JP2016010863A - Droplet discharge method and droplet discharge device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce color irregularity, uneven density and uneven brightness of a droplet discharge device using a plurality of heads (nozzle array).SOLUTION: A droplet discharge method corrects an amount of droplets discharged per unit area for forming dot rows on the basis of a first correction amount table corresponding to a first nozzle array, a second correction amount table corresponding to a second nozzle array and nozzle array usage rates of the first nozzle array and the second nozzle array for forming the dot rows obtained on the basis of gradation of the dot rows formed.

Description

  The present invention relates to a droplet discharge method and a droplet discharge device.

  2. Description of the Related Art Conventionally, as a droplet discharge device, an ink jet printer that forms an image by discharging droplets (ink droplets) onto the surface of a print medium is known. Inkjet printers transport ink from each nozzle while moving the print medium, such as paper and cloth, in the transport direction, and scanning the head in which a plurality of nozzles are formed in the scan direction that intersects the print medium transport direction. The dot forming operation for discharging the ink is alternately repeated, and the dot rows (dot rows) arranged in the scanning direction are formed side by side in the transport direction to form an image on the print medium. In such an ink jet printer, in order to form a higher-definition image at high speed, a plurality of heads in which finer nozzles are arranged at high density have been used.

When a plurality of heads are used, a difference in ink discharge characteristics for each head may cause color unevenness. In Patent Document 1, as a technique for improving the color unevenness, the correction result based on the correction value of the ink discharge characteristic of each head is weighted according to the usage rate of the head for each dot row to correct the ink discharge amount. A method has been proposed.
In addition, when pixels are formed with a plurality of dots, the ease of ink bleeding varies depending on the timing at which dots that are in close proximity are formed, which may cause uneven density and uneven gloss. In Patent Document 2, as a technique for suppressing this density unevenness, the dots to be suppressed for blurring are formed by increasing the usage rate of the preceding nozzles that discharge ink at an early timing, thereby promoting the drying of the ink. A method for suppressing the occurrence of bleeding has been proposed.

JP 2009-143135 A JP 2010-137536 A

  However, there is a problem that it is impossible to improve both the color unevenness, the density unevenness, and the gloss unevenness. Specifically, in the method described in Patent Document 1, uneven density and uneven gloss may occur depending on the ink gradation of an image to be formed. In the method described in Patent Document 2, ink ejection characteristics are generated. This is a problem that color unevenness may occur due to the difference between the two.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following application examples or forms.

  [Application Example 1] A droplet discharge method according to this application example includes a transport operation for moving a print medium in a transport direction, and a first nozzle array and a second nozzle array in which a plurality of nozzles are arranged in the transport direction. By alternately repeating a droplet discharge operation for discharging a droplet from the nozzle to the print medium while scanning and moving in a scanning direction intersecting the transport direction, a dot row composed of dots arranged in the scanning direction is formed. A plurality of droplet discharge methods formed in the transport direction, wherein a first correction amount table corresponding to the first nozzle row, a second correction amount table corresponding to the second nozzle row, and the dot row to be formed Per unit area for forming the dot row based on the nozzle row usage rate of the first nozzle row and the second nozzle row for forming the dot row obtained based on the gradation of To discharge And correcting the amount of serial droplets.

The droplet discharge method according to this application example includes a transport operation for moving the print medium in the transport direction, and a first nozzle row and a second nozzle row in which a plurality of nozzles are arranged in the transport direction in a scanning direction that intersects the transport direction. A droplet discharge method in which a plurality of dot rows composed of dots arranged in the scan direction are formed in the transport direction by alternately repeating the droplet discharge operation of discharging droplets from the nozzles onto the print medium while performing scanning movement. is there.
According to this application example, the first correction amount table corresponding to the first nozzle row, the second correction amount table corresponding to the second nozzle row, and the nozzle row usage rate based on the gradation of the dot row to be formed Based on this, the amount of droplets per unit area forming the dot row is corrected.

  The first correction amount table is a correction amount table for correcting the amount of liquid droplets ejected by the nozzles of the first nozzle row obtained based on the first pattern composed of the dot rows formed by the first nozzle row. is there. That is, based on the first correction amount table, it is possible to correct the ejection of droplets from the nozzles of the first nozzle row in accordance with the droplet ejection characteristics of the nozzles of the first nozzle row. As a result, color unevenness due to a characteristic difference between the first nozzle row and the second nozzle row can be suppressed.

  The second correction amount table is a correction amount table for correcting the amount of liquid droplets ejected by the nozzles of the second nozzle row obtained based on the second pattern composed of the dot rows formed by the second nozzle row. is there. That is, based on the second correction amount table, it is possible to correct the ejection of droplets from the nozzles of the second nozzle row in accordance with the droplet ejection characteristics of the nozzles of the second nozzle row. As a result, color unevenness due to a characteristic difference between the first nozzle row and the second nozzle row can be suppressed.

  The nozzle row usage rate is the nozzle row usage rate of the first nozzle row and the second nozzle row for forming a dot row obtained based on the gradation of the dot row to be formed. That is, based on the nozzle row usage rate, the nozzle row usage rates of the first nozzle row and the second nozzle row are determined according to the gradation of the dot row to be formed. As a result, density unevenness and gloss unevenness (hereinafter referred to as density unevenness including gloss unevenness) caused by a difference in timing at which adjacent dots are formed can be suppressed.

  Therefore, according to this application example, it is possible to suppress color unevenness due to a characteristic difference between the first nozzle row and the second nozzle row, density unevenness caused by a difference in timing at which adjacent dots are formed, and the like.

  Application Example 2 In the droplet discharge method according to the application example, the gradation is an average gradation of the dot row to be formed.

  According to this application example, since the nozzle row usage rates of the first nozzle row and the second nozzle row are determined based on the average gradation of the dot rows to be formed, the first nozzle row and the second nozzle row Color unevenness due to characteristic differences, density unevenness caused by differences in timing at which adjacent dots are formed, and the like can be performed more easily.

  Application Example 3 In the droplet discharge method according to the application example described above, the dot row is formed by weighting the first correction amount table and the second correction amount table based on the nozzle row usage rate. Therefore, the amount of the liquid droplets discharged per unit area is corrected.

  According to this application example, the amount of liquid droplets discharged per unit area to form a dot row by weighting the first correction amount table and the second correction amount table based on the nozzle row usage rate is determined. to correct. That is, since the correction is performed by weighting each of the first correction amount table and the second correction amount table based on the corrected nozzle row usage rates of the first nozzle row and the second nozzle row, the correction is performed more appropriately. be able to.

  Application Example 4 A droplet discharge device according to this application example includes a transfer unit that moves a print medium in the transfer direction, and a first nozzle in which a plurality of nozzles that discharge droplets to the print medium are arranged in the transfer direction. A scanning movement unit that scans and moves a row, a second nozzle row, the first nozzle row and the second nozzle row in a scanning direction intersecting the conveyance direction, and drive control of the conveyance unit and the scanning movement unit; A controller that forms a plurality of dot rows composed of dots arranged in the scanning direction in the transport direction by controlling ejection of the droplets from the nozzles, and corresponds to the first nozzle row The first nozzle for forming the dot row obtained based on the first correction amount table to be performed, the second correction amount table corresponding to the second nozzle row, and the gradation of the dot row to be formed Of the second nozzle row A nozzle column usage, the amount of the liquid droplets ejected per unit area in order to form the dot rows is characterized in that it is corrected based on.

According to this application example, the droplet discharge device includes a transport unit that moves the print medium in the transport direction, and a first nozzle row and a second nozzle in which a plurality of nozzles that eject droplets onto the print medium are arranged in the transport direction. A scanning movement unit that scans and moves the row, the first nozzle row and the second nozzle row in a scanning direction that intersects the conveyance direction, drive control of the conveyance unit and the scanning movement unit, and ejection control of droplets from the nozzles Thus, a control unit is provided that forms a plurality of dot rows composed of dots arranged in the scanning direction in the transport direction. Further, in order to form a dot row obtained based on the first correction amount table corresponding to the first nozzle row, the second correction amount table corresponding to the second nozzle row, and the gradation of the dot row to be formed. Based on the nozzle row usage rates of the first nozzle row and the second nozzle row, the amount of liquid droplets discharged per unit area is corrected in order to form a dot row.
Therefore, according to the droplet discharge device of this application example, color unevenness due to a characteristic difference between the first nozzle row and the second nozzle row, density unevenness caused by a difference in timing at which adjacent dots are formed, and the like are suppressed. Images can be obtained.

