an image defect due to poor ejection occurs in a mixed-color area, the combination of the maximum total ink amount and the maximum defective nozzle ink amount ratio that can sufficiently eliminate the image defect with normal nozzle missing correction is determined in advance (hereinafter, these maximum values are referred to as the "second judgment reference value" and "third judgment reference value," respectively).

[0048] <1.5.1 Criteria for determining whether white correction is necessary in monochrome areas> The following describes how to determine the first judgment reference value for determining whether white correction is necessary when eliminating image defects caused by defective nozzles in a single-color region. First, print data is prepared, including density data representing an image including a single-color region in which the density continuously and monotonically changes in the transport direction of the substrate 12 (hereinafter referred to as a "single-color gradation region"), as shown in FIG. 10(A). When printing is performed using this print data while ink ejection from one nozzle in the ink ejection head corresponding to that single color is stopped (hereinafter referred to as "virtual defective nozzle printing"), a printed image is obtained that includes image defects caused by missing dots (visually recognized as white streaks), as shown in FIG. 10(B). To determine the first judgment reference value, normal corrected density data is obtained by performing normal nozzle dropout correction for the single-color gradation region on the density data included in the print data, and white correction (nozzle dropout correction using white ink) for the single-color gradation region is also obtained by performing white correction on the density data included in the print data.

[0049] Next, a monochromatic gradation area in a printed image (hereinafter referred to as the "normally corrected printed image") obtained by performing virtual defective nozzle printing using print data including normal correction density data is visually identified as a portion of the monochromatic gradation area where the image defect is eliminated. This area is then used to determine the maximum density of the monochromatic area that can sufficiently eliminate the image defect with normal nozzle drop correction. Here, the monochromatic density corresponds to the amount of ink of the monochromatic color per pixel. Hereinafter, this will be referred to as the "monochromatic ink amount," and will be expressed as a percentage, with the maximum amount of ink of the monochromatic color usable per pixel being 100%. In a monochromatic area, the ink amount of ink colors other than the monochromatic color is zero, so the monochromatic ink amount is equal to the total ink amount. Therefore, in this embodiment, the monochromatic ink amount corresponding to the maximum value visually determined from the monochromatic gradation area in the normal corrected printed image as described above is used as a provisional first reference value. Then, if it is confirmed by visual inspection from the monochromatic gradation region in the printed image (hereinafter referred to as the "white-corrected printed image") obtained by performing virtual defective nozzle printing using print data including the white correction density data that the provisional first judgment reference value is not over-corrected, the provisional first judgment reference value is set as the first judgment reference value. If it is determined that the provisional first judgment reference value is over-corrected, the minimum value of the monochromatic density at which the image defect is eliminated without over-correction is determined by visual inspection from the monochromatic gradation region, and the ink amount of the monochromatic color that is determined to be able to effectively eliminate the image defect between the ink amount of the monochromatic color corresponding to the minimum value and the ink amount of the monochromatic color corresponding to the maximum value is determined by visual inspection, and this is set as the first judgment reference value. However, the first judgment reference value may also be determined by a method other than this as a value between the ink amount of the monochromatic color corresponding to the minimum value and the ink amount of the monochromatic color corresponding to the maximum value.

[0050] The above-described normal-corrected printed image and white-corrected printed image were actually formed on the substrate 12 for each of cyan, magenta, yellow, black, blue, and orange, and the resulting single-color gradation regions were visually evaluated as described above. It was confirmed that the above-described image defects were sufficiently eliminated in the normal-corrected printed image in areas where the single-color ink amount was 60% or less, and that over-correction did not occur in the white-corrected printed image when the single-color ink amount was 60%. Therefore, in this embodiment, the first judgment reference value is set to 60%. As a result, when an image defect occurs in a single-color region due to poor ejection from a defective nozzle, the region including the position corresponding to the defective nozzle is determined to be a normal-corrected region if the single-color ink amount is 60% or less, and the region is determined to be a white-corrected region if the single-color ink amount is greater than 60%.

[0051] <1.5.2 Criteria for determining whether white correction is necessary in color mixture areas> Next, we will explain how to calculate the second and third judgment criteria for determining whether white correction is necessary when eliminating image defects caused by defective nozzles in a color mixture area. First, for each of the various types of color mixture shown in Figures 11(A) to 11(C), print data is prepared, including density data representing an image including the color mixture area of that type. In Figure 11, the "Xn / Zm" markings at the top of each color mixture area indicate that the color mixture area is formed by ejecting n% of the ink volume of X color and m% of the ink volume of Z color. For example, the "C90 / M10" markings at the left of the three color mixture areas shown in Figure 11(A) indicate that the left color mixture area is formed by ejecting 90% of the ink volume of cyan (C) ink and 10% of the ink volume of magenta (M) ink.

[0052] For each of the multiple print data prepared as described above (eight print data in the example shown in Figure 11), it is assumed that ink ejection from one nozzle in the ink ejection head that is supposed to eject one ink color that makes up the mixed color corresponding to the print data has stopped, and normal corrected density data is obtained by performing normal nozzle dropout correction on the mixed color area of the density data included in the print data, and white correction is obtained by performing white correction on the mixed color area of the density data included in the print data.

[0053] Next, a print image (normally corrected printed image) is formed on the substrate 12 by performing printing (virtual defective nozzle printing) while stopping ink discharge from one nozzle in the ink discharge head corresponding to the one ink color using print data including the normal correction density data, and it is visually determined whether the image defect caused by the stoppage of ink discharge from the one nozzle has been eliminated in the normal corrected printed image. Also, a white corrected printed image is formed on the substrate 12 by performing printing (virtual defective nozzle printing) while stopping ink discharge from one nozzle in the ink discharge head corresponding to the one ink color using print data including white correction density data, and it is visually determined whether the image defect caused by the stoppage of ink discharge from the one nozzle has been eliminated in the white corrected printed image. Visual evaluation of the normal-corrected printed image and the white-corrected printed image was performed for multiple print data corresponding to various forms of color mixing. It was confirmed that, in a color mixing area containing an image defect due to a defective nozzle, the image defect was eliminated in the normal-corrected printed image corresponding to the color mixing area when the total ink volume was 90% or less, or when the ratio of the ink volume of the ink color to be ejected from the defective nozzle (hereinafter referred to as the "defective nozzle color") to the total ink volume (defective nozzle ink volume ratio) was 60% or less. Furthermore, in a color mixing area containing an image defect due to a defective nozzle, when the total ink volume was greater than approximately 90% and the defective nozzle ink volume ratio was greater than approximately 60%, no over-correction was observed in the white-corrected printed image corresponding to the color mixing area. Therefore, in this embodiment, the second judgment criterion value is set to 90% and the third judgment criterion value is set to 60%. As a result, if an image defect occurs in a mixed color area due to poor ejection from a defective nozzle, the area of this mixed color area that includes the position corresponding to the defective nozzle is determined to be a normal correction area if the total ink amount is 90% or less or the defective nozzle ink amount ratio is 60% or less, and if the total ink amount is greater than 90% and the defective nozzle ink amount ratio is greater than 60%, the area is determined to be a white correction area.

[0054] 11, for the sake of convenience, eight print data are prepared for the visual evaluation of the normal-corrected printed image and the white-corrected printed image, but in reality, more print data corresponding to various forms of color mixing are prepared, and practical judgment criteria (second and third judgment criteria values) for determining whether or not white correction is required in the color mixing area are determined using these print data. Furthermore, the specific numerical values of the above-mentioned first judgment criteria value (60%), second judgment criteria value (90%), and third judgment criteria value (60%) are merely examples, and it goes without saying that other numerical values are possible.

[0055] <1.6 Transparency Correction> In this embodiment, if the substrate used as the print medium for printing is a substrate other than a white substrate (for example, a transparent substrate or a silver substrate), when the above-mentioned nozzle missing correction is performed, a process is performed to correct the density data included in the print data so that clear ink is ejected from the clear ink ejection nozzle corresponding to the nozzle adjacent to the defective nozzle (defective-adjacent nozzle). Hereinafter, this process will be referred to as "transparency correction."

[0056] Here, let's assume that the nozzle indicated by reference numeral 511 in Figure 12 is a defective nozzle among the multiple nozzles included in the cyan ink ink ejection head 150(C). In this case, when the above-described nozzle missing correction is performed, a larger amount of cyan ink is ejected from the nozzles adjacent to the defective nozzle (the nozzles indicated by reference numerals 512 and 513). Furthermore, when transparency correction is performed, transparent ink is ejected from the transparent ink ejection nozzles corresponding to the defective adjacent nozzle (the nozzles indicated by reference numerals 514 and 515).

[0057] In the above example where transparency correction is performed on a single-color region, when the transparency correction is performed, during printing, clear ink is first ejected onto the substrate (transparent substrate) 12 from the clear ink ejection nozzle corresponding to the defective adjacent nozzle. Then, cyan ink is ejected from the defective adjacent nozzle. That is, in the region where transparency correction has been performed, cyan ink 6(C) is ejected onto the clear ink 6(T) ejected onto the substrate (transparent substrate) 12, as shown schematically in FIG. 13(A).

[0058] As with white correction, in transparency correction, the wet spread range of a color ink (cyan ink in the above example) on the substrate 12 is larger when the color ink is ejected onto transparent ink ejected onto the substrate 12 than when the color ink is ejected directly onto the substrate 12. As described above, the wet spread range refers to the area occupied by dots formed on the printing medium by ejecting ink. Therefore, the size of dots formed on the substrate 12 as the printing medium by ejecting color ink is larger when the color ink is ejected onto transparent ink ejected onto the substrate 12 than when the color ink is ejected directly onto the substrate 12 (see FIG. 9). Therefore, by ejecting transparent ink in advance at a position (a position on the substrate 12) where color ink is ejected from the defective-adjacent nozzle, the color ink ejected from the defective-adjacent nozzle spreads sufficiently on the substrate 12, thereby enhancing the effect of nozzle missing correction (the effect of suppressing image defects caused by defective nozzles and preventing a decline in print quality).

