Printing device and printing method

Abstract

To provide an inkjet printing device capable of forming an excellent printed image while suppressing an image defect due to dot omission even when printing an image including a linear pattern with a narrow width.SOLUTION: It is determined whether or not to perform correction using correction auxiliary ink (white ink or transparent ink) for each correction individual region to be corrected so as to suppress an image defect due to dot omission in a printed image to be formed on a base material. A correction execution region is determined by removing a predetermined thinning number of pixels (for instance, one pixel) from both ends in a conveying direction of the base material in the correction individual region determined to be corrected using the correction auxiliary ink. Print data is corrected so that colored ink is discharged for forming the printed image after the correction auxiliary ink is discharged in the correction execution region. A printed image is formed on the base material on the basis of the print data after the correction.SELECTED DRAWING: Figure 25

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 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, i.e., dot omissions occur. 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. 32, 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 [Patent Document 2] Japanese Patent Application Publication No. 2019-155593 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] Furthermore, Japanese Patent Application Laid-Open Publication No. 2019-155593 describes a printing method in which white ink or clear ink (transparent ink) is ejected as induction ink at the location of a missing dot caused by a faulty nozzle (defective nozzle). This publication also describes an embodiment in which the greater the amount of ink ejected from the faulty nozzle onto pixels adjacent to the location of the missing dot, the greater the amount of induction ink ejected at the location of the missing dot. This embodiment makes it possible to more fully compensate for missing dots even in areas where high-density printing is performed.

[0010] However, with printing methods that use such white ink or clear ink as guide ink to compensate for missing dots, when printing an image that includes a narrow linear pattern of a few pixels in width, such as an image that includes characters or barcodes, even if the occurrence of image defects due to missing dots is suppressed, a good printed image may not be obtained.

[0011] Therefore, it is desirable for inkjet printing devices to be able to produce good printed images while correcting image defects caused by missing dots, even when printing images that include narrow linear patterns such as characters or barcodes. [Means for solving the problem]

[0012] 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 recording unit that ejects a plurality of types of ink, including a first ink and a correction auxiliary ink, onto the printing medium; a conveying unit that moves the print medium relative to the recording unit; an ejection control unit that controls the ejection of the plurality of types of ink by the recording unit; a correction area determination unit that determines a correction area consisting of one or more continuous areas to be corrected using the correction supplemental ink in the print image formed on the print medium; Equipped with the transport unit includes a mechanism for moving the print medium relative to the recording unit in a predetermined transport direction that is perpendicular to the width direction of the print medium and parallel to the print medium, The recording unit a first ink ejection head including a plurality of ink ejection ports for ejecting the first ink; a correction auxiliary ink ejection head that is disposed upstream of the first ink ejection head in the transport direction and includes a plurality of ink ejection ports that eject the correction auxiliary ink, a wetting and spreading range of the first ink on the printing medium is larger when the first ink is ejected onto the correction auxiliary ink ejected onto the printing medium than when the first ink is ejected directly onto the printing medium; the correction area determination unit determines, for each continuous area included in the correction area, an area obtained by removing, in the conveying direction, an amount of pixels equal to the thinning number from both ends of the continuous area in the conveying direction when the number of pixels in the conveying direction in the continuous area is greater than twice a predetermined thinning number, as a correction execution area; The ejection control unit controls the first ink ejection head and the correction auxiliary ink ejection head so that the correction auxiliary ink is ejected into the correction execution area before the first ink is ejected into the correction execution area to form the print image.

[0013] 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.

[0014] 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 based on the print data so that the correction area includes a continuous rectangular area, with the range in the transport direction being the range in which missing pixels, which are pixels to be formed on the printing medium by ink to be ejected from the defective ejection port, are continuous in the transport direction, and the range in the width direction being the range in which a predetermined number of pixels are adjacent to the missing pixels in the width direction, centered on the missing pixels.

[0015] A fourth aspect of the present invention is a method for producing a composition according to any one of the first to third aspects of the present invention, the recording unit further includes a second ink ejection head that is disposed downstream of the correction auxiliary ink ejection head in the transport direction and includes a plurality of ink ejection ports that eject a second ink; a wetting and spreading range of the second ink on the printing medium is larger when the second ink is ejected onto the correction auxiliary ink 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 correction auxiliary 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 second ink ejection head and the correction auxiliary ink ejection head so that the correction auxiliary ink is ejected into the correction execution area before the second ink is ejected into the correction execution area to form the print image.

[0016] A fifth aspect of the present invention is a printing method for forming a print image on a print medium based on print data using a printing device including a recording unit that ejects multiple types of ink onto the print medium and a transport unit that moves the print medium relative to the recording unit, the method comprising: a step of ejecting one ink of the plurality of types of ink as a first ink from the recording unit onto the printing medium to form the print image; ejecting another ink of the plurality of types of ink from the recording unit onto the print medium as a correction supplemental ink; determining a correction area consisting of one or more continuous areas to be corrected using the correction supplemental ink in the printed image formed on the printing medium; Equipped with the transport unit includes a mechanism for moving the print medium relative to the recording unit in a predetermined transport direction that is perpendicular to the width direction of the print medium and parallel to 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 correction auxiliary ink ejected onto the printing medium than when the first ink is ejected directly onto the printing medium; the step of determining the correction area includes determining, for each continuous area included in the correction area, an area obtained by removing, in the conveying direction, an amount of pixels equal to the thinning number from both ends of the continuous area in the conveying direction when the number of pixels in the conveying direction in the continuous area is greater than twice a predetermined thinning number, as the correction execution area; In the step of ejecting the first ink, before the first ink is ejected into the correction execution area to form the print image, in the step of ejecting the correction auxiliary ink, the correction auxiliary ink is ejected into the correction execution area.

[0017] 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]

[0018] According to a first aspect of the present invention, a printing device is provided with a correction auxiliary ink ejection head that ejects correction auxiliary ink, located upstream of a first ink ejection head that ejects a first ink for forming a print image on a print medium in the transport direction by the transport unit, and a correction area determination unit determines a correction area in the print image formed on the print medium to be corrected using the correction auxiliary ink. Here, white ink is typically used as the correction auxiliary ink when the print medium is white, and transparent ink is typically used when the print medium is other than white. However, transparent ink may also be used when the print medium is white. The correction area determined by the correction area determination unit includes one or more continuous areas (hereinafter referred to as "correction individual areas" as described below). For each correction individual area included in this correction area, if the number of pixels in the transport direction in each correction individual area is greater than twice the predetermined thinning number, an area obtained by removing the number of pixels (e.g., one or two pixels) from both ends of each correction individual area in the transport direction in the thinning number of pixels is determined to be the correction execution area. When a print image is formed on a print medium based on the print image, correction auxiliary ink is ejected into the correction execution area before the first ink is ejected into the correction execution area to form the print image. The wet spread range of the first ink on the print medium is larger when the first ink is ejected onto the correction auxiliary ink ejected onto the print medium than when the first ink is ejected directly onto the print medium. Therefore, the dot size formed on the print medium by the first ink ejected into the correction execution area is larger than it should be. This corrects image defects due to missing dots even if a nozzle corresponding to an area where high density printing is performed is defective, effectively suppressing degradation of print image quality caused by defective nozzles. Furthermore, correction using correction auxiliary ink is performed in a correction execution area obtained by removing the thinning number of pixels from both ends of each continuous area (each correction individual area) included in the correction area in the transport direction. This prevents the wet spread range of the first ink ejected into each correction individual area from extending beyond the correction individual area.As a result, even when printing an image that includes narrow linear patterns such as characters or barcodes, deterioration in print quality due to bleeding caused by the use of correction supplementary ink is suppressed.

