JP2006305958A - Printer, computer program, and printing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve a printer which can obtain more suitable information for making correction. <P>SOLUTION: Correction information for making correction to suppress density irregularities between train regions is acquired on the basis of the read result of a density of a center part in a movement direction in each train region where each dot train constituting a specific density pattern printed by discharging ink from nozzles on the basis of image data for printing an image of a specific density is formed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a printing apparatus, a computer program, and a printing method for suppressing image density unevenness.

2. Related Art Inkjet printers (hereinafter referred to as printers) are known as printing apparatuses that form images by ejecting ink onto paper as a medium. The printer includes a dot forming operation in which ink is ejected from a plurality of nozzles moving in the carriage movement direction to form dots on a sheet, and a crossing direction (hereinafter referred to as a conveyance direction) in which the sheet is intersected with the movement direction by a conveyance unit. The transfer operation is also alternately repeated. Thereby, a plurality of raster lines composed of a plurality of dots along the moving direction are formed in the intersecting direction, and an image is printed. (For example, see Patent Document 1). In order to suppress the occurrence of density unevenness in such a printer, an image printed at a predetermined density may be read, and image data of an image to be printed may be corrected based on the read information.
JP-A-6-166247

  However, in the printer as described above, there is a possibility that the ink spreads more than the area to be originally printed at the edge of the image due to bleeding of the ink discharged onto the paper. For this reason, the area of the printed image is unclear. For example, when the image is read to correct the image data as described above, the area that should not be read at the edge portion of the image is read. Thus, there is a problem that appropriate information for correction cannot be obtained and image data cannot be corrected appropriately.

  SUMMARY An advantage of some aspects of the invention is that it realizes a printing apparatus, a computer program, and a printing method capable of obtaining more appropriate information for correction. There is.

  The main invention is to form a dot row on a medium by ejecting ink while being moved in a moving direction intersecting the predetermined direction based on image data for printing an image provided in plural along a predetermined direction. Correction information is acquired based on the result of reading the density of the central portion in the moving direction in each dot row constituting the specific density pattern printed based on the image data for printing the image of the specific density and the nozzle of And correcting the image data for printing the image based on the correction information so as to suppress density unevenness between the row regions in which the dot rows along the moving direction are formed by the nozzles. And a controller.

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

  At least the following will be made clear by the description of the present specification and the accompanying drawings.

A plurality of nozzles provided along a predetermined direction, and based on image data for printing an image, ejecting ink while moving in a moving direction intersecting the predetermined direction to form a dot row on the medium; The density of the central portion in the moving direction in each row region in which each dot row forming a specific density pattern printed by ejecting ink from the nozzles based on image data for printing an image of a specific density is formed Correction information for correcting to suppress density unevenness between each of the row regions is acquired based on the read result, and image data for printing an image is corrected based on the correction information. And a controller.
According to such a printing apparatus, when acquiring the correction information, only the density reading result of the central portion in the moving direction of the row area in which each dot row constituting the specific density pattern is formed is used. The acquired correction information does not include the density reading result near the edge of the specific density pattern. For this reason, it is possible to obtain appropriate correction information based on a reading result of a more appropriate density for correction.

  Here, when a rectangular region virtually defined on a medium such as paper is defined as a “unit region” whose size and shape are determined according to the print resolution, the “row region” refers to the movement direction An area composed of a plurality of unit areas arranged in a row. For example, the “unit area” is a square having a size of about 35.28 μm × 35.28 μm (≈ 1/720 inch × 1/720 inch) when the printing resolution is 720 dpi (moving direction) × 720 dpi (transport direction). It becomes a shape area. When the print resolution is 360 dpi × 720 dpi, the “unit region” is a rectangular region having a size of about 70.56 μm × 35.28 μm (≈ 1/360 inch × 1/720 inch). When ink droplets are ideally ejected, the ink droplets land at the center position of the unit region, and then the ink droplets spread on the medium to form dots in the unit region. For example, when the print resolution is 720 dpi × 720 dpi, the “row region” is a band-like region having a width of about 35.28 μm (≈ 1/720 inch) in the transport direction, and is ideally formed from the nozzle moving in the movement direction. When ink droplets are ejected intermittently, a dot row is formed in this row region.

In such a printing apparatus, the specific density pattern and another specific density pattern having a density different from the specific density pattern are arranged in the movement direction and printed on the medium, and each dot row constituting the other specific density pattern It is preferable to obtain correction information corresponding to the other specific density pattern based on the reading result of the density of the central portion in the moving direction in each row region where the pattern is formed.
According to such a printing apparatus, since the correction information is acquired for each specific density pattern and other density patterns, the image data is corrected more appropriately based on correction information corresponding to a plurality of densities. Is possible.

