Printing apparatus, control method thereof, and computer program

Abstract

To suppress deterioration of image quality due to positional deviation and granularity of dots.SOLUTION: A control apparatus executes: halftone processing of generating dot data representing a type of a dot of a pixel of interest to be formed on a medium to be printed by performing error diffusion processing on the pixel of interest while sequentially changing the pixel of interest along one direction of an arrangement direction for one pixel row among a plurality of pixel rows along the arrangement direction included in image data and then sequentially changing the pixel of interest along the other direction for the other one pixel row; correction processing of correcting discharge timing of an ink droplet by a correction value on the basis of the dot data; and printing processing including a pass operation, where the correction value includes a first correction value for correcting positional deviation in a movement direction between a dot formed by a current pass operation and a dot formed by a previous pass operation, and a second correction value for reducing granularity of an image configured of dots formed by a plurality of pass operations.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a printing apparatus, a control method thereof, and a computer program.

Background Art

[0002] As a conventional printing apparatus, an inkjet printing system of Patent Document 1 is known. In this inkjet printing system, grid lines are printed in each of the forward and return paths of bidirectional printing, and the ejection timing of ink droplets is corrected so that the deviation in the main scanning direction of these grid lines becomes the smallest.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the inkjet printing system of the above Patent Document 1, by correcting the ejection timing of ink droplets, the deviation in the landing position of ink droplets in the main scanning direction is reduced. However, in an image that spreads in the main scanning direction and the sub-scanning direction, there is a possibility that the image quality may deteriorate due to deterioration of granularity even after the above correction.

[0005] The present invention has been made to solve such problems, and an object thereof is to provide a printing apparatus, a control method thereof, and a computer program capable of suppressing a decrease in image quality caused by positional deviation and granularity.

Means for Solving the Problems

[0006] A printing apparatus according to an aspect of the present disclosure includes a head that discharges ink droplets onto a print medium, a carriage that moves the head in a moving direction, a conveyance device that conveys the print medium along a conveyance direction intersecting the moving direction, and a control device. The control device performs error diffusion processing on a target pixel while sequentially changing the target pixel along one direction in the arrangement direction for one pixel column among a plurality of pixel columns along the arrangement direction of the image data, and then sequentially changing the target pixel along the other direction for another pixel column to generate dot data representing the type of dot of the target pixel formed on the print medium, which is halftone processing. Based on the dot data, correction processing corrects the discharge timing of the ink droplets from the head with a correction value. Based on the dot data whose discharge timing has been corrected by the correction processing, while moving the head along the moving direction, a path operation forms dots on the print medium with the ink droplets discharged from the head, and a conveyance operation conveys the print medium along the conveyance direction, which is printing processing. The correction value includes a first correction value that corrects a positional deviation in the moving direction between the dot formed by the current path operation and the dot formed by the previous path operation, and a second correction value that reduces the graininess of an image composed of the dots formed by a plurality of the path operations.

[0007] A method for controlling a printing apparatus according to an aspect of the present disclosure is a method for controlling a printing apparatus including a head that discharges ink droplets onto a printing medium, a carriage that moves the head in a moving direction, and a conveyance device that conveys the printing medium along a conveyance direction intersecting the moving direction. The method includes: performing halftone processing in which, for one pixel column among a plurality of pixel columns along an array direction of image data, after sequentially changing a target pixel along one direction of the array direction, while sequentially changing the target pixel along another direction for another one pixel column, error diffusion processing is performed on the target pixel to generate dot data representing a dot type of the dot of the target pixel formed on the printing medium; performing correction processing for correcting a discharge timing of ink droplets from the head with a correction value based on the dot data; performing a pass operation of forming dots on the printing medium with the ink droplets discharged from the head while moving the head along the moving direction based on the dot data whose discharge timing has been corrected by the correction processing; and performing a conveyance operation of conveying the printing medium along the conveyance direction, which is a printing process. The correction value includes a first correction value for correcting a positional deviation in the moving direction between the dot formed by the current pass operation and the dot formed by the previous pass operation, and a second correction value for reducing graininess of an image composed of dots formed by a plurality of the pass operations.

[0008] A computer program according to an aspect of the present disclosure causes a computer of a printing apparatus including a head that discharges ink droplets onto a printing medium, a carriage that moves the head in a moving direction, and a conveyance device that conveys the printing medium along a conveyance direction intersecting the moving direction, to perform halftone processing for generating dot data representing a dot type of a target pixel formed on the printing medium by performing error diffusion processing on the target pixel while sequentially changing the target pixel along one direction in an array direction for one pixel column among a plurality of pixel columns along the array direction of image data, then sequentially changing the target pixel along the other direction for another pixel column, and dot data generation; correction processing for correcting the discharge timing of ink droplets from the head with a correction value; a pass operation for forming dots on the printing medium with the ink droplets discharged from the head while moving the head along the moving direction based on the dot data whose discharge timing has been corrected by the correction processing; and a conveyance operation for conveying the printing medium along the conveyance direction, including printing processing, wherein the correction value includes a first correction value for correcting a positional deviation in the moving direction between the dot formed by the current pass operation and the dot formed by the previous pass operation, and a second correction value for reducing the graininess of an image composed of the dots formed by a plurality of the pass operations.

Effect of the Invention

[0009] By correcting the discharge timing of ink droplets with the first correction value, it is possible to reduce the positional deviation of dots in the moving direction of the head. Further, by correcting the discharge timing of ink droplets with the second correction value, it is possible to improve the graininess of the image.

[0010] The above object, other objects, features, and advantages of the present disclosure will become apparent from the following detailed description of the preferred embodiments with reference to the accompanying drawings.

Brief Description of the Drawings

[0011]

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Modes for Carrying Out the Invention

[0012] (First Embodiment) <Printing Apparatus> As shown in FIG. 1, the printing apparatus 10 according to the first embodiment of the present disclosure is an apparatus that discharges ink from the head 20 onto the print medium A while moving the head 20 in the moving direction, and prints an image on the print medium A. For example, it is an inkjet printer of the serial head type. The print medium A is, for example, a sheet such as paper and fabric.

[0013] Hereinafter, the moving direction in which the head 20 moves is referred to as the left - right direction. The direction that intersects (for example, is orthogonal to) this moving direction and in which the print medium A is conveyed is referred to as the front - rear direction. Also, the direction that intersects (for example, is orthogonal to) the moving direction of the head 20 and the conveying direction of the print medium A is referred to as the up - down direction. However, the directions related to the printing apparatus 10 are not limited to this.

[0014] The printing apparatus 10 includes a head 20. The head 20 has a plurality of nozzles 21 and a plurality of drive elements 22 (FIG. 2). The plurality of nozzles 21 are arranged in the front - rear direction to form nozzle rows, and the plurality of nozzle rows are arranged in the left - right direction. The nozzles 21 open to the ejection surface 23 which is the lower surface of the head 20. The drive element 22 is a piezoelectric element, a heating element, an electrostatic actuator, etc., and is provided for each nozzle 21, and applies ejection energy such as pressure for ejecting ink droplets from the nozzle 21 to the ink in the head 20.

[0015] Furthermore, the printing apparatus 10 includes a cartridge 11 and a platen 12. The cartridge 11 is detachable from the housing, stores ink, and is connected to the head 20 by a tube 11a. For example, four cartridges 11 communicate with the nozzles 21 of the four nozzle rows respectively, and ink is supplied to the nozzles 21. Also, the platen 12 is positioned at a predetermined distance below the head 20. The flat upper surface of the platen 12 is arranged to face the ejection surface 23 of the head 20 and supports the print medium A from below.

[0016] Furthermore, the printing apparatus 10 includes a moving device 30 that moves the head 20 in the left - right direction. The moving device 30 has a carriage 31, two guide rails 32, an endless belt 33, and a moving motor 34. The carriage 31 is box - shaped and mounts the head 20. The two guide rails 32 extend left - right across the platen 12 disposed directly below, are arranged apart from each other front - rear so as to sandwich all the nozzles 21 therebetween, and support the carriage 31 movably. The endless belt 33 is connected to the carriage 31 and is connected to the moving motor 34 via a pulley 35 provided on the guide rail 32. Therefore, when the moving motor 34 is rotationally driven, the endless belt 33 runs, and the carriage 31 and the head 20 mounted on the carriage 31 are moved in the left - right direction along the guide rail 32.

[0017] Furthermore, the printing apparatus 10 includes a conveying device 40 that conveys the printing medium A in the front - rear direction. The conveying device 40 has, for example, a conveying roller 41 and a conveying motor 42 (FIG. 2). The conveying roller 41 has an axis extending in the left - right direction, and the conveying motor 42 is connected to the axis of the conveying roller 41. When the conveying motor 42 is rotationally driven, the conveying roller 41 rotates about its axis, and conveys the printing medium A in the front - rear direction on the platen 12.

