JP2011037069A - Fluid jetting apparatus, fluid jetting method, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fluid jetting apparatus which suppresses degradation of an image quality, and also to provide a fluid jetting method and a program. <P>SOLUTION: The fluid jetting apparatus has: (1) a first nozzle array in which first nozzles for jetting a fluid are lined in a predetermined direction; (2) a second nozzle array in which second nozzles for jetting a fluid are lined in the predetermined direction and which has an overlapping region disposed where an end on one side in the predetermined direction overlaps an end on the other side in the predetermined direction of the first nozzle array; and (3) a control part which carries out halftone processing of converting input image data to dot data which shows the presence or absence of dot formation. The control part carries out halftone processing of converting image data corresponding to the overlapping region to the dot data for jetting the fluid from the first nozzles that belong to the overlapping region, and halftone processing of converting the image data corresponding to the overlapping region to the dot data for jetting the fluid from the second nozzles that belong to the overlapping region, independently of each other. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a fluid ejecting apparatus, a fluid ejecting method, and a program.

  As one of the fluid ejecting apparatuses, there is an ink jet printer (hereinafter referred to as a printer) that forms an image by ejecting ink (fluid) from a nozzle provided in a head. There is a printer that forms an image by arranging a plurality of short heads in the paper width direction and ejecting ink from the heads onto a medium conveyed under the plurality of heads.

  However, the interval between nozzles arranged in the paper width direction is very small. For this reason, if the arrangement of the heads arranged in the paper width direction is shifted, the density of the image portion formed at the joint of the heads becomes darker or lighter. In view of this, there has been proposed a printer in which a plurality of heads are arranged by overlapping the end portions of each head (a part of the nozzle row).

JP-A-6-255175

In the printer described above, the dots to be formed at the joints of the heads (dot data after halftone processing) are distributed to any one of the heads arranged in the paper width direction. At this time, if the positional relationship between the heads arranged in the paper width direction is ideal, dots can be formed as indicated by the image data.
However, if the positional relationship of the heads aligned in the paper width direction shifts or the medium conveyed under the heads meanders, the dots formed on the heads aligned in the paper width direction will overlap and the medium will not fill well. End up. As a result, the density of the image formed at the joint of the heads becomes light and the image quality deteriorates.
Therefore, an object of the present invention is to suppress image quality deterioration.

The main invention for solving the above-mentioned problems is (1) a first nozzle row in which first nozzles for ejecting fluid are arranged in a predetermined direction, and (2) a second nozzle for ejecting fluid in the predetermined direction. A second nozzle row, which is arranged to form an overlapping region in which an end portion on one side in the predetermined direction overlaps an end portion on the other side in the predetermined direction of the first nozzle row; (3) A control unit that performs halftone processing for converting input image data into dot data that indicates the presence or absence of dot formation, and the image data corresponding to the overlap region is fluidized from the first nozzle belonging to the overlap region. A halftone process for converting the image data corresponding to the overlap area to the dot data for ejecting fluid from the second nozzle belonging to the overlap area. And the halftone processing for converting the data, and a control unit which performs independently, is a fluid ejecting apparatus, comprising a.
Other features of the present invention will become apparent from the description of this specification and the accompanying drawings.

FIG. 1A is an overall configuration block diagram of the printer, and FIG. 1B is a schematic diagram of the printer. FIG. 2A is a diagram showing the arrangement of the heads provided in the head unit, and FIG. 2B is a diagram showing the nozzle arrangement on the lower surface of the head. FIG. 3A is a diagram illustrating a state of density unevenness due to the head arrangement of the printer of the comparative example, and FIG. 3B is a diagram illustrating a printing method of the comparative example using a printer in which ends of adjacent heads are overlapped. FIG. 4 is a diagram showing a state of density unevenness correction. It is a figure which shows the mode of dot formation when a paper meanders and is conveyed. It is a figure which shows the density fluctuation in the printing method of a comparative example. It is a figure which shows the density fluctuation in the printing method of this embodiment. FIG. 9 is a diagram illustrating a print data creation processing flow for carrying out a printing method of a comparative example; It is a figure which shows a mode that halftoned data is allocated to the nozzle row of an upstream head, and the nozzle row of a downstream head. It is a figure which shows the usage rate of a 1st nozzle row and a 2nd nozzle row. It is a creation processing flow of print data for carrying out the printing method of the present embodiment. It is a figure which shows a mode that the duplication area | region data of high gradation is duplicated and inserted in input image data, and the duplication area data is multiplied by the usage rate of each nozzle row. FIG. 12A is a diagram showing a dither mask, and FIG. 12B is a diagram showing a state of halftone processing by the dither method. It is a figure which shows the nozzle usage rate for correct | amending the density | concentration of an overlapping area image. It is a figure which shows the example which a certain raster line influences the density | concentration of an adjacent raster line. It is a figure which shows a test pattern. This is the result of reading a cyan correction pattern with a scanner. 17A and 17B are diagrams illustrating a specific method for calculating the density unevenness correction value H. FIG. It is a figure which shows the correction value table regarding each nozzle row. It is a figure which shows a mode that the correction value corresponding to each gradation value is calculated regarding the nth row | line area | region of cyan.

=== Summary of disclosure ===
At least the following will become apparent from the description of the present specification and the accompanying drawings.

That is, (1) a first nozzle row in which first nozzles for ejecting fluid are arranged in a predetermined direction, and (2) a second nozzle row in which second nozzles for ejecting fluid are arranged in the predetermined direction, A second nozzle row disposed so as to form an overlapping region in which an end portion on one side in a predetermined direction overlaps an end portion on the other side in the predetermined direction of the first nozzle row; and (3) input image data as dots A control unit that performs a halftone process for converting to dot data indicating presence / absence of formation, and converts the image data corresponding to the overlap region to the dot data for ejecting fluid from the first nozzle belonging to the overlap region. Halftone processing for converting, and halftone processing for converting the image data corresponding to the overlapping region into the dot data for ejecting fluid from the second nozzle belonging to the overlapping region A fluid jet apparatus characterized by comprising a control unit which performs independently.
According to such a fluid ejecting apparatus, the dots by the first nozzle belonging to the overlapping region and the dots by the second nozzle belonging to the overlapping region can be randomly overlapped, and the positional relationship of the nozzle rows is deviated or a conveyance error occurs. Even so, for example, it is possible to reduce the density fluctuation of the image (difference in the degree of filling of the medium by the fluid).

In the fluid ejecting apparatus, the control unit duplicates the image data corresponding to the overlapping area in the input image data, and inserts the image data corresponding to the duplicated overlapping area into the input image data. Data obtained by multiplying the image data corresponding to the overlapping area by the usage rate of the other end of the first nozzle row is subjected to halftone processing, and the image data corresponding to the inserted overlapping area is converted to the second data. Halftone processing is performed on the data obtained by multiplying the usage rate at the one end of the nozzle array.
According to such a fluid ejecting apparatus, it is not necessary to set a threshold for halftone processing for each nozzle row.

In this fluid ejecting apparatus, the usage rate of a certain first nozzle belonging to the overlapping region is higher than the usage rate of the first nozzle located on the other side of the first nozzle, The usage rate of a certain second nozzle belonging to the overlapping region is higher than the usage rate of the second nozzle located on the one side of the second nozzle.
According to such a fluid ejecting apparatus, the boundary between the images formed by the different nozzle rows can be made inconspicuous.

In this fluid ejecting apparatus, the control unit performs dot dispersion type halftone processing.
According to such a fluid ejecting apparatus, it is possible to randomly overlap dots by the first nozzle belonging to the overlapping region and dots by the second nozzle belonging to the overlapping region.

In this fluid ejecting apparatus, a halftone process for converting the dot data for ejecting fluid from the first nozzle belonging to the overlapping region and a fluid ejecting from the second nozzle belonging to the overlapping region Based on the result of performing the halftone process for converting into the dot data independently, a part of the dots formed by the nozzles belonging to the overlapping region are formed by the first nozzle. And the dots formed by the second nozzle are overlapped.
According to such a fluid ejecting apparatus, for example, even if the positional relationship between the nozzle rows is deviated or a conveyance error occurs, it is possible to reduce, for example, image density fluctuation (difference in medium filling due to fluid).

In this fluid ejecting apparatus, the control unit corrects the gradation value indicated by the image data corresponding to the overlapping region to a dark gradation value.
According to such a fluid ejecting apparatus, it is possible to form an image with a desired density even when dots are overlapped (the medium can be filled with a desired degree of filling with fluid).

Further, (1) a first nozzle row in which first nozzles for ejecting fluid are arranged in a predetermined direction, and a second nozzle row in which second nozzles for ejecting fluid are arranged in the predetermined direction, the first nozzle row in the predetermined direction A fluid ejecting method for a fluid ejecting apparatus, comprising: a second nozzle array disposed so as to form an overlapping region in which an end on one side overlaps an end on the other side in the predetermined direction of the first nozzle array. (2) When performing halftone processing for converting input image data into dot data indicating the presence / absence of dot formation, fluid is ejected from the first nozzle belonging to the overlap region to the image data corresponding to the overlap region A halftone process for converting the dot data into the dot data to cause the image data corresponding to the overlapping area to be ejected from the second nozzle belonging to the overlapping area. And (3) ejecting fluid from the first nozzle and the second nozzle based on the result of the halftone process, and (4) A fluid ejecting method characterized by comprising:
According to such a fluid ejecting method, the dots by the first nozzle belonging to the overlapping region and the dots by the second nozzle belonging to the overlapping region can be randomly overlapped, and the positional relationship of the nozzle rows is deviated or a conveyance error occurs. Even so, for example, it is possible to reduce the density fluctuation of the image (difference in the degree of filling of the medium by the fluid).

Further, (1) a first nozzle row in which first nozzles for ejecting fluid are arranged in a predetermined direction, and a second nozzle row in which second nozzles for ejecting fluid are arranged in the predetermined direction, the first nozzle row in the predetermined direction And (2) an input image. The fluid ejecting apparatus includes: a second nozzle row having an overlapping region in which an end portion on one side overlaps with an end portion on the other side in the predetermined direction of the first nozzle row; The dot data for ejecting fluid from the first nozzle belonging to the overlap area to the image data corresponding to the overlap area when performing halftone processing for converting data into dot data indicating the presence or absence of dot formation And halftone processing for converting the image data corresponding to the overlapping area into the dot data for ejecting fluid from the second nozzle belonging to the overlapping area. Be performed and down process, the independently a program for executing the (3).
According to such a program, the dots by the first nozzle belonging to the overlapping area and the dots by the second nozzle belonging to the overlapping area can be randomly overlapped, and the positional relationship between the nozzle rows is shifted or a transport error occurs. In addition, for example, it is possible to reduce the density fluctuation of the image (difference in the degree of filling of the medium by the fluid).

