Printing apparatus and printing method

Abstract

To provide a printer in which image quality is less likely to deteriorate even if halftone processing is performed using a dither mask repeatedly.SOLUTION: And a head unit that forms the output image on a medium based on a processing result of the halftone processing unit, in which a direction in which a plurality of heads discharge liquid is defined as a first direction, a direction in which the medium is transported is defined as a second direction, and a direction orthogonal to the first direction and the second direction is defined as a third direction. The output image includes a mixed region and an independent region, a length of the mixed region in the third direction is a first length, a length of the independent region in the third direction is a second length, and the number of elements of the dither mask in the third direction is N times or 1 / N times a total number of the number of pixels corresponding to the first length and the number of pixels corresponding to the second length.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a printing device and a printing method. [Background technology]

[0002] In printing technologies that eject liquid onto a medium, gradation is expressed by the distribution of dots. These dot distributions are given blue noise or green noise characteristics to eliminate bias in the dot distribution and improve image quality. When forming these dots, multiple dot groups may overlap in a given area. For example, in large printers with multiple print heads of a given length, the ends of two print heads may be arranged so that they overlap, resulting in overlapping groups of dots formed by the nozzle rows of one print head and the nozzle rows of the other print head.

[0003] When forming an image by overlapping groups of dots, if the dot formation positions between groups deviate from the normal positions at the time of design, this results in reduced granularity and density fluctuations, significantly degrading image quality. To solve this problem, the applicant of this application has proposed, in Patent Documents 1 and 2 listed below, technology for generating dither masks that keep image quality degradation within a specified range even if the dot formation positions between groups deviate. This technology is also used for image processing and printing. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-245618 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-103437 Summary of the Invention [Problem to be solved by the invention]

[0005] These technologies significantly improve print quality by reducing the effects of misalignment when multiple head scans or multiple nozzle arrays are used in overlapping areas, and their implementation method incorporates these characteristics into the threshold array of the dither mask used in the halftone process when it is created. However, when applying these technologies to printers with two or more overlapping areas, further improvements were required in the following areas: When there are multiple mixed areas (areas where the dot placement formed with each scan may be misaligned) where dots are formed by overlapping scans of multiple nozzle arrays, and a single dither mask is used repeatedly, the relative positional relationship between each mixed area and the dither mask changes for each mixed area, which can prevent the dither mask from achieving the expected effect, and there was room for consideration of the size of the dither mask. [Means for solving the problem]

[0006] One aspect of the printing device according to the present invention is 1. A printing device for forming an output image on a medium corresponding to an original image, comprising: a halftone processing unit that uses a dither mask to determine whether or not to form a dot in each of a plurality of pixels that make up the output image based on an input tone value of the original image; a head unit having a plurality of heads including a first head, a second head, and a third head, the plurality of heads ejecting liquid based on a processing result of the halftone processing unit, thereby forming the output image on the medium; Equipped with a direction in which the plurality of heads eject liquid with respect to the medium is defined as a first direction; a direction in which the medium is transported and which is perpendicular to the first direction is defined as a second direction; a direction perpendicular to the first direction and the second direction is a third direction; the plurality of heads are arranged in the third direction in order from the first head, When viewed from the second direction, a plurality of nozzles included in a rear end portion of a first nozzle row of the first head and a plurality of nozzles included in a front end portion of a second nozzle row of the second head overlap with each other, When viewed from the second direction, a plurality of nozzles included in a rear end portion of the second nozzle row and a plurality of nozzles included in a front end portion of a third nozzle row of the third head overlap with each other, The output image is a mixed region in which a plurality of dots are formed by liquid ejected from at least some of the plurality of nozzles included in the rear end portion of the first nozzle row and liquid ejected from at least some of the plurality of nozzles included in the front end portion of the second nozzle row; a single region in which a plurality of dots are formed by liquid ejected from a plurality of nozzles included between the front end and the rear end of the second nozzle row, the length of the mixed region in the third direction is a first length, the length of the single region in the third direction is a second length; The number of elements in the third direction of the dither mask is N times or 1 / N times (N is a natural number) the total number of pixels corresponding to the first length and the second length.

[0007] One aspect of the printing method according to the present invention is to 1. A printing method for forming an output image on a medium corresponding to an original image, comprising: using a dither mask, performing halftone processing to determine whether or not to form a dot in each of a plurality of pixels that make up the output image based on the input tone value of the original image; forming the output image on the medium by ejecting liquid from a plurality of heads including a first head, a second head, and a third head based on the result of the halftone processing; a direction in which the plurality of heads eject liquid with respect to the medium is defined as a first direction; a direction in which the medium is transported and which is perpendicular to the first direction is defined as a second direction; a direction perpendicular to the first direction and the second direction is a third direction; the plurality of heads are arranged in the third direction in order from the first head, When viewed from the second direction, a plurality of nozzles included in a rear end portion of a first nozzle row of the first head and a plurality of nozzles included in a front end portion of a second nozzle row of the second head overlap with each other, When viewed from the second direction, a plurality of nozzles included in a rear end portion of the second nozzle row and a plurality of nozzles included in a front end portion of a third nozzle row of the third head overlap with each other, The output image is a mixed region in which a plurality of dots are formed by liquid ejected from at least some of the plurality of nozzles included in the rear end portion of the first nozzle row and liquid ejected from at least some of the plurality of nozzles included in the front end portion of the second nozzle row; a single region in which a plurality of dots are formed by liquid ejected from a plurality of nozzles included between the front end and the rear end of the second nozzle row, the length of the mixed region in the third direction is a first length, the length of the single region in the third direction is a second length; The number of elements in the third direction of the dither mask is N times or 1 / N times (N is a natural number) the total number of pixels corresponding to the first length and the second length. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram illustrating the configuration of a printing apparatus. [Figure 2] FIG. 4 is a flowchart showing the steps of a printing method. [Figure 3] FIG. 1 is a block diagram showing the configuration of a printer. [Figure 4] FIG. [Figure 5] FIG. 4 is a diagram showing an example of an arrangement of nozzles on the bottom surface of a head module. [Figure 6] FIG. 10 is an explanatory diagram conceptually illustrating a part of a dither mask. [Figure 7] An explanatory diagram showing the concept of turning dot formation on and off using a dither mask. [Figure 8]5A and 5B are views showing an example of real grouping and virtual grouping for an output image in the first embodiment. [Figure 9] FIG. 10 is a diagram showing an example of the size of a dither mask. [Figure 10] 10A and 10B are views showing examples of real grouping and virtual grouping for an output image in the second embodiment. [Figure 11] 13A and 13B are diagrams showing the relationship between the misalignment of the second head and the actually used nozzles and surplus nozzles in the third embodiment. [Figure 12] FIG. 10 is a diagram showing a modified example in which nozzle rows are arranged in a staggered pattern. [Figure 13] FIG. 10 is a diagram showing a modified example in which nozzle rows are arranged obliquely with respect to the main scanning direction. [Figure 14] FIG. 10 is a diagram showing a modified example in which nozzle rows are arranged obliquely and in a staggered pattern. DETAILED DESCRIPTION OF THE INVENTION

[0009] Preferred embodiments of the present invention will be described below with reference to the drawings. The drawings used are for the convenience of explanation. Note that the embodiments described below do not unduly limit the content of the present invention as defined in the claims. Furthermore, not all of the configurations described below are necessarily essential components of the present invention.

[0010] 1. First embodiment 1-1. Printer configuration FIG. 1 is a block diagram showing the configuration of a printing device 1 according to a first embodiment. As shown in FIG. 1, the printing device 1 includes an image processing device 10 that processes an original image and outputs output image data, and a printer 20 capable of forming a full-color image. The printer 1 forms an output image corresponding to the original image on a medium P. As shown in FIG. 1, the image processing device 10 processes input image data to generate print data PD, which is then output to the printer 20. The image processing device 10 is, for example, a personal computer, and can be connected to external devices 3, such as digital cameras, memory cards, and USB memory sticks, via various ports (not shown), and can also be connected to external devices 3, such as various servers and information terminals, via a network. The image processing device 10 acquires input image data from, for example, the external device 3. The printer 20 forms an output image corresponding to the input image data on a medium P based on the print data PD. The printer 20 is, for example, an inkjet printer capable of forming full-color images.