In this printing apparatus, the specific density pattern and the other specific density pattern are adjacent to each other.
According to such a printing apparatus, it is possible to narrow a region occupied by the printed specific density pattern and the other specific density pattern on the medium by making the specific density pattern and another specific density pattern adjacent to each other. . Further, even when the specific density pattern and another specific density pattern are adjacent to each other, when acquiring correction information, the central portion in the moving direction of each dot row constituting the specific density pattern and the other specific density pattern is obtained. Since only the density reading result is used, more appropriate correction information can be acquired.

In such a printing apparatus, it is preferable that an average value of reading densities of different portions in the central portion is used as the reading result.
According to such a printing apparatus, the reading result for obtaining the correction information is not only a single density of the central part in the movement direction of each dot row, but also a plurality of densities of different parts in the central part. Since it is an average value of a plurality of read densities, it is possible to obtain correction information based on a more accurate density as the density of the central portion.

In this printing apparatus, the specific density pattern and the other specific density pattern are printed on the medium as a correction pattern together with the specific density pattern and the ruled line along the predetermined direction arranged at an interval in the moving direction. The center portion is preferably specified with reference to the ruled line.
According to such a printing apparatus, the positions of the specific density pattern and the other specific density pattern are specified on the basis of the ruled line printed in the same manner as the specific density pattern and the other specific density pattern. It is possible to accurately specify the positions of the specific density pattern and other specific density patterns without including a shift or the like.

In this printing apparatus, the image forming apparatus includes a reading unit for reading the correction pattern, the image data indicates a gradation value for each unit area formed on the medium, and the reading unit has the specific density. The density of the unit area included in the specific density pattern printed based on the gradation value indicating the color density and the other specific density pattern printed based on the other gradation value indicating the specific density is determined in the reading unit. It is desirable to read as density data for each minimum reading area.
According to such a printing apparatus, it is possible to read the density in each unit area of the correction pattern printed with the gradation value indicated in the image data as density data. Therefore, it is possible to associate the gradation value indicated in the image data with the density data of the correction pattern printed based on the gradation value.

In the printing apparatus, the controller detects a centroid position in the density distribution in the moving direction based on density data of the minimum reading area arranged in the moving direction on the ruled line, and the centroid position in the detected density distribution. It is desirable to detect the position of the ruled line in the moving direction based on
According to such a printing apparatus, the position of the ruled line is detected by detecting the position of the center of gravity in the density distribution in the moving direction based on the density data of the minimum reading area arranged in the moving direction on the ruled line. Since the position of the ruled line is detected only from the density data of the reading area, the reliability is higher than that of the ruled line, so that the position of the ruled line can be detected reliably and accurately.

In such a printing apparatus, it is preferable that the reading resolution of the reading unit is higher than the printing resolution at which the correction pattern is printed.
According to such a printing apparatus, the reading resolution of the reading unit is higher than the printing resolution at which the correction pattern is printed. Therefore, even if the printed ruled line is a ruled line having a width of 1 dot, for example, Density data exists over a plurality of minimum reading areas. For this reason, it is possible to acquire more accurate density data when the ruled line is read.

A plurality of nozzles provided along a predetermined direction for ejecting ink while moving in a moving direction intersecting the predetermined direction based on image data for printing an image to form a dot row on a medium And a central portion in the moving direction in each row region in which each dot row forming a specific density pattern printed by ejecting ink from the nozzles based on image data for printing an image of a specific density is formed Correction information for correcting to suppress density unevenness between the row regions is acquired based on the read result of the density, and image data for printing an image is corrected based on the correction information. And the specific density pattern and another specific density pattern having a density different from the specific density pattern are adjacent to each other in the movement direction. Correction information corresponding to the other specific density pattern is obtained based on the reading result of the density of the central portion in the moving direction in each row region in which each dot row constituting the other specific density pattern is formed. The average density value of the different portions in the central portion is used as the reading result, and the specific density pattern and the other specific density patterns are spaced apart from the specific density pattern in the moving direction. Along with the arranged ruled lines along the predetermined direction, the correction pattern is printed on the medium, the central portion is specified on the basis of the ruled lines, and has a reading unit for reading the correction pattern, and the image data is The gradation value for each unit area formed on the medium is shown, and the reading unit prints based on the gradation value indicating the specific density. The density of the unit area of the other specific density pattern printed based on the specified specific density pattern and the gradation value indicating the other specific density is read as density data for each minimum reading area in the reading unit. The controller detects the centroid position in the density distribution in the moving direction based on the density data of the minimum reading area arranged in the moving direction on the ruled line, and based on the detected centroid position in the density distribution, The position of the ruled line in the movement direction is detected, and the reading resolution of the reading unit is higher than the printing resolution at which the correction pattern is printed.
According to such a printing apparatus, the effects of the present invention can be achieved more effectively because the above-described effects can be achieved.

  A plurality of nozzles provided along a predetermined direction for ejecting ink while moving in a moving direction intersecting the predetermined direction based on image data for printing an image to form a dot row on a medium The movement in each row region in which each dot row constituting a specific density pattern printed by ejecting ink from the nozzles based on image data for printing an image of a specific density on a printing apparatus having An image for acquiring correction information for correcting to suppress density unevenness between the row regions based on the density reading result of the central portion in the direction, and printing an image based on the correction information A computer program for realizing a function of correcting data can also be realized.