[0019] 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]

[0020] [Figure 1] 1 is a diagram illustrating the overall configuration of a printing system according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram illustrating an example of the configuration of an inkjet printing apparatus according to the embodiment. [Figure 3] FIG. 2 is a plan view schematically showing the configuration of a recording unit in the 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 embodiment. [Figure 5] 5A to 5C are diagrams for explaining the arrangement of nozzles in a head module in the embodiment. [Figure 6] FIG. 2 is a block diagram showing a hardware configuration of the print control device in the embodiment. [Figure 7] 10A to 10C are diagrams for explaining an overview of white correction in the embodiment. [Figure 8] FIG. 1A is a diagram for explaining ink ejection when white correction is performed on a single-color area in the above 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 colored 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 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 embodiment. [Figure 12] 10A to 10C are diagrams for explaining an overview of transparency correction in the embodiment. [Figure 13] FIG. 1A is a diagram for explaining ink ejection when transparency correction is performed on a single-color area in the above embodiment, and FIG. 1B is a diagram for explaining ink ejection when transparency correction is performed on a mixed-color area. [Figure 14] 1A and 1B are diagrams for explaining image defects (streak-like density reduction such as white streaks) caused by missing dots due to defective nozzles in a printed character image. [Figure 15] 10A and 10B are diagrams for explaining problems that arise when white correction is performed to suppress image defects due to missing dots caused by defective nozzles in a printed image of characters. [Figure 16] 10A to 10C are diagrams for explaining edge thinning processing for determining a correction execution region in the embodiment. [Figure 17] 10A and 10B are diagrams showing examples of printed images obtained by printing characters while performing white correction with edge thinning processing in the embodiment. [Figure 18] FIG. 2 is a block diagram showing a detailed functional configuration of a density correction processing unit in the embodiment. [Figure 19] FIG. 10 is a diagram showing an example of a template for white correction in the embodiment. [Figure 20] 5A to 5C are diagrams for explaining creation of a correction pattern in the embodiment. [Figure 21] 5A to 5C are diagrams for explaining creation of a correction pattern in the embodiment. [Figure 22] FIG. 10 is a diagram showing an example of a template for white correction in the embodiment. [Figure 23]FIG. 10 is a diagram showing an example of a template for white correction in the embodiment. [Figure 24] FIG. 10 is a diagram showing an example of a template for white correction in the embodiment. [Figure 25] 10 is a flowchart for explaining a procedure for density correction in the embodiment. [Figure 26] FIG. 10 is a block diagram showing a detailed functional configuration of a density correction processing unit in a first modified example of the embodiment. [Figure 27] 10 is a flowchart illustrating a procedure for density correction in a first modified example of the embodiment. [Figure 28] FIG. 10 is a block diagram showing a detailed functional configuration of a density correction processing unit in a second modified example of the embodiment. [Figure 29] 10 is a flowchart illustrating a procedure for density correction in a second modified example of the embodiment. [Figure 30] FIG. 10 is a diagram for explaining an outline of yellow correction in the third modified example of the embodiment. [Figure 31] FIG. 10 is a diagram for explaining ink ejection in a region where yellow correction has been performed in a third modified example of the embodiment. [Figure 32] 10A and 10B are diagrams for explaining density uniformization correction and nozzle missing correction in a conventional example. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0022] <1. Overall configuration of the printing system> FIG. 1 is a diagram illustrating the overall configuration of a printing system according to an 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 PDF files. 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 as the printing ink. 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.

[0023] <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.

[0024] 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.

[0025] 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 colored inks ...

[0026] 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.

[0027] 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, colored ink is 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, colored ink is ejected onto uncured transparent ink.

[0028] 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).

[0029] 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.

[0030] 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.

[0031] FIG. 5 is a diagram illustrating 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 arranged side by side in the main scanning direction (the width direction of the substrate 12). In the example shown in FIG. 5, the head module 151 includes four rows of nozzle groups. The portion labeled with reference numeral 41 in FIG. 5 schematically shows the landing positions on the substrate 12 of the ink ejected from each nozzle 152. The multiple nozzles 152 in the head module 151 are arranged so that the landing positions of the ink ejected from the nozzles 152 included in the first row of nozzle groups, the landing positions of the ink ejected from the nozzles 152 included in the second row of nozzle groups, the landing positions of the ink ejected from the nozzles 152 included in the third row of nozzle groups, and the landing positions of the 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.

[0032] 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.

[0033] 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."

[0034] <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, a mouse 225, and the like. 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.

[0035] 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.

[0036] <4. White Correction> In this embodiment, when the substrate 12 used as the print medium for printing is a white substrate, when the above-described nozzle missing 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."

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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).

[0041] The wet spread range of a colored ink (cyan ink in the above example) on the substrate 12 is larger when the colored ink is ejected onto white ink that has been ejected onto the substrate 12 than when the colored ink is ejected directly onto the substrate 12. Here, "colored ink" refers to ink other than transparent ink that has a color different from the color of the substrate (printing medium). The "wet spread range" refers to the area occupied by dots formed on the printing medium by ejecting the ink. Therefore, the size of dots formed on the substrate 12 (printing medium) by ejecting the colored ink is larger when the colored ink is ejected onto white ink that has been ejected onto the substrate 12 than when the colored ink is ejected directly onto the substrate 12. An example of the results of an experiment related to this is shown in Figure 9. The area marked with the symbol 61 in Figure 9 shows the dot size (ink) obtained when the colored ink is ejected directly onto a certain film substrate, and the area marked with the symbol 62 in Figure 9 shows the dot size (ink) obtained when the colored ink is ejected onto the certain substrate after ejecting white ink. It is understood that for any colored ink (including black ink), the wetting and spreading range is increased by ejecting white ink onto the substrate in advance. In light of the above, by ejecting white ink in advance at the position (position on the substrate 12) where colored ink is ejected from the defective-adjacent nozzle, the colored 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 the occurrence of image defects caused by defective nozzles and preventing a decline in print quality). In this way, white ink functions as ink (hereinafter referred to as "correction auxiliary ink") that assists in the correction of image defects such as missing dots in a printed image using colored ink (in the example of FIG. 7, cyan ink ejected from the defective-adjacent nozzle).

[0042] 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 colored inks ejected onto the white ink wet and spread is also effectively increased.

[0043] 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).

[0044] <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").

[0045] 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).

[0046] <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.

[0047] 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.

[0048] 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%.

[0049] <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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] <6. Transparency Correction> In this embodiment, if the substrate 12 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 as correction supplement ink 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 "transparent correction."

[0054] 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).

[0055] 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 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 on top of the clear ink 6(T) ejected onto the substrate 12, as shown schematically in FIG. 13(A).

[0056] As with white correction, in transparency correction, the wet spread range of a colored ink (cyan ink in the above example) on the substrate 12 is larger when the colored ink is ejected onto transparent ink ejected onto the substrate 12 than when the colored 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 colored ink is larger when the colored ink is ejected onto transparent ink ejected onto the substrate 12 than when the colored 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 the colored ink is to be ejected from the defective-adjacent nozzle, the colored 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).

[0057] 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 colored inks ejected onto the transparent ink also effectively increases.

[0058] 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).

[0059] <7. Determining the area to perform correction> When printing an image that includes narrow linear patterns such as characters or barcodes, if the above-described white correction or transparency correction is performed, ink bleeding may occur, resulting in a deterioration in the quality of the printed image. This point will be explained below.