=== About the printing system ===
An embodiment will be described with a printing system in which a line head printer (hereinafter, printer 1) in an inkjet printer and a computer 50 are connected as a fluid ejecting apparatus.

  FIG. 1A is an overall configuration block diagram of the printer 1, and FIG. 1B is a schematic diagram of the printer 1, and shows a state in which the printer 1 transports a sheet S (medium). The printer 1 that has received print data from the computer 50, which is an external device, controls each unit (conveyance unit 20, head unit 30) by the controller 10 and prints an image on the paper S. Further, the detector group 40 monitors the situation in the printer 1, and the controller 10 controls each unit based on the detection result.

  The controller 10 is a control unit for controlling the printer 1. The interface unit 11 is for transmitting and receiving data between the computer 50 as an external device and the printer 1. The CPU 12 is an arithmetic processing unit for controlling the entire printer 1. The memory 13 is for securing an area for storing a program of the CPU 12, a work area, and the like. The CPU 12 controls each unit by a unit control circuit 14 according to a program stored in the memory 13.

  The transport unit 20 includes a transport belt 21 and transport rollers 22A and 22B, sends the paper S to a printable position, and transports the paper S in the transport direction at a predetermined transport speed. The paper S fed onto the transport belt 21 is transported by the transport belt 21 being rotated by the transport rollers 22A and 22B. In addition, the sheet S on the conveyor belt 21 may be electrostatically attracted or vacuum attracted from below.

  The head unit 30 is for ejecting ink droplets onto the paper S, and has a plurality of heads 31. A plurality of nozzles that are ink ejecting portions are provided on the lower surface of the head 31. Each nozzle is provided with a pressure chamber (not shown) containing ink and a drive element (piezo element) for changing the volume of the pressure chamber to eject ink.

  In such a printer 1, when the controller 10 receives print data, the controller 10 first sends the paper S onto the transport belt 21. Thereafter, the paper S is transported on the transport belt 21 without stopping at a constant speed, and faces the nozzle surface of the head 31. Then, while the sheet S is conveyed under the head unit 30, ink droplets are intermittently ejected from each nozzle based on the image data. As a result, a dot row (hereinafter also referred to as a raster line) along the transport direction is formed on the paper S, and an image is printed. The image data is composed of a plurality of pixels arranged two-dimensionally, and each pixel (data) indicates whether or not to form a dot in an area (pixel area) on the medium corresponding to each pixel.

<About nozzle arrangement>
FIG. 2A is a diagram showing the arrangement of the heads 31 provided in the head unit 30, and FIG. 2B is a diagram showing the nozzle arrangement on the lower surface of the head 31. In the printer 1 of the present embodiment, as shown in FIG. 2A, a plurality of heads 31 are arranged side by side in the paper width direction intersecting the transport direction, and the end portions of the heads 31 are arranged in an overlapping manner. Further, the heads 31A and 31B adjacent in the paper width direction are arranged shifted in the transport direction (arranged in a staggered manner). Of the heads 31A and 31B adjacent in the paper width direction, the head 31A on the downstream side in the transport direction is referred to as “downstream head 31A”, and the head 31B on the upstream side in the transport direction is referred to as “upstream head 31B”. The heads 31A and 31B adjacent in the paper width direction are collectively referred to as “adjacent heads”.

  As shown in FIG. 2B, on the lower surface of each head 31, a black nozzle row K for ejecting black ink, a cyan nozzle row C for ejecting cyan ink, a magenta nozzle row M for ejecting magenta ink, and a yellow ink Is formed. Each nozzle row is composed of 180 nozzles (# 1 to # 180). The nozzles of each nozzle row are arranged at a constant interval (for example, 180 dpi) in the paper width direction. It should be noted that the nozzles belonging to each nozzle row are numbered sequentially from the left side in the paper width direction (# 1 to # 180).

  The heads 31 </ b> A and 31 </ b> B arranged in the paper width direction are arranged by overlapping the eight nozzles at the end of the nozzle row of each head 31. Specifically, the eight nozzles (# 1 to # 8) at the left end of the nozzle row of the downstream head 31A and the eight nozzles (# 173 to ##) at the right end of the nozzle row of the upstream head 31B. 180), the eight nozzles (# 173 to # 180) at the right end of the nozzle row of the downstream head 31A and the eight nozzles (# 1 to # 1) at the left end of the nozzle row of the upstream head 31B. # 8) is duplicated. As shown in the figure, in the adjacent heads 31 </ b> A and 31 </ b> B, a portion where the nozzles overlap is referred to as an “overlap region”. Further, the nozzles (# 1 to # 8, # 173 to # 180) belonging to the overlapping area are referred to as “overlapping nozzles”.

  Further, the positions of the overlapping nozzles at the end portions of the heads 31A and 31B aligned in the paper width direction are the same. That is, the position in the paper width direction of the end nozzle of the downstream head 31A is equal to the position in the paper width direction of the corresponding end nozzle of the upstream head 31B. For example, the leftmost nozzle # 1 of the downstream head 31A and the eighth nozzle # 173 from the right of the upstream head 31B are equal in the paper width direction, and the eighth nozzle # 8 from the left of the downstream head 31A is the same. The position in the paper width direction is the same as the rightmost nozzle # 180 of the upstream head 31B. Further, the rightmost nozzle # 180 of the downstream head 31A and the eighth nozzle # 8 from the left of the upstream head 31B have the same position in the paper width direction, and the eighth nozzle # 173 from the right of the downstream head 31A is the same. The position in the paper width direction is the same as the leftmost nozzle # 1 of the upstream head 31B.

  By arranging the plurality of heads 31 in the head unit 30 in this way, the nozzles can be arranged at equal intervals (180 dpi) over the entire region in the paper width direction. As a result, a dot row in which dots are arranged at equal intervals (180 dpi) can be formed over the paper width.

=== About Printing Overview of the Present Embodiment ===
<About density unevenness>
FIG. 3A is a diagram illustrating how uneven density occurs due to the head arrangement of the printer of the comparative example. Here, density unevenness that occurs when the ends of the adjacent heads 31 </ b> A and 31 </ b> B do not overlap will be described using a printer of a comparative example different from the present embodiment as an example. In the printer of the comparative example, by design, the distance between the leftmost nozzle (# 1) of the nozzle row of the downstream head 31A and the rightmost nozzle (# 180) of the nozzle row of the upstream head 31B is the nozzle pitch ( For example, it is set to 180 dpi.

  However, since the nozzle pitch is very small, the positional relationship between the adjacent heads 31A and 31B tends to shift. The left diagram in FIG. 3A shows a case where the downstream head 31A is shifted to the right in the paper width direction and the distance between the two heads 31A and 31B is wider than the designed distance (180 dpi). In this case, the interval between the raster line formed at the end nozzle # 1 of the downstream head 31A and the raster line formed at the end nozzle # 180 of the upstream head 31B is wider than the nozzle pitch 180 dpi, and the image White streaks appear on the top.

  Conversely, the right diagram in FIG. 3A shows a case where the downstream head 31A is shifted to the left in the paper width direction and the distance between the two heads 31A and 31B is narrower than the designed distance. In this case, the raster line formed at the end nozzle # 1 of the downstream head 31A and the raster line formed at the end nozzle # 180 of the upstream head 31B overlap, and black lines are generated on the image. As described above, when the positional relationship between the adjacent heads 31A and 31B is deviated, density unevenness (white stripes or black stripes) occurs on the image, and the image quality deteriorates.

  Therefore, when density unevenness shown in FIG. 3A occurs, density unevenness correction is performed. If the raster lines formed on the end nozzles (# 1, # 180) overlap each other and appear dark as shown in the right diagram of FIG. 3A, the dot size formed by the end nozzles should be reduced. Thus, density correction can be performed.

  However, as shown in the left diagram of FIG. 3A, when the raster lines formed in the end nozzles (# 1, # 180) are spaced apart and are visually perceived as light, dots are formed in the spaced portions. Can not be formed. That is, since the dots cannot be filled in the white stripe area, the density unevenness is not corrected.

  FIG. 3B is a diagram illustrating a printing method of a comparative example using a printer in which the ends of adjacent heads 31A and 31B are overlapped, and FIG. 3C is a diagram illustrating a state of density unevenness correction. 3B and 3C, the end portions of the adjacent heads 31A and 31B are overlapped as in the printer 1 (FIG. 2) of the present embodiment. However, for simplicity of explanation, the number of overlapping nozzles is reduced to four. Yes. The dots formed on the downstream head 31A are indicated by white circles, and the dots formed on the upstream head 31B are indicated by black circles.

  In the printing method of the comparative example, dots to be formed in the overlapping region (head joint) are divided into the overlapping nozzles (# 1 to # 4) of the downstream head 31A and the overlapping nozzles (# 5 to ##) of the upstream head 31B. 8) It is formed by one of the nozzles. In FIG. 3B, one raster line is formed by alternately forming dots by the overlapping nozzles (example: # 1) of the downstream head 31A and the overlapping nozzles (example: # 5) of the upstream head 31B. .

  The left diagram in FIG. 3B shows dots formed when the positional relationship between the adjacent heads 31A and 31B is as designed. On the other hand, the right diagram in FIG. 3B shows a case where the downstream head 31A is displaced to the right in the paper width direction. Similar to the left diagram of FIG. 3A, even if the downstream head 31A is displaced so as to be separated from the upstream head 31B, in the right diagram of FIG. 3B, the end portions of the adjacent heads 31A and 31B are overlapped. It is possible to prevent white streaks from occurring as shown in the left figure of 3A.

  However, as shown in the right diagram of FIG. 3B, when the positional relationship between the adjacent heads 31A and 31B is shifted, dots (white circles) formed on the overlapping nozzles (# 1 to # 4) of the downstream head 31A and the upstream head 31B. Dots (black circles) formed on the overlapping nozzles (# 5 to # 8) overlap. Even if dots are formed in an overlapping manner, the dot size does not increase so much, and the filling of the medium becomes worse. In particular, as shown in the right diagram of FIG. 3B, when the adjacent heads 31A and 31B are displaced so that they are separated from each other, the amount of ink ejected toward the medium portion allocated to the overlapping area is reduced (per unit area). Less ink jetting). As a result, the density of the image portion formed at the joint (overlapping area) of the head becomes light. Therefore, when the positional relationship between the adjacent heads is shifted, the filling of the medium becomes worse, and the image density becomes lighter, the overlapping nozzles (# 1 to # 4, # 5 to # 8) are used as shown in FIG. 3C. It is preferable to increase the dot size to be formed. As a result, the lightness of the image density can be corrected.