[0018] Furthermore, as shown in FIG. 2, the printing apparatus 10 includes a control device 50, and a communication interface 53, an input device 13, a head drive circuit 54, a moving drive circuit 55, and a conveying drive circuit 56 that are electrically connected to the control device 50. Note that the control device 50 may be constituted by a single device, or may be configured such that a plurality of devices are distributed and cooperate to perform the operation of the control device 50.

[0019] The communication interface 53 is a connection device that connects to an external device existing independently from outside the printing apparatus 10, and may be connected to the external device by wired communication such as a USB cable or wireless communication such as a LAN. Examples of the external device include a computer, a mobile terminal, a server, a storage medium, and a camera. Thereby, the control device 50 acquires data such as image data from the external device via the communication interface 53. The image data is data representing an image to be printed, and is, for example, raster data.

[0020] The input device 13 is a device that inputs data to the control device 50, and a push button, a pointing device, or the like is used. The input device 13 is operated by a user to input print conditions such as the resolution of an image to be printed to the control device 50. Note that the communication interface 53 may be used as the input device 13.

[0021] The control device 50 is configured by, for example, a computer and includes an arithmetic unit 51 and a storage unit 52. The storage unit 52 is a memory accessible from the arithmetic unit 51 and has at least one of, for example, a RAM, a ROM, an E2PROM, and an NVRAM. The storage unit 52 stores data input from the communication interface 53 and the input device 13, as well as a computer program and various types of data used for data processing by the arithmetic unit 51.

[0022] The arithmetic unit 51 includes circuits such as a processor such as a CPU, an integrated circuit such as an ASIC, or both. By executing a computer program while the arithmetic unit 51 refers to the stored data in the storage unit 52, the control device 50 controls the operations of each part of the printing apparatus 10. Thereby, the printing apparatus 10 executes various processes such as a halftone process for generating dot data based on image data that is the object of printing processing, a correction process for correcting the ejection timing of ink droplets in the printing process, and a printing process for printing an image on the print medium A based on the dot data whose ejection timing has been corrected. Note that these processes will be described later.

[0023] The head drive circuit 54 is electrically connected to the drive element 22 of the head 20. The control device 50 generates a control signal for driving the drive element 22 based on image data or the like, and the head drive circuit 54 generates a drive signal for the drive element 22 based on this control signal. Then, the drive element 22 is driven based on the drive signal so as to apply ejection energy to the ink in the head 20 at the ejection timing based on the image data. Thereby, ink droplets are ejected from the nozzles 21 of the head 20.

[0024] The movement drive circuit 55 is electrically connected to the movement motor 34 of the movement device 30. The control device 50 generates a control signal for driving the movement motor 34 based on image data or the like, and the movement drive circuit 55 generates a drive signal for the movement motor 34 based on this control signal. Then, the movement motor 34 is driven based on the drive signal so as to move the carriage 31 on which the head 20 is mounted in the left - right direction at a variable speed and stop the carriage 31 at an arbitrary position within its movable range.

[0025] The conveyance drive circuit 56 is electrically connected to the conveyance motor 42 of the conveyance device 40. The control device 50 generates a control signal for driving the conveyance motor 42 based on image data or the like, and the conveyance drive circuit 56 generates a drive signal for the conveyance motor 42 based on this control signal. Then, the conveyance motor 42 is driven based on the drive signal so as to intermittently or continuously convey the printing medium A on the platen 12 in the front - rear direction and stop the printing medium A at a predetermined position on the platen 12.

[0026] <Printing process> The control device 50 executes printing processing based on the ejection timing of ink droplets corrected by correction processing and the dot data generated by halftone processing. In the printing processing, the control device 50 alternately executes a pass operation and a conveyance operation to print an image on the print medium A. In this pass operation, the control device 50 ejects ink droplets from the nozzles 21 of the head 20 onto the print medium A while moving the head 20 along the left-right direction. Thereby, dots are formed on the print medium A, and a pass image composed of the dots is formed.

[0027] In the conveyance operation, the control device 50 conveys the print medium A in the front-rear direction. Thereby, a plurality of pass images are arranged in the front-rear direction on the print medium A, and an image composed of the plurality of pass images is printed on the print medium A. This pass image is a partial image of a part of the image and is an image printed on the print medium A by one pass operation.

[0028] <Multi-pass method> When the resolution of the image in the front-rear direction is larger than the resolution of the head 20, a multi-pass method is used in which at least a part of the pass images are printed while shifting the dots in the front-rear direction. By overlapping a plurality of pass images while shifting the dots in the front-rear direction, the number of dots in the front-rear direction becomes larger than the number of dots in one pass image. Therefore, an image with a resolution larger than the resolution of the head 20 can be printed.

[0029] Specifically, as shown in FIG. 3, dots B are formed for each pixel region A0 of the print medium A by the pass operation, and a pass image composed of these dots B is printed on the print medium A. This pixel region A0 is a region of the print medium A corresponding to the pixel C of the image data. A plurality of pixel regions A0 are arranged side by side in the left-right direction to form a pixel region column. A plurality of pixel region columns are arranged in the front-rear direction.

[0030] When the resolution of the image is an even multiple (e.g., 2 times) of the resolution of the head 20, the first pass operation and the second pass operation are alternately executed as the pass operations of the printing process. Here, at least a part of the second pass image formed by the second pass operation is superimposed on at least a part of the first pass image formed by the first pass operation on the print medium A. Also, the first dot B1 of the first pass image and the second dot B2 of the second pass image are alternately arranged in the front-rear direction. The interval b between the first dot B1 and the second dot B2 is 1 / 2 of the interval n between the nozzles 21, and the resolution of the image is 2 times the resolution of the head 20.

[0031] When the resolution of the image is an odd multiple (e.g., 3 times) of the resolution of the head 20, the first pass operation to the third pass operation are repeatedly executed in this order as the pass operations of the printing process. Here, at least a part of the second pass image and the third pass image formed by the second pass operation and the third pass operation are superimposed on at least a part of the first pass image formed by the first pass operation on the print medium A. Also, as shown in FIG. 4, the first dot B1 of the first pass image, the second dot B2 of the second pass image, and the third dot B3 of the third pass image are repeatedly arranged in this order in the front-rear direction. Among the first dot B1 to the third dot B3, the interval b between the adjacent dots B is 1 / 3 of the interval n between the nozzles 21, and the resolution of the image is 3 times the resolution of the head 20.

[0032] <Data Processing> The image data to be subjected to this printing process is data - processed so as to conform to the printing conditions input by the input device 13 or the like. For example, the image data is subjected to resolution conversion processing and color conversion processing. In the resolution conversion processing, the control device 50 converts the resolution of the image data into the resolution of the image data of the image to be printed on the printing medium A by the printing device 10 according to the resolution of the printing conditions. Also, in the color conversion processing, the control device 50 converts the image data composed of the color components of red (R), green (G), and blue (B) into the image data composed of the color components of the ink colors of the printing device 10, for example, cyan (C), magenta (M), yellow (Y), and black (K) based on the color conversion table stored in the storage unit 52. This image data for each CMYK color is composed of a plurality of pixels C, and each pixel C is represented by a gradation value of 0 to 255 gradations.

[0033] The image data whose resolution and color have been converted in this way is further subjected to halftone processing and interlace processing. In the halftone processing, the control device 50 converts the image data represented by 256 - gradation gradation values into dot data represented by dots B. In the interlace processing, the control device 50 allocates the dot data for each pass operation of the printing process in accordance with the arrangement of the nozzles 21 of the printing device 10 and the conveyance amount of the printing medium A, and outputs it to the head drive circuit 54.

[0034] <Halftone Processing> In the halftone processing, for one pixel column among a plurality of pixel columns along the array direction of the image data, after sequentially changing the target pixel C0 along one direction of the array direction, while sequentially changing the target pixel C0 along the other direction for another pixel column, error diffusion processing is performed on the target pixel C0 to generate dot data representing the type of dot B of the target pixel C0 formed on the printing medium A.

[0035] Specifically, through halftone processing, image data represented by 256 gradation values is converted into image data represented by dots B. For example, when the head 20 is capable of ejecting four types of ink droplets, there are four types of dots B formed by the ink droplets. The four types of dots B include a dotless dot where the amount of ink droplets is 0, a small dot where the amount of ink droplets is less than a predetermined range, a medium dot where the amount of ink droplets is within the predetermined range, and a large dot where the amount of ink droplets is greater than or equal to the predetermined range.

[0036] In the halftone processing, an error diffusion method using an error diffusion matrix is performed. This error diffusion matrix is stored in advance in the storage unit 52. As shown in FIGS. 5 and 6, each cell in the error diffusion matrix represents one pixel C in the image data, and the number in the cell represents the error diffusion coefficient (weight value). The pixel C marked with a circle represents the target pixel C0. The closer to the target pixel C0, the larger the error diffusion coefficient of the pixel C.