[0060] Consider the case where the characters "manufacturing" are printed using an inkjet printing device. If the inkjet printing device includes a defective nozzle in the ink ejection head that ejects the ink corresponding to the color of the characters, and prints the characters without performing nozzle missing correction, a printed image like the one shown in FIG. 14 is formed on substrate 12, which serves as a print medium. Here, the vertical direction in the figure is the transport direction, and substrate 12 is a white substrate. In this printed image, streaks of density reduction due to missing dots (white streaks extending vertically in the example shown in FIG. 14) appear in the linear pattern that makes up the characters "manufacturing." However, if the characters are printed while performing white correction as nozzle missing correction to address missing dots caused by such defective nozzles, bleeding may occur near the transport direction edges of the linear pattern that makes up the characters, within the area where white streaks would appear if nozzle missing correction was not performed, as shown in FIG. 15.

[0061] In this embodiment, when performing white correction as nozzle defect correction to prevent a decrease in the quality of a printed image due to dot omission caused by a defective nozzle, after white ink is ejected onto a correction region (in this example, a white correction region) which is a region where ink is ejected from the defective nozzle and nozzles in its vicinity, ink for image formation (in this example, colored ink such as black ink for forming a character image) is ejected. This correction region is usually composed of a number of continuous regions (at least one continuous region) corresponding to the image to be printed. For example, for the printed image of the character "造" shown in the example of FIG. 14, as shown in FIG. 16, a rectangular continuous region AC1 having a range of 31 pixels continuous in the conveyance direction as the conveyance direction range and a range of 5 pixels continuous in the width direction of the substrate 12 (hereinafter referred to as the "substrate width direction") as the substrate direction range, a rectangular continuous region AC2 having a range of 2 pixels continuous in the conveyance direction as the conveyance direction range and a range of 5 pixels continuous in the substrate width direction as the substrate direction range, a rectangular continuous region AC3 having a range of 2 pixels continuous in the conveyance direction as the conveyance direction range and a range of 5 pixels continuous in the substrate width direction as the substrate direction range, and a rectangular continuous region AC4 having a range of 4 pixels continuous in the conveyance direction as the conveyance direction range and a range of 5 pixels continuous in the substrate width direction as the substrate direction range constitute the correction region. When colored ink such as black ink for forming the image of the character "造" is ejected after white ink is ejected onto each continuous region (hereinafter referred to as "correction individual region") constituting such a correction region, the wet spreading range of the colored ink ejected at the end in the conveyance direction in each of the correction individual regions AC1 to AC4 protrudes from the correction individual region, and the protruding portion is visually recognized as bleeding.

[0062] Therefore, in this embodiment, as shown in FIG. 16 , in the correction individual area ACk (k=1 to 4), one pixel is removed from both ends in the transport direction (both ends in the vertical direction in the figure), and the correction individual area after removing this one pixel is designated as the “correction execution area ADk.” White ink for white correction is ejected to the correction execution area ADk, not the correction individual area ACk (white ink is not ejected to the one-pixel portion in the transport direction at both ends of the correction individual area ACk). However, for correction individual areas AC2 and AC3, which are two pixels wide in the transport direction, corresponding correction execution areas AD2 and AD3 cannot be set, so white ink as correction supplementary ink is not ejected. Note that hereinafter, the process of removing a predetermined number of pixels in the transport direction from both ends of a continuous rectangular area serving as a correction individual area is referred to as “edge thinning processing.” In the edge thinning processing shown in FIG. 16 , the number of pixels in the transport direction removed at both ends of the correction individual area (hereinafter referred to as the “thinning number”) is one.

[0063] In this way, in white correction, a correction execution area is determined by performing end thinning processing on each individual correction area included in the correction area, and white ink for white correction is ejected only into each correction execution area. More specifically, in this end thinning processing, for correction individual areas included in the correction area where the number of pixels in the transport direction is greater than twice the thinning number, the correction execution area is determined by performing end thinning processing on the individual correction area, that is, by removing the number of pixels in the transport direction from both ends of the rectangular continuous area that is the individual correction area in the transport direction by the thinning number. For correction individual areas where the number of pixels in the transport direction is less than twice the thinning number, no correction execution area is set. Furthermore, white ink for white correction is not ejected without gaps into each correction execution area, but is ejected according to a periodic pattern in pixel units such that one pixel area to which white ink is ejected and one pixel area to which white ink is not ejected appear alternately (details will be described later with reference to Figures 19 to 24). In the example shown in Figure 16, white ink is ejected only onto the shaded pixel portions in each of the correction execution areas AD1 and AD4. White ink is not ejected onto the end regions of the correction individual areas AC1 and AC4 that have been removed by the end thinning process, and white ink is not ejected onto either of the correction individual areas AC2 and AC3. The thinning number is a predetermined, relatively small natural number, and is 1 in the example shown in Figure 16, but is not limited to this. However, considering that images such as characters can contain a fair number of linear patterns with narrow widths in the transport direction, it is preferable to set the thinning number to 1 or 2.

[0064] FIG. 17 is a diagram showing an example of a printed image obtained by printing characters while performing white correction with edge thinning in this embodiment. In this example, the defective nozzles included in the ink ejection head when forming the printed images shown in FIGS. 14 and 15 are assumed to be the same. As shown in FIG. 15, when the characters "manufacturing" are printed while performing white correction without edge thinning as described above, the occurrence of image defects (white streaks) due to missing dots caused by nozzle defects is suppressed in the printed image, but bleeding occurs near the edges of the correction individual area in the transport direction. In contrast, in this embodiment, in which the characters "manufacturing" are printed while performing white correction with edge thinning as described above, the correction execution area to which white ink should be ejected is determined as described above, so that, as shown in FIG. 17, image defects (white streaks) due to missing dots caused by nozzle defects are suppressed and the bleeding seen in the example of FIG. 15 is suppressed.

[0065] The above has described the case where white correction is performed when printing an image that includes narrow linear patterns such as characters or barcodes, but in transparency correction as well, the wet spread range of colored ink on the substrate 12 is larger when the colored ink is ejected onto transparent ink that serves as correction supplementary ink and is ejected onto the substrate 12 than when the colored ink is ejected directly onto the substrate 12. Therefore, even when transparency correction is performed when printing an image that includes narrow linear patterns such as characters or barcodes, it is possible to prevent image defects due to missing dots caused by nozzle defects and to prevent bleeding by determining the correction execution area using the edge thinning process described above and ejecting transparent ink only onto the correction execution area.

[0066] <8.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).

[0067] <8.1 Functional Configuration> 18 is a block diagram showing a detailed functional configuration of the density correction processing unit 24 in this embodiment. As shown in FIG. 18, 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 edge processing unit 247a, a white correction pattern creation unit 248a, a transparent correction determination unit 245b, a transparent correction target nozzle identification unit 246b, a transparent correction edge processing unit 247b, a transparent correction pattern creation unit 248b, an ink ejection control unit 250, and a UV-LED setting unit 249. The ink ejection control unit 250 includes a first correction processing unit 2501, a second correction processing unit 2502, and a third correction processing unit 2503.

[0068] 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.

[0069] 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 colored 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 2501 in the ink ejection control unit 250.

[0070] 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.

[0071] 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.

[0072] The white correction determination unit 245a determines whether or not to perform white correction for each of the areas where ink is ejected from the defective nozzle and the nozzles in the vicinity thereof, based on the defective nozzle information 72, the substrate information 73, and the print data 74. The determination result 75a is then output from the white correction determination unit 245a.