  For example, in the manufacturing process of the printer 1 or the like, it is assumed that the positional relationship between the adjacent heads 31A and 31B is detected, and the density unevenness correction value is calculated when the positional relationship between the adjacent heads is not as designed. Then, in the printer 1 in which the adjacent heads 31A and 31B are displaced as shown in the right diagram of FIG. 3B, the density unevenness correction value is set so as to increase the dot size formed by the overlapping nozzles. In this case, if the positional relationship between the adjacent heads 31A and 31B is the positional relationship when the density unevenness correction value is calculated, the density unevenness can be corrected.

  However, the positional relationship between the adjacent heads 31A and 31B may deviate from the positional relationship between the adjacent heads 31A and 31B when the density unevenness correction value is calculated due to the aging of the printer 1 and the change in the usage environment. If the positional relationship between the adjacent heads is deviated, the way in which dots are overlapped by the heads 31A and 31B changes, and the degree of filling of the medium also changes. That is, in the printing method of the comparative example (FIG. 3B), if the positional relationship between the adjacent heads 31A and 31B shifts due to secular change or the like, the density unevenness can be eliminated with the correction value H set in the manufacturing process of the printer 1 or the like. It will disappear.

  FIG. 4 is a diagram illustrating how dots are formed when the paper S is meandered and conveyed. The positional relationship between adjacent heads is not limited to the case where the positional relationship between adjacent heads actually deviates due to secular change or the like, and the manner in which density unevenness occurs (medium embedding condition) differs. In the same way as in the case of the case, the generation of density unevenness may be different. For example, the sheet S may be conveyed while meandering due to the characteristics of the conveyance unit 20 or the like. FIG. 4 is a diagram showing dots formed when the paper S is conveyed while being shifted to the left in the paper width direction.

  The positional relationship between the adjacent heads 31A and 31B in FIG. 4 is as designed, and the overlapping nozzle (e.g., # 1) of the downstream head 31A and the corresponding overlapping nozzle (e.g., # 5) of the upstream head 31B. Are assumed to be equal in the paper width direction. In the printing method of the comparative example, dots are alternately formed by the overlapping nozzles of the downstream head 31A and the overlapping nozzles of the upstream head 31B. In FIG. 4, when one dot row is formed along the paper width direction, ink droplets are ejected from nozzle # 1 # 3 among the overlapping nozzles (white circles) of the downstream head 31A, and the overlapping nozzles ( Ink droplets are ejected from nozzle # 6 # 8 of black circles).

  First, as shown in the left diagram of FIG. 4, when a certain area on the sheet S and the upstream head 31B face each other, ink droplets are ejected from the upstream head 31B. As a result, as shown in the center diagram of FIG. 4, dots (black circles) formed by the upstream head 31B are formed in a certain area on the paper S side by side in the paper width direction. Thereafter, the sheet S is conveyed while shifting (meandering) to the left side in the sheet width direction after a certain area of the sheet S passes under the upstream head 31B until it faces the downstream head 31A. . Then, as shown in the right diagram of FIG. 4, dots (white circles) formed by the downstream head 31A are formed at positions on the right side of the positions of the dots that should be originally formed by the downstream head 31A.

  Thus, even if the positional relationship between the adjacent heads 31A and 31B is as designed, when the paper S is transported while being shifted to the left in the transport direction as in the example shown in FIG. Dots (white circles) formed by the downstream head 31A are shifted to the right in the paper width direction with respect to the black circles). That is, dots are formed in the same manner as when the downstream head 31A is displaced to the right in the paper width direction with respect to the upstream head 31B. For this reason, the dots formed by the heads 31A and 31B overlap each other, the medium is poorly filled, and the image density becomes light. Furthermore, since dots are formed in the same manner as when the positional relationship between the adjacent heads 31A and 31B is shifted away, the amount of ink per unit area is reduced and the image density is further reduced.

  However, in the printer shown in FIG. 4, the actual positional relationship between the adjacent heads 31A and 31B is as designed, and it is set that it is not necessary to perform density unevenness correction in the manufacturing process of the printer, so the image density is low. As a result, the image quality deteriorates. Further, even when the actual positional relationship between the adjacent heads 31A and 31B is deviated and a density unevenness correction value is set, the manner of dot overlap (medium embedding method) changes due to meandering during the conveyance of the paper S. Therefore, the density unevenness correction value that has been set cannot correct the density unevenness.

  FIG. 4 shows a case where the sheet S is conveyed to the left side in the sheet width direction in an overlapping region between the right end portion of the upstream head 31B and the left end portion of the downstream head 31A. On the other hand, in the overlapping region of the left end of the upstream head 31B and the right end of the downstream head 31A (not shown), when the paper S is conveyed shifted to the left in the paper width direction, the upstream head 31B Dots are formed in the same manner as when the downstream head 31A is displaced to the right (when the adjacent head is displaced in the approaching direction). In this case, the dots formed by the heads 31A and 31B overlap each other, and the filling of the medium worsens. However, the amount of ink ejected per unit area of the medium corresponding to the overlapping region increases, so that the image is as high as in the case shown in FIG. The concentration does not fade.

  That is, in the printer 1 in which the heads 31A and 31B arranged in the paper width direction are shifted in the transport direction (in the printer 1 in which the heads 31 are arranged in a staggered manner), the positional relationship between the adjacent heads 31A and 31B is as designed. Even if the density unevenness correction value is set according to the positional relationship between adjacent heads, the paper S is conveyed while meandering in the paper width direction, so that the dots formed by the heads 31A and 31B. Will overlap (dot embedding) will change. Therefore, even if the images are formed in the same overlapping area (joint of the same head), the image density changes when the paper S is conveyed while meandering, and is set according to the positional relationship between adjacent heads ( In some cases, the density unevenness correction value cannot correct the density unevenness.

  Further, so far, the positional relationship of the adjacent heads 31A and 31B in the paper width direction and the density unevenness generated when the paper S is shifted in the paper width direction during conveyance, that is, the density unevenness generated due to the shift of the dot interval aligned in the paper width direction. Although described, it is not limited to this. In the printer 1 of the present embodiment, since the downstream head 31A and the upstream head 31B are separated in the transport direction (being arranged in a staggered manner), the distance in the transport direction between the downstream head 31A and the upstream head 31B. The ejection timing of the ink droplets by the heads 31A and 31B is adjusted according to (design interval). As a result, for example, as shown in the left diagram of FIG. 3B, dots (white circles) due to the overlapping nozzles of the downstream head 31A and dots (black circles) due to the overlapping nozzles of the upstream head 31B can be arranged at equal intervals in the transport direction. it can.

  However, when the positional relationship of the adjacent heads 31A and 31B in the transport direction is shifted, the positions of the dots formed by the heads 31A and 31B in the transport direction are shifted. For this reason, the dots formed by the heads 31A and 31B overlap each other, resulting in poor media filling, resulting in a light image density. Further, even if the positional relationship in the transport direction of the adjacent head is as designed or the ejection timing is adjusted according to the positional relationship in the transport direction of the adjacent head, the transport unevenness (speed unevenness) of the paper S occurs. Then, the dots formed by the heads 31A and 31B overlap each other, and the filling of the medium becomes worse. Even in such a case, uneven density cannot be corrected.

  FIG. 5 is a diagram illustrating density fluctuations in the printing method of the comparative example. The left diagram in FIG. 5 is a diagram illustrating dots formed when the positional relationship between the adjacent heads 31A and 31B is as designed, or when density unevenness correction is performed according to the positional relationship between the adjacent heads. On the other hand, the right diagram in FIG. 5 shows dots formed when the positional relationship between adjacent heads is shifted in the paper width direction and the transport direction, or when a transport error (meandering or uneven speed) occurs. FIG.

  Note that one square in the drawing represents one pixel area (area on the medium corresponding to the pixel) and dots formed in the pixel area. Dots formed by the downstream head 31A are indicated by lower right hatched cells, and dots formed by the upstream head 31B are indicated by lower left hatched cells. In addition, it is assumed that the image data indicates that dots are formed in all pixel regions (regions on the medium corresponding to the pixels).

  In the printing method of the comparative example, dots to be formed in the overlapping region are transferred in the transport direction and the overlapping nozzles (# 1 to # 8) of the downstream head 31A and the overlapping nozzles (# 173 to # 180) of the upstream head 31B. They are formed alternately in the paper width direction. In other words, in the printing method of the comparative example, one overlapping nozzle of either the downstream head 31A or the upstream head 31B is assigned to one pixel associated with the overlapping region. In other words, in the printing method of the comparative example, the dots to be formed in the overlapping region are formed by the overlapping nozzles of either the downstream head 31A or the upstream head 31B.

  As shown in the left diagram of FIG. 5, the positional relationship between the adjacent heads 31A and 31B is as designed (or density correction is set according to the positional relationship), and no conveyance error (meandering or uneven speed) occurs. In this case, dots formed by overlapping nozzles are formed without gaps, the medium is well filled, and a desired image density can be obtained.

  However, if the positional relationship between adjacent heads shifts due to changes over time or a transport error occurs, dots from the heads 31A and 31B overlap as shown in the right diagram of FIG. As a result, the image density formed in the overlapping region becomes light. In particular, when the adjacent head is displaced in the direction away from the paper width direction, the amount of ink ejected per unit area is reduced, so that the image density formed in the overlapping region becomes lighter.

  Summarizing the above, a printing method of a comparative example in which a certain dot to be formed in the overlapping region (a dot formed by one pixel data) is formed by one of the overlapping nozzles of the downstream head 31A or the upstream head 31B. In an ideal state (when the positional relationship between adjacent heads is not shifted and no conveyance error occurs), the medium is well filled and a desired image density is obtained. However, when a positional deviation or a conveyance error occurs between adjacent heads, the dots formed by the heads 31A and 31B overlap each other, resulting in poor media filling, resulting in a lighter image density formed in the overlapping region.

  That is, in the printing method of the comparative example, the density difference (density fluctuation) of the image formed in the overlapping region is large between the ideal state and the case where the positional deviation or conveyance error of the adjacent head occurs. In addition, recalculating the density unevenness correction value H according to the positional deviation of the adjacent heads 31A and 31B due to secular change or the like places extra effort on the user, and also according to the transport error (meandering or speed unevenness). It is difficult to perform density unevenness correction.