[0011] 1, the image processing device 10 includes a processing unit 11, a storage unit 12, a communication unit 13, an operation unit 14, and a display unit 15. Note that the image processing device 10 may have a configuration in which some of the components in FIG. 1 are omitted or modified, or other components are added.

[0012] The processing unit 11 acquires input image data and performs image processing. Specifically, the processing unit 11 executes an image processing program 121 stored in the storage unit 12, and performs image processing on input image data 122 stored in the storage unit 12. The input image data 122 is, for example, RGB image data. In addition, the processing unit 11 performs various processes in response to operation signals from the operation unit 14, a process for displaying various images on the display unit 15, a process for controlling the communication unit 13 for data communication with the external device 3, and the like. The processing unit 11 is realized by, for example, a CPU (Central Processing Unit) or a DSP (Digital Signal Processor).

[0013] The processing unit 11 executes the image processing program 121 to function as a resolution conversion processing unit 111, a color conversion processing unit 112, a halftone processing unit 113, and a rasterization processing unit 114. That is, the image processing device 10 functions as a resolution conversion processing unit 111, a color conversion processing unit 112, a halftone processing unit 113, and a rasterization processing unit 114. The image processing system includes a color filter processing unit 112, a halftone processing unit 113, and a rasterization processing unit 114.

[0014] Fig. 2 is a flowchart showing the steps of a printing method performed by the printing device 1. In Fig. 2, first, in a resolution conversion processing step S1, the processing unit 11 of the image processing device 10 functions as a resolution conversion processing unit 111, and performs processing to convert the resolution (i.e., the number of pixels per unit length) of the input image data 122, which is RGB image data, into a resolution that can be printed by the printer 20.

[0015] Next, in a color conversion processing step S2, the processing unit 11 functions as a color conversion processing unit 112, and converts the resolution-converted input image data 122 into multi-tone data of multiple ink colors that can be used by the printer 20, while referring to a color conversion table LUT stored in the storage unit 12. This multi-tone data is stored in the storage unit 12 as image data 123. The number of gradations of the image data 123 is, for example, 256, and each pixel of the image data 123 has a gradation value of 0 to 255.

[0016] Next, in a halftone processing step S3, the processing unit 11 functions as a halftone processing unit 113 and converts the image data 123 into image data 124 with a smaller number of gradations. In this embodiment, the halftone processing unit 113 uses a dither mask DM stored in the storage unit 12 to perform halftone processing to generate image data 124 that determines whether or not to form a dot at each of the multiple pixels that make up the output image, based on the gradation values ​​of the original image corresponding to the image data 123. The image data 124 is stored in the storage unit 12. If the printer 20 can form only one size dot, the halftone processing is a binary process that determines whether or not to form a dot, and the image data 124 has two gradations. If the printer 20 can form only two types of dots (small and large), the halftone processing is a ternary process that determines whether or not to form a dot, and the image data 124 has three gradations. If the printer 20 can form only three types of ink dots (small, medium, and large), the halftone processing is a quaternary process that determines whether or not to form a dot, and the image data 124 has four gradations. In the following description, it is assumed that each head module 41 is capable of forming one type of dot, and that the image processing device 10 performs binarization processing as halftone processing. Details of halftone processing will be described later.

[0017] Next, in a rasterization process step S4, the processing unit 11 functions as a rasterization processing unit 114, rearranges the halftone processed image data 124 in the data order to be transferred to the printer 20, and outputs the final print data PD to the printer 20. The print data PD includes raster data indicating the dot recording status during each main scan, and data indicating the sub-scan feed amount.

[0018] Finally, in an output image formation step S5, the printer 20 forms an output image on the medium P based on the print data PD. The print data PD corresponds to image data 124 that is the result of the halftone process. Therefore, the printer 20 forms an output image on the medium P by ejecting liquid from multiple heads based on the results of the halftone process.

[0019] 1, the storage unit 12 has a ROM (Read Only Memory) and a RAM (Random Access Memory), neither of which is shown. The ROM stores various programs such as an image processing program 121, a color conversion table LUT, a dither mask DM, and other predetermined data, while the RAM stores input image data 122 acquired via the communication unit 13. The RAM is also used as a working area for the processing unit 11, and stores programs and data read from the ROM, data input from the operation unit 14, image data 123, 124 generated by the processing unit 11, and the like.

[0020] The communication unit 13 performs various controls to establish data communication between the processing unit 11 and the external device 3. The communication unit 13 also acquires input image data 122 from the external device 3 and stores it in the storage unit 12.

[0021] The operation unit 14 is an input device configured with operation keys, button switches, etc., and outputs an operation signal to the processing unit 11 in response to an operation by a user.

[0022] The display unit 15 is a display device configured by an LCD (Liquid Crystal Display) or the like, and displays various images based on display signals output from the processing unit 11. The display unit 15 may be provided with a touch panel that functions as the operation unit 14. For example, the display unit 15 displays information relating to various states of the image processing device 10.

[0023] At least part of the resolution conversion processing unit 111, color conversion processing unit 112, halftone processing unit 113, and rasterization processing unit 114 may be realized by dedicated hardware. Also, part of the information stored in the storage unit 12, and part of the resolution conversion processing unit 111, color conversion processing unit 112, halftone processing unit 113, and rasterization processing unit 114 may be provided in the printer 20. For example, the printer 20 may receive image data that has not been halftoned from the image processing device 10, perform halftoning, and then perform printing.

[0024] 1-2. Printer configuration Next, the configuration of the printer 20 according to this embodiment will be described with reference to Figures 3 and 4. As shown in Figure 3, the printer 20 includes a head unit 40 that ejects droplets, a drive signal generation unit 50 that drives the head unit 40, a transport mechanism 70 that transports the printing medium P, and a control unit 60 that executes various processes.

[0025] The head unit 40 includes M head modules 41. In this embodiment, M is a natural number greater than or equal to four, but M may be 1, meaning there may be one head module 41. The drive signal generation unit 50 generates and outputs a drive signal Vin for driving the head unit 40. The transport mechanism 70 changes the relative position of the medium P with respect to the head unit 40. The control unit 60 controls the operation of each unit of the printer 20, such as the head unit 40 and the drive signal generation unit 50.

[0026] As shown in FIG. 4 , in this embodiment, the printer 20 is a line printer that ejects droplets from the head unit 40 onto a medium P transported by a transport mechanism 70 to form an image on the medium P. In other words, the head unit 40 is a line head. As indicated by the arrows X, Y, and Z in FIG. 4 , in the following description, the first direction in which the head module 41 of the head unit 40 ejects liquid is referred to as the Z direction, the second direction in which the medium P is transported and perpendicular to the Z direction is referred to as the X direction, and the third direction perpendicular to the Z direction and the X direction is referred to as the Y direction. Regarding the X direction, the direction from upstream to downstream of the medium P is referred to as the +X direction. Regarding the Y direction, the direction from the right side (the far side of the page) to the left side (the near side of the page) of the transported medium P as viewed from the +X direction is referred to as the +Y direction. Regarding the Z direction, the direction from the head unit 40 toward the medium P is referred to as the +Z direction. The -X direction, -Y direction, and -Z direction are the opposite directions of the +X direction, +Y direction, and +Z direction, respectively. These directions will also be indicated appropriately in other figures as necessary. Since the medium P moves in the +X direction relative to the head unit 40, the ink dots formed on the medium P are aligned sequentially from the downstream side to the upstream side on the medium P as printing progresses.

[0027] The transport mechanism 70 that transports the medium P from the upstream side to the downstream side includes a transport motor 71 that serves as a drive source for transport, and a motor driver 72 that drives the transport motor 71. 4, the transport mechanism 70 includes a platen 77 provided below the head unit 40 (in the +Z direction in FIG. 3), transport rollers 73 and 74 that rotate when a transport motor 71 is activated, and guide rollers 75 and 76 that follow the rotation of the transport rollers 73 and 74. The medium P is transported in the +X direction in the figure (from upstream to downstream) along a transport path defined by the transport roller 73, guide roller 75, platen 77, guide roller 76, and transport roller 74.

[0028] The printer 20 includes a carriage 42, which houses a head unit 40 equipped with M head modules 41. In addition to the head unit 40, the carriage 42 also houses a drive signal generation unit 50 (not shown in FIG. 4) and four ink cartridges 43. The carriage 42 is located on the opposite side of the transport path of the medium P from the platen 77, i.e., above the platen 77 (in the -Z direction).