  A plurality of nozzles provided along a predetermined direction for ejecting ink while moving in a moving direction intersecting the predetermined direction based on image data for printing an image to form a dot row on a medium And printing a specific density pattern printed by ejecting ink from the nozzles based on image data for printing an image of a specific density, and each dot row constituting the specific density pattern is formed Obtaining correction information for correcting density unevenness between the row regions based on the density reading result of the central portion in the moving direction in each row region; and And a step of correcting image data for printing an image based on the printing method.

=== Configuration of Printing Apparatus ===
An embodiment of a printing system as a printing apparatus according to the present embodiment will be described with reference to the drawings.
FIG. 1 is an explanatory diagram showing an external configuration of a printing system, and FIG. 2 is a block diagram for explaining a main part of the printing system. The printing system 700 includes an inkjet printer 1 as a printing unit (hereinafter simply referred to as printer 1), a scanner 400 as a reading unit, a computer 720, a display device 704, an input device 708, and a recording / reproducing device 710. It has. The printer 1 can print an image on a medium such as paper, cloth, or film. In the following description, a sheet S (see FIG. 5), which is a typical medium, will be described as an example.

  The computer 720 is communicably connected to the printer 1 and the scanner 400, and has an application program, a printer driver 725 (see FIG. 10) installed therein, and print data corresponding to the image to cause the printer 1 to print an image. Is output to the printer 1. In addition, it is also possible to take in the information of the original read from the scanner 400 by operating the operation unit of the scanner 400 or the computer 720 into the memory in the computer 720, or to process the taken-in information.

  The controller 100 according to this embodiment includes a computer 720, a printer controller 60 included in the printer 1, and a scanner controller 103 included in the scanner 400, which are connected to each other via an interface.

  The printer controller 60 is a controller for controlling the printer 1. The printer controller 60 is connected to a computer 720 via an interface (not shown), and includes a CPU, a memory 63, and a unit control circuit 64 for controlling each unit of the printer 1. The printer controller 60 transmits and receives data to and from the computer 720, and the CPU controls each unit 20, 30, 40 via the unit control circuit 64 in accordance with a program stored in the memory 63. . The memory 63 is for securing an area for storing a program to be executed, a work area, and the like, and includes storage means such as a RAM, an EEPROM, and a ROM. In this embodiment, a part of the memory 63 will be described later. Correction values as correction information to be stored are also stored.

  The scanner controller 103 is a controller for controlling the scanner 400. The scanner controller 103 is connected to a computer 720 via an interface (not shown), and drives a memory 117 including a CPU, EEPROM, RAM, program ROM, and the like, and a CCD image sensor 14 included in the scanner 400. It has a CCD drive control circuit, a pulse motor drive control circuit for driving the pulse motor 183, and an exposure lamp control circuit for controlling the exposure lamp 7.

  The CPU of the scanner controller 103 is electrically connected to a CCD drive control circuit, a pulse motor drive control circuit, and an exposure lamp control circuit, and controls each drive control circuit based on a control signal from the computer 720.

  The input device 708 is, for example, a keyboard 708A or a mouse 708B, and is used to input application program operations, printer driver 725 settings, and the like. As the recording / reproducing device 710, for example, a flexible disk drive device 710A or a CD-ROM drive device 710B is used.

  The printer driver 725 is a program for realizing a function of displaying a screen for setting printing conditions and the like on the display device 704 and a function of converting image data output from the application program into print data. is there. The printer driver 725 is recorded on a recording medium (computer-readable recording medium) such as a flexible disk or a CD-ROM. The printer driver 725 can also be downloaded to the computer 720 via the Internet. And this program is comprised from the code | cord | chord for implement | achieving various functions.

  Here, the “printing apparatus” is a printing system connected to a computer, but the printer 1 alone and the printer 1 and the scanner 400 are connected by a cable, and the printer 1 and the scanner 400 are a single unit. It is a form provided in the housing | casing, Comprising: You may operate | move with a single controller.

=== Configuration of Scanner ===
FIG. 3 is a front view for explaining the configuration of the scanner 400, and FIG. 4 is a plan view for explaining the configuration of the scanner 400. In FIG. 4, the document table cover 13 is removed for convenience of explanation.

  The scanner 400 includes an original table glass 12 on which an original document 5 is placed, an original table cover 13 for pressing the reading surface of the original document 5 placed on the original table glass 12 toward the original table glass 12, and an original table. A reading carriage 16 that faces the glass 12 and scans along the document 5 while keeping a certain distance from the document 5, a drive unit 18 for scanning the reading carriage 16, and a moving direction of the reading carriage 16 is set to a predetermined value. A regulation guide 6 for regulating the direction and a support rail 4 for supporting the reading carriage 16 are provided.

