JP2009274233A - Liquid ejecting apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid ejecting apparatus capable of suppressing deterioration of image quality of a printed image caused by a movement error of a head. <P>SOLUTION: In the liquid ejecting apparatus, while a nozzle row in which a plurality of nozzles ejecting a liquid are arranged in a predetermined direction and a medium are relatively moved in a direction intersecting the predetermined direction, a liquid ejecting operation to allow the nozzle row to eject the liquid and a moving operation to relatively move the nozzle row and the medium in the predetermined direction are alternately repeated. In the first liquid ejecting operation, ejection of the liquid to an area on the medium corresponding to a certain pixel data from the first nozzles in the nozzle row is controlled on the basis of the certain pixel data, and in the second liquid ejecting operation after the first liquid ejecting operation, ejection of the liquid to the area on the medium corresponding to the certain pixel data from the second nozzles different from the first nozzles in the nozzle row is controlled on the basis of the certain pixel data. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a liquid ejection apparatus.

  As a liquid ejecting apparatus, a head having a nozzle row in which nozzles are arranged in a predetermined direction forms an image by ejecting ink onto a medium while moving in a direction crossing the predetermined direction, and relatively moves the head and the medium in a predetermined direction. An ink jet printer (hereinafter referred to as a printer) is known. In addition, since there is variation in nozzle characteristics, a printing method has been proposed in which a plurality of types of nozzles form dot rows arranged in the intersecting direction (see Patent Document 1). For this purpose, for example, dots are formed by a nozzle in a previous pass (one movement in a direction crossing a predetermined direction of the head), and a subsequent pass is formed between the dots formed in the previous pass. The dots may be formed by another nozzle. As a result, variations in nozzle characteristics are alleviated, and a higher quality image can be obtained.

JP 2002-11859 A

However, in the above printing method, when a head movement error or the like occurs, for example, dots formed by another nozzle are not formed between dots formed by a certain nozzle. As a result, the dot interval is too large and the light is visually recognized, causing deterioration in the image quality of the printed image.
Accordingly, an object of the present invention is to suppress image quality deterioration.

  A main invention for solving the problem is a liquid that discharges liquid from the nozzle row while relatively moving a nozzle row and a medium in which a plurality of nozzles that discharge liquid are aligned in a predetermined direction in a direction intersecting the predetermined direction. A liquid discharge apparatus that alternately repeats a discharge operation and a movement operation that relatively moves the nozzle row and the medium in the predetermined direction, and in the first liquid discharge operation, based on certain pixel data, In the second liquid ejection operation after the first liquid ejection operation, the certain pixel data is controlled by controlling the liquid ejection from the first nozzle of the nozzle row to the area on the medium corresponding to the certain pixel data. Based on the above, the liquid discharge for controlling the liquid discharge to the area on the medium corresponding to the certain pixel data from the second nozzle different from the first nozzle in the nozzle row It is the location.

  Other features of the present invention will become apparent from the description of this specification and the accompanying drawings.

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

That is, a liquid discharge operation for discharging liquid from the nozzle row while relatively moving a nozzle row in which a plurality of nozzles for discharging liquid are arranged in a predetermined direction and a medium in a direction intersecting the predetermined direction, and the nozzle row A liquid ejecting apparatus that alternately repeats a moving operation for relatively moving the medium in the predetermined direction. In the first liquid ejecting operation, based on certain pixel data, , Controlling the liquid ejection to the region on the medium corresponding to the certain pixel data, and in the second liquid ejecting operation after the first liquid ejecting operation, based on the certain pixel data, A liquid ejection apparatus that controls liquid ejection from a second nozzle different from the first nozzle to an area on the medium corresponding to the certain pixel data.
According to such a liquid ejecting apparatus, even if an error occurs in the movement operation, it is possible to prevent the dot interval (liquid trace interval) from becoming larger than instructed by the data. For example, if the liquid ejecting apparatus is a printer, it is possible to prevent the area on the medium in which the first nozzle and the second nozzle are associated from being visually recognized.

In this liquid ejection apparatus, a predetermined amount of liquid is ejected from a nozzle different from the first nozzle and the second nozzle based on a gradation value indicated by pixel data different from the certain pixel data, When the gradation value indicated by the certain pixel data is equal to the gradation value indicated by the other pixel data, the first nozzle and the second nozzle respectively in the region on the medium corresponding to the certain pixel data. Discharging a predetermined amount of liquid;
According to such a liquid ejecting apparatus, it is possible to prevent the dot interval from becoming larger than instructed by the data.

In the liquid ejecting apparatus, when the gradation value indicated by the certain pixel data is equal to or more than a threshold value, the first nozzle and the second nozzle are respectively disposed in the region on the medium corresponding to the certain pixel data. When the predetermined liquid amount is ejected and the gradation value indicated by the certain pixel data is less than the threshold value, the predetermined liquid is supplied from the first nozzle to an area on the medium corresponding to the certain pixel data. The amount is discharged, and the liquid is not discharged from the second nozzle.
According to such a liquid ejecting apparatus, for example, when the liquid ejecting apparatus is a printer, when the gradation value is equal to or higher than the threshold value and the dark gradation value, the dot interval is larger than indicated by the data. Therefore, it is possible to prevent the gap from becoming conspicuous, and a higher quality image can be obtained. On the contrary, when the gradation value is less than the threshold value and is a light gradation value, it is possible to prevent the dots from being formed by the first nozzle and the second nozzle and being visually recognized darkly, and a higher quality image. Is obtained.

In such a liquid ejection device, the halftone process converts the gradation value indicated by each pixel data into dot data indicating the dot size to be formed in the area on the medium corresponding to each pixel data, and Forming dots having a size equal to or smaller than the dot size indicated by the dot data of the pixel data in the first nozzle and the second nozzle in an area on the medium corresponding to the pixel data, respectively;
According to such a liquid ejecting apparatus, it is possible to prevent the liquid from being excessively ejected to a region on the medium in which the first nozzle and the second nozzle are associated with each other.

In this liquid ejecting apparatus, when the distance from the first nozzle to the central portion of the nozzle row is longer than the distance from the second nozzle to the central portion, the second nozzle is more than the first nozzle. When the nozzle is formed with a large size dot and the distance from the first nozzle to the central portion is shorter than the distance from the second nozzle to the central portion, the first nozzle than the second nozzle To form large size dots.
According to such a liquid ejection device, since the nozzles at the end of the nozzle row have a larger variation in ejection characteristics than the nozzles at the center, more liquid is ejected from the central nozzle with less variation in ejection characteristics. As a result, the liquid is discharged with high accuracy.

In this liquid ejecting apparatus, after the gradation value indicated by the certain pixel data is distributed to the first gradation value for the first nozzle and the second gradation value for the second nozzle, The first gradation value is converted into the first dot data by halftone processing for converting the gradation value indicated by the data into dot data indicating the dot size to be formed in the area on the medium corresponding to the pixel data. Then, the second gradation value is converted into the second dot data, and dots having the dot size indicated by the first dot data are formed in the first nozzle in an area on the medium corresponding to the certain pixel data. And causing the second nozzle to form dots having the dot size indicated by the second dot data.
According to such a liquid ejecting apparatus, it is possible to prevent the liquid from being excessively ejected to a region on the medium in which the first nozzle and the second nozzle are associated with each other.

In this liquid ejecting apparatus, when the distance from the first nozzle to the central portion of the nozzle row is longer than the distance from the second nozzle to the central portion, dots formed by the first nozzle The gradation value indicated by the certain pixel data is distributed to the first gradation value and the second gradation value so that the dot formed by the second nozzle is larger than the first nozzle value, When the distance from the nozzle to the central portion is shorter than the distance from the second nozzle to the central portion, the dots formed by the first nozzle are better than the dots formed by the second nozzle. Distributing the gradation value indicated by the certain pixel data to the first gradation value and the second gradation value so as to increase.
According to such a liquid ejection device, since the nozzles at the end of the nozzle row have a larger variation in ejection characteristics than the nozzles at the center, more liquid is ejected from the central nozzle with less variation in ejection characteristics. As a result, the liquid is discharged with high accuracy.

In this liquid ejection apparatus, liquid is ejected from a nozzle different from the first nozzle and the second nozzle based on a gradation value indicated by pixel data different from the certain pixel data, and the gradation A gradation value indicated by the certain pixel data equal to a value is converted into a light gradation value, and the first nozzle and the region are arranged in the area on the medium corresponding to the certain pixel data based on the light gradation value. The liquid is discharged from each of the second nozzles.
According to such a liquid ejecting apparatus, it is possible to prevent the liquid from being excessively ejected to a region on the medium in which the first nozzle and the second nozzle are associated with each other.