[0029] The four ink cartridges 43 are provided in one-to-one correspondence with the four colors of yellow, cyan, magenta, and black, and each ink cartridge 43 is filled with ink of the color corresponding to that ink cartridge 43. Each of the M head modules 41 receives a supply of ink from one of the four ink cartridges 43. Each head module 41 is filled with ink supplied from the ink cartridge 43 and ejects the filled ink as droplets toward the medium P. This makes it possible to eject ink of all four colors from the M head modules 41, thereby achieving full-color printing. The mechanism for ejecting droplets is well known, so a description thereof will be omitted.

[0030] The printer 20 according to this embodiment includes four ink cartridges 43 corresponding to the four colors of ink, but this is not necessarily limited to four colors of ink. The printer 20 may include three or fewer ink cartridges 43 corresponding to three or fewer colors or five or more colors of ink. The printer 20 may also include ink cartridges 43 filled with ink of a color different from the four colors, or may include ink cartridges 43 corresponding to only some of the four colors. In other words, the printer 20 may be capable of ejecting ink of one or more colors from the head module 41. Instead of being mounted on the carriage 42, each ink cartridge 43 may be provided in a different location on the printer 20, and ink may be supplied to each head module 41 of the head unit 40 via a tube or the like. The printer 20 may also print in a single color, for example, black. In that case, the head unit 40 may include a single head module 41.

[0031] In the printer 20, while droplets are being ejected from the head module 41, the medium P is transported in the +X direction by the transport mechanism 70 at a predetermined transport speed Vm. While the medium P is being transported, droplets are ejected from the nozzles N of the head module 41 to form ink dots on the medium P, thereby recording an image on the medium P. In other words, the image is recorded as a collection of ink dots formed by droplets ejected from each nozzle N arranged in the Y direction at the printing resolution. When focusing on one head module 41, the ink dots formed by droplets ejected from the nozzles N of that head module 41 are aligned in the width direction (Y direction) of the medium P. For this reason, in such line printers, the arrangement of ink dots along the width direction of the medium P is called a "raster."

[0032] The timing of transport of the medium P and the timing of ejection of droplets from each head module 41 of the head unit 40 are controlled by the control unit 60. Under the control of the control unit 60, each head module 41 ejects ink onto the medium P at the timing when the medium P is transported to a desired position on the platen 77 by the transport mechanism 70, thereby forming an image on the medium P.

[0033] 3, the control unit 60 forms an image on the medium P according to the image data 124 by controlling the drive signal generation unit 50, the transport mechanism 70, etc., based on image data 124 representing the on / off states of dots, which is included in the print data PD output from the image processing device 10. Specifically, the control unit 60 controls the motor driver 72 to drive the transport motor 71 so as to transport the long medium P in the transport direction (+X direction), and controls the drive signal generation unit 50 to control whether or not ink is ejected from each head module 41 and the timing of ink ejection. In this way, the control unit 60 adjusts the arrangement of ink dots formed by ink ejected onto the medium P, and executes a printing process that forms an image on the medium P based on the image data 124.

[0034] The control unit 60 includes a CPU 61 and a storage unit 62. The storage unit 62 temporarily stores data required for executing various processes, such as print data PD supplied from the image processing device 10. The storage unit 62 also includes a RAM (Random Access Memory) in which control programs for executing various processes, such as printing, are temporarily loaded, and a PROM, which is a type of non-volatile semiconductor memory, that stores control programs for controlling each part of the printer 20.

[0035] The CPU 61 of the control unit 60 generates signals such as a print signal SI and a drive waveform signal Com for controlling the operation of the drive signal generation unit 50 and driving each head module 41 based on various data such as image data 124 stored in the memory unit 62, and also generates various signals such as a control signal for controlling the operation of the motor driver 72 based on various data stored in the memory unit 62. In this way, the control unit 60 (CPU 61) generates various signals such as the print signal SI and drive waveform signal Com and supplies them to each part of the printer 20, thereby comprehensively controlling the operation of each part of the printer 20 and realizing various processes such as printing processing.

[0036] Halftone processing is a binary process indicating whether or not to form ink dots when droplets ejected from each head module 41 can form only one type of ink dot. If two types of ink dots (small, large) can be formed, halftone processing is a ternary process indicating none, small, and large. If three types of ink dots (small, medium, and large) can be formed, halftone processing is a quaternary process indicating none, small, medium, and large. If the ink cartridge 43 contains light ink such as light magenta or light cyan, halftone processing with even more gradations is possible. In this embodiment, each head module 41 can form only one type of dot, and the image processing device 10 performs binarization processing as halftone processing. Note that the CPU 61 may receive image data that has not been halftone processed from the image processing device 10 and perform halftone processing before printing.

[0037] The drive signal generation unit 50 generates drive signals Vin for driving each of the M head modules 41 included in the head unit 40, based on the print signal SI and the drive waveform signal Com supplied from the control unit 60. Details of the generation of these signals will not be explained here.

[0038] FIG. 5 is a perspective view of the head module 41, showing an example of the arrangement of nozzles N on the bottom surface of one head module 41, as seen from the +Z direction. Because the printer 20 is a line printer, the width of each head module 41 in the Y direction is greater than the width of the medium P, but in order to form a head module 41 that ejects droplets across this width, multiple short heads, each equipped with a predetermined number of nozzles N, are arranged so that they partially overlap in the X direction. For ease of understanding, FIG. 5 shows only the first head 41a, second head 41b, third head 41c, and fourth head 41d, each equipped with 32 nozzles N in the Y direction. The head 41 a, the second head 41 b, the third head 41 c, the fourth head 41 d, etc. are positioned and fixed to the head unit 40 by screws 45 .

[0039] The Y-direction pitch pt of the nozzles N included in each of these heads can be set appropriately depending on the printing resolution (dpi: dots per inch). The Y-direction resolution of the printer 20 depends on the configuration of the head unit 40, specifically the spacing between the nozzles N, while the X-direction resolution depends on the intervals between droplets ejected from the head module 41 and the speed at which the medium P is transported by the transport mechanism 70. These can be freely set depending on the design of the printer 20.

[0040] 5, the head module 41 has a plurality of heads including a first head 41a, a second head 41b, a third head 41c, and a fourth head 41d that eject ink (liquid), and the plurality of heads eject ink (liquid) based on the processing result of the halftone processing unit 113, thereby forming an output image DP on a medium P. The plurality of heads including the first head 41a, the second head 41b, the third head 41c, and the fourth head 41d are arranged in a line at regular intervals in the Y direction, starting from the first head 41a.

[0041] As shown in FIG. 5, when viewed from the X direction, the nozzles N included in the rear end (right end) of the first nozzle row NL1 of the first head 41a overlap with the nozzles N included in the front end (left end) of the second nozzle row NL2 of the second head 41b. Also, when viewed from the X direction, the nozzles N included in the rear end (right end) of the second nozzle row NL2 overlap with the nozzles N included in the front end (left end) of the third nozzle row NL3 of the third head 41c. Also, when viewed from the X direction, the nozzles N included in the rear end (right end) of the third nozzle row NL3 overlap with the nozzles N included in the front end (left end) of the fourth nozzle row NL4 of the fourth head 41d. In FIG. 5, two adjacent heads are arranged alternately, and the eight nozzles N at the ends of each nozzle row are arranged to overlap when viewed from the X direction. In an actual head module 41, the number of nozzles N in each head is several hundred, and the overlap of the nozzles N between two adjacent heads may be more than one hundred.

[0042] In the printer 20, an output image DP is formed on the medium P by ejecting droplets from each nozzle N of the head module 41 to form ink dots on the medium P while the medium P is transported by the transport mechanism 70. In other words, the output image DP is formed as a collection of ink dots formed by droplets ejected from each nozzle N arranged in the Y direction. Therefore, the output image DP includes an independent region L1 where multiple dots are formed only by ink ejected from the first head 41a, and a mixed region LA1 where multiple dots are formed by ink ejected from both the first head 41a and the second head 41b. The output image DP also includes an independent region L2 where multiple dots are formed only by ink ejected from the second head 41b, and a mixed region LA2 where multiple dots are formed by ink ejected from both the second head 41b and the third head 41c. The output image also includes a single region L3 where multiple dots are formed only by ink ejected from the third head 41c, and a mixed region LA3 where multiple dots are formed by ink ejected from the third head 41c and ink ejected from the fourth head 41d. In the output image DP, the arrangement of ink dots along the width direction of the medium P is called a "raster."