  The reading carriage 16 includes an exposure lamp 7 as a light source for irradiating the document 5 with light through the document table glass 12, a lens 8 for condensing the reflected light from the document 5, and the reflected light from the document 5 to the lens 8. 4, a CCD image sensor 14 that receives the reflected light transmitted through the lens 8, and a guide receiving portion 15 that engages with the regulation guide 6.

  The CCD image sensor 14 is composed of a linear sensor in which photodiodes for converting an optical signal into an electric signal are arranged in a line. The CCD image sensor 14 is arranged along a direction (hereinafter referred to as a main scanning direction) substantially orthogonal to a moving direction of the reading carriage 16 (hereinafter referred to as a sub-scanning direction), and is irradiated within a predetermined time by each photodiode. The amount of light detected is detected.

The regulation guide 6 and the support rail 4 are provided so as to be spaced apart in the main scanning direction so as to sandwich the document reading area, and their longitudinal directions are along the sub-scanning direction.
The regulation guide 6 is formed of a stainless steel cylindrical material, and penetrates through guide receiving portions 15 formed of thrust bearings provided at two positions on one end side in the main scanning direction of the reading carriage 16. The guide receiving portions 15 provided at two positions provided on the reading carriage 16 are spaced apart in the sub-scanning direction in order to scan the reading carriage 16 stably.
The support rail 4 has a support surface 4a parallel to the document table glass 12, and an end portion of the reading carriage 16 opposite to the guide receiving portion 15 is placed on the support surface 4a. That is, the CCD image sensor 14 of the reading carriage 16 is configured to be parallel to the document table glass 12 while being supported by the regulation guide 6 and the support rail 4.

  The drive unit 18 includes an annular timing belt 181 fixed to the reading carriage 16 and a pulley 182 that meshes with the timing belt 181, a pulse motor 183 disposed on one end side in the sub-scanning direction, and the other The idler pulley 184 is arranged on the end side and applies tension to the timing belt 181. The reading carriage 16 moves along the regulation guide 6 by fixing the timing belt 181 with one end 16a in the main scanning direction and conveying the annular timing belt 181 by the pulse motor 183.

  The pulse motor 183 is driven by the scanner controller 103 of the controller 100. The read image can be enlarged and reduced in the sub-scanning direction by the scanning speed of the reading carriage 16 that is changed according to the speed of the pulse motor 183. It becomes possible.

  The scanner 400 has a home position sensor 2 (hereinafter referred to as an HP sensor) for detecting that the reading carriage 16 has reached a reference position (hereinafter referred to as a home position) on the upstream side in the document reading direction. is doing. The HP sensor 2 is a transmissive optical sensor, and a light-shielding plate (not shown) protruding from the reading carriage 16 when the reading carriage 16 is moved in the direction opposite to the original reading direction is an HP sensor 2. By blocking the light, it is detected that the reading carriage 16 has reached the home position. The position of the reading carriage 16 is determined by the scanner controller 103 based on the number of pulses given to the pulse motor and the amount of movement of the reading carriage 16 by one pulse after being detected by the HP sensor 2 with reference to this home position. Managed.

  On the upper surface of the document table glass 12, that is, the document placement surface 12a, a document regulating plate 11 is provided on which the leading edge of the document 5 abuts on the upstream side in the document reading direction by the reading carriage 16. The position of the document abutting portion 11a against which the document 5 of the document restriction plate 11 is abutted becomes the document reading start position of the scanner 400, that is, the reference position of the read data.

  In the scanner 400, the light from the exposure lamp 7 is irradiated onto the document 5, and the reflected light is imaged on the CCD image sensor 14 via the four mirrors 9 and the lens 8, while the reading carriage 16 is placed on the document 5. Move along. At this time, a voltage value indicating the amount of light received by the CCD image sensor 14 is read in a predetermined cycle, and an image corresponding to the distance moved by the reading carriage 16 in one cycle is captured as line data.

=== Configuration of Printer ===
<About printer configuration>
FIG. 5 is a schematic diagram of the overall configuration of the printer 1 of the present embodiment, FIG. 6 is a side sectional view of the overall configuration of the printer 1 of the present embodiment, and FIG. FIG. Hereinafter, the basic configuration of the printer 1 of the present embodiment will be described with reference to these drawings.

  The ink jet printer 1 according to the present embodiment includes a transport unit 20, a carriage unit 30, a head unit 40, a sensor 50, and a printer controller 60. The printer 1 that has received print data from the computer 720 as an external device controls each unit (conveyance unit 20, carriage unit 30, and head unit 40) by the printer controller 60. The printer controller 60 controls each unit based on the print data received from the computer 720 and prints an image on the paper S. The situation in the printer 1 is monitored by a sensor 50, and the sensor 50 outputs a detection result to the printer controller 60. The printer controller 60 controls each unit based on the detection result output from the sensor 50 and the command signal of the computer 720.

