Printing apparatus and printing method

Abstract

To provide a technique capable of reducing color shading due to vertically-arranged heads.SOLUTION: A recording head includes a plurality of color nozzle groups which have mutually-different colors of color ink droplets to be discharged between a forward path and a return path to a band region in the bidirectional printing. A compensation unit causes a recording medium to form a reference patch by discharging first and second color ink droplets in a prescribed recording density ratio with a reference timing difference for a timing difference of discharge between the first color ink droplet from the first color nozzle group and the second color ink droplet from the second color nozzle group generated according to the position in the band region in the main-scanning direction, causes the recording medium to form a plurality of first patches by discharging the first and second color ink droplets with the different recording density ratios with the first timing difference, and compensates for a color shift due to the timing difference to form a print image on the basis of the recording density ratio corresponding to the first patch for color shift compensation selected from the plurality of first patches.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to a printing apparatus that performs main scanning and sub-scanning, and a printing method.

Background Art

[0002] A serial printer performs printing by discharging ink droplets from a recording head onto a recording medium while performing main scanning that reciprocates the recording head along the main scanning direction, and performs sub-scanning that feeds the recording medium in the feeding direction while printing is not being performed. The feeding direction is opposite to the sub-scanning direction, which is the relative movement direction of the recording head. In bidirectional printing, ink droplets are discharged from the recording head onto the recording medium in both the forward and reverse paths during main scanning.

[0003] Patent Document 1 discloses a "vertically arranged head", which is a recording head having a color nozzle row in which a yellow nozzle group, a magenta nozzle group, and a cyan nozzle group are arranged in a single row in the sub-scanning direction. The vertically arranged head has a black nozzle row parallel to the color nozzle row. In the sub-scanning direction, the length of each color nozzle group in the color nozzle row is 1 / 3 of the length of the black nozzle row. Since the vertically arranged head requires only two nozzle rows, it can be formed at a low cost, and high-speed monochrome printing can be achieved by using a black nozzle row that is three times as long as the color nozzle groups. When a serial printer equipped with the above-described vertically arranged head performs high-speed bidirectional band printing during color printing, among a plurality of band regions corresponding to the length of each color nozzle group, magenta ink droplets are discharged in the reverse path in the band region where cyan and yellow ink droplets are discharged in the forward path. Also, cyan and yellow ink droplets are discharged in the forward path in the band region where magenta ink droplets are discharged in the reverse path.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

[0005] It was found that the printed image formed in the aforementioned band region exhibits different coloration depending on the position in the main scanning direction. Therefore, countermeasures are needed to address the color unevenness caused by different coloration depending on the position in the main scanning direction during bidirectional color printing with a vertically arranged head. [Means for solving the problem]

[0006] The present invention provides a printing apparatus comprising a recording head having a row of black nozzles arranged in a sequence for ejecting black ink droplets, and a group of color nozzles arranged along the row of black nozzles for ejecting color ink droplets, wherein the group of color nozzles is arranged sequentially in the direction of the arrangement of the black nozzles, A drive unit that performs a main scan to change the relative position of the recording head and the recording medium in the forward and return paths along a main scan direction intersecting the aforementioned alignment direction, and a sub-scan to change the relative position of the recording head and the recording medium along a sub-scan direction intersecting the main scan direction, The recording medium comprises a control unit that controls bidirectional printing, in which the color ink droplets are deposited in a single main scan between sub-scans in both the forward and return paths, from the color nozzle groups assigned to each band region corresponding to the length in the sub-scan direction of each of the color nozzle groups that eject the color ink droplets, The plurality of color nozzle groups include a first color nozzle group and a second color nozzle group, the colors of the color ink droplets ejected in the forward and return paths to the band region in the bidirectional printing process are different from each other. The color ink droplets ejected by the first color nozzle group are referred to as first color ink droplets, and the color ink droplets ejected by the second color nozzle group are referred to as second color ink droplets. The control unit includes a compensation unit that compensates for color misregistration caused by a timing difference in the ejection of the first color ink droplets and the second color ink droplets according to the position within the band region in the main scanning direction. The compensation unit forms a reference patch on the recording medium by ejecting the first color ink droplets and the second color ink droplets with a predetermined recording density ratio at a reference timing difference that is the basis of the timing difference. forms a plurality of first patches on the recording medium by ejecting the first color ink droplets and the second color ink droplets with a plurality of different recording density ratios at a first timing difference that is different from the reference timing difference. The reference patch is positioned between the first patches. on the recording medium, and forms a printed image by compensating for color misregistration caused by the timing difference based on the recording density ratio corresponding to a first color misregistration compensation patch selected from the plurality of first patches. Furthermore, the printing apparatus of the present invention comprises a recording head having a row of black nozzles arranged in a sequence of black nozzles for ejecting droplets of black ink, and a group of color nozzles arranged in a sequence of color nozzles arranged along the row of black nozzles for ejecting droplets of color ink, wherein the group of color nozzles is arranged sequentially in the direction of the arrangement of the black nozzles. A drive unit that performs a main scan to change the relative position of the recording head and the recording medium in the forward and return paths along a main scan direction intersecting the aforementioned alignment direction, and a sub-scan to change the relative position of the recording head and the recording medium along a sub-scan direction intersecting the main scan direction, The recording medium comprises a control unit that controls bidirectional printing, in which the color ink droplets are deposited in a single main scan between sub-scans in both the forward and return paths, from the color nozzle groups assigned to each band region corresponding to the length in the sub-scan direction of each of the color nozzle groups that eject the color ink droplets, The plurality of color nozzle groups include a first color nozzle group and a second color nozzle group, the colors of the color ink droplets ejected in the forward and return paths to the band region in the bidirectional printing process are different from each other. The color ink droplets ejected by the first color nozzle group are referred to as first color ink droplets, and the color ink droplets ejected by the second color nozzle group are referred to as second color ink droplets. The control unit includes a compensation unit that compensates for color misalignment caused by the timing difference in ejection between the first color ink droplet and the second color ink droplet, which occurs depending on their position within the band region in the main scanning direction. The aforementioned compensation unit is A reference patch is formed on the recording medium by aligning and ejecting the first color ink droplet and the second color ink droplet, which have a predetermined recording density ratio, on either the forward path or the return path at a reference timing difference, which is the basis for the timing difference. Multiple first patches are formed on the recording medium by ejecting multiple first color ink droplets and second color ink droplets with different recording density ratios at a first timing difference different from the aforementioned reference timing difference. The invention includes a method for forming a printed image by compensating for the color shift due to the timing difference based on the recording density ratio corresponding to a first color shift compensation patch selected from the plurality of first patches. Furthermore, the printing apparatus of the present invention comprises a recording head having a row of black nozzles arranged in a sequence for ejecting black ink droplets, and a group of color nozzles arranged along the row of black nozzles for ejecting color ink droplets, wherein the group of color nozzles is arranged sequentially in the direction of the arrangement of the black nozzles, A drive unit that performs a main scan to change the relative position of the recording head and the recording medium in the forward and return paths along a main scan direction intersecting the aforementioned alignment direction, and a sub-scan to change the relative position of the recording head and the recording medium along a sub-scan direction intersecting the main scan direction, The recording medium comprises a control unit that controls bidirectional printing, in which the color ink droplets are deposited in a single main scan between sub-scans in both the forward and return paths, from the color nozzle groups assigned to each band region corresponding to the length in the sub-scan direction of each of the color nozzle groups that eject the color ink droplets, The plurality of color nozzle groups include a first color nozzle group and a second color nozzle group, the colors of the color ink droplets ejected in the forward and return paths to the band region in the bidirectional printing process are different from each other. The color ink droplets ejected by the first color nozzle group are referred to as first color ink droplets, and the color ink droplets ejected by the second color nozzle group are referred to as second color ink droplets. The control unit includes a compensation unit that compensates for color misalignment caused by the timing difference in ejection between the first color ink droplet and the second color ink droplet, which occurs depending on their position within the band region in the main scanning direction. The aforementioned compensation unit is A reference patch is formed on the recording medium by ejecting the first color ink droplet and the second color ink droplet at a predetermined recording density ratio using a reference timing difference, which is the basis for the aforementioned timing difference. Multiple first patches are formed on the recording medium by aligning and ejecting multiple first color ink droplets and second color ink droplets with different recording density ratios on either the forward path or the return path at a first timing difference different from the aforementioned reference timing difference. The invention includes a method for forming a printed image by compensating for the color shift due to the timing difference based on the recording density ratio corresponding to a first color shift compensation patch selected from the plurality of first patches. Furthermore, the printing apparatus of the present invention comprises a recording head having a row of black nozzles arranged in a sequence for ejecting black ink droplets, and a group of color nozzles arranged along the row of black nozzles for ejecting color ink droplets, wherein the group of color nozzles is arranged sequentially in the direction of the arrangement of the black nozzles, A drive unit that performs a main scan to change the relative position of the recording head and the recording medium in the forward and return paths along a main scan direction intersecting the aforementioned alignment direction, and a sub-scan to change the relative position of the recording head and the recording medium along a sub-scan direction intersecting the main scan direction, The recording medium comprises a control unit that controls bidirectional printing, in which the color ink droplets are deposited in a single main scan between sub-scans in both the forward and return paths, from the color nozzle groups assigned to each band region corresponding to the length in the sub-scan direction of each of the color nozzle groups that eject the color ink droplets, The plurality of color nozzle groups include a first color nozzle group and a second color nozzle group, the colors of the color ink droplets ejected in the forward and return paths to the band region in the bidirectional printing process are different from each other. The color ink droplets ejected by the first color nozzle group are referred to as first color ink droplets, and the color ink droplets ejected by the second color nozzle group are referred to as second color ink droplets. The control unit includes a compensation unit that compensates for color misalignment caused by the timing difference in ejection between the first color ink droplet and the second color ink droplet, which occurs depending on their position within the band region in the main scanning direction. The aforementioned compensation unit is A reference patch is formed on the recording medium by ejecting the first color ink droplet and the second color ink droplet at a predetermined recording density ratio using a reference timing difference, which is the basis for the aforementioned timing difference. Multiple first patches are formed on the recording medium by ejecting multiple first color ink droplets and second color ink droplets with different recording density ratios at a first timing difference different from the aforementioned reference timing difference. Based on the recording density ratio corresponding to the first color shift compensation patch selected from the plurality of first patches, the color shift due to the timing difference is compensated to form a printed image. The recording medium includes a first recording medium and a second recording medium which has less color shift due to the timing difference than the first recording medium. The control unit, The system accepts the setting of the type of recording medium used to form the printed image. When the aforementioned type corresponds to the first recording medium, the compensation unit compensates for the color shift due to the timing difference to form the printed image. When the aforementioned type corresponds to the second recording medium, there is an embodiment in which no processing is performed to compensate for the color shift due to the timing difference.