[0059] Furthermore, in this embodiment, when transparent ink is ejected onto a target area due to transparency correction, the UV-LED 159(a) stops irradiating the transparent ink with ultraviolet light. By stopping UV irradiation onto the transparent ink in this manner, the wet spreading range of the transparent ink increases, and the wet spreading range of the color inks ejected onto the transparent ink also effectively increases.

[0060] In the above example where transparency correction is performed on the mixed color region, when the transparency correction is performed, during printing, clear ink is first ejected onto the substrate 12 from the clear ink ejection nozzles 514, 515 corresponding to the defective adjacent nozzles. Then, cyan ink is ejected from the defective adjacent nozzles 512, 513 in the cyan ink ejection head 150(C), and then magenta ink is ejected from the defective adjacent nozzles 509, 510 in the magenta ink ejection head 150(M). That is, in the region where transparency correction has been performed, cyan ink 6(C) is ejected onto the clear ink 6(T) ejected onto the substrate 12, and magenta ink 6(M) is ejected onto the cyan ink 6(C), as shown schematically in FIG. 13(B).

[0061] <1.7 Density correction> In the inkjet printing device 10 according to this embodiment, the above-described white correction and transparency correction are performed in addition to the conventional density uniformity correction and missing nozzle correction. In this specification, a series of processes including density uniformity correction, missing nozzle correction, white correction, and transparency correction is referred to as "density correction." Execution of the print control program P in the print control device 200 realizes a density correction processing unit 24, which is a functional component for performing density correction. Note that white correction and transparency correction are selectively performed depending on the type of substrate 12 used for printing (whether it is a white substrate or a substrate other than a white substrate).

[0062] <1.7.1 Functional configuration> Fig. 14 is a block diagram showing a detailed functional configuration of the density correction processing unit 24 in this embodiment. As shown in Fig. 14, the density correction processing unit 24 includes a correction coefficient calculation unit 241, a defective nozzle detection unit 242, a substrate determination unit 243, a print data storage unit (image memory) 244, a white correction determination unit 245a, a white correction target nozzle identification unit 246a, a white correction pattern creation unit 247a, a transparent correction determination unit 245b, a transparent correction target nozzle identification unit 246b, a transparent correction pattern creation unit 247b, an ink ejection control unit 248, and a UV-LED setting unit 249. The ink ejection control unit 248 includes a first correction processing unit 2481, a second correction processing unit 2482, and a third correction processing unit 2483.

[0063] The correction coefficient calculation unit 241 calculates a correction coefficient 71 for performing density uniformity correction based on the imaging data 70 obtained by capturing an image of the print image of the above-described inspection chart with the imaging unit 16. For example, when focusing on a certain nozzle, if the density obtained by ejecting ink from that nozzle is 4 / 5 times the original density, the correction coefficient 71 corresponding to that nozzle is set to 1.25.

[0064] The defective nozzle detection unit 242 detects defective nozzles, which are nozzles that are in a state of poor ejection, from among the many nozzles included in the color ink ink ejection head 150 based on the imaging data 70. Then, defective nozzle information 72 that identifies the defective nozzle is output from the defective nozzle detection unit 242. Note that if no defective nozzles are detected, only density uniformity correction is performed by the first correction processing unit 2481 in the ink ejection control unit 248.

[0065] The substrate determination unit 243 determines the substrate to be used as the print medium for printing, for example, based on the set printing conditions. Then, substrate information 73 that identifies the substrate is output from the substrate determination unit 243.

[0066] The print data storage unit 244 temporarily stores the print data (RIP-processed data) 74 transmitted from the print data generating device 30. The print data storage unit 244 is realized by the memory 212 (see FIG. 6) as hardware.

[0067] The white correction determination unit 245a determines whether or not to perform white correction based on the defective nozzle information 72, the substrate information 73, and the print data 74. Then, the determination result 75a is output from the white correction determination unit 245a. In this embodiment, a determination is made based on the substrate information 73 that white correction will not be performed if the substrate used for printing is other than a white substrate. Furthermore, based on the defective nozzle information 72 and the print data 74, a determination is made to perform white correction if a defective nozzle is present and the area into which ink is ejected from the defective nozzle and its neighboring nozzles includes an area where high-density monochromatic printing is performed using ink of the color that should be ejected from the defective nozzle, more specifically, if the area includes an area where printing is performed with a total ink amount (= ink amount of the monochromatic color) greater than the first determination reference value.

[0068] Furthermore, if a defective nozzle is present and the area into which ink is ejected from the defective nozzle and its neighboring nozzles includes an area where high-density mixed printing is performed using two or more colors of ink, including the color that should be ejected from the defective nozzle (defective nozzle color), where the density of the defective nozzle color is high, more specifically, if the area includes an area where printing is performed where the total ink amount is greater than the second judgment reference value and the defective nozzle ink amount ratio (the ratio of the ink amount of the defective nozzle color to the total ink amount) is greater than the third judgment reference value, a determination is made to perform white correction.

[0069] In other words, even if a defective nozzle is present, if the area into which ink is ejected from the defective nozzle and its neighboring nozzles does not include an area where high-density monochromatic printing is performed using the ink of the color that should be output from the defective nozzle (ink of the defective nozzle color), and also does not include an area where high-density mixed-color printing using two or more ink colors, including the ink of the defective nozzle color, is performed with a high proportion of ink from the defective nozzle, then a determination is made not to perform white correction.In this way, white correction is performed only in areas where image defects caused by the presence of a defective nozzle cannot be fully resolved by normal nozzle drop correction, thereby reducing unnecessary consumption of white ink.

[0070] If the determination result 75a output from the white correction determination unit 245a indicates that white correction is to be performed, the white correction target nozzle identifying unit 246a identifies nozzles that eject white ink for white correction (hereinafter referred to as "white correction target nozzles") from among the many nozzles included in the ink ejection head 150(W) for white ink, based on the defective nozzle information 72 and the print data 74. Then, white correction target nozzle information 76a that identifies the white correction target nozzles is output from the white correction target nozzle identifying unit 246a.

[0071] In this embodiment, a template is prepared that defines the pattern in which white ink is ejected onto pixels within a printing area through white correction. The template is referenced by the white correction target nozzle identification unit 246a and the white correction pattern creation unit 247a. For example, a template such as that shown in FIG. 15 is prepared. In FIG. 15, the pixel portions in the column labeled 64 correspond to defective nozzles, and the shaded pixel portions are the pixel portions to which white ink is to be ejected. Note that, in the main scanning direction, each nozzle corresponds to one pixel portion. In the example shown in FIG. 15, the columns labeled 64L and 64R include the shaded pixel portions. Therefore, of the many nozzles included in the white ink inkjet head 150(W), the nozzles that eject ink onto pixel portions in the column labeled 64L and the nozzles that eject ink onto pixel portions in the column labeled 64R are identified as nozzles to be corrected by the white correction target nozzle identification unit 246a.

[0072] The white correction pattern creation unit 247a creates a white correction pattern 77a that represents a pattern such as that shown in the template described above over the entire printing area, based on the white correction target nozzle information 76a and the printing data 74. In this embodiment, the area onto which white ink is to be ejected based on this white correction pattern 77a is treated as a correction area (this correction area will be referred to as a "white correction area" when it needs to be distinguished from a transparent correction area described below). Therefore, creating the white correction pattern 77a corresponds to determining a correction area.

[0073] As described above, in this embodiment, white correction is performed on areas where high-density monochromatic printing is performed and areas where high-density mixed-color printing (printing with a large total ink volume) with a high proportion of defective nozzle ink volume is performed. Here, for example, assume that a defect occurs in a cyan ink ejection nozzle ejecting ink in the dotted line area indicated by reference numeral 57 in FIG. 16 , and high-density monochromatic printing using cyan ink is performed in the rectangular area indicated by reference numeral 58. In this case, the white correction pattern 77a created by the white correction pattern creation unit 247a is as shown in FIG. 17 so that white correction is performed only on the area where high-density monochromatic printing using cyan ink is performed. Even when white correction is performed on an area where high-density mixed-color printing with a high proportion of defective nozzle ink volume is performed, the white correction pattern 77a created by the white correction pattern creation unit 247a, as shown in FIG. 17, is used so that white correction is performed only on the area where white correction is performed. However, for the sake of convenience, the white correction pattern 77a will be described below only in the case where white correction is performed in an area where single-color high-density printing is performed.

[0074] The transparency correction determination unit 245b determines whether or not to perform transparency correction based on the defective nozzle information 72, the substrate information 73, and the print data 74. The determination result 75b is then output from the transparency correction determination unit 245b. In this regard, in the present embodiment, a determination is made based on the substrate information 73 that transparency correction will not be performed if the substrate used for printing is a white substrate.