  Therefore, in this embodiment, the ideal state (the state where the positional relationship between the adjacent heads is as designed or the density unevenness correction value corresponding to the positional relationship between the adjacent heads is set and no conveyance error occurs) and the position of the adjacent head An object is to reduce the density fluctuation of the image formed in the overlapping area as much as possible in the state where the deviation or the conveyance error has occurred. That is, an object is to suppress image quality deterioration.

<About printing overview of this embodiment>
FIG. 6 is a diagram showing density fluctuations in the printing method of the present embodiment. The left diagram in FIG. 6 is formed in an ideal state (in which the positional relationship between adjacent heads is as designed, or a density unevenness correction value corresponding to the positional relationship between adjacent heads is set and no conveyance error occurs). FIG. On the other hand, the right diagram in FIG. 6 is a diagram showing dots formed when a positional deviation or a transport error occurs between adjacent heads. It should be noted that dots formed by the downstream head 31A are indicated by lower right hatched cells, and dots formed by the upstream head 31B are indicated by lower left hatched cells. In addition, it is assumed that the image data indicates that dots are formed in all pixel regions (regions on the medium corresponding to the pixels).

  In the printing method of the present embodiment, some dispersed dots among the dots formed by the overlapping nozzles are divided into dots formed by the overlapping nozzles of the downstream head 31A and the overlapping nozzles of the upstream head 31B. Make dots that overlap. That is, in the printing method of the present embodiment, since dots that should be formed are originally overlapped in different pixel areas, a part of the pixel area where dots should be formed in order to obtain a desired image density, Dots are not formed.

  Therefore, in the printing method of this embodiment, even in an ideal state, as shown in the left diagram of FIG. 6, dots are not formed in some pixel areas (white areas), and some pixel areas The dots formed by the downstream head 31A and the dots formed by the upstream head 31B are formed so as to overlap each other (cross hatching portion). In the remaining pixel area, one dot by the downstream head 31A (lower right hatching) or one dot by the upstream head 31B (lower left hatching) is formed.

  Then, when a positional deviation of adjacent heads or a transport error (meandering or uneven speed) occurs, dots are formed as shown on the right side of FIG. Due to the positional deviation or transport error of the adjacent head, the filling of the medium is reduced in the portion where the dots by the heads 31A and 31B are newly overlapped. However, due to the positional deviation of adjacent heads and transport errors, the dots formed in an overlapped state in the ideal state are displaced, and a new medium portion can be filled. Therefore, compared with the printing method of the comparative example (FIG. 5), in the printing method of the present embodiment, even in the ideal state (the left diagram of FIG. 6), when the positional deviation of the adjacent head or the conveyance error occurs. In addition (right figure in FIG. 6), the variation in the filling of the medium is small, and the variation in the image density can be reduced.

  In an ideal state, it is preferable that dot positions where dots formed by the downstream head 31A and dots formed by the upstream head 31B are intentionally overlapped are dispersed (positioned randomly). If dots formed by overlapping both heads 31A and 31B are gathered in one place, a dot that overlaps a certain dot in the ideal state is newly replaced with a different dot due to head misalignment or transport error. It only overlaps, and instead of the dots overlapping and the media filling becoming worse, the media cannot be newly filled. Then, as the dots are newly overlapped due to the positional deviation of the head and the conveyance error, the medium is poorly filled, and the density becomes lighter than in the ideal state. That is, the density fluctuation cannot be reduced.

  As described above, in the printing method of the present embodiment, in the ideal state, the dots formed by the downstream head 31A and the dots formed by the upstream head 31B are randomly and randomly formed. Therefore, when creating print data, among the dispersed pixels among the pixels in which dots are to be formed in order to obtain a desired image density, the pixels for the downstream head 31A are also the pixels for the upstream head 31B. Are also “pixels that form dots”.

  By doing so, for example, after the density unevenness correction value is calculated according to the initial positional relationship of the adjacent head when the printer 1 is manufactured, even if the positional relationship of the adjacent head is shifted due to secular change, it is formed in the overlapping region. Therefore, the density correction can be performed by the density unevenness correction value at the time of manufacturing the printer 1. In addition, even when the paper S is conveyed correctly, even when the paper S is meandered and uneven in speed, the density variation of the image formed in the overlapping region is small, so that the image quality deteriorates. And the density correction process becomes easy. However, in the printing method of the present embodiment, some dots are printed in an overlapping state even in an ideal state (the left figure in FIG. 6), so the image density formed in the overlapping region is higher than the desired density. It will be faint. Therefore, it is preferable to perform density correction processing on the image formed in the overlapping area (details will be described later).

=== About Print Data Creation Processing ===
<< Print data creation process of comparative example >>
FIG. 7 is a diagram showing a print data creation processing flow for implementing the printing method of the comparative example (FIG. 5). FIG. 8 shows the halftoned data corresponding to the overlap area in the nozzles of the upstream head 31B. FIG. 9 is a diagram showing a state of assignment to a row (hereinafter referred to as a first nozzle row) and a nozzle row (hereinafter referred to as a second nozzle row) of the downstream head 31A, and FIG. 9 illustrates the first nozzle row and the second nozzle. It is a figure which shows the utilization factor of a column. Hereinafter, a print data creation process (comparative example) for implementing the printing method of the comparative example (FIG. 5) as described above will be described.

  In the printing method of the comparative example, the dots to be formed in the overlapping region in order to obtain a desired image density are either the first nozzle row (upstream head 31B) or the second nozzle row (downstream head 31A). Always form with overlapping nozzles. For example, as shown in FIG. 5, when the image data indicates that dots are formed on all the pixels associated with the overlapping area, the first nozzle row or the second nozzle row is applied to all the pixels. A dot is formed by any one of the overlapping nozzles. A print data creation process for performing such printing will be described below. In the present embodiment, it is assumed that print data is created by a printer driver installed in the computer 50 connected to the printer 1.

  As shown in FIG. 7, when receiving image data from various application programs (S001), the printer driver performs resolution conversion processing (S002). The resolution conversion process is a process of converting image data received from various application programs into a resolution for printing on the medium S. The image data after the resolution conversion process is 256 gradation (high gradation) RGB data represented by an RGB color space. Therefore, the printer driver next converts RGB data into YMCK data corresponding to the ink of the printer 1 by color conversion processing (S003). If the density unevenness correction value H is set in the printer 1, the printer driver corrects 256-gradation YMCK data with the correction value H (S004).

  Next, the printer driver converts the data of 256 gradations (high gradation) into low gradation data that can be formed by the printer 1 by halftone processing (S005). Here, for ease of explanation, the printer 1 can form one type of dot. Therefore, one pixel is expressed by two gradations of “form a dot” or “do not form a dot”. Therefore, the printer driver converts 256 gradation data into two gradation data by halftone processing.

  Next, in the image distribution process (S006), the printer driver converts the halftoned data corresponding to the overlapping area to the overlapping nozzles (# 173 to # 180) of the first nozzle row and the first as shown in FIG. Distribute to overlapping nozzles (# 1 to # 8) in two nozzle rows. The upper diagram of FIG. 8 shows two-gradation data after halftone processing. Black squares represent pixels that form dots, and white portions represent pixels that do not form dots. Further, the data enclosed by the alternate long and short dash line is the halftoned data assigned to the first nozzle row, and the data enclosed by the dotted line is the halftoned data assigned to the second nozzle row. The halftoned data surrounded by overlapping is halftoned data corresponding to the overlapping area.

  The second drawing from the top in FIG. 8 shows data distributed to the first nozzle row and the second nozzle row by the printer driver. However, the overlapping area data surrounded by the dotted line is data assigned to both the overlapping nozzle of the first nozzle array and the overlapping nozzle of the second nozzle array. Therefore, if the data shown in the second diagram from the top in FIG. 8 is maintained, the dots formed by the overlapping nozzles in the first nozzle row and the dots formed by the overlapping nozzles in the second nozzle row are all overlapped. Therefore, the printer driver determines whether the dot indicated by the overlapping area data (halftoned data) is formed on the overlapping nozzle of the first nozzle row or the overlapping nozzle of the second nozzle row (see FIG. (S007 in FIG. 7, masking process). Therefore, the overlap mask shown in the third figure from the top in FIG. 8 is used.

  Here, in the printing method of the comparative example shown in FIG. 5 described above, regardless of the position of the overlapping nozzle (position in the paper width direction), the overlapping nozzle of the downstream head 31A and the overlapping nozzle of the upstream head 31B In addition, dots are alternately formed in the transport direction. That is, regardless of the position of the overlapping nozzle, the usage rate of the overlapping nozzle of the downstream head 31A and the usage rate of the overlapping nozzle of the upstream head 31B are constant (50%).

  However, in the overlap mask shown in FIG. 8, the usage rate of the first nozzle row and the usage rate of the second nozzle row are set to be different depending on the position of the overlapping nozzle. In the first nozzle row located on the left side in the paper width direction, the left nozzle (for example, # 173) of the overlapping nozzles (# 173 to # 180) has a higher nozzle usage rate, and the second nozzle located on the right side in the paper width direction. In the nozzle row, the right nozzle of the overlapping nozzles (# 1 to # 8) has a higher usage rate of the (# 8) nozzle. By doing so, since the image formed by the first nozzle row is gradually shifted to the image formed by the second nozzle row, the image portion formed by the joint of the heads 31 can be made inconspicuous. The nozzle usage rate is a ratio of dots formed by the overlapping nozzles of the downstream head 31A or the overlapping nozzles of the upstream side 31B among the dots constituting the raster line (dot row along the transport direction). . Further, the total usage rate of each nozzle row being 100% means that dots to be formed are necessarily formed.

  The printer driver associates each pixel constituting the overlapping area data with each pixel constituting the overlap mask, and outputs overlapping area data corresponding to each nozzle row. In the printer driver, as shown in FIG. 8, when a certain pixel of the overlapping area data indicates “dot formation (black pixel)” and an overlap mask corresponding to the pixel indicates “dot formation (black pixel)” , "Dot formation (black pixel)" is output, a certain pixel in the overlapping area data indicates "no dot (white pixel)", and an overlap mask corresponding to the pixel indicates "no dot (white pixel)" When it is shown, “No dot (white pixel)” is output. On the other hand, when a certain pixel in the overlap area data indicates “no dot (white pixel)”, the printer driver does not display “dot” even if the overlap mask corresponding to the pixel indicates “dot formation (black pixel)”. Even if “None (white pixel)” is indicated, “No dot (white pixel)” is output. The lowermost diagram in FIG. 8 shows the data output by the mask process.