[0007] Also, the printing method of the present invention is a black nozzle row in which a plurality of black nozzles for discharging black ink droplets are arranged, and a plurality of color nozzle groups in which a plurality of color nozzles for discharging color ink droplets are arranged along the black nozzle row, and having the plurality of color nozzle groups arranged in order in the arrangement direction of the plurality of black nozzles, a recording head; a driving unit that performs main scanning for changing the relative position between the recording head and the recording medium in the forward path and the return path along the main scanning direction intersecting the arrangement direction, and performs sub-scanning for changing the relative position between the recording head and the recording medium along the sub-scanning direction intersecting the main scanning direction; a printing method that performs bidirectional printing in which color ink droplets are landed by one main scan during sub-scanning in both the forward path and the return path from the color nozzle group assigned to each band region corresponding to the length in the sub-scanning direction of each color nozzle group that discharges color ink droplets on the recording medium; the plurality of color nozzle groups include a first color nozzle group and a second color nozzle group in which the colors of the color ink droplets discharged in the forward path and the return path with respect to the band region are different from each other in the bidirectional printing; The color ink droplets ejected by the first color nozzle group are referred to as first color ink droplets, and the color ink droplets ejected by the second color nozzle group are referred to as second color ink droplets. The aforementioned printing method is A reference patch formation step, which involves forming a reference patch on the recording medium by ejecting the first color ink droplet and the second color ink droplet at a predetermined recording density ratio using a reference timing difference, which is a reference for the timing difference of ejection between the first color ink droplet and the second color ink droplet that occurs according to their positions within the band region in the main scanning direction; Multiple first patches are produced by ejecting the first color ink droplets and the second color ink droplets with multiple different recording density ratios at a first timing difference different from the aforementioned reference timing difference. The reference patch is positioned between the first patches. A first patch formation step in which a patch is formed on the recording medium, The embodiment includes a print image forming step of forming a print image by compensating for the color shift due to the timing difference based on the recording density ratio corresponding to a first color shift compensation patch selected from the plurality of first patches. Furthermore, the printing method of the present invention is A recording head having a row of black nozzles arranged in a line, each of which ejects black ink droplets, and a group of multiple color nozzles arranged along the row of black nozzles, each of which ejects color ink droplets, and the group of multiple color nozzles arranged in order in the direction of the arrangement of the multiple black nozzles, The drive unit includes a drive unit that performs a main scan to change the relative position of the recording head and the recording medium in the forward and return paths along a main scan direction intersecting the aforementioned alignment direction, and a sub-scan to change the relative position of the recording head and the recording medium along a sub-scan direction intersecting the main scan direction, A printing method for performing bidirectional printing in which, in the recording medium, the color ink droplets are deposited in one main scan between sub-scans in both the forward and return paths, from the color nozzle groups assigned to each band region corresponding to the length in the sub-scan direction of each of the color nozzle groups that eject the color ink droplets, The plurality of color nozzle groups include a first color nozzle group and a second color nozzle group, the colors of the color ink droplets ejected in the forward and return paths to the band region in the bidirectional printing process are different from each other. The color ink droplets ejected by the first color nozzle group are referred to as first color ink droplets, and the color ink droplets ejected by the second color nozzle group are referred to as second color ink droplets. The aforementioned printing method is A reference patch formation step, in which a reference patch is formed on the recording medium by aligning and ejecting the first color ink droplet and the second color ink droplet, which have a predetermined recording density ratio, on either the forward path or the return path, based on a reference timing difference, which is the reference for the timing difference of ejection between the first color ink droplet and the second color ink droplet that occurs according to their position within the band region in the main scanning direction; A first patch formation step involves forming multiple first patches on the recording medium by ejecting multiple first color ink droplets and second color ink droplets with multiple different recording density ratios at a first timing difference different from the aforementioned reference timing difference. The embodiment includes a print image forming step of forming a print image by compensating for the color shift due to the timing difference based on the recording density ratio corresponding to a first color shift compensation patch selected from the plurality of first patches. Furthermore, the printing method of the present invention is A recording head having a row of black nozzles arranged in a line, each of which ejects black ink droplets, and a group of multiple color nozzles arranged along the row of black nozzles, each of which ejects color ink droplets, and the group of multiple color nozzles arranged in order in the direction of the arrangement of the multiple black nozzles, The drive unit includes a drive unit that performs a main scan to change the relative position of the recording head and the recording medium in the forward and return paths along a main scan direction intersecting the aforementioned alignment direction, and a sub-scan to change the relative position of the recording head and the recording medium along a sub-scan direction intersecting the main scan direction, A printing method for performing bidirectional printing in which, in the recording medium, the color ink droplets are deposited in one main scan between sub-scans in both the forward and return paths, from the color nozzle groups assigned to each band region corresponding to the length in the sub-scan direction of each of the color nozzle groups that eject the color ink droplets, The plurality of color nozzle groups include a first color nozzle group and a second color nozzle group, the colors of the color ink droplets ejected in the forward and return paths to the band region in the bidirectional printing process are different from each other. The color ink droplets ejected by the first color nozzle group are referred to as first color ink droplets, and the color ink droplets ejected by the second color nozzle group are referred to as second color ink droplets. The aforementioned printing method is A reference patch formation step, which involves forming a reference patch on the recording medium by ejecting the first color ink droplet and the second color ink droplet at a predetermined recording density ratio using a reference timing difference, which is a reference for the timing difference of ejection between the first color ink droplet and the second color ink droplet that occurs according to their positions within the band region in the main scanning direction; A first patch formation step involves forming multiple first patches on the recording medium by ejecting multiple first color ink droplets and second color ink droplets with multiple different recording density ratios in a first timing difference different from the aforementioned reference timing difference, aligned on either the forward path or the return path. The embodiment includes a print image forming step of forming a print image by compensating for the color shift due to the timing difference based on the recording density ratio corresponding to a first color shift compensation patch selected from the plurality of first patches. Furthermore, the printing method of the present invention includes a recording head having a row of black nozzles arranged in a row of black nozzles that eject black ink droplets, and a group of multiple color nozzles arranged along the row of black nozzles that eject color ink droplets, the group of multiple color nozzles arranged in order in the direction of the arrangement of the multiple black nozzles, The drive unit includes a drive unit that performs a main scan to change the relative position of the recording head and the recording medium in the forward and return paths along a main scan direction intersecting the aforementioned alignment direction, and a sub-scan to change the relative position of the recording head and the recording medium along a sub-scan direction intersecting the main scan direction, A printing method for performing bidirectional printing in which, in the recording medium, the color ink droplets are deposited in one main scan between sub-scans in both the forward and return paths, from the color nozzle groups assigned to each band region corresponding to the length in the sub-scan direction of each of the color nozzle groups that eject the color ink droplets, The plurality of color nozzle groups include a first color nozzle group and a second color nozzle group, the colors of the color ink droplets ejected in the forward and return paths to the band region in the bidirectional printing process are different from each other. The color ink droplets ejected by the first color nozzle group are referred to as first color ink droplets, and the color ink droplets ejected by the second color nozzle group are referred to as second color ink droplets. The aforementioned printing method is A reference patch formation step, which involves forming a reference patch on the recording medium by ejecting the first color ink droplet and the second color ink droplet at a predetermined recording density ratio using a reference timing difference, which is a reference for the timing difference of ejection between the first color ink droplet and the second color ink droplet that occurs according to their positions within the band region in the main scanning direction; A first patch formation step involves forming multiple first patches on the recording medium by ejecting multiple first color ink droplets and second color ink droplets with multiple different recording density ratios at a first timing difference different from the aforementioned reference timing difference. A print image forming step includes: forming a print image by compensating for the color shift due to the timing difference based on the recording density ratio corresponding to a first color shift compensation patch selected from the plurality of first patches, The recording medium includes a first recording medium and a second recording medium which has less color shift due to the timing difference than the first recording medium. The aforementioned printing method is The process further includes a step of receiving a setting for the type of recording medium used to form the printed image, If the type corresponds to the first recording medium, the reference patch formation step, the first patch formation step, and the print image formation step are performed. When the aforementioned type corresponds to the second recording medium, there is an embodiment in which the reference patch formation step, the first patch formation step, and the printed image formation step are not performed. [Brief explanation of the drawing]

[0008] [Figure 1] A schematic diagram illustrating an example of a printing device. [Figure 2] A schematic diagram showing an example of the nozzle surface of a recording head and a dot pattern on a recording medium. [Figure 3] A plan view illustrating an example of color bidirectional band printing. [Figure 4] A schematic diagram illustrating an example of an adjustment pattern including a reference patch, a first patch, and a second patch. [Figure 5] A schematic diagram illustrating examples of the formation conditions for each patch included in a cyan and magenta color mixing adjustment pattern. [Figure 6] A schematic diagram illustrating examples of the formation conditions for each patch included in the magenta and yellow color mixing adjustment pattern. [Figure 7] This diagram schematically illustrates an example of calculating a correction value corresponding to the timing difference Ti of ink droplet ejection. [Figure 8] A schematic diagram illustrating an example of generating a color conversion LUT as correction data. [Figure 9] A schematic diagram illustrating an example of generating a dot generation LUT as correction data. [Figure 10]A flowchart schematically illustrating an example of the correction data generation process. [Figure 11] A flowchart schematically illustrating an example of print control processing. [Figure 12] A schematic diagram illustrating an example of forming a printed image using color bidirectional band printing. [Figure 13] A schematic flowchart illustrating an example of color shift compensation processing using a color conversion LUT. [Figure 14] A schematic flowchart illustrating an example of color shift compensation processing using a dot generation LUT. [Figure 15] A schematic flowchart illustrating an example of switching whether or not to generate correction data depending on the type of recording medium. [Figure 16] This diagram schematically illustrates an example of color shift occurring due to a timing difference T in ink droplet ejection. [Modes for carrying out the invention]

[0009] The embodiments of the present invention will be described below. Of course, the following embodiments are merely illustrative of the present invention, and not all of the features shown in the embodiments are necessarily essential to the solution of the invention.

[0010] (1) Summary of the technology included in the present invention: First, an overview of the technology included in the present invention will be described with reference to the examples shown in Figures 1 to 16. Note that the figures in this application are schematic examples, and the magnification in each direction shown in these figures may differ, and the figures may not be consistent. Of course, the elements of this technology are not limited to the specific examples indicated by the reference numerals. In the "Overview of the Technology Included in the Present Invention," the text in parentheses indicates supplementary explanation of the preceding word.

[0011] [Aspect 1] A printing apparatus 1 according to one aspect of this technology includes a recording head 30 having a black nozzle row 33K in which a plurality of black nozzles 34K for ejecting black ink droplets 37K are arranged, and a plurality of color nozzle groups 33G in which a plurality of color nozzles 34A for ejecting color ink droplets 37A are arranged along the black nozzle row 33K, as illustrated in Figure 2. The plurality of color nozzle groups 33G are arranged sequentially in the arrangement direction D4 of the plurality of black nozzles 34K. The printing apparatus 1 includes a drive unit 50 and a control unit U1, as illustrated in Figure 1. The drive unit 50 performs a main scan P0 in which the relative position between the recording head 30 and the recording medium ME0 is changed in the forward path P1 and the return path P2 along the main scan direction D1 intersecting the arrangement direction D4, as illustrated in Figure 3, and performs a sub-scan in which the relative position between the recording head 30 and the recording medium ME0 is changed along the sub-scan direction D2 intersecting the main scan direction D1. The control unit U1 controls bidirectional printing in which the color ink droplets 37A are deposited in the recording medium ME0 in one main scan P0 between sub-scans in both the forward path P1 and the return path P2, from the color nozzle group 33G assigned to each band region B0 corresponding to the length L0 in the sub-scan direction D2 of each color nozzle group 33G that ejects the color ink droplets 37A. The plurality of color nozzle groups 33G include a first color nozzle group 331 and a second color nozzle group 332 whose colors of the color ink droplets 37A ejected in the band region B0 in the forward path P1 and the return path P2 are different from each other in the bidirectional printing.

[0012] Here, as illustrated in Figures 5 and 6, the color ink droplet 37A ejected by the first color nozzle group 331 is designated as the first color ink droplet 371, and the color ink droplet 37A ejected by the second color nozzle group 332 is designated as the second color ink droplet 372. The control unit U1 includes a compensation unit U2 (see Figure 1) that compensates for color shift caused by the timing difference T of ejection between the first color ink droplet 371 and the second color ink droplet 372, which occurs depending on the position X within the band region B0 in the main scanning direction D1. The compensation unit U2 performs the following processing, as illustrated in Figures 4, 10, 11, etc. (Process 1) The compensation unit U2 causes the first color ink droplet 371 and the second color ink droplet 372 to be ejected at a predetermined recording density ratio at a reference timing difference T0, which is the reference for the timing difference T, thereby forming a reference patch PA0 on the recording medium ME0. (Process 2) The compensation unit U2 causes a plurality of first patches PA1 to form on the recording medium ME0 by ejecting a plurality of first color ink droplets 371 and second color ink droplets 372 with different recording density ratios at a first timing difference T1 that is different from the reference timing difference T0. (Process 3) The compensation unit U2 compensates for the color shift due to the timing difference T based on the recording density ratio R1 corresponding to the first color shift compensation patch PA1z selected from the plurality of first patches PA1 to form a printed image IM0.

[0013] Reference patch PA0 indicates the printed color when the timing difference T between the ejection of the first color ink droplet 371 and the second color ink droplet 372 is reference timing difference T0. Multiple first patches PA1 indicate candidate correction colors when the timing difference T between the ink droplet ejection is different from the reference timing difference T0. When a first color shift compensation patch PA1z is selected from the multiple first patches PA1, the color shift due to the timing difference T is compensated based on the recording density ratio R1 corresponding to the first color shift compensation patch PA1z. Based on the above, the above embodiment can provide a printing apparatus capable of reducing color unevenness caused by vertically arranged heads.

[0014] Here, changing the relative position between the recording head and the recording medium means changing the relative positional relationship between the recording head and the recording medium. Changing the relative position between the recording head and the recording medium includes moving the recording head without moving the recording medium, moving the recording medium without moving the recording head, and moving both the recording head and the recording medium. In this application, "first," "second," ... are terms used to identify each component included in a group of similar components, and do not imply any order. Furthermore, the above-mentioned supplementary statement also applies in the following embodiments.

[0015] [Aspect 2] As illustrated in Figures 5 and 6, the first timing difference T1 may be greater than the reference timing difference T0. The compensation unit U2 may form a plurality of second patches PA2 on the recording medium ME0 by ejecting a plurality of first color ink droplets 371 and second color ink droplets 372 with a plurality of different recording density ratios at a second timing difference T2 that is smaller than the reference timing difference T0. As illustrated in Figures 7, 10, and 11, the compensation unit U2 may form the printed image IM0 by compensating for the color shift due to the timing difference T based on a recording density ratio R1 corresponding to the first color shift compensation patch PA1z and a recording density ratio R2 corresponding to a second color shift compensation patch PA2z selected from the plurality of second patches PA2.

[0016] Multiple first patches PA1 represent candidate correction colors when the ink droplet ejection timing difference T is greater than the reference timing difference T0. Multiple second patches PA2 represent candidate correction colors when the ink droplet ejection timing difference T is smaller than the reference timing difference T0. When a first color shift compensation patch PA1z is selected from the multiple first patches PA1, and a second color shift compensation patch PA2z is selected from the multiple second patches PA2, the color shift due to the timing difference T is compensated based on the recording density ratio R1 corresponding to the first color shift compensation patch PA1z and the recording density ratio R2 corresponding to the second color shift compensation patch PA2z. Based on the above, the above embodiment can provide a printing apparatus that can further reduce color unevenness caused by vertically arranged heads.

[0017] [Aspect 3] As illustrated in Figure 4, the compensation unit U2 may cause the recording medium ME0 to form a first reference patch PA01, which is placed between the first patches PA1, and a second reference patch PA02, which is placed between the second patches PA2, as the reference patch PA0. In the above case, since the first reference patch PA01 is placed between the first patches PA1, the first color misalignment compensation patch PA1z can be easily selected from multiple first patches PA1, and since the second reference patch PA02 is placed between the second patches PA2, the second color misalignment compensation patch PA2z can be easily selected from multiple second patches PA2. Therefore, the above embodiment can provide a printing apparatus that can easily reduce color unevenness caused by vertically arranged heads.

[0018] [Aspect 4] As illustrated in Figure 4, the compensation unit U2 may control the ejection of the first color ink droplet 371 and the second color ink droplet 372, which form the reference patch PA0 on the recording medium ME0, to align with either the forward path P1 or the return path P2. As a result, a reference patch PA0 indicating the printed color at the reference timing difference T0 of ink droplet ejection is accurately formed. Therefore, the above embodiment can provide a preferred example of forming a reference patch.

[0019] [Aspect 5] As illustrated in Figure 4, the compensation unit U2 may control the ejection of the first color ink droplets 371 and the second color ink droplets 372, which form the plurality of first patches PA1 and the plurality of second patches PA2 on the recording medium ME0, to align the ejection to either the forward path P1 or the return path P2. As a result, multiple first patches PA1 representing candidate correction colors at a first timing difference T1 that is greater than the reference timing difference T0 are accurately formed, and multiple second patches PA2 representing candidate correction colors at a second timing difference T2 that is less than the reference timing difference T0 are accurately formed. Therefore, the above embodiment can provide a preferred example of forming multiple first patches and multiple second patches.

[0020] [Aspect 6] As illustrated in Figures 5 and 6, the first timing difference T1 may be the maximum Tmax of the timing difference T in the bidirectional printing. The second timing difference T2 may be the minimum Tmin of the timing difference T in the bidirectional printing. In the above case, multiple first patches PA1 indicate candidate correction colors when the ink droplet ejection timing difference T is the maximum Tmax. Multiple second patches PA2 indicate candidate correction colors when the ink droplet ejection timing difference T is the minimum Tmin. Therefore, the above embodiment can provide a printing apparatus that can further reduce color unevenness caused by vertically arranged heads.