=== About Inkjet Printers ===
Hereinafter, a printing system in which an inkjet printer (hereinafter referred to as printer 1) and a computer are connected will be described as an example of a “liquid ejecting apparatus”.

  FIG. 1 is a configuration block diagram of a printing system. FIG. 2A is a schematic sectional view of the printer 1, and FIG. 2B is a schematic top view of the printer 1. First, print data is transmitted from the computer 60 to the printer 1. When the printer 1 receives the print data, the controller 10 controls each unit (conveyance unit 20, drive unit 30, head unit 40) to form an image on the print tape T. The status in the printer 1 is monitored by the detector group 50, and the controller 10 controls each unit based on the detection result.

  The transport unit 20 transports the print tape T from the upstream side to the downstream side in the direction in which the print tape T continues (hereinafter referred to as the transport direction). The roll-shaped printing tape T1 before printing is supplied to the printing region by the conveyance roller 21 driven by a motor, and then the printed printing tape T2 is wound into a roll shape by a winding mechanism. In the printing area during printing, the printing tape T is vacuum-sucked from below, and the printing tape T is held at a predetermined position.

  The drive unit 30 freely moves the head unit 40 in the transport direction and the width direction of the printing tape T (direction intersecting the transport direction). The drive unit 30 includes a first stage 31 that moves the head unit 40 in the transport direction, a second stage 32 that moves the first stage 31 in the width direction, and a motor that moves them.

  FIG. 3 shows the nozzle arrangement on the lower surface of the head 41. The head unit 40 has a head 41. On the lower surface of the head 41, a plurality of nozzles that are ink discharge portions are provided. A yellow ink nozzle row Y, a magenta ink nozzle row M, a cyan ink nozzle row C, and a black ink nozzle row K are formed on the lower surface of the head 41. Each nozzle row includes 180 nozzles and is aligned at a constant interval (180 dpi) in the width direction (corresponding to a predetermined direction). Young numbers are assigned in order from the nozzles on the back side in the width direction (# 1, # 2,..., # 180).

  Next, the printing procedure of the printer 1 will be described. First, the head unit 40 is moved in the transport direction (corresponding to a direction intersecting the predetermined direction) by the first stage 31 with respect to the printing tape T supplied to the printing area by the transport unit 20, and the nozzles are moved during this movement. Ink is ejected (corresponding to a liquid ejection operation). As a result, a dot row along the transport direction is formed on the printing tape T. Thereafter, the head unit 40 is moved in the width direction by the second stage 32 via the first stage 31 (corresponding to a moving operation). Then, again, while the head unit 40 moves in the transport direction, ink is ejected from the nozzles, and a dot row is formed in a region different from the previous one. By repeating this operation, an image is printed on the printing tape T supplied to the printing area (image forming operation). Thereafter, the printing tape T that has not been printed by the transport unit 20 is supplied to the printing area (transport operation), and an image is formed again. By alternately repeating this image forming operation and the conveying operation of the printing tape T, an image is printed on a continuous printing tape T (hereinafter referred to as a medium).

=== About the printing method of the comparative example ===
FIG. 4A is a diagram illustrating band printing which is a printing method of a comparative example. For illustration purposes, the number of nozzles is reduced. In band printing, when a band image is printed by one movement (pass) of the head 41 in the transport direction, the head 41 is moved in the width direction by the band image by the drive unit 30, and the head passes. The band image is printed again in the next pass so as to be aligned with the band image formed in the width direction. Therefore, in band printing, a dot row (hereinafter referred to as a raster line) along the transport direction is formed by one nozzle.

  By the way, the nozzle located at the end of the nozzle row is more likely to cause ejection abnormality than the central nozzle due to various factors. For example, as shown in FIG. 4A, dots (black circles) formed on the nozzle # 1 # 2 located at the end in the width direction are dots (white circles) formed on the other nozzles # 3 to # 7. It is assumed that the dot diameter is smaller than ○). In band printing, since one raster line is formed by one nozzle, the raster lines formed by the nozzles # 1 and # 2 at the end appear as streaks on the image, leading to the cause of image quality deterioration. Therefore, a printing method called “partial overlap printing” has been proposed.

  FIG. 4B is a diagram illustrating partial overlap printing, which is a printing method of a comparative example. For the sake of explanation here, dots (black circles ●) formed by nozzles # 1 to # 5 located at the far side end in the width direction are dots more than dots (white circles ○) formed by other nozzles due to abnormal ejection. Suppose the diameter is small. Further, it is assumed that the nozzles # 176 to # 180 located on the front side in the width direction do not cause the ejection abnormality even in the nozzles located at the end of the nozzle row.

  In the band printing shown in FIG. 4A, the interval between the raster line formed in the nozzle # 7 on the foremost side in the width direction and the raster line formed on the nozzle # 1 on the innermost side in the width direction is the nozzle pitch (180 dpi). The drive unit 30 moves the head 41 so that In other words, the drive unit 30 moves the head 41 so that the distance between the position of the frontmost nozzle # 7 in the previous pass 1 and the position of the innermost nozzle # 1 in the subsequent pass 2 is 180 dpi. .

  On the other hand, in the “partial overlap printing” shown in FIG. 4B, the front five nozzles # 176 to # 180 in the first pass 1 and the five rear nozzles # 1 to # 5 in the second pass 2 The drive unit 30 moves the head 41 so that they overlap. Specifically, the drive unit 30 is configured so that the nozzle # 176 in pass 1 and the nozzle # 1 in pass 2 overlap (adjacent in the transport direction), and the nozzle # 177 in pass 1 and nozzle # 2 in pass 2 overlap. The head 41 is moved. Thus, one raster line is formed by two nozzles in a region in which each of the five nozzles (# 1 to # 5 and # 176 to # 180) on both ends of the nozzle row is associated. In the partial overlap printing of this comparative example, dots are formed by nozzle # 176 in pass 1 at an interval twice the predetermined interval, and then the drive unit 30 moves the head 41 and passes in pass 2. Between the dots formed by one nozzle # 176, the nozzle # 1 is caused to form dots at an interval twice the predetermined interval. As a result, a raster line composed of dots alternately formed by two nozzles (# 1, # 176) is formed in a region (hereinafter referred to as a POL region) to which the nozzles at the end of the nozzle row are associated. It is formed.

  In the above-described band printing, each nozzle (# 1 # 2) on the back side that causes ejection abnormality forms one raster line, so that the raster line (● raster line) stands out on the image. As a result, the image quality is deteriorated. On the other hand, in the partial overlap printing of the comparative example, since a single raster line is formed by the nozzles on the back side that generate the discharge abnormality and the nozzles that do not generate the discharge abnormality, the dots (●) of the discharge abnormality are conspicuous. Difficult to reduce image degradation.

  That is, since the nozzles at the end of the nozzle row are more likely to cause ejection abnormalities and have larger variations in ink ejection than the nozzles at the center, nozzles at the end (# 1 to # 5 and # 176 to # 180) If the raster line formed by the above is formed by a plurality of nozzles, image quality deterioration can be suppressed accordingly.

  FIG. 5 is a diagram illustrating how dots are formed when a movement error occurs during partial overlap printing of the comparative example. It is assumed that when the drive unit 30 moves the head 41 between the pass 1 and the pass 2 in the width direction, the head unit 41 is moved more than a predetermined movement amount. As a result, the rear end nozzles (# 1 to # 5) in pass 2 are positioned on the front side in the width direction with respect to the front end nozzles (# 176 to # 180) in pass 1. For example, the nozzle # 1 in the pass 2 is positioned closer to the front side in the width direction than the nozzle # 176 in the pass 1.

  Then, between the dots formed by the nozzles (# 176 to # 180) at the front end of pass 1 (◯), the dots (●) by the nozzles (# 1 to # 5) at the back end of pass 2 Is not formed. That is, in the area on the medium other than the POL area, dots are arranged at a predetermined interval in the transport direction, whereas in the POL area, every other dot in the transport direction (at an interval twice the predetermined interval). Will be formed. That is, in the POL area of the comparative example, there are more dot intervals than instructed by the print data, and the dots are viewed lighter than the other areas, and density unevenness occurs in the entire image.

  Therefore, in the present embodiment, in order to alleviate the discharge variation of the end nozzles, the raster line formed by the end nozzles is subjected to printing errors formed by a plurality of nozzles. The purpose is to suppress density unevenness (lightness of the POL region) caused by the above.