  In the overlap mask used in the printing method of the comparative example, regarding the dot formation, the overlap mask for the first nozzle row and the overlap mask for the second nozzle row show opposite pixels. For example, when the overlap mask for the first nozzle row indicates “dot formation (black pixel)”, the overlap mask for the second nozzle row corresponding to the pixel indicates “no dot (white pixel)”. Therefore, the dots to be formed in the overlapping region are always formed by the overlapping nozzles of either the first nozzle row or the second nozzle row, and the dots by the overlapping nozzles of both nozzle rows are formed by overlapping. Absent. Therefore, when the overlapping area data for the first nozzle row and the overlapping area data for the second nozzle row shown in the bottom row of FIG. 8 are combined, the overlapping region data shown in the top row of FIG. 8 is obtained.

  As described above, the printer driver calculates the logical product of the overlap masks corresponding to the respective nozzle rows with respect to the overlapping area data. As a result, it is possible to determine which of the first nozzle row and the second nozzle row should form dots to be formed in the overlapping region.

  Thus, after the masking process (S007) for the overlapping area data can identify the pixels (dots) responsible for the formation of each nozzle row, the printer driver transfers the matrix image data to the printer 1 by the rasterizing process. Rearrange in the order to be performed (S008). The printer driver transmits the data having undergone these processes to the printer 1 together with command data corresponding to the printing method. The printer 1 performs printing based on the received print data.

  In summary, in the print data creation process of the comparative example, the image data corresponding to the overlapping area is first halftoned, and the halftoned data is distributed to each overlapping nozzle of the adjacent head. By doing so, the dots to be formed in the overlapping region are always formed by any one of the overlapping nozzles of the adjacent head, and the dots by the overlapping nozzles of the adjacent head are not formed in the same pixel region. In this case, if no adjacent head misalignment or transport error (meandering or uneven speed) occurs (left figure in FIG. 5), a desired image density can be obtained. However, when an adjacent head misalignment or conveyance error occurs (right diagram in FIG. 5), dots formed on the adjacent heads overlap each other, resulting in poor media filling and light image density. In other words, the density fluctuation of the image becomes large in the ideal state and in the case where the positional deviation or the conveyance error of the adjacent head occurs.

<< Print Data Creation Processing of the Present Embodiment >>
In the present embodiment, as shown in FIG. 6, a part of dots formed in the overlapping region is formed randomly (randomly) by overlapping dots by the overlapping nozzles of the adjacent heads 31A and 31B. By doing so, misalignment of adjacent heads and transport errors (meandering and uneven speed) occurred, and even though the dots by the overlapping nozzles of adjacent heads newly overlapped to reduce the filling of the medium, they overlapped in the ideal state. The dots can be shifted and the medium can be newly filled. As a result, it is possible to reduce the filling of the medium both in the ideal state and in the case where an adjacent head misalignment or transport error occurs. That is, the density fluctuation of the image can be reduced.

  In the present embodiment, dot data (halftoned) regarding the overlapping nozzles of the downstream head 31A so that the dots due to the overlapping nozzles of the downstream head 31A and the dots due to the overlapping nozzles of the upstream head 31B overlap randomly (distributed). Print data is created so that there is no correlation between the data) and the dot data related to the overlapping nozzles of the upstream head 31B.

  Specifically, in the present embodiment, halftone processing for converting image data corresponding to the overlapping region into dot data corresponding to the overlapping nozzle of the upstream head 31B, and image data corresponding to the overlapping region to the downstream head 31A. The halftone process for converting into dot data corresponding to the overlapping nozzles is performed independently (performed separately). Hereinafter, the print data creation process of this embodiment will be described in detail.

  FIG. 10 shows a print data creation processing flow for carrying out the printing method of the present embodiment (for example, FIG. 6). When the printer driver in the computer 50 connected to the printer 1 receives image data from the application software (S101), it performs resolution conversion processing (S102) and color conversion processing in the same manner as the print data creation processing of the comparative example. (S103) and density correction processing (S104, details will be described later). Thereafter, halftone processing is performed in the print data creation processing of the comparative example (FIG. 7), whereas duplication / insertion processing of overlapping area data is performed in the print data creation processing of the present embodiment (FIG. 10). (S105).

  FIG. 11 is a diagram showing a state in which the overlapping area data of high gradation is duplicated and inserted into the input image data, and the overlapping area data is multiplied by the usage rate of each nozzle row. The upper diagram of FIG. 11 shows high gradation data (256 gradation data) before halftone processing. The first nozzle array (the nozzle array of the upstream head 31B) and the second nozzle array (the nozzle array of the downstream head 31A). ). One square in the figure corresponds to one pixel, and the number written in the pixel is the gradation value of the pixel. Here, for ease of explanation, the gradation value of all pixels is assumed to be 100. In addition, pixels (data) surrounded by a thick line are data “overlapping region data” corresponding to the overlapping region of the first nozzle row and the second nozzle row. In the image data, the direction corresponding to the paper width direction is defined as the X direction, and the direction corresponding to the transport direction is defined as the Y direction.

  After the density correction process (S104 in FIG. 10), the printer driver duplicates the overlapping area data and inserts it into the input image data (upper figure in FIG. 11) which is high gradation data before the halftone process. Here, the duplicated overlapping area data is inserted (on the right side in the X direction) after the overlapping area data in the input image data (hereinafter, the original overlapping area data). The result is the second data from the top in FIG. 11, and two overlapping area data are arranged in the X direction. The original overlapping region data corresponds to data corresponding to the overlapping nozzles of the first nozzle row, and the duplicate overlapping region data corresponds to data corresponding to the overlapping region of the second nozzle row.

  Next, the printer driver multiplies two overlapping area data by the usage rate of each nozzle row. In the print data creation process of the comparative example, since the halftoned data is distributed to the first nozzle row and the second nozzle row, an overlap mask (FIG. 8) corresponding to the usage rate (FIG. 9) of each nozzle row is used. use. On the other hand, in the print data creation process of this embodiment, since the high gradation data before halftone is distributed to the first nozzle array and the second nozzle array, the gradation value (high gradation value) indicated by each pixel. Is multiplied by the nozzle usage rate. The data shown at the bottom of FIG. 11 is the result of multiplying the overlapping area data by the usage rate of each nozzle row.

  In addition, the nozzle usage rate of this embodiment is also changed according to the position of an overlapping nozzle similarly to the nozzle usage rate of a comparative example (FIG. 9). As shown in the third diagram from the top in FIG. 11, in the usage rate of the first nozzle row, the usage rate is higher for the first nozzle row side (left side) of the overlapping nozzles, and the usage rate is gradually lower. It has become. On the other hand, in the usage rate of the second nozzle row, the usage rate is lower as the nozzle on the first nozzle row side (left side) of the overlapping nozzles is gradually increased. When the usage rate of the first nozzle row and the usage rate of the second nozzle row are totaled, the usage rate is 100%.

  For example, the leftmost pixel (column) of the original overlapping region data is data assigned to the nozzle # 173 of the first nozzle row, and the leftmost pixel (column) of the duplicate overlapping region data is the nozzle of the second nozzle row. Data assigned to # 1. The usage rate of nozzle # 173 in the first nozzle row is 89%, the usage rate of nozzle # 1 in the second nozzle row is 11%, and the gradation value of the pixel before distribution is “100”. In this case, as shown at the bottom of FIG. 11, the gradation value of the data assigned to the nozzle # 173 of the first nozzle row is “89”, and the gradation of the data assigned to the nozzle # 1 of the second nozzle row. The value is “11”. As described above, by changing the usage rate according to the position of the overlapping nozzle, it is possible to perform printing while making the density difference between the image formed in the overlapping region and the image formed in the non-overlapping region inconspicuous. .

  FIG. 12A is a diagram showing a dither mask, and FIG. 12B is a diagram showing a state of halftone processing by the dither method. Here, an example in which halftone processing is performed by the dither method is shown. The dither method is a method for determining the presence or absence of dot formation based on the magnitude relationship between the threshold value stored in the dither mask and the gradation value indicated by each pixel. According to the dither method, it is possible to generate dots at a density corresponding to the gradation value indicated by the pixel for each unit area (for each area to which one dither mask is assigned). Further, in the dither method, dots can be generated by being dispersed according to the setting of the threshold value of the dither mask, and the graininess of the image can be improved.

  The dither mask shown in FIG. 12A is composed of “X direction × Y direction = 256 pixels × 256 pixels”, and a threshold value is set for each pixel. Therefore, the number of pixels (256 pixels) in the X direction (direction corresponding to the paper width direction) of the dither mask is larger than the total number of pixels (16 pixels) in the X direction of the overlapping area data of the first nozzle row and the second nozzle row. A sufficiently large dither mask is set.

  FIG. 12B shows a position where a dither mask (thick line) is associated with the non-overlap area data and the overlap area data of the first nozzle row and the second nozzle row. The printer driver associates a dither mask in order from the left side in the X direction and the upper side in the Y direction in high-gradation (256 gradation) two-dimensional image data, and compares the pixel of interest with the corresponding dither mask threshold value. Then, the presence / absence of dot formation is determined. When the determination of the presence / absence of dot formation for “256 pixels × 256 pixels” in the upper left in the two-dimensional image data is completed, the presence / absence of dot formation for “256 pixels × 256 pixels” on the right side of the determined pixel in the X direction is determined. Make a decision. In this way, when the determination of the presence / absence of dot formation is completed over the entire area in the X direction of the two-dimensional image data, the printer driver then proceeds to the left side in the X direction with respect to the pixels below the 256th pixel from the top in the Y direction. Whether or not dots are formed is determined in order.

  FIG. 12B shows the correspondence between 256 pixels in the X direction and the Y direction from the second pixel from the left and the first pixel from the top (pixel corresponding to nozzle # 174) in the overlapping area data of the first nozzle row. The position of the dither mask to be displayed. For example, the printer driver compares the upper left threshold “1” of the dither mask with the gradation value “77” indicated by the corresponding pixel. In this case, the printer driver determines that the dot is formed because the gradation value indicated by the pixel is larger than the threshold value.

  By the way, in the printing method of this embodiment, the dots by the overlapping nozzles in the first nozzle row (downstream head 31A) and the dots by the overlapping nozzles in the second nozzle row (upstream head 31B) overlap randomly (distributed). For this purpose, the dot data related to the overlapping nozzles in the first nozzle row and the dot data related to the overlapping nozzles in the second nozzle row are made to have no correlation. “Non-correlated data” means that a part of the dots formed in the overlapping region is formed by overlapping the dots by the overlapping nozzles in the first nozzle row and the dots by the overlapping nozzles in the second nozzle row. This is data to be printed so as to obtain a printed dot. In other words, “uncorrelated data” means that the dots due to the overlapping nozzles in the first nozzle row and the dots due to the overlapping nozzles in the second nozzle row do not overlap or do not overlap at all. Thus, the data to be printed.