[0037] As shown in FIG. 7, the image data has a plurality of pixels C, and the plurality of pixels C are arranged in an array direction to form a pixel column. The plurality of pixel columns are arranged along an intersection direction that intersects the array direction. The array direction of the pixel C corresponds to the direction in which the dot B is formed by the pass operation of the printing process, that is, the moving direction (left - right direction) of the head 20. In this case, the intersection direction corresponds to the front - rear direction. In FIG. 7, the position of the pixel C is represented by (i, j), where i represents the order of the pixel columns from the back, and j represents the order of the pixel C from the left in the pixel column.

[0038] In the halftone process, the control device 50 changes the target pixel C0 one by one in order along the array direction of the pixel C as shown by the dashed line in FIG. 7, for example, starting from the pixel C(1, 1) at the upper left corner of the image data. Here, the changing direction of the target pixel C0 in the pixel column is alternately changed to the right, which is one direction of the array direction, and to the left, which is the other direction of the array direction. For example, the control device 50 changes the target pixel C0 to the right in the first pixel column C1, then changes the target pixel C0 to the left in the next second pixel column C2, and changes the target pixel C0 to the right in the next third pixel column C3. Thus, for example, when the pixel C(3, 6) is the target pixel C0, the pixels C (pixels C with shading) to the left of the target pixel C0 in the third pixel column C3, and the pixels C (pixels C with shading) in the first pixel column C1 and the second pixel column C2 behind the third pixel column C3 have completed the halftone process.

[0039] The control device 50 associates the target pixel C0 in the error diffusion matrix of FIG. 5 or FIG. 6 with the target pixel C0 of the image data to be subjected to this halftone process. When the target pixel C0 is changed to the right in the pixel column, the error diffusion matrix of FIG. 5 is used, and when the target pixel C0 is changed to the left in the pixel column, the error diffusion matrix of FIG. 6 is used.

[0040] Then, the control device 50 acquires the peripheral pixels around the target pixel C0 among the pixels C in the image data. The peripheral pixels include the first peripheral pixel Ca1 associated with the error diffusion coefficient "1" of the error diffusion matrix and the second peripheral pixel Ca2 associated with the error diffusion coefficient "2" of the error diffusion matrix. When the pixel C(3, 6) is the target pixel C0, the first peripheral pixel Ca1 is the pixels C(1, 6), C(2, 5), C(2, 7), and C(3, 4), and the second peripheral pixel Ca2 is the pixels C(3, 5) and C(2, 6).

[0041] Then, through error diffusion processing, the control device 50 calculates a corrected gradation value Da (= D + E) in which the gradation value D of the target pixel C0 is corrected by adding the error value E of the surrounding pixels Ca1 and Ca2 to the gradation value D of the target pixel C0. The gradation value D of this target pixel C0 is, for example, a gradation value of 256 gradations of image data. The error value E is the sum of the product of the first coefficient K1 and the total ΣE1 of the error values E of the four first surrounding pixels Ca1, and the product of the second coefficient K2 and the total ΣE2 of the error values E of the two second surrounding pixels Ca2 (= K1 × ΣE1 + K2 × ΣE2). The error value E is the difference between the corrected gradation value Da of the surrounding pixels Ca1 and Ca2 and a predetermined threshold Th (= Da - Th).

[0042] The first coefficient K1 is (error diffusion coefficient "1" × number of first surrounding pixels Ca1) / number of surrounding pixels Ca, which is (1 × 4) / 8 = 1 / 2. The second coefficient K2 is (error diffusion coefficient "2" × number of second surrounding pixels Ca2) / number of surrounding pixels, which is (2 × 2) / 8 = 1 / 2. The number of surrounding pixels is (error diffusion coefficient "1" × number of first surrounding pixels Ca1) + (error diffusion coefficient "2" × number of second surrounding pixels Ca2), which is (1 × 4) + (2 × 2) = 8.

[0043] For example, when the halftone process is binarization that determines the presence or absence of dot B, the threshold Th is a value that distinguishes between no dot and dot present. Also, when the halftone process is four-valued determination of four types of dots B, the threshold Th includes a first threshold T1 that distinguishes between no dot and small dot, a second threshold T2 that distinguishes between small dot and medium dot, and a third threshold T3 that distinguishes between medium dot and large dot.

[0044] Then, the control device 50 compares the corrected gradation value Da of the target pixel C0 with the threshold value Th to determine the type of dot. For example, in the halftone processing of four-level quantization, when the corrected gradation value Da is less than the first threshold value T1, the control device 50 determines that the type of dot of the target pixel C0 is dotless, and stores the corrected gradation value Da in the storage unit 52 as the error value E of the pixel C. Further, when the corrected gradation value Da is equal to or greater than the first threshold value T1 and less than the second threshold value T2, the control device 50 determines that the type of dot of the target pixel C0 is a small dot, and stores the difference between the corrected gradation value Da and the first threshold value T1 in the storage unit 52 as the error value E of the pixel C.

[0045] Further, when the corrected gradation value Da is equal to or greater than the second threshold value T2 and less than the third threshold value T3, the control device 50 determines that the type of dot of the target pixel C0 is a medium dot, and stores the difference between the corrected gradation value Da and the second threshold value T2 in the storage unit 52 as the error value E of the pixel C. Further, when the corrected gradation value Da is equal to or greater than the third threshold value T3, the control device 50 determines that the type of dot of the target pixel C0 is a large dot, and stores the difference between the corrected gradation value Da and the third threshold value T3 in the storage unit 52 as the error value E of the pixel C. In this way, the type of dot of the target pixel C0 is determined and the error value E is calculated. This dot type is used as dot data. Further, the error value E is used as the error values E of the peripheral pixels Ca1 and Ca2 when other pixels C are the target pixel C0.

[0046] Then, the control device 50 performs halftone processing on all the pixels C in the image data, and converts the image data represented by gradation values into dot data represented by the types of dots B. In this halftone processing using error diffusion processing, the type of dot B is determined for each pixel C based on the corrected gradation value Da including the error values E of the peripheral pixels Ca1 and Ca2 in the gradation value D of the target pixel C0. Therefore, since the error generated in the target pixel C0 is diffused to the peripheral pixels C, local gradation variations can be smoothed over the entire image.

[0047] <Correction processing> In this way, dot data is generated by halftone processing using error diffusion processing. However, in the pass operation, ink droplets are ejected from the head 20 while moving the head 20 along the left-right direction. Therefore, there may be a positional deviation in the left-right direction between the dot B formed by the current pass operation and the dot B formed by the previous pass operation immediately before it. Note that the printing process is bidirectional printing, and the moving direction of the head 20 may be different between the current pass operation and the previous pass operation. Also, the printing process may be unidirectional printing, and the moving direction of the head 20 may be the same between the current pass operation and the previous pass operation.

[0048] Also, in the error diffusion processing, the change direction of the target pixel C0 in the image data is alternately changed in one direction and the other direction in the array direction of the pixels C. When the printing process is executed based on the dot data generated by this bidirectional error diffusion processing, the graininess of the image composed of the dots B may be prominent. Therefore, in order to reduce the positional deviation of such dots B and improve the graininess of the image, the control device 50 executes a correction process of correcting the ejection timing of the ink droplets from the head 20 with a correction value based on the dot data.

[0049] This correction value has a first correction value and a second correction value, and is stored in advance in the storage unit 52. The first correction value is a correction value for correcting the positional deviation in the moving direction of the head 20 between the dot B formed by the current pass operation and the dot B formed by the previous pass operation. Also, the second correction value is a correction value for reducing the graininess of the image composed of the dots B formed by a plurality of pass operations.

[0050] That is, as shown in the example of FIG. 7, in the two-way error diffusion process, the direction of moving the target pixel C0 along the array direction of the pixels C of the image data is alternately changed between one direction and the other direction, and dot data is generated. According to the processing direction of this error diffusion process, one dot data and the other dot data are alternately generated as dot data. This one dot data is the dot data when the target pixel C0 moves in one direction, and the other dot data is the dot data when the target pixel C0 moves in the other direction.

[0051] This one dot data and the other dot data are alternately generated and assigned to the pass operation of the printing process. The generation period of this dot data is two cycles. As shown in the table of FIG. 8, these dot data are sequentially used by a plurality of pass operations in the printing process. Therefore, the pass operation based on one dot data and the pass operation based on the other dot data are alternately executed. Among these pass operations, correction processing is executed so as to correct only the ejection timing of the ink droplets for either one of them.