=== Outline of Printing Method of the Present Embodiment ===
FIG. 6 is a diagram illustrating a printing method according to the present embodiment. For example, when printing an image in which raster lines in which dots are arranged at predetermined intervals in the transport direction print an array with a nozzle pitch (180 dpi) in the width direction, in this embodiment, end nozzles # 176 to # 180 in pass 1 are printed. In addition, the end nozzles # 1 to # 5 in pass 2 also form dots at predetermined intervals in the transport direction, like the other nozzles. Hereinafter, nozzles that form dots at predetermined intervals in the POL area in the previous pass (pass 1), that is, nozzles # 176 to # 180 on the front side in the width direction are referred to as “first nozzles”, and the subsequent pass The nozzles that form dots at predetermined intervals in the POL area in (Pass 2), that is, the nozzles # 1 to # 5 on the far side in the width direction are referred to as “second nozzles”. The first nozzle and the second nozzle are collectively referred to as an “end nozzle”. Therefore, when the movement error of the head 41 does not occur, the dots formed by the first nozzle and the dots formed by the second nozzle are formed so as to overlap each other.

  Further, even if a movement error of the head 41 occurs as shown in FIG. 6 and dots by the second nozzles (# 1 to # 5) are formed on the near side in the width direction from the predetermined position, this embodiment Then, the first nozzles (# 176 to # 180) form dots at predetermined intervals. Therefore, dots that are not printed in the partial overlap printing (FIG. 5) of the comparative example are printed in this embodiment (hatched dots), the dots arranged in the transport direction are wider than the predetermined interval, and the POL area is visually recognized lightly. Can be prevented. That is, as in the comparative example, due to the movement error of the head 41 or the like, the dots formed by the second nozzle are not formed between the dots formed by the first nozzle, and the gap between the dots is larger than indicated by the print data. It can be prevented from becoming large. As a result, it is possible to prevent density unevenness from occurring between the image in the POL area and the image in other areas.

  Here, it is assumed that one pixel on the data corresponds to one cell which is virtually determined on the medium. The density (gradation value) indicated by the pixel is pixel data. Then, based on certain pixel data, it is assumed that liquid ejection from a nozzle assigned to the pixel data is controlled with respect to an area on the medium corresponding to the pixel.

  In order to perform printing as in the present embodiment (FIG. 6), when creating print data, the first nozzle and the second nozzle are assigned to one pixel data corresponding to the POL area on the medium. It is done. In other words, ink from the first nozzle and the second nozzle is ejected based on one pixel data. That is, in the printing system according to the present embodiment, the first nozzle and the second nozzle are started from the first nozzle in the previous pass (first liquid ejection operation) based on the pixel data to which the first nozzle and the second nozzle are assigned (corresponding to certain pixel data). The medium corresponding to the pixel data from the second nozzle in the subsequent pass (second liquid ejection operation) is controlled by discharging ink (liquid) to the area on the medium corresponding to the pixel data. The ejection of ink (liquid) to the upper region is controlled. In addition, the end nozzle is based on a gradation value indicated by pixel data to which a nozzle different from the end nozzle (first nozzle / second nozzle) is assigned (corresponding to pixel data different from certain pixel data). When a predetermined ink amount (liquid amount) is ejected from another nozzle and the gradation value indicated by the pixel data to which the end nozzle is assigned is equal to the gradation value, the first nozzle and the second nozzle A predetermined amount of ink is discharged from each. On the other hand, in the partial overlap printing of the comparative example, the first nozzle or the second nozzle is assigned to one pixel data corresponding to the POL area. A raster line in which dots from the first nozzle and dots from the second nozzle are alternately arranged is formed.

  In other words, in order to alleviate the variation in the discharge characteristics of the end nozzles, a certain area (area on the medium corresponding to one pixel data) of the area (POL area) on the medium to which the end nozzles are associated. On the other hand, even if a movement error of the head 41 occurs due to ink being ejected from both of the two nozzles (the first nozzle and the second nozzle), the dot interval exceeds the predetermined interval indicated by the print data. Can be prevented. Therefore, in the present embodiment, a large gap is generated between dots particularly when printing is performed with a high gradation value (for example, in the case of solid printing). For example, in a white medium, a white background portion is conspicuous. Can be prevented and image deterioration can be suppressed.

  However, in the POL area, the dots formed by the first nozzle and the dots formed by the second nozzle are formed so as to overlap each other, so that there is a tendency to print darker than the gradation value specified by the print data. Therefore, when printing lightly with a low gradation value, the darkness of the POL area may become more conspicuous than the area on the medium other than the POL area.

  Therefore, for example, when a threshold value is provided for the pixel data corresponding to the POL area, and the gradation value indicated by the pixel data corresponding to the POL area (corresponding to certain pixel data) is equal to or greater than the threshold value, A first nozzle and a second nozzle are assigned to the pixel data, and a predetermined ink amount is ejected from each of the first nozzle and the second nozzle. As a result, in the region corresponding to the pixel data, the dots formed by the first nozzle and the dots formed by the second nozzle are formed so as to overlap each other, and it is possible to prevent the dot interval from becoming too empty. On the other hand, when the gradation value indicated by the pixel data corresponding to the POL area is less than the threshold value and printing is light, the first nozzle or the second nozzle is assigned to the pixel data. For example, when the first nozzle is assigned, a predetermined amount of ink is ejected from the first nozzle, and no ink is ejected from the second nozzle. As a result, dots are formed by the first nozzle or the second nozzle in an area corresponding to the pixel data.

  By doing so, in the case of printing darkly, even if the movement error of the head 41 occurs and the dots formed by the first nozzle and the dots formed by the second nozzle are shifted in the width direction, the print data It is possible to prevent the dot interval from being instructed more than indicated by, and faintly visible. Conversely, when printing lightly, since the number of dots formed is smaller than when printing darkly, the movement error of the head 41 causes a gap between dots more than indicated by the print data. However, the gap is not noticeable and can be said to be no problem.

  Further, based on the gradation value indicated by the pixel data to which the nozzles different from the end nozzles (the first nozzle and the second nozzle) are assigned, a predetermined ink amount is ejected from the nozzles other than the end nozzles. When the gradation value indicated by the pixel data to which the partial nozzle is assigned is equal to the gradation value, the gradation value is set to a low gradation value (equivalent to a light gradation value, for example, 80% of the gradation value). May be ejected from the first nozzle and the second nozzle by a smaller amount of ink than a predetermined amount of ink.

  Also, a density correction method for preventing the POL area from being printed darker than the other areas by forming the dots by the first nozzle and the dots by the second nozzle to overlap in the POL area. Is not limited to this. Hereinafter, a method for correcting the density of the POL area will be described.

=== Regarding Density Correction of POL Region: Correction Example 1 ===
FIG. 7 is a print data creation processing flow. It is assumed that the density correction processing for the POL area is performed by the computer 60 during creation of print data in accordance with a printer driver stored in the memory of the computer 60. The print data created in the computer 60 is transmitted to the printer 1, and the printer 1 performs printing according to the print data. In the present embodiment, since the printer driver of the computer 60 performs density correction in the POL area, the printing system in which the computer 60 and the printer 1 are connected corresponds to the liquid ejecting apparatus. In the case where the controller 10 of the printer 1 plays the role of the computer 60, the printer 1 alone corresponds to the liquid ejection device.

  The resolution conversion process (S001) is a process for converting the image data output from the application program into a resolution for printing on a medium. Note that the image data after the resolution conversion process is 256-gradation data (RGB data) represented by an RGB color space. The image data is a collection of pixel data. Pixel data is a gradation value indicated by a pixel. One pixel is expressed with 256 gradations, and the higher the gradation value is, the higher the density of a region on the medium corresponding to the pixel is.

  The color conversion process (S002) is a process for converting RGB data into CMYK data represented by a CMYK color space corresponding to the ink of the printer 1.

  The halftone process (S003) is a process for converting high gradation number data into gradation number data that can be formed by the printer 1 (dot data indicating the dot size).

  FIG. 8A is a diagram illustrating types of dots that can be printed by the printer 1 of the present embodiment. One pixel of this embodiment includes “form extra large dots”, “form large dots”, “form medium dots”, “form small dots”, “form very small dots”, “ It is expressed with 6 gradations of “no dot is formed”.

  The overlapping pixel data density correction process (S004) is a process for correcting the density of pixel data corresponding to the POL area (that is, pixel data to which the first nozzle and the second nozzle are assigned, hereinafter referred to as overlapping pixel data). . Details will be described later.

  The rasterization process (S005) is a process in which matrix image data is rearranged for each pixel data in the order of data to be transferred to the printer 1. The print data generated through these processes is transmitted to the printer 1 by the printer driver together with command data (conveyance amount, etc.) corresponding to the printing method.