[0073] In this regard, 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. When the substrate used for printing is a white substrate, and 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 a single-color high-density print 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 single color) greater than the first determination reference value. In this case, within the area into which ink is ejected from the defective nozzle and its neighboring nozzles, a range in which missing pixels that should be formed on the substrate 12 by ink that should be ejected from the defective nozzle are continuous in the transport direction is defined as the transport direction range, and a range in which a predetermined number of pixels (five pixels in the example shown in FIG. 16 ) are adjacent to the missing pixel in the substrate width direction is defined as the substrate width direction range. This rectangular continuous area is treated as a correction individual area (referred to as a "white correction individual area" when it should be distinguished from correction individual areas in transparent correction and normal correction, which will be described later). The determination result 75a output from the white correction determination unit 245a also includes correction individual area information indicating each correction individual area. For example, if only characters such as those shown in Fig. 16 are printed in the entire print area, correction individual area information indicating four correction individual areas AC1 to AC4 and determination information indicating that white correction is required in all of these four correction individual areas AC1 to AC4 are output as the determination result 75a. Note that, for correction individual areas indicated by the correction individual area information that do not require white correction and that should undergo normal nozzle missing correction, information indicating that white correction is not required is included in the determination result 75a.

[0074] 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 mixed-color high-density printing of two or more colors of ink, including the ink of the color that should be ejected from the defective nozzle (defective nozzle color), occurs, where the density of the defective nozzle color is high; more specifically, if the area includes an area where printing occurs 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. In this case, too, within the area into which ink is ejected from the defective nozzle and its neighboring nozzles, a continuous rectangular area is treated as the correction individual area (white correction individual area), where the transport direction range is the range in which missing pixels, which are pixels that should be formed on the substrate 12 by ink that should be ejected from the defective nozzle, are continuous in the transport direction, and the substrate width direction range is the range in which a predetermined number of pixels (e.g., 3 or 5 pixels) adjacent to the missing pixel in the substrate width direction are centered on the missing pixel.

[0075] 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.

[0076] If the determination result 75a output from the white correction determination unit 245a indicates that white correction is to be performed on any of the individual correction regions, the white correction target nozzle identification 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 individual correction region information and determination information included in the determination result 75a and the defective nozzle information 72. Then, white correction target nozzle information 76a that identifies the white correction target nozzles is output from the white correction target nozzle identification unit 246a. This white correction target nozzle information 76a includes correction individual region information, and identifies the white correction target nozzles in association with each white correction individual region that is each individual correction region that requires white correction.

[0077] 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. This template specifies the white ink ejection pattern on a pixel-by-pixel basis and is referenced by the white correction target nozzle identifying unit 246a and the white correction pattern creating unit 248a. For example, a template such as that shown in FIG. 19 is prepared. In FIG. 19, 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 (substrate width direction), each nozzle corresponds to one pixel portion. In the example shown in FIG. 19, the columns labeled 64L and 64R include the shaded pixel portions. Therefore, of the many nozzles included in the white ink ink ejection 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 correction target nozzles by the white correction target nozzle identifying unit 246a.

[0078] The white correction edge processing unit 247a determines a correction execution area (referred to as a "white correction execution area" when it is to be distinguished from the "correction execution area" in transparency correction described below) corresponding to each white correction individual area by performing the above-mentioned edge thinning process on each correction individual area (each white correction individual area) that requires white correction based on the correction individual area information included in the white correction target nozzle information 76a (see FIG. 16), and outputs white correction execution area information 77a. This white correction execution area information 77a includes execution area information indicating each correction execution area, and identifies white correction target nozzles in association with each correction execution area. Note that a correction execution area is not set for correction individual areas indicated by the correction individual area information included in the white correction target nozzle information 76a where the number of pixels in the transport direction is twice or less the number of pixels to be thinned out (see correction individual areas AC2 and AC3 shown in FIG. 16).

[0079] Based on the white correction execution area information 77a, the white correction pattern creation unit 248a creates a white correction execution pattern 78a that specifies a white ink ejection pattern pixel-by-pixel across the entire printing area using the template described above. This white correction execution pattern 78a is composed of white correction individual execution patterns in which the white ink ejection pattern is specified pixel-by-pixel using the template described above in correction execution areas corresponding to each white correction individual area. In the example shown in FIG. 16, the white correction individual execution pattern is a pattern that specifies a white ink ejection pattern pixel-by-pixel using the template described above in each of the correction execution areas AD1 and AD4 corresponding to the correction individual areas AC1 and AC4, respectively. In this embodiment, the area to which white ink should be ejected based on the white correction execution pattern 78a created in this manner is treated as a white correction execution area across the entire printing area (hereinafter referred to as a "global white correction execution area"). Therefore, creating the white correction execution pattern 78a is equivalent to determining a global white correction execution area.

[0080] 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. 20 , 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 execution pattern 78a created by the white correction pattern creation unit 248a is as shown in FIG. 21 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 execution pattern 78a created by the white correction pattern creation unit 248a, as shown in FIG. 21 , 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 execution pattern 78a will be described below only as an example of white correction being performed in an area where monochrome high-density printing is performed.

[0081] The transparency correction determination unit 245b determines whether or not to perform transparency correction for each of the areas where ink is ejected from the defective nozzle and the nozzles nearby, based on the defective nozzle information 72, the substrate information 73, and the print data 74. The transparency correction determination unit 245b then outputs the determination result 75b.

[0082] In this regard, in this embodiment, if the substrate used for printing is a white substrate, a determination is made based on the substrate information 73 that transparency correction will not be performed. If the substrate used for printing is other than a white substrate, and if a defective nozzle is present based on the defective nozzle information 72 and the print data 74, and the area into which ink is ejected from the defective nozzle and its neighboring nozzles includes an area where single-color high-density printing is performed with ink of the color that should be ejected from the defective nozzle, or more specifically, if the area includes printing where the total ink amount (= ink amount of that single color) is greater than the transparency correction first determination reference value corresponding to the first determination reference value in the white correction determination unit 245a, a determination is made to perform transparency correction. In this case, within the region into which ink is ejected from the defective nozzle and its neighboring nozzles, the range in the transport direction where missing pixels, which are pixels to be formed on the substrate 12 by ink ejected from the defective nozzle, are continuous in the transport direction, and the range in the substrate width direction where a predetermined number of pixels (e.g., three or five pixels) are adjacent to the missing pixel in the substrate width direction is treated as a continuous rectangular correction individual region (referred to as a "transparent correction individual region" when distinguished from the correction individual regions in the aforementioned transparency correction and normal correction). The determination result 75b output from the transparency correction determination unit 245b also includes correction individual region information indicating each correction individual region. Note that, for correction individual regions indicated by the correction individual region information that do not require transparency correction and should undergo normal nozzle missing correction, information indicating that transparency correction is not required is included in the determination result 75b.

[0083] 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 to be ejected from the defective nozzle (defective nozzle color), is performed, where the density of the defective nozzle color is high, more specifically, if the area includes a print where the total ink amount is greater than the second transparency correction reference value corresponding to the second reference value in the white correction determination 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 transparency correction reference value corresponding to the third reference value in the white correction determination unit 245a. In this case, too, within the area into which ink is ejected from the defective nozzle and its neighboring nozzles, a rectangular continuous area is treated as the correction individual area (transparent correction individual area), where the transport direction range is the range in which missing pixels, which are pixels to be formed on the substrate 12 by ink to be ejected from the defective nozzle, are continuous in the transport direction, and the substrate width direction range is the range in which a predetermined number of pixels (e.g., 3 or 5 pixels) adjacent to the missing pixel are centered on the missing pixel.

[0084] 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).

[0085] If the determination result 75b output from the transparency correction determination unit 245b indicates that transparency correction is to be performed on any of the individual correction regions, 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 correction individual region information and determination information included in the determination result 75b and the defective nozzle information 72. 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. This transparency correction target nozzle information 76b includes correction individual region information and identifies transparent correction target nozzles in association with each transparent correction individual region that is a correction individual region that requires transparency correction.