1 is a block diagram illustrating an overall configuration of an ink jet printer as a droplet discharge device according to a first embodiment. 1 is a perspective view of an ink jet printer as a droplet discharge device according to Embodiment 1. FIG. Explanatory drawing showing an example of the arrangement of nozzles Explanatory drawing showing an example of the arrangement of nozzles Explanatory drawing describing a headset as a virtual headset Illustration of an example of normal processing Illustration of dot formation example in normal processing (A), (b) Explanatory drawing of an example of an upper end process The graph which shows typically the usage rate of the head in each pass 1-6 Graph showing head usage rate in the area from top edge processing to normal processing Explanatory drawing of color unevenness correction value acquisition processing Illustration of color unevenness correction value Block diagram when printing under the user in the prior art Flow chart of processing performed by the printer driver in the prior art Flow chart of uneven color correction processing (A) Dot generation rate table used for halftone processing, (b) Graph of relationship between gradation value and ink amount when ink is ejected with reference amount, (c) Ink of amount different from reference amount Graph of relationship between gradation value and ink amount when ink is ejected Explanatory diagram showing the meaning of the ink amount table Explanatory drawing of a 1st correction amount table and a 2nd correction amount table The graph which shows the relationship between an ink gradation and the usage rate of a head 1st nozzle row Block diagram when printing under the user Flow chart of processing performed by the printer driver Flow chart of correction processing that achieves both color unevenness and density unevenness Graph showing correction example of nozzle row usage rate

  DESCRIPTION OF EMBODIMENTS Embodiments embodying the present invention will be described below with reference to the drawings. The following is one embodiment of the present invention and does not limit the present invention. In the following drawings, the scale may be different from the actual scale for easy understanding.

(Embodiment 1)
FIG. 1 is a block diagram showing an overall configuration of an inkjet printer 100 as a “droplet ejection device” according to the first embodiment, and FIG. 2 is a perspective view.
Note that the inkjet printer 100 is installed on the XY plane in the XYZ axes appended to the drawing. Further, the ± X direction (X-axis direction) will be described as a scanning direction, the Y direction will be described later, and the Z direction will be described as a height direction.
First, the basic configuration of the inkjet printer 100 will be described.

<Basic configuration of inkjet printer>
The ink jet printer 100 includes a transport unit 20 as a “transport section”, a carriage unit 30 as a “scan moving section”, a head unit 40, and a controller 60 as a “control section”. The inkjet printer 100 that has received print data from a personal computer 110 (a computer used by a user; hereinafter referred to as a PC 110), which is an external device, controls each unit (conveyance unit 20, carriage unit 30, and head unit 40) by a controller 60. Control. The controller 60 controls each unit based on the print data received from the PC 110 and prints an image (image formation) on the paper 10 as a “print medium”.

  The print data includes, for example, general RGB digital image information obtained by a digital camera or the like, and general image processing application software (hereinafter referred to as an application) and printer driver software (hereinafter referred to as a printer driver) provided in the PC 110. The image forming data is converted so that it can be printed by the inkjet printer 100.

  The transport unit 20 is for moving the paper 10 in a predetermined transport direction (Y direction shown in FIG. 2). The transport unit 20 includes a paper feed roller 21, a transport motor 22, a transport roller 23, a platen 24, a paper discharge roller 25, and the like. The paper feed roller 21 is a roller for feeding the paper 10 inserted into the paper insertion opening into the ink jet printer 100. The transport roller 23 is a roller that transports the paper 10 fed by the paper feed roller 21 to a printable region, and is driven by the transport motor 22. The platen 24 supports the paper 10 being printed. The paper discharge roller 25 is a roller for discharging the paper 10 to the outside of the printer, and is provided on the downstream side in the transport direction with respect to the printable area.

  The carriage unit 30 is for moving (scanning) a later-described head 41 in a predetermined movement direction (X-axis direction shown in FIG. 2, also referred to as a scanning direction hereinafter). The carriage unit 30 includes a carriage 31, a carriage motor 32, and the like. The carriage 31 can reciprocate in the scanning direction and is driven by a carriage motor 32. Further, the carriage 31 detachably holds an ink cartridge 6 that stores ink.

The head unit 40 is for ejecting ink onto the paper 10 as “droplets” (hereinafter also referred to as ink droplets). The head unit 40 includes a head 41 having a plurality of nozzles. Since the head 41 is mounted on the carriage 31, when the carriage 31 moves in the scanning direction, the head 41 also moves in the scanning direction. By intermittently ejecting ink while the head 41 is moving in the scanning direction, a dot row (hereinafter also referred to as a raster line) composed of dots arranged in the scanning direction is formed on the paper 10.
The head 41 includes two heads (a first nozzle group 41A and a second nozzle group 41B). The configuration of the head 41 will be described later.

The controller 60 is a control unit for controlling the ink jet printer 100. The controller 60 includes an interface unit 61, a CPU 62, a memory 63, a unit control circuit 64, and the like. The interface unit 61 transmits and receives data between the PC 110 that is an external device and the inkjet printer 100. The CPU 62 is an arithmetic processing unit for controlling the entire printer. The memory 63 is for securing an area for storing the program of the CPU 62, a work area, and the like, and includes storage elements such as a RAM and an EEPROM.
The CPU 62 controls each unit (conveyance unit 20, carriage unit 30, head unit 40) via the unit control circuit 64 in accordance with a program stored in the memory 63.

  Further, the controller 60 is provided with a drive signal generation unit 65. The drive signal generation unit 65 includes a first drive signal generation unit 65A and a second drive signal generation unit 65B. The first drive signal generator 65A generates a first drive signal for driving the piezo elements of the first nozzle group 41A. The second drive signal generator 65B generates a second drive signal for driving the piezo elements of the second nozzle group 41B. Each drive signal generator generates a drive signal for odd-numbered dots when forming dots on odd-numbered dots (described later), and for even-numbered dots when forming dots on even-numbered dots (described later) Drive signal is generated. The drive signal generation units are independent of each other. For example, when the first drive signal generation unit 65A generates a drive signal for odd-numbered dots, the second drive signal generation unit 65B is for odd-numbered dots. Drive signals for even-numbered dots can also be generated.

  When performing printing, the controller 60 alternately performs “droplet discharge operation” for discharging ink as droplets from the head 41 moving in the scanning direction and “transport operation” for moving the paper 10 in the transport direction. The image composed of a plurality of dots is printed on the paper 10 repeatedly. The droplet discharge operation may be referred to as “pass”, and the n-th pass may be referred to as “pass n”.

<Configuration of head>
FIG. 3 is an explanatory diagram illustrating an example of an arrangement of nozzles included in the head 41. The head 41 includes two nozzle groups, a first nozzle group 41A and a second nozzle group 41B. Each nozzle group is provided with eight nozzle rows. On the lower surface of the head 41, discharge ports of these nozzles are opened. The eight nozzle rows are dark cyan (C), dark magenta (M), yellow (Y), dark black (K), light cyan (LC), light magenta (LM), light black (LK), and pole, respectively. Light black (LLK) ink is ejected.

  In each nozzle row, 180 nozzles (nozzles # 1A to # 180A and nozzles # 1B to # 180B) arranged in the transport direction are provided at a nozzle pitch of 180 dpi. In FIG. 3, the lower number is assigned to the nozzle on the downstream side (+ Y side) in the transport direction. Each nozzle is provided with a piezo element (not shown) as a drive element for ejecting ink droplets from each nozzle.

The first nozzle group 41A is provided downstream of the second nozzle group 41B in the transport direction. Also, the first nozzle group 41A and the second nozzle group 41B are provided so that the positions of the four nozzles in the transport direction overlap. For example, the position in the transport direction of the nozzle # 177A of the first nozzle group 41A is the same as the position in the transport direction of the nozzle # 1B of the second nozzle group 41B. Thus, when a nozzle # 177A of the first nozzle group 41A can form a dot for a certain pixel in a certain droplet discharge operation, a dot is also formed for the pixel by the nozzle # 1B of the second nozzle group 41B. Is possible.
A combination of nozzle rows that eject the same ink (ink configured with the same composition) between the first nozzle group 41A and the second nozzle group 41B is referred to as a “headset”.