  FIG. 8B is a diagram illustrating a state in which overlapping pixel data is replaced with pixel data for the first nozzle and pixel data for the second nozzle. In the first correction example, when the overlapped pixel data after the halftone processing instructs to form “extra large dots”, the “large” smaller size than the extra large dots is given to the first nozzle and the second nozzle. Dots "are formed. Therefore, the overlapping pixel data “form extra large dots”, the pixel data for the first nozzle “form large dots”, and the pixel data for the second nozzle “form large dots” Replace with Similarly, when the overlapping pixel data instructs to form “large dots”, the data is set so that the first nozzle and the second nozzle form “medium dots” smaller in size than the large dots. replace.

  As described above, in the correction example 1, a dot smaller than the dot size indicated by the overlapping pixel data (or the dot indicated by the overlapping pixel data) in the area on the medium corresponding to the overlapping pixel data (corresponding to certain pixel data). The overlapped pixel data after the halftone process is replaced with pixel data for end nozzles so that dots of a size or smaller are formed in the first nozzle and the second nozzle. In addition, when the overlapping pixel data instructs to form “minimal dots”, it is preferable to form minimal dots on either the first nozzle or the second nozzle. At this time, by making the number of minimum dots formed by the first nozzle and the number of minimum dots by the second nozzle approximately the same, variations in the discharge of the end nozzles can be alleviated.

  FIG. 9A shows how dots are formed when density correction processing is not performed on the POL area, and FIG. 9B shows how dots are formed when density correction processing of Correction Example 1 is performed on the POL area. It is a figure which shows a mode. Assume that all pixel data after halftone processing is instructed to form “large dots”. In addition, it is assumed that the second nozzle is shifted from the first nozzle in the width direction. In FIG. 9A, “large dots” are respectively formed by the first nozzle and the second nozzle for the overlapping pixel data “large dot formation” after the halftone process. By doing so, even when the second nozzle is displaced in the width direction with respect to the first nozzle due to the movement error of the head 41, as in the case of performing partial overlap printing, it is more than indicated by the print data. It is possible to prevent a large gap from occurring between the dots. On the other hand, in the POL area, large dots are formed so as to overlap by the first nozzle and the second nozzle, so that a large number of large dots are formed compared to the area other than the POL area.

  On the other hand, in FIG. 9B, the overlapped pixel data “large dot formation” is subjected to the density correction method of correction example 1 and the first nozzle pixel data “medium dot formation” and the second nozzle “medium dot formation” are also used. Replace with the pixel data for. As a result, “large dots” are formed in areas other than the POL area, and “medium dots” having a size smaller than the large dots are formed in the POL area by the first nozzle and the second nozzle. That is, in the POL area, the number of dots formed is larger than in the area other than the POL area, but the formed dot size is small. As a result, the amount of ink ejected toward the region other than the POL region can be made equal to the amount of ink ejected toward the POL region, and the POL region is darker than the other regions. It can be prevented from being visually recognized, and uneven density is eliminated.

  FIG. 10 is an image diagram of density correction processing in correction example 1 during print data creation. In the correction example 1, as shown in the flow of FIG. 7, the density correction process is performed on the pixel data after the halftone process. If the square in the figure is one pixel and “large” is marked on the pixel, a “large dot” is formed in the area on the medium corresponding to that pixel, and “medium” is marked on the pixel. Then, it is assumed that “medium dots” are formed in the area on the medium corresponding to the pixel. According to the pixel data after halftone processing, all the pixel data are shown to form “large dots”.

  Thereafter, in the density correction process, the data of the overlapping pixels (inside the bold line) to which the end nozzles are assigned are replaced with the pixel data for the first nozzle and the pixel data for the second nozzle. When the overlapping pixel data indicates “large dot formation”, it is replaced with pixel data for the first nozzle called “medium dot formation” and pixel data for the second nozzle called “medium dot formation”. Therefore, in the image data after the density correction processing in FIG. 10, “medium” is written in the pixel data for the first nozzle and the pixel data for the second nozzle surrounded by a thick line. Note that pixel data other than overlapping pixel data is not converted and remains “large dot formation”. Finally, each pixel data is rearranged so as to be assigned to the corresponding nozzle in the order in which the ink is ejected by the rasterizing process, and transmitted to the printer 1.

  As a result, as shown in FIG. 9B, “medium dots” are formed in the POL area so that the “medium dots” are overlapped by the first nozzle and the second nozzle, and “large dots” are formed in areas other than the POL area. The As a result, it is possible to prevent the POL area from being viewed darker than the other areas, and density unevenness is eliminated.

  In summary, in this correction example 1, the overlapping pixel data corresponding to the POL area is smaller than the dot size indicated by the overlapping pixel data as pixel data for the first nozzle and pixel data for the second nozzle. The data is converted into data in which size dots (dots smaller than the dot size indicated by the overlapping pixel data) are formed. As a result, it is possible to correct the density of the POL region that is formed by overlapping the dots formed by the first nozzle and the dots formed by the second nozzle.

  Further, in the correction example 1, for example, when a large dot is instructed to the POL area, a medium dot is formed from the two end nozzles, and as a result, toward the POL area. The amount of ink ejected is made equal. Therefore, when an image having the same density is printed, the POL area is printed with dots of a smaller size than the other areas, so that an image with higher graininess and higher image quality can be obtained.

<Modification of Correction Example 1>
In the above-described correction example 1, as shown in FIG. 8B, when the overlapping pixel data indicates “large dot formation”, all of the overlapping pixel data is converted into medium dots by the first nozzle and the second nozzle, respectively. Although it is replaced with data to be formed, it is not limited to this.

  For example, when there are ten overlapping pixel data indicating “large dot formation”, five of the overlapping pixel data are designated as “medium dot formation” pixel data for the first nozzle and pixel data for the second nozzle. Replace with Then, the remaining five overlapping pixel data may be replaced with the first nozzle pixel data “medium dot formation” and the second nozzle pixel data “small dot formation”. By doing so, if “medium dots” are formed in the first nozzle and the second nozzle for all overlapping pixel data indicating “large dot formation”, the POL area is still printed darkly. By forming “small dots” in the second nozzle for the overlapped pixel data of the portion, the density of the POL region can be corrected more reliably. As described above, even if the same overlapping pixel data is used, the pixel data for the first nozzle and the pixel data for the second nozzle may be replaced with different data by the overlapping pixel data. As a result, the density correction process for the POL region can be performed with higher accuracy than correction example 1.

  Therefore, in the manufacturing process or the like, the density correction processing of correction example 1, that is, all the overlapping pixel data indicating the same data is set so that the pixel data for the first nozzle and the pixel data for the second nozzle are the same combination. It is better to actually print a test pattern or the like. As a result, in the density correction process of the correction example 1, when the density correction of the POL area is insufficient, and even if it is printed darker than other areas, even overlapping pixel data indicating the same data, For some overlapping pixel data, the data may be replaced so that dots of a smaller size are formed from the end nozzles. On the other hand, when the density correction process of Correction Example 1 is performed, if the POL area is printed too lightly, even if it is overlapping pixel data indicating the same data, Data may be replaced so that a large size dot is formed from the end nozzle.

=== Regarding Density Correction of POL Region: Correction Example 2 ===
In the present embodiment, in the POL region in which one end nozzle (first nozzle) and the other end nozzle (second nozzle) of the nozzle row of the head 41 are associated with each other, the first nozzle and the second nozzle The dots are formed to overlap. By doing so, the dispersion | variation in the discharge characteristic of an edge part nozzle (a 1st nozzle and a 2nd nozzle) is relieve | moderated. In the second correction example, in order to further reduce variation in the ejection characteristics of the end nozzles, the overlapped pixel data after the halftone process is changed into pixel data for the first nozzle and pixel data for the second nozzle. When replacing with, gradation is given. Therefore, the density correction process of the correction example 2 is performed after the halftone process, as in the correction example 1 (FIG. 7).

  FIG. 11A is a diagram showing a pattern in which overlapping pixel data indicating “extra-large dot formation” is replaced with pixel data for the first nozzle and pixel data for the second nozzle with gradation, after halftone processing. It is. FIG. 11B is a diagram showing a state in which dots in the POL area are formed according to the pattern shown in FIG. 11A. For the sake of explanation, it is assumed that the number of nozzles in the nozzle row is reduced and all the pixel data indicate “extra large dot formation”. In FIG. 11B, the second nozzle is attached to the front side in the width direction with respect to the first nozzle.