[0052] For example, when the resolution of the image is an even multiple (e.g., 2 times) of the resolution of the head 20, according to the printing process of the multi-pass method, as shown in the table of FIG. 8, the first pass operation and the second pass operation are alternately executed. In this case, the period of the pass operation of the multi-pass method is two cycles of the first pass operation and the second pass operation, and is an integer multiple of two cycles, which is the generation period of the dot data according to the processing direction of the error diffusion process.

[0053] Thereby, one dot data is used for all the first pass operations in the printing process, and the other dot data is used for all the second pass operations. Therefore, as shown in FIG. 3, all the first dots B1 formed by the first pass operation are one dots Ba based on one dot data, and all the second dots B2 formed by the second pass operation are the other dots Bb based on the other dot data.

[0054] Also, as shown in FIG. 8, when the resolution of the image is four times the resolution of the head 20, the first pass operation to the fourth pass operation are repeatedly executed in this order by the printing process of the multi-pass method. In this case, the cycle of the pass operation of the multi-pass method is four cycles, which is an integer multiple of two cycles, which is the generation cycle of dot data according to the processing direction of the error diffusion process.

[0055] As a result, one dot data is used for all the first pass operations and the third pass operations in the printing process, and the other dot data is used for all the second pass operations and the fourth pass operations. Therefore, all the first dots B1 formed by the first pass operation and all the dots B formed by the third pass operation are one dots Ba based on one dot data. Also, all the second dots B2 formed by the second pass operation and all the dots B formed by the fourth pass operation are the other dots Bb based on the other dot data.

[0056] In this way, all the first dots B1 in the printing process are composed only of the one dots Ba, and all the second dots B2 are composed only of the other dots Bb. In such a case, the control device 50 can correct the first correction value with the second correction value and correct the ejection timing of the ink droplets with the corrected value, thereby improving the granularity of the image.

[0057] Also, the control device 50 corrects the ejection timing of the ink droplets based on either one of the one dot data and the other dot data with the first correction value corrected by the second correction value. As a result, the position of the other dot Bb based on the other dot data is corrected by the first correction value along the left-right direction with respect to the position of the one dot Ba based on the one dot data. Therefore, the positional deviation between the one dot Ba and the other dot Bb in the left-right direction can be reduced. Also, although this first correction value is corrected by the second correction value, for example, when the resolution of the image is two times or more the resolution of the head 20, the positional deviation between the one dot Ba and the other dot Bb is difficult to become apparent, so the robustness of the granularity can be improved.

[0058] For example, the graph in FIG. 9A shows the image granularity evaluation value when the resolution of the image (300 dpi) is an even multiple of the resolution of the head 20 (150 dpi). The vertical axis of this graph indicates the image granularity evaluation value, and the horizontal axis indicates the gradation value of the image data. The image granularity evaluation value is calculated based on a predetermined evaluation formula for evaluating granularity. In FIG. 9A, the granularity evaluation value F0 is the granularity evaluation value when the ejection timing of the ink droplets is corrected with the first correction value without using the second correction value. The granularity evaluation value F+1 is the granularity evaluation value when the ejection timing of the ink droplets is corrected with the first correction value corrected with the second correction value. The granularity evaluation value F+1 is smaller than the granularity evaluation value F0. Therefore, by using the first correction value corrected with the second correction value for correcting the ejection timing of the ink droplets, the granularity of the image can be improved.

[0059] Also, when the resolution of the image is an odd multiple (e.g., 3 times) of the resolution of the head 20, according to the printing process of the multi-pass method, as shown in the table of FIG. 8, the first pass operation, the second pass operation, and the third pass operation are repeatedly executed in this order. In this case, the cycle of the pass operation of the multi-pass method is 3 cycles of the first pass operation to the third pass operation, and is not an integer multiple of 2 cycles, which is the generation cycle of dot data according to the processing direction of the error diffusion process.

[0060] In such a case, one dot data is used for the first first pass operation in the printing process, the other dot data is used for the second first pass operation, and one dot data is used for the third first pass operation. As a result, as shown in FIG. 4, the first dot B1 formed by the first first pass operation is the one dot Ba based on one dot data, and the first dot B1 formed by the second first pass operation is the other dot Bb based on the other dot data. Thus, the first dot B1 has a mixture of the one dot Ba and the other dot Bb.

[0061] In such a case, even if the first correction value is corrected with the second correction value and the ejection timing of the ink droplets is corrected with the corrected value, the graininess of the image is not improved. However, by correcting the ejection timing with the first correction value without using the second correction value, it is possible to reduce the deterioration of the image quality due to misregistration.

[0062] For example, the graphs of FIGS. 10A and 10B show the graininess evaluation values of an image when the resolution of the image (300 dpi) is an odd multiple of the resolution of the head 20 (100 dpi). The vertical axis of this graph indicates the graininess evaluation value of the image, and the horizontal axis indicates the gradation value of the image data. The graininess evaluation value of the image is calculated based on a predetermined evaluation formula for evaluating graininess. In both FIGS. 10A and 10B, the graininess evaluation value G0 when the ejection timing of the ink droplets is corrected with the first correction value without using the second correction value is smaller than the graininess evaluation values G+1 to G+6 and G-1 to G-6 when the ejection timing of the ink droplets is corrected with the first correction value corrected with the second correction value. Therefore, even if the first correction value corrected with the second correction value is used for correcting the ink droplets and the ejection timing, the graininess of the image is not improved.

[0063] <Control Method of Printing Apparatus> The printing apparatus 10 is controlled by the control apparatus 50 according to a flowchart showing an example of the control method of FIG. 11. First, the control apparatus 50 acquires the image data of the target image for printing from the communication interface 53 or the storage unit 52 (step S10), and acquires the printing conditions from the input device 13, the communication interface 53, or the storage unit 52 (step S11). Then, the control apparatus 50 executes a resolution conversion process on the image data according to the printing conditions (step S12) to convert the image data to a user-specified resolution. Further, the control apparatus 50 executes a color conversion process on the image data (step S13) to convert the image data to a predetermined or user-specified color.

[0064] Then, the control device 50 performs halftone processing using two-way error diffusion processing on the image data (step S14) to generate dot data representing the type of dot B. As this dot data, one dot data and the other dot data are alternately generated according to the processing direction of the error diffusion processing. The generation period of the one dot data and the other dot data is two cycles.

[0065] Then, the control device 50 performs an interlace process on the dot data (step S15) and assigns the dot data to each of a plurality of pass operations in the printing process. At this time, the one dot data and the other dot data corresponding to the processing direction of the error diffusion processing are alternately assigned to the pass operations.

[0066] Then, the control device 50 executes a resolution determination process to determine whether the resolution of the image is greater than the resolution of the head 20 and whether the resolution of the image is an odd multiple of the resolution of the head 20 (step S16). When the resolution of the image is an odd multiple of the resolution of the head 20 (step S16: YES), the period of the pass operation of the printing process is an odd period and is not an integer multiple of the generation period of the dot data. For this reason, the control device 50 corrects the ejection timing of the ink droplets with the first correction value without using the second correction value in the correction process (step S17). This correction process is executed for only one of the one dot data and the other dot data. For example, the control device 50 corrects the ejection timing of the ink droplets based on the other dot data to the ejection timing of the ink droplets based on the first correction value and corrects the other dot data.

[0067] Then, the control device 50 executes printing processing based on dot data in which the ejection timing of ink droplets is corrected by the first correction value (step S18). In this printing processing, the control device 50 alternately executes a pass operation and a conveyance operation. In the pass operation, ink droplets are ejected to form dots B on the printing medium A. Regarding this pass operation, the control device 50 alternately executes a pass operation based on one dot data and a pass operation based on the other dot data. For example, when the correction processing is not executed for one dot data but is executed for the other dot data, the ejection timing of the ink droplets based on the other dot data is corrected by the first correction value. Therefore, since the position of the other dot Bb based on the other dot data is corrected, the positional deviation of the other dot Bb with respect to the one dot Ba based on the one dot data can be reduced.

[0068] On the other hand, when the resolution of the image is larger than the resolution of the head 20 and the resolution of the image is an even multiple of the resolution of the head 20 (step S16: NO), the period of the pass operation of the printing processing is an even period and is an integer multiple of the generation period of the dot data. Therefore, the control device 50 corrects the first correction value with the second correction value and executes correction processing with this correction value (step S19). This correction processing is executed for only one of the one dot data and the other dot data. For example, the control device 50 corrects the dot data by correcting the ejection timing based on the first correction value corrected by the second correction value from the ejection timing of the ink droplets based on the other dot data.

[0069] Then, the control device 50 executes printing processing based on dot data in which the ejection timing of ink droplets is corrected by the first correction value corrected by the second correction value (step S18). By correcting the ejection timing of ink droplets by this first correction value, the positional deviation of the other dot Bb with respect to one dot Ba can be reduced. Furthermore, by correcting the ejection timing of ink droplets by the second correction value, the granularity of the image formed by one dot Ba and the other dot Bb can be improved. Furthermore, even if the first correction value is corrected by the second correction value, the positional deviation is unlikely to deteriorate, so the robustness of the granularity can be improved.