[0043] In the single areas L1, L2, and L3, the interval between dots formed on the medium P is equal to the pitch pt between two adjacent nozzles N, and the dot interval does not fluctuate. For example, if the maximum print resolution is 720 dpi, the pitch pt is 25.4 mm / 720 ≒ 35 μm. In contrast, in the mixed area LA1, dots formed by the first head 41a and dots formed by the second head 41b are mixed, so the dot formation positions In Fig. 5, there is a misalignment Δd between the nozzles N of the first head 41a and the nozzles N of the second head 41b. In Fig. 5, this misalignment Δd is depicted as being smaller than the pitch pt between two adjacent nozzles N, but depending on the mechanical mounting accuracy of the first head 41a and the second head 41b, the misalignment Δd may be several times larger than the nozzle pitch pt. ​​Also, although Fig. 5 depicts a misalignment Δd in the Y direction, misalignment in the X direction may also occur.

[0044] 1-3. Halftone processing The following describes halftone processing for generating dot data, that is, image data 124. Halftone processing is performed, for example, by an ordered dither method using a dither mask DM that provides a dot arrangement with excellent dispersion.

[0045] Fig. 6 is a conceptual diagram illustrating a portion of the dither mask DM. As shown in Fig. 6, the dither mask DM stores threshold values ​​selected evenly from a range of gradation values ​​from 1 to 255 for a total of n x m elements, including n elements in the arrangement direction of the nozzles N (Y direction, hereinafter also referred to as the main scanning direction) and m elements in the direction intersecting the arrangement direction of the nozzles N (X direction, hereinafter also referred to as the sub-scanning direction). The dither mask DM is created in advance and stored in the storage unit 12.

[0046] FIG. 7 is an explanatory diagram illustrating the concept of dot formation using a dither mask DM. For convenience of illustration, only some elements are shown. To determine whether or not to form a dot, as shown in FIG. 7, the tone values ​​of the image data are compared with the thresholds stored at the corresponding locations in the dither mask DM. If the tone values ​​of the image data are greater than the thresholds stored in the dither mask DM, dots are formed; if the tone values ​​of the image data are smaller, dots are not formed. The hatched pixels in the diagram indicate pixels where dots will be formed. Using a dither mask DM in this way allows the simple process of comparing the tone values ​​of the image data with the thresholds set in the dither mask DM to determine whether or not to form a dot for each pixel, thereby enabling rapid tone number conversion processing. Furthermore, once the tone values ​​of the image data are determined, whether or not a dot is formed at each pixel is determined solely by the thresholds set in the dither mask DM. As is clear from this, with the ordered dither method, the dot formation status and the dispersion of the formed dots can be controlled by the storage locations of the thresholds set in the dither mask DM.

[0047] As described above, in the printer 20 of this embodiment, the output image includes single areas where only a single head is involved in dot formation, and mixed areas where two heads are involved in dot formation. In the example shown in Figure 5, in the single area L1, dots are formed only by the first head 41a, in the mixed area LA1, dots are formed by the first head 41a and the second head 41b, and in the single area L2, dots are formed only by the second head 41b. To form dots in each raster, the first head 41a is always used in the single area L1, and the second head 41b is always used in the single area L2, but in the mixed area LA1, either the first head 41a or the second head 41b can be used.

[0048] For example, half of the pixels included in the mixed region may have dots formed by one head, and the remaining half may have dots formed by the other head.

[0049] As mentioned above, the first head 41a and the second head 41b are positioned and fixed by screws 45 or the like, and therefore, as shown in FIG. 5, there is a misalignment Δd in the Y direction between the nozzles N of the first head 41a and the nozzles N of the second head 41b. Therefore, in the mixed area LA1, the dot formation positions are shifted, and therefore, if a dither mask DM in which the arrangement of threshold values ​​used in halftone processing by the dither method is simply made to have blue noise characteristics is used, there is a risk of a decrease in the granularity of the image and fluctuations in density. On the other hand, since the nozzle pitch pt of the first head 41a and the second head 41b is constant, in the single area L1 and the single area L2, the dot shapes are As a result, there is a large difference in graininess and density between the single regions L1, L2 and the mixed region LA2, which can cause a difference in the appearance of the image between the single regions L1, L2 and the mixed region LA1, resulting in a decrease in the quality of the output image.

[0050] Therefore, in this embodiment, in order to reduce the difference in graininess and density between the single-pixel region and the mixed-pixel region, the output image is virtually divided into a first pixel group and a second pixel group, and the characteristics of the distribution of pixels on which dots are formed in the first pixel group and the characteristics of the distribution of pixels on which dots are formed in the second pixel group are assumed to have no correlation in terms of dispersion. "No correlation in pixel distribution" means that the dot arrangement in one pixel group is not referenced in determining the dot arrangement in the other pixel group. Note that the two characteristics may be made to have no correlation only when the input tone value of the original image is equal to or greater than a predetermined intermediate value. This is because when the input tone value is small, the dots are originally sufficiently far apart, and dot overlap due to misalignment does not occur.

[0051] In a mixed region, pixels on which dots are formed by one head are included in a first pixel group, and pixels on which dots are formed by the other head are included in a second pixel group. Furthermore, multiple pixels included in a single region are divided, for example, half into the first pixel group and half into the second pixel group.

[0052] The distribution of pixels in the first pixel group on which dots are formed may have blue noise characteristics or green noise characteristics, and the distribution of pixels in the second pixel group on which dots are formed may have blue noise characteristics or green noise characteristics. By having the distribution of pixels on which dots are formed have blue noise characteristics or green noise characteristics, the dispersibility of the dot arrangement can be increased, particularly in the frequency range to which the human eye is highly sensitive, thereby improving the granularity of the output image and increasing the quality of the output image.

[0053] In other words, if the distribution of pixels on which dots are formed in the first pixel group and the second pixel group respectively has blue noise characteristics or green noise characteristics, and if the distribution of pixels on which dots are formed in the first pixel group and the second pixel group respectively is not correlated, then even if the dot formation position shifts in either the X direction or the Y direction in the mixed region, the reduction in granularity and fluctuations in density can be suppressed, and the quality of the output image can be improved.

[0054] Furthermore, when the separation distance between a first pixel selected from the first pixel group and a second pixel selected from the second pixel group is at least equal to or less than the expected deviation between the two pixel groups, the probability of simultaneous dot formation on a pair of the first pixel and the second pixel may be set to approximate a value determined in correspondence with the square of the input tone value. This reduces variations in overlapping of the formed dots and reduces differences in density unevenness in the image, even if there is a difference in the deviation between the formation positions of dots formed corresponding to the first pixel group and dots formed corresponding to the second pixel group in at least a portion of the output image. Note that ensuring that the dot formation positions of the first pixel group and the second pixel group are not correlated is a sufficient condition for this requirement. If there is no correlation between two pixels, the probability of simultaneous dot formation on a pair of the first pixel and the second pixel is the product of the dot formation probabilities of both, i.e., the square of the input tone value if both have the same input tone value. The method of approximating the probability that a dot will be formed simultaneously on a pair of a first pixel and a second pixel to a value determined in accordance with the square of the input tone value is disclosed in JP 2012-204939 A and elsewhere, and as this is a well-known technique, a detailed explanation will be omitted.

[0055] Also, for example, the dither mask DM1 consisting of threshold values ​​at positions corresponding to each pixel of the first pixel group and the dither mask DM2 consisting of threshold values ​​at positions corresponding to each pixel of the second pixel group are set to blue noise characteristics and green noise characteristics, respectively, so that these characteristics are not correlated. For example, the dither mask DM1 for the first pixel group and the dither mask DM2 for the second pixel group may be created separately, using different initial settings.

[0056] In the following, the division of all pixels contained in the output image into groups based on which head will form dots will be referred to as "actual grouping." Furthermore, the virtual division of all pixels contained in the output image into first and second pixel groups will be referred to as "virtual grouping." Actual and virtual grouping are performed according to predetermined patterns.