  Up to this point, for the sake of explanation, discharge is performed to the five second nozzles (# 1 to # 5) on the back side of the nozzle row and the five first nozzles (# 176 to # 180) on the near side of the nozzle row. As there is a possibility that an abnormality will occur, printing is performed so that the dots from the first nozzle and the dots from the second nozzle overlap. By the way, even with the same end nozzle, the nozzle on the center side of the nozzle row (for example, # 176 and # 5) is compared with the nozzle on the end side of the nozzle row (for example, # 180 and # 1). The degree of occurrence of discharge abnormality is small. That is, among the end nozzles (the first nozzle and the second nozzle), it can be said that the center side nozzle is more accurate than the end side nozzle. Therefore, in this correction example 2, as shown in FIG. 11A, when the overlapping pixel data indicates “extra-large dot formation”, a larger dot is formed by the nozzle on the center side of the nozzle row among the end nozzles. Thus, the dot data for the first nozzle and the dot data for the second nozzle are replaced.

  In FIG. 11B, in order to show that the nozzle on the center side is less likely to cause a discharge abnormality than the nozzle on the end side, out of the five end nozzles at both ends of the nozzle row, Dots formed by two nozzles (# 1 to # 2, # 179 to # 180) are indicated by triangles (Δ), and three nozzles (# 3 to # 5, # 176 to # 176 on the center side) are shown. The dots formed by 177) are indicated by circles (◯) in the same manner as the dots formed by the nozzles other than the end nozzles.

  Then, when the overlapping pixel data after the halftone process is shown to form “extra large dots”, in this correction example 2, the nozzle row of the five first nozzles (# 176 to # 180) The data is replaced so that the “extra large dot” is formed in the nozzle # 176 at the most central side, and the “minimal dot” is formed in the nozzle # 1 corresponding to the nozzle # 176. As a result, as shown in FIG. 11B, on the far side of the POL area, the raster line (◯) of extra large dots formed by the first nozzle # 176 and the raster line of minimal dots formed by the second nozzle # 1 (Δ) is formed. As a result, the dots (Δ) formed due to the abnormal discharge of the nozzle # 1 on the end side are less noticeable, and image quality deterioration due to the abnormal discharge of the end nozzle can be reduced. Then, the “large dot” is formed in the second nozzle # 177 from the center of the nozzle row of the five first nozzles, and the “small dot” is formed in the nozzle # 2 corresponding to the nozzle # 177. So replace the data. In this way, the influence of the dots from the first nozzles (# 177 to # 180) decreases from the back side to the front side in the width direction, and conversely, the influence of the dots of the second nozzles (# 1 to # 5). growing. By doing so, in the POL region, the dot by the nozzle on the center side of the nozzle row has a greater influence than the dot by the nozzle on the end side, so that the discharge abnormality of the end nozzle can be alleviated.

  In other words, since the nozzles on the end side of the nozzle row are more likely to have a discharge abnormality, the dot size formed on the end side of the nozzle row becomes smaller in the five end nozzles. The overlapping pixel data is replaced with the pixel data for the first nozzle and the pixel data for the second nozzle so that the dot size to be formed becomes larger as the nozzle on the center side becomes larger. Relieve discharge abnormalities. As a result, a higher quality image can be obtained. Therefore, the distance from a certain first nozzle (for example, nozzle # 180) to the center of the nozzle row is from the second nozzle (for example, nozzle # 5) that forms dots in the same row area as the first nozzle to the nozzle row. When the distance is longer than the distance to the central portion, dots having a larger size are formed on the second nozzle than on the first nozzle. On the other hand, the distance from a certain first nozzle (for example, nozzle # 176) to the center of the nozzle row is the center of the nozzle row from the second nozzle (for example, nozzle # 1) that forms dots in the same row area as the first nozzle. When the distance is shorter than the distance to the part, the first nozzle has a larger size dot than the second nozzle.

  FIG. 12 is a diagram showing a pattern in which, after halftone processing, the overlapping pixel data indicating “large dot formation” is replaced with pixel data for the first nozzle and pixel data for the second nozzle with gradation. It is. In the printer 1 of this embodiment, each head 41 has five end nozzles. Also, the dot size that can be formed by the printer 1 is five (FIG. 8A). Therefore, when the overlapping pixel data indicating “extra-large dot formation” is converted into the pixel data for the end nozzles, it is possible to form dots having a smaller size from the center side of the nozzle row to the end side nozzles. However, overlapping pixel data for forming dots of a size smaller than the extra large dots does not necessarily cause the end nozzles to form smaller size dots for the five end nozzles. Can not.

  For example, when the overlapping pixel data indicating “large dot formation” is converted into the pixel data for the first nozzle, the first nozzle # 176 and the second nozzle No. 177 on the most central side of the nozzle row are “ “Medium dots” are formed. Then, “small dots” are formed on the first nozzles # 178 and # 179 on the end side further than that, and “minimal dots” are formed on the first nozzle # 180 on the most end side of the nozzle row. To convert the data. Conversely, “minimum dots” are formed in the second nozzle # 1 on the most end side of the nozzle row, and “small dots” are formed on the second nozzles # 2 and # 3 on the center side. Further, the data is converted so that “medium dots” are formed in the second nozzles # 4 and # 5 on the center side. By doing so, even if all the dots formed by the five end nozzles are not provided with gradation, the first nozzle and the second nozzle corresponding to the first nozzle and the nozzle corresponding to the end of the nozzle row are used. The influence of the dots formed is small, and conversely, the influence of the dots formed by the nozzles on the center side of the nozzle row can be increased, reducing the abnormal discharge of the end nozzles, resulting in a higher quality image. can get.

  Then, by storing the replacement pattern of the overlapping pixel data as shown in FIG. 11A and FIG. 12 in the memory of the computer 60, the computer 60 gives the gradation of the overlapping pixel data after the halftone process, It is replaced with the first nozzle pixel data and the second nozzle pixel data.

  Further, in FIG. 11B, it is assumed that all the overlapping pixel data indicates “extra-large dot formation”, but the actual print image is not limited to this. For example, it is assumed that the farthest overlapping pixel data indicates “large dot formation”, and the second overlapping pixel data from the back side indicates “extra large dot formation”. At this time, in the POL region, the “middle dot” is formed by the first nozzle # 176 at the innermost side, that is, the center side of the nozzle row, and the second first nozzle # 175 from the center side (back side). As a result, a “large dot” is formed. Therefore, the size does not necessarily increase as the dots formed by the nozzles on the center side of the nozzle row. However, based on the same overlapping pixel data, the first nozzle located on the center side of the nozzle row forms a larger dot than the second nozzle on the back side of the POL region, and the nozzle on the near side of the POL region. The second nozzle located on the center side of the row forms a larger dot than the first nozzle. Therefore, the discharge abnormality of the end nozzles can be alleviated as compared with the case where the first nozzle and the second nozzle form dots of the same size based on the same pixel data.

=== Regarding Density Correction of POL Region: Correction Example 3 ===
FIG. 13 is a flowchart of print data creation in the third correction example. In the correction example 3, unlike the correction examples 1 and 2, the density correction process (S103) is performed on the overlapping pixel data before the halftone process (S104).

  FIG. 14 is an image diagram of density correction processing in correction example 3 during print data creation. The pixel data before the halftone process is data having a high gradation number (256 gradations). Here, it is assumed that all the pixel data indicate “tone value 200”. Thereafter, in the density correction process, the gradation value of the overlapping pixel data to which the end nozzles are assigned is reduced to half “100”. That is, the gradation value “200” of the overlapping pixel data is distributed to the first gradation value “100” for the first nozzle and the second gradation value “100” for the second nozzle.

  Next, by the halftone process, the overlapping pixel data is changed from high gradation data “gradation value 100” to low gradation data “medium dot formation (corresponding to first dot data and second dot data)”. Converted. On the other hand, pixel data other than overlapping pixel data is converted from “gradation value 200” to data “large dot formation”. Finally, at the time of rasterization processing, the pixel data of the region surrounded by the solid line in the image data after the halftone processing in the figure is assigned to the nozzle row of pass 1 and the pixel data of the region surrounded by the dotted line is assigned. Assign to pass 2 nozzle row.

  That is, before the density correction process, all the pixel data indicate the gradation value 200, and if the halftone process is performed without the density correction process, all the pixel data is converted into data “large dot formation”. However, the halftone process is performed after the gradation value of the overlapped pixel data is halved by the density correction process, whereby the overlapped pixel data is converted into data of “medium dot formation”. As described above, the data obtained by performing the halftone process by halving the gradation value of the overlapping pixel data is allocated as common data to the first nozzle and the second nozzle. As a result, similar to the correction example 1 (FIG. 9B), in the POL area, the medium dots formed by the first nozzle and the medium dots formed by the second nozzle are formed so as to overlap each other. By doing so, the POL region is visually recognized darker than when the large dots are overlapped by the first nozzle and the second nozzle without performing the density correction processing of the POL region (FIG. 9A). Can be prevented.