[0075] Furthermore, based on the defective nozzle information 72 and the print data 74, if a defective nozzle is present and the area into which ink is ejected from the defective nozzle and its neighboring nozzles includes an area where high-density monochrome printing is performed using ink of the color that should be ejected from the defective nozzle, or more specifically, if the area includes an area where printing is performed in which the total ink amount (= ink amount of that monochrome) is greater than the transparent correction first judgment reference value corresponding to the first judgment reference value in the white correction judgment unit 245a, the transparent correction judgment unit 245b makes a judgment to perform transparent correction. Furthermore, if a defective nozzle is present and the area into which ink is ejected from the defective nozzle and its neighboring nozzles includes an area where a high-density mixed print of two or more colors of ink including the color that should be ejected from the defective nozzle (defective nozzle color) is performed, and where a high density print of the defective nozzle color is performed, more specifically, if the area includes a print where the total ink amount is greater than the second transparent correction judgment reference value corresponding to the second judgment reference value in the white correction judgment unit 245a and the defective nozzle ink amount ratio (the ratio of the ink amount of the defective nozzle color to the total ink amount) is greater than the third transparent correction judgment reference value corresponding to the third judgment reference value in the white correction judgment unit 245a, the transparent correction judgment unit 245b will make a judgment to perform transparent correction.

[0076] In other words, even if a defective nozzle is present, if the area into which ink is ejected from the defective nozzle and its neighboring nozzles does not include an area where a single-color high-density print is performed using the ink of the defective nozzle, or an area where a mixed-color high-density print is performed using two or more ink colors, including the ink of the defective nozzle, with a high proportion of ink from the defective nozzle, a determination is made not to perform transparency correction. In this way, transparency correction is performed only in areas where image defects caused by the presence of a defective nozzle cannot be sufficiently corrected by normal nozzle drop correction, thereby reducing the waste of transparent ink. The first, second, and third transparency correction reference values can be calculated in advance using the same method as the previously described method for calculating the first, second, and third reference values used in the white correction determination unit 245a (see FIGS. 10 and 11).

[0077] If the determination result 75b output from the transparency correction determination unit 245b indicates that transparency correction should be performed, the transparency correction target nozzle identifying unit 246b identifies nozzles that eject transparent ink for transparency correction (hereinafter referred to as "transparent correction target nozzles") from among the many nozzles included in the transparent ink ejection head 150(E) based on the defective nozzle information 72 and the print data 74. Then, transparency correction target nozzle information 76b that identifies the transparent correction target nozzles is output from the transparency correction target nozzle identifying unit 246b.

[0078] The transparent correction pattern creation unit 247b creates a transparent correction pattern 77b that represents a pattern such as that shown in the template described above over the entire printing area, based on the transparent correction target nozzle information 76b and the print data 74. In this embodiment, the area onto which transparent ink is to be ejected based on this transparent correction pattern 77b is treated as a transparent correction area. Therefore, creating the transparent correction pattern 77b corresponds to determining a transparent correction area.

[0079] 14, the ink discharge control unit 248 corrects the density data included in the print data 74 and controls the discharge of ink from each ink discharge head 150 based on the corrected density data 78. As described above, the ink discharge control unit 248 includes a first correction processing unit 2481, a second correction processing unit 2482, and a third correction processing unit 2483. If the determination results 75a and 75b output from the white correction determination unit 245a and the transparency correction determination unit 245b, respectively, indicate that neither white correction nor transparency correction will be performed, the first correction processing unit 2481 corrects the density data included in the print data 74. If the determination result 75a indicates that white correction will be performed, the second correction processing unit 2482 corrects the density data included in the print data 74. If the determination result 75b indicates that transparency correction will be performed, the third correction processing unit 2483 corrects the density data included in the print data 74.

[0080] The first correction processing unit 2481 performs density uniformity correction and nozzle missing correction based on the correction coefficients 71, defective nozzle information 72, and print data 74. As a result, correction is applied to the density data included in the print data 74, and density data 78 is generated as normal corrected density data for controlling the ejection of ink from each ink ejection head 150.

[0081] The second correction processing unit 2482 performs density uniformity correction, nozzle missing correction, and white correction based on the correction coefficients 71, defective nozzle information 72, correction pattern 77a, and print data 74. As a result, corrections are made to the density data included in the print data 74, and density data 78 is generated as white-corrected density data for controlling the ejection of ink from each ink ejection head 150.

[0082] The third correction processing unit 2483 performs density uniformity correction, nozzle missing correction, and transparency correction based on the correction coefficients 71, defective nozzle information 72, transparent correction pattern 77b, and print data 74. As a result, corrections are made to the density data included in the print data 74, and density data 78 is generated as transparency-corrected density data for controlling the ejection of ink from each ink ejection head 150.

[0083] Each ink ejection head 150, including the ink ejection head 150(W) for white ink and the ink ejection head 150(E) for transparent ink, is configured to eject ink droplets of a plurality of different droplet sizes. Specifically, a piezoelectric element (piezoelectric element) is provided corresponding to each nozzle in the ink ejection head 150. The size of the ink droplets ejected from the nozzles can be varied by changing the voltage waveform of the drive signal applied to the piezoelectric element. In this embodiment, the second correction processing unit 2482 corrects the density data so that the white ink is ejected in the correction area at the smallest droplet size of the plurality of droplet sizes. That is, the ink ejection control unit 248 controls the ejection of white ink from the ink ejection head 150(W) so that the white ink is ejected in the correction area at the smallest droplet size of the plurality of droplet sizes. This prevents the white ink from being consumed more than necessary in order to widen the wetting and spreading range of the color inks. However, white ink may be ejected in a droplet size other than the smallest droplet size into the correction area. The ink ejection control unit 248 controls the ejection of white ink in the same manner as it controls the ejection of clear ink.

[0084] The time it takes for a color ink to be cured by ultraviolet light irradiation from the UV-LED 159(c) after being ejected from the ink ejection head 150 onto the substrate 12 varies depending on the color of the ink. Referring to FIG. 3 , for example, it can be seen that the time it takes for black ink to be cured after being ejected from the ink ejection head 150(K) onto the substrate 12 is significantly shorter than the time it takes for blue ink to be cured after being ejected from the ink ejection head 150(B) onto the substrate 12. Therefore, with regard to white correction, if the droplet size of the white ink ejected from the ink ejection head 150(W) is constant, it is conceivable that the wet spreading range of the black ink will be smaller than the wet spreading range of the blue ink. Therefore, the ejection of white ink from the ink ejection head 150(W) may be controlled so that the size of the white ink increases as the distance from the ink ejection head 150 corresponding to the color ink ejected onto the white ink in the white correction region decreases. For the same reason, the ejection of transparent ink from ink ejection head 150(E) may be controlled so that the size of the transparent ink increases as the distance from ink ejection head 150 corresponding to the color ink ejected onto the transparent ink in the transparent correction area to UV-LED 159(c) decreases.

[0085] The UV-LED setting unit 249 controls ultraviolet radiation by the UV-LED 159(b) for white ink by providing an ultraviolet radiation control signal 79 to the UV-LED 159(b) based on the determination result 75a output from the white correction determination unit 245a, and also controls ultraviolet radiation by the UV-LED 159(a) for transparent ink by providing an ultraviolet radiation control signal 79 to the UV-LED 159(a) based on the determination result 75b output from the transparent correction determination unit 245b. Specifically, if the determination result 75a of the white correction determination unit 245a indicates that white correction should be performed, the UV-LED setting unit 249 stops ultraviolet radiation by the UV-LED 159(b), and if the determination result 75b of the transparent correction determination unit 245b indicates that transparent correction should be performed, the UV-LED setting unit 249 stops ultraviolet radiation by the UV-LED 159(b). Note that when the determination result 75a indicates that white correction should be performed, the UV-LED setting unit 249 may reduce the intensity of ultraviolet light irradiation by the UV-LED 159(b). In other words, if the wetting and spreading range of the color ink is sufficiently wide when the color ink is ejected onto the white ink, it is not necessary to stop ultraviolet light irradiation of the white ink by the UV-LED 159(b). This also applies to the control of ultraviolet light irradiation by the UV-LED 159(a) by the UV-LED setting unit 249 when the determination result 75b indicates that transparency correction should be performed.

[0086] In this embodiment, the calculation of the correction coefficient 71 by the correction coefficient calculation unit 241 and the identification of defective nozzles by the defective nozzle detection unit 242 are performed based on the image data 70, but the present invention is not limited to this. If an inkjet printing apparatus 10 that does not include an image capture unit 16 is used, the calculation of the correction coefficient 71 and the identification of defective nozzles may be performed by an operator visually checking the printed image of the inspection chart.

[0087] Alternatively, instead of the substrate determination unit 243, a configuration may be adopted that includes a component that receives input of substrate information 73 by an operator, and processing by the white correction determination unit 245a (processing that determines whether or not to perform white correction) and processing by the transparency correction determination unit 245b (processing that determines whether or not to perform transparency correction) may be performed based on the substrate information 73 received by the component.

[0088] In this embodiment, a correction area determination unit is realized by a white correction determination unit 245a, a white correction target nozzle identification unit 246a, a white correction pattern creation unit 247a, a transparent correction determination unit 245b, a transparent correction target nozzle identification unit 246b, and a transparent correction pattern creation unit 247b, and an ultraviolet irradiation control unit is realized by a UV-LED setting unit 249.

[0089] <1.7.2 Correction pattern template> In the above description, it is assumed that the template shown in FIG. 15 is prepared as the template that serves as the basis for the white correction pattern 77a and the transparent correction pattern 77b created by the white correction pattern creation unit 247a and the transparent correction pattern creation unit 247b, respectively. However, the templates that can be used are not limited to the template shown in FIG. 15. For example, the templates shown in FIG. 18, FIG. 19, and FIG. 20 can also be used. Templates other than those shown in FIGS. 15, 18, and 20 can also be used. Note that, in order to ensure a margin of error in printing position and a sufficient wet spread range for white correction and transparent correction, it is preferable to perform white printing or transparent printing in the ±2 pixel area and printing with an increased amount of ink in the ±1 pixel area for the pixel area corresponding to the defective nozzle. Therefore, it is preferable to use the templates shown in FIG. 18 or 20. Note that, while the nozzles to be corrected are identified using the templates described above, these templates can be used in both white correction and transparent correction. However, for convenience, the following description of such templates will be limited to the case of white correction.