[0021] [Aspect 7] As illustrated in Figure 15, the recording medium ME0 may include a first recording medium ME1 and a second recording medium ME2 which has less color shift due to the timing difference T than the first recording medium ME1. The control unit U1 may accept a setting for the type of recording medium ME0 that will form the printed image IM0. If the type corresponds to the first recording medium ME1, the control unit U1 may compensate for the color shift due to the timing difference T in the compensation unit U2 to form the printed image IM0. If the type corresponds to the second recording medium ME2, the control unit U1 does not need to perform the process of compensating for the color shift due to the timing difference T. In the above case, if the color shift due to the timing difference T of ink droplet ejection is small, it is not necessary to perform a process to compensate for the color shift, and therefore the above embodiment can improve user convenience.

[0022] [Aspect 8] The compensation unit U2 may acquire the reading result SC0 of the reference patch PA0 and the plurality of first patches PA1, and select the first color shift compensation patch PA1z from the plurality of first patches PA1 based on the reading result SC0. In this embodiment, a color shift compensation patch for compensating for color shift due to the timing difference T of ink droplet ejection is automatically selected, thereby improving user convenience.

[0023] [Aspect 9] By the way, as illustrated in Figures 10, 11, etc., a printing method according to one embodiment of this technology includes the following steps. (A1) A reference patch formation step ST1 in which a reference patch PA0 is formed on the recording medium ME0 by ejecting the first color ink droplet 371 and the second color ink droplet 372 at a predetermined recording density ratio at a reference timing difference T0, which is the reference for the timing difference T of ejection between the first color ink droplet 371 and the second color ink droplet 372 that occurs according to the position X in the band region B0 in the main scanning direction D1. (A2) A first patch formation step ST2 in which a plurality of first patches PA1 are formed on the recording medium ME0 by ejecting a plurality of first color ink droplets 371 and second color ink droplets 372 with a plurality of different recording density ratios at a first timing difference T1 which is different from the reference timing difference T0. (A3) A printing image forming step ST4 in which a printed image IM0 is formed by compensating for the color shift due to the timing difference T based on the recording density ratio R1 corresponding to the first color shift compensation patch PA1z selected from the plurality of first patches PA1. The above embodiment can provide a printing method that can reduce color unevenness caused by vertically arranged heads.

[0024] Furthermore, this technology is applicable to a printing system including the aforementioned printing device, a method for controlling the printing system, a control program for the aforementioned printing device, a control program for the aforementioned printing system, a computer-readable medium on which any of the aforementioned control programs are recorded, and so on. The aforementioned printing device may also be composed of multiple distributed parts.

[0025] (2) Specific examples of printing devices: Figure 1 schematically illustrates a printing device 1. The printing device 1 includes a control unit U1 that includes a compensation unit U2. In this specific example, the printing device 1 is assumed to be the printer 2 itself, but the printing device 1 may also be a combination of the printer 2 and the host device HO1. Note that the printer 2 may include additional elements not shown in Figure 1. Figure 2 schematically illustrates the nozzle surface 30a of the recording head 30 and the dot pattern on the recording medium ME0. Figure 3 is a plan view schematically illustrating color bidirectional band printing.

[0026] The printer 2 shown in Figure 1 is a serial printer, a type of inkjet printer, and includes a controller 10, a semiconductor memory RAM 21, a communication I / F 22, a storage unit 23, an operation panel 24, a recording head 30, a drive unit 50, etc. Here, RAM is an abbreviation for Random Access Memory, and I / F is an abbreviation for Interface. The printer 2 may also include a reading unit 60 that reads images such as the adjustment pattern CH0 shown in Figure 4. The reading unit 60 shown in Figure 1 is connected to the controller 10 and outputs the image reading result SC0 to the controller 10. The printer 2 may also include a colorimeter that measures the color of patches. The controller 10, RAM 21, communication interface 22, memory unit 23, and operation panel 24 are connected to a bus and are capable of inputting and outputting information from each other.

[0027] The controller 10 includes a processor CPU 11, a color conversion unit 12, a halftone processing unit 13, a rasterization processing unit 14, a drive signal transmission unit 15, etc. Here, CPU is an abbreviation for Central Processing Unit. Based on the original image data DA1 acquired from either the host device HO1, a memory card (not shown), etc., the controller 10 controls the main scan and sub-scan by the drive unit 50, and the ejection of ink droplets 37 by the recording head 30. The original image data DA1 can be any image data that can be converted into ink amount data DA2, for example, each pixel may contain two colors: R, G, and B. 8 Tone and 2 16RGB data having integer values ​​for gradation can be applied. Here, R means red, G means green, and B means blue. The controller 10 also accepts the setting of the print mode from the host device HO1, the operation panel 24, etc., and controls the main scan and sub scan by the drive unit 50, as well as the ejection of ink droplets 37 by the recording head 30, according to the set print mode. Print modes include a mode for color printing, a mode for monochrome printing, a mode for bidirectional printing, a mode for unidirectional printing, a mode for band printing, an interlaced printing mode, etc. The controller 10 can be configured using an SoC, where SoC is an abbreviation for System on a Chip. The CPU 11 is the device that primarily handles information processing and control in the printer 2.

[0028] The color conversion unit 12, for example, refers to a color conversion LUT that defines the correspondence between the gradation values ​​of R, G, and B and the gradation values ​​of C, M, Y, and K, and converts the RGB data to C, M, Y, and K for each pixel. 8 Tone and 2 16 The data is converted to ink quantity data DA2, which has integer values ​​for the gradation. Here, C stands for cyan, M for magenta, Y for yellow, K for black, and LUT is an abbreviation for lookup table. The ink quantity data DA2 represents the amount of ink 36 used in units of pixel PX0. If the resolution of the RGB data is different from the output resolution, the color conversion unit 12 converts the resolution of the RGB data to the output resolution and then converts the converted RGB data to ink quantity data DA2. The color conversion unit 12 only needs to be able to generate ink quantity data DA2 at the output resolution from the RGB data, so it may first generate ink quantity data at the resolution of the RGB data from the RGB data, and then generate ink quantity data DA2 by converting the resolution of the ink quantity data to the output resolution.

[0029] The halftone processing unit 13 reduces the number of gradations in the gradation values ​​of each pixel PX0 constituting the ink amount data DA2 by performing a predetermined halftone processing, such as the dithering method, error diffusion method, or density pattern method, and generates halftone data DA3. The halftone data DA3 represents the formation state of dots 38 in units of pixel PX0. The halftone data DA3 may be binary data representing the presence or absence of dot formation, or it may be multi-level data with 3 or more gradations that can handle dots of different sizes, such as small, medium, and large. For example, binary data can be data where 1 corresponds to dot formation and 0 corresponds to no dot. For example, quaternary data that can be represented by 2 bits for each pixel can be data where 3 corresponds to large dot formation, 2 to medium dot formation, 1 to small dot formation, and 0 to no dot. The rasterization processing unit 14 generates raster data RA0 by performing a rasterization process that rearranges the halftone data DA3 in the order in which the dots 38 are formed by the drive unit 50.

[0030] The drive signal transmission unit 15 generates and outputs a drive signal SG1 corresponding to the voltage signal applied to the drive element 32 of the recording head 30 to the drive circuit 31 of the recording head 30 from the raster data RA0. For example, if the raster data RA0 is "dot formation", the drive signal transmission unit 15 outputs a drive signal SG1 that ejects ink droplets for dot formation. Also, if the raster data RA0 is quaternary data, the drive signal transmission unit 15 outputs a drive signal SG1 that ejects ink droplets for large dots if the raster data RA0 is "large dot formation", a drive signal SG1 that ejects ink droplets for medium dots if the raster data RA0 is "medium dot formation", and a drive signal SG1 that ejects ink droplets for small dots if the raster data RA0 is "small dot formation".

[0031] Each of the above parts 11 to 15 may be composed of an ASIC, and may directly read the data to be processed from RAM 21 or directly write the processed data to RAM 21. Here, ASIC is an abbreviation for Application Specific Integrated Circuit.

[0032] The drive unit 50 controlled by the controller 10 includes a carriage drive unit 51 and a roller drive unit 55. The drive unit 50 moves the carriage 52 back and forth along the main scanning direction D1 by the carriage drive unit 51, and moves the recording medium ME0 along the transport path 59 in the feed direction D3 by the roller drive unit 55. As shown in Figure 2, the main scanning direction D1 is the direction that intersects with the alignment direction D4 of the nozzles 34, for example, the direction perpendicular to the alignment direction D4. The feed direction D3 is the direction that intersects with the main scanning direction D1, for example, the direction perpendicular to the main scanning direction D1. In Figure 1, the feed direction D3 is to the right, the left side is called the upstream side, and the right side is called the downstream side. The sub-scanning direction D2 shown in Figure 3 is the opposite direction to the feed direction D3. The carriage drive unit 51, in accordance with the control of the controller 10, moves the carriage 52 in the forward direction D11 along the main scanning direction D1 during the forward path P1 of the main scan P0, as shown in Figure 3, and moves the carriage 52 in the reverse direction D12 opposite to the forward direction D11 during the return path P2 of the main scan P0. Note that the main scanning direction D1 is a general term for the forward direction D11 and the reverse direction D12. The carriage drive unit 51 can be said to perform the main scan P0, which changes the relative position between the recording head 30 and the recording medium ME0 in the forward path P1 and the return path P2 along the main scanning direction D1 which intersects the alignment direction D4 of the black nozzles 34K. The roller drive unit 55 includes a transport roller pair 56 and a paper discharge roller pair 57. The roller drive unit 55, in accordance with the control of the controller 10, performs a sub-scan to send the recording medium ME0 in the feed direction D3 by rotating the drive transport roller of the transport roller pair 56 and the drive paper discharge roller of the paper discharge roller pair 57. The roller drive unit 55 performs a sub-scan, which changes the relative position between the recording head 30 and the recording medium ME0 along the sub-scan direction D2 that intersects the main scanning direction D1. The recording medium ME0 is a material that holds the printed image and is made of paper, resin, metal, etc. The material of the recording medium ME0 is not particularly limited, and various materials such as resin, metal, and paper are possible. The shape of the recording medium ME0 is also not particularly limited, and various shapes such as rectangles and rolls are possible, and it may also be a three-dimensional shape.

[0033] A recording head 30 is mounted on the carriage 52. The carriage 52 may also be equipped with an ink cartridge 35 that supplies ink 36, ejected as ink droplets 37, to the recording head 30. Of course, ink 36 may also be supplied to the recording head 30 via a tube from an ink cartridge 35 installed outside the carriage 52. The carriage 52 on which the recording head 30 is mounted is fixed to an endless belt (not shown) and is movable in the forward direction D11 and the return direction D12 along a guide 53. The guide 53 is a long member whose longitudinal direction is oriented in the main scanning direction D1. The carriage drive unit 51 is composed of a servo motor and moves the carriage 52 in the forward direction D11 and the return direction D12 according to commands from the controller 10.

[0034] During sub-scanning, the transport roller pair 56 located upstream of the recording head 30 moves the nipped recording medium ME0 toward the recording head 30 by the rotation of the drive transport roller. During sub-scanning, the paper discharge roller pair 57 located downstream of the recording head 30 moves the nipped recording medium ME0 toward a paper discharge tray (not shown) by the rotation of the drive paper discharge roller. The roller drive unit 55 is composed of a servo motor and operates the transport roller pair 56 and the paper discharge roller pair 57 according to commands from the controller 10, moving the recording medium ME0 toward the feed direction D3.

[0035] The platen 58 is located below the transport path 59 and supports the recording medium ME0 located in the transport path 59 by contacting it. The recording head 30, controlled by the controller 10, ejects ink droplets 37 toward the recording medium ME0 supported by the platen 58, thereby adhering ink 36 to the recording medium ME0.

[0036] The recording head 30 has a plurality of nozzles 34 on its nozzle surface 30a that eject ink droplets 37, and performs printing by ejecting ink droplets 37 onto the recording medium ME0 on the platen 58. Here, a nozzle means a small hole from which ink droplets are ejected, and a nozzle row means an arrangement of a plurality of nozzles. The nozzle surface 30a is the ejection surface for the ink droplets 37. The recording head 30 includes a drive circuit 31, a drive element 32, etc. The drive circuit 31 applies a voltage signal to the drive element 32 according to a drive signal SG1 input from the drive signal transmission unit 15. The drive element 32 can be a piezoelectric element that applies pressure to the ink 36 in a pressure chamber communicating with the nozzle 34, a drive element that generates bubbles in the pressure chamber by heat to eject ink droplets 37 from the nozzle 34, etc. Ink 36 is supplied to the pressure chamber of the recording head 30 from an ink cartridge 35. The ink 36 in the pressure chamber is ejected as ink droplets 37 from the nozzle 34 toward the recording medium ME0 by the drive element 32. As a result, ink droplets 37 form dots 38 on the recording medium ME0. While the recording head 30 moves in the main scanning direction D1, dots 38 are formed according to the raster data RA0, and the recording medium ME0 is repeatedly fed in the feed direction D3 for one sub-scan, thereby forming a printed image IM0 on the recording medium ME0.

[0037] RAM21 is a large-capacity, volatile semiconductor memory that stores raw image data DA1, etc., received from the host device HO1 or other memory (not shown). The communication I / F22 is connected to the host device HO1 by wire or wireless connection and inputs and outputs information to the host device HO1. The host device HO1 includes computers such as personal computers and tablet terminals, mobile phones such as smartphones, digital cameras, digital video cameras, etc. The storage unit 23 can use non-volatile semiconductor memory such as flash memory, magnetic storage devices such as hard disks, etc. The operation panel 24 includes an output unit 25, an input unit 26, etc. The output unit 25 is composed of a display unit such as a liquid crystal panel that displays information corresponding to various instructions and information indicating the status of the printer 2. The output unit 25 may also output this information as audio. The input unit 26 is composed of an operation input unit such as operation keys such as cursor keys and select keys. The input unit 26 may also be a touch panel that accepts operations on the display screen.