  In the correction example 1, the overlapping pixel data is replaced with the pixel data for the first nozzle and the pixel data for the second nozzle so that the dot size to be formed is reduced after the halftone process is performed on the overlapping pixel data. . On the other hand, in the correction example 3, since the halftone process is performed after the gradation value of the overlapping pixel data is halved, the dot size formed in the POL area is reduced, and the number of dots generated in the POL area is smaller. May be less. However, as a result, since the amount of liquid ejected toward the POL area is reduced as compared with the case where the density correction process is not performed, it is possible to prevent the POL area from being visually recognized darkly.

  FIG. 15 is a diagram illustrating a state in which the gradation value of the overlapping pixel data before the halftone process is replaced with the pixel data for the first nozzle and the pixel data for the second nozzle with gradation. . In FIG. 14, the gradation value of the overlapping pixel data is divided in half, but the present invention is not limited to this. When the gradation value indicated by the overlapping pixel data is “200”, the first nozzle and the second nozzle to which the overlapping pixel data is assigned have more levels on the nozzle closer to the center of the nozzle row. The tone value “150” is distributed, and the smaller gradation value “50” is distributed to the nozzle farther from the center of the nozzle row. By doing so, a lot of liquid is ejected from the nozzle in the center with higher accuracy. For example, in FIG. 15, in the first nozzle on the back side in pass 1 and the second nozzle in pass 2 corresponding thereto, the first nozzle is closer to the center part of the nozzle row, so the overlapping pixel data is When the gradation value “150 (corresponding to the first gradation value)” of the pixel data for one nozzle and the gradation value “50 (corresponding to the second gradation value)” of the pixel data for the second nozzle are distributed. good. By doing so, it is possible to reduce the influence of variations in the discharge characteristics of the end nozzles on the image.

  In this way, when the gradation value of the overlapped pixel data is distributed as the pixel data for the first nozzle and the pixel data for the second nozzle with gradation instead of half, as shown in FIG. The overlapping pixel data after the halftone process cannot be the common data for the first nozzle and the second nozzle. Therefore, as shown in FIG. 15, before the halftone process, the overlapping pixel data may be distributed to the pixel data for the first nozzle and the pixel data for the second nozzle.

=== Regarding Density Correction of POL Region: Correction Example 4 ===
In this correction example 4, since the image printed in the POL area approaches the density (gradation value) indicated by the pixel data, the correction value H (for each column area) for each pixel column (details will be described later). ) Is calculated. Note that a pixel column refers to a pixel in which a plurality of pixels are arranged in a direction corresponding to the transport direction on print data. An area on the medium corresponding to the pixel column is referred to as a “column area”.

  FIGS. 16A to 16C are diagrams illustrating a printing method according to the present embodiment in the case where the density correction processing as in correction examples 1 to 3 is not performed on the POL area. FIG. 16A is a diagram illustrating a state of dots printed when there is no movement error of the head 41 and the first nozzle and the second nozzle are aligned in the transport direction. The ink droplet ejected from the first nozzle and the ink droplet ejected from the second nozzle overlap and land on the POL area. Therefore, larger dots are formed in the POL area than in other areas. That is, the density of the fourth to sixth column areas that are the POL area is visually recognized as being higher than the density of the first to third column areas other than the POL area. Therefore, in this correction example 4, the printer 1 is actually made to print a test pattern. From the test pattern result, it is detected how dark the column area belonging to the POL area is printed compared to other column areas, and a correction value H for each column area is calculated.

  In addition, a large dot formed in the fourth row region may protrude from the third row region adjacent to the fourth row region that is the POL region. At this time, even if the third row region is not the POL region, the third row region is visually recognized darker than the other first and second row regions. That is, even in an image formed in the row region by the same nozzle, the density may be different due to the influence of the nozzle associated with the adjacent row region. In such a case, the density unevenness cannot be suppressed by simply using the correction value associated with the nozzle. Therefore, by calculating the correction value H for each row region, it is possible to prevent the dots formed by the end nozzles from affecting the regions other than the POL region and causing uneven density.

  Similarly, FIG. 16B shows a state of dots printed when the second nozzle is attached to the back side in the width direction with respect to the first nozzle. In this case, the dots formed by the second nozzle are formed so as to protrude from the third row region. As a result, even if the third row region is not the POL region, it is visually recognized darkly. Therefore, the density of the third row region can be corrected by the correction value H for each row region.

  On the other hand, FIG. 16C shows a state of dots printed when the second nozzle is attached to the front side in the width direction with respect to the first nozzle. In this case, dots by the second nozzle that should be formed in the fourth row region are formed near the fifth row region. As a result, even if the fourth row area is a POL area, it is not printed as dark as the row areas belonging to other POL areas. For this reason, if the density correction processing for the fourth row region is performed as in the case of the row regions belonging to other POL regions, the fourth row region will be visually recognized as faint. Therefore, density correction can be performed more accurately by performing density correction processing using the correction value H for each row region.

  The same applies to the case where the density correction processing of correction examples 1 to 3 is performed on the POL area. For example, according to the correction example 1, when the overlapping pixel data indicates “large dot formation” as shown in FIG. 9B, the POL area is still not formed even if the middle dot is formed by the first nozzle and the second nozzle. In some cases, it may be visually recognized darker than other areas. At this time, the test pattern is printed based on the print data subjected to the density correction process in the correction example 1, and the correction value H for each row region is calculated. The darkness that did not exist can be corrected. On the contrary, by performing the density correction process, even if the POL area is printed too lightly, the lightness of the POL area can be corrected by the correction value H. That is, by performing density correction processing of correction examples 1 to 3 on the POL area, and further performing density correction of the column area corresponding to the pixel column based on the correction value H for each pixel column, Density unevenness is further suppressed, and a high-quality image can be obtained.

  In addition, the characteristics differ depending not only on the head 41 but also on each nozzle. For this reason, whether the nozzle is an end nozzle or any other nozzle, for example, the ink discharge amount may be smaller or larger than a predetermined amount. In this case, the row region formed by the nozzles ejecting a smaller amount of ink than the predetermined amount is visually recognized light, and the row region formed by the nozzles ejecting an amount of ink larger than the predetermined amount is viewed dark. . Such a row region can be corrected by the correction value H. That is, with the correction value H for each pixel column, it is possible to eliminate not only the POL area but also the density unevenness in areas other than the POL area. In addition, according to the correction value H for each pixel column, the density of the column region adjacent to the column region to which the nozzle to which the ejected ink droplet is bent is also determined by only the nozzle associated with its own column region. Instead, the correction is performed in consideration of nozzles associated with adjacent row regions.

  FIG. 17 is a flow of a method for calculating the correction value H. Hereinafter, a method for calculating the correction value H will be described. The correction value H is assumed to be similar to the manufacturing process of the printer 1.

<S201: Print Test Pattern>
FIG. 18A is a diagram showing a test pattern, and FIG. 18B is a diagram showing a correction pattern. The computer 60 causes the printer 1 to print a test pattern as shown in FIG. 18A according to the printer driver. At this time, based on the pixel data to which the end nozzles are assigned, ink is ejected from the first nozzle and the second nozzle to the area of the medium corresponding to the pixel data. In addition, the test pattern may be printed on the POL area in a state where the density correction processes of the correction examples 1 to 3 are performed, or the test pattern may be printed in a state where the density correction process is not performed. And

  The test pattern is composed of four correction patterns formed for each nozzle row of different colors (cyan, magenta, yellow, and black). Each 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 tone value of the belt-like pattern is called a command tone value, the command tone value of the belt-like pattern having a density of 30% is Sa (76), the command tone value of the belt-like pattern having a density of 50% is Sb (128), and the density is 70. The command gradation value of the% band-shaped pattern is represented as Sc (179).