  FIG. 4 is an explanatory diagram showing another example of the nozzle arrangement of the head 41. In the example shown in FIG. 4, the headset shown in FIG. 3 is arranged at a closer position. More specifically, in the example of FIG. 4, the first nozzle group 41A and the second nozzle group 41B are arranged so as to be alternately arranged for every two nozzle rows. Each nozzle row is provided with 400 nozzles (nozzles # 1A to # 400A, nozzles # 1B to # 400B) arranged in the transport direction at a nozzle pitch of 300 dpi. , And ½ pitch (1/600 inch) offset.

  Further, the first nozzle group 41A and the second nozzle group 41B are provided so that the positions in the transport direction of the six nozzles overlap. For example, the position in the transport direction of the nozzle # 395A of the first nozzle group 41A is the same as the position in the transport direction of the nozzle # 1B of the second nozzle group 41B. As a result, when a dot can be formed by the nozzle # 395A of the first nozzle group 41A for a certain pixel in a certain droplet discharge operation, a dot is also formed by the nozzle # 1B of the second nozzle group 41B for that pixel. Is possible.

<Nozzle row and nozzle notation>
Before describing the dot formation method, the nozzle row and nozzle notation method will be described.
FIG. 5 is an explanatory diagram illustrating a headset as a virtual headset 42X.

On the left side of FIG. 5, for example, the dark black nozzle row of the first nozzle group 41A and the dark black nozzle row of the second nozzle group 41B are shown. In the following description, the dark black nozzle row of the first nozzle group 41A is referred to as a first head 42A, and the dark black nozzle row of the second nozzle group 41B is referred to as a second head 42B. For simplification of explanation, the number of nozzles in each nozzle row is 15. The first head 42A corresponds to the “first nozzle row” in the present invention, and the second head 42B corresponds to the “second nozzle row” in the present invention.
Four nozzles (nozzle # 12A to nozzle # 15A) on the upstream side in the transport direction of the first head 42A and four nozzles (nozzle # 1B to nozzle # 4B) on the downstream side in the transport direction of the second head 42B are: The transport direction position is duplicated. In the following description, these four nozzles in each nozzle row are referred to as overlapping nozzles.

Each nozzle of the first head 42A is indicated by a circle, and each nozzle of the second head 42B is indicated by a triangle. Further, nozzles that do not eject ink (that is, nozzles that do not form dots) are marked with a cross.
Here, among the overlapping nozzles of the first head 42A, the nozzle # 12A and the nozzle # 13A eject ink, and the nozzle # 14A and the nozzle # 15A do not eject ink. Of the overlapping nozzles of the second head 42B, the nozzle # 1B and the nozzle # 2B do not eject ink, and the nozzle # 3B and the nozzle # 4B eject ink.
In such a case, as described in the central portion of FIG. 5, the two heads (the first head 42A and the second head 42B) constituting the headset can be represented as one virtual headset 42X. . In the following description, the state of dot formation will be described using one virtual headset 42X instead of drawing two heads separately.

  As shown on the right side of FIG. 5, in this virtual headset 42X, even when the round nozzles form dots on odd-numbered dots (described later), the triangular nozzles are even-numbered dots (described later). ) Can form dots. Of course, when the round nozzles form dots on the odd-numbered dots, the triangular nozzles can also form dots on the odd-numbered dots.

  In addition, although the operation | movement which discharges an ink droplet from each nozzle and forms a dot is performed based on the print data which the controller 60 received, here, in order to demonstrate easily, discharge based on an individual print data The presence or absence of this is omitted from the explanation. That is, a description will be given based on a state in which dots are formed for dots at all positions where dots can be formed by ejecting ink droplets from the corresponding nozzles based on the print data.

<Dot formation method by normal processing>
FIG. 6 is an explanatory diagram of an example of normal processing. The normal processing is processing (droplet discharge operation and transport operation) performed when printing the central portion of the paper 10 (the region that is neither the upper end nor the lower end of the paper 10). The controller 60 performs normal processing described below by controlling each unit.

In FIG. 6, the relative position by the step movement for each transport amount 9D of the paper 10 by the transport unit 20 is shown in an oblique direction so that the virtual headset 42X does not overlap. That is, in FIG. 6, the virtual headset 42 </ b> X is depicted as moving with respect to the paper 10, but actually the paper 10 moves in the transport direction. In FIG. 6, the positional relationship of the virtual headset 42X in the X direction does not make sense. Arrows P1 to P4 indicate directions in which the virtual headset 42X is scanned and moved in the scanning direction (X-axis direction).
In the normal process, the paper 10 is transported by a transport amount 9D for nine dots in a transport operation performed between passes. For example, dots are formed by pass 1 to pass 6 in area A (area on paper 10) in FIG. 6, and dots are formed by pass 2 to pass 7 in area B.

  In the odd-numbered pass, each nozzle is positioned at an odd-numbered raster line (dot row along the scanning direction), for example. After the odd-numbered pass, the even-numbered pass is performed after the paper 10 has been transported by the transport amount 9D for nine dots. Therefore, in the even-numbered pass, each nozzle is in the even-numbered raster line. Become position. In this way, the positions of the nozzles are alternately odd-numbered or even-numbered raster line positions for each pass.

FIG. 7 is an explanatory diagram of an example of dot formation in the area A and the area B of FIG. Here, in FIG. 7, for example, a case where one pixel is formed by four dots that are adjacent vertically and horizontally is shown.
On the left side of FIG. 7, the relative positions of the nozzles in each pass are shown. A black-filled nozzle forms one dot per pixel in the pass. For example, nozzle # 8B in pass 2 forms dots at a rate of one for two dot positions. The nozzles hatched with diagonal lines form dots at a rate of one for every two pixels. For example, nozzle # 10A in pass 4 forms dots at a rate of one for four dot positions.

  A nozzle hatched with diagonal lines forms only half of the dots compared to a black-filled nozzle. The nozzles that are hatched by the oblique lines are hereinafter referred to as POL nozzles. Four nozzles (nozzle # 10A to nozzle # 13A) on the upstream side (-Y side) in the transport direction of the first head 42A in a certain pass, and the first head after two transport operations have been performed from that pass The four nozzles (nozzle # 1A to nozzle # 4A) on the downstream side (+ Y side) of 42A in the transport direction overlap in the transport direction. Such a nozzle becomes a POL nozzle. For example, nozzle # 10A to nozzle # 13A in pass 4 and nozzle # 1A to nozzle # 4A in pass 6 are POL nozzles because the positions in the transport direction overlap.

  Similarly, four nozzles (nozzle # 12B to nozzle # 15B) on the upstream side in the transport direction of the second head 42B of a certain pass and the second head 42B after two transport operations are performed from that pass. The positions of the four nozzles (nozzle # 3B to nozzle # 6B) on the downstream side in the transport direction overlap in the transport direction. Such a nozzle becomes a POL nozzle. For example, nozzle # 12B to nozzle # 15B in pass 2 and nozzle # 3B to nozzle # 6B in pass 4 are POL nozzles because the positions in the transport direction overlap.

  On the right side of FIG. 7, nozzles that form dots in each pixel are shown. For example, the first raster line (the line whose raster number is 1) is composed of dots formed as odd-numbered dots by nozzle # 8B and dots formed as even-numbered dots by nozzle # 10A and nozzle # 1A. Is done. Here, for simplification of explanation, each raster line is composed of only 8 dots.

  In the upper left of FIG. 7, the positions of dots formed by each head are shown. For example, in pass 1, the nozzles (nozzles # 1A to # 13A) of the first head 42A form dots at odd-numbered dots, and the nozzles (nozzles # 3B to # 15B) of the second head 42B are even-numbered dots. To form dots.

  Each raster line is composed of dots formed by two or three nozzles. In other words, two or three nozzles are associated with each raster line. For example, the first raster line is associated with nozzle # 8B for pass 2, nozzle # 10A for pass 4, and nozzle # 1A for pass 6. Each raster line is composed of dots formed by at least one nozzle of the first head 42A and dots formed by at least one nozzle of the second head 42B. In other words, at least one nozzle of the first head 42A and at least one nozzle of the second head 42B are associated with each raster line.