[0038] The recording head 30 shown in Figure 2 has multiple nozzle rows 33 on its nozzle surface 30a, each containing multiple nozzles 34 arranged in the alignment direction D4 at predetermined nozzle pitch intervals. Each nozzle row 33 ejects ink droplets 37 toward the recording medium ME0. The alignment direction D4 shown in Figures 2 and 3 is perpendicular to the main scanning direction D1, but the alignment direction D4 may not be perpendicular to the main scanning direction D1 but may intersect it at an angle. In other words, the alignment direction D4 may coincide with the feed direction D3 as shown in Figure 3, or it may be offset from the feed direction D3 by a range of less than 90°. The multiple nozzles 34 included in each nozzle row 33 may be arranged in a single row, or in a staggered pattern, i.e., in two rows. The alignment direction of the multiple nozzles 34 arranged in a staggered pattern is the alignment direction of the nozzles focusing on each of the two rows.

[0039] The recording head 30 shown in Figure 2 is a vertically arranged head and has two rows of nozzles 33, consisting of a black nozzle row 33K and a color nozzle row 33A. Multiple black nozzles 34K are arranged in the alignment direction D4 of the black nozzle row 33K. Each black nozzle 34K ejects a black ink droplet 37K, which is a K ink droplet 37. When the black ink droplet 37K lands on the recording medium ME0, a black dot 38K, which is a K dot 38, is formed on the recording medium ME0. The color nozzle row 33A is divided into multiple color nozzle groups 33G in the alignment direction D4. Multiple color nozzles 34A are arranged in each color nozzle group 33G along the black nozzle row 33K. Each color nozzle 34A ejects a color ink droplet 37A, which is a color ink droplet 37. In the color nozzle row 33A shown in Figure 2, the yellow nozzle group 33Y, the magenta nozzle group 33M, and the cyan nozzle group 33C are arranged in the sub-scanning direction D2. Therefore, the multiple color nozzle groups 33G are arranged sequentially in the direction D4 of the arrangement of the multiple black nozzles 34K.

[0040] The yellow nozzle group 33Y consists of multiple yellow nozzles 34Y arranged along the black nozzle row 33K, each ejecting a yellow ink droplet 37Y, which is a yellow ink droplet 37. When the yellow ink droplet 37Y lands on the recording medium ME0, a yellow dot 38Y, which is a yellow dot 38, is formed on the recording medium ME0. The magenta nozzle group 33M consists of multiple magenta nozzles 34M arranged along the black nozzle row 33K, each ejecting a magenta ink droplet 37M, which is a black ink droplet 37. When the magenta ink droplet 37M lands on the recording medium ME0, a magenta dot 38M, which is a magenta dot 38, is formed on the recording medium ME0. The cyan nozzle group 33C consists of multiple cyan nozzles 34C arranged along the black nozzle row 33K, each ejecting a cyan ink droplet 37C, which is a cyan ink droplet 37. When the cyan ink droplet 37C lands on the recording medium ME0, a cyan dot 38C, which is a cyan dot 38, is formed on the recording medium ME0. In Figure 2, multiple rows of magenta nozzles 34M are connected to rows of multiple yellow nozzles 34Y, and multiple rows of cyan nozzles 34C are connected to rows of multiple magenta nozzles 34M. However, the arrangement of the multiple color nozzle groups 33G is not limited to the arrangement shown in Figure 2. As long as the multiple color nozzles 34A of each color nozzle group 33G are arranged along the black nozzle row 33K, the arrangement of multiple magenta nozzles 34M may be offset from the arrangement of multiple yellow nozzles 34Y, or the arrangement of multiple cyan nozzles 34C may be offset from the arrangement of multiple magenta nozzles 34M.

[0041] Figure 2 shows that the color nozzle row 33A has n nozzles in each color nozzle group 33G, with yellow nozzles Y1 to Yn, magenta nozzles M1 to Mn, and cyan nozzles C1 to Cn arranged in the sub-scanning direction D2. Figure 2 also shows that the black nozzle row 33K has 3n nozzles, with black nozzles K1 to K3n arranged in the sub-scanning direction D2. The recording head 30, which is a vertically arranged head, can be manufactured inexpensively because it only requires two rows of nozzles 33, and high-speed monochrome printing can be achieved by using a black nozzle row 33K that is three times the length of the color nozzle row 33G.

[0042] The printer 2 equipped with the recording head 30 described above is capable of performing bidirectional color band printing, as shown in Figure 3. Bidirectional printing means printing in which ink droplets 37 are deposited onto the recording medium ME0 by the main scan P0 in both the forward path P1 and the return path P2 to form dots 38. In Figure 3, the forward path P1 means the main scan P0 going from the "Home" side to the "Full" side. In Figure 3, the return path P2 means the main scan P0 going from the "Full" side to the "Home" side. Color band printing of the vertically arranged head means printing in which the color ink droplets 37A required for printing are deposited on the recording medium ME0 by the main scan P0 between sub-scans from the color nozzle group 33G assigned to each band region B0 corresponding to the length L0 in the sub-scan direction D2 of each color nozzle group 33G to form color dots. The controller 10 controls bidirectional printing, in which the color ink droplets 37A required for printing are deposited from the color nozzle group 33G assigned to each band region B0 during one main scan P0 between sub-scans in both the forward path P1 and the return path P2.

[0043] As shown in Figure 3, the band region B0 consists of band regions B1, B2, B3, and B4 in the order of sub-scan direction D2, and the printed image IM0 is formed by dots 38 of cyan ink droplets 37C and magenta ink droplets 37M. In the example shown in Figure 3, during the forward path P1, which is the mth main scan P0, all the cyan ink droplets 37C necessary for printing are ejected into band region B1. This operation is indicated as "C(m)" in Figure 3. After a sub-scan of length L0, during the return path P2, which is the m+1th main scan P0, all the magenta ink droplets 37M necessary for printing are ejected into band region B1, and all the cyan ink droplets 37C necessary for printing are ejected into band region B2. This operation is indicated as "M(m+1)" and "C(m+1)" in Figure 3. After a sub-scan of length L0, during the forward path P1, which is the m+2th main scan P0, all magenta ink droplets 37M required for printing are ejected into band region B2, and all cyan ink droplets 37C required for printing are ejected into band region B3. This operation is shown in Figure 3 as "M(m+2)" and "C(m+2)". After a sub-scan of length L0, during the return path P2, which is the m+3rd main scan P0, all magenta ink droplets 37M required for printing are ejected into band region B3, and all cyan ink droplets 37C required for printing are ejected into band region B4. This operation is shown in Figure 3 as "M(m+3)" and "C(m+3)". Furthermore, after a sub-scan of length L0, during the forward path P1, which is the m+4th main scan P0, all magenta ink droplets 37M required for printing are ejected into band region B4. This operation is shown in Figure 3 as "M(m+4)".

[0044] Therefore, when printer 2 performs bidirectional color band printing, it ejects magenta ink droplets 37M on the return path P2 into band region B0 where cyan ink droplets 37C are ejected on the forward path P1, and ejects magenta ink droplets 37M on the forward path P1 into band region B0 where cyan ink droplets 37C are ejected on the return path P2. As a result, there is a timing difference in the ejection of cyan ink droplets 37C and magenta ink droplets 37M depending on their position within band region B0 in the main scanning direction D1. This timing difference causes uneven color development between C and M. Similarly, when printer 2 performs bidirectional color band printing, it ejects yellow ink droplets 37Y on the return path P2 into band area B0 where magenta ink droplets 37M are ejected on the forward path P1, and ejects yellow ink droplets 37Y on the forward path P1 into band area B0 where magenta ink droplets 37M are ejected on the return path P2. As a result, there is a timing difference in the ejection of magenta ink droplets 37M and yellow ink droplets 37Y depending on their position within band area B0 in the main scanning direction D1. This timing difference causes uneven color development of M and Y.

[0045] When C, M, and Y are mixed, a magenta ink droplet 37M is ejected on the return path P2 into the band region B0 where cyan ink droplet 37C and yellow ink droplet 37Y are ejected on the forward path P1. Conversely, a magenta ink droplet 37M is ejected on the forward path P1 into the band region B0 where cyan ink droplet 37C and yellow ink droplet 37Y are ejected on the return path P2. Therefore, depending on the position within the band region B0 in the main scanning direction D1, there is a timing difference in the ejection of the cyan ink droplet 37C and yellow ink droplet 37Y and the magenta ink droplet 37M. This timing difference causes uneven color development between C and Y and M.

[0046] As explained above, the multiple color nozzle groups 33G include a first color nozzle group 331 and a second color nozzle group 332, the colors of the color ink droplets 37A ejected in the forward path P1 and the return path P2 relative to the band region B0 in bidirectional printing are different from each other. In the example shown in Figure 2, the cyan nozzle group 33C is assigned to the first color nozzle group 331, and the magenta nozzle group 33M is assigned to the second color nozzle group 332. Here, the color ink droplets 37A ejected by the first color nozzle group 331 are referred to as the first color ink droplets 371, and the color ink droplets 37A ejected by the second color nozzle group 332 are referred to as the second color ink droplets 372. In the example shown in Figure 2, the cyan ink droplet 37C is assigned to the first color ink droplet 371, and the magenta ink droplet 37M is assigned to the second color ink droplet 372. Of course, the first color nozzle group 331, the second color nozzle group 332, the first color ink droplet 371, and the second color ink droplet 372 are determined relatively. For example, the magenta nozzle group 33M may be assigned to the first color nozzle group 331, the yellow nozzle group 33Y to the second color nozzle group 332, the magenta ink droplet 37M to the first color ink droplet 371, and the yellow ink droplet 37Y to the second color ink droplet 372.

[0047] Figure 16 schematically illustrates how color shift occurs depending on the timing difference T of ejection between color ink droplets 37A of different colors. In the example shown in Figure 16, cyan ink droplets 37C land in band region B1 from the cyan nozzle group 33C on the forward path P1, and magenta ink droplets 37M land from the magenta nozzle group 33M on the return path P2. The upper part of Figure 16 shows the timing difference T of ejection of the color ink droplets 37A with respect to position X in the main scanning direction D1 in band region B1. In band region B2, cyan ink droplets 37C land from the cyan nozzle group 33C on the return path P2, and magenta ink droplets 37M land from the magenta nozzle group 33M on the forward path P1. The lower part of Figure 16 shows the timing difference T of ejection of the color ink droplets 37A with respect to position X in the main scanning direction D1 in band region B2.

[0048] In the case of band region B1, the timing difference T between the ejection of cyan ink droplet 37C and magenta ink droplet 37M is greatest at the "Home" position (Tmax) and least at the "Full" position (Tmin), as shown in the upper part of Figure 16. If no color unevenness correction is performed, the color of M in band region B1 gradually intensifies from the "Full" position to the "Home" position. This is presumed to be because, at the "Home" position where the timing difference T is large, the cyan ink that landed first soaks into the recording medium ME0, causing the color of the magenta ink that landed later to be more prominent. Alternatively, at the "Full" position where the timing difference T is small, it is presumed that a large amount of the cyan ink that landed first remains on the surface of the recording medium ME0, so even if the magenta ink lands later, more of the cyan ink color remains. In the case of band region B2, the timing difference T between the ejection of cyan ink droplet 37C and magenta ink droplet 37M is smallest at the "Home" position (Tmin) and largest at the "Full" position (Tmax), as shown in the lower part of Figure 16. If no color unevenness correction is performed, the color of M in band region B1 gradually intensifies from the "Home" position to the "Full" position. This is presumed to be because, at the "Full" position where the timing difference T is large, the cyan ink that landed first soaks into the recording medium ME0, causing the color of the magenta ink that landed later to be more prominent. Alternatively, at the "Home" position where the timing difference T is small, a large amount of the cyan ink that landed first remains on the surface of the recording medium ME0, so even if the magenta ink lands later, more of the cyan ink color remains.

[0049] In this specific example, to compensate for color misalignment that occurs in bidirectional printing due to the nozzle arrangement of the vertically arranged head, an adjustment pattern CH0 illustrated in Figure 4 is formed on the recording medium ME0, and color misalignment is compensated by selecting a color misalignment compensation patch. The control unit U1 includes a compensation unit U2 that compensates for color misalignment caused by the timing difference T of ejection between the first color ink droplet 371 and the second color ink droplet 372, which occurs depending on the position X within the band region B0 in the main scanning direction D1. For the purpose of explaining the adjustment pattern CH0, Figure 16 shows a reference timing difference T0, which is the reference for the timing difference T, a first timing difference T1 that is greater than the reference timing difference T0, the position X1 where this first timing difference T1 occurs, a second timing difference T2 that is less than the reference timing difference T0, and the position X2 where this second timing difference T2 occurs.

[0050] Figure 4 schematically illustrates an adjustment pattern CH0 that includes multiple reference patches PA0, multiple first patches PA1, and multiple second patches PA2. The adjustment pattern CH0 is formed on the recording medium ME0. For convenience, in Figure 4, the scanning directions of the cyan nozzle group 33C and the magenta nozzle group 33M are indicated by arrows when the adjustment pattern CH0 is a mixture of C and M. Figure 5 schematically illustrates the formation conditions of each patch included in the C and M mixture adjustment pattern. The controller 10 forms a reference patch PA0 on the recording medium ME0 by ejecting a first color ink droplet 371 and a second color ink droplet 372 with a predetermined recording density ratio at a reference timing difference T0. The reference timing difference T0 can be, for example, the average of the maximum timing difference Tmax and the minimum timing difference Tmin (Tmax + Tmin) / 2, as shown in Figure 16. In this case, the reference timing difference T0 is also the timing difference T at a position midway between the "Home" position and the "Full" position in the main scanning direction D1. The predetermined recording density ratio of the first color ink droplet 371 and the second color ink droplet 372 can be, for example, an equal ratio. In the example shown in Figure 5, a cyan ink droplet 37C is applied to the first color ink droplet 371, a magenta ink droplet 37M is applied to the second color ink droplet 372, and the recording density of the cyan ink droplet 37C is 50%, and the recording density of the magenta ink droplet 37M is 50%. Here, the recording density (RD) refers to the ratio of the number of dots formed by ink droplets to a predetermined number of pixels PX0. If dots of different sizes are formed, the ratio refers to the ratio when converted to the largest dot (e.g., large dot). A pixel is the smallest element that makes up an image, to which a color can be independently assigned. For example, if Nd large dots are formed for 100 pixels PX0, the recording density RD will be Nd%.