[0086] The transparent correction end processing unit 247b performs the aforementioned end thinning process on each transparent correction individual area that requires transparent correction based on the correction individual area information included in the transparent correction target nozzle information 76b (see FIG. 16), thereby determining a correction execution area (referred to as a "transparent correction execution area" when distinguished from the "correction execution area" in the white correction described above) corresponding to each transparent correction individual area, and outputs transparent correction execution area information 77b. This transparent correction execution area information 77b includes execution area information indicating each correction execution area, and identifies transparent correction target nozzles in association with each correction execution area. Note that a correction execution area is not set for correction individual areas indicated by the correction individual area information included in the transparent correction target nozzle information 76b where the number of pixels in the transport direction is less than twice the number of pixels to be thinned.

[0087] Based on the transparent correction execution area information 77b, the transparent correction pattern creation unit 248b creates a transparent correction execution pattern 78b that represents a pattern such as that shown in the template described above in the entire print area. This transparent correction execution pattern 78b is composed of transparent correction execution patterns in which the transparent ink ejection pattern is specified pixel by pixel using the template described above in the correction execution areas corresponding to each transparent correction execution area. In this embodiment, the area to which transparent ink is to be ejected based on the transparent correction execution pattern 78b created in this manner is treated as a transparent correction execution area in the entire print area. Therefore, creating the transparent correction execution pattern 78b is equivalent to determining a transparent correction execution area in the entire print area (hereinafter referred to as a "global transparent correction execution area").

[0088] As shown in FIG. 18 , the ink ejection control unit 250 corrects the density data included in the print data 74 and controls the ejection of ink from each ink ejection head 150 based on the corrected density data 82. As described above, the ink ejection control unit 250 includes a first correction processing unit 2501, a second correction processing unit 2502, and a third correction processing unit 2503. 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 2501 corrects the density data included in the print data 74. If the determination result 75a indicates that white correction will be performed for any of the individual correction regions, the second correction processing unit 2502 corrects the density data included in the print data 74. If the determination result 75b indicates that transparency correction will be performed for any of the individual correction regions, the third correction processing unit 2503 corrects the density data included in the print data 74.

[0089] The first correction processing unit 2501 performs density uniformization correction and nozzle missing correction based on the correction coefficients 71, defective nozzle information 72, determination results 75a and 75b, and print data 74. As a result, correction is applied to the density data included in the print data 74, and density data 82 is generated as normal corrected density data for controlling the ejection of ink from each ink ejection head 150.

[0090] The second correction processing unit 2502 performs density uniformization correction, nozzle missing correction, and white correction based on the correction coefficients 71, defective nozzle information 72, determination results 75a, white correction execution pattern 78a, and print data 74. As a result, corrections are made to the density data included in the print data 74, and density data 82 is generated as white correction density data for controlling the ejection of ink from each ink ejection head 150.

[0091] The third correction processing unit 2503 performs density uniformity correction, nozzle missing correction, and transparency correction based on the correction coefficients 71, defective nozzle information 72, determination results 75b, transparency correction execution pattern 78b, and print data 74. As a result, corrections are made to the density data included in the print data 74, and density data 82 is generated as transparency-corrected density data for controlling the ejection of ink from each ink ejection head 150.

[0092] 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, and the size of the ink droplets ejected from the nozzle can be changed by changing the voltage waveform of the drive signal applied to the piezoelectric element. In this embodiment, the second correction processing unit 2502 corrects the density data so that the white ink is ejected in the correction area at the smallest droplet size among the plurality of droplet sizes. That is, the ink ejection control unit 250 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 among the plurality of droplet sizes. This prevents the white ink from being consumed more than necessary to widen the wetting and spreading range of the colored ink. 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 250 controls the ejection of white ink in the same manner as it controls the ejection of clear ink.

[0093] The time it takes for the colored inks to be cured by ultraviolet light irradiation from the UV-LEDs 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 colored ink ejected onto the white ink in the white correction region decreases from the UV-LEDs 159(c). 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 colored ink ejected onto the transparent ink in the transparent correction area to UV-LED 159(c) decreases.

[0094] 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 colored ink is sufficiently wide when the colored 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.

[0095] 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.

[0096] 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.

[0097] 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 end processing unit 247a, a white correction pattern creation unit 248a, a transparent correction determination unit 245b, a transparent correction target nozzle identification unit 246b, a transparent correction end processing unit 247b, and a transparent correction pattern creation unit 248b, and an ultraviolet irradiation control unit is realized by a UV-LED setting unit 249.

[0098] <8.2 Correction Pattern Template> In the above description, it is assumed that the template shown in FIG. 19 is prepared as the template that serves as the basis for the white correction execution pattern 78a and the transparent correction execution pattern 78b created by the white correction pattern creation unit 248a and the transparent correction pattern creation unit 248b, respectively. However, the templates that can be used are not limited to the template shown in FIG. 19. For example, the templates shown in FIG. 22, FIG. 23, and FIG. 24 can also be used. The templates shown in FIGS. 19 and 23 correspond to correction individual regions in which three pixels are adjacently arranged in the width direction of the substrate, and the templates shown in FIGS. 22 and 24 correspond to correction individual regions in which five pixels are adjacently arranged in the width direction of the substrate. Templates other than those shown in FIGS. 19 and 22 to 24 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 ±2 pixel regions and printing with an increased amount of ink in ±1 pixel regions for pixels corresponding to defective nozzles. Therefore, it is preferable to use the templates shown in FIG. 22 or 24. The nozzles to be corrected are identified using the templates described above, and these templates can be used in both cases of performing white correction and transparent correction. However, for the sake of convenience, the following description of such templates will only be given in the case of performing white correction.

[0099] 19 or 23 is adopted, of the many nozzles included in the inkjet head 150(W) for white ink, the nozzles that eject ink onto pixel portions in the column marked with reference numeral 64L and the nozzles that eject ink onto pixel portions in the column marked with reference numeral 64R are identified as nozzles that are subject to white correction. When the template shown in Fig. 22 or 24 is adopted, of the many nozzles included in the inkjet head 150(W) for white ink, the nozzles that eject ink onto pixel portions in the column marked with reference numeral 64L1, the nozzles that eject ink onto pixel portions in the column marked with reference numeral 64R1, the nozzles that eject ink onto pixel portions in the column marked with reference numeral 64L2, and the nozzles that eject ink onto pixel portions in the column marked with reference numeral 64R2 are identified as nozzles that are subject to white correction.

[0100] 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 19 or Figure 22 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 23 or Figure 24 is adopted, two pixel portions onto which white ink is ejected and two pixel portions onto which white ink is not ejected appear alternately.

[0101] <8.3 Procedure> The density correction procedure in this embodiment will be described below with reference to Fig. 25. It is assumed that the print data 74 to be processed is already stored in the print data storage unit 244 (see Fig. 18).

[0102] In this embodiment, the main part of the density correction processing unit 24 shown in Fig. 18 (configuration other than components realized by hardware) is realized in software by the CPU 211 performing density correction processing according to the procedure shown in Fig. 25 in accordance with the print control program P in the control device 200 shown in Fig. 6. In this density correction processing, the CPU 211 operates as follows.

[0103] 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 colored 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.

[0104] Thereafter, defective nozzles are detected from among the many nozzles included in the ink ejection head 150 for colored inks 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).

[0105] 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.

[0106] 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:

[0107] 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.

[0108] 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.