[0090] 15 or 19 is adopted, of the many nozzles included in the inkjet head 150(W) for white ink, the nozzles that eject ink to pixel portions in the column labeled 64L and the nozzles that eject ink to pixel portions in the column labeled 64R are identified as nozzles that are subject to white correction. When the template shown in Fig. 18 or 20 is adopted, of the many nozzles included in the inkjet head 150(W) for white ink, the nozzles that eject ink to pixel portions in the column labeled 64, the nozzles that eject ink to pixel portions in the column labeled 64L1, the nozzles that eject ink to pixel portions in the column labeled 64R1, the nozzles that eject ink to pixel portions in the column labeled 64L2, and the nozzles that eject ink to pixel portions in the column labeled 64R2 are identified as nozzles that are subject to white correction.

[0091] Furthermore, when focusing on the transport direction of the substrate 12 with respect to the pixel portions onto which white ink is ejected, when the template shown in Figure 15 or Figure 18 is adopted, one pixel portion onto which white ink is ejected and one pixel portion onto which white ink is not ejected appear alternately, and when the template shown in Figure 19 or Figure 20 is adopted, two pixel portions onto which white ink is ejected and two pixel portions onto which white ink is not ejected appear alternately.

[0092] <1.7.3 Procedure> The density correction procedure in this embodiment will be described below with reference to Fig. 21. It is assumed that the print data 74 to be processed is already stored in the print data storage unit 244 (see Fig. 14).

[0093] In this embodiment, the main part (configuration other than the components realized by hardware) of the density correction processing unit 24 shown in Fig. 14 is realized in software by the CPU 211 in the control unit 200 shown in Fig. 6 performing density correction processing according to the procedure shown in Fig. 21 in accordance with the print control program P. In this density correction processing, the CPU 211 operates as follows.

[0094] After the density correction process starts, the recording unit 15 and the conveying unit are controlled to print an inspection chart for inspecting the state of the nozzles in the ink ejection heads 150 for color inks (specifically, the ink ejection head 150(B) for blue ink, the ink ejection head 150(O) for orange ink, the ink ejection head 150(C) for cyan ink, the ink ejection head 150(M) for magenta ink, the ink ejection head 150(Y) for yellow ink, and the ink ejection head 150(K) for black ink) (step S110). Then, the imaging unit 16 is caused to capture a printed image obtained by printing the inspection chart (step S112). As a result, the imaging unit 16 outputs the captured image data 70.

[0095] Thereafter, defective nozzles are detected from among the many nozzles included in the ink ejection head 150 for color ink based on the imaging data 70 (step S114). Next, correction coefficients 71 for performing density uniformity correction are calculated based on the imaging data 70 (step S116).

[0096] After calculating the correction coefficient 71, the substrate (print medium) used for printing is determined based on, for example, the set printing conditions, and substrate information 73 that identifies the substrate is generated (step S118). Then, it is determined based on the substrate information 73 whether the substrate used for printing is a white substrate (step S120). If the result of this determination is that the substrate used for printing is a white substrate, the process proceeds to step S121, and if the substrate used for printing is not a white substrate, the process proceeds to step S141.

[0097] In step S121, it is determined whether or not it is necessary to perform white correction based on the print data 74 and the information about the defective nozzle detected in step S116 (the above-mentioned defective nozzle information 72). Specifically, if it is determined based on the defective nozzle information 72 that there is no defective nozzle, it is determined that there is no need to perform white correction, and if it is determined based on the defective nozzle information 72 that there is a defective nozzle, it is determined based on the defective nozzle information 72 and the print data 74 as follows:

[0098] In other words, if the amount of ink for printing in the area where ink is ejected from the defective nozzle and its neighboring nozzles (this is an area on the substrate 12, hereinafter referred to as the "area to be determined") satisfies the following formulas (1a) and (1b), or the following formulas (2a) and (2b), it is determined that white correction needs to be performed; otherwise (if either formula (1a) or (1b) is not satisfied, and either formula (2a) or (2b) is not satisfied), it is determined that white correction does not need to be performed. IA(C)+IA(M)+IA(Y)+IA(K)+IA(O)+IA(B) > CR1 …(1a) IA(Z) / {IA(C)+IA(M)+IA(Y)+IA(K)+IA(O)+IA(B)}= 1 …(1b) IA(C)+IA(M)+IA(Y)+IA(K)+IA(O)+IA(B) > CR2 …(2a) 1 > IA(Z) / {IA(C)+IA(M)+IA(Y)+IA(K)+IA(O)+IA(B)}> CR3 …(2b) In the above formula, IA(C), IA(M), IA(Y), IA(K), IA(O), and IA(B) represent the ink amounts of cyan, magenta, yellow, black, orange, and blue, respectively (expressed as percentages with the maximum amount of each color ink per pixel being 100%). Furthermore, Z is one of C, M, Y, K, O, and B, and represents the color of ink to be ejected from the defective nozzle onto the target area. Therefore, IA(Z) represents the ink amount to be ejected from the defective nozzle onto the target area. Furthermore, in the above formula, CR1, CR2, and CR3 represent the first, second, and third judgment reference values, respectively, determined in advance as described above (see FIGS. 10 and 11). In this embodiment, CR1=60, CR2=90, CR3=0.6 …(3) is.

[0099] 3, the recording unit 150 in this embodiment includes ink ejection heads 150(C), 150(M), 150(Y), and 150(B) that eject the process colors cyan, magenta, yellow, and black, respectively, as well as ink ejection heads 150(O) and 150(B) that eject the special colors orange and blue, respectively. However, if the recording unit 150 does not include ink ejection heads 150(O) and 150(B) that eject the special colors orange and blue, respectively, the terms IA(O) and IA(B) are omitted from the above equations (1a) to (2b). Note that the above equations (1a) and (1b) indicate that the target area is a region where high-density monochromatic printing is performed using the ink of the color that should be ejected from the defective nozzle, while the above equations (2a) and (2b) indicate that the target area is a region where high-density mixed-color printing is performed using the ink of the color that should be ejected from the defective nozzle and other inks.

[0100] If it is determined based on the determination result 75a obtained by the determination using the above-mentioned formulas (1a) to (2b) that white correction needs to be performed, the process proceeds to step S122, and if it is determined that white correction does not need to be performed, the process proceeds to step S130. Note that if a defective nozzle exists but it is determined that white correction does not need to be performed, normal nozzle missing correction is performed in step S130, as described below.

[0101] In step S122, the nozzles that are subject to white correction are identified based on the print data 74 and the information on the defective nozzles detected in step S116 (the defective nozzle information 72), and white correction target nozzle information 76a is generated.

[0102] Next, the white correction pattern 77a described above is created (step S124) based on the print data 74 and the information on the nozzles to be corrected identified in step S122 (the above-mentioned correction target nozzle information 76a). In other words, a white correction area is determined, which is an area on the substrate 12 onto which white ink should be ejected in order to widen the wet spreading range of the color ink.

[0103] After the white correction pattern 77a is created, the UV-LED 159(b) for white ink is stopped from irradiating with ultraviolet light based on the determination result 75a in step S121 (step S126). As a result, as described above, when white correction is performed, UV-LED 159(b) is stopped from irradiating with ultraviolet light onto the white ink ejected from the ink ejection head 150(W) onto the substrate 12.

[0104] After the ultraviolet radiation from UV-LED 159(b) is stopped, etc., the density uniformity correction, nozzle defect correction, and white correction described above are performed based on the correction coefficient 71 calculated in step S116, information about the defective nozzle detected in step S114 (the above-mentioned defective nozzle information 72), the white correction pattern 77a created in step S124, and the print data 74 (step S128) (see Figures 37, 7, and 8).

[0105] If the result of the determination in step S120 is that the substrate 12 used for printing is a substrate other than a white substrate, the process proceeds to step S141, where it is determined whether or not there is a need to perform transparency correction based on the print data 74 and the information on the defective nozzles detected in step S114 (the above-mentioned defective nozzle information 72). Specifically, if it is determined based on the defective nozzle information 72 that there are no defective nozzles, it is determined that there is no need to perform transparency correction, and if it is determined based on the defective nozzle information 72 that there are defective nozzles, it is determined based on the defective nozzle information 72 and the print data 74, in the same manner as in step S121 described above, whether or not there is a need to perform transparency correction.

[0106] That is, if the amount of ink for printing in the area (target area) where ink is ejected from the defective nozzle and its neighboring nozzles satisfies the previously described formulas (1a) and (1b) or the previously described formulas (2a) and (2b), it is determined that transparency correction needs to be performed, and if not, it is determined that transparency correction does not need to be performed. However, for the first judgment reference value CR1, the second judgment reference value CR2, and the third judgment reference value CR3 in these formulas, values calculated for transparency correction using the same method as the previously described method for calculating the first judgment reference value, the second judgment reference value, and the third judgment reference value used in step S121 (see FIGS. 10 and 11) are used. That is, in this method, instead of forming a white-corrected print image using corrected print data obtained by performing white correction, a transparent-corrected print image is formed using corrected print data obtained by performing transparency correction, thereby determining in advance the first transparency-correction judgment reference value CR1, the second transparency-correction judgment reference value CR2, and the third transparency-correction judgment reference value CR3, which correspond to the first transparency-correction judgment reference value CR1, the second transparency-correction judgment reference value CR2, and the third transparency-correction judgment reference value CR3, respectively, used in step S121. In step S141, the first transparency-correction judgment reference value CR1, the second transparency-correction judgment reference value CR2, and the third transparency-correction judgment reference value CR3 are used to determine whether or not transparency correction is required according to the above-mentioned formulas (1a) to (2b).