  In the printer 1 of the present embodiment, when a band image is printed by one movement (pass) of the head unit 40 in the transport direction, the head unit 40 moves in the width direction by the amount of the band image and is printed first. It is assumed that band printing is performed so that the band image is printed again in the next pass so that the band image is aligned with the transport direction. That is, a raster line formed in another pass is not printed between raster lines formed in a certain pass. As described above, the density of a certain row region differs depending on the characteristics of the nozzle associated with the row region and the nozzle associated with the row region adjacent to the row region. In band printing, raster lines formed in other passes are not printed between raster lines formed in a certain pass. Therefore, if the correction pattern is formed by two passes, the correction value H for each row region can be calculated. Therefore, it is assumed that the correction pattern is composed of 710 (= (180 + 175) × 2) raster lines formed in two passes. When the correction value H of the row region to which nozzles other than the end nozzles are assigned is not calculated, it is preferable to form a correction pattern using only the end nozzles and the nozzles adjacent thereto.

<S202: Acquisition of Reading Tone Value>
Next, the printed test pattern is read with a scanner. For example, as shown in FIG. 18A, a reading range may be a range (dotted line) surrounding a cyan correction pattern on a sheet on which a test pattern is printed. Similarly, correction patterns formed by other nozzle rows are also read. When the read image of the correction pattern (the range of the alternate long and short dash line) is tilted, the tilt θ of the image is detected, and rotation processing corresponding to the tilt θ is performed on the image data.

  Note that an area corresponding to the “column area” is also referred to as a “pixel column” on the image data obtained by reading the correction pattern. Then, unnecessary pixels in the read image data are trimmed in a range larger than the correction pattern (a range indicated by a one-dot chain line). Thus, on the read image data, the number of pixel columns in the direction corresponding to the conveyance direction is set to be the same as the number of raster lines (number of column regions) of the correction pattern. That is, the pixel column and the column region are associated one to one. For example, the pixel column positioned at the top corresponds to the first column region, and the pixel column positioned below it corresponds to the second column region.

  FIG. 19 is a graph showing the result of reading a belt-like pattern having a density of 30% to 70%. After associating the pixel columns with the column regions on a one-to-one basis, the density of each column region is calculated for each strip pattern. The average value of the read gradation values of each pixel in the pixel column corresponding to a certain column area is set as the read gradation value of that column area. In FIG. 19, the horizontal axis represents the row area number, and the vertical axis represents the read gradation value. As shown in the graph, although each strip pattern is uniformly formed with each command gradation value, the reading gradation value varies for each row region. In particular, when the test pattern is printed without performing the density correction processing of correction examples 1 to 3, the density of the column area belonging to the POL area is higher than the density of the column area belonging to the other areas. Become. This variation in density for each row area causes uneven density in the printed image.

<S203: Calculation of Correction Value H>
In order to reduce the density variation for each row region as shown in FIG. 19, it is only necessary to eliminate the density variation for each row region at the same gradation value. That is, the density unevenness is improved by bringing the density of each row region close to a certain value.

  Therefore, the average value Cbt of the read gradation values of all the row regions in the same command gradation value, for example, Sb is set as the “target value Cbt”. Then, the gradation value of the pixel corresponding to each column region is corrected so that the read gradation value of each column region at the command gradation value Sb approaches the target value Cbt. When the test pattern is performed without performing the density correction process on the POL area, the reading gradation value of the column area belonging to the POL area is high, and the average value of the reading gradation values of all the column areas is set as the target value. If this happens, the target value will increase. Therefore, the average value of the read gradation values in the row area other than the POL area may be set as the target value.

  In the row region i in which the read gradation value Cbi with respect to the command gradation value Sb is lower than the target value Cbt, the levels before the halftone process and before the density correction process are printed so as to be printed darker than the setting of the command gradation value Sb. Correct the key value. On the other hand, in the row region j (Cbj) having a reading gradation value higher than the target value Cbt, the gradation value is corrected so that printing is lighter than the setting of the instruction gradation value Sb.

FIG. 20A is a diagram illustrating a method of calculating the target gradation value Sbt of the i-th row area whose reading result is lower than the target gradation value Cbt. The horizontal axis indicates the command gradation value, and the vertical axis indicates the read gradation value. On the graph, cyan reading results (Cai, Cbi, Cci) in the i-th row area are plotted against the command gradation values (Sa, Sb, Sc). 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)}
FIG. 20B is a diagram illustrating a method of calculating the target gradation value Sbt of the j-th row area where the reading result is higher than the target gradation value Cbt. On the graph, the reading result of cyan in the j column region is plotted. The target command tone value Sbt for representing the j-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 AB).
Sbt = Sa + (Sb−Sa) × {(Cbt−Caj) / (Cbj−Caj)}
Thus, after calculating the target command gradation value Sbt for expressing the density of each column region with the target value Cbt with respect to the command gradation value Sb, the command gradation value of each column region is calculated by the following equation. A correction value H for Sb is calculated.
Hb = (Sbt−Sb) / Sb
Similarly, three correction values (Ha, Hb, Hc) for the three command gradation values (Sa, Sb, Sc) are calculated for each row region. Further, not only cyan but also correction values H of other nozzle rows are calculated. Note that the correction pattern of this embodiment is formed in two passes of the head unit 40 by a band printing method. Therefore, an average value of the correction values H of the corresponding two row areas may be set as the correction value H of the row areas.

<S204: Storage of Correction Value H>
FIG. 21 is a correction value table. After calculating the correction value H, the correction value H is stored in the memory 53 of the printer 1. In the correction value table, three correction values (Ha_i, Hb_i, Hc_i) corresponding to the three command gradation values are associated with each column region i. In the correction value table, the correction value H of the row area to be printed in one pass of the head unit 40 is stored. Then, the correction value H of the row area numbers 176 to 180 becomes the correction value H of the POL area.

<About printing under the user>
FIG. 22 is a flow of print data creation processing when density correction processing is performed using the correction value H set for each row region. In the manufacturing process of the printer 1, a correction value H for correcting density unevenness is calculated, and after the correction value H is stored in the memory 53 of the printer, the printer 1 is shipped. When the user installs the printer driver when using the printer 1, the printer driver requests the printer 1 to transmit the correction value H stored in the memory 53 to the computer 60. The printer driver stores the correction value H sent from the printer 1 in a memory in the computer 60.

  Upon receiving a print command from the user, the printer driver creates print data according to the print data creation process flow of FIG. At this time, as shown in FIG. 22, after the color conversion process (S302), the gradation value of the pixel data indicated by the high gradation is corrected according to the correction value H of the column area to which the pixel data is assigned. (S303, details will be described later). Thereafter, when the density correction processing of correction examples 1 to 3 is not performed on the POL area (1), the pixel data corrected with the correction value H is subjected to halftone processing. On the other hand, when the density correction process of correction example 1 or correction example 2 is performed on the POL area (2), the pixel data corrected with the correction value H is subjected to the halftone process, and further corresponds to the POL area. The pixel data to be replaced is replaced with pixel data for the first nozzle and pixel data for the second nozzle. When the density correction process of the correction example 3 is performed on the POL area (3), the gradation value of the pixel data corresponding to the POL area among the pixel data corrected with the correction value H is halved. And so on (for example, FIGS. 14 and 15), and halftone processing is performed.

  Next, a process of correcting the high gradation value indicated by the pixel data with the correction value H in S303 will be described. The printer driver corrects the gradation value of each pixel data (hereinafter referred to as gradation value S_in before correction) based on the correction value H of the column region corresponding to the pixel data (corrected gradation value). S_out).

If the gradation value S_in before correction is the same as any of the command gradation values Sa, Sb, Sc, the correction values Ha, Hb, Hc stored in the memory of the computer 60 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. 23 is a diagram illustrating a correction method when the gradation value S_in before correction of the i-th row region of cyan is different from the command gradation value. The horizontal axis is the gradation value S_in before correction, and the vertical axis is the gradation value S_out after correction. When the gradation value S_in before correction is between the command gradation values Sa and Sb, correction is performed by the following equation by linear interpolation based on the correction value Ha of the command gradation value Sa and the correction value Hb of the command gradation value Sb. The later gradation value S_out is calculated.
S_out = Sa + (S′bt−S′at) × {(S_in−Sa) / (Sb−Sa)}
When the gradation value S_in before correction is smaller than the command gradation value Sa, the gradation value S_out after correction is obtained by linear interpolation between the gradation value 0 (minimum gradation value) and the command gradation value Sa. Is calculated. When the gradation value S_in before correction is larger than the command gradation value Sc, the gradation value S_out after correction is calculated by linear interpolation between the gradation value 255 (maximum gradation value) and the instruction gradation value Sc. To do. In addition, the present invention is not limited to this, and a correction value H_out corresponding to a gradation value S_in before correction different from the command gradation value may be calculated, and a gradation value S_out after correction may be calculated (S_out = S_in × ( 1 + H_out)).