  When only one nozzle is associated with an odd-numbered dot or an even-numbered dot of a certain raster line, the nozzle forms dots at a ratio of one to two dots. For example, only one nozzle # 8B is associated with the odd-numbered dots of the first raster line (other nozzles are not associated). Therefore, nozzle # 8B forms dots at a rate of one for two dots.

  On the other hand, when two nozzles are associated with odd-numbered dots or even-numbered dots in a certain raster line, the two nozzles form dots at a ratio of one to four dots, respectively. (It becomes a POL nozzle). For example, nozzle # 10A and nozzle # 1A are associated with even-numbered dots in the first raster line. For this reason, nozzle # 10A and nozzle # 1A each form dots at a rate of four dots (becomes POL nozzles).

  In normal processing, the position at which the first head 42A forms dots (position in the scanning direction) and the position at which the second head 42B forms dots in a certain pass are different. Specifically, when the first head 42A forms dots at odd-numbered dots, the second head 42B forms dots at even-numbered dots. Conversely, when the first head 42A forms dots at even-numbered dots, the second head 42B forms dots at odd-numbered dots. Since the first drive signal generator 65A and the second drive signal generator 65B described above can generate drive signals independently of each other, such dot formation becomes possible.

  Further, in the normal process, when a certain pass is compared with the next pass, the positions where each head forms dots are different. For example, when the first head 42A forms dots in odd-numbered dots and the second head 42B forms dots in even-numbered dots in a certain pass, the first head 42A forms dots in even-numbered dots in the next pass. The second head 42B forms dots at odd-numbered dots.

  By forming dots in this way, dots are formed in a staggered pattern by one head, and dots are formed in a staggered pattern by the other head so that the space between the dots is filled. Is done. When attention is paid to the right side of FIG. 7, the round dots formed by the first head 42A have a staggered pattern, and the triangular dots formed by the second head 42B also have a staggered pattern. Yes. In terms of the dot formation order, the dots are formed by the first head 42A so that the dots are formed after the dots are formed by the second head 42B in a staggered pattern.

  When a raster line is formed by normal processing, half dots are formed by the first head 42A and the remaining half dots are formed by the second head 42B. In other words, the usage rate of each head when forming these raster lines is 50% (constant) for the first head 42A and 50% (constant) for the second head 42B. Note that this is a case where suppression of color unevenness and density unevenness is not taken into consideration, and a corresponding method will be described later.

  In the area A, dots are formed by the passes 1 to 6, and in the area B, the dots are formed by the passes 2 to 7, so that the pass is shifted by one time between the area A and the area B. Since the pass is shifted by one time, the nozzles associated with each raster line are common to each region, but the position of the dots formed by each nozzle (the position in the scanning direction) is an odd number dot or an even number dot. Is different. For example, for the first raster line, nozzle # 8B in pass 2 forms dots at odd-numbered dots, but for nozzle 10 at the tenth raster line, nozzle # 8B in pass 3 forms dots at even-numbered dots. .

  Although not shown here, dots are formed in the 19th to 27th raster lines located upstream of the region B in the transport direction in substantially the same manner as in the region A by pass 3 to pass 8. For example, nozzle # 8B, nozzle # 10A, and nozzle # 1A are associated with the 19th raster line, and nozzle # 8B forms dots at odd-numbered dots on the 19th raster line. In the 28th to 36th raster lines located upstream of the 19th to 27th raster lines in the transport direction, dots are formed in substantially the same manner as in the region B by pass 4 to pass 9. As described above, when the normal processing is continuously performed, the dot formation similar to the region A and the region B is repeatedly performed.

  For example, when a high-definition image is formed on the paper 10 by forming dots on the paper 10, the paper 10 is securely held at a predetermined position (and height) during the droplet discharge operation. In the carrying operation, it is necessary to accurately move the paper 10 to a predetermined position. For this reason, the transport unit 20 fixes (holds) the paper 10 by means such as pinching, pressing, and sucking. These fixing (holding) means must be configured so as not to interfere with the movement of the carriage unit 30 and the head unit 40. In other words, printing is started and ended also in a state (position) in which the upper end portion and lower end portion of the paper 10 are securely fixed (held). As a result, for example, in the configuration in which the first nozzle group 41A and the second nozzle group 41B having nozzle rows arranged in the transport direction (Y direction) are aligned in the transport direction (Y direction) as in the present embodiment, the paper 10 In some cases, it is necessary to form dots only with nozzles that can be handled by the corresponding head (the first head 42A or the second head 42B) for each of the upper end portion and the lower end portion.

<Dot formation method by top edge processing>
In the following, an example of the upper end process when a POL-controlled image cannot be formed between a plurality of heads will be described. The upper end process is a process (droplet discharge operation and transport operation) performed when printing the upper end region (+ Y side end region) of the paper 10. The controller 60 performs upper end processing described below by controlling each unit.

FIGS. 8A and 8B are explanatory diagrams of an example of the upper end process, and FIGS. 8A and 8B: (1) to (4) are virtual in each path of the upper end process (pass 1 to path 4). 8A and 8B show the positions of the headset 42X and the ejected ink droplets. FIGS. 8A and 8B show the virtual headset 42X in each pass (pass 5 and pass 6) of the normal process subsequent to the upper end process. And the positions of the ejected ink droplets.
FIG. 8B: (1) to (6) show dots formed on the paper 10 in pass 1 to pass 6. That is, the result of overlapping the positions of the ink droplets in FIG. 8A: (1) to (6) in order is shown in FIG. 8B: (1) to (6).

In the example shown here, upper end processing is performed in pass 1 to pass 4, and normal processing is performed after pass 5. In the upper end processing, in the transport operation performed between passes, the sheet 10 is transported with a transport amount D for one dot (a transport amount shorter than the transport amount 9D in the normal process).
In the upper end processing, in the odd-numbered pass, each nozzle is positioned at the odd-numbered raster line. After the odd-numbered pass, the paper 10 is transported by a transport amount for one dot, so in the even-numbered pass, each nozzle is positioned at the even-numbered raster line. As described above, also in the upper end processing, the positions of the nozzles alternately become the positions of odd-numbered or even-numbered raster lines for each pass.

  In the normal processing described above, in order to form dots in a staggered pattern by each head, the dot formation position of the first head 42A and the dot formation position of the second head 42B in a certain pass are different. For example, when the first head 42A forms dots at odd-numbered dots, the second head 42B forms dots at even-numbered dots.

  On the other hand, in the upper end process, the dot formation position of the first head 42A and the dot formation position of the second head 42B in a certain pass are the same. For example, in pass 1, the first head 42A and the second head 42B both form dots at odd-numbered dots.

  Further, in the above-described normal processing, in order to form dots in a staggered pattern by each head, the dot formation position of each head is different between a certain pass and the next pass. For example, when the first head 42A forms dots in odd-numbered dots and the second head 42B forms dots in even-numbered dots in a certain pass, the first head 42A forms dots in even-numbered dots in the next pass. The second head 42B forms dots on odd-numbered dots.

  In contrast, in the upper end process, the dot formation position of each head is changed in the order of odd-numbered dots (pass 1) → even-numbered dots (pass 2) → even-numbered dots (pass 3) → odd-numbered dots (pass 4). Is done. That is, in the upper end process, the dot formation position of each head may not necessarily differ between a certain pass and the next pass. For example, in pass 2 and pass 3, the dot formation positions are the same even-numbered dots.

  The reason for the above difference between the normal process and the upper end process is that dots are formed in a staggered pattern by each head in the normal process, whereas in the upper end process, the first half 2 of the four passes. This is because dots are formed in a staggered pattern in a single pass, and dots are formed in a staggered pattern in the latter two passes so as to fill in the space between the dots in the staggered pattern.

  By the above dot forming method, the first to the 25th raster lines (raster lines on the upper end side of the paper 10) are formed only by the first head 42A. In other words, the head usage rate when forming the first to 25th raster lines is 100% for the first head 42A and 0% for the second head 42B.