[0109] By making a determination using the above-described formulas (1a) to (2b), a determination result 75a is obtained indicating whether or not white correction is required for each determination area determined by a defective nozzle. This determination result 75a includes correction individual area information indicating the previously described correction individual areas included in each determination area (e.g., each of areas AC1 to AC4 shown in FIG. 16) and determination information indicating whether or not white correction is required for each correction individual area. If it is determined based on this determination result 75a that white correction needs to be performed for any of the correction individual areas, the process proceeds to step S122; if it is determined that white correction does not need to be performed (for any of the correction individual areas), the process proceeds to step S130. Note that if a defective nozzle is present 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.

[0110] In step S122, the above-mentioned white correction target nozzles are identified based on the correction individual area information and determination information included in the determination result 75a and the information on the defective nozzles detected in step S116 (the above-mentioned defective nozzle information 72), and white correction target nozzle information 76a is generated. This white correction target nozzle information 76a includes correction individual area information and identifies the white correction target nozzles in association with each white correction individual area.

[0111] Thereafter, the aforementioned end thinning process is performed on each white correction individual area (each individual correction area requiring white correction) based on the correction individual area information included in the white correction target nozzle information 76a (see FIG. 16), thereby determining a correction execution area (white correction execution area) corresponding to each white correction individual area, and outputting white correction execution area information 77a (step S123). This white correction execution area information 77a includes execution area information indicating each correction execution area, and identifies white correction target nozzles in association with each correction execution area (white correction execution area). Note that a correction execution area is not set for correction individual areas where the number of pixels in the transport direction is twice or less than the number to be thinned out, among the white correction individual areas indicated by the correction individual area information included in the white correction target nozzle information 76a.

[0112] Next, the white correction execution pattern 78a described above is created based on the white correction execution area information 77a (step S124). In other words, a global white correction execution area is determined, which is an area on the substrate 12 onto which white ink should be ejected in the entire printing area in order to widen the wet spreading range of the colored ink.

[0113] After the white correction execution pattern 78a 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.

[0114] After the ultraviolet radiation from UV-LED 159(b) has been stopped, etc., the density uniformity correction, nozzle defect correction, and white correction described above are performed (step S128) 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 judgment result 75a obtained in step S121, the white correction execution pattern 78a created in step S124, and the print data 74 (see Figures 32, 7, and 8).

[0115] 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.

[0116] 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).

[0117] By performing step S141, a determination result 75b is obtained that indicates whether white correction is required for each determination area determined by the defective nozzle. This determination result 75b includes correction individual area information that indicates the previously described correction individual areas (e.g., each of areas AC1 to AC4 shown in FIG. 16) included in each determination area, and determination information that indicates whether transparency correction is required for each correction individual area. If transparency correction is required for any of the correction individual areas based on this determination result 75b, processing proceeds to step S142. If transparency correction is not required (for any of the correction individual areas), processing proceeds to step S130. Note that if a defective nozzle is present but transparency correction is determined not to be required, normal nozzle missing correction is performed in step S130, as described below.

[0118] In step S142, the transparent correction target nozzles described above are identified and transparent correction target nozzle information 76b is generated based on the correction individual area information and determination information included in the determination result 75a and the defective nozzle information 72. This transparent correction target nozzle information 76b includes correction individual area information and identifies transparent correction target nozzles in association with each transparent correction individual area.

[0119] Thereafter, the aforementioned edge thinning process is performed on each transparent correction individual area (each individual correction area requiring transparent correction) based on the correction individual area information included in the white correction target nozzle information 76a, thereby determining a correction execution area (transparent correction execution area) corresponding to each transparent correction individual area, and outputting transparent correction execution area information 77b (step S143). This transparent correction execution area information 77b includes execution area information indicating each correction execution area, and identifies transparent correction target nozzles by associating each correction execution area (each transparent correction execution area). Note that a correction execution area is not set for correction individual areas where the number of pixels in the transport direction is twice or less than the number of pixels to be thinned out among the transparent correction individual areas indicated by the correction individual area information included in the transparent correction target nozzle information 76b.

[0120] Next, the above-mentioned transparent correction execution pattern 78b is created based on the transparent correction execution area information 77b (step S144). In other words, a global transparent correction execution area is determined, which is an area on the substrate 12 where transparent ink should be ejected in the entire printing area in order to widen the wet spreading range of the colored ink.

[0121] After creating the transparency correction execution pattern 78b, the UV-LED 159(a) for transparent ink is stopped from irradiating with 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 irradiating with ultraviolet light onto the white ink ejected from the ink ejection head 150(E) onto the substrate 12.

[0122] 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 transparency correction execution pattern 78b created in step S144, and the print data 74 (step S148).

[0123] 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, the determination result 75a obtained in step S121 or the determination result 75b obtained in step S141, and the print data 74 (see FIG. 32).

[0124] This density correction ends when the process of step S128, the process of step S148, or the process of step S130 ends.

[0125] 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 edge processing unit 247a is realized in step S123, the white correction pattern creation unit 248a is realized in step S124, and the white correction pattern creation unit 249a is realized in step S130. Steps S120 and S141 implement a transparent correction determination unit 245b, step S142 implements a transparent correction target nozzle identification unit 246b, step S143 implements a transparent correction end processing unit 247b, step S144 implements a transparent correction pattern creation unit 248b, steps S126 and S146 implement a UV-LED setting unit 249, step S128 implements a second correction processing unit 2502, step S148 implements a third correction processing unit 2503, and step S130 implements a first correction processing unit 2501 (see FIG. 18). Note that the ink discharge control unit 250 is implemented by well-known control processing for the recording unit 15 and the conveying unit for printing based on the print control program P, step S130 implementing the first correction processing unit 2501, step S128 implementing the second correction processing unit 2502, and step S148 implementing the third correction processing unit 2503.

[0126] 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 82 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.

[0127] <9. 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. 25). 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 25). For this reason, the following will only describe the effects of this embodiment when focusing on white correction.

[0128] According to this embodiment, when a defective nozzle is detected in a color ink ejection head 150, white correction is performed to correct density data for a correction execution area (area on the substrate 12) where ink is ejected from the defective nozzle and its neighboring nozzles, which is set as an area where high-density monochrome printing is performed using the ink of the color that should be ejected from the defective nozzle. This white correction corrects density data so that white ink is ejected from the white ink ejection nozzles adjacent to the defective nozzle. The wet spread of the colored ink on the substrate 12 is larger when the colored ink is ejected onto white ink ejected onto the substrate 12 than when the colored 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 colored 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.

[0129] Furthermore, when nozzle missing correction is to be performed in a single-color area, whether to perform normal nozzle missing correction or white correction (nozzle missing correction using white ink) is determined based on a predetermined reference value (first reference value) for the total ink amount equivalent to the density of the single-color area (see equations (1a) and (1b) above). This allows for appropriate nozzle missing correction to be performed according to the density of the printed image, and also reduces unnecessary use of white ink. The color of the ink (white ink) used to widen the wet-spread range of the colored 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 colored inks does not stand out on the printed image.

[0130] Furthermore, according to the above embodiment, even when missing nozzle correction is required to suppress image defects caused by defective nozzles in mixed-color areas, 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 missing nozzle 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 the above-mentioned formulas (2a) and (2b)). This allows appropriate missing nozzle correction to be performed according to the total ink volume and the defective nozzle ink volume ratio. Therefore, while avoiding over-correction by white correction and unnecessary use of white ink, applying white correction under appropriate conditions in mixed-color areas can improve the effectiveness of noise missing correction compared to conventional methods.

[0131] Furthermore, according to this embodiment, white correction (nozzle missing correction using white ink) is performed on a global white correction execution area consisting of white correction execution areas obtained by performing the above-described edge thinning process (see FIG. 16) on each white correction individual area (see FIG. 25). This prevents the wet spreading range of colored ink ejected at the edges in the transport direction of each individual correction area (for example, areas AC1 to AC4 shown in FIG. 16) from spilling out of the individual correction area. As a result, even when printing images that include narrow linear patterns such as characters or barcodes, it is possible to prevent degradation of print quality due to bleeding caused by white correction (see FIG. 17).