=== Other Embodiments ===
Each of the above embodiments is 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 partial overlap printing>
In the above-described embodiment, the raster line formed by the end nozzles is formed by a plurality of nozzles in order to alleviate the variation in the ejection characteristics of the end nozzles of the nozzle row. However, the present invention is not limited to this. For example, even in an area where overlap printing is performed using a nozzle that is not an end nozzle, the dot spacing is more than specified by the print data by printing so that dots from a plurality of nozzles overlap. Can be prevented. Also, not only in partial overlap printing, but also in overlap printing where all raster lines are formed by multiple nozzles, the dot spacing is indicated by print data by printing so that dots from multiple nozzles overlap. It is possible to prevent vacancy from being made.

<About serial printers>
In the above-described embodiment, after the continuous medium is transported to the printing area, an image is formed while the head unit 40 is alternately moved in the transport direction and the width direction of the continuous medium, and the image is not printed again after the image formation. Although an example of an inkjet printer that conveys an area of a continuous medium to a printing area and repeats this to print an image on the continuous medium is exemplified, the present invention is not limited thereto. For example, an operation (liquid ejection operation / pass) of forming a raster line while moving the head in the movement direction (corresponding to the conveyance direction in the printer 1) by the carriage, and a direction intersecting the cut sheet paper in the movement direction. The present invention can also be applied to a serial printer that alternately repeats an operation (moving operation) for conveying in the conveying direction (corresponding to the width direction in the printer 1 described above). In this case, a plurality of nozzles are assigned to a certain row area on the medium (in overlap printing), and ink is ejected from one nozzle and the other nozzle based on the same pixel data so that the dots overlap. Print. As a result, it is possible to prevent the dot interval from being abnormally instructed by the print data, and to suppress density unevenness.

<About liquid ejection device>
In the above-described embodiment, the ink jet printer is exemplified as the liquid ejecting apparatus (part) for performing the liquid ejecting method, but is not limited thereto. If it is a liquid ejection device, it can be applied to various industrial devices, not a printer (printing device). For example, a textile printing device for patterning a fabric, a display manufacturing device such as a color filter manufacturing device or an organic EL display, a DNA chip manufacturing device for manufacturing a DNA chip by applying a solution in which DNA is dissolved in a chip, a circuit board manufacturing The present invention can be applied even to an apparatus or the like.
The liquid discharge method may be a piezo method that discharges liquid by applying voltage to the drive element (piezo element) to expand and contract the ink chamber, or generates bubbles in the nozzle using a heating element. It is also possible to use a thermal method in which liquid is discharged by the bubbles.

1 is a configuration block diagram of a printing system. 2A is a schematic sectional view of the printer, and FIG. 2B is a schematic top view of the printer. It is a figure which shows the nozzle arrangement | sequence of the lower surface of a head. FIG. 4A is a diagram illustrating band printing of a comparative example, and FIG. 4B is a diagram illustrating overlap printing of the comparative example. It is a figure which shows the printing of the comparative example when a movement error arises in the head. It is a figure which shows the printing method of this embodiment. It is a print data creation processing flow. FIG. 8A is a diagram showing types of dots that can be printed by the printer 1, and FIG. 8B is a diagram showing replacement of overlapping pixel data. 9A shows how dots are formed when density correction processing is not performed, and FIG. 9B is a diagram showing how dots are formed when density correction processing according to Correction Example 1 is performed. It is an image figure of the density correction process of the correction example 1. FIG. 11A shows a state in which overlapping pixel data is replaced with gradation, and FIG. 11B shows a state of dot formation. It is a figure which shows the pattern which replaces duplication pixel data with a gradation property. It is a flow of print data creation in the correction example 3. It is an image figure of the density correction process of the correction example 3. It is a figure which shows a mode that it replaces with overlapping pixel data gradation property. 16A to 16C are diagrams illustrating the printing method according to the present embodiment when the density correction process is not performed. It is a flow of a correction value calculation method. FIG. 18A is a diagram showing a test pattern, and FIG. 18B is a diagram showing a correction pattern. It is the figure which showed the reading result of the strip | belt-shaped pattern with the graph. 20A and 20B are diagrams illustrating a method for calculating a target gradation value. It is a correction value table. It is a print data creation processing flow for performing density correction processing using correction values. It is a figure which shows the correction method when the gradation value before correction | amendment differs from a command gradation value.

Explanation of symbols

1 printer, 10 controller, 11 interface unit,
12 CPU, 13 memory, 14 unit control circuit,
20 transport units, 21 transport rollers,
30 drive unit, 31 first stage, 32 second stage,
40 head units, 41 heads, 42 heads,
50 detector groups, 60 computers

Claims (8)

A liquid ejection operation for ejecting liquid from the nozzle row while relatively moving a nozzle row and a medium in which a plurality of nozzles for ejecting liquid are arranged in a predetermined direction in a direction intersecting the predetermined direction; and the nozzle row and the medium And a liquid ejecting apparatus that alternately repeats a moving operation for relatively moving in a predetermined direction,
In the first liquid ejection operation, the liquid ejection from the first nozzle of the nozzle row to the area on the medium corresponding to the certain pixel data is controlled based on the certain pixel data.
In the second liquid ejection operation after the first liquid ejection operation, corresponding to the certain pixel data from the second nozzle different from the first nozzle in the nozzle row based on the certain pixel data. Controlling liquid ejection to an area on the medium that
Liquid ejection device. The liquid ejection device according to claim 1,
Based on a gradation value indicated by pixel data different from the certain pixel data, a predetermined liquid amount is ejected from a nozzle different from the first nozzle and the second nozzle,
When the gradation value indicated by the certain pixel data is equal to the gradation value indicated by the other pixel data, the first nozzle and the second nozzle respectively in the region on the medium corresponding to the certain pixel data. Discharging a predetermined amount of liquid,
Liquid ejection device. The liquid ejection device according to claim 2,
When the gradation value indicated by the certain pixel data is greater than or equal to a threshold value, the predetermined amount of liquid is ejected from the first nozzle and the second nozzle to an area on the medium corresponding to the certain pixel data, respectively. ,
When the gradation value indicated by the certain pixel data is less than the threshold value, the predetermined amount of liquid is ejected from the first nozzle to an area on the medium corresponding to the certain pixel data, and the second nozzle Does not discharge liquid from the
Liquid ejection device. The liquid ejection device according to claim 1,
The halftone process converts the gradation value indicated by each pixel data into dot data indicating the dot size to be formed in the area on the medium corresponding to each pixel data,
Forming dots on each of the first nozzle and the second nozzle in a region on the medium corresponding to the certain pixel data, each having a dot size or less indicated by the dot data of the certain pixel data;
Liquid ejection device. The liquid ejection device according to claim 4,
When the distance from the first nozzle to the central portion of the nozzle row is longer than the distance from the second nozzle to the central portion, a dot having a size larger than that of the first nozzle is formed in the second nozzle. Let
When the distance from the first nozzle to the central portion is shorter than the distance from the second nozzle to the central portion, the first nozzle is formed with a larger size dot than the second nozzle.
Liquid ejection device. The liquid ejection device according to claim 1,
After distributing the gradation value indicated by the certain pixel data to the first gradation value for the first nozzle and the second gradation value for the second nozzle,
The first gradation value is converted into the first dot data by halftone processing for converting the gradation value indicated by the pixel data into dot data indicating the dot size to be formed in the area on the medium corresponding to the pixel data. Converting the second gradation value into the second dot data,
In the area on the medium corresponding to the certain pixel data, dots having a dot size indicated by the first dot data are formed on the first nozzle, and dots having a dot size indicated by the second dot data are formed on the second nozzle. To form,
Liquid ejection device. The liquid ejection device according to claim 6,
When the distance from the first nozzle to the central portion of the nozzle row is longer than the distance from the second nozzle to the central portion, the dots are formed by the second nozzle rather than the dots formed by the first nozzle. Distributing the gradation value indicated by the certain pixel data to the first gradation value and the second gradation value so that the dot to be generated is larger,
When the distance from the first nozzle to the central portion is shorter than the distance from the second nozzle to the central portion, the dots formed by the first nozzle rather than the dots formed by the second nozzle The gradation value indicated by the certain pixel data is distributed to the first gradation value and the second gradation value so that is larger.
Liquid ejection device. The liquid ejection device according to claim 1,
Based on a gradation value indicated by pixel data different from the certain pixel data, liquid is ejected from a nozzle different from the first nozzle and the second nozzle,
Converting the gradation value indicated by the certain pixel data equal to the gradation value into a light gradation value;
Based on the light gradation value, liquid is ejected from the first nozzle and the second nozzle to an area on the medium corresponding to the certain pixel data, respectively.
Liquid ejection device.