[0057] FIG. 8 is a diagram showing an example of actual grouping and virtual grouping for an output image. In FIG. 8, the upper row schematically shows a portion of the first nozzle array NL1 of the first head 41a and a portion of the second nozzle array NL2 of the second head 41b shown in FIG. 5, with 16 nozzles N from the right end of the first nozzle array NL1 indicated by black circles and 16 nozzles N from the left end of the second nozzle array NL2 indicated by white circles. In FIG. 8, PxR in the middle row shows an actual grouping pattern for a plurality of pixels on which dots are formed by these nozzles N, and PxI in the lower row shows a virtual grouping pattern for the plurality of pixels. In the pattern PxR, pixels on which dots are formed by the first head 41a are indicated by black circles, and pixels on which dots are formed by the second head 41b are indicated by white circles. In the pattern PxI, pixels included in the first pixel group are indicated by black circles, and pixels included in the second pixel group are indicated by white circles.

[0058] In the example of FIG. 8, as shown by pattern PxR, in the mixed region LA1, pixels on which dots are formed by the first head 41a and pixels on which dots are formed by the second head 41b are randomly arranged. Furthermore, as shown by pattern PxI, in the mixed region LA1, pixels included in the first pixel group and pixels included in the second pixel group are randomly arranged in the same pattern as pattern PxR. That is, in the mixed region LA1, each pixel on which dots are formed by the first head 41a is included in the first pixel group, and each pixel on which dots are formed by the second head 41b is included in the second pixel group. Furthermore, as shown by pattern PxI, in the single regions L1 and L2, pixels included in the first pixel group and pixels included in the second pixel group are randomly arranged. That is, in the example of FIG. 8, the virtual grouping pattern PxI randomly arranges pixels included in the first pixel group and pixels included in the second pixel group, regardless of whether the region is a single region or a mixed region.

[0059] Incidentally, since it is not realistic to create a large-sized dither mask DM corresponding to the total number of pixels of the output image, it is common to create a relatively small-sized dither mask DM and perform halftone processing while shifting the dither mask DM in the Y direction (main scanning direction) and X direction (sub-scanning direction) relative to the image data. If, as in the past, the size of the dither mask DM in the Y direction were an appropriate size such as a power of 2, the positional relationship between each of the multiple mixed areas and the dither mask DM would differ from one another, causing a shift in the positional relationship between the dither mask DM and each corresponding pixel for each mixed area, and there is a possibility that deterioration in the quality of the output image will not be sufficiently suppressed.

[0060] Therefore, in this embodiment, in order to prevent deviation in the positional relationship between the dither mask DM and each corresponding pixel for each mixed area, the number of elements in the Y direction of the dither mask DM is set to a predetermined value according to the Y direction length of the single area and the Y direction length of the mixed area. Fig. 9 shows an example of the relationship that must be satisfied between the Y direction length of the dither mask DM and the Y direction lengths of the single area and the mixed area.

[0061] As shown in FIG. 9, the mixed area LA1 is formed by the ink (liquid) ejected from at least some of the nozzles N included in the rear end (right end) of the first nozzle row NL1 of the first head 41a. , and a region where multiple dots are formed by ink (liquid) ejected from at least some of the multiple nozzles N included in the front end (left end) of the second nozzle row NL2 of the second head 41b. The single region L2 is a region where multiple dots are formed by ink (liquid) ejected from the multiple nozzles N included between the front end (left end) and rear end (right end) of the second nozzle row NL2. At this time, the length of the mixed region LA1 in the Y direction is defined as a first length d Y1 The length of the independent region L2 is the second length d Y2 Then, the number of elements in the Y direction of the dither mask DM is the first length d Y1 The number of pixels corresponding to n Y1 and the second length d Y2 The number of pixels corresponding to n Y2 The total number of Y1 +n Y2 It is N times or 1 / N times (N is a natural number) of

[0062] In the example in Figure 9, n Y1 =8, n Y2 = 16, the number of elements in the Y direction of the dither mask DM is N times or 1 / N times 24. As shown in FIG. 9, for example, the number of elements in the Y direction of the dither mask DM is n Y1 +n Y2 For example, if the number of elements in the Y direction of the dither mask DM is n Y1 +n Y2 If the number of elements in the Y direction of the dither mask DM is 1, 1 / 2, or 1 / 3 of the original number, the positional relationship between the dither mask DM and the corresponding pixels in the mixed areas LA1 and LA2 will be the same, and the dither mask DM optimized for the mixed areas LA1 and LA2 will be applied, so the quality of the output image will not be reduced. Y1 +n Y2When the pixel density is twice as large as the pixel density of the mixed areas LA1 and LA2, the positional relationship between the dither mask DM and the corresponding pixels is different for the mixed areas LA1 and LA2. However, the optimized dither mask DM1 is applied to each of the mixed areas LA1 and LA2, so the quality of the output image does not decrease.

[0063] 1-4.Effects As described above, in the printing device 1 according to the first embodiment, all pixels in an output image are virtually grouped into a first pixel group and a second pixel group. The distribution characteristics of pixels on which dots are formed in the first pixel group and the distribution characteristics of pixels on which dots are formed in the second pixel group are assumed to have no correlation in terms of dispersion. In a mixed region where dots are formed by two heads, the pixels on which dots are formed by one head are included in the first pixel group, and the pixels on which dots are formed by the other head are included in the second pixel group. This minimizes the reduction in graininess and fluctuations in density even if the dot formation positions are misaligned, thereby improving the quality of the output image. Meanwhile, in a single region where dots are formed by a single head, the dot formation positions are not misaligned. However, by dividing the pixels in the single region into half each into the first pixel group and the second pixel group, the image quality of the single region is slightly degraded. As a result, the difference in graininess and density between the single region and the mixed region is reduced.

[0064] Furthermore, in the printing device 1 according to the first embodiment, the number of elements in the dither mask DM in the main scanning direction (Y direction) is N times or 1 / N times the total number of pixels corresponding to the length of the mixed area in the main scanning direction and the number of pixels corresponding to the length of the single area in the main scanning direction, so even if the dither mask DM is repeatedly used in the main scanning direction in halftone processing, the relative positional relationship between each mixed area and the dither mask DM does not change. Therefore, according to the printing device 1 according to the first embodiment, the expected effect of the dither mask DM is exerted in the halftone processed image, so that the quality of the output image is less likely to deteriorate.

[0065] Furthermore, in the printing device 1 according to the first embodiment, the multiple pixels that make up the output image are divided into a first pixel group and a second pixel group, and the distribution of pixels in the first pixel group where dots are formed and the distribution of pixels in the second pixel group where dots are formed each have blue noise characteristics or green noise characteristics, respectively, which increases the dispersion of dots in the output image in the frequency range where the human eye is highly sensitive. As a result, the printing device 1 according to the first embodiment prevents a decrease in graininess in the output image, thereby improving image quality.

[0066] 2. Second embodiment In the following, in the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals. The description that overlaps with the first embodiment will be omitted or simplified, and the differences from the first embodiment will be mainly described.

[0067] In the second embodiment, the actual grouping pattern is a pattern in which the ratio of the number of pixels on which dots are formed by one head to the number of pixels on which dots are formed by the other head in each column of the mixed area gradually decreases or increases in the main scanning direction (Y direction). Figure 10 shows an example of an actual grouping pattern in the second embodiment. Note that in Figure 10, the same elements as in Figure 8 are assigned the same symbols.

[0068] For example, in the example of FIG. 13, in the real grouping pattern PxR, for each pixel row (each column) in the mixed area LA1 where multiple pixels are lined up in the X direction, the number of pixels on which dots are formed by the first head 41a gradually increases in the +Y direction, and the number of pixels on which dots are formed by the second head 41b gradually decreases in the +Y direction. On the other hand, the virtual grouping pattern PxI is a random pattern, and in each column of the mixed area LA1, the number of pixels in the first pixel group and the number of pixels in the second pixel group are the same or the difference is 2. Therefore, for each column of the mixed area LA1, if the number of pixels on which dots are formed by the first head 41a is fewer than the number of pixels in the first pixel group, each pixel on which dots are formed by the first head 41a is included in the first pixel group. In such a column, the number of pixels on which dots are formed by the second head 41b is greater than the number of pixels in the second pixel group, so each pixel on which dots are formed by the second head 41b is included in either the first pixel group or the second pixel group. Similarly, for each column in the mixed area LA1, if the number of pixels on which dots are formed by the second head 41b is fewer than the number of pixels in the second pixel group, then the pixels on which dots are formed by the second head 41b are included in the second pixel group. In such a column, the number of pixels on which dots are formed by the first head 41a is greater than the number of pixels in the first pixel group, so the pixels on which dots are formed by the first head 41a are included in either the first pixel group or the second pixel group.