[0051] The controller 10 forms multiple first patches PA1 on the recording medium ME0 by ejecting multiple first color ink droplets 371 and second color ink droplets 372 with multiple different recording density ratios at a first timing difference T1. The first timing difference T1 shown in Figure 16 is the maximum timing difference Tmax, but the first timing difference T1 only needs to be a different timing difference from the reference timing difference T0 and the second timing difference T2, and a timing difference larger than the reference timing difference T0 is preferable. The recording density ratio of the first color ink droplet 371 and the second color ink droplet 372 can be, for example, the recording density ratio shown in Figure 5. The multiple first patches PA1 shown in Figures 4 and 5 include first patches PA11 to PA16. The recording density of C in the first patches PA11 to PA16 is constant at 50%, which is the same as the recording density of C in the reference patch PA0. The recording densities of M in the first patches PA11, PA12, PA13, PA14, PA15, and PA16 are 50%, 45%, 40%, 35%, 30%, and 25%, respectively. When T1 > T0, the magenta ink droplet 37M, which is ejected after the cyan ink droplet 37C, usually develops a stronger color, and the first patch PA1 develops a stronger M color than the reference patch PA0. Therefore, in each first patch PA1, the recording densities of M are kept below the recording densities of C.

[0052] The controller 10 forms a plurality of second patches PA2 on the recording medium ME0 by ejecting the first color ink droplets 371 and the second color ink droplets 372 with different recording density ratios at the second timing difference T2. The second timing difference T2 shown in FIG. 16 is the minimum timing difference Tmin, but the second timing difference T2 may be a timing difference different from the reference timing difference T0 and the first timing difference T1, and a timing difference smaller than the reference timing difference T0 is preferable. The recording density ratio between the first color ink droplets 371 and the second color ink droplets 372 can be, for example, the recording density ratio shown in FIG. 5. The plurality of second patches PA2 shown in FIGS. 4 and 5 include second patches PA21 to PA26. The recording density of C in the second patches PA21 to PA26 is constant at 50% and is the same as the recording density of C in the reference patch PA0. The recording densities of M in the second patches PA21, PA22, PA23, PA24, PA25, and PA26 are 75%, 70%, 65%, 60%, 55%, and 50%, respectively. When T2 < T0, usually, the color development of M in the second patch PA2 is weaker than that in the reference patch PA0. Therefore, in each second patch PA2, the recording density of M is set to be not less than the recording density of C.

[0053] The adjustment pattern CH0 shown in FIG. 4 includes an adjustment pattern CH1 in which the first patches PA11 to PA16 and a plurality of reference patches PA0 are arranged in a row along the main scanning direction D1, and an adjustment pattern CH2 in which the second patches PA21 to PA26 and a plurality of reference patches PA0 are arranged in a row along the main scanning direction D1. The plurality of reference patches PA0 include a plurality of first reference patches PA01 included in the adjustment pattern CH1 and a plurality of second reference patches PA02 included in the adjustment pattern CH2. In the adjustment pattern CH1, the first patches PA11 to PA16 are arranged in order, and the first reference patches PA01 are respectively arranged between the first patches PA1. In the adjustment pattern CH2, the second patches PA21 to PA26 are arranged in order, and the second reference patches PA02 are respectively arranged between the second patches PA2. The controller 10 forms the adjustment pattern CH0 of the patch arrangement shown in FIG. 4 on the recording medium ME0.

[0054] To compensate for color shift due to timing difference T, the first color shift compensation patch PA1z is selected from the first patches PA11 to PA16, and the second color shift compensation patch PA2z is selected from the second patches PA21 to PA26. The selection of the first color shift compensation patch PA1z and the second color shift compensation patch PA2z may be made by the user or by printer 2. Since the first reference patch PA01 is placed between the first patches PA1, the first color shift compensation patch PA1z can be easily selected from multiple first patches PA1. Also, since the second reference patch PA02 is placed between the second patches PA2, the second color shift compensation patch PA2z can be easily selected from multiple second patches PA2. Figure 4 shows that the first patch PA13 is selected as the first color shift compensation patch PA1z, and the second patch PA24 is selected as the second color shift compensation patch PA2z. As shown in Figure 5, in the first patch PA13, which is the first color shift compensation patch PA1z, the ratio of the recording density of the magenta ink droplet 37M to the recording density of the cyan ink droplet 37C is 40 / 50. In this case, the recording density ratio R1 corresponding to the first color shift compensation patch PA1z is 40 / 50. Also, in the second patch PA24, which is the second color shift compensation patch PA2z, the ratio of the recording density of the magenta ink droplet 37M to the recording density of the cyan ink droplet 37C is 60 / 50. In this case, the recording density ratio R1 corresponding to the second color shift compensation patch PA2z is 60 / 50.

[0055] The controller 10 controls the ejection of first color ink droplets 371 and second color ink droplets 372, which form multiple reference patches PA0, multiple first patches PA1, and multiple second patches PA2, to align with the forward path P1. By combining this with the back feed of the recording medium ME0, each patch can be formed with a desired timing difference T. Of course, the controller 10 may also control the ejection of first color ink droplets 371 and second color ink droplets 372, which form multiple reference patches PA0, multiple first patches PA1, and multiple second patches PA2, to align with the return path P2. Furthermore, the arrangement of the patches of adjustment pattern CH0 is not limited to the example shown in FIG. 4. For example, each of the adjustment patterns CH1, CH2 may be arranged in a row along the sub-scanning direction D2, or may be arranged diagonally intersecting the main scanning direction D1 and the sub-scanning direction D2.

[0056] FIG. 6 schematically illustrates the formation conditions of each patch included in the mixing adjustment pattern of M and Y. The formation conditions of each patch in this case are the same as those of each patch shown in FIG. 5. The recording densities of the first color ink droplets 371 and the second color ink droplets 372 in the reference patch PA0 are both 50%. When T1>T0, usually, the color development of the yellow ink droplets 37Y ejected after the magenta ink droplets 37M becomes stronger, and the color development of Y in the first patch PA1 becomes stronger than that in the reference patch PA0. Therefore, in each first patch PA1, the recording density of Y is set to be not higher than the recording density of M. When T2<T0, usually, the color development of Y in the second patch PA2 becomes weaker than that in the reference patch PA0. Therefore, in each second patch PA2, the recording density of Y is set to be not lower than the recording density of M. Although not shown, for the mixing adjustment pattern of C, M, and Y, the formation conditions of each patch can also be set, and an adjustment pattern can be formed according to the formation conditions of each patch.

[0057] FIG. 7 schematically illustrates the state of calculating a correction value according to the timing difference T of the ejection of the color ink droplets 37A. As described above, when the timing difference T is the first timing difference T1, the first color shift compensation patch PA1z is selected from a plurality of first patches PA1. Therefore, the recording density ratio R corresponding to the first timing difference T1, that is, the ratio of the recording density of the second color ink droplets 37 to the recording density of the first color ink droplets 371, becomes the recording density ratio R1 corresponding to the first color shift compensation patch PA1z. When the timing difference T is the second timing difference T2, the second color shift compensation patch PA2z is selected from a plurality of second patches PA2. Therefore, the recording density ratio R corresponding to the second timing difference T2 becomes the recording density ratio R2 corresponding to the second color shift compensation patch PA2z.

[0058] The timing difference Ti between the first timing difference T1 and the second timing difference T2 can be calculated by linear interpolation, where Xi is the position between positions X1 and X2 shown in Figure 16.

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[0059] The recording density ratio Ri is a correction value used to compensate for color shift due to timing difference T, and is used to generate the correction data exemplified in Figures 8 and 9. The correction data may be a color conversion LUT as exemplified in Figure 8, or a dot generation LUT as shown in Figure 9.

[0060] Figure 8 schematically shows an example of generating a color conversion LUT as correction data. The original color conversion LUT shown in Figure 8 is the color conversion LUT used by the color conversion unit 12 in Figure 1 when color shift due to timing difference T is not compensated for. The original color conversion LUT is data that represents the correspondence between the coordinate values ​​(R, G, B) of the input RGB color space and the coordinate values ​​(C, M, Y, K) of the output CMYK color space. If j is the variable that identifies the grid points set in the RGB color space, the original color conversion LUT shown in Figure 8 is data that has output coordinate values ​​(C0j, M0j, Y0j, K0j) associated with the input coordinate values ​​(Rj, Gj, Bj) for each grid point. The color conversion unit 12 can convert the original image data DA1 to ink amount data DA2 while referring to the original color conversion LUT.

[0061] The controller 10 or host device HO1 sequentially generates different color conversion LUTs for Ti according to the timing difference Ti, based on the recording density ratio Ri. The controller 10 or host device HO1 determines the output coordinate values ​​(C1j, M1j, Y1j, K1j) from the output coordinate values ​​(C0j, M0j, Y0j, K0j) of the original color conversion LUT based on the recording density ratio Ri for each grid point, and generates a color conversion LUT for Ti having output coordinate values ​​(C1j, M1j, Y1j, K1j) associated with the input coordinate values ​​(Rj, Gj, Bj) for each grid point. When compensating for color shift in the mixing of C and M, if the recording density ratio of the magenta ink droplet 37M to the cyan ink droplet 37C is Ri, then as a simple example, C1j=C0j, M1j=Ri×M0j, Y1j=Y0j, and K1j=K0j may also be used. However, the output coordinate value M1j has a limited range, and the sum of the output coordinate values ​​C1j, M1j, Y1j, and K1j has an upper limit. These factors are taken into consideration when determining the output coordinate values ​​(C1j, M1j, Y1j, K1j). A color conversion LUT requires a lot of data. For this reason, the controller 10 or host device HO1 generates different color conversion LUTs for different timing differences Ti, such as a color conversion LUT for a timing difference of 100 milliseconds, a color conversion LUT for a timing difference of 200 milliseconds, ..., a color conversion LUT for a timing difference of 500 milliseconds.

[0062] Figure 9 schematically shows an example of generating a dot generation LUT as correction data. The original dot generation LUT shown in Figure 9 is the dot generation LUT used in the halftone processing unit 13 in Figure 1 when color shift due to timing difference T is not compensated for. The original dot generation LUT is data that shows the correspondence between the ink amount and the dot generation rate for each of C, Y, M, and K. In the graphs of the original dot generation LUT and the dot generation LUT for Ti shown in Figure 9, the horizontal axis is the ink amount and the vertical axis is the dot generation rate for dot 38. If there are three types of dots, small dots, medium dots, and large dots, the original dot generation LUT will be data that shows the generation rates of small dots, medium dots, and large dots. The halftone processing unit 13 can convert the ink amount data DA2 into the generation rate of each small, medium, and large dot while referring to the original dot generation LUT and then generate four-value halftone data DA3.

[0063] The controller 10 or host device HO1 sequentially generates different dot generation LUTs for Ti according to the timing difference Ti, based on the recording density ratio Ri. Based on the recording density ratio Ri, the controller 10 or host device HO1 determines the generation rate of small, medium, and large dots in the Ti dot generation LUT according to the amount of ink from the generation rate of small, medium, and large dots in the original dot generation LUT according to the amount of ink, and generates a Ti dot generation LUT having the obtained dot generation rate. When compensating for color shift in the mixing of C and M, if the recording density ratio of the magenta ink droplet 37M to the cyan ink droplet 37C is Ri, as a simple example, the generation rate of small, medium, and large dots in the Ti dot generation LUT for M according to the amount of ink may be the dot generation rate obtained by multiplying the generation rate of small, medium, and large dots in the original dot generation LUT for M according to the amount of ink by the recording density ratio Ri. However, there is a range of possible dot generation rates for each color's dot generation LUT, and there is an upper limit to the total amount of ink ejected to a single pixel PX0, so these are taken into consideration when determining the generation rate of small, medium, and large dots according to the amount of ink. The controller 10 or host device HO1 generates different dot generation LUTs for different timing differences Ti, such as a dot generation LUT for a timing difference of 100 milliseconds, a dot generation LUT for a timing difference of 200 milliseconds, ..., a dot generation LUT for a timing difference of 500 milliseconds.

[0064] (3) Specific examples of processes performed by a printing device: Figure 10 schematically illustrates the correction data generation process. The correction data generation process is performed by the compensation unit U2 shown in Figure 1, for example, by the controller 10 shown in Figure 1. In this case, when the input unit 26 receives an operation from the user to start the correction data generation process, the correction data generation process starts. Alternatively, part of the correction data generation process may be performed by the host device HO1 shown in Figure 1. In this case, when the host device HO1 receives an operation from the user to start the correction data generation process, the correction data generation process starts. The adjustment pattern formation process in steps S102 to S112 shown in Figure 10 corresponds to the reference patch formation process ST1, the first patch formation process ST2, and the second patch formation process ST3. The processing in steps S114 to S118 corresponds to the print image formation process ST4. Hereafter, the term "step" may be omitted, and the step number may be indicated in parentheses. Furthermore, it will be explained assuming that the controller 10 performs the correction data generation process.

[0065] When the correction data generation process starts, the controller 10 sets one patch to be printed from the adjustment pattern CH0 shown in Figure 4 (S102). The patch to be set is one of the reference patch PA0, the first patch PA1, and the second patch PA2. In the example shown in Figure 4, the first patch PA11, the first reference patch PA01, the first patch PA12, ..., and the first patch PA16 are set in that order from adjustment pattern CH1, and then the second patch PA21, the second reference patch PA02, the second patch PA22, ..., and the second patch PA26 are set in that order from adjustment pattern CH2.

[0066] Next, the controller 10 controls the recording head 30 to eject a first color ink droplet 371 of a set recording density to form a set patch on the forward path P1 (S104). The formation conditions for each patch are shown, for example, in Figures 5 and 6. When forming a mixed color adjustment pattern of C and M, the controller 10 will eject a cyan ink droplet 37C of a set recording density from the cyan nozzle group 33C to the recording head 30. Next, the controller 10 controls the carriage 52, on which the recording head 30 is mounted, to return to the print start position of the set patch in the main scanning direction D1, and to perform a sub-scan of length L0 (S106).

[0067] Next, the controller 10 measures the timing difference of ink droplet ejection assigned to the set patch, starting from the start of ejection of the first color ink droplet 371 (S108). The controller 10 measures the reference timing difference T0 when the patch is the reference patch PA0, the first timing difference T1 when the patch is the first patch PA1, and the second timing difference T2 when the patch is the second patch PA2.

[0068] Next, the controller 10 controls the recording head 30 to eject a second color ink droplet 372 of a set recording density to form a set patch on the forward path P1 (S110). As described above, the formation conditions for each patch are shown, for example, in Figures 5 and 6. When forming a mixed color adjustment pattern of C and M, the controller 10 causes the recording head 30 to eject a magenta ink droplet 37M of a set recording density from the magenta nozzle group 33M.