[0070] (Second Embodiment) As shown in FIG. 11, the printing apparatus 10 according to the first embodiment executed correction processing based on the result of the resolution determination processing. In contrast, as shown in FIG. 12, the printing apparatus 10 according to the second embodiment executes correction processing based on the result of the resolution determination processing and in addition, based on the result of the method determination processing of the singling method. As shown in FIG. 13, in the printing processing of the singling method, dots B are complementarily formed by a plurality of pass operations on one partial region of the medium to be printed.

[0071] For example, the control device 50 divides each dot data of one dot data and the other dot data into a plurality of partial dot data. Then, the control device 50 forms the dot B (filled circle) of the partial image H1 by a pass operation based on the partial dot data, and then forms the dot B (white) of the partial image H2 by a pass operation based on the partial dot data. At least a part of the current partial image H2 overlaps at least a part of the previous partial image H1. In this overlapping portion H3 (one partial region), the dot B of the current partial image H2 and the dot B of the previous partial image H1 are complementarily formed at different positions in the left-right direction.

[0072] In this way, so that the partial images complement each other, the control device 50 attaches a mask to the partial dot data of the partial image H2 so that the dot B of the partial image H2 is not formed at the formation position of the dot B of the partial image H1. Further, the control device 50 attaches a mask to the partial dot data of the partial image H1 so that the dot B of the partial image H1 is not formed at the formation position of the dot B of the partial image H2. In this way, the partial image H1 and the partial image H2 are overlapped so that the mask position of the partial image H1 is complemented by the dot B of the partial image H2 and the mask position of the partial image H2 is complemented by the dot B of the partial image H1, making these joints less noticeable.

[0073] Note that the printing process method may be a gradation singling method. In this case, in the overlapping portion H3, the partial dot data is generated such that the mask becomes more in the previous partial image H1 toward the front and less in the current partial image H2 toward the front. By the previous pass operation based on such partial dot data, the previous partial image H1 is formed such that the dot B becomes less toward the front in the overlapping portion H3. By the current pass operation based on the partial dot data, the current partial image H2 is formed such that the dot B becomes more toward the front in the overlapping portion H3. In this way, since the previous partial image H1 and the current partial image H2 in the overlapping portion H3 are gradated, these joints become even less noticeable.

[0074] In the flowchart of FIG. 12 showing an example of the control method of the printing apparatus 10 according to the second embodiment, a method determination process of S20 is executed between S16 and S17 and between S19 and S11 of FIG. 11. Specifically, the printing apparatus 10, and the control device 50, acquire the image data and the printing conditions of the image to be printed (steps S10, S11), and execute a resolution conversion process and a color conversion process according to the printing conditions (steps S12, S13). Then, the control device 50 executes a halftone process using a two-way error diffusion process on the image data to generate dot data including one-way dot data and the other-way dot data (step S14).

[0075] Then, the control device 50 performs an interlace process on the dot data (step S15), and assigns one dot data and the other dot data to each of a plurality of pass operations. Here, when the printing process method is the singling method based on the printing conditions, the control device 50 divides each of the one dot data and the other dot data into a plurality of partial dot data, and assigns the plurality of partial dot data to the plurality of pass operations respectively. For example, when the printing process mode has a high-speed mode and a high-quality mode, and the high-quality mode is input as the printing condition, the printing process method is the singling method.

[0076] And, when the resolution of the image is larger than the resolution of the head 20 and the resolution of the image is an odd multiple of the resolution of the head 20 (step S16: YES), the control device 50 executes correction processing using the first correction value (step S17). Then, the control device 50 executes a printing process based on the dot data in which the ejection timing of the ink droplets is corrected by the first correction value (step S18). This correction processing is executed for only one of the one dot data and the other dot data, so that the positional deviation of the other dot Bb with respect to the one dot Ba can be reduced.

[0077] On the other hand, when the resolution of the image is larger than the resolution of the head 20 and the resolution of the image is an even multiple of the resolution of the head 20 (step S16: NO), the control device 50 executes a method determination process and determines whether to perform the printing process in the singling method based on the printing conditions (step S20). When the control device 50 performs the printing process in the singling method (step S20: YES), the control device 50 executes correction processing using the first correction value without using the second correction value (step S17), and executes a printing process based on the dot data in which the ejection timing of the ink droplets is corrected by the first correction value (step S18).

[0078] In this single-ringing method, each dot data of one dot data and the other dot data is divided into a plurality of partial dot data. Therefore, if only one of the one dot data and the other dot data is corrected by the first correction value corrected by the second correction value, a plurality of dot Bs will overlap or shift significantly. For this reason, in the printing process by the single-ringing method, by not correcting the first correction value with the second correction value, it is possible to reduce the deterioration of image quality.

[0079] On the other hand, when the control device 50 does not perform the printing process in the single-ringing method (step S20: NO), each dot data of the one dot data and the other dot data is not divided into a plurality of partial dot data. Therefore, the control device 50 corrects the first correction value with the second correction value, and executes the correction process with this correction value (step S19). Then, the control device 50 executes the printing process based on the dot data in which the discharge timing of the ink droplets is corrected by the first correction value corrected by the second correction value (step S18). Since this correction process is executed only for one of the one dot data and the other dot data, it is possible to improve the granularity and robustness of the image while reducing the positional deviation of dot B.

[0080] In addition, in FIG. 12 above, the control device 50 executed the correction process based on the result of the method determination process of the single-ringing method in addition to the result of the resolution determination process. However, the control device 50 may execute the correction process based on the result of the method determination process of the single-ringing method without using the result of the resolution determination process. In this case, in the flowchart of FIG. 12, the control device 50 executes the method determination process of S20 instead of the resolution determination process of S16.

[0081] (Third Embodiment) As shown in FIG. 11, the printing apparatus 10 according to the first embodiment executed correction processing based on the result of the resolution determination processing. On the other hand, as shown in FIG. 14, the printing apparatus 10 according to the third embodiment executes correction processing according to the result of the overlapping determination processing of the target image for printing in addition to the result of the resolution determination processing. In the flowchart of FIG. 14, the processes of S21 to S23 are executed instead of S19 in FIG. 11.

[0082] Specifically, in the printing apparatus 10, the control device 50 acquires the image data of the target image for printing and the printing conditions (steps S10, S11), and executes resolution conversion processing and color conversion processing according to the printing conditions (steps S12, S13). Then, the control device 50 executes halftone processing using bidirectional error diffusion processing on the image data to generate dot data including one-way dot data and the other-way dot data (step S14). Then, the control device 50 executes interlace processing on the dot data (step S15), and alternately assigns the one-way dot data and the other-way dot data to the pass operation.

[0083]

[0084]

[0085] When the resolution of the image is greater than the resolution of the head 20 and the resolution of the image is an odd multiple of the resolution of the head 20 (step S16: YES), the control device 50 executes correction processing using the first correction value (step S17). This correction processing is executed on only one of the one-way dot data and the other-way dot data, so that the positional deviation of the other-way dot Bb with respect to the one-way dot Ba can be reduced. On the other hand, when the resolution of the image is greater than the resolution of the head 20 and the resolution of the image is an even multiple of the resolution of the head 20 (step S16: NO), the control device 50 executes an overlapping determination process for determining whether or not the diagrams and drawings overlap when viewed along the left-right direction when the target image for printing includes diagrams and drawings (step S21).In this overlapping determination process, the control device 50 performs image analysis on the dot data of the target image of the printing process to obtain the positions of the diagram and the drawing. As shown in FIG. 15A, when at least part of the positions of the diagram and the drawing in the front-rear direction coincide, at least part of the diagram and the drawing are arranged side by side in the left-right direction. When the diagram and the drawing overlap when viewed along the left-right direction in this way (step S21: YES), the control device 50 executes a correction process for correcting the ejection timing of the ink droplets with the first correction value without using the second correction value (step S17).

[0086] On the other hand, as shown in FIG. 15B, when the positions of the diagram and the drawing in the front-rear direction are different from each other, the diagram and the drawing are not arranged side by side in the left-right direction. When the diagram and the drawing do not overlap when viewed along the left-right direction in this way (step S21: NO), the control device 50 executes a correction process for correcting the ejection timing of the ink droplets in the printing process of the diagram with the first correction value without using the second correction value (step S22). Further, the control device 50 executes a correction process for correcting the ejection timing of the ink droplets in the printing process of the picture with the first correction value corrected by the second correction value (step S23). These correction processes are executed for only one of the one dot data and the other dot data.