  Here, as a comparative example, it is assumed that the usage rate of the nozzles to be multiplied by the overlapping area data is set to a constant “50%” regardless of the position of the overlapping nozzles. Then, the gradation value indicated by the overlapping area data of the first nozzle row is the same as the gradation value indicated by the overlapping area data of the second nozzle row. For example, when the gradation value indicated by the overlapping area data is “100” as shown in FIG. 11, the multiplication of a certain usage rate results in the pixel levels belonging to the overlapping area data of the first nozzle row and the second nozzle row. The key value is “50”. Furthermore, unlike FIG. 12A, the dither mask is configured with a threshold value of “8 pixels × 8 pixels”, the number of pixels in the X direction (8 pixels) constituting the dither mask, and X belonging to the overlapping area data for one nozzle row. It is assumed that the number of pixels in the direction (eight) is equal. Assume that the printer driver associates the dither mask with only the overlapping area data of the first nozzle row and associates the same dither mask with only the overlapping region data of the second nozzle row, and determines whether or not dots are formed. .

  In this case, in a certain pixel associated with the overlapping nozzle of the first nozzle row and a pixel of the overlapping nozzle of the second nozzle row corresponding to the pixel, the gradation value indicated by the pixel also indicates whether or not dots are formed. The threshold value for determination is also the same value. As a result, the dot data for overlapping nozzles in the first nozzle row and the dot data for overlapping nozzles in the second nozzle row are exactly the same. That is, the dots formed by the overlapping nozzles in the first nozzle row and the dots formed by the overlapping nozzles in the second nozzle row all overlap. In this case, the image density in the ideal state becomes light, and density fluctuation when an adjacent head misalignment or conveyance error occurs cannot be reduced.

  On the other hand, in the print data creation process of the present embodiment, as shown in FIG. 11, the usage rate of the nozzle is changed depending on the position of the overlapping nozzle (position in the X direction). That is, the nozzle usage rate is reversed between a certain overlapping nozzle in the first nozzle row and a corresponding overlapping nozzle in the second nozzle row. Therefore, even with the gradation value of the pixel at the same position, different usage rates are multiplied, and the gradation value indicated by the pixel for the first nozzle row and the gradation value indicated by the pixel for the second nozzle row are different. As a result, it is possible to prevent all the dots due to the overlapping nozzles in the first nozzle row and the dots due to the overlapping nozzles in the second nozzle row from overlapping, and the high gradation data of the overlapping nozzles in each nozzle row is converted to uncorrelated dot data. Halftone processing can be performed.

  Further, in the print data creation process of the present embodiment, as shown in FIG. 12A, the number of pixels in the X direction (256 pixels) constituting the dither mask is the pixels in the X direction belonging to the overlapping area data for one nozzle row. It is sufficiently larger than the number (8). Therefore, the threshold for performing dot determination can be different between a certain pixel of the overlapping nozzle of the first nozzle row and a pixel of the overlapping nozzle of the second nozzle row corresponding to the pixel. That is, the presence or absence of dot formation can be determined with a threshold having no correlation with respect to pixels at the same position. As a result, it is possible to prevent all the dots due to the overlapping nozzles in the first nozzle row and the dots due to the overlapping nozzles in the second nozzle row from overlapping, and the high gradation data of the overlapping nozzles in each nozzle row is converted to uncorrelated dot data. Halftone processing can be performed.

  For example, in FIG. 12B, the upper left pixel (pixel assigned to the nozzle # 174 of the first nozzle row) associated with the dither mask and the pixel for the second nozzle row (assigned to the nozzle # 2) corresponding to the pixel. Different pixels among the pixels constituting the dither mask are associated with each other, and the presence or absence of dot formation is determined based on different threshold values. Therefore, a dot is formed at the top pixel (tone value = 77, threshold = 1) of the nozzle # 174 of the first nozzle row, but the top of the corresponding nozzle # 2 of the second nozzle row. In the pixel (tone value = 22), a dot is formed if the associated threshold value is large, and no dot is formed if the associated threshold value is small.

  That is, in the present embodiment, by using a dither mask larger than the overlapping area data, the overlapping nozzle pixels in the first nozzle row and the corresponding overlapping nozzle pixels in the second nozzle row (pixels at the same position). The presence or absence of dot formation can be determined by the threshold value of a different pixel among the pixels constituting the dither mask. As a result, the dot data for overlapping nozzles in the first nozzle row and the dot data for overlapping nozzles in the second nozzle row can be halftoned into uncorrelated dot data. Dots by overlapping nozzles in the second nozzle row can be randomly (distributed) to overlap.

  Further, in the print data creation process of the present embodiment, as shown in FIG. 11, the duplicated overlapping area data is inserted next to the overlapping area data in the input image data. That is, the halftone process is performed with the overlapping area data of each nozzle row adjacent to each other in the X direction. Therefore, when the dither mask (the length in the X direction) is sufficiently larger than the overlap area data (the length in the X direction), it is adjacent when the printer driver associates one dither mask with the image data. The probability that two overlapping area data to be associated with each other at the same time increases. As a result, pixels (threshold values) having different dither masks are associated with the overlapping region data of each nozzle row.

  Further, when the printer driver associates one dither mask with image data, the boundary of the dither mask may be located in the overlapping area data as shown in FIG. 12B. Also in this case, in the two adjacent overlapping area data, the left overlapping area data in the X direction (data to which the dither mask is first associated) is associated with the pixel (threshold value) on the right in the X direction of the dither mask. In the overlap region data on the right side in the X direction (data to which a dither mask is associated later), the pixel (threshold value) on the left side in the X direction of the dither mask is associated.

  In this way, by arranging two overlapping area data in the X direction, dithering is performed for a certain pixel for overlapping nozzles in the first nozzle row and a corresponding pixel for overlapping nozzles in the second nozzle row. Pixels (threshold values) with different masks can be associated with each other. As a result, the overlapping nozzle dot data of the first nozzle array and the overlapping nozzle dot data of the second nozzle array can be halftone processed into uncorrelated dot data.

  Further, here, halftone processing (dot dispersion type halftone processing) is performed in which dots are dispersed (irregularly) as in the dither method. As shown in FIG. 6, in order to disperse (randomly) dots formed by overlapping nozzles in each nozzle row, dot dispersion type (frequency modulation type) halftone processing may be performed. In addition to the dither method, for example, an error diffusion method, an FM mask method, and the like can be given.

  On the other hand, it is not preferable to perform halftone processing (amplitude modulation type halftone processing) called a halftone dot. In the halftone dot, each gradation value is expressed by changing the area of the dot. For this reason, the probability that dots overlap due to overlapping nozzles in each nozzle row will increase too much, or conversely, the probability that dots will not overlap will increase too much. That is, unless dot dispersion type halftone processing is performed, it is impossible to disperse (randomly) dots by overlapping nozzles in each nozzle row.

  After performing the halftone process in this way, the printer driver distributes the halftone-completed data to each nozzle row in the image distribution process (S108). The halftone results of the original overlapping region data shown in FIGS. 11 and 12 are distributed to the overlapping nozzles of the first nozzle row, and the halftone results of the duplicate overlapping region data are distributed to the overlapping nozzles of the second nozzle row. Finally, the printer driver rearranges the matrix-like image data in the order to be transferred to the printer 1 by the rasterizing process (S109), and transmits it to the printer 1 together with the command data.

  In the printer 1 that has received the print data, printing is performed based on the received print data. The controller 10 of the printer 1 ejects ink droplets from the overlapping nozzles of the first nozzle row based on the halftone result of the original overlapping region data, and converts the overlapping nozzles of the second nozzle row to the halftone result of the duplicated overlapping region data. Based on this, ink droplets are ejected.

  In summary, in the print data creation process of the present embodiment, the image data corresponding to the overlap region is inserted into the input image data, and the overlap region data of the first nozzle row (upstream head 31B) is converted into dot data. And halftone processing for converting the overlapping area data of the second nozzle row (downstream head 31A) into dot data are performed independently. As a result, the high gradation overlapping area data of each nozzle row can be converted into non-correlated dot data, and the dots by the overlapping nozzles of the first nozzle row and the dots by the overlapping nozzles of the second nozzle row are randomly selected. They can be formed in layers. By doing so, the density fluctuation can be suppressed even if the positional deviation or the conveyance error of the adjacent head occurs. Since the printer driver creates print data, the computer 50 in which the printer driver is installed and the controller 10 of the printer 1 correspond to a “control unit”, and the printing system in which the computer 50 and the printer 1 are connected is “fluid ejecting”. It corresponds to "apparatus". However, when the controller 10 of the printer 1 creates print data, the controller 10 corresponds to a “control unit” and the printer 1 alone corresponds to a “fluid ejecting device”.

<Modification>
In the above-described embodiment, as shown in FIG. 11, the usage rate of each nozzle row is changed depending on the position of the overlapping nozzle (position in the X direction), but this is not limitative. For example, the usage rate of the two nozzle rows may be constant, for example, 50% each, regardless of the position of the overlapping nozzle. In this case, in all raster lines (dot rows along the transport direction) formed in the overlapping region, the dots by the first nozzle row and the dots by the second nozzle row are configured in the same ratio.

  However, as in the previous embodiment (FIG. 11), in the first nozzle row, the nozzle usage rate is decreased for the right overlapping nozzle, and conversely, in the second nozzle row, the nozzle usage rate is decreased for the right overlapping nozzle. When the height is increased, the joints of images formed by different nozzle rows can be made inconspicuous. Further, the usage rate of the first nozzle row and the usage rate of the second nozzle row are reversed. Therefore, even for pixels at the same position in the overlapping area data, the gradation values indicated by the pixels for the first nozzle row and the levels indicated by the pixels for the second nozzle row are multiplied by the usage rate of each nozzle row. The key value can be varied. Therefore, it becomes easy to perform the halftone process on the overlapping area data of each nozzle row to dot data having no correlation.

  In the above-described embodiment, as shown in FIG. 11, the duplicated overlapping area data is inserted adjacent to the original overlapping area data. However, the present invention is not limited to this. The duplicated overlapping area data may be added to the input image data, for example, at the end. However, by making the original overlapping area data and the duplicated overlapping area data adjacent to each other, as shown in FIG. 12B, it becomes easy to associate the pixels (threshold values) having different dither masks with the two overlapping area data. As a result, it is possible to perform halftone processing of the overlapping area data of each nozzle row to dot data having no correlation more reliably.