FIG. 9 is a graph schematically showing the usage rates of the first head 42A and the second head 42B in each pass (pass 1 to pass 6).
Up to this point, for the sake of easy understanding, the description has been made in the range where the dots are visible. Therefore, as shown in FIG. 9, the change in the usage rate of each head (difference in the raster number direction) is shown stepwise, but in actual use, innumerable dots formed by several picoliters of ink droplets Therefore, the usage rate of each head can be shown by approximating the change to a straight line or a curve as shown in the following figures.

FIG. 10 is a graph showing the head usage rates of the first head 42A and the second head 42B in the region from the upper end processing to the normal processing.
In FIG. 10, a headset formed by the first head 42 </ b> A and the second head 42 </ b> B is represented by a row of the first head 42 </ b> A and the second head 42 </ b> B arranged in the Y direction as in the virtual headset 42 </ b> X illustrated in FIG. 5. Similarly to FIG. 6, the relative positions due to the movement of the paper 10 by the transport unit 20 are shown in an oblique direction so that the first head 42A and the second head 42B do not overlap. That is, in FIG. 10, the first head 42 </ b> A and the second head 42 </ b> B are depicted as moving with respect to the paper 10, but actually the paper 10 moves in the transport direction (Y direction). In FIG. 10, the positional relationship between the first head 42A and the second head 42B in the X direction does not make sense. Further, the usage rate of each head (the usage rate for each nozzle belonging to each head for each raster line) is shown in the same manner as in FIG.

Passes 1 to 4 are upper end processes in which an image is formed only by the first head 42A. Passes 5 to 8 are transition processes in which the usage rate of the second head 42B gradually increases, and passes 9 and after. The usage rate of the first head 42A and the second head 42B is normal processing of 50%. An area formed after pass 5 is an image area that is POL-controlled between the two heads.
Note that the migration process shown in FIG. 10 is one example. By increasing the number of passes required for the transfer process and the number of raster lines in the area to be transferred, the rate of change in the usage rate of the second head 42B can be reduced. If there is a difference in the ink ejection characteristics between the first head 42A and the second head 42B, the smaller the rate of change, the less conspicuous the influence will be.

  Note that such a transition process is the same not only at the upper end of the paper 10 but also at the lower end. That is, a transition process for gradually decreasing the usage rate of the first head 42A is performed at the lower end, and an image is formed only by the second head 42B at the lower end. Further, the transfer process described here is a method in the case where the suppression of color unevenness and density unevenness is not taken into consideration, as in the normal process described above. A method for suppressing color unevenness and density unevenness will be described below.

<Correction of color unevenness>
One difference in ink ejection characteristics is a difference in ejection amount. Each nozzle row (first head 42A, second head 42B) may not have the same amount of ink ejected from each nozzle row due to the influence of manufacturing errors and the like. For this reason, the nozzle row that ejects a larger amount of ink than the reference amount prints darkly, and the nozzle row that ejects a smaller amount of ink than the reference amount prints lightly. As a result, color unevenness may occur in the printed image.

  Therefore, the color unevenness of the printed image is suppressed by the following color unevenness correction process. Hereinafter, the procedure of color unevenness correction processing will be described.

<Color unevenness correction value acquisition processing>
FIG. 11 is an explanatory diagram of an uneven color correction value acquisition process performed in the manufacturing factory of the inkjet printer 100. In the manufacturing factory of the ink jet printer 100, a computer for obtaining correction values and a colorimeter connected to the computer are prepared. When the inkjet printer 100 is manufactured at the factory, the inkjet printer 100 is connected to a computer for obtaining correction values. Each module depicted in the computer of FIG. 11 is configured by software and hardware.

  First, a printing module of a computer generates print data based on test pattern printing data and transmits the print data to the inkjet printer 100. This printing module is equivalent to a so-called printer driver. Data for test pattern printing is stored in advance in a computer memory.

Next, the inkjet printer 100 that has received the print data prints a test pattern, and the measurer measures the color of the printed test pattern using a colorimeter. The test pattern includes a pattern (first pattern) composed of dot rows formed by the first nozzle row (first head 42A), a second pattern so that a correction value for color unevenness can be obtained for each nozzle row. A large number of patch patterns such as a pattern (second pattern) composed of a dot array formed by the nozzle array (second head 42B) is included. The control module acquires the color measurement result of each patch pattern from the colorimeter.
Next, the correction value calculation module compares the color measurement result with reference color data stored in advance, and calculates a color unevenness correction value for each nozzle row.
Finally, the writing module writes the color unevenness correction value in the memory of the inkjet printer 100. The ink jet printer 100 is shipped from the factory in a state where the color unevenness correction value for each nozzle row is stored in the memory.

  FIG. 12 is an explanatory diagram of color unevenness correction values. Color unevenness correction values are prepared for the first nozzle group (first nozzle group 41A) and the second nozzle group (second nozzle group 41B), respectively. Also, three types of color unevenness correction values (small dots, medium dots, large dots) are prepared for each nozzle row (for each ink color).

  In FIG. 12, when the correction value is “100”, it means that the same ink amount as the reference amount is ejected from the nozzle. For example, the cyan nozzle row (second nozzle row) of the second nozzle group ejects the same ink amount as the reference amount when ejecting small dots.

  When the correction value is 100 or more, it means that a larger amount of ink than the reference amount is ejected from the nozzle. For example, the cyan nozzle row (first nozzle row) of the first nozzle group ejects an ink amount larger than the reference amount when ejecting small dots. For this reason, when this nozzle row forms dots, a dark image is obtained.

  When the correction value is 100 or less, it means that an ink amount smaller than the reference amount is ejected from the nozzle. For example, the cyan nozzle row of the first nozzle group ejects an ink amount smaller than the reference amount when ejecting large dots. For this reason, when this nozzle row forms dots, a light image is obtained.

  In the above description, the color unevenness correction value is acquired by measuring the test pattern, but the present invention is not limited to this. For example, the color unevenness correction value similar to that in FIG. 12 may be acquired by directly measuring the ink amount of the ejected ink droplets.

<Processing during printing>
FIG. 13 is a block diagram at the time of print processing under the user. FIG. 14 is a flowchart of processing performed by the printer driver. The printer driver is a program that runs on the PC 110, and implements each module in FIG. 13 and each process in FIG. 14 in cooperation with the hardware (CPU, memory, etc.) of the PC 110.
Each figure is a figure in the prior art that does not include processing for suppressing density unevenness. The following is a description regarding correction processing for color unevenness, and does not include description regarding processing for suppressing density unevenness.

  First, the printer driver acquires a color unevenness correction value (see FIG. 12) from the memory of the inkjet printer 100 (S1, see FIG. 14). The printer driver stores the acquired color unevenness correction value in the memory of the PC 110.

  Next, the printer driver performs resolution conversion processing by the resolution conversion module (S2). The resolution conversion process is a process of converting image data (text data, image data, etc.) output from an application into image data having a resolution (print resolution) to be printed on the paper 10. For example, when the print resolution is specified as 1440 × 720 dpi, the image data in the vector format received from the application is converted into image data having a resolution of 1440 × 720 dpi. Each pixel data of the image data after the resolution conversion process is data indicating a gradation value of 256 gradations in the RGB color space.

  Note that the image indicated by the image data after resolution conversion is composed of pixels arranged in a matrix. Each pixel has a gradation value of 256 gradations in the RGB color space. The pixel data after the resolution conversion indicates the gradation value of the corresponding pixel. Pixel data corresponding to one column of pixels arranged in the horizontal direction among pixels arranged in a matrix may be referred to as “raster data” in the following description. Note that the direction in which the corresponding pixels of the raster data are arranged corresponds to the moving direction (scanning direction) of the head 41 when printing an image.

  Next, the printer driver performs color conversion processing by the color conversion module (S3). The color conversion process is a process of converting RGB color space data into color space data corresponding to the ink color of the inkjet printer 100. The pixel data after the color conversion processing is data indicating 256 gradation levels represented by an 8-dimensional color space of C, M, Y, K, LC, LM, LK, and LLK.

  Next, the printer driver extracts raster data (S4). Specifically, pixel data corresponding to one column of pixels arranged in the horizontal direction is extracted from image data of a certain color (for example, cyan).

  Next, the printer driver performs color unevenness correction processing on the extracted raster data by the color unevenness correction module (S5). This color unevenness correction process will be described later.