  The transport unit 20 functions as a transport mechanism that transports the paper S, transports the paper S to a printable position, and transports the paper S by a predetermined transport amount in a predetermined direction (hereinafter referred to as a transport direction) during printing. It is for making it happen.

  The transport unit 20 includes a paper feed roller 21, a transport motor 22 (also referred to as a PF motor), a transport roller 23, a platen 24, and a paper discharge roller 25. The paper feed roller 21 is a roller for feeding the paper S inserted into the paper insertion slot into the printer 1. The paper feed roller 21 has a D-shaped cross-sectional shape, and the length of the circumferential portion is set longer than the transport distance to the transport roller 23. For this reason, by rotating the paper feed roller once from a state in which the circumferential portion is separated from the paper surface, the paper S can be transported by the length of the circumferential portion and the leading edge of the paper S can reach the transport roller 23. Is possible. The transport motor 22 is a motor for transporting paper in the transport direction, and is constituted by, for example, a DC motor. The transport roller 23 is a roller that transports the paper S fed by the paper feed roller 21 to a printable area, and is driven by the transport motor 22. The platen 24 supports the paper S being printed from the back side of the paper S. The paper discharge roller 25 is a roller for transporting the paper S in the transport direction downstream of the platen 24 in the transport direction. The paper discharge roller 25 rotates in synchronization with the transport roller 23.

  The carriage unit 30 includes a carriage 31 and a carriage motor 32 (hereinafter also referred to as a CR motor). The carriage motor 32 is a motor for reciprocating the carriage 31 in a predetermined direction (hereinafter referred to as a carriage movement direction), and is constituted by a DC motor, for example. The carriage 31 detachably holds an ink cartridge 90 that stores ink. The carriage 31 is attached with a head 41 for ejecting ink from nozzles serving as ejection units. For this reason, as the carriage 31 reciprocates, the head 41 and the nozzle also reciprocate in the carriage movement direction (movement direction).

  The head unit 40 is for ejecting ink onto the paper S. The head unit 40 has a head 41. The head 41 has a plurality of nozzles, and ejects ink intermittently from each nozzle. Then, the head 41 moves in the carriage movement direction, and ink is intermittently ejected from the nozzles, so that a raster line as a dot row is formed on the paper S along the carriage movement direction. The arrangement of the nozzles, the configuration of the head 41, the driving circuit for driving the head 41, and the driving method of the head 41 will be described later.

  The sensor 50 includes a linear encoder 51, a rotary encoder 52, a paper detection sensor 53, a paper width sensor 54, and the like. The linear encoder 51 is for detecting a position in the carriage movement direction, and detects a slit formed in the slit plate and a belt-like slit plate installed along the carriage movement direction. A photo interrupter. The rotary encoder 52 is for detecting the amount of rotation of the transport roller 23, and is a disc-shaped slit plate that rotates as the transport roller 23 rotates, and a photo interrupter that detects a slit formed in the slit plate. Have

  The paper detection sensor 53 is for detecting the leading end position of the paper S to be printed. The paper detection sensor 53 is provided at a position where the front end position of the paper S can be detected while the paper feed roller 21 is transporting the paper S toward the transport roller 23. The paper detection sensor 53 is a mechanical sensor that detects the leading edge of the paper S by a mechanical mechanism. More specifically, the paper detection sensor 53 has a lever that can rotate in the paper transport direction, and this lever is disposed so as to protrude into the transport path of the paper S. As the paper S is transported, the leading edge of the paper comes into contact with the lever, and the lever is rotated. Therefore, the paper detection sensor 53 detects the position of the leading edge of the paper S and the presence or absence of the paper S by detecting the movement of the lever with a photo interrupter or the like.

  The paper width sensor 54 is attached to the carriage 31. In the present embodiment, as shown in FIG. 7, the position in the transport direction is attached at substantially the same position as the nozzle on the most upstream side. The paper width sensor 54 is a reflection type optical sensor that receives the reflected light of the light irradiated on the paper S from the light emitting unit at the light receiving unit and detects the presence or absence of the paper S based on the received light intensity at the light receiving unit. To do. The paper width sensor 54 detects the position of the edge of the paper S while being moved by the carriage 31 and detects the width of the paper S. The paper width sensor 54 can also detect the leading edge of the paper S depending on the situation.

<Regarding nozzle arrangement and head configuration>
As shown in FIG. 7, on the lower surface of the head 41, a black ink nozzle row Nk, a cyan ink nozzle row Nc, a magenta ink nozzle row Nm, and a yellow ink nozzle row Ny are formed. Each nozzle row includes n nozzles (for example, n = 180) that are ejection ports for ejecting ink of each color. The plurality of nozzles in each nozzle row are aligned at a constant interval (nozzle pitch: k · D) along the direction intersecting the moving direction of the carriage 31, that is, along the transport direction of the paper S. Here, D is a minimum dot pitch in the transport direction, that is, an interval at the highest resolution of dots formed on the paper S. K is an integer of 1 or more. For example, when the nozzle pitch is 180 dpi (1/180 inch) and the dot pitch in the transport direction is 720 dpi (1/720 inch), k = 4. In the illustrated example, the nozzles in each nozzle row are assigned a smaller number (# 1 to #n) toward the downstream nozzle. That is, the nozzle # 1 is located downstream of the nozzle #n in the transport direction. If such a nozzle array is provided in the head 41, the range in which dots are formed by a single dot forming operation is widened, and the printing time can be shortened. Further, since these nozzle rows are provided for each color of ink, multi-color printing can be performed by appropriately discharging ink from these nozzle rows.