[0069] 10, in the column at one end of the mixed area LA1 close to the single area L1, the proportion of pixels on which dots are formed by the first head 41a is close to 100%, and the proportion of pixels on which dots are formed by the second head 41b is close to 0%. On the other hand, in the column at the other end of the mixed area LA1 close to the single area L2, the proportion of pixels on which dots are formed by the first head 41a is close to 0%, and the proportion of pixels on which dots are formed by the second head 41b is close to 100%. Therefore, in the output image, the boundary between the mixed area LA1 and the single areas L1 and L2 becomes unclear and difficult to see, improving the image quality of the output image.

[0070] According to the printing device 1 according to the second embodiment described above, other effects similar to those of the first embodiment can be obtained.

[0071] 3. Third embodiment In the following, for the third embodiment, components similar to those in the first or second embodiment are given the same symbols, and explanations that overlap with those in the first or second embodiment are omitted or simplified, and the differences from the first and second embodiments are mainly described.

[0072] As mentioned above, it is possible that the misalignment Δd between the nozzles of multiple heads may become several times larger than the nozzle pitch pt, but in this embodiment, each head is provided with extra nozzles so that even in such cases, dots in some pixels of the output image are not missing.

[0073] For example, as shown in Figure 11, the first head 41a, the second nozzle row NL2 of the second head 41b, and the third nozzle row NL3 of the third head 41c each include 36 nozzles N, of which 32 nozzles N are actually used nozzles that are used to form dots, and the remaining 4 nozzles N are surplus nozzles that are not used to form dots. Liquid is ejected from the nozzles in use, but no liquid is ejected from the four redundant nozzles.

[0074] 11 shows the relationship between the positional deviation Δd of the second head 41b relative to the first head 41a and the third head 41c and the actually used nozzles and the surplus nozzles, with the first head 41a and the third head 41c being assumed to be non-misaligned. In FIG. 11, the actually used nozzles that eject liquid are indicated by white circles, and the surplus nozzles that do not eject liquid are indicated by black circles. In the first nozzle row NL1 and the third nozzle row NL3, the two nozzles N at each end are surplus nozzles, and the other 32 nozzles N are actually used nozzles.

[0075] 11, C1 corresponds to the case where there is no misalignment of the second head 41b. In this case, two nozzles N on each end of the second nozzle row NL2 become surplus nozzles, and the other 32 nozzles N become actually used nozzles. C2 corresponds to the case where the arrangement of the second head 41b is misaligned by two nozzles in the -Y direction. In this case, four nozzles N on the left end of the second nozzle row NL2 become surplus nozzles, and the other 32 nozzles N become actually used nozzles. C3 corresponds to the case where the arrangement of the second head 41b is misaligned by one nozzle in the -Y direction. In this case, three nozzles N on the left end and one nozzle N on the right end of the second nozzle row NL2 become surplus nozzles, and the other 32 nozzles N become actually used nozzles. C4 corresponds to the case where the arrangement of the second head 41b is shifted by one nozzle in the +Y direction, in which case the one nozzle N on the left end and the three nozzles N on the right end of the second nozzle row NL2 become surplus nozzles, and the other 32 nozzles N become actually used nozzles. C5 corresponds to the case where the arrangement of the second head 41b is shifted by two nozzles in the +Y direction, in which case the four nozzles N on the right end of the second nozzle row NL2 become surplus nozzles, and the other 32 nozzles N become actually used nozzles.

[0076] In any of the cases C1 to C5, the second nozzle row NL2 includes surplus nozzles at at least one of the leading and trailing ends that do not eject liquid. Of the 32 actually-used nozzles in the second nozzle row NL2, the leftmost 8 nozzles N are responsible for forming dots in the mixed region LA1, the rightmost 8 nozzles N are responsible for forming dots in the mixed region LA2, and the remaining 16 nozzles N are responsible for forming dots in the single region L2.

[0077] Therefore, the mixed area LA1 is an area where multiple dots are formed by ink (liquid) ejected from eight actually used nozzles that are at least a part of the multiple nozzles N included in the rear end (right end) of the first nozzle row NL1 and ink (liquid) ejected from eight actually used nozzles that are at least a part of the multiple nozzles N included in the front end (left end) of the second nozzle row NL2. Also, the single area L2 is an area where multiple dots are formed by ink (liquid) ejected from 16 actually used nozzles that are the multiple nozzles N included between the front end (left end) and rear end (right end) of the second nozzle row NL2. The length of the mixed area LA1 in the Y direction is defined as a first length d Y1 The length of the independent region L2 is the second length d Y2 Then, in the third embodiment, as in the first embodiment, the number of elements in the Y direction of the dither mask DM is the first length d Y1 The number of pixels corresponding to n Y1 and the second length d Y2 The number of pixels corresponding to n Y2 The total number of Y1 +n Y2 It is set to N times or 1 / N times (N is a natural number) of the

[0078] According to the printing device 1 of the third embodiment described above, each head has a surplus nozzle, so that in a mixed region where dots are formed by two heads, even if the misalignment in arrangement between the nozzles N of the two heads is greater than the nozzle pitch, it is possible to prevent dots from being missing in the output image. In addition, the printing device 1 of the third embodiment can achieve the same effects as the first or second embodiment.

[0079] 4. Variations In the above-described embodiments, the nozzle row of each head is configured with a plurality of nozzles N aligned in a single row in the Y direction (main scanning direction), but it may be configured with a plurality of nozzles N aligned in two rows in the Y direction. 12, the first nozzle row NL1, the second nozzle row NL2, and the third nozzle row NL3 each have a configuration in which 32 nozzles N are arranged in two rows of 16 nozzles each in the Y direction. In this case, the first nozzle row NL1, the second nozzle row NL2, and the third nozzle row NL3 may each have a so-called staggered configuration in which the 16 nozzles N included in one row are shifted by half the nozzle pitch pt relative to the 16 nozzles N included in the other row. In this case, the mixed area LA1 is an area in which multiple dots are formed by ink (liquid) ejected from the eight nozzles N (four nozzles × two rows) included at the rear end (right end) of the first nozzle row NL1 and the eight nozzles N (four nozzles × two rows) included at the front end (left end) of the second nozzle row NL2. In addition, the single region L2 is an area where multiple dots are formed by ink (liquid) ejected from 16 nozzles N (8 nozzles x 2 rows) included between the front end (left end) and rear end (right end) of the second nozzle row NL2.

[0080] Furthermore, the nozzle array of each head may be configured with multiple nozzles N arranged diagonally with respect to the Y direction (main scanning direction). For example, in the example shown in FIG. 13, the first nozzle array NL1, the second nozzle array NL2, and the third nozzle array NL3 each have 32 nozzles N arranged in a row at an angle of 45 degrees with respect to the Y direction. In this case, the mixed area LA1 is an area where multiple dots are formed by ink (liquid) ejected from the eight nozzles N included in the rear end (right end) of the first nozzle array NL1 and the eight nozzles N included in the front end (left end) of the second nozzle array NL2. Furthermore, the single area L2 is an area where multiple dots are formed by ink (liquid) ejected from the 16 nozzles N included between the front end (left end) and rear end (right end) of the second nozzle array NL2.

[0081] Furthermore, the nozzle arrays of each head may be configured with multiple nozzles N arranged in two rows diagonally with respect to the Y direction (main scanning direction). For example, in the example shown in FIG. 14, the first nozzle array NL1, the second nozzle array NL2, and the third nozzle array NL3 each have 32 nozzles N arranged in two rows of 16 nozzles each in a direction tilted 45° with respect to the Y direction. In this case, the mixed area LA1 is an area where multiple dots are formed by ink (liquid) ejected from eight nozzles N (four nozzles × two rows) included in the rear end (right end) of the first nozzle array NL1 and eight nozzles N (four nozzles × two rows) included in the front end (left end) of the second nozzle array NL2. The single area L2 is an area where multiple dots are formed by ink (liquid) ejected from 16 nozzles N (eight nozzles × two rows) included between the front end (left end) and rear end (right end) of the second nozzle array NL2.

[0082] In any of the examples of FIGS. 12, 13, and 14, the length of the mixed region LA1 in the Y direction is the first length d Y1 The length of the independent region L2 is the second length d Y2 Then, the number of elements in the Y direction of the dither mask DM is the first length d Y1 The number of pixels corresponding to n Y1 and the second length d Y2 The number of pixels corresponding to n Y2 The total number of Y1 +n Y2 The setting is N times or 1 / N times (N is a natural number) of the above. According to the printing device 1 according to these modifications, the same effects as any of the above embodiments can be obtained.