[0107] Based on the determination result 75b obtained in step S141, if it is necessary to perform transparency correction, the process proceeds to step S142, and if it is not necessary to perform transparency correction, the process proceeds to step S130.

[0108] In step S142, the transparent correction target nozzles described above are identified based on the print data 74 and the defective nozzle information 72, and transparent correction target nozzle information 76b is generated.

[0109] Next, the transparent correction pattern 77b described above is created (step S144) based on the print data 74 and the information on the nozzles to be corrected identified in step S142 (the above-mentioned correction target nozzle information 76). In other words, a transparent correction area is determined, which is an area on the substrate 12 onto which transparent ink should be ejected in order to widen the wet spreading range of the color ink.

[0110] After the transparent correction pattern 77b is created, the UV-LED 159(a) for transparent ink is stopped from emitting ultraviolet light based on the determination result 75b in step S141 (step S146). As a result, as described above, when transparency correction is performed, UV-LED 159(a) is stopped from emitting ultraviolet light to the white ink ejected from the ink ejection head 150(E) onto the substrate 12.

[0111] After the ultraviolet radiation from UV-LED 159(a) is stopped, the density uniformity correction, nozzle defect correction, and transparency correction described above are performed based on the correction coefficient 71 calculated in step S116, the defective nozzle information 72 detected in step S114, the transparent correction pattern 77b created in step S144, and the print data 74 (step S148).

[0112] As described above, if it is determined that white correction is unnecessary, the process proceeds to step S130, and if it is determined that transparency correction is unnecessary, the process also proceeds to step S130 (steps S121, S141). In step S130, density uniformity correction and normal nozzle missing correction are performed based on the information about the defective nozzle detected in step S114 (the above-mentioned defective nozzle information 72), the correction coefficient 71 calculated in step S116, and the print data 74 (see FIG. 37).

[0113] This density correction ends when the process of step S128, the process of step S148, or the process of step S130 ends.

[0114] In the density correction process in which the CPU 211 operates as described above, the defective nozzle detection unit 242 is realized in step S114, the correction coefficient calculation unit 241 is realized in step S116, the substrate determination unit 243 is realized in step S118, the white correction determination unit 245a is realized in steps S120 and S121, the white correction target nozzle specification unit 246a is realized in step S122, the white correction pattern creation unit 247a is realized in step S124, and the white correction pattern creation unit 248a is realized in step S125. Steps S120 and S141 implement a transparent correction determination unit 245b, step S142 implements a transparent correction target nozzle identification unit 246b, step S144 implements a transparent correction pattern creation unit 247b, steps S126 and S146 implement a UV-LED setting unit 249, step S128 implements a second correction processing unit 2482, step S148 implements a third correction processing unit 2483, and step S130 implements a first correction processing unit 2481 (see FIG. 14). Note that the ink discharge control unit 248 is implemented by step S130 which implements well-known control processing for the recording unit 15 and the conveying unit for printing based on the print control program P, step S128 which implements the second correction processing unit 2482, and step S148 which implements the third correction processing unit 2483.

[0115] After the CPU 211 performs the density correction process according to the above procedure, the CPU 211 controls the ejection of ink from each ink ejection head 150 and the transport of the substrate by the transport unit based on the density data 78 obtained by the density correction in accordance with the print control program P, thereby performing actual printing on the substrate 12. As can be seen from FIG. 3, the inks are ejected onto the substrate 12 in the following order: white ink, blue ink, orange ink, cyan ink, magenta ink, yellow ink, and black ink. Here, for example, if a defect is detected in a cyan ink ejection nozzle, in the white correction region, white ink is ejected onto the substrate 12 first, and then cyan ink is ejected onto the white ink. In the transparent correction region, transparent ink is ejected onto the substrate 12 first, and then cyan ink is ejected onto the transparent ink.

[0116] <1.8 Effects> According to this embodiment, if the substrate 12 used for printing is a white substrate, white correction (missing nozzle correction using white ink) is performed in the area where missing nozzle correction should be performed, and if the substrate 12 used for printing is a substrate other than a white substrate, transparency correction (missing nozzle correction using transparent ink) is performed in the area where missing nozzle correction should be performed (see FIG. 21). However, as can be seen from the above, similar effects can be obtained whether white correction is performed or transparency correction is performed (see FIGS. 7, 8, 9, 12, 13, and 21). For this reason, the following will only describe the effects of this embodiment when focusing on white correction.

[0117] According to this embodiment, when a defective nozzle is detected in a color ink ink ejection head 150, white correction is performed to correct density data so that white ink is ejected from the white ink ejection nozzles adjacent to the defective nozzle in an area (area on the substrate 12) where ink is ejected from the defective nozzle and its neighboring nozzles and where high-density monochrome printing is performed using the ink of the color that should be ejected from the defective nozzle. Here, the wet spread of the color ink on the substrate 12 is larger when the color ink is ejected onto white ink ejected onto the substrate 12 than when the color ink is ejected directly onto the substrate 12. Therefore, by ejecting ink from each ink ejection head 150 based on density data after white correction, the color ink spreads sufficiently on the substrate 12 in the area targeted for white correction, thereby enhancing the effectiveness of nozzle missing correction (the effect of suppressing image defects caused by defective nozzles and preventing degradation of print quality) compared to conventional methods. In other words, even if a defect occurs in a nozzle corresponding to an area where high-density monochrome printing is performed, degradation of the image quality of the printed image caused by the defective nozzle is effectively suppressed.

[0118] Furthermore, when nozzle missing correction is to be performed in an area where a single-color, high-density print is performed, whether to perform normal nozzle missing correction or white correction (nozzle missing correction using white ink) is determined based on a predetermined judgment reference value (first judgment reference value) for the total ink amount corresponding to the density of the single-color area (see the above-mentioned formulas (1a) and (1b)). This allows for appropriate nozzle missing correction according to the density of the print image and reduces unnecessary use of white ink. The color of the ink (white ink) used to widen the wet-spread range of the color inks is the same as the color of the substrate 12. Therefore, the color of the ink ejected onto the substrate 12 to widen the wet-spread range of the color inks does not stand out in the printed image.

[0119] Furthermore, according to the above embodiment, even when nozzle missing correction is required to suppress image defects caused by defective nozzles in a mixed-color area, white correction is performed when the total ink volume corresponding to the density of the mixed-color area is large and the defective nozzle ink volume ratio is large. In this case, whether normal nozzle missing correction or white correction should be performed is determined based on a predetermined judgment reference value (second judgment reference value) for the total ink volume and a predetermined judgment reference value (third judgment reference value) for the defective nozzle ink volume ratio (see equations (2a) and (2b)). For example, assume that regions R1 to R6 are target regions, which are defective image areas where ink is ejected from a defective nozzle and its neighboring nozzles, and that the ink volumes shown in FIG. 22 are used for printing each of regions R1 to R6. FIG. 22 shows the ink volumes of cyan (C), magenta (M), yellow (Y), and black (K) used for printing, the total ink volume, and the defective nozzle ink volume ratio for each of regions R1 to R6. Regions R1 and R2 are monochromatic regions printed with one ink color, while regions R3 to R6 are mixed-color regions printed with two or more ink colors. In each of regions R1 to R6 shown in FIG. 22, the defective nozzle ejects cyan (C) ink. The bottom column of the table in FIG. 22 shows the necessity of white correction for each region R1 to R6, based on the results of determinations using the previously described formulas (1a) to (2b). The effects of determining the necessity of white correction for regions R4 to R6, which are mixed-color regions among regions R1 to R6 shown in FIG. 22, will be explained below with reference to FIGS. 23 to 26. In FIGS. 23 to 26, the regions enclosed by dotted-line rectangles correspond to regions R1 to R6, respectively. FIGS. 23(A) to 26(A) show printed images obtained by printing using print data that has undergone normal nozzle dropout correction, while FIGS. 23(B) to 26(B) show printed images obtained by printing using print data that has undergone white correction. Furthermore, for the convenience of illustration, the print images shown in FIGS. 23 to 26 have been adjusted in hue and brightness from the actual images.

[0120] As shown in Figure 23(A), when printing is performed using print data that has undergone normal nozzle drop correction for region R3, the image defect caused by the defective nozzle is not eliminated, and streaks of reduced density due to missing dots are visible, but as shown in Figure 23(B), when printing is performed using print data that has undergone white correction for region R3, the image defect caused by the defective nozzle is eliminated. As shown in Figure 22, in this embodiment, it is determined that white correction is necessary for region R3.

[0121] As shown in Figure 24(A), when printing is performed using print data that has undergone normal nozzle dropout correction for region R4, the image defects caused by the defective nozzle are eliminated, but as shown in Figure 23(B), when printing is performed using print data that has undergone white correction for region R4, streaky density increases due to over-correction are visible, and the image defects caused by the defective nozzle are not fully eliminated. As shown in Figure 22, in this embodiment, it is determined that white correction is not necessary for region R4.

[0122] As shown in Figure 25(A), when printing is performed using print data that has undergone normal nozzle drop correction for region R5, the image defect caused by the defective nozzle is not eliminated, and streaks of reduced density due to missing dots are visible, but as shown in Figure 25(B), when printing is performed using print data that has undergone white correction for region R5, the image defect caused by the defective nozzle is eliminated. As shown in Figure 22, in this embodiment, it is determined that white correction is necessary for region R5.