  Next, the printer driver performs halftone processing by the halftone module (S6). The halftone process is a process of converting 256-gradation pixel data into 4-gradation pixel data, which is the number of gradations that the inkjet printer 100 can form. The four-tone pixel data after the halftone process is data indicating the size of the dot formed in the corresponding pixel. Specifically, the data indicates any one of large dots, medium dots, small dots, and no dots.

  Note that the printer driver uses a dot generation rate table (see FIG. 16A described later) during halftone processing. This dot generation rate table is a data table indicating the probability (dot generation rate) that small dots, medium dots, and large dots are generated for each of the gradation values of 256 gradations. Specifically, for example, a small dot generation rate of 40% and a medium dot / large dot generation rate of 0% are associated with the gradation value 20. That is, if the gradation value of 256 gradations of a certain pixel data is 20, as a result of the halftone process, the pixel data is converted into pixel data (4 gradations) indicating a small dot with a probability of 40%, It is converted into pixel data (4 gradations) indicating no dot with a probability of 60%.

  Next, the printer driver determines whether or not halftone processing of all pixel data has been completed (S7). For example, if there is another raster data of cyan, NO is determined, and NO is also determined if there is raster data of another color.

  Next, the printer driver performs rasterization processing by the rasterization module (S8). The rasterization process is a process of extracting pixel data of pixels to be formed with dots in each pass from the image data and rearranging the pixel data for each pass.

  Finally, the printer driver adds command data to the pixel data rasterized by the command output module to generate print data, and transmits the print data to the inkjet printer 100 (S9). The inkjet printer 100 controls each unit according to command data in the print data, and ejects ink from each nozzle according to the pixel data in the print data, whereby dots are formed on the paper 10 and an image is printed.

<Color unevenness correction processing>
FIG. 15 is a flowchart of the uneven color correction process (S5).
First, the printer driver obtains a color unevenness correction value of the corresponding color by the reading module (see FIG. 13) (S5a). For example, when color unevenness correction processing is performed on raster data of cyan image data, a cyan color unevenness correction value is acquired. At this time, the printer driver acquires both the color unevenness correction value corresponding to the first nozzle row (first head 42A) and the color unevenness correction value corresponding to the second nozzle row (second head 42B).
Next, a correction amount table is created for each nozzle row (S5b). That is, the first correction amount table for correcting the amount of ink droplets ejected by the nozzles of the first nozzle row (first head 42A) obtained based on the first pattern, and the first correction amount table obtained based on the second pattern. A second correction amount table for correcting the amount of ink droplets ejected by the nozzles of the two-nozzle row (second head 42B) is created.

Here, before describing the correction amount table, the amount of ink ejected will be described with reference to FIGS.
FIG. 16A is a dot generation rate table used for halftone processing. The horizontal axis in the figure indicates 256 gradation values. The vertical axis represents the dot generation rate. As shown in the figure, for example, the gradation value 20 is associated with a small dot generation rate of 40% and a medium dot / large dot generation rate of 0%.

  FIG. 16B is a graph showing the relationship between the gradation value and the ink amount when ink is ejected at the reference amount. The horizontal axis in the figure indicates 256 gradation values. The vertical axis represents the ink amount when the ink amount (droplet amount) per unit area ejected when the gradation value is 256 is 1. As shown in the figure, when ink is ejected at a reference amount, an ink amount proportional to the gradation value is ejected.

  FIG. 16C is a graph showing the relationship between the gradation value and the ink amount when an amount of ink different from the reference amount is ejected. The thin line in the graph is the same as the graph of FIG. 16B, and the thick line is a graph of the relationship between the gradation value and the ink amount when an amount of ink different from the reference amount is ejected. Here, a graph is shown in the case where ink is ejected from a nozzle row in which the color unevenness correction value for small dots is 110, the color unevenness correction value for medium dots is 108, and the color unevenness correction value for large dots is 96. As shown in the figure, at a low gradation value in which small dots and medium dots are mainly ejected, the ejected ink amount is larger than the reference amount. On the other hand, at high gradation values where large dots are mainly ejected, the amount of ink ejected is smaller than the reference amount.

  The relationship between the gradation value and the ink amount as shown in FIG. 16C can be calculated based on the dot generation rate table and the color unevenness correction value. Therefore, in the process of S5b, the printer driver first determines the gradation value and the ink amount as shown in FIG. 16C based on the dot generation rate table and the color unevenness correction value acquired in S5a. An ink amount table showing the relationship is calculated.

  FIG. 17 is an explanatory diagram of the meaning indicated by the ink amount table. A broken line graph in the drawing is a graph of the ink amount in FIG. 16B, that is, a graph of an ink amount table when ink is ejected at a reference amount. A solid line graph in the figure is a graph of an ink amount table when an amount of ink different from the reference amount is ejected. Among the solid line graphs, the thin line graph is a graph of the ink amount table of the first nozzle row (first head 42A), and the thick line graph is a graph of the ink amount table of the second nozzle row (second head 42B). is there.

  For example, when the gradation value indicated by the pixel data is 120, if ink is to be ejected without correcting the gradation value, an ink amount larger than the reference amount is ejected from the first nozzle row (first head 42A). Thus, an ink amount smaller than the reference amount is ejected from the second nozzle row (second head 42B). On the other hand, if the gradation value corresponding to the reference amount of the gradation value 120 in the ink amount table of the first nozzle array (first head 42A) is 100, the first nozzle array (first head) according to the gradation value 100. 42A), it is considered that the ink can be ejected from the first nozzle row (first head 42A) with the reference value of the gradation value 120. Further, if the gradation value corresponding to the reference amount of the gradation value 120 in the ink amount table of the second nozzle array (second head 42B) is 150, the second nozzle array (second head) according to the gradation value 150. 42B), it is considered that the ink can be ejected from the second nozzle row (second head 42B) with the reference amount of the gradation value 120.

  Therefore, the printer driver associates the gradation value 100 with the gradation value 120 in the correction amount table of the first nozzle row (first head 42A). In other words, a correction amount table is generated such that when the input gradation value (input gradation value) is 120, the gradation value 100 is output. The printer driver creates a correction amount table for the first nozzle row (first head 42A) by associating output gradation values based on the ink amount table with other input gradation values.

  The printer driver creates such a correction amount table for each nozzle row. In the present embodiment, a first correction amount table for the first nozzle row (first head 42A) and a second correction amount table for the second nozzle row (second head 42B) are created. As is clear from the above description, the first correction amount table is created based on the color unevenness correction value of the first nozzle row (first head 42A) and the dot generation rate table, and the second correction amount table. Is generated based on the color unevenness correction value of the second nozzle row (second head 42B) and the dot generation rate table.

  FIG. 18 is an explanatory diagram of the first correction amount table and the second correction amount table. In this way, a correction amount table in which the input gradation value and the output gradation value are associated is created for each nozzle row.

  Note that the created correction amount table is stored in the memory when performing color unevenness correction processing for raster data of a certain color, and the correction amount table is stored again during color unevenness correction processing for another raster data of the same color. May be used. That is, when the correction amount table has already been created, the printer driver may omit the process of creating the correction amount table (S5b).

After creating the correction amount table, the printer driver acquires the usage rate data for the raster number corresponding to the raster data extracted in S4 based on the usage rate of each head (see FIG. 10) (S5c).
If the raster line corresponding to the raster data belongs to the upper end region, the usage rate of the first nozzle row (first head 42A) is 1 (100%), and the second nozzle row (second head 42B). The usage rate is 0 (0%). If the raster line corresponding to the raster data belongs to the normal area, the usage rate of the first nozzle row (first head 42A) is 0.5 (50%), and the second nozzle row (second head) The usage rate of 42B) is also 0.5 (50%). There is a transition region between the upper end region and the normal region, and in this transition region, there is a raster line in which the usage rate of the first nozzle row (first head 42A) is between 0.5 and 1. For example, a raster line in which the usage rate of the first nozzle row (first head 42A) is 0.75 (75%) exists in the transition region.
The relationship between the raster number and the usage rate is uniquely determined once the dot formation method is determined.