[0083] In addition, in the printing device 1 according to each of the above embodiments, a portion of the hardware configuration may be replaced with software (computer program), or at least a portion of the software configuration may be replaced with hardware. The software (computer program) may be stored on a computer-readable information storage medium. The information storage medium may be a storage device such as a flexible disk, a CD-ROM, various types of RAM or ROM, or a hard disk.

[0084] The present invention has substantially the same configuration as the configuration described in this embodiment, for example, functions, methods, and The present invention includes configurations that achieve the same results or have the same purpose and effect. The present invention also includes configurations that replace non-essential parts of the configurations described in this embodiment. The present invention also includes configurations that achieve the same effects or purposes as the configurations described in this embodiment. The present invention also includes configurations that add publicly known technology to the configurations described in this embodiment.

[0085] The above-described embodiment and modifications are merely examples, and the present invention is not limited to these. For example, the embodiments and modifications can be combined as appropriate.

[0086] The following can be derived from the above-described embodiment and modifications.

[0087] One aspect of the printing device is 1. A printing device for forming an output image on a medium corresponding to an original image, comprising: a halftone processing unit that uses a dither mask to determine whether or not to form a dot in each of a plurality of pixels that make up the output image based on an input tone value of the original image; a head unit having a plurality of heads including a first head, a second head, and a third head, the plurality of heads ejecting liquid based on a processing result of the halftone processing unit, thereby forming the output image on the medium; Equipped with a direction in which the plurality of heads eject liquid with respect to the medium is defined as a first direction; a direction in which the medium is transported and which is perpendicular to the first direction is defined as a second direction; a direction perpendicular to the first direction and the second direction is a third direction; the plurality of heads are arranged side by side in the third direction, When viewed from the second direction, a plurality of nozzles included in a rear end portion of a first nozzle row of the first head and a plurality of nozzles included in a front end portion of a second nozzle row of the second head overlap with each other, When viewed from the second direction, a plurality of nozzles included in a rear end portion of the second nozzle row and a plurality of nozzles included in a front end portion of a third nozzle row of the third head overlap with each other, The output image is a mixed region in which a plurality of dots are formed by liquid ejected from at least some of the plurality of nozzles included in the rear end portion of the first nozzle row and liquid ejected from at least some of the plurality of nozzles included in the front end portion of the second nozzle row; a single region in which a plurality of dots are formed by liquid ejected from a plurality of nozzles included between the front end and the rear end of the second nozzle row, the length of the mixed region in the third direction is a first length, the length of the single region in the third direction is a second length; The number of elements in the third direction of the dither mask is N times or 1 / N times (N is a natural number) the total number of pixels corresponding to the first length and the second length.

[0088] In this printing device, the number of elements in the dither mask in the third direction is N times or 1 / N times the total number of pixels corresponding to the length of the mixed area in the third direction and the number of pixels corresponding to the length of the single area in the third direction, so even if the dither mask is used repeatedly in the third direction in halftone processing, the relative positional relationship between each mixed area and the dither mask does not change. Therefore, with this printing device, the expected effect of the dither mask is exerted in the halftone processed image, so the quality of the output image is less likely to deteriorate.

[0089] In one aspect of the printing device, the plurality of pixels constituting the output image are divided into a first pixel group and a second pixel group; a distribution of pixels in which dots are formed in the first pixel group has blue noise characteristics or green noise characteristics, The distribution of pixels in the second pixel group on which dots are formed may have blue noise characteristics or green noise characteristics.

[0090] In this printing device, the multiple pixels that make up the output image are divided into a first pixel group and a second pixel group, and the distribution of pixels in the first pixel group where dots are formed and the distribution of pixels in the second pixel group where dots are formed each have blue noise characteristics or green noise characteristics, so the output image can have improved dot dispersion in the frequency range where the human eye is highly sensitive.As a result, this printing device can suppress a decrease in graininess in the output image and improve image quality.

[0091] In one aspect of the printing device, the plurality of pixels constituting the output image are divided into a first pixel group and a second pixel group; When the distance between a first pixel selected from the first pixel group and a second pixel selected from the second pixel group is at least equal to or less than an expected deviation between the two pixel groups, the probability that dots will be formed simultaneously on the pair of the first pixel and the second pixel may approximate a value determined in correspondence to the square of the input gradation value.

[0092] According to this printing device, even if there is a difference in the misalignment of the formation positions of the dots formed corresponding to the first pixel group and the dots formed corresponding to the second pixel group in at least a part of the output image, the variation in the overlap of the formed dots is suppressed, and the difference in density unevenness of the image is suppressed.

[0093] In one aspect of the printing device, The second nozzle row may include nozzles from which liquid is not ejected at at least one of the leading end and the trailing end.

[0094] This printing device can prevent missing dots in the output image even if the misalignment between the nozzles of the first head and the nozzles of the second head or the misalignment between the nozzles of the second head and the nozzles of the third head is greater than the nozzle pitch.

[0095] In one aspect of the printing device, The head unit may be a line head.

[0096] In one aspect of the printing device, the plurality of pixels constituting the output image are divided into a first pixel group and a second pixel group; For each pixel column in which a plurality of pixels are aligned in the second direction in the mixed region, when the number of pixels on which dots are formed by the first head is smaller than the number of pixels in the first pixel group, each pixel on which dots are formed by the first head is included in the first pixel group, When the number of pixels on which dots are formed by the second head is smaller than the number of pixels in the second pixel group, each pixel on which dots are formed by the second head may be included in the second pixel group.

[0097] With this printing device, in each pixel row in the mixed area, the proportion of pixels on which dots are formed by the second head included in the first pixel group and the proportion of pixels on which dots are formed by the first head included in the second pixel group are reduced, making it easier for the dither mask to achieve the expected effect in halftone-processed images and less likely to result in a decrease in the quality of the output image.

[0098] One aspect of the printing method is 1. A printing method for forming an output image on a medium corresponding to an original image, comprising: using a dither mask, performing halftone processing to determine whether or not to form a dot in each of a plurality of pixels that make up the output image based on the input tone value of the original image; forming the output image on the medium by ejecting liquid from a plurality of heads including a first head, a second head, and a third head based on the result of the halftone processing; a direction in which the plurality of heads eject liquid with respect to the medium is defined as a first direction; a direction in which the medium is transported and which is perpendicular to the first direction is defined as a second direction; a direction perpendicular to the first direction and the second direction is a third direction; the plurality of heads are arranged side by side in the third direction, When viewed from the second direction, a plurality of nozzles included in a rear end portion of a first nozzle row of the first head and a plurality of nozzles included in a front end portion of a second nozzle row of the second head overlap with each other, When viewed from the second direction, a plurality of nozzles included in a rear end portion of the second nozzle row and a plurality of nozzles included in a front end portion of a third nozzle row of the third head overlap with each other, The output image is a mixed region in which a plurality of dots are formed by liquid ejected from at least some of the plurality of nozzles included in the rear end portion of the first nozzle row and liquid ejected from at least some of the plurality of nozzles included in the front end portion of the second nozzle row; a single region in which a plurality of dots are formed by liquid ejected from a plurality of nozzles included between the front end and the rear end of the second nozzle row, the length of the mixed region in the third direction is a first length, the length of the single region in the third direction is a second length; The number of elements in the third direction of the dither mask is N times or 1 / N times (N is a natural number) the total number of pixels corresponding to the first length and the second length.

[0099] In this printing method, the number of elements in the dither mask in the third direction is N times or 1 / N times the total number of pixels corresponding to the length of the mixed area in the third direction and the number of pixels corresponding to the length of the single area in the third direction, so even if the dither mask is used repeatedly in the third direction in halftone processing, the relative positional relationship between each mixed area and the dither mask does not change. Therefore, with this printing method, the expected effect of the dither mask is exerted in the halftone processed image, so the quality of the output image is less likely to deteriorate.

[0100] In one aspect of the printing method, the plurality of pixels constituting the output image are divided into a first pixel group and a second pixel group; a distribution of pixels in which dots are formed in the first pixel group has blue noise characteristics or green noise characteristics, The distribution of pixels in the second pixel group on which dots are formed may have blue noise characteristics or green noise characteristics.