[0069] Next, the controller 10 determines whether all patches included in the adjustment pattern CH0 have been printed (S112). If there are patches remaining to be printed, the process returns to S102; if all patches have been printed, the process proceeds to S114. As shown in Figure 4, in the middle of the adjustment patterns CH1 and CH2, if the next patch to be set is located towards the forward direction D11, the controller 10 controls the recording medium ME0 to backfeed by one sub-scan in S102 to align it with the printing start position of the set patch. The adjustment pattern formation process in S102 to S112 is performed for each of the following: the color mixing adjustment pattern of C and M, the color mixing adjustment pattern of M and Y, and the color mixing adjustment pattern of C, M, and Y.

[0070] In accordance with the adjustment pattern formation process described above, the controller 10 forms a reference patch PA0 on the recording medium ME0 by ejecting a first color ink droplet 371 and a second color ink droplet 372 with a predetermined recording density ratio at a reference timing difference T0. At this time, the controller 10 aligns the ejection of the first color ink droplet 371 and the second color ink droplet 372 that form the reference patch PA0 on the recording medium ME0 with the forward path P1. Furthermore, the controller 10 forms multiple first patches PA1 on the recording medium ME0 by ejecting multiple first color ink droplets 371 and second color ink droplets 372 with multiple different recording density ratios at a first timing difference T1. At this time, the controller 10 aligns the ejection of the first color ink droplet 371 and the second color ink droplet 372 that form the first patches PA1 on the recording medium ME0 with the forward path P1. In addition, the controller 10 forms multiple second patches PA2 on the recording medium ME0 by ejecting multiple first color ink droplets 371 and second color ink droplets 372 with multiple different recording density ratios at a second timing difference T2. At that time, the controller 10 aligns the ejection of the first color ink droplet 371 and the second color ink droplet 372, which form the second patch PA2 on the recording medium ME0, with the forward path P1.

[0071] After the adjustment pattern CH0 is formed, the controller 10 selects a first color shift compensation patch PA1z from a plurality of first patches PA1 and a second color shift compensation patch PA2z from a plurality of second patches PA2 (S114). Note that two or more first color shift compensation patches PA1z may be selected from the plurality of first patches PA1, and two or more second color shift compensation patches PA2z may be selected from the plurality of second patches PA2. To select the first color shift compensation patch PA1z and the second color shift compensation patch PA2z, the controller 10 may perform control to print different identification information corresponding to the first patches PA11 to PA16 and the second patches PA21 to PA26, respectively. In this case, the controller 10 should accept a selection operation for identification information indicating the first color shift compensation patch PA1z selected from the first patches PA11 to PA16, and accept a selection operation for identification information indicating the second color shift compensation patch PA2z selected from the second patches PA21 to PA26.

[0072] If the printer 2 is equipped with a reading unit 60, the controller 10 may have the reading unit 60 read the recording medium ME0 having the adjustment pattern CH0, obtain the reading result SC0 for each patch, and obtain a first color shift compensation patch PA1z and a second color shift compensation patch PA2z based on the reading result SC0. The reading result SC0 includes the reading results of a plurality of first reference patches PA01, first patches PA11 to PA16, a plurality of second reference patches PA02, and second patches PA21 to PA26. The controller 10 can select the patch from the first patches PA11 to PA16 that yields the reading result closest to the average of the reading results of the first reference patch PA01 as the first color shift compensation patch PA1z. The controller 10 can also select the patch from the second patches PA21 to PA26 that yields the reading result closest to the average of the reading results of the second reference patch PA02 as the second color shift compensation patch PA2z. If the printer 2 is equipped with a colorimeter, the controller 10 may have the colorimeter read the adjustment pattern CH0, obtain the reading result SC0 for each patch, and obtain a first color shift compensation patch PA1z and a second color shift compensation patch PA2z based on the reading result SC0.

[0073] After selecting the first color shift compensation patch PA1z and the second color shift compensation patch PA2z, the controller 10 determines the recording density ratio Ri as a correction value based on the recording density ratio R1 corresponding to the first color shift compensation patch PA1z and the recording density ratio R2 corresponding to the second color shift compensation patch PA2z (S116). If multiple first color shift compensation patches PA1z are selected, the average of the recording density ratios corresponding to each first color shift compensation patch PA1z may be used as the recording density ratio R1. If multiple second color shift compensation patches PA2z are selected, the average of the recording density ratios corresponding to each second color shift compensation patch PA2z may be used as the recording density ratio R2. As explained with reference to Figures 7 and 16, the timing difference Ti corresponding to position Xi in the main scanning direction D1 in the band region B0 can be calculated using position X1 corresponding to the first timing difference T1 and position X2 corresponding to the second timing difference T2, according to equations (1) and (2) described above. Once the timing difference Ti is obtained, the recording density ratio Ri as a correction value can be calculated using the recording density ratio R1 corresponding to the first color shift compensation patch PA1z and the recording density ratio R2 corresponding to the second color shift compensation patch PA2z, according to equation (3) described above.

[0074] After determining the recording density ratio Ri, the controller 10 generates correction data based on the recording density ratio Ri to compensate for color shift due to timing difference Ti (S118), and terminates the correction data generation process. The correction data includes a color conversion LUT as described with reference to Figure 8, a dot generation LUT as described with reference to Figure 9, etc. If the correction data is a color conversion LUT, the controller 10 generates different color conversion LUTs for Ti in stages according to the timing difference Ti, based on the recording density ratio Ri. If the correction data is a dot generation LUT, the controller 10 generates different dot generation LUTs for Ti in stages according to the timing difference Ti, based on the recording density ratio Ri.

[0075] Figure 11 schematically illustrates a print control process that compensates for color shift due to timing difference T as needed. The print control process is performed by the compensation unit U2 shown in Figure 1, for example, by the controller 10 shown in Figure 1. In this case, the print control process starts when the color conversion unit 12 acquires the original image data DA1. Alternatively, part of the print control process may be performed by the host device HO1 shown in Figure 1. In this case, the print control process starts when the host device HO1 receives an operation from the user to print the original image data DA1. The print control process shown in Figure 11 corresponds to the print image forming process ST4. Hereafter, the explanation will assume that the controller 10 performs the print control process.

[0076] When the print control process starts, the controller 10 acquires the original image data DA1 (S202). The original image data acquisition process in S202 includes processes such as storing the original image data DA1 received from the host device HO1 in RAM 21, and storing the original image data DA1 from a memory (not shown) in RAM 21. Next, the controller 10 converts the original image data DA1 to ink amount data DA2 in the color conversion unit 12 while referring to a color conversion LUT in normal mode, for example, the original color conversion LUT shown in Figure 8 (S204).

[0077] Next, the controller 10, in the halftone processing unit 13, converts the ink amount of the ink amount data DA2 into a dot generation rate while referring to a dot generation LUT in normal mode, for example, the original dot generation LUT shown in Figure 9, and then generates halftone data DA3 (S206). Next, the controller 10 generates raster data RA0 by performing a rasterization process in the rasterization processing unit 14, which rearranges the halftone data DA3 in the order in which the dots 38 are formed by the drive unit 50 (S208).

[0078] Next, the controller 10 determines whether or not to compensate for color shift due to timing difference T (S210). For example, if the set print mode is a color bidirectional band printing mode, the controller 10 compensates for color shift due to timing difference T in S212 to S214, but does not perform the process of compensating for color shift due to timing difference T if the set print mode is any other mode. Other modes include a monochrome printing mode, a unidirectional printing mode, an interlaced printing mode, etc. If the controller 10 does not perform processing to compensate for color shift due to timing difference T, it proceeds to processing S216, where the drive signal transmission unit 15 generates a drive signal SG1 from the raster data RA0 and outputs it to the drive circuit 31 of the recording head 30. As a result, the printed image IM0 is formed on the recording medium ME0.

[0079] When the controller 10 compensates for color shift due to timing difference T, it obtains the timing difference Ti of ink droplet ejection corresponding to the position Xi in the main scanning direction D1 for each band region B0 of the printed image IM0 (S212). For example, if the correction data is a color conversion LUT, the process of compensating for color shift is performed on the ink amount data DA2 obtained in S204. In this case, the controller 10 can determine which position Xi in which band region B0 each part of the ink amount data DA2 corresponds to. Also, if the correction data is a dot generation LUT, the process of compensating for color shift is performed on the halftone data DA3 obtained in S206. In this case, the controller 10 can determine which position Xi in which band region B0 each part of the halftone data DA3 corresponds to.

[0080] The timing difference Ti corresponding to position Xi can basically be calculated according to equations (1) and (2) described above. Here, if the recording head 30 always moves from the "Home" position to the "Full" position on the forward path P1, and moves from the "Full" position to the "Home" position on the return path P2, then the "Home" position can be set to position X1 and the "Full" position to position X2. However, as illustrated in Figure 12, if the recording head 30 does not move to a part of the printed image IM0 where color ink droplets 37A are not ejected, then it is necessary to shift position X1 from the "Home" position or position X2 from the "Full" position.

[0081] Figure 12 schematically shows an example of forming a mixed color print image IM0 of C and M by bidirectional color band printing. In the example shown in Figure 12, in the band region B1, a group of cyan nozzles 33C that moves from the "Home" position to the "Full" position on the outbound path P1 ejects cyan ink droplets 37C, and a group of magenta nozzles 33M that moves from the "Full" position to the "Home" position on the return path P2 ejects magenta ink droplets 37M. In this case, the timing difference Ti corresponding to position Xi can be calculated according to equation (1) for the outbound path P1, with the "Home" position as position X1 and the "Full" position as position X2.

[0082] In band region B2, the cyan nozzle group 33C, which moves from the "Full" position to the "Home" position on the return path P2, ejects cyan ink droplets 37C, and the magenta nozzle group 33M, which moves from the "Home" position to the "Full" position on the outbound path P1, ejects magenta ink droplets 37M. In this case, the timing difference Ti corresponding to position Xi can be calculated according to equation (2) for the return path P2, with the "Home" position as position X1 and the "Full" position as position X2. Ink droplets 37 are not ejected in band regions B3 and B4. Therefore, the carriage 52 equipped with the recording head 30 does not move in band regions B3 and B4.

[0083] In band region B5, a group of cyan nozzles 33C, which moves from an intermediate position 101 closer to "Full" than the "Home" position to an intermediate position 102 closer to "Home" than the "Full" position during the outbound journey P1, ejects cyan ink droplets 37C. In the same band region B5, a group of magenta nozzles 33M, which moves from an intermediate position 102 to an intermediate position 101 during the return journey P2, ejects magenta ink droplets 37M. In this case, the timing difference Ti can be calculated by setting intermediate position 102 to position X2. If intermediate position 101 is set to position X1A, then position X1A corresponds to a position closer to "Full" from intermediate position 101 by the difference between the "Full" position and intermediate position 102 in band region B1. Therefore, the timing difference Ti corresponding to position Xi can be calculated by setting intermediate position 101 to position X1A and intermediate position 102 to position X2, according to equation (1) for the outbound journey P1.

[0084] In band region B6, a cyan nozzle group 33C that moves from intermediate position 102 to intermediate position 101 during the return journey P2 ejects cyan ink droplets 37C, and a magenta nozzle group 33M that moves from intermediate position 101 to intermediate position 102 during the outward journey P1 ejects magenta ink droplets 37M. In this case, the timing difference Ti can be calculated by setting intermediate position 101 as position X1. If intermediate position 102 is set as position X2A, then position X2A corresponds to a position closer to "Home" from intermediate position 102 by the difference between intermediate position 101 and the "Home" position in band region B2. Therefore, the timing difference Ti corresponding to position Xi can be calculated by setting intermediate position 101 as position X1 and intermediate position 102 as position X2A, according to equation (2) for the return journey P2.

[0085] After obtaining the timing difference Ti, the controller 10 performs color shift compensation processing (S214). For example, if the correction data is a color conversion LUT, the controller 10 can compensate for the color shift due to the timing difference Ti according to the process illustrated in Figure 13. If the correction data is a dot generation LUT, the controller 10 can compensate for the color shift due to the timing difference Ti according to the process illustrated in Figure 14.

[0086] Figure 13 schematically illustrates a color shift compensation process using a color conversion LUT. The memory unit 23 shown in Figure 1 is assumed to store different color conversion LUTs for Ti according to the stepwise timing difference Ti, from the color conversion LUT for Tmin to the color conversion LUT for Tmax. When the color shift compensation process shown in Figure 13 is started, the controller 10 selects a color conversion LUT for Ti according to the timing difference Ti of ink droplet ejection (S302). Next, in the color conversion unit 12, the controller 10 converts the original image data DA1 into ink amount data DA2 while referring to the selected color conversion LUT for Ti (S304). The ink amount in the resulting ink amount data DA2 is corrected so as to compensate for the color shift caused by the timing difference T of ink droplet ejection. Next, in the halftone processing unit 13, the controller 10 converts the ink amount of the ink amount data DA2 into a dot generation rate while referring to a dot generation LUT in normal mode, for example, the original dot generation LUT shown in Figure 9, and then generates halftone data DA3 (S306). Finally, in the rasterization processing unit 14, the controller 10 generates raster data RA0 from the halftone data DA3 by performing rasterization (S308).

[0087] As mentioned above, the color conversion LUT for Ti is only provided in steps for the timing difference Ti. Therefore, the controller 10 may use a color conversion LUT for Ti corresponding to the timing difference Ti and a color conversion LUT for Ti+1 corresponding to the timing difference Ti+1 to compensate for the color shift due to the timing difference (let's call it Td) between the timing difference Ti and the timing difference Ti+1. For example, the controller 10 may convert the original image data DA1 to a first ink amount while referring to the color conversion LUT for Ti, convert the original image data DA1 to a second ink amount while referring to the color conversion LUT for Ti+1, and generate ink amount data DA2 in which the color shift due to the timing difference Td is compensated by performing linear interpolation between the first ink amount and the second ink amount.

[0088] Figure 14 schematically illustrates a color shift compensation process using a dot generation LUT. The memory unit 23 shown in Figure 1 is assumed to store different dot generation LUTs for Ti according to the stepwise timing difference Ti, from the dot generation LUT for Tmin to the dot generation LUT for Tmax. When the color shift compensation process shown in Figure 14 is started, the controller 10 selects a dot generation LUT for Ti according to the timing difference Ti of ink droplet ejection (S402). Next, in the halftone processing unit 13, the controller 10 converts the ink amount of the ink amount data DA2 into a dot generation rate while referring to the selected dot generation LUT for Ti, and generates halftone data DA3 (S404). The resulting halftone data DA3 is corrected so that the color shift due to the timing difference T of ink droplet ejection is compensated for. Finally, the controller 10 generates raster data RA0 from the halftone data DA3 by performing rasterization processing in the rasterization processing unit 14 (S406).