  Each nozzle has an ink flow path communicating with an ink cartridge 90 containing ink, and a pressure chamber (not shown) is provided in the middle of the ink flow path. Each pressure chamber is configured such that its volume contracts and expands by, for example, a piezo element (not shown) as a drive element provided to eject ink droplets from each nozzle.

<About driving the head>
FIG. 8 is an explanatory diagram of a drive circuit for the head 41. This drive circuit is provided in the unit control circuit 64 described above. As illustrated, the drive circuit includes an original drive signal generation unit 644A and a drive signal shaping unit 644B. In this embodiment, this drive circuit is provided for each nozzle row, that is, for each nozzle row of each color of black (K), cyan (C), magenta (M), and yellow (Y). The piezo elements are individually driven. In the figure, the number in parentheses at the end of each signal name indicates the number of the nozzle to which the signal is supplied.

  The above-described piezo element is deformed each time the driving pulses W1 and W2 (see FIG. 9) are supplied to cause pressure fluctuations in the ink in the pressure chamber. That is, when a voltage of a predetermined time width is applied between the electrodes provided at both ends of the piezoelectric element, the piezoelectric element is deformed according to the voltage application time, and an elastic film (side wall) that partitions a part of the pressure chamber is formed. Deform. The volume of the pressure chamber changes according to the deformation of the piezo element, and the pressure fluctuation occurs in the ink in the pressure chamber due to the volume change of the pressure chamber. Ink drops are ejected from the corresponding nozzles # 1 to #n due to pressure fluctuations generated in the ink.

The original drive signal generator 644A generates an original drive signal ODRV that is used in common by the nozzles # 1 to #n. The original drive signal ODRV in the present embodiment is a signal that outputs two types of drive pulses W1 and W2 once each within a time during which the carriage 31 moves a distance corresponding to one unit area corresponding to the print resolution.
The drive signal shaping unit 644B receives the print signal PRT (i) together with the original drive signal ODRV from the original signal generation unit. The print signal PRT (i) is a signal whose level changes based on the above-described 2-bit print data. The drive signal shaping unit 644B shapes the original drive signal ODRV according to the level of the print signal PRT (i) and outputs it as the drive signal DRV (i) to the piezoelectric elements of the nozzles # 1 to #n. The piezo elements of the nozzles # 1 to #n are driven based on the drive signal DRV from the drive signal shaping unit 644B.

<About the head drive signal>
FIG. 9 is a timing chart illustrating each signal. That is, FIG. 3 shows a timing chart of each signal of the original drive signal ODRV, the print signal PRT (i), and the drive signal DRV (i).

  The original drive signal ODRV is a signal used in common for the nozzles # 1 to #n, and is output from the original drive signal generation unit 644A to the drive signal shaping unit 644B. The original drive signal ODRV of the present embodiment includes the first pulse W1 and the second pulse W2 within the time during which the carriage 31 moves a distance corresponding to one unit area corresponding to the printing resolution (hereinafter referred to as one unit area section). And have two pulses. The first pulse W1 is a drive pulse for ejecting a small size ink droplet (hereinafter referred to as a small ink droplet) from the nozzle. The second pulse W2 is a drive pulse for discharging a medium size ink droplet (hereinafter referred to as a medium ink droplet) from the nozzle. That is, by supplying the first pulse W1 to the piezo element, a small ink droplet is ejected from the nozzle. When the small ink droplets land on the paper S, small sized dots (small dots) are formed. Similarly, by supplying the second pulse W2 to the piezo element, a medium ink droplet is ejected from the nozzle. When the medium ink droplets land on the paper S, medium-sized dots (medium dots) are formed.

  The print signal PRT (i) is a signal corresponding to each unit area data assigned to each unit area in the print data transferred from the computer or the like. That is, the print signal PRT (i) is a signal corresponding to the unit area data included in the print data. The print signal PRT (i) of the present embodiment is a signal having 2-bit information for one unit area. Note that the drive signal shaping unit 644B shapes the original drive signal ODRV according to the signal level of the print signal PRT (i) and outputs the drive signal DRV (i).