[0101] In one aspect of the printing method, the plurality of pixels constituting the output image are divided into a first pixel group and a second pixel group; When the distance between a first pixel selected from the first pixel group and a second pixel selected from the second pixel group is at least equal to or less than an expected deviation between the two pixel groups, the probability that dots will be formed simultaneously on the pair of the first pixel and the second pixel may approximate a value determined in correspondence to the square of the input gradation value.

[0102] In one aspect of the printing method, The second nozzle row may include nozzles from which liquid is not ejected at at least one of the leading end and the trailing end.

[0103] In one aspect of the printing method, The head unit having the plurality of heads may be a line head.

[0104] In one aspect of the printing method, the plurality of pixels constituting the output image are divided into a first pixel group and a second pixel group; For each pixel column in which a plurality of pixels are aligned in the second direction in the mixed region, when the number of pixels on which dots are formed by the first head is smaller than the number of pixels in the first pixel group, each pixel on which dots are formed by the first head is included in the first pixel group, When the number of pixels on which dots are formed by the second head is smaller than the number of pixels in the second pixel group, each pixel on which dots are formed by the second head may be included in the second pixel group. [Explanation of symbols]

[0105] 1...printing device, 3...external device, 10...image processing device, 11...processing unit, 12...storage unit, 13...communication unit, 14...operation unit, 15...display unit, 20...printer, 40...head unit, 41...head module, 41a...first head, 41b...second head, 41c...third head, 41d...fourth head, 42...carriage, 43...ink cartridge, 45...screw, 50...drive signal generating unit, 60...control unit, 61...CPU, 62...storage unit, 70...transport mechanism, 71...transport motor, 72...motor driver, 73, 74...transport roller, 75, 76...guide roller, 77...platen , 111...resolution conversion processing unit, 112...color conversion processing unit, 113...halftone processing unit, 114...rasterization processing unit, 121...image processing program, 122...input image data, 123...image data, 124...image data, DP...output image, L1, L2, L3...single area, LA1, LA2, LA3...mixed area, LUT...color conversion table, DM, DM1, DM2...dither mask, N...nozzle, NL1...first nozzle row, NL2...second nozzle row, NL3...third nozzle row, NL4...fourth nozzle row, P...medium, PxR...actual grouping pattern, PxI...virtual grouping pattern

Claims

1. 1. A printing device for forming an output image on a medium corresponding to an original image, comprising: a halftone processing unit that uses a dither mask to determine whether or not to form a dot in each of a plurality of pixels that make up the output image based on an input tone value of the original image; a head unit having a plurality of heads including a first head, a second head, and a third head, the plurality of heads ejecting liquid based on a processing result of the halftone processing unit, thereby forming the output image on the medium; Equipped with a direction in which the plurality of heads eject liquid onto the medium is defined as a first direction; a direction in which the medium is transported, the direction being perpendicular to the first direction, being a second direction; a direction perpendicular to the first direction and the second direction is a third direction; the plurality of heads are arranged in the third direction in order from the first head, When viewed from the second direction, a plurality of nozzles included in a rear end portion of a first nozzle row of the first head overlap with a plurality of nozzles included in a front end portion of a second nozzle row of the second head, When viewed from the second direction, a plurality of nozzles included in a rear end portion of the second nozzle row and a plurality of nozzles included in a front end portion of a third nozzle row of the third head overlap with each other, The output image is a mixed region in which a plurality of dots are formed by liquid ejected from at least some of the plurality of nozzles included in the rear end portion of the first nozzle row and liquid ejected from at least some of the plurality of nozzles included in the front end portion of the second nozzle row; a single region in which a plurality of dots are formed by liquid ejected from a plurality of nozzles included between the front end and the rear end of the second nozzle row, a length of the mixed region in the third direction is a first length; a length of the single region in the third direction is a second length; the number of elements in the third direction of the dither mask is N times or 1 / N times (N is a natural number) the total number of pixels corresponding to the first length and the second length; A printing device characterized by:

2. the plurality of pixels constituting the output image are divided into a first pixel group and a second pixel group; a distribution of pixels in which dots are formed in the first pixel group has blue noise characteristics or green noise characteristics, the distribution of pixels in which dots are formed in the second pixel group has blue noise characteristics or green noise characteristics; 2. The printing device according to claim 1.

3. the plurality of pixels constituting the output image are divided into a first pixel group and a second pixel group; when the separation distance between a first pixel selected from the first pixel group and a second pixel selected from the second pixel group is at least equal to or less than an expected amount of deviation between the two pixel groups, the probability that dots will be formed simultaneously on the pair of the first pixel and the second pixel approximates a value determined in correspondence with the square of the input tone value; 2. The printing device according to claim 1.

4. the second nozzle row includes nozzles from which liquid is not ejected at least one of the front end portion and the rear end portion; 2. The printing device according to claim 1.

5. The head unit is a line head.

2. The printing device according to claim 1.

6. the plurality of pixels constituting the output image are divided into a first pixel group and a second pixel group; For each pixel column in which a plurality of pixels are aligned in the second direction in the mixed region, when the number of pixels on which dots are formed by the first head is smaller than the number of pixels in the first pixel group, each pixel on which dots are formed by the first head is included in the first pixel group, When the number of pixels on which dots are formed by the second head is smaller than the number of pixels in the second pixel group, each pixel on which dots are formed by the second head is included in the second pixel group.

2. The printing device according to claim 1.

7. 1. A printing method for forming an output image on a medium corresponding to an original image, comprising: using a dither mask, performing halftone processing to determine whether or not to form a dot in each of a plurality of pixels that make up the output image based on the input tone value of the original image; forming the output image on the medium by ejecting liquid from a plurality of heads including a first head, a second head, and a third head based on the result of the halftone processing; a direction in which the plurality of heads eject liquid onto the medium is defined as a first direction; a direction in which the medium is transported, the direction being perpendicular to the first direction, being a second direction; a direction perpendicular to the first direction and the second direction is a third direction; the plurality of heads are arranged in the third direction in order from the first head, When viewed from the second direction, a plurality of nozzles included in a rear end portion of a first nozzle row of the first head overlap with a plurality of nozzles included in a front end portion of a second nozzle row of the second head, When viewed from the second direction, a plurality of nozzles included in a rear end portion of the second nozzle row and a plurality of nozzles included in a front end portion of a third nozzle row of the third head overlap with each other, The output image is a mixed region in which a plurality of dots are formed by liquid ejected from at least some of the plurality of nozzles included in the rear end portion of the first nozzle row and liquid ejected from at least some of the plurality of nozzles included in the front end portion of the second nozzle row; a single region in which a plurality of dots are formed by liquid ejected from a plurality of nozzles included between the front end and the rear end of the second nozzle row, a length of the mixed region in the third direction is a first length; a length of the single region in the third direction is a second length; the number of elements in the third direction of the dither mask is N times or 1 / N times (N is a natural number) the total number of pixels corresponding to the first length and the second length; A printing method characterized by:

8. the plurality of pixels constituting the output image are divided into a first pixel group and a second pixel group; a distribution of pixels in which dots are formed in the first pixel group has blue noise characteristics or green noise characteristics, the distribution of pixels in which dots are formed in the second pixel group has blue noise characteristics or green noise characteristics; 8. The printing method according to claim 7.

9. the plurality of pixels constituting the output image are divided into a first pixel group and a second pixel group; when the separation distance between a first pixel selected from the first pixel group and a second pixel selected from the second pixel group is at least equal to or less than an expected amount of deviation between the two pixel groups, the probability that dots will be formed simultaneously on the pair of the first pixel and the second pixel approximates a value determined in correspondence with the square of the input tone value; 8. The printing method according to claim 7.

10. the second nozzle row includes nozzles from which liquid is not ejected at least one of the front end portion and the rear end portion; 8. The printing method according to claim 7.

11. the head unit having the plurality of heads is a line head; 8. The printing method according to claim 7.

12. the plurality of pixels constituting the output image are divided into a first pixel group and a second pixel group; For each pixel column in which a plurality of pixels are aligned in the second direction in the mixed region, when the number of pixels on which dots are formed by the first head is smaller than the number of pixels in the first pixel group, each pixel on which dots are formed by the first head is included in the first pixel group, When the number of pixels on which dots are formed by the second head is smaller than the number of pixels in the second pixel group, each pixel on which dots are formed by the second head is included in the second pixel group.

8. The printing method according to claim 7.

Images