[0123] As shown in FIG. 26(A), when printing is performed using print data that has undergone normal nozzle drop correction for region R6, image defects caused by defective nozzles are almost completely eliminated, but slight streak-like density reductions due to missing dots are visible. However, because brightness and other factors have been adjusted for convenience of illustration, such streak-like density reductions are not considered to be a problem in practice. On the other hand, as shown in FIG. 26(B), when printing is performed using print data that has undergone white correction for region R6, streak-like density increases due to over-correction are expected, but because the actual printed image for region R6 has high density and low brightness (see FIG. 22), such streak-like density increases are not actually visible. As shown in FIG. 22, in this embodiment, it is determined that white correction is not necessary for region R6.

[0124] As can be seen from the above, in this embodiment, even when nozzle missing correction should be performed to suppress the occurrence of image defects caused by defective nozzles in mixed color regions, whether to perform normal nozzle missing correction or white correction is selected based on a predetermined judgment reference value (see step S121 in FIG. 21, FIG. 22, and the above-mentioned formulas (2a), (2b), and (3)), and appropriate nozzle missing correction is performed according to the total ink amount and the proportion of ink amount in the defective nozzle. This prevents over-correction by white correction and unnecessary use of white ink, while applying white correction under appropriate conditions in mixed color regions can improve the effectiveness of noise missing correction compared to conventional methods (see FIGS. 23(B), 24(A), 25(B), and 26(A)).

[0125] As described above, according to this embodiment, when nozzle defect correction is required to suppress image defects caused by defective nozzles in both single-color and mixed-color regions, whether normal nozzle defect correction or white correction (transparent correction when a substrate other than a white substrate is used) should be performed is appropriately determined based on a predetermined reference value. Therefore, white correction (transparent correction when a substrate other than a white substrate is used) is performed under appropriate conditions. This realizes an inkjet printing device 10 that enables high-quality prints. Furthermore, because degradation of the image quality of printed images caused by defective nozzles is appropriately and effectively suppressed, the need for reprinting is reduced compared to conventional methods, enabling reductions in substrate and ink consumption. In this way, it is possible to contribute to the achievement of the SDGs (Sustainable Development Goals).

[0126] <1.9 Variations> <1.9.1 First modified example> In the first embodiment described above, if the substrate 12 used for printing is a white substrate, white correction (nozzle missing correction using white ink) is performed in the area where nozzle missing correction should be performed, and if the substrate 12 used for printing is a substrate other than a white substrate, transparency correction (nozzle missing correction using transparent ink) is performed in the area where nozzle missing correction should be performed (see FIG. 21). However, if there is no need to assume the use of a substrate other than a white substrate as the substrate 12 used for printing, the configuration related to transparency correction may be omitted from the first embodiment described above. Below, an inkjet printing apparatus in which the configuration related to transparency correction is omitted from the first embodiment described above will be described as a first modified example of the first embodiment.

[0127] In this modified example, the substrate determination unit 243, the transparent correction determination unit 245b, the transparent correction target nozzle identification unit 246b, the transparent correction pattern creation unit 247b, and the third correction processing unit 2483 are deleted from the functional configuration of the density correction processing unit 24 in the first embodiment shown in Fig. 14, and control of the UV-LEDs 159(a) by the UV-LED setting unit 249 is no longer necessary. Therefore, the density correction processing unit 24 in this modified example has a configuration as shown in Fig. 27. Furthermore, in this modified example, steps S118, S120, and S141 to S148 are deleted from the density correction procedure (density correction process) in the first embodiment shown in Fig. 21, resulting in a procedure as shown in Fig. 28.

[0128] According to this modified example, when it is not anticipated that a substrate other than a white substrate will be used as the printing medium, in both the single-color area and the mixed-color area where nozzle missing correction should be performed, whether normal nozzle missing correction or white correction should be performed is appropriately determined based on a predetermined reference value, so that white correction is performed under appropriate conditions, and the same effect as in the first embodiment described above can be obtained.

[0129] <1.9.2 Second modified example> In the first embodiment described above, if the substrate 12 used for printing is a white substrate, white correction (nozzle missing correction using white ink) is performed in the area where nozzle missing correction should be performed, and if the substrate 12 used for printing is not a white substrate, transparency correction (nozzle missing correction using transparent ink) is performed in the area where nozzle missing correction should be performed (see FIG. 21). However, if it is not necessary to assume that a white substrate will be used as the substrate 12 used for printing, the configuration related to white correction may be omitted from the first embodiment described above. Below, an inkjet printing apparatus in which the configuration related to white correction is omitted from the first embodiment described above will be described as a second modified example of the first embodiment.

[0130] In this modified example, the substrate determination unit 243, the white correction determination unit 245a, the white correction target nozzle identification unit 246a, the white correction pattern creation unit 247a, and the second correction processing unit 2482 are deleted from the functional configuration of the density correction processing unit 24 in the first embodiment shown in Fig. 14, and control of the UV-LEDs 159(b) by the UV-LED setting unit 249 is no longer necessary. Therefore, the density correction processing unit 24 in this modified example has a configuration as shown in Fig. 29. Furthermore, in this modified example, steps S118, S120, and S121 to S128 are deleted from the density correction procedure (density correction process) in the first embodiment shown in Fig. 21, resulting in a procedure as shown in Fig. 30.

[0131] According to this modified example, when the use of a white substrate as the printing medium is not anticipated, in both single-color areas and mixed-color areas where nozzle missing correction should be performed, whether normal nozzle missing correction or transparent correction should be performed is appropriately determined based on a predetermined reference value, so that transparent correction is performed under appropriate conditions, and the same effect as in the first embodiment described above can be obtained.

[0132] <1.9.3 Third Variation> In the first embodiment described above, in order to increase the wet spread range of the color ink on the substrate 12 as a result of nozzle missing correction, white ink or transparent ink is ejected onto the substrate 12 in the correction area before the color ink is ejected onto the substrate 12, depending on whether the substrate 12 is a white substrate or a substrate other than a white substrate. However, the present invention is not limited to this. Therefore, it is also possible to use ink other than white ink or transparent ink to increase the wet spread range of the color ink. Furthermore, as described below, it is also possible to use yellow ink to enhance the effect of nozzle missing correction when a defect occurs in a black ink ejection nozzle. Below, an example in which yellow ink is used to increase the wet spread range of the black ink instead of the white correction in the first embodiment will be described as a third modified example of the first embodiment.

[0133] In this modified example, when a defect occurs in a black ink ejection nozzle, yellow ink, which has a higher lightness value than black ink, is ejected onto the substrate 12 in the correction area before black ink is ejected onto the substrate 12 in order to enhance the effect of nozzle missing correction. Also, instead of the white correction in the first embodiment, a process is performed to correct the density data so that yellow ink, which has a higher lightness value than black ink, is ejected from the ink ejection head 150(Y) so that the wetting and spreading range of the black ink is increased (hereinafter, this process will be referred to as "yellow correction").

[0134] Note that the area onto which yellow ink is ejected in order to enhance the effect of nozzle missing correction is limited to an area other than the area onto which yellow ink is ejected to form the print image. By limiting the area onto which yellow ink is ejected in this way, a decrease in print quality caused by using yellow ink to increase the wet spread range of black ink is prevented.

[0135] Here, let's assume that the nozzle designated by reference numeral 521 in Figure 31 among the multiple nozzles included in the black ink ink ejection head 150(K) is a defective nozzle. In this case, by performing the above-described nozzle missing correction, a larger amount of black ink than would normally be ejected from the defective adjacent nozzles (nozzles designated by reference numerals 522 and 523). Furthermore, by performing yellow correction, yellow ink is ejected from the yellow ink ejection nozzles (nozzles designated by reference numerals 524 and 525) corresponding to the defective adjacent nozzles.

[0136] When yellow correction is performed, during printing, yellow ink is first ejected onto the substrate 12 from the yellow ink ejection nozzle corresponding to the defective adjacent nozzle. Then, black ink is ejected from the defective adjacent nozzle. That is, in the area where yellow correction has been performed, black ink 6(K) is ejected onto the yellow ink 6(Y) ejected onto the substrate 12, as shown schematically in FIG.

[0137] As yet another example, when a defect occurs in a black ink ejection nozzle, in order to enhance the effect of nozzle missing correction, blue ink with little color difference from the black ink may be ejected onto the substrate 12 in the correction area before the black ink is ejected onto the substrate 12. In such a case, instead of the white correction in the first embodiment, a process of correcting density data (hereinafter, this process will be referred to as "blue correction") may be performed so that blue ink with little color difference from the black ink is ejected from the ink ejection head 150(B) to increase the wet spread range of the black ink, and ejection control similar to that in the case of yellow correction may be performed.

[0138] In this modified example, white ink or transparent ink is not used. Therefore, even in an inkjet printing device that prints using only process color inks, by adopting the configuration of this modified example, it is possible to effectively suppress the occurrence of image defects in printed images caused by the presence of defective black ink ejection nozzles (such as streaky density reductions due to missing dots).