Next, the printer driver corrects the gradation value of each pixel data of the raster data based on the correction amount table and the usage rate data (S5d).
For example, when the gradation value of the pixel data is 120 and the usage rate of the first nozzle row (first head 42A) is 1, the corrected gradation value is 100. When the gradation value of the pixel data is 120 and the usage rate of the first nozzle row (first head 42A) is 0.5, the corrected gradation value is 125 (= 100 × 0.5 + 150 ×). 0.5). When the gradation value of the pixel data is 120 and the usage rate of the first nozzle row (first head 42A) is 0.75, the corrected gradation value is 112.5 (= 100 × 0. 75 + 150 × 0.25). As described above, the printer driver obtains each output gradation value (for example, 100 and 150) based on the correction amount table of each nozzle row using the gradation value (for example, 120) of the pixel data as the input gradation value, The corrected gradation value (for example, 112.5) is calculated by adding the output gradation value weighted with each usage rate (for example, 0.75 and 0.25).

  When the printer driver corrects the gradation values of all the pixel data of the raster data, the color unevenness correction process is terminated.

<Density unevenness correction>
When different inks are ejected to the same position or the positions of dots that are in close proximity, the ink that is ejected later tends to bleed depending on the dry state of the ink ejected earlier. Therefore, for example, if the ink ejected later is an ink that has a lower lightness and is more conspicuous than the ink ejected earlier, the ink bleed becomes more conspicuous. In addition, when the ink ejected earlier has a characteristic of being easily mixed with other inks, the ink ejected later is more likely to bleed. As described above, the drying state changes depending on the timing at which ink is ejected, and the degree of bleeding varies, resulting in uneven density and gloss.

In order to suppress such density unevenness, there is a method of controlling the timing of ejecting ink from each nozzle, in other words, controlling the amount of ink ejected by the timing so that the influence of bleeding is not noticeable. Taken.
As one method for suppressing density unevenness, there is a method of changing the usage rate of the nozzle row in accordance with the ink gradation.

<Nozzle row usage rate correction amount table>
FIG. 19 is a graph showing the relationship between the ink gradation and the usage rate of the first nozzle row (first head 42A).
This graph plots the usage rate of the first nozzle row from the example of the nozzle row usage rate correction amount table obtained based on the gradation of the dot row to be formed. As the gradation of the dot row to be formed, the value of the average gradation of the dot row is used.
The nozzle row usage rate correction amount table is a data table for correcting the nozzle row usage rates of the first nozzle row (first head 42A) and the second nozzle row (second head 42B) for forming a dot row.
In the case of this example, in the graph, the usage rate of the first nozzle row (first head 42A) is low in the region where the ink gradation is relatively low (for example, the usage rate is 40% or less in the region where the gradation is 180 or less. And the usage rate of the second nozzle row (second head 42B) is set high (in this region, the usage rate is 60% or more).

  As described above, in the normal processing region (see FIG. 10), the dot formation order is such that after the dots are formed in a staggered pattern by the second nozzle row (second head 42B), the space between the dots is filled. The dots are formed by the first nozzle row (first head 42A). Therefore, by correcting the nozzle row usage rate in this way, in the normal processing region, when printing with a relatively low ink gradation is performed, the second nozzle row (second head 42B) is formed first. The rate of dots increases, and as a result, the rate at which drying is accelerated increases. By further promoting drying, uneven density due to bleeding is reduced.

  The nozzle row usage rate correction amount table is not limited to the data table plotted in the graph shown in FIG. It may be a data table plotted on a different curve or straight line according to the specification of density unevenness correction. Further, instead of a data table common to the rasters in the nozzle row, for example, a data table having a different value for each raster number may be used. The occurrence and the level of density unevenness vary depending on the amount of ink to be ejected, drying characteristics, ejection timing, printing medium, bleeding characteristics, and the like. Therefore, the nozzle row usage rate correction amount table should be obtained by appropriate evaluation. desirable.

<Correction of color unevenness and density unevenness>
In the above, the dot formation method including the upper and lower end processing, the color unevenness correction method, and the density unevenness correction method have been described.
In the present embodiment, in the dot forming method including upper and lower end processing, the amount of ink droplets to be ejected is corrected so that both color unevenness and density unevenness can be suppressed at the same time. That is, the ink droplet amount is corrected based on the first correction amount table, the second correction amount table, and the nozzle row usage rate correction amount table in the transition processing and normal processing regions of the upper and lower ends. This will be specifically described below.

FIG. 20 is a block diagram at the time of printing processing under the user in the present embodiment. A usage rate correction module is added to FIG. 13 showing the prior art.
FIG. 21 is a flowchart of processing performed by the printer driver in this embodiment. Instead of the color unevenness correction process (S5) in FIG. 14 showing the prior art, color unevenness and density unevenness correction processing (S50) is performed. In the process of S50, the printer driver performs color unevenness correction processing by the color unevenness correction module on the extracted raster data using the usage rate data corrected by the usage rate correction module based on the nozzle row usage rate correction amount table. Do.

FIG. 22 is a flowchart of the correction process (S50) that achieves both color unevenness and density unevenness.
First, similarly to S5a, the printer driver acquires color unevenness correction values for the corresponding colors corresponding to the first nozzle row (first head 42A) and the second nozzle row (second head 42B) (S50a).
Next, similarly to S5b, a correction amount table is created for each nozzle row (S50b). That is, the first correction amount table for correcting the amount of ink droplets ejected by the nozzles of the first nozzle row (first head 42A) obtained based on the first pattern, and the first correction amount table obtained based on the second pattern. A second correction amount table for correcting the amount of ink droplets ejected by the nozzles of the two nozzle row (second head 42B) is created.

Next, the printer driver obtains the usage rate data for the raster number corresponding to the raster data extracted in S4 based on the usage rate of each head (see FIG. 10) (S50c).
Next, as described below, based on the nozzle row usage rate correction amount table, the usage rate of the nozzle row acquired here is corrected, and the gradation value is weighted by the corrected usage rate of the nozzle row. Correction is performed (S50d, S50e).

<Nozzle row usage rate correction>
FIG. 23 is a graph showing a correction example of the usage rate of the nozzle row, and shows the usage rates of the first nozzle row and the second nozzle row in each region of the upper end process, the transition process, the normal process, and the lower end process. In FIG. 23, the broken line is a graph when the usage rate correction of the nozzle row for density unevenness correction is not performed, and the solid line is the usage rate of the nozzle row for density unevenness correction corresponding to the gradation value 120. It is a graph at the time of correcting. Although the change in the usage rate of the migration processing area is shown by a straight line, it actually changes stepwise as can be seen from FIG.

In the upper end processing, printing is performed only by the first nozzle row (first head 42A), and in the lower end processing, printing is performed only by the second nozzle row (second head 42B), and thus density unevenness correction is not performed. That is, the usage rate of the nozzle row is not corrected.
As described above, the color unevenness is corrected by weighting the usage rate of the nozzle row and correcting the gradation value based on the correction amount table for each nozzle row. Further, as described above, the density unevenness correction corrects the nozzle row usage rate based on the nozzle row usage rate correction amount table in accordance with the gradation.
In the correction to achieve both color unevenness and density unevenness, the usage rate of the nozzle row corrected based on the nozzle row usage rate correction amount table is weighted, and the gradation value is corrected based on the correction amount table for each nozzle row. .

For example, when the gradation value of the pixel data is 120, the usage rate of the first nozzle row (first head 42A) is 0.38 due to the correction based on the nozzle row usage rate correction amount table (see FIG. 19). Further, the usage rate of the first nozzle row (first head 42A) in each of the upper end process, the transition process, the normal process, and the lower end process is a value indicated by a solid line in FIG. 23 corrected by this usage rate (0.38). It becomes.
That is, when the gradation value of the pixel data is 120, the final gradation correction value in the normal processing region is 131 (= 100 × 0.38 + 150 × 0.62). Further, for example, when the usage rate before density unevenness correction of the first nozzle row (first head 42A) in the transition processing region is 0.7, the usage rate of the corrected first nozzle row (first head 42A) is , 0.59 (= (0.7 × 0.38) / (0.7 × 0.38 + 0.3 × 0.62)), the usage rate of the second nozzle row (second head 42B) is 0.41. Since (= (0.3 × 0.62) / (0.7 × 0.38 + 0.3 × 0.62), the corrected gradation value is 120.5 (= 100 × 0.59 + 150 × 0). .41).