[0089] As mentioned above, the dot generation LUT for Ti is only provided in steps for the timing difference Ti. Therefore, the controller 10 may use a dot generation LUT for Ti corresponding to the timing difference Ti and a dot generation LUT for Ti+1 corresponding to the timing difference Ti+1 to compensate for the color shift due to the timing difference (let's call it Td) between the timing difference Ti and the timing difference Ti+1. For example, the controller 10 may convert the ink amount data DA2 to a first dot generation rate while referring to the dot generation LUT for Ti, convert the ink amount data DA2 to a second dot generation rate while referring to the dot generation LUT for Ti+1, and generate halftone data DA3 in which the color shift due to the timing difference Td is compensated by performing linear interpolation between the first dot generation rate and the second dot generation rate.

[0090] As explained above, the controller 10 compensates for the color shift due to the timing difference T based on the recording density ratio R1 corresponding to the first color shift compensation patch PA1z and the recording density ratio R2 corresponding to the second color shift compensation patch PA2z, according to the processes S114~118 and S202~S214 shown in Figures 10 and 11.

[0091] After the color misalignment compensation process, the controller 10 generates a drive signal SG1 from the raster data RA0 in the drive signal transmission unit 15 and outputs it to the drive circuit 31 of the recording head 30 (S216), thereby ending the print control process. As a result, the printed image IM0 is formed on the recording medium ME0. Based on the above, the controller 10 compensates for the color shift due to the timing difference T based on the recording density ratios R1 and R2 to form the printed image IM0.

[0092] The reference patch PA0 shown in Figure 4 shows the printed color when the timing difference T between the ejection of the first color ink droplet 371 and the second color ink droplet 372 is the reference timing difference T0. The multiple first patches PA1 shown in Figure 4 show candidate correction colors when the timing difference T of ink droplet ejection is greater than the reference timing difference T0. The multiple second patches PA2 shown in Figure 4 show candidate correction colors when the timing difference T of ink droplet ejection is less than the reference timing difference T0. Based on the recording density ratio R1 corresponding to the first color shift compensation patch PA1z selected from the multiple first patches PA1, and the recording density ratio R2 corresponding to the second color shift compensation patch PA2z selected from the multiple second patches PA2, the color shift due to the timing difference T of ink droplet ejection is compensated. Therefore, this specific example can reduce color unevenness caused by vertically arranged heads.

[0093] (4) Variations: Various modifications of this invention are conceivable. For example, the combination of ink colors is not limited to C, M, Y, and K, but may include orange, green, white, colorless, etc. Of course, this technology can also be applied even if the printing device 1 does not use any of the C, M, and Y inks, but uses two or more colors of ink other than black. When the host device HO1 converts the original image data DA1 into ink volume data DA2, the printer 2 may receive the ink volume data DA2 from the host device HO1 and form the printed image IM0. Furthermore, when the host device HO1 generates halftone data DA3 from the ink volume data DA2, the printer 2 may receive the halftone data DA3 from the host device HO1 and form the printed image IM0. Furthermore, when the host device HO1 generates raster data RA0 from the halftone data DA3, the printer 2 may receive the raster data RA0 from the host device HO1 and form the printed image IM0.

[0094] The entity performing the above-described processing is not limited to the CPU; it may also be an electronic component other than the CPU, such as an ASIC. Of course, multiple CPUs may cooperate to perform the above-described processing, or a CPU and another electronic component (such as an ASIC) may cooperate to perform the above-described processing. Furthermore, the above-mentioned processes can be modified as needed.

[0095] In the adjustment pattern CH1 described above, a first reference patch PA01 is placed between each first patch PA1, and in the adjustment pattern CH2 described above, a second reference patch PA02 is placed between each second patch PA2, but the pattern is not limited to these. For example, the first patches PA1 may be adjacent to each other, the first reference patch PA01 may be separated from multiple first patches PA1, the second patches PA2 may be adjacent to each other, and the second reference patch PA02 may be separated from multiple second patches PA2. Also, the reference patch PA0 may not be divided into a first reference patch PA01 and a second reference patch PA02, but rather a reference patch PA0 may be placed between the first patch PA1 and the second patch PA2.

[0096] The printing device 1 may print an adjustment pattern that does not include the second patch PA2. In this case, the controller 10 or host device HO1 can compensate for the color shift due to the timing difference T of ink droplet ejection based on the recording density ratio R1 corresponding to the first color shift compensation patch PA1z selected from a plurality of first patches PA1. In this case, the first timing difference T1 only needs to be a different timing difference from the reference timing difference T0, and may be smaller than the reference timing difference T0. Here, let X0 be the intermediate position between the "Home" position and the "Full" position. Position X0 is the position where the reference timing difference T0 is. The timing difference Ti corresponding to position Xi can be calculated by linear interpolation.

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[0097] Based on the above, color shifts caused by the timing difference T of ink droplet ejection are compensated based on the recording density ratio R1 corresponding to the first color shift compensation patch PA1z selected from multiple first patches PA1. Therefore, even when the second patch PA2 is not present in the adjustment pattern, color unevenness caused by the vertically arranged heads can be reduced.

[0098] As illustrated in Figure 15, a process may be performed to switch whether or not to generate correction data depending on the type of recording medium ME0. The recording medium setting process and condition-based processing shown in Figure 15 are performed by the control unit U1 shown in Figure 1, for example, by the controller 10 shown in Figure 1. In this case, when the input unit 26 receives an operation from the user to start the recording medium setting process, the controller 10 displays a setting screen for the type of recording medium ME0 that will form the printed image IM0 on the output unit 25 and accepts the setting of the type of recording medium ME0 that will form the printed image IM0 (S502). In addition, at least a part of the recording medium setting process may be performed by the host device HO1 shown in Figure 1. In this case, when the host device HO1 receives an operation from the user to start the recording medium setting process, the host device HO1 displays the aforementioned setting screen on the display unit and accepts the setting of the type of recording medium ME0 that will form the printed image IM0.

[0099] As shown in Figure 15, plain paper is relatively prone to ink bleeding, and color shifts due to the timing difference T of ink droplet ejection are more likely to occur. As shown in Figure 15, glossy paper is relatively resistant to ink bleeding, and color shifts due to the timing difference T of ink droplet ejection are relatively small. This is presumed to be because a large amount of the first color ink droplet 371 that landed first remains on the surface of the glossy paper, so even when the second color ink droplet 372 lands later, the color of the first color ink droplet 371 remains more prominent. Alternatively, if the recording medium ME0 is plain paper, it is presumed that the color of the second color ink droplet 372 that landed later is more strongly expressed because the first color ink droplet 371 that landed first soaks into the plain paper. In the example shown in Figure 15, plain paper is an example of the first recording medium ME1, and glossy paper is an example of the second recording medium ME2, which has less color shift due to the timing difference T than the first recording medium ME1.

[0100] After processing in S502, the controller 10 stores the setting of the type of recording medium ME0 in the storage unit 23 (S504), and terminates the recording medium setting process. Of course, the host device HO1 may also store the setting of the type of recording medium ME0.

[0101] When the color conversion unit 12 acquires the original image data DA1, the controller 10 starts conditional processing and branches the processing according to the type of recording medium ME0 that is set (S512). If the type of recording medium ME0 that is set corresponds to plain paper, the controller 10 performs the correction data generation process shown in Figure 10 (S514) and terminates the conditional processing. If the type of recording medium ME0 that is set corresponds to glossy paper, the controller 10 terminates the conditional processing without performing the process in S514. In the judgment process of S210 in the print control process shown in Figure 11, the controller 10 only needs to determine whether the type of recording medium ME0 that is set corresponds to plain paper and whether the set print mode is a mode for performing bidirectional color band printing. When the condition is met, the controller 10 compensates for the color shift due to the timing difference T in S212 to S216 and forms the print image IM0, and when the condition is not met, it forms the print image IM0 in S216 without performing the process to compensate for the color shift due to the timing difference T. Therefore, when the type of recording medium ME0 corresponds to the first recording medium ME1, the control unit U1 compensates for the color shift due to the timing difference T in the compensation unit U2 to form the printed image IM0. On the other hand, when the type of recording medium ME0 corresponds to the second recording medium ME2, the control unit U1 does not perform the process of compensating for the color shift due to the timing difference T.

[0102] Alternatively, the decision process in S512 may be performed by the host device HO1 shown in Figure 1. In this case, when the host device HO1 receives a request from the user to print the original image data DA1, it starts conditional processing and branches the processing according to the type of recording medium ME0 that is set (S512). If the type of recording medium ME0 that is set corresponds to plain paper, the correction data generation process is performed (S514), and if the type of recording medium ME0 that is set corresponds to glossy paper, the correction data generation process is not performed.

[0103] The example shown in Figure 15 demonstrates that if the color shift due to the timing difference T of ink droplet ejection is small, it is not necessary to perform a process to compensate for the color shift, thus improving user convenience.

[0104] (5) Conclusion: As described above, according to the present invention, it is possible to provide technologies that can reduce color unevenness caused by vertically arranged heads in various embodiments. Of course, even a technology consisting only of the constituent elements of an independent claim can obtain the basic functions and effects described above. Furthermore, configurations obtained by substituting or changing the combinations of each configuration disclosed in the above-mentioned examples, configurations obtained by substituting or changing the combinations of each configuration disclosed in the prior art and the above-mentioned examples, etc., are also possible. The present invention also includes these configurations, etc. [Explanation of Symbols]

[0105] 1...Printing device, 2...Printer, 10...Controller, 11...CPU, 12...Color conversion unit, 13...Halftone processing unit, 14...Rasterization processing unit, 15...Drive signal transmission unit, 23...Storage unit, 24...Operation panel, 30...Recording head, 31...Drive circuit, 32...Drive element, 33...Nozzle row, 33A...Color nozzle row, 33K...Black nozzle row, 33G...Color nozzle group, 34...Nozzle, 34A...Color nozzle, 34K...Black nozzle, 37...Ink droplet, 37A...Color ink droplet, 37K...Black ink droplet, 38...Dot, 50...Drive unit, 51...Carriage drive unit, 52...Carriage, 55...Roller drive unit, 60...Reading unit, 331...First color nozzle group, 332...Second color nozzle group, 371...First color ink droplet, 372...Second color ink droplet, B0...Band area, CH0, CH1, CH2...Adjustment pattern, D1...Main scanning direction, D2...Sub-scanning direction, D3...Feeding method Direction, D4…Alignment direction, D11…Forward direction, D12…Return direction, DA1…Original image data, DA2…Ink amount data, DA3…Halftone data, HO1…Host device, IM0…Printed image, L0…Length, ME0…Recording medium, ME1…First recording medium, ME2…Second recording medium, P0…Main scan, P1…Forward path, P2…Return path, PA0…Reference patch, PA01…First reference patch, PA02…Second reference patch, PA1…First patch, PA1z…First color PA2...Second patch for color shift compensation, PA2z...Second color shift compensation patch, R1, R2...Recording density ratio, PX0...Pixel, RA0...Raster data, SC0...Reading result, ST1...Reference patch formation process, ST2...First patch formation process, ST3...Second patch formation process, ST4...Printed image formation process, T...Timing difference, T0...Reference timing difference, T1...First timing difference, T2...Second timing difference, U1...Control unit, U2...Compensation unit, X...Position.

Claims

1. A printing apparatus comprising a recording head having a row of black nozzles arranged in a line, each of which ejects black ink droplets, and a group of color nozzles arranged along the row of black nozzles, wherein the group of color nozzles is arranged sequentially in the direction in which the black nozzles are arranged, A drive unit that performs a main scan to change the relative position of the recording head and the recording medium in the forward and return paths along a main scan direction intersecting the aforementioned alignment direction, and a sub-scan to change the relative position of the recording head and the recording medium along a sub-scan direction intersecting the main scan direction, The recording medium comprises a control unit that controls bidirectional printing, in which the color ink droplets are deposited in a single main scan between sub-scans in both the forward and return paths, from the color nozzle groups assigned to each band region corresponding to the length in the sub-scan direction of each of the color nozzle groups that eject the color ink droplets, in the recording medium, The plurality of color nozzle groups include a first color nozzle group and a second color nozzle group, the colors of the color ink droplets ejected in the forward and return paths to the band region in the bidirectional printing process are different from each other. The color ink droplets ejected by the first color nozzle group are referred to as first color ink droplets, and the color ink droplets ejected by the second color nozzle group are referred to as second color ink droplets. The control unit includes a compensation unit that compensates for color misalignment caused by the timing difference in ejection between the first color ink droplet and the second color ink droplet, which occurs depending on their position within the band region in the main scanning direction. The aforementioned compensation unit is A reference patch is formed on the recording medium by ejecting the first color ink droplet and the second color ink droplet at a predetermined recording density ratio using a reference timing difference, which is the basis for the aforementioned timing difference. By ejecting multiple first color ink droplets and second color ink droplets with different recording density ratios at a first timing difference different from the aforementioned reference timing difference, multiple first patches are formed on the recording medium such that the reference patch is positioned between the first patches. A printing apparatus that forms a printed image by compensating for the color shift due to the timing difference based on the recording density ratio corresponding to a first color shift compensation patch selected from the plurality of first patches.

2. A printing apparatus comprising a recording head having a row of black nozzles arranged in a line, each of which ejects black ink droplets, and a group of color nozzles arranged along the row of black nozzles, wherein the group of color nozzles is arranged sequentially in the direction in which the black nozzles are arranged, A drive unit that performs a main scan to change the relative position of the recording head and the recording medium in the forward and return paths along a main scan direction intersecting the aforementioned alignment direction, and a sub-scan to change the relative position of the recording head and the recording medium along a sub-scan direction intersecting the main scan direction, The recording medium comprises a control unit that controls bidirectional printing, in which the color ink droplets are deposited in a single main scan between sub-scans in both the forward and return paths, from the color nozzle groups assigned to each band region corresponding to the length in the sub-scan direction of each of the color nozzle groups that eject the color ink droplets, in the recording medium, The plurality of color nozzle groups include a first color nozzle group and a second color nozzle group, the colors of the color ink droplets ejected in the forward and return paths to the band region in the bidirectional printing process are different from each other. The color ink droplets ejected by the first color nozzle group are referred to as first color ink droplets, and the color ink droplets ejected by the second color nozzle group are referred to as second color ink droplets. The control unit includes a compensation unit that compensates for color misalignment caused by the timing difference in ejection between the first color ink droplet and the second color ink droplet, which occurs depending on their position within the band region in the main scanning direction. The aforementioned compensation unit is A reference patch is formed on the recording medium by aligning and ejecting the first color ink droplet and the second color ink droplet, which have a predetermined recording density ratio, on either the forward path or the return path at a reference timing difference, which is the basis for the timing difference. Multiple first patches are formed on the recording medium by ejecting multiple first color ink droplets and second color ink droplets with different recording density ratios at a first timing difference different from the aforementioned reference timing difference. A printing apparatus that forms a printed image by compensating for the color shift due to the timing difference based on the recording density ratio corresponding to a first color shift compensation patch selected from the plurality of first patches.