[0139] 2. Second embodiment <2.1 Overview> Generally, each of the ink ejection head 150(W) that ejects white ink, the ink ejection head 150(B) that ejects blue ink, the ink ejection head 150(O) that ejects orange ink, the ink ejection head 150(C) that ejects cyan ink, the ink ejection head 150(M) that ejects magenta ink, the ink ejection head 150(Y) that ejects yellow ink, and the ink ejection head 150(K) that ejects black ink that constitute the recording unit 15 includes a plurality of ink ejection heads 150. For example, each of the ink ejection heads 150(W), ink ejection head 150(B), ink ejection head 150(O), ink ejection head 150(C), ink ejection head 150(M), ink ejection head 150(Y), and ink ejection head 150(K) is configured by arranging a plurality of ink ejection heads 150 in a staggered pattern, as shown in FIG. Therefore, density unevenness and color unevenness may occur in an area where an area where ink is ejected by one ink ejection head 150 overlaps with an area where ink is ejected by an adjacent ink ejection head 150 (hereinafter referred to as a "head joint area"). For example, density unevenness and color unevenness may occur in an area where ink is ejected from nozzles included in the portion labeled with reference numeral 66 in FIG. 33 or an area where ink is ejected from nozzles included in the portion labeled with reference numeral 67 in FIG. 33. Therefore, in this embodiment, unlike the first embodiment, white correction is performed to suppress such degradation in print quality caused by ink being ejected from multiple ink ejection heads 150 onto the same area (area on the substrate 12). Furthermore, if the substrate used for printing is a substrate other than a white substrate, transparency correction is performed instead of white correction. However, for convenience of explanation, it is assumed below that the substrate used for printing is a white substrate, and white correction is performed as a correction to suppress the degradation in print quality in the head joint area.

[0140] The overall configuration of the printing system (see Figure 1), the configuration of the inkjet printing device 10 (see Figure 2), the configuration of the recording unit 15 (see Figure 3), the configuration of the ink ejection surface of the ink ejection head 150 (see Figure 4), the arrangement of the nozzles 152 in the head module 151 (see Figure 5), and the hardware configuration of the print control device 200 (see Figure 6) are the same as those in the first embodiment.

[0141] <2.2 Density correction> The density correction in this embodiment will be described below.

[0142] <2.2.1 Functional configuration> FIG. 34 is a block diagram showing a detailed functional configuration of the density correction processing unit 24 in this embodiment. As can be seen from FIGS. 34 and 27, the density correction processing unit 24 in this embodiment includes a white correction candidate area acquisition unit 251 in addition to the components in the first modified example of the first embodiment (a modified example in which the components related to transparency correction in the first embodiment are omitted). The correction coefficient calculation unit 241, the defective nozzle detection unit 242, the print data storage unit 244, the correction pattern creation unit 247a, the ink ejection control unit 248, and the UV-LED setting unit 249 perform the same operations as the correction coefficient calculation unit 241, the defective nozzle detection unit 242, the print data storage unit 244, the white correction pattern creation unit 247a, the ink ejection control unit 248, and the UV-LED setting unit 249 in the first modified example of the first embodiment, respectively. Note that in this embodiment, the white correction candidate area acquisition unit 251, the white correction determination unit 245, the correction target nozzle identification unit 246, and the correction pattern creation unit 247 implement a correction area determination unit.

[0143] The white correction candidate area acquisition unit 251 obtains a white correction candidate area 81 as a candidate area for white correction, based on head information 80 including information on the positions of the head modules 151 in the ink ejection head 150. In this embodiment, the white correction candidate area 81 is a head joint area such as an area where ink is ejected from nozzles included in the parts denoted by reference numerals 66 and 67 in FIG.

[0144] The white correction determination unit 245 determines whether to perform white correction based on the substrate information 73, the white correction candidate area 81, and the print data 74. The determination result 75 is then output from the white correction determination unit 245. In this regard, in this embodiment, as in the first embodiment, a determination is made based on the substrate information 73 that white correction will not be performed if the substrate used for printing is other than a white substrate. Furthermore, a determination is made based on the white correction candidate area 81 and the print data 74 that white correction will be performed if the white correction candidate area 81 includes an area where monochromatic printing will be performed. In this way, white correction is performed only in areas where density unevenness is noticeable, thereby reducing the waste of white ink. Note that, although white correction is performed only in areas where monochromatic printing will be performed in this embodiment, white correction may also be performed in areas where mixed-color printing will be performed to reduce color unevenness.

[0145] If the determination result 75 output from the white correction determination unit 245 indicates that white correction is to be performed, the correction target nozzle identification unit 246 identifies the nozzles to be corrected from among the many white ink ejection nozzles included in the white ink ink ejection head 150(W) based on the white correction candidate area 81 and the print data 74. Then, correction target nozzle information 76 identifying the nozzles to be corrected is output from the correction target nozzle identification unit 246. Note that, because the head module portion corresponding to the white correction candidate area 81 includes many nozzles, typically, more white ink ejection nozzles are identified as nozzles to be corrected than in the first embodiment and its first modified example. Therefore, the correction pattern creation unit 247 creates a correction pattern 77 so that the area to be ejected of white ink (correction area) is wider than in the first embodiment.

[0146] In this embodiment, a plurality of templates are prepared in advance as templates that serve as the basis for the correction pattern 77, and the template to be adopted is determined based on the printing rate determined from the print data 74. For example, the template shown in FIG. 18 and the template shown in FIG. 35 are prepared in advance, and if the printing rate is higher than a predetermined threshold, the template shown in FIG. 18 is adopted, and if the printing rate is equal to or lower than the predetermined threshold, the template shown in FIG. 35 is adopted. When the template shown in FIG. 35 is adopted, as in the case where the template shown in FIG. 18 is adopted, the nozzles that eject ink to pixel portions in the column labeled 64, the nozzles that eject ink to pixel portions in the column labeled 64L1, the nozzles that eject ink to pixel portions in the column labeled 64R1, the nozzles that eject ink to pixel portions in the column labeled 64L2, and the nozzles that eject ink to pixel portions in the column labeled 64R2 are identified as nozzles to be corrected, out of the many nozzles included in the inkjet head 150(W) for white ink, Furthermore, when focusing on the transport direction of the substrate 12 with respect to the pixel portions onto which white ink is ejected, when the template shown in Figure 35 is adopted, one pixel portion onto which white ink is ejected and three pixel portions onto which white ink is not ejected appear alternately.

[0147] <2.2.2 Procedure> Hereinafter, the procedure for density correction in this embodiment will be described with reference to FIG. In this embodiment, the main part (configuration other than the components realized by hardware) of the density correction processing unit 24 shown in Fig. 34 is realized in software by the CPU 211 in the control unit 200 shown in Fig. 6 performing density correction processing according to the procedure shown in Fig. 36 in accordance with the print control program P. In this density correction processing, the CPU 211 operates as follows.

[0148] The processing of steps S210 to S216 is similar to the processing of steps S110 to S116 in the first modified example of the first embodiment (see FIG. 28).

[0149] In step S217, the CPU 211 determines the above-mentioned white correction candidate area 81 based on the head information 80 as described above.

[0150] In step S221, the CPU 211 determines whether or not it is necessary to perform white correction based on the print data 74 and the white correction candidate area 81 obtained in step S217. If it is determined that it is necessary to perform white correction, the process proceeds to step S222, and if it is not necessary to perform white correction, the process proceeds to step S230. In this embodiment, if the white correction candidate area 81 includes an area where monochrome printing is performed, the CPU 211 determines that it is necessary to perform white correction.

[0151] In step S222, the CPU 211 identifies the nozzles to be corrected, based on the print data 74 and the white correction candidate area 81 determined in step S217.

[0152] The processing in steps S224 to S230 is the same as the processing in steps S124 to S130 in the first modified example of the first embodiment.

[0153] In the density correction process in which the CPU 211 operates as described above, as in the first modified example of the first embodiment, a defective nozzle detection unit 242 is realized in step S214, a correction coefficient calculation unit 241 is realized in step S216, a white correction determination unit 245 is realized in step S221, a correction target nozzle identification unit 246 is realized in step S222, a correction pattern creation unit 247 is realized in step S224, a UV-LED setting unit 249 is realized in step S226, a second correction processing unit 2482 is realized in step S228, and a first correction processing unit 2481 is realized in step S230, and in this embodiment, a white correction candidate area acquisition unit 251 is realized in step S217 (see FIG. 34).

[0154] <2.3 Effects> According to this embodiment, white correction is performed on the head-joining region where a single color is printed, correcting density data so that white ink is ejected from a white ink ejection nozzle identified based on a predetermined pattern. As described above, the wet spread range of color ink on the substrate 12 is larger when the color ink is ejected onto white ink already ejected onto the substrate 12 than when the color ink is ejected directly onto the substrate 12. Therefore, by ejecting ink from each ink ejection head 150 based on density data after white correction, the color ink spreads sufficiently on the substrate 12 in the region targeted for white correction, effectively suppressing density unevenness in the head-joining region. As described above, an inkjet printing device 10 that enables high-quality printouts is realized. Note that in this embodiment, white correction is performed only on the correction region where a single color is printed. However, white correction may also be performed on a correction region similarly determined for the region where mixed colors are printed. In this case, color unevenness in the head-joining region is also effectively suppressed. In this way, density and color variations in the print head joining area are effectively suppressed, reducing the need for reprinting compared to conventional methods and enabling reductions in substrate and ink consumption, which will contribute to the achievement of the SDGs.

[0155] <3.Other> The present invention is not limited to the above-described embodiments (including modified examples), and various modifications can be made without departing from the spirit of the present invention. For example, although the above-described embodiments illustrate an inkjet printing apparatus 10 that prints using UV ink, the present invention can also be applied to inkjet printing apparatuses that print using ink that hardens when exposed to radiation other than ultraviolet light.

[0156] Furthermore, the above-described embodiments have exemplified a so-called one-pass type inkjet printing apparatus in which a printed image is formed on a substrate by ejecting ink from an ink ejection head while the substrate is transported relative to the ink ejection head. However, the present invention can also be applied to a so-called shuttle type inkjet printing apparatus in which a printed image is formed on a substrate by ejecting ink from an ink ejection head while the ink ejection head is transported relative to the substrate. In the latter case, the means for transporting the ink ejection head relative to the substrate constitutes a transport unit that transports the print medium.