  In the above-described embodiment, the overlapping area data of the first nozzle array and the overlapping area data of the second nozzle array are subjected to halftone processing using the same dither mask. However, the present invention is not limited to this. For example, a dither mask for each nozzle row may be prepared, and halftone processing may be performed using different dither masks for overlapping region data of each nozzle row. By doing so, the overlapping area data of each nozzle row can be halftone processed into dot data having no correlation.

  However, as shown in the above-described embodiment, even if the overlapping area data is duplicated and inserted, multiplied by the usage ratio of each nozzle row, and then halftoned using the same dither mask, Overlapping area data can be converted into uncorrelated dot data. By using the same dither mask, the memory capacity for storing the dither mask can be reduced, and the processing of the printer driver can be simplified.

  Further, in the above-described embodiment, after duplicating / inserting the overlapping area data, the overlapping area data of each nozzle array is multiplied by the usage rate of each nozzle array, but this is not restrictive. Halftone processing may be performed without multiplying the overlapping area data by the usage rate. At this time, the overlapping area data of each nozzle row can be converted into dot data having no correlation by associating the overlapping area data of each nozzle row with a pixel (threshold value) having a different dither mask. However, if the overlapping area data is not multiplied by the usage rate, the image portion formed in the overlapping area is printed darkly. Therefore, it is preferable to correct the density to a light gradation value before duplicating / inserting the overlapping area data.

=== Regarding Density Correction of Overlapping Region Image ===
In the printing method of the present embodiment, the adjacent head even in the ideal state (the positional relationship between the adjacent heads is as designed or the density unevenness correction value corresponding to the positional relationship between the adjacent heads is set and no conveyance error occurs). The dots by the overlapping nozzles are printed with random overlapping. Therefore, if it is originally (if the density is indicated by the image data), for example, a dot is formed without a gap as shown in the left diagram of FIG. As shown in the drawing, the medium is insufficiently filled by the amount formed by overlapping some dots, and the density of the image formed in the overlapping region (hereinafter referred to as the overlapping region image) becomes light.

  In other words, in the printing method of the present embodiment, the density of the overlapping area image is printed slightly light even in the ideal state, so the density correction is performed so that the density of the overlapping area image is printed at a desired density. To do. Hereinafter, the density correction method will be described.

<Example 1>
FIG. 13 is a diagram showing the usage rate of each nozzle row for correcting the density of the overlapping region image. In the print data creation process described above, the sum of the usage rate of the first nozzle row and the usage rate of the second nozzle row is set to 100%. The total usage rate of each nozzle row being 100% means that a desired image density can be obtained by combining dots respectively formed by overlapping nozzles in each nozzle row. However, when a part of dots is formed by being overlapped as in the printing method of the present embodiment, the medium is not sufficiently filled and a desired density cannot be obtained.

  Therefore, in Example 1 of density correction, the total value of the usage rates of the two nozzle rows is set higher than 100% as shown in FIG. For example, when the total usage rate is 100%, as shown in FIG. 11, the gradation value (89) of the pixel of the overlapping nozzle (for example, # 173) in the first nozzle row and the corresponding second nozzle row The total value (100) with the gradation value (11) of the pixels of the overlapping nozzles (for example, # 1) is the gradation value (100) before being multiplied by the nozzle usage rate. On the other hand, when the overlap area data is multiplied by a use ratio whose total use ratio is higher than 100%, the gradation value of the overlapping nozzle pixel of the first nozzle array and the corresponding overlap of the second nozzle array The total value of the gradation values of the nozzle pixels is higher (a dark gradation value) than the gradation value before the nozzle usage rate is multiplied.

  As a result, the gradation value of the overlapping nozzle of each nozzle row becomes a high (dark) gradation value, which means that the dot generation rate of the overlapping nozzle of each nozzle row becomes high (or the dot size) in the halftone processing result. Becomes larger). Therefore, even if a part of each dot of the upstream head 31B and the downstream head 31A overlaps, the medium can be filled by that amount. By doing this, it is possible to print an overlapping area image having a desired density even in an ideal state, and even if a positional deviation of adjacent heads or a transport error occurs, the density fluctuation is small, so an overlapping area image having a desired density can be obtained. Can print. In this case, the density correction process S104 in the print data creation flow of FIG. 10 need not be performed.

<Example 2>
In the first embodiment, when the overlapping area data is multiplied by the usage rate of each nozzle, the gradation value of the overlapping area data is corrected to a high (dark) gradation value. On the other hand, in the second embodiment, the printer driver sets the gradation value of the overlapping area data to a high gradation value in the density correction process (S104) before duplicating / inserting the overlapping area data (S105 in FIG. 10). To correct. For example, the gradation value of the overlapping area data is corrected to a high gradation value (dark gradation value) at a certain ratio (by a certain correction value) with respect to the input image data in the uppermost diagram in FIG.

  As a result of multiplying the overlapping area data corrected to a high gradation value by the usage rate of each nozzle row and performing halftone processing, it is possible to increase the dot generation rate of the overlapping nozzles (or increase the dot size). Can do). Therefore, even if a part of each dot of the upstream head 31B and the downstream head 31A overlaps, the medium can be filled by that amount. That is, even in an ideal state, even if there is a positional deviation or conveyance error between adjacent heads, an overlapping area image having a desired density can be printed.

<Example 3>
For the following description, “pixel region” and “column region” are defined. The “pixel region” is a region on the medium corresponding to the pixel, and the “column region” is a region in which the pixel region is arranged in the transport direction, and a plurality of pixels (hereinafter referred to as “X” direction) on the image data. Corresponds to a pixel column).

  FIG. 14 is a diagram illustrating an example in which a certain raster line affects the density of an adjacent raster line. In the second embodiment, the overlapping area data of the input image data is corrected to a high gradation value at a certain rate (by a certain correction value) as much as the overlapping nozzle dots are printed. However, density unevenness also occurs due to a problem of nozzle processing accuracy.

  For example, in FIG. 14, the raster line formed in the second row region is formed closer to the third row region due to the flight curve of the ink droplets ejected from the nozzles. As a result, the second row region is visually recognized as light, and the third row region is visually recognized as dark. On the other hand, the amount of ink droplets ejected to the fifth row region is smaller than the prescribed amount, and the dots formed in the fifth row region are small. As a result, the fifth row region becomes light. This appears as uneven density on the image. Therefore, correction is made so that the lightly printed row region is printed dark, and the darkly printed row region is corrected so as to be printed lightly. The reason why the third row region becomes dark is not due to the influence of the nozzle assigned to the third row region, but to the influence of the nozzle assigned to the adjacent second row region.

  Therefore, in the third embodiment, the correction value H for each row region (pixel row) is calculated in consideration of the influence of adjacent nozzles. The correction value H may be calculated for each model of the printer 1 during the manufacturing process and maintenance of the printer 1. Here, the correction value H is calculated according to the correction value acquisition program installed in the computer 50 connected to the printer 1. Hereinafter, a specific calculation method of the correction value for each row region will be described.

  FIG. 15 is a diagram showing a test pattern. The correction value acquisition program first causes the printer 1 to print a test pattern. The figure shows a correction pattern formed by one nozzle row of the nozzle rows (YMCK) of each head 31. As a test pattern, a correction pattern for each nozzle row (YMCK) is printed.

  The correction pattern is composed of strip-shaped patterns of three types of density. Each belt-like pattern is generated from image data having a certain gradation value. The gradation value for forming the belt-like pattern is called a command gradation value, the command gradation value of the belt-like pattern having a density of 30% is Sa (76), and the command gradation value of the belt-like pattern having a density of 50% is Sb (128). ), The command gradation value of the belt-like pattern having a density of 70% is expressed as Sc (179). One correction pattern is composed of raster lines (row regions) of the number of nozzles arranged in the paper width direction in the head unit 30.

  Note that when creating print data for printing the correction pattern, the halftone process for the overlapping area data of the upstream head 31B and the halftone process for the overlapping area data of the downstream head 31A are performed independently. . Also in the correction pattern, the dots formed by the overlapping nozzles of the upstream head 31B and the dots formed by the overlapping nozzles of the downstream head 31A are randomly overlapped.

  FIG. 16 shows the result of reading a cyan correction pattern with a scanner. Next, the correction value acquisition program acquires the result of the scanner reading the test pattern. Hereinafter, explanation will be given by taking cyan read data as an example. The correction value acquisition program calculates the density (reading gradation value) of each row region for each strip pattern after associating the pixel rows in the read data with the row regions constituting the correction pattern on a one-to-one basis. . Specifically, the average value of the read gradation values of each pixel belonging to the pixel column corresponding to a certain row region is set as the read gradation value of that row region. In the graph of FIG. 16, the horizontal axis is the row area number, and the vertical axis is the read gradation value of each row area.

  Although each belt-like pattern is uniformly formed with each command gradation value, as shown in FIG. 16, the reading gradation value varies for each row region. For example, in the graph of FIG. 16, the read gradation value Cbi of the i column region is relatively lower than the read gradation value of the other column region, and the read gradation value Cbj of the j column region is read of the other column region. It is relatively higher than the gradation value. That is, the i-th row region is visually recognized as light, and the j-th row region is viewed as dark. Such variation in the read gradation value of each row region is uneven density occurring in the print image. It should be noted that the reading gradation value is lower (lighter) in the row region formed by the overlapping nozzles than in the row region formed by other non-overlapping nozzles.

  By bringing the read gradation value of each row area close to a certain value, it is possible to improve density unevenness due to the lightness of the overlapping area image and the processing accuracy of the nozzles. Therefore, the average value Cbt of the read gradation values in all the row regions is set as the “target value Cbt” at the same command gradation value (for example, Sb / density 50%). Then, the gradation value indicated by the pixel column data corresponding to each column region is corrected so that the read gradation value of each column region in the command gradation value Sb approaches the target value Cbt.

  Specifically, the gradation value indicated by the pixel column data corresponding to the column region i having a reading gradation value lower than the target value Cbt in FIG. 16 is corrected to a gradation value darker than the command gradation value Sb. On the other hand, the gradation value indicated by the pixel column data corresponding to the column region j having a reading gradation value higher than the target value Cbt is corrected to a gradation value lighter than the command gradation value Sb. In this way, for the same gradation value, the correction value H for correcting the gradation value of the pixel column data corresponding to each column region is calculated in order to bring the density of all the column regions close to a constant value.