  This drive signal DRV is a signal obtained by blocking the original drive signal ODRV in accordance with the level of the print signal PRT. That is, when the print data is “1”, the print signal PRT is at a high level, and the drive signal shaping unit 644B passes the drive pulse corresponding to the original drive signal ODRV as it is to obtain the drive signal DRV (i). On the other hand, when the print data is “0”, the print signal PRT becomes the low level, and the drive signal shaping unit 644B blocks the drive pulse corresponding to the original drive signal ODRV. Then, the drive signal DRV (i) from the drive signal shaping unit 644B is individually supplied to the corresponding piezoelectric element. Further, the piezo element is driven according to the supplied drive signal DRV (i).

  When the print signal PRT (i) corresponds to the 2-bit data “01”, only the first pulse W1 is output in the first half of one unit area section. As a result, small ink droplets are ejected from the nozzles, and small dots are formed on the paper S. When the print signal PRT (i) corresponds to the 2-bit data “10”, only the second pulse W2 is output in the second half of the one unit area section. As a result, medium ink droplets are ejected from the nozzles, and medium dots are formed on the paper S. When the print signal PRT (i) corresponds to the 2-bit data “11”, the first pulse W1 and the second pulse W2 are output in one unit region section. As a result, small ink droplets and medium ink droplets are continuously ejected from the nozzles, and large-sized dots (large dots) are formed on the paper S. That is, the printer 1 can form dots of a plurality of types (here, three types). When the print signal PRT (i) corresponds to the 2-bit data “00”, neither the first pulse W1 nor the second pulse W2 is output in one unit region section. As a result, no ink droplets of any size are ejected from the nozzles, and no dots are formed on the paper S.

  As described above, the drive signal DRV (i) in one unit region section is shaped to have four different waveforms according to four different values of the print signal PRT (i).

=== Printer driver ===
<About the printer driver>
FIG. 10 is a schematic explanatory diagram of basic processing performed by the printer driver 725. In addition, about the component already demonstrated, the same code | symbol is attached | subjected and description is abbreviate | omitted.
In the computer 720, computer programs such as a video driver 722, an application program 721, and a printer driver 725 are operating under an operating system installed in the computer 720.
The video driver 722 has a function of displaying a predetermined screen on the display device 704 in accordance with a display command from the application program 721 or the printer driver 725.

  The application program 721 has a function of performing image editing, for example, and is a program for creating data relating to an image (image data). The user can give an instruction to print an image edited by the application program 721 via the user interface of the application program 721. Upon receiving a print command, the application program 721 outputs image data to the printer driver 725.

  The printer driver 725 receives image data from the application program 721, converts the received image data into printable print data, and outputs the converted print data to the printer 1. The image data has unit area data as data corresponding to each unit area of the image to be printed. Each unit area data is expressed by a gradation value for each color such as RGB or CMYK, and the gradation value is converted according to each processing stage described later, and finally the print data At this stage, the print data (data such as the color and size of the dots) corresponding to the dots formed on the paper is converted. Here, the gradation value corresponding to each unit area indicated by the image data indicates that each unit area has a density set by the gradation value. For example, printing is performed with black ink. In this case, the gradation value indicating density 0 (white) is “0”, and the gradation value indicating density 100% (black) is set to “255”.

  The print data is data in a format that can be interpreted by the printer 1, and is data having the unit area data and various command data. The command data is data for instructing the printer 1 to execute a specific operation, for example, data indicating the carry amount.

  The printer driver 725 converts the image data output from the application program 721 and the image data read by the scanner 400 into print data, so that resolution conversion processing, color conversion processing, image data correction processing, halftone processing, Perform rasterization processing. Hereinafter, various processes performed by the printer driver 725 will be described.

  The resolution conversion process is the resolution when printing image data (text data, image data, etc.) output from the application program 721 or an image on the paper S (the interval between dots when printing, and is also called the print resolution). ). For example, when the print resolution is specified as 720 × 720 dpi, the image data received from the application program 721 is converted into image data having a resolution of 720 × 720 dpi.

  This conversion method includes interpolation and thinning of unit area data. For example, when the resolution of the image data is lower than the designated print resolution, new unit area data is generated between adjacent unit area data by performing linear interpolation or the like. On the contrary, when the resolution of the image data is higher than the print resolution, the resolution of the image data is made equal to the print resolution by thinning out the unit area data at a constant rate.

In this resolution conversion processing, image data is also adjusted in size so as to correspond to the size of a print area to be printed (an area where ink is actually ejected).
Each unit area data in the image data output from the application program 721 is a multi-level (for example, 256 levels) gradation value represented by an RGB color space. Hereinafter, unit region data indicating RGB gradation values is referred to as RGB unit region data, and image data composed of RGB unit region data is referred to as RGB image data.

  The color conversion process is a process of converting each RGB unit area data of the RGB image data into data indicating gradation values of multiple levels (for example, 256 levels) represented by a CMYK color space. Here, CMYK is the color of ink that the printer 1 has. That is, C means cyan, M means magenta, Y means yellow, and K means black. Hereinafter, unit area data indicating CMYK gradation values is referred to as CMYK unit area data, and image data composed of CMYK unit area data is referred to as CMYK image data. The color conversion processing is performed by the printer driver 725 referring to a table (color conversion lookup table LUT) in which RGB gradation values and CMYK gradation values are associated with each other.