[0087] Then, the control device 50 executes the printing process based on the dot data corrected in step S17 or steps S22 and S23 (step S18). In this way, the image quality of a diagram mainly composed of lines such as a table is easily affected by the positional deviation of dot B along the moving direction of the head 20. Also, the image quality of a picture such as a painting or a photograph is easily affected by granularity. For this reason, when these cannot be printed separately, the control device 50 corrects the ejection timing of the ink droplets with the first correction value and prints the diagram and the picture on the printing medium A.

[0088] In addition, when it is possible to print the diagram and the drawing separately, the quality degradation caused by the positional deviation of dot B can be reduced by correcting the diagram with the first correction value. Further, the quality degradation caused by granularity can be reduced by correcting the drawing with the first correction value corrected by the second correction value.

[0089] In FIG. 14 described above, the control device 50 executed the correction process based on the result of the overlap determination process in addition to the result of the resolution determination process. However, the control device 50 may execute the correction process based on the result of the overlap determination process without using the result of the resolution determination process. In this case, in the flowchart of FIG. 12, the control device 50 executes the overlap determination process in S21 instead of the resolution determination process in S16. Further, the control device 50 may execute the correction process based on the result of the resolution determination process, the result of the overlap determination process, and the result of the singling method determination process of the singling method.

[0090] (Fourth Embodiment) In the printing apparatus 10 according to the first to third embodiments, the control device 50 used the predetermined first correction value and second correction value stored in advance in the storage unit 52 for the correction process. On the other hand, in the printing apparatus 10 according to the fourth embodiment, the control device 50 may use the acquired first correction value and second correction value for the correction process. In this case, as shown in FIG. 2, the printing apparatus 10 further includes a scanner 14. The scanner 14 is electrically connected to the control device 50, photoelectrically reads the image information of the print medium A on which an image such as the test chart I is printed, and outputs the read image data to the control device 50.

[0091] The control device 50 acquires the first correction value and the second correction value according to a flowchart showing an example of control shown in FIG. 16. First, when the control device 50 acquires a test print instruction from the user, for example, from the input device 13, the control device 50 executes a test print process (step S30). In this test print process, as shown in FIG. 17, the control device 50 causes the test chart I including a plurality of groups of first marks J as shown in FIGS. 17(a) to (f) to be printed on the print medium A using the head 20.

[0092] The first mark J is a mark that linearly extends in the front-rear direction. Each of the plurality of groups has a basic first mark J1 with the ejection timing of ink droplets uncorrected and a comparative first mark J2 for comparison with the basic first mark J1. The comparative first mark J2 in the plurality of groups has different correction amounts for the ejection timing of ink droplets from each other. For this reason, the difference between the ejection timing of ink droplets when printing the comparative first mark J2 and the ejection timing based on dot data is different for the plurality of groups. The basic first mark J1 is printed by a pass operation based on either one of one dot data and the other dot data, and the comparative first mark J2 is printed by a pass operation based on the other.

[0093] Subsequently, the control device 50 executes a first acquisition process for acquiring a first correction value based on the printed first mark J (step S31). Here, the control device 50 reads the test chart I with the scanner 14 and acquires the image data of the test chart I. The control device 50 performs image processing on the test chart I and acquires the positions in the left-right direction of the basic first mark J1 and the comparative first mark J2 for each of the plurality of groups.

[0094] Then, the control device 50 acquires the interval J3 between the position of the basic first mark J1 and the position of the comparative first mark J2 in the left-right direction. The control device 50 acquires the position of the comparative first mark J2 with the minimum among these intervals J3. Further, the control device 50 has previously associated and stored in the storage unit 52 the position of the comparative first mark J2 of each group and the correction amount of the ejection timing of ink droplets. For this reason, the control device 50 acquires the correction amount of the ejection timing corresponding to the position of the comparative first mark J2 with the minimum interval J3 as the first correction value. By correcting the ejection timing of ink droplets only for either one of one dot data and the other dot data using such a first correction value, the positional deviation in the left-right direction between one dot Ba and the other dot Bb is reduced.

[0095] Subsequently, the control device 50 executes an arithmetic process of calculating a granularity evaluation value of an image when another pixel column is shifted pixel by pixel along the arrangement direction with respect to one pixel column among a plurality of pixel columns along the arrangement direction of the dot data (step S32). For example, the second mark L as shown in FIG. 18 is used for this arithmetic process. The second mark L spreads in a planar shape, and the dimension in the left-right direction is larger than that of the first mark J. Each of the plurality of second marks L shown in FIGS. 18(a) to (n) has a basic dot B whose ink droplet ejection timing is not corrected and a comparison dot B whose ink droplet ejection timing is to be corrected.

[0096] The plurality of comparison dots B shown in FIGS. 18(a) to (n) have different correction amounts for the ink droplet ejection timing. This correction amount corresponds to the shift amount of the pixel columns along the left-right direction in the dot data. As shown in FIG. 19A, in the dot data of the second mark L, a plurality of pixels C form a column in the left-right direction, and this odd pixel column C2n-1 (n: natural number) and the even pixel column C2n are alternately arranged along the front-rear direction. One dot Ba of one dot data is arranged as the basic dot B in the pixel column C2n-1, and the other dot Bb of the other dot data is arranged as the comparison dot B in the pixel column C2n. With respect to this pixel column C2n-1, the pixel column C2n is shifted to the right pixel by pixel. Also, as shown in FIG. 19B, with respect to the pixel column C2n-1, the pixel column C2n is shifted to the left pixel by pixel.

[0097] The second mark L in FIGS. 18(a) to (g) is a mark when the pixel column C2n is shifted to the right with respect to the pixel column C2n-1, and the second mark L in FIGS. 18(h) to (n) is a mark when the pixel column C2n is shifted to the left with respect to the pixel column C2n-1. In FIGS. 18(a) and (h), the displacement amount of the pixel column C2n with respect to the pixel column C2n-1 is 0 pixels, in FIGS. 18(b) and (i) the displacement amount is 1 pixel, in FIGS. 18(c) and (j) the displacement amount is 2 pixels, in FIGS. 18(d) and (k) the displacement amount is 3 pixels, in FIGS. 18(e) and (l) the displacement amount is 4 pixels, in FIGS. 18(f) and (m) the displacement amount is 5 pixels, and in FIGS. 18(g) and (n) the displacement amount is 6 pixels. Thus, the second mark L in FIGS. 18(a) to (n) is created by simulation by shifting the pixel column C2n to the right or left with respect to the pixel column C2n-1 by, for example, 0 to 6 pixels.

[0098] Based on the second mark L, the control device 50 calculates a granularity evaluation value of the second mark L by a predetermined evaluation formula stored in the storage unit 52. The granularity evaluation values F0 to F+6 in FIG. 9A are granularity evaluation values when the pixel column C2n is shifted to the right with respect to the pixel column C2n-1 and the displacement amount of the pixel column is 0 to 6 pixels. The granularity evaluation values F0 to F-6 in FIG. 9B are granularity evaluation values when the pixel column C2n is shifted to the left with respect to the pixel column C2n-1 and the displacement amount of the pixel column is 0 to 6 pixels.

[0099] Subsequently, the control device 50 executes a second acquisition process for acquiring a second correction value based on the granularity evaluation value (step S33). Here, the control device 50 acquires the second mark L with the minimum granularity evaluation value from the granularity evaluation values of the plurality of second marks L. As shown in FIGS. 9A and 9B, among the granularity evaluation values F0 to F+6 and F0 to F-6, the granularity evaluation value F+1 is the minimum. Since the displacement amount of the pixel column of this second mark L and the correction amount of the ejection timing of the ink droplets are stored in the storage unit 52 in advance in association with each other, the control device 50 acquires, as the second correction value, the correction amount corresponding to the displacement amount of the pixel column of the second mark L with the minimum granularity evaluation value. By using such a second correction value for correcting the ejection timing of the ink droplets, the granularity of an image including the one dot Ba and the other dot Bb can be improved.

[0100] In the above description, the control device 50 obtains the correction amount corresponding to one granularity evaluation value as the second correction value. However, the second correction value may be obtained based on the correction amounts corresponding to a plurality of granularity evaluation values. In this case, for example, the control device 50 arranges a plurality of granularity evaluation values in ascending order, and obtains a predetermined number of granularity evaluation values starting from the smallest one. Then, the control device 50 may obtain the correction amounts corresponding to the displacement amounts of the pixel columns of these granularity evaluation values, and obtain a representative value (for example, an average value or a median value) of these correction amounts as the second correction value.

[0101] <Modification Example 1> In the printing apparatus 10 according to Modification Example 1, the control device 50 obtains the second correction value based on the representative value of the displacement amount of the pixel column indicating the granularity evaluation value within a predetermined range in the second acquisition process. As the representative value, an average value, a median value, etc. are used.