  As described above, the printer driver obtains each output gradation value (for example, 100 and 150) based on the correction amount table of each nozzle row using the gradation value (for example, 120) of the pixel data as the input gradation value, By adding the output tone values weighted with the nozzle row usage rates corrected based on the nozzle row usage rate correction amount table (eg, 0.38 and 0.62), the corrected tone values (eg, , 131).

  If the printer driver corrects the gradation values of all the pixel data of the raster data, the correction process for uneven color and uneven density ends.

As described above, according to the droplet discharge method and the droplet discharge apparatus according to the present embodiment, the following effects can be obtained.
A first correction amount table corresponding to the first nozzle row (first head 42A), a second correction amount table corresponding to the second nozzle row (second head 42B), and nozzles based on the gradation of the dot row to be formed Based on the column usage rate correction amount table, the amount of droplets forming the dot row is corrected.

  In the first correction amount table, the nozzles of the first nozzle row (first head 42A) obtained based on the first pattern composed of the dot rows formed by the first nozzle row (first head 42A) are ejected. It is a correction amount table for correcting the amount of ink droplets to be performed. That is, based on the first correction amount table, ink droplets are ejected from the nozzles of the first nozzle row (first head 42A) according to the ink droplet ejection characteristics of the nozzles of the first nozzle row (first head 42A). It can be corrected. Specifically, for example, when the ink droplet ejection amount from the nozzles of the first nozzle row (the first head 42A) is smaller (eg, greater than a predetermined amount) (for example, a design value), a predetermined amount Correction can be made by the first correction amount table so that ejection is performed. As a result, color unevenness due to a characteristic difference between the first nozzle row (first head 42A) and the second nozzle row (second head 42B) can be suppressed.

  In the second correction amount table, the nozzles of the second nozzle row (second head 42B) obtained based on the second pattern composed of the dot rows formed by the second nozzle row (second head 42B) are ejected. It is a correction amount table for correcting the amount of ink droplets to be performed. That is, based on the second correction amount table, ink droplets are ejected from the nozzles of the second nozzle row (second head 42B) according to the ink droplet ejection characteristics of the nozzles of the second nozzle row (second head 42B). It can be corrected. Specifically, for example, when the ink droplet ejection amount from the nozzles of the second nozzle row (second head 42B) is less (or more) than a predetermined amount (for example, a design value), a predetermined amount Correction can be made by the second correction amount table so as to be discharged. As a result, color unevenness due to a characteristic difference between the first nozzle row (first head 42A) and the second nozzle row (second head 42B) can be suppressed.

  The nozzle row usage rate correction amount table includes a first nozzle row (first head 42A) and a second nozzle row (second head 42B) for forming a dot row obtained based on the gradation of the dot row to be formed. 12 is a correction amount table for correcting the nozzle row usage rate. That is, based on the nozzle row usage rate correction amount table, the nozzle row usage rates of the first nozzle row (first head 42A) and the second nozzle row (second head 42B) according to the gradation of the dot row to be formed. Can be corrected. As a result, it is possible to suppress density unevenness, gloss unevenness, and the like caused by differences in timing at which adjacent dots are formed. That is, for example, in the case where the ease of ink bleeding changes due to the difference in timing at which adjacent dots are formed and there is a tendency to cause uneven density, the first nozzle row ( By changing the nozzle row usage rate of the first head 42A) and the second nozzle row (second head 42B), the unevenness of these dots can be suppressed by changing the timing at which the dots constituting the dot row are formed. .

  Therefore, according to the present embodiment, color unevenness due to a characteristic difference between the first nozzle row (first head 42A) and the second nozzle row (second head 42B), or a difference in timing at which adjacent dots are formed. The generated density unevenness can be suppressed.

  Further, since the nozzle row usage rate of the first nozzle row (first head 42A) and the second nozzle row (second head 42B) is corrected based on the average gradation of the dot row to be formed, for each dot row Ink droplet ejection control can be performed more easily.

  Further, the amount of ink droplets ejected to form a dot row is corrected by weighting the first correction amount table and the second correction amount table based on the nozzle row usage rate correction amount table. That is, each of the first correction amount table and the second correction amount table is weighted based on the corrected nozzle row usage rate of the first nozzle row (first head 42A) and the second nozzle row (second head 42B). Therefore, it can correct more appropriately.

The inkjet printer 100 includes a transport unit 20 that moves the paper 10 in the transport direction, a first nozzle row (first head 42A) in which a plurality of nozzles that eject ink droplets on the paper 10 are arranged in the transport direction, and a second head. A carriage unit 30 that scans and moves a nozzle row (second head 42B), a first nozzle row (first head 42A), and a second nozzle row (second head 42B) in a scanning direction that intersects the carrying direction; A controller 60 is provided that controls the drive of the unit 20 and the carriage unit 30 and controls the ejection of ink droplets from the nozzles, thereby forming a plurality of dot rows composed of dots arranged in the scanning direction in the transport direction. Further, the first correction amount table obtained based on the first pattern composed of the dot rows formed by the first nozzle row (first head 42A) and the second nozzle row (second head 42B) are used. A second correction amount table obtained on the basis of the second pattern composed of the arranged dot rows and a first nozzle row for forming the dot rows obtained based on the gradation of the dot rows to be formed ( The amount of ink droplets ejected to form a dot row based on the nozzle row usage rate correction amount table for correcting the nozzle row usage rate of the first head 42A) and the second nozzle row (second head 42B) is It is corrected.
Therefore, according to the ink jet printer 100 of the present embodiment, color unevenness due to a difference in characteristics between the first nozzle row (first head 42A) and the second nozzle row (second head 42B) and adjacent dots are formed. It is possible to obtain an image in which uneven density caused by a difference in timing is suppressed.

  DESCRIPTION OF SYMBOLS 10 ... Paper, 20 ... Conveyance unit, 21 ... Feed roller, 22 ... Conveyance motor, 23 ... Conveyance roller, 24 ... Platen, 25 ... Discharge roller, 30 ... Carriage unit, 31 ... Carriage, 32 ... Carriage motor, 40 ... head unit, 41 ... head, 41A ... first nozzle group, 41B ... second nozzle group, 42A ... first head, 42B ... second head, 42X ... virtual headset, 60 ... controller, 61 ... interface unit, 62 ... CPU, 63 ... Memory, 64 ... Unit control circuit, 65 ... Drive signal generator, 65A ... First drive signal generator, 65B ... Second drive signal generator, 100 ... Inkjet printer, 110 ... PC (personal computer) .

Claims (4)

A transport operation for moving the print medium in the transport direction, and the nozzles from the nozzles while scanning and moving a first nozzle row and a second nozzle row in which a plurality of nozzles are arranged in the transport direction in a scan direction intersecting the transport direction. A droplet discharge method for forming a plurality of dot rows composed of dots arranged in the scanning direction in the transport direction by alternately repeating a droplet discharge operation for discharging droplets on a print medium,
A first correction amount table corresponding to the first nozzle row;
A second correction amount table corresponding to the second nozzle row;
Nozzle row usage rate of the first nozzle row and the second nozzle row for forming the dot row, obtained based on the gradation of the dot row to be formed,
And a droplet ejection method for correcting the amount of the droplets ejected per unit area to form the dot row based on the above.   The droplet discharge method according to claim 1, wherein the gradation is an average gradation of the dot rows to be formed.   Based on the nozzle row usage rate, the first correction amount table and the second correction amount table are weighted to correct the amount of the droplets discharged per unit area in order to form the dot row. The droplet discharge method according to claim 1, wherein: A transport unit that moves the print medium in the transport direction;
A first nozzle row and a second nozzle row in which a plurality of nozzles for discharging droplets to the print medium are arranged in the transport direction;
A scanning moving unit that scans and moves the first nozzle row and the second nozzle row in a scanning direction intersecting the transport direction;
A control unit that forms a plurality of dot rows composed of dots arranged in the scanning direction in the transport direction by performing drive control of the transport unit and the scanning moving unit and ejection control of the droplets from the nozzles And comprising
A first correction amount table corresponding to the first nozzle row;
A second correction amount table corresponding to the second nozzle row;
Nozzle row usage rate of the first nozzle row and the second nozzle row for forming the dot row, obtained based on the gradation of the dot row to be formed,
And a droplet discharge device for correcting the amount of the droplets discharged per unit area in order to form the dot row.

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