  The image data correction process is a process executed for each row region in order to suppress density unevenness between the row regions in the multicolor printed image. The image data correction process will be described in detail later.

  The halftone process is a process for converting CMYK unit area data having multi-stage gradation values into CMYK unit area data having small-stage gradation values that can be expressed by the printer 1. For example, CMYK unit area data indicating 256 gradation values is converted into 2-bit CMYK unit area data indicating 4 gradation values by halftone processing. This 2-bit CMYK unit area data includes, for example, “no dot formation” (binary value “00”), “small dot formation” (also “01”), “medium dot formation” for each color. (Also “10”) and “large dot formation” (also “11”).

  For such a halftone process, for example, a dither method or the like is used, and 2-bit CMKY unit area data is created so that the printer 1 can form dots dispersedly. Further, the method used for the halftone process is not limited to the dither method, and a γ correction method, an error diffusion method, or the like may be used.

  The rasterizing process is a process for changing the CMYK image data subjected to the halftone process in the order of data to be transferred to the printer 1. The rasterized data is output to the printer 1 as the print data.

  Each process of the printer driver 725 can also be executed on image data read by the scanner 400. For example, resolution conversion is performed on image data of RGB components read by the scanner 400. Print data is generated by executing processing, color conversion processing, image data correction processing, halftone processing, and rasterization processing, and an image is printed on a sheet or the like by the printer 1 based on the image data read by the scanner 400 It is possible to print.

=== About printing operation ===
FIG. 11 is a flowchart of the operation during printing. Each operation described below is executed by the printer controller 60 controlling each unit in accordance with a program stored in the memory. This program has code for executing each operation.

  Print command reception (S001): The printer controller 60 receives a print command from the computer 720 via the interface. This print command is included in the header of print data transmitted from the computer 720. The printer controller 60 analyzes the contents of various commands included in the received print data, and performs the following paper feed operation, transport operation, dot formation operation, and the like using each unit.

  Paper Feed Operation (S002): The printer controller 60 performs a paper feed operation. The paper feeding operation is a process of moving the paper S to be printed and positioning it at a printing start position (so-called cueing position). That is, the printer controller 60 rotates the paper feed roller 21 and sends the paper S to be printed to the transport roller 23. Subsequently, the printer controller 60 rotates the transport roller 23 to position the paper S sent from the paper feed roller 21 at the print start position. When the paper S is positioned at the printing start position, at least some of the nozzles of the head 41 are opposed to the paper S.

  Dot Forming Operation (S003): The printer controller 60 performs a dot forming operation. The dot forming operation is an operation of forming dots on the paper S by intermittently ejecting ink from the head 41 moving along the carriage movement direction. At this time, the printer controller 60 drives the carriage motor 32 to move the carriage 31 in the carriage movement direction. Further, the printer controller 60 discharges ink from the head 41 based on the print data while the carriage 31 is moving. When the ink ejected from the head 41 lands on the paper S, dots are formed on the paper S as described above. At this time, when ink is ejected from the nozzles while moving the carriage 31, a raster line (dot row) along the moving direction is formed on the paper S.

  Transport Operation (S004): The printer controller 60 performs a transport operation. The transport operation is a process of moving the paper S relative to the head 41 along the transport direction. The printer controller 60 drives the carry motor 22 and rotates the carry roller 23 to carry the paper S in the carrying direction. By this transport operation, the head 41 can form dots at positions different from the positions of dots already formed by the dot formation operation described above.

  Paper discharge determination (S005): The printer controller 60 determines paper discharge for the paper S being printed. At the time of this determination, if data for printing on the paper S being printed remains, the paper is not discharged. Then, the printer controller 60 alternately repeats the dot formation operation and the conveyance operation until there is no data to be printed, and gradually prints an image composed of dots on the paper S. When there is no more data to be printed on the paper S being printed, the printer controller 60 discharges the paper S. That is, the printer controller 60 discharges the printed paper S to the outside by rotating the paper discharge roller 25. Note that whether or not to discharge paper may be determined based on a paper discharge command included in the print data.

  Print end determination (S006): The printer controller 60 determines whether or not to continue printing. When printing on the next sheet S, a new sheet is fed by the sheet feeding operation (S002), printing is continued, and printing is continued. If printing is not performed on the next sheet S, the printing operation is terminated.

=== Regarding Cause of Density Unevenness in Image ===
Density unevenness that occurs in an image printed in multiple colors using CMYK inks is basically caused by density unevenness that occurs in each ink color. For this reason, density unevenness in an image printed in multiple colors is suppressed by suppressing density unevenness of each ink color separately.

  Therefore, in the following, the cause of density unevenness occurring in an image printed in a single color with any color ink will be described. FIG. 12 is a diagram for explaining density unevenness that occurs in the transport direction of the paper S in a single-color printed image.

  The density unevenness in the conveyance