[0157] In the above embodiments, white correction was performed on white substrates, and transparency correction was performed on substrates other than white substrates. However, transparency correction may also be performed on white substrates. That is, depending on the printing device, the recording unit 15 may be equipped with an ink ejection head 150(E) that ejects transparent ink and a UV-LED 159(a) that cures the transparent ink, but may not be equipped with a UV-LED 150(W) that ejects white ink and a UV-LED 150(b) that cures the white ink. In this case, a determination process similar to step S141 in FIG. 21 may be performed to determine whether transparency correction is necessary based on the print data 74 and information about the defective nozzles detected in step S114 (the above-mentioned defective nozzle information 72).

[0158] Furthermore, the first and second embodiments and their modifications may be combined within the scope of the present invention and technically compatible therewith. [Explanation of symbols]

[0159] 10...Inkjet printing device 12...Base material (print media) 15...Recording section 16...imaging unit 24...Density correction processing section 100...Printing machine body 150...Ink ejection head 151...Head module 152...Nozzle 159...UV-LED 200...print control device (control unit) 241...Correction coefficient calculation unit 242...defective nozzle detection unit 243...Base material determination section 244...print data storage unit 245a...White correction determination unit 246a...White correction target nozzle identification section 247a...White correction pattern creation unit 245b...Transparency correction determination section 246b...Transparent correction target nozzle identification section 247b...Transparent correction pattern creation unit 248...Ink discharge control unit 249...UV-LED setting section 251...White correction candidate area acquisition unit 2481...First correction processing unit 2482...Second correction processing unit 2483...Third correction processing unit

Claims

1. A printing device that forms a print image on a printing medium by ejecting ink onto the printing medium based on print data, a conveying unit that conveys the print medium; a first ink ejection head including a plurality of ink ejection ports that ejects a first ink onto the print medium transported by the transport unit; a second ink ejection head including a plurality of ink ejection ports that ejects a second ink onto the printing medium transported by the transport unit; a third ink ejection head that is disposed upstream of the first ink ejection head and the second ink ejection head in the direction in which the print medium is transported by the transport unit, and that includes a plurality of ink ejection ports and ejects a third ink onto the print medium being transported by the transport unit; an ejection control unit that controls the ejection of the first ink by the first ink ejection head, the ejection of the second ink by the second ink ejection head, and the ejection of the third ink by the third ink ejection head; a correction area determination unit that determines a correction area to be corrected using the third ink in the print image formed on the print medium; Equipped with a wetting and spreading range of the first ink on the printing medium is larger when the first ink is ejected onto the third ink ejected onto the printing medium than when the first ink is ejected directly onto the printing medium; a wetting and spreading range of the second ink on the printing medium is larger when the third ink is ejected onto the third ink that has been ejected onto the printing medium than when the second ink is ejected directly onto the printing medium; a wetting and spreading range of the first ink and the second ink on the printing medium when the first ink and the second ink are ejected so as to mix is larger when the first ink and the second ink are ejected onto the third ink ejected onto the printing medium than when the first ink and the second ink are ejected directly onto the printing medium; The ejection control unit controls the first ink ejection head, the second ink ejection head, and the third ink ejection head so that the third ink is ejected into the correction area before the first ink is ejected into the correction area to form the print image, and so that the third ink is ejected into the correction area before the second ink is ejected into the correction area to form the print image.

2. 2. The printing device according to claim 1, wherein the correction area determination unit determines the correction area based on the position of a defective orifice, which is an ink ejection orifice having an ejection defect, among a plurality of ink ejection orifices included in the first ink ejection head or the second ink ejection head.

3. 3. The printing device according to claim 2, wherein the correction area determination unit determines the correction area so that an area where the third ink is ejected from an ink ejection port corresponding to an ink ejection port adjacent to the defective ejection port and included in the third ink ejection head is included in the correction area.

4. The correction area determination unit if the correction area is a monochromatic area onto which only one of the first ink and the second ink is ejected, determining the correction area based on the print data so that only an area onto which the amount of the one ink is ejected that is greater than a predetermined first reference value is included in the correction area; 3. The printing device according to claim 2, wherein, when the correction area is an area where both the first ink and the second ink are ejected and a mixed color area where the color of the first ink and the color of the second ink are mixed, the correction area is determined based on the print data so that only areas where the total ink amount is greater than a predetermined second judgment reference value and where the ratio of the ink amount of the ink color of the ink ejection head including the defective ejection port out of the first ink ejection head and the second ink ejection head to the total ink amount is greater than a predetermined third judgment reference value are included in the correction area.

5. The printing device according to claim 4 , wherein the second determination reference value is greater than the first determination reference value.

6. 3. The printing device according to claim 2, wherein the correction area determination unit determines the correction area so that one pixel onto which the third ink is ejected and one pixel onto which the third ink is not ejected are arranged alternately in the direction in which the printing medium is transported by the transport unit.

7. 3. The printing device according to claim 2, wherein the correction area determination unit determines the correction area so that two pixels onto which the third ink is ejected and two pixels onto which the third ink is not ejected are arranged alternately in the direction in which the printing medium is transported by the transport unit.

8. each of the first ink ejection head and the second ink ejection head includes a plurality of ink ejection heads arranged in a staggered pattern; 2. The printing device according to claim 1, wherein the correction area determination unit determines the correction area so that an area where an area where ink is ejected by one ink ejection head overlaps with an area where ink is ejected by another ink ejection head in each of the first ink ejection head and the second ink ejection head is included in the correction area.

9. 9. The printing device according to claim 8, wherein the correction area determination unit determines the correction area so that one pixel onto which the third ink is ejected and one pixel onto which the third ink is not ejected are arranged alternately in the direction in which the printing medium is transported by the transport unit.

10. 9. The printing device according to claim 8, wherein the correction area determination unit determines the correction area so that one pixel onto which the third ink is ejected and three pixels onto which the third ink is not ejected are arranged alternately in the direction in which the printing medium is transported by the transport unit.

11. 11. The printing device according to claim 1, wherein the correction area determination unit determines the correction area so that an area onto which the third ink is ejected to form the print image is not included in the correction area.

12. The printing device according to claim 1 , wherein the first ink, the second ink, and the third ink are ultraviolet curable inks.

13. a first ultraviolet irradiation unit that cures the first ink ejected onto the printing medium from the first ink ejection head and the second ink ejected onto the printing medium from the second ink ejection head by irradiating them with ultraviolet light; a second ultraviolet irradiation unit that cures the third ink ejected onto the printing medium from the third ink ejection head by irradiating it with ultraviolet light; an ultraviolet irradiation control unit that controls ultraviolet irradiation by the second ultraviolet irradiation unit; Further provided with 13. The printing device according to claim 12, wherein when the third ink is ejected onto the correction area, the ultraviolet irradiation control unit stops ultraviolet irradiation by the second ultraviolet irradiation unit or reduces the intensity of ultraviolet irradiation by the second ultraviolet irradiation unit.

14. the third ink ejection head is configured to be capable of ejecting the third ink in a plurality of droplet sizes; 13. The printing device according to claim 12, wherein the ejection control unit controls the ejection of the third ink from the third ink ejection head so that the droplet size of the third ink ejected from the third ink ejection head increases as the distance from the ink ejection head corresponding to the color ink ejected as the first ink or the second ink onto the third ink in the correction area to the first ultraviolet irradiation unit decreases.

15. the third ink ejection head is configured to be capable of ejecting the third ink in a plurality of droplet sizes; 11. A printing device according to claim 1, wherein the ejection control unit controls the ejection of the third ink from the third ink ejection head so that the third ink is ejected into the correction area with the smallest droplet size among the plurality of droplet sizes by the third ink ejection head.

16. the color of the printing medium is white; the first ink and the second ink are different process or spot color inks; The printing device of claim 1 , wherein the third ink is a white ink.

17. the first ink and the second ink are different process or spot color inks; The printing device according to claim 1 , wherein the second ink is a transparent ink.

18. The printing device of claim 1 , wherein the first ink, the second ink, and the third ink are selected based on a lightness value or a color difference.

19. A printing method using a printing device that includes a transport unit that transports a print medium, a first ink ejection head that ejects a first ink onto the print medium transported by the transport unit, a second ink ejection head that ejects a second ink onto the print medium transported by the transport unit, and a third ink ejection head that ejects a third ink onto the print medium transported by the transport unit, and that forms a print image on the print medium based on print data, comprising: ejecting the first ink from the first ink ejection head to form the print image; ejecting the second ink from the second ink ejection head to form the printed image; determining a correction area to be corrected using the third ink in the printed image formed on the printing medium; ejecting the third ink from the third ink ejection head onto the correction area before the first ink is ejected onto the correction area to form the print image; ejecting the third ink from the third ink ejection head onto the correction area before the second ink is ejected onto the correction area to form the print image; Equipped with a wetting and spreading range of the first ink on the printing medium is larger when the first ink is ejected onto the third ink ejected onto the printing medium than when the first ink is ejected directly onto the printing medium; a wetting and spreading range of the second ink on the printing medium is larger when the third ink is ejected onto the third ink that has been ejected onto the printing medium than when the second ink is ejected directly onto the printing medium; A printing method in which, when the first ink and the second ink are ejected so as to mix, the wetting and spreading range of the first ink and the second ink on the printing medium is larger when the first ink and the second ink are ejected onto the third ink ejected onto the printing medium than when the first ink and the second ink are ejected directly onto the printing medium.

Images