3. A printing apparatus comprising a recording head having a row of black nozzles arranged in a line, each of which ejects black ink droplets, and a group of color nozzles arranged along the row of black nozzles, wherein the group of color nozzles is arranged sequentially in the direction in which the black nozzles are arranged, A drive unit that performs a main scan to change the relative position of the recording head and the recording medium in the forward and return paths along a main scan direction intersecting the aforementioned alignment direction, and a sub-scan to change the relative position of the recording head and the recording medium along a sub-scan direction intersecting the main scan direction, The recording medium comprises a control unit that controls bidirectional printing, in which the color ink droplets are deposited in a single main scan between sub-scans in both the forward and return paths, from the color nozzle groups assigned to each band region corresponding to the length in the sub-scan direction of each of the color nozzle groups that eject the color ink droplets, in the recording medium, The plurality of color nozzle groups include a first color nozzle group and a second color nozzle group, the colors of the color ink droplets ejected in the forward and return paths to the band region in the bidirectional printing process are different from each other. The color ink droplets ejected by the first color nozzle group are referred to as first color ink droplets, and the color ink droplets ejected by the second color nozzle group are referred to as second color ink droplets. The control unit includes a compensation unit that compensates for color misalignment caused by the timing difference in ejection between the first color ink droplet and the second color ink droplet, which occurs depending on their position within the band region in the main scanning direction. The aforementioned compensation unit is A reference patch is formed on the recording medium by ejecting the first color ink droplet and the second color ink droplet at a predetermined recording density ratio using a reference timing difference, which is the basis for the aforementioned timing difference. Multiple first patches are formed on the recording medium by aligning and ejecting multiple first color ink droplets and second color ink droplets with different recording density ratios on either the forward path or the return path at a first timing difference different from the aforementioned reference timing difference. A printing apparatus that forms a printed image by compensating for the color shift due to the timing difference based on the recording density ratio corresponding to a first color shift compensation patch selected from the plurality of first patches.

4. A printing apparatus comprising a recording head having a row of black nozzles arranged in a line, each of which ejects black ink droplets, and a group of color nozzles arranged along the row of black nozzles, wherein the group of color nozzles is arranged sequentially in the direction in which the black nozzles are arranged, A drive unit that performs a main scan to change the relative position of the recording head and the recording medium in the forward and return paths along a main scan direction intersecting the aforementioned alignment direction, and a sub-scan to change the relative position of the recording head and the recording medium along a sub-scan direction intersecting the main scan direction, The recording medium comprises a control unit that controls bidirectional printing, in which the color ink droplets are deposited in a single main scan between sub-scans in both the forward and return paths, from the color nozzle groups assigned to each band region corresponding to the length in the sub-scan direction of each of the color nozzle groups that eject the color ink droplets, in the recording medium, The plurality of color nozzle groups include a first color nozzle group and a second color nozzle group, the colors of the color ink droplets ejected in the forward and return paths to the band region in the bidirectional printing process are different from each other. The color ink droplets ejected by the first color nozzle group are referred to as first color ink droplets, and the color ink droplets ejected by the second color nozzle group are referred to as second color ink droplets. The control unit includes a compensation unit that compensates for color misalignment caused by the timing difference in ejection between the first color ink droplet and the second color ink droplet, which occurs depending on their position within the band region in the main scanning direction. The aforementioned compensation unit is A reference patch is formed on the recording medium by ejecting the first color ink droplet and the second color ink droplet at a predetermined recording density ratio using a reference timing difference, which is the basis for the aforementioned timing difference. Multiple first patches are formed on the recording medium by ejecting multiple first color ink droplets and second color ink droplets with different recording density ratios at a first timing difference different from the aforementioned reference timing difference. Based on the recording density ratio corresponding to the first color shift compensation patch selected from the plurality of first patches, the color shift due to the timing difference is compensated to form a printed image. The recording medium includes a first recording medium and a second recording medium which has less color shift due to the timing difference than the first recording medium. The control unit, The system accepts the setting of the type of recording medium used to form the printed image. When the aforementioned type corresponds to the first recording medium, the compensation unit compensates for the color shift due to the timing difference to form the printed image. A printing apparatus that, when the aforementioned type corresponds to the second recording medium, does not perform a process to compensate for color shift due to the timing difference.

5. The aforementioned first timing difference is greater than the aforementioned reference timing difference. The aforementioned compensation unit is Multiple second patches are formed on the recording medium by ejecting the first color ink droplets and the second color ink droplets with multiple different recording density ratios at a second timing difference smaller than the aforementioned reference timing difference. A printing apparatus according to any one of claims 1 to 4, which forms the printed image by compensating for the color shift due to the timing difference based on a recording density ratio corresponding to the first color shift compensation patch and a recording density ratio corresponding to a second color shift compensation patch selected from the plurality of second patches.

6. The printing apparatus according to claim 5, wherein the compensation unit causes the recording medium to form a first reference patch, which is positioned between the first patches, and a second reference patch, which is positioned between the second patches, as the reference patch.

7. The printing apparatus according to claim 5, wherein the compensation unit controls the ejection of the first color ink droplets and the second color ink droplets that form the plurality of second patches on the recording medium to be aligned with either the forward path or the return path.

8. The aforementioned first timing difference is the maximum of the timing difference in the bidirectional printing. The printing apparatus according to claim 5, wherein the second timing difference is the minimum timing difference in the bidirectional printing.

9. The printing apparatus according to any one of claims 1 to 4, wherein the compensation unit acquires the reading results of the reference patch and the plurality of first patches, and selects the first color misalignment compensation patch from the plurality of first patches based on the reading results.

10. A recording head having a row of black nozzles arranged in a line, each of which ejects black ink droplets, and a group of multiple color nozzles arranged along the row of black nozzles, each of which ejects color ink droplets, and the group of multiple color nozzles arranged in order in the direction of the arrangement of the multiple black nozzles, The drive unit includes a drive unit that performs a main scan to change the relative position of the recording head and the recording medium in the forward and return paths along a main scan direction intersecting the aforementioned alignment direction, and a sub-scan to change the relative position of the recording head and the recording medium along a sub-scan direction intersecting the main scan direction, A printing method for performing bidirectional printing in which, in the recording medium, the color ink droplets are deposited in one main scan between sub-scans in both the forward and return paths, from the color nozzle groups assigned to each band region corresponding to the length in the sub-scan direction of each of the color nozzle groups that eject the color ink droplets, The plurality of color nozzle groups include a first color nozzle group and a second color nozzle group, the colors of the color ink droplets ejected in the forward and return paths to the band region in the bidirectional printing process are different from each other. The color ink droplets ejected by the first color nozzle group are referred to as first color ink droplets, and the color ink droplets ejected by the second color nozzle group are referred to as second color ink droplets. The aforementioned printing method is A reference patch formation step, which involves forming a reference patch on the recording medium by ejecting the first color ink droplet and the second color ink droplet at a predetermined recording density ratio using a reference timing difference, which is a reference for the timing difference of ejection between the first color ink droplet and the second color ink droplet that occurs according to their positions within the band region in the main scanning direction; A first patch formation step involves ejecting a plurality of first color ink droplets and a second color ink droplet with different recording density ratios at a first timing difference different from the aforementioned reference timing difference, thereby forming a plurality of first patches on the recording medium such that the reference patch is positioned between the first patches. A printing method comprising: a print image forming step of forming a print image by compensating for the color shift due to the timing difference based on the recording density ratio corresponding to a first color shift compensation patch selected from the plurality of first patches.

11. A recording head having a row of black nozzles arranged in a line, each of which ejects black ink droplets, and a group of multiple color nozzles arranged along the row of black nozzles, each of which ejects color ink droplets, and the group of multiple color nozzles arranged in order in the direction of the arrangement of the multiple black nozzles, The drive unit includes a drive unit that performs a main scan to change the relative position of the recording head and the recording medium in the forward and return paths along a main scan direction intersecting the aforementioned alignment direction, and a sub-scan to change the relative position of the recording head and the recording medium along a sub-scan direction intersecting the main scan direction, A printing method for performing bidirectional printing in which, in the recording medium, the color ink droplets are deposited in one main scan between sub-scans in both the forward and return paths, from the color nozzle groups assigned to each band region corresponding to the length in the sub-scan direction of each of the color nozzle groups that eject the color ink droplets, The plurality of color nozzle groups include a first color nozzle group and a second color nozzle group, the colors of the color ink droplets ejected in the forward and return paths to the band region in the bidirectional printing process are different from each other. The color ink droplets ejected by the first color nozzle group are referred to as first color ink droplets, and the color ink droplets ejected by the second color nozzle group are referred to as second color ink droplets. The aforementioned printing method is A reference patch formation step, in which a reference patch is formed on the recording medium by aligning and ejecting the first color ink droplet and the second color ink droplet, which have a predetermined recording density ratio, on either the forward path or the return path, based on a reference timing difference, which is the reference for the timing difference of ejection between the first color ink droplet and the second color ink droplet that occurs according to their position within the band region in the main scanning direction; A first patch formation step involves forming multiple first patches on the recording medium by ejecting multiple first color ink droplets and second color ink droplets with multiple different recording density ratios at a first timing difference different from the aforementioned reference timing difference. A printing method comprising: a print image forming step of forming a print image by compensating for the color shift due to the timing difference based on the recording density ratio corresponding to a first color shift compensation patch selected from the plurality of first patches.

12. A recording head having a row of black nozzles arranged in a line, each of which ejects black ink droplets, and a group of multiple color nozzles arranged along the row of black nozzles, each of which ejects color ink droplets, and the group of multiple color nozzles arranged in order in the direction of the arrangement of the multiple black nozzles, The drive unit includes a drive unit that performs a main scan to change the relative position of the recording head and the recording medium in the forward and return paths along a main scan direction intersecting the aforementioned alignment direction, and a sub-scan to change the relative position of the recording head and the recording medium along a sub-scan direction intersecting the main scan direction, A printing method for performing bidirectional printing in which, in the recording medium, the color ink droplets are deposited in one main scan between sub-scans in both the forward and return paths, from the color nozzle groups assigned to each band region corresponding to the length in the sub-scan direction of each of the color nozzle groups that eject the color ink droplets, The plurality of color nozzle groups include a first color nozzle group and a second color nozzle group, the colors of the color ink droplets ejected in the forward and return paths to the band region in the bidirectional printing process are different from each other. The color ink droplets ejected by the first color nozzle group are referred to as first color ink droplets, and the color ink droplets ejected by the second color nozzle group are referred to as second color ink droplets. The aforementioned printing method is A reference patch formation step, which involves forming a reference patch on the recording medium by ejecting the first color ink droplet and the second color ink droplet at a predetermined recording density ratio using a reference timing difference, which is a reference for the timing difference of ejection between the first color ink droplet and the second color ink droplet that occurs according to their positions within the band region in the main scanning direction; A first patch formation step involves forming multiple first patches on the recording medium by ejecting multiple first color ink droplets and second color ink droplets with multiple different recording density ratios in a first timing difference different from the aforementioned reference timing difference, aligned on either the forward path or the return path. A printing method comprising: a print image forming step of forming a print image by compensating for the color shift due to the timing difference based on the recording density ratio corresponding to a first color shift compensation patch selected from the plurality of first patches.

13. A recording head having a row of black nozzles arranged in a line, each of which ejects black ink droplets, and a group of multiple color nozzles arranged along the row of black nozzles, each of which ejects color ink droplets, and the group of multiple color nozzles arranged in order in the direction of the arrangement of the multiple black nozzles, The drive unit includes a drive unit that performs a main scan to change the relative position of the recording head and the recording medium in the forward and return paths along a main scan direction intersecting the aforementioned alignment direction, and a sub-scan to change the relative position of the recording head and the recording medium along a sub-scan direction intersecting the main scan direction, A printing method for performing bidirectional printing in which, in the recording medium, the color ink droplets are deposited in one main scan between sub-scans in both the forward and return paths, from the color nozzle groups assigned to each band region corresponding to the length in the sub-scan direction of each of the color nozzle groups that eject the color ink droplets, The plurality of color nozzle groups include a first color nozzle group and a second color nozzle group, the colors of the color ink droplets ejected in the forward and return paths to the band region in the bidirectional printing process are different from each other. The color ink droplets ejected by the first color nozzle group are referred to as first color ink droplets, and the color ink droplets ejected by the second color nozzle group are referred to as second color ink droplets. The aforementioned printing method is A reference patch formation step, which involves forming a reference patch on the recording medium by ejecting the first color ink droplet and the second color ink droplet at a predetermined recording density ratio using a reference timing difference, which is a reference for the timing difference of ejection between the first color ink droplet and the second color ink droplet that occurs according to their positions within the band region in the main scanning direction; A first patch formation step involves forming multiple first patches on the recording medium by ejecting multiple first color ink droplets and second color ink droplets with multiple different recording density ratios at a first timing difference different from the aforementioned reference timing difference. A print image forming step includes: forming a print image by compensating for the color shift due to the timing difference based on the recording density ratio corresponding to a first color shift compensation patch selected from the plurality of first patches, The recording medium includes a first recording medium and a second recording medium which has less color shift due to the timing difference than the first recording medium. The aforementioned printing method is The process further includes a step of receiving a setting for the type of recording medium used to form the printed image, If the type corresponds to the first recording medium, the reference patch formation step, the first patch formation step, and the print image formation step are performed. A printing method in which, when the aforementioned type corresponds to the second recording medium, the reference patch formation step, the first patch formation step, and the print image formation step are not performed.

Images