[0132] As described above, according to this embodiment, when nozzle missing correction is required to suppress image defects caused by defective nozzles in both single-color and mixed-color regions, whether normal nozzle missing correction, white correction (when a white substrate is used), or transparent correction (when a substrate other than a white substrate is used) is appropriately determined based on a predetermined reference value. Therefore, white correction or transparent correction is performed under appropriate conditions. Furthermore, for each individual correction region determined to require white correction or transparent correction, the previously described edge thinning process is performed, and white ink or transparent ink is ejected as correction supplement ink only in the correction execution region obtained. Therefore, even when printing images containing narrow linear patterns such as characters or barcodes, nozzle missing correction can be effectively performed while suppressing degradation of print quality due to bleeding caused by white correction or transparent correction. This type of nozzle missing correction, including white correction or transparent correction, realizes an inkjet printing device 10 that enables high-quality printouts. Furthermore, because degradation of image quality of printed images caused by defective nozzles is appropriately and effectively suppressed as described above, the need for reprinting is reduced compared to conventional methods, enabling reductions in substrate and ink consumption. In this way, we can contribute to achieving the SDGs (Sustainable Development Goals).

[0133] <10. Variations> <10.1 First Modification> In the above embodiment, 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. 25). However, if it is not necessary to assume that a substrate other than a white substrate is used as the substrate 12 used for printing, the configuration related to transparency correction may be omitted from the above embodiment. Below, an inkjet printing device in which the configuration related to transparency correction is omitted from the above embodiment will be described as a first modified example of the above embodiment.

[0134] In this modified example, the substrate determination unit 243, the transparency correction determination unit 245b, the transparency correction target nozzle identification unit 246b, the transparency correction end processing unit 247b, the transparent correction pattern creation unit 248b, and the third correction processing unit 2503 are deleted from the functional configuration of the density correction processing unit 24 in the above embodiment shown in Figure 18, 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 Figure 26. Furthermore, in this modified example, steps S118, S120, and S141 to S148 are deleted from the density correction procedure (density correction process) in the above embodiment shown in Figure 25, resulting in a procedure as shown in Figure 27.

[0135] According to this modified example, when it is not assumed that a substrate other than a white substrate will be used as the printing medium, whether to perform normal nozzle missing correction or white correction is appropriately determined based on a predetermined reference value in both single-color and mixed-color regions where nozzle missing correction should be performed, so white correction is performed under appropriate conditions, achieving the same effects as in the above-described embodiment. Furthermore, since white ink is ejected as correction supplementary ink only in the correction execution region obtained by performing the above-described edge thinning process on each individual correction region determined to require white correction, even when printing images that include narrow linear patterns such as characters or barcodes, it is possible to effectively perform nozzle missing correction while suppressing degradation of print quality due to bleeding caused by white correction.

[0136] <10.2 Second Modification> In the above embodiment, 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. 25). 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 above embodiment. Below, an inkjet printing device in which the configuration related to white correction is omitted from the above embodiment will be described as a second modified example of the above embodiment.

[0137] 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 edge processing unit 247a, the white correction pattern creation unit 248a, and the second correction processing unit 2502 are deleted from the functional configuration of the density correction processing unit 24 in the above embodiment shown in Fig. 18, 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. 28. Furthermore, in this modified example, steps S118, S120, and S121 to S128 are deleted from the density correction procedure (density correction process) in the above embodiment shown in Fig. 25, resulting in a procedure as shown in Fig. 29.

[0138] According to this modified example, when the use of a white substrate as the printing medium is not anticipated, whether normal nozzle missing correction or transparency correction should be performed is appropriately determined based on a predetermined reference value in both single-color and mixed-color regions where nozzle missing correction is required, so transparency correction is performed under appropriate conditions, achieving the same effects as in the above-described embodiment. Furthermore, since transparent ink is ejected as correction supplementary ink only in the correction execution region obtained by performing the above-described edge thinning process on each individual correction region determined to require transparency correction, even when printing images that include narrow linear patterns such as characters or barcodes, nozzle missing correction can be effectively performed while suppressing degradation of print quality due to bleeding caused by transparency correction.

[0139] <10.3 Third Modification> In the above embodiment, in order to increase the wet spread range of the colored ink on the substrate 12 as a result of nozzle chipping correction, white ink or transparent ink was ejected as correction auxiliary ink onto the substrate 12 before the colored ink was ejected onto the substrate 12 in the correction area, depending on whether the substrate 12 was a white substrate or a substrate other than a white substrate. However, the present invention is not limited to this. Therefore, it is also conceivable to use ink other than white ink or transparent ink as correction auxiliary ink to increase the wet spread range of the colored ink. Furthermore, as described below, it is conceivable to use yellow ink to enhance the effectiveness of nozzle chipping correction when a defect occurs in a black ink ejection nozzle. Below, an example is described as a third modification of the above embodiment, in which yellow ink is used as correction auxiliary ink to increase the wet spread range of the black ink, instead of the white correction in the above embodiment.

[0140] In this modified example, when a defect occurs in a black ink ejection nozzle, in order to enhance the effect of nozzle missing correction, yellow ink, which has a higher lightness value than the black ink, is ejected onto the substrate 12 in the correction area before the black ink is ejected onto the substrate 12. Also, instead of the white correction in the above embodiment, a process is performed to correct the density data so that yellow ink, which has a higher lightness value than the 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").

[0141] 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.

[0142] Here, let's assume that the nozzle designated by reference numeral 521 in Figure 30 is a defective nozzle out of the multiple nozzles included in the black ink ink ejection head 150(K). In this case, by performing the above-described nozzle missing correction, a larger amount of black ink is ejected from the defective adjacent nozzles (nozzles designated by reference numerals 522 and 523) than would otherwise be ejected. 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.

[0143] 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.

[0144] As yet another example, in order to enhance the effect of nozzle missing correction when a defect occurs in a black ink ejection nozzle, blue ink, which has little color difference from the black ink, may be ejected as correction auxiliary ink 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 above embodiment, a process of correcting density data (hereinafter, this process will be referred to as "blue correction") may be performed so that blue ink, which has little color difference from the black ink, is ejected from the ink ejection head 150(B) so that the wetting and spreading range of the black ink is increased, and ejection control similar to that in the case of yellow correction may be performed.

[0145] 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, adopting the configuration of this modified example makes it possible to effectively suppress the occurrence of image defects in printed images caused by the presence of defective black ink-ejecting nozzles (such as streaky density reductions due to missing dots). Furthermore, yellow ink or blue ink is ejected as correction supplement ink only in the correction execution area obtained by performing the edge thinning process described above on each individual correction area (e.g., each of areas AC1 to AC4 shown in FIG. 16 ) that is determined to require yellow correction or blue correction. Therefore, even when printing an image that includes narrow linear patterns such as characters or barcodes, nozzle dropout correction can be effectively performed while suppressing degradation of print quality due to bleeding caused by yellow correction or blue correction.

[0146] <11.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.

[0147] 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.