[0102] For example, as shown in FIG. 9A, the granularity evaluation values F0 to F+3 are within a predetermined range below the granularity evaluation value Fb when the gradation value of the image is within a predetermined range Fa. The displacement amount of the pixel column in the dot data for the second mark L of these granularity evaluation values F0 to F+3 is 0 to +3 pixels. Further, as shown in FIG. 9B, the granularity evaluation values F0 to F-1 are within a predetermined range below the granularity evaluation value Fb when the gradation value of the image is within a predetermined range Fa. The displacement amount of the pixel column in the dot data for the second mark L of this granularity evaluation value F-1 is 0 to -1 pixel. Note that the displacement amount when the pixel column C2n is shifted to the right with respect to the pixel column C2n-1 is represented by +, and the displacement amount when the pixel column C2n is shifted to the left with respect to the pixel column C2n-1 is represented by -. Also, the predetermined range Fa may be the range of the gradation value of the image to be printed.

[0103] Then, the control device 50 calculates the representative value of these displacement amounts: -1 to +3 pixels, and obtains the correction value corresponding to the representative value as the second correction value. For example, when the representative value is the average value, the representative value of the displacement amount is (-1 + 0 + 1 + 2 + 3) / 5 = 1. Also, when the representative value is the median value, the representative value of the displacement amount is 1.

[0104] <Modification Example 2> In the printing apparatus 10 according to Modification Example 2, the control device 50 acquires the first correction value and the second correction value in accordance with a flowchart showing an example of control shown in FIG. 20. First, when the control device 50 acquires, for example, a test print instruction from the user from the input device 13, the control device 50 executes a test print process (step S34). In this test print process, the control device 50 prints the test chart I of the first mark J shown in FIG. 17 and the test chart I of the second mark L shown in FIG. 18 on the print medium A. The area of the second mark L printed by this test print process is larger than the area of the first mark J.

[0105] In this test print process, the control device 50 prints the first mark J with fewer types of ink droplets than the second mark L. That is, the head 20 discharges a plurality of types of ink droplets having different amounts. The plurality of types of ink droplets include, for example, small ink droplets having an amount less than a predetermined range, medium ink droplets having an amount within the predetermined range, and large ink droplets having an amount greater than or equal to the predetermined range. In this case, the second mark L is printed with two or three types of ink droplets out of small ink droplets, medium ink droplets, and large ink droplets. When the second mark L is printed with two types of ink droplets, the first mark J is printed with one type of ink droplet. When the second mark L is printed with three types of ink droplets, the first mark J is printed with one or two types of ink droplets.

[0106] Subsequently, the control device 50 executes correction value acquisition processing to acquire a first correction value based on the printed first mark J and a second correction value based on the printed second mark L (step S35). In this correction value acquisition processing, for the first mark J, similar to the first acquisition processing in step S31 of FIG. 16, the control device 50 reads the test chart I of the printed first mark J with the scanner 14, and based on the image data, obtains the first mark J for which the interval J3 between the position of the basic first mark J1 and the position of the comparison first mark J2 in the left - right direction is minimized. Then, the control device 50 acquires the correction amount of the ejection timing corresponding to the first mark J as the first correction value.

[0107] Also, the control device 50 reads the test chart I of the printed second mark L with the scanner 14 to acquire the image data of the second mark L. Then, the control device 50 executes predetermined image analysis on this image data to acquire the granularity evaluation value of the second mark L. Then, the control device 50 acquires the correction amount of the ejection timing corresponding to the second mark L with the minimum granularity evaluation value as the second correction value.

[0108] <Modification Example 3> As shown in FIG. 1, the printing apparatus 10 according to Modification Example 3 further includes a distance measuring sensor 15. The distance measuring sensor 15 is electrically connected to the control device 50, detects the dimension of the gap between the ejection surface 23 of the head 20 and the print medium A facing the ejection surface 23, and outputs the dimension to the control device 50. When the dimension of the print medium A is input by the communication interface 53 or the input device 13, the control device 50 may also acquire the dimension of the gap between the ejection surface 23 and the print medium A based on the dimension, and the predetermined positions on the upper surfaces of the ejection surface 23 and the platen 12.

[0109] The control device 50 acquires the second correction value according to a flowchart showing an example of the control shown in FIG. 21. The first correction value may be acquired by the processing in steps S30 and S31 of FIG. 16.

[0110] First, the control device 50 acquires the dimension of the gap between the head 20 and the printing medium A based on the detection signal of the distance measuring sensor 15, and executes matrix acquisition processing for acquiring the error diffusion matrix used for error diffusion processing from a plurality of error diffusion matrices according to the dimension (step S36). Here, these are pre-associated and stored in the storage unit 52 so that the error diffusion matrix differs according to the dimension of the gap. Therefore, the control device 50 acquires the error diffusion matrix corresponding to the dimension of the gap based on this correspondence relationship.

[0111] Subsequently, the control device 50 executes correction value acquisition processing for acquiring the second correction value for each error diffusion matrix (step S37). These are pre-associated and stored in the storage unit 52 so that the second correction value differs according to the error diffusion matrix. In this way, the control device 50 acquires the second correction value corresponding to the error diffusion matrix based on this correspondence relationship. As a result, the second correction value corresponding to the dimension of the gap is acquired, and since this second correction value is used for correcting the ejection timing of the ink droplets, it is possible to reduce the deterioration of the image quality caused by the dimension of the gap.

[0112] <Modification Example 4> In the printing apparatus 10 according to Modification Example 4, the control device 50 acquires the second correction value along the flowchart showing an example of the control shown in FIG. 22. Note that the first correction value may be acquired by the processes of steps S30 and S31 in FIG. 16.

[0113] First, the control device 50 executes type acquisition processing for acquiring the type of ink droplets ejected from the head 20 in the printing process (step S38). Here, the type of dot B in the dot data to be printed corresponds to the size of the ink droplets. Therefore, the control device 50 acquires the type of ink droplets used in the printing process based on the type of this dot B.

[0114] Subsequently, the control device 50 executes a second acquisition process of acquiring a second correction value according to the type of ink droplets used in the printing process (step S39). The type of ink droplets and the second correction value are associated with each other in advance and stored in the storage unit 52 so that the second correction value varies according to the type of ink droplets.

[0115] For example, the larger the gap dimension, the more the mist amount of the ejected ink increases. Therefore, the type of ink droplets used in the printing process is stored in the storage unit 52 in advance so as to vary according to the gap dimension, such as not ejecting small ink droplets. Specifically, when the gap dimension is larger than a predetermined dimension, a combination of medium ink droplets and large ink droplets as the types of ink droplets used in the printing process is stored in the storage unit 52 in advance. When the gap dimension is smaller than the predetermined dimension, a combination of small ink droplets, medium ink droplets, and large ink droplets as the types of ink droplets used in the printing process is stored in the storage unit 52 in advance.

[0116] That is, when small ink droplets are used in the printing process, the gap dimension is smaller than when small ink droplets are not used in the printing process. Therefore, when small ink droplets are used in the printing process, the second correction value for the case where the gap dimension is small is associated. When small ink droplets are not used in the printing process, the gap dimension is larger than when small ink droplets are used in the printing process. Therefore, when small ink droplets are not used in the printing process, the second correction value for the case where the gap dimension is large is associated. The second correction value for the case where the gap dimension is small is different from the second correction value for the case where the gap dimension is large.

[0117] In this way, the control device 50 can acquire the second correction value according to the type of ink droplets and use the second correction value to correct the ejection timing of the ink droplets, thereby reducing the image quality degradation caused by the gap dimension.

[0118] In other words, the types of ink droplets used in the printing process include, for example, combinations of medium ink droplets and large ink droplets, combinations of small ink droplets and medium ink droplets, and combinations of small ink droplets, medium ink droplets, and large ink droplets. A second correction value is associated with the combination of medium ink droplets and large ink droplets, another second correction value is associated with the combination of small ink droplets and medium ink droplets, and yet another second correction value is associated with the combination of small ink droplets, medium ink droplets, and large ink droplets. By switching this second correction value according to the type of ink droplets corresponding to the gap dimension, it is possible to reduce the image quality degradation caused by the gap dimension.

[0119] <Modification Example 5> In the printing apparatus 10 according to Modification Example 5, as shown in FIG. 23, a plurality (for example, four) of heads 20 and the same number of cartridges 16 as the heads 20 are mounted on the carriage 31. The head 20 has a first head 20a that discharges first ink droplets and a second head 20b that is different from the first head 20a and discharges second ink droplets. In the example of FIG. 23, one first head 20a and three second heads 20b are arranged in the left-right direction. For example, the first ink is black ink, and the second ink is color ink (magenta ink, cyan ink, and yellow ink).