17A and 17B are diagrams illustrating a specific method for calculating the density unevenness correction value H. FIG. First, FIG. 17A shows a state in which the target command tone value (example Sbt) is calculated for the command tone value (example Sb) in the i-th row region where the read tone value is lower than the target value Cbt. The horizontal axis indicates the gradation value, and the vertical axis indicates the read gradation value in the test pattern result. On the graph, the read gradation values (Cai, Cbi, Cci) are plotted against the command gradation values (Sa, Sb, Sc). For example, the target command tone value Sbt for representing the i-th row region with the target value Cbt with respect to the command tone value Sb is calculated by the following equation (linear interpolation based on the straight line BC).
Sbt = Sb + {(Sc−Sb) × (Cbt−Cbi) / (Cci−Cbi)}

Similarly, as shown in FIG. 17B, in a j-row area where the read gradation value is higher than the target value Cbt, a target command for the j-row area to be represented by the target value Cbt with respect to the command gradation value Sb. The gradation value Sbt is calculated by the following equation (linear interpolation based on the straight line AB).
Sbt = Sa + {(Sb−Sa) × (Cbt−Caj) / (Cbj−Caj)}

Thus, the target command tone value Sbt of each row region with respect to the command tone value Sb is calculated. Then, the cyan correction value Hb for the command gradation value Sb of each row region is calculated by the following equation. Similarly, correction values for other command gradation values (Sa, Sc) and correction values for other colors (yellow, magenta, black) are also calculated.
Hb = (Sbt−Sb) / Sb

  FIG. 18 is a diagram illustrating a correction value table for each nozzle row (CMYK). The correction values H calculated as described above are collected in the correction value table shown in the figure. In the correction value table, correction values (Ha, Hb, Hc) respectively corresponding to three command gradation values (Sa, Sb, Sc) are set for each row region. Such a correction value table is stored in the memory 13 of the printer 1 on which the test pattern is printed in order to calculate the correction value H. Thereafter, the printer 1 is shipped to the user.

  When the user starts using the printer 1, the user installs a printer driver in the computer 50 connected to the printer 1. Then, the printer driver requests the printer 1 to transmit the correction value H stored in the memory 13 to the computer 50. The printer driver stores the correction value H transmitted from the printer 1 in a memory in the computer 50.

If the gradation value S_in before correction is the same as one of the command gradation values Sa, Sb, Sc, the correction value H corresponding to each command gradation value and stored in the memory of the computer 50 The values Ha, Hb, and Hc can be used as they are. For example, if the gradation value S_in before correction is S_in = Sc, the gradation value S_out after correction is obtained by the following equation.
S_out = Sc × (1 + Hc)

  FIG. 19 is a diagram illustrating how the correction value H corresponding to each gradation value is calculated for the nth row region of cyan. The horizontal axis is the gradation value S_in before correction, and the vertical axis is the correction value H_out corresponding to the gradation value S_in before correction. When the gradation value S_in before correction is different from the command gradation value, the correction value H_out corresponding to the gradation value S_in before correction is calculated.

For example, as shown in FIG. 19, when the gradation value S_in before correction is between the command gradation values Sa and Sb, the linearity of the correction value Ha of the command gradation value Sa and the correction value Hb of the command gradation value Sb. A correction value H_out is calculated by the following equation by interpolation.
H_out = Ha + {(Hb−Ha) × (S_in−Sa) / (Sb−Sa)}
S_out = S_in × (1 + H_out)

  When the gradation value S_in before correction is smaller than the command gradation value Sa, the correction value H_out is calculated by linear interpolation between the minimum gradation value 0 and the command gradation value Sa, and the gradation value before correction is calculated. When S_in is larger than the command tone value Sc, the correction value H_out is calculated by linear interpolation between the maximum tone value 255 and the command tone value Sc.

  In this way, the printer driver uses the correction value H set for each color, each column region to which the pixel data belongs, and each gradation value, so that the printer driver performs the gradation value S_in ( 256 gradation data) is corrected. By doing so, the gradation value S_in of the pixel corresponding to the row region where the density is visually recognized is corrected to the dark gradation value S_out, and the gradation value S_in indicated by the pixel corresponding to the row region where the density is visually recognized is dark. Is corrected to a light gradation value S_out. Further, even if a part of dots formed by the overlapping nozzles of the upstream head 31B and the downstream head 31A are randomly overlapped, it is possible to prevent the overlapping area image from being printed lightly.

=== Other Embodiments ===
Each of the above embodiments has been described mainly for a printing system having an ink jet printer, but includes disclosure of a density unevenness correction method and the like. The above-described embodiments are for facilitating understanding of the present invention, and are not intended to limit the present invention. The present invention can be changed and improved without departing from the gist thereof, and it is needless to say that the present invention includes equivalents thereof. In particular, the embodiments described below are also included in the present invention.

<About the printer>
In the above-described embodiment, a printer (so-called line head printer) that forms an image by arranging a plurality of heads over the width of the paper and conveying the paper under the fixed head is taken as an example. Not limited to this. For example, the plurality of heads are arranged in the nozzle row direction so that the end portions of the nozzle rows of the plurality of heads overlap. The operation of forming an image while moving the plurality of heads in the direction intersecting the nozzle row direction with respect to the paper and the operation of conveying the paper in the nozzle row direction with respect to the plurality of heads are alternately repeated. A printer (a so-called serial printer) may be used. Also in this case, it is preferable to perform the halftone process for the overlapping nozzles of each head independently.

<About fluid ejection device>
In the above-described embodiment, the ink jet printer is exemplified as the fluid ejecting apparatus, but the present invention is not limited thereto. The fluid ejecting apparatus can be applied to various industrial apparatuses instead of a printer. For example, a textile printing apparatus for applying a pattern to a fabric, a display manufacturing apparatus such as a color filter manufacturing apparatus or an organic EL display, a DNA chip manufacturing apparatus for manufacturing a DNA chip by applying a solution in which DNA is dissolved to a chip, and the like. Also, the present invention can be applied.
The fluid ejection method may be a piezo method in which fluid is ejected by applying a voltage to the drive element (piezo element) to expand and contract the ink chamber, or bubbles are generated in the nozzle using a heating element. It is also possible to use a thermal method in which liquid is ejected by the bubbles. The fluid is not limited to liquid such as ink, but may be powder.

1 Printer, 10 Controller, 11 Interface section,
12 CPU, 13 memory, 14 unit control circuit,
20 transport unit, 21 transport belt, 22A, 22B transport roller,
30 head units, 31 heads,
40 detector groups, 50 computers

Claims (8)

(A) a first nozzle row in which first nozzles for ejecting fluid are arranged in a predetermined direction;
(B) The second nozzle row in which the second nozzles for ejecting the fluid are arranged in the predetermined direction, and one end portion in the predetermined direction is the other end portion in the predetermined direction of the first nozzle row A second nozzle row arranged to form an overlapping region overlapping with
(C) a control unit that performs halftone processing for converting input image data into dot data indicating the presence or absence of dot formation;
Halftone processing for converting the image data corresponding to the overlapping region into the dot data for ejecting fluid from the first nozzle belonging to the overlapping region, and the image data corresponding to the overlapping region to the overlapping region A control unit that independently performs halftone processing for converting into the dot data for ejecting fluid from the second nozzle to which the nozzle belongs,
A fluid ejecting apparatus comprising: The fluid ejection device according to claim 1,
The controller is
Duplicating the image data corresponding to the overlap region of the input image data,
Insert the image data corresponding to the duplicated duplicated area into the input image data,
Data obtained by multiplying the image data corresponding to the overlapping region by the usage rate of the other end of the first nozzle row is halftone processed.
Data obtained by multiplying the image data corresponding to the inserted overlapping area by the usage rate of the one end of the second nozzle row is halftone processed.
Fluid ejection device. The fluid ejecting apparatus according to claim 2,
The usage rate of a certain first nozzle belonging to the overlapping region is higher than the usage rate of the first nozzle located on the other side of the first nozzle,
The usage rate of a certain second nozzle belonging to the overlapping region is higher than the usage rate of the second nozzle located on the one side of the second nozzle,
Fluid ejection device. The fluid ejection device according to any one of claims 1 to 3,
The control unit performs dot dispersion type halftone processing.
Fluid ejection device. The fluid ejection device according to any one of claims 1 to 4,
Halftone processing for converting the dot data for ejecting fluid from the first nozzle belonging to the overlapping region and halftone processing for converting the dot data for ejecting fluid from the second nozzle belonging to the overlapping region Based on the results of independent processing,
A part of dispersed dots among the dots formed by the nozzles belonging to the overlapping region is a dot in which the dots formed by the first nozzle and the dots formed by the second nozzle overlap.
Fluid ejection device. The fluid ejection device according to any one of claims 1 to 5,
The control unit corrects the gradation value indicated by the image data corresponding to the overlapping region to a dark gradation value;
Fluid ejection device. (A) A first nozzle row in which first nozzles for ejecting fluid are arranged in a predetermined direction, and a second nozzle row in which second nozzles for ejecting fluid are arranged in the predetermined direction, one side in the predetermined direction A second nozzle row arranged to form an overlapping region where the end portion of the first nozzle row overlaps with the other end portion in the predetermined direction of the first nozzle row, and a fluid ejecting method for a fluid ejecting apparatus,
(B) When performing halftone processing for converting input image data into dot data indicating the presence / absence of dot formation, fluid is ejected from the first nozzle belonging to the overlap region to the image data corresponding to the overlap region. Halftone processing for converting to the dot data for, and halftone processing for converting the image data corresponding to the overlapping region to the dot data for ejecting fluid from the second nozzle belonging to the overlapping region, Doing independently,
(C) ejecting fluid from the first nozzle and the second nozzle based on the result of the halftone process;
A fluid ejecting method comprising (D). (A) A first nozzle row in which first nozzles for ejecting fluid are arranged in a predetermined direction, and a second nozzle row in which second nozzles for ejecting fluid are arranged in the predetermined direction, one side in the predetermined direction A second nozzle row that is arranged to form an overlapping region in which an end portion of the first nozzle row overlaps with an end portion on the other side in the predetermined direction of the first nozzle row,
(B) When performing halftone processing for converting input image data into dot data indicating the presence / absence of dot formation, fluid is ejected from the first nozzle belonging to the overlap region to the image data corresponding to the overlap region. Halftone processing for converting to the dot data for, and halftone processing for converting the image data corresponding to the overlapping region to the dot data for ejecting fluid from the second nozzle belonging to the overlapping region, To perform independently,
A program for executing (C).