[0148] In addition, 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 159(b) that cures the white ink. In this case, a determination process similar to step S141 in FIG. 25 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). [Explanation of symbols]

[0149] 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...printing control device 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...Edge processing section for white correction 248a...White correction pattern creation unit 245b...Transparency correction determination section 246b...Transparent correction target nozzle identification section 247b...Transparency correction edge processing portion 248b...Transparent correction pattern creation unit 249...UV-LED setting section 250...Ink discharge control unit 2501...first correction processing unit 2502...Second correction processing unit 2503...Third correction processing unit ACk…Correction individual area (k=1~4) ADk...correction execution area (k=1,4)

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 recording unit that ejects a plurality of types of ink, including a first ink and a correction auxiliary ink, onto the printing medium; a conveying unit that moves the print medium relative to the recording unit; an ejection control unit that controls the ejection of the plurality of types of ink by the recording unit; a correction area determination unit that determines a correction area consisting of one or more continuous areas to be corrected using the correction supplemental ink in the print image formed on the print medium; Equipped with the transport unit includes a mechanism for moving the print medium relative to the recording unit in a predetermined transport direction that is perpendicular to the width direction of the print medium and parallel to the print medium, The recording unit a first ink ejection head including a plurality of ink ejection ports for ejecting the first ink; a correction auxiliary ink ejection head that is disposed upstream of the first ink ejection head in the transport direction and includes a plurality of ink ejection ports that eject the correction auxiliary ink, a wetting and spreading range of the first ink on the printing medium is larger when the first ink is ejected onto the correction auxiliary ink that has been ejected onto the printing medium than when the first ink is ejected directly onto the printing medium; the correction area determination unit determines, for each continuous area included in the correction area, an area obtained by removing, in the conveying direction, an amount of pixels corresponding to the thinning number from both ends of the continuous area in the conveying direction when the number of pixels in the conveying direction in the continuous area is greater than twice a predetermined thinning number, as a correction execution area; A printing device in which the ejection control unit controls the first ink ejection head and the correction auxiliary ink ejection head so that the correction auxiliary ink is ejected into the correction execution area before the first ink is ejected into the correction execution area to form the print image.

2. The printing device according to claim 1, wherein the ejection control unit controls the correction auxiliary ink ejection head so that the correction auxiliary ink is not ejected into each continuous area included in the correction area in which the number of pixels in the transport direction is less than twice the thinning number.

3. 2. The printing device according to claim 1, wherein the thinning number is one or two.

4. The printing apparatus 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.

5. 5. The printing device according to claim 4, wherein the correction area determination unit determines the correction area based on the print data so that the correction area includes a continuous rectangular area, the range in the transport direction being a range in which missing pixels, which are pixels to be formed on the printing medium by ink to be ejected from the defective ejection port, are continuous in the transport direction, and the range in the width direction being a range in which a predetermined number of pixels are adjacent to the missing pixel in the width direction, with the missing pixel as the center.

6. 6. The printing device according to claim 5, wherein the correction area determination unit determines the correction area so that a range in the width direction of three or five adjacent pixels in the width direction centered on the missing pixel is set as the range in the width direction of the rectangular continuous area.

7. 5. The printing device according to claim 4, wherein the correction area determination unit determines the correction execution area so that one pixel onto which the correction supplementary ink is ejected and one pixel onto which the correction supplementary ink is not ejected are arranged alternately in the transport direction.

8. 5. The printing device according to claim 4, wherein the correction area determination unit determines the correction execution area so that two pixels onto which the correction supplementary ink is ejected and two pixels onto which the correction supplementary ink is not ejected are arranged alternately in the transport direction.

9. the recording unit further includes a second ink ejection head that is disposed downstream of the correction auxiliary ink ejection head in the transport direction and includes a plurality of ink ejection ports that eject a second ink; a wetting and spreading range of the second ink on the printing medium is larger when the second ink is ejected onto the correction auxiliary ink 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 be mixed, 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 correction auxiliary ink ejected onto the printing medium than when the first ink and the second ink are ejected directly onto the printing medium; 9. A printing device according to claim 1, wherein the ejection control unit controls the second ink ejection head and the correction auxiliary ink ejection head so that the correction auxiliary ink is ejected into the correction execution area before the second ink is ejected into the correction execution area to form the print image.

10. 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; 10. A printing device according to claim 9, 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 is mixed with the color of the second ink, 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.

11. 9. The printing device according to claim 1, wherein the correction area determination unit determines the correction area so that an area onto which the correction supplementary 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 plurality of types of ink are ultraviolet curable inks.

13. a first ultraviolet irradiation unit that cures, by ultraviolet irradiation, ink ejected from the recording unit out of the plurality of types of ink other than the correction auxiliary ink; a second ultraviolet irradiation unit that cures the correction auxiliary ink ejected from the recording unit 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 correction auxiliary ink is ejected into the correction execution 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 correction auxiliary ink ejection head is configured to be able to eject the correction auxiliary ink in a plurality of droplet sizes, The printing device described in claim 12, wherein the ejection control unit controls the ejection of the correction auxiliary ink from the correction auxiliary ink ejection head so that the droplet size of the correction auxiliary ink ejected from the correction auxiliary ink ejection head increases the closer the distance from the ink ejection head corresponding to the ink ejected onto the correction auxiliary ink in the correction execution area to the first ultraviolet irradiation unit.

15. the correction auxiliary ink ejection head is configured to be able to eject the correction auxiliary ink in a plurality of droplet sizes, A printing device described in any one of claims 1 to 8, wherein the ejection control unit controls the ejection of the correction auxiliary ink from the correction auxiliary ink ejection head so that the correction auxiliary ink is ejected into the correction execution area with the smallest droplet size among the multiple droplet sizes by the correction auxiliary ink ejection head.

16. the color of the print medium is white; the colored inks among the plurality of types of ink other than the correction auxiliary ink are process color or spot color inks that are different from one another; The printing device according to claim 1 , wherein the correction auxiliary ink is a white ink.

17. the colored inks among the plurality of types of ink other than the correction auxiliary ink are process color or spot color inks that are different from one another; The printing device according to claim 1 , wherein the correction auxiliary ink is a transparent ink.

18. 9. A printing device according to claim 1, wherein the ink ejected onto the correction auxiliary ink in the correction execution area from among the plurality of types of ink other than the correction auxiliary ink and the correction auxiliary ink are selected based on a brightness value or a color difference.

19. A printing method for forming a print image on a print medium based on print data using a printing device including a recording unit that ejects multiple types of ink onto the print medium and a transport unit that moves the print medium relative to the recording unit, the method comprising: a step of ejecting one ink of the plurality of types of ink as a first ink from the recording unit onto the print medium to form the print image; a step of ejecting another ink of the plurality of types of ink from the recording unit onto the print medium as a correction auxiliary ink; determining a correction area consisting of one or more continuous areas to be corrected using the correction supplemental ink in the printed image formed on the printing medium; Equipped with the transport unit includes a mechanism for moving the print medium relative to the recording unit in a predetermined transport direction that is perpendicular to the width direction of the print medium and parallel to 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 correction auxiliary ink that has been ejected onto the printing medium than when the first ink is ejected directly onto the printing medium; the step of determining the correction area includes, for each continuous area included in the correction area, determining, when the number of pixels in the transport direction in the continuous area is greater than twice a predetermined thinning number, an area obtained by removing, in the transport direction, an amount of pixels equal to the thinning number from both ends of the continuous area as the correction execution area; A printing method in which, before the first ink is ejected into the correction execution area to form the print image in the step of ejecting the first ink, the correction auxiliary ink is ejected into the correction execution area in the step of ejecting the correction auxiliary ink.

20. 20. The printing method according to claim 19, wherein the step of determining the correction area determines the correction area based on the print data so that the correction area includes a continuous rectangular area having a range in the transport direction in which missing pixels, which are pixels to be formed on the printing medium by ink to be ejected from a defective ejection port that is an ink ejection port having an ejection defect among the multiple ink ejection ports included in the first ink ejection head, are continuous, and a range in the width direction in which a predetermined number of pixels are adjacent to the missing pixel in the width direction, with the missing pixel as the center.

Images