[0120] The cartridge 16 is detachable from the carriage 31 and communicates with the nozzle 21 through the ink flow path 24 of the head 20 without passing through, for example, a tube. The cartridge 16 has a first cartridge 16a and a second cartridge 16b. The first cartridge 16a is disposed on the first head 20a and communicates with the nozzle 21 of the first head 20a. The first cartridge 16a stores the first ink and supplies the first ink to the first head 20a. The second cartridge 16b is disposed on the second head 20b and communicates with the nozzle 21 of the second head 20b. The second cartridge 16b stores the second ink and supplies the second ink to the second head 20b.

[0121] The first correction value has a first correction value for correcting the ejection timing of the first ink droplets by the first head 20a and a first correction value for correcting the ejection timing of the second ink droplets by the second head 20b. As described above, with the mutually different first head 20a and second head 20b, the positional deviation of dot B is different for each head 20. Therefore, by using the first correction value for correcting the positional deviation for each head 20, it is possible to reduce the image quality degradation caused by the positional deviation.

[0122] Unless the above-described all embodiments exclude each other, they may be combined with each other. Further, from the above description, many improvements and other embodiments of the present disclosure will be apparent to those skilled in the art. Therefore, the above description should be construed only as an example and is provided for the purpose of teaching those skilled in the art the best mode of carrying out the present disclosure. Without departing from the spirit of the present disclosure, the details of its structure and / or function can be substantially changed.

Explanation of Signs

[0123] 10: Printing apparatus 11: Cartridge 16: Cartridge 16a: First cartridge 16b: Second cartridge 20: Head 20a: First head 20b: Second head 31: Carriage 40: Conveying device 50: Control device

Claims

1. A head that discharges ink droplets onto a printing medium, A carriage that moves the head in a moving direction, A conveyance device that conveys the printing medium along a conveyance direction intersecting the moving direction, A control device, and includes, The control device, For one pixel column among a plurality of pixel columns along the array direction of the image data, after sequentially changing a target pixel along one direction of the array direction, while sequentially changing the target pixel along the other direction for another pixel column, error diffusion processing is performed on the target pixel to generate dot data representing the type of dot of the target pixel formed on the printing medium, a halftone process, Based on the dot data, a correction process for correcting the discharge timing of the ink droplets from the head by a correction value, Based on the dot data whose discharge timing has been corrected by the correction process, while moving the head along the moving direction, a pass operation of forming dots on the printing medium by the ink droplets discharged from the head, and a printing process including a conveyance operation of conveying the printing medium along the conveyance direction are executed, The correction value, A first correction value for correcting the positional deviation in the moving direction between the dot formed by the current pass operation and the dot formed by the previous pass operation, A second correction value for reducing the graininess of the image composed of the dots formed by a plurality of the pass operations, And has, A printing device.

2. The control device, Executes a resolution determination process for determining whether the resolution of the image in the conveyance direction is an odd multiple of the resolution of the head, When the resolution of the image is an odd multiple of the resolution of the head, the discharge timing is corrected by the first correction value without using the second correction value in the correction process, The printing apparatus according to claim 1.

3. The control device executes a resolution determination process for determining whether the resolution of the image in the conveyance direction is an odd multiple of the resolution of the head, and when the resolution of the image is not an odd multiple of the resolution of the head, corrects the ejection timing by the first correction value and the second correction value in the correction process. The printing apparatus according to claim 1.

4. The control device executes a method determination process for determining whether to perform the printing process in a singling method in which dots are complementarily formed by a plurality of the pass operations on one partial area of the printing medium, In the correction process, when performing the printing process in the singling method, corrects the ejection timing by the first correction value without using the second correction value, and when not performing the printing process in the singling method, corrects the ejection timing by the first correction value and the second correction value. The printing apparatus according to claim 1.

5. The control device when printing a diagram and a drawing on the printing medium by the printing process, performs an overlap determination process for determining whether the diagram and the drawing overlap when viewed along the moving direction, and when the diagram and the drawing overlap, corrects the ejection timing by the first correction value without using the second correction value in the correction process. The printing apparatus according to claim 1.

6. The control device when the diagram and the drawing do not overlap, in the correction process, corrects the ejection timing of the ink droplets in the printing process of the diagram by the first correction value without using the second correction value, Correcting the ejection timing of ink droplets in the printing process of the drawing by the first correction value and the second correction value. The printing apparatus according to claim 5.

7. The control device A test printing process of printing a first mark extending in the conveyance direction on the printing medium, A first acquisition process of acquiring the first correction value based on the printed first mark, For one pixel column among a plurality of pixel columns along the arrangement direction of the dot data of the second mark whose dimension in the moving direction is larger than that of the first mark, when another pixel column is shifted pixel by pixel along the arrangement direction, calculating an image granularity evaluation value of the image, A second acquisition process of acquiring the second correction value based on the granularity evaluation value, and executing the above. The printing apparatus according to claim 1.

8. In the second acquisition process, the control device acquires the second correction value based on a representative value of the shift amount of the pixel columns indicating the granularity evaluation value within a predetermined range. The printing apparatus according to claim 7.

9. The head ejects a plurality of types of ink droplets having different amounts, The control device A test printing process of printing a first mark extending in the conveyance direction and a second mark whose dimension in the moving direction is larger than that of the first mark on the printing medium, Executing a correction value acquisition process of acquiring the first correction value based on the printed first mark and acquiring the second correction value based on the printed second mark, In the test printing process, printing the first mark with fewer types of ink droplets than the second mark. The printing apparatus according to claim 1.

10. The area of the second mark printed by the test printing process is wider than the area of the first mark. The printing apparatus according to claim 9.

11. The control device matrix acquisition processing for acquiring an error diffusion matrix used for the error diffusion processing according to the dimension of the gap between the head and the medium to be printed, and second acquisition processing for acquiring the second correction value for each of the error diffusion matrices, and executes the processing. The printing apparatus according to claim 1.

12. The control device type acquisition processing for acquiring the type of ink droplets ejected from the head in the printing process, and second acquisition processing for acquiring the second correction value according to the type of the ink droplets, and executes the processing. The printing apparatus according to claim 1.

13. comprising a cartridge for supplying ink to the head, the carriage mounts the head and the cartridge, the head has a first head for ejecting first ink droplets and a second head that is different from the first head and ejects second ink droplets, the cartridge has a first cartridge for supplying first ink to the first head and a second cartridge for supplying second ink to the second head, the first correction value has a first correction value for correcting the ejection timing of the first ink droplets by the first head and a first correction value for correcting the ejection timing of the second ink droplets by the second head. The printing apparatus according to claim 1.

14. a head for ejecting ink droplets onto a medium to be printed, a carriage for moving the head in a moving direction, a transport device for transporting the medium to be printed along a transport direction intersecting the moving direction, and a control method for a printing apparatus comprising: For one pixel column among a plurality of pixel columns along the array direction of the image data, after sequentially changing a target pixel along one direction of the array direction, while sequentially changing the target pixel along the other direction for another pixel column, performing error diffusion processing on the target pixel to generate dot data representing the type of dot of the target pixel formed on the print medium, the halftone processing; Based on the dot data, a correction process for correcting the ejection timing of ink droplets from the head with a correction value; Based on the dot data whose ejection timing has been corrected by the correction process, while moving the head along the moving direction, a pass operation for forming dots on the print medium with the ink droplets ejected from the head, and a transport operation for transporting the print medium along the transport direction, and executing a printing process including the above; The correction value is A first correction value for correcting the positional deviation in the moving direction between the dot formed by the current pass operation and the dot formed by the previous pass operation; A second correction value for reducing the graininess of an image composed of dots formed by a plurality of the pass operations; and has A control method for a printing apparatus.

15. A head for ejecting ink droplets onto a print medium; A carriage for moving the head in a moving direction; A transport device for transporting the print medium along a transport direction intersecting the moving direction; In a computer of a printing apparatus including the above, For one pixel column among a plurality of pixel columns along the array direction of the image data, after sequentially changing a target pixel along one direction of the array direction, while sequentially changing the target pixel along the other direction for another pixel column, performing error diffusion processing on the target pixel to generate dot data representing the type of dot of the target pixel formed on the print medium, the halftone processing; Based on the dot data, a correction process for correcting the ejection timing of ink droplets from the head with a correction value; Based on the dot data whose ejection timing has been corrected by the correction process, a pass operation for forming dots on the print medium with the ink droplets ejected from the head while moving the head along the moving direction, and a conveyance operation for conveying the print medium along the conveyance direction, and executing a printing process including the same; The correction value A first correction value for correcting the positional deviation in the moving direction between the dots formed by the current pass operation and the dots formed by the previous pass operation; A second correction value for reducing the graininess of an image composed of the dots formed by a plurality of the pass operations; has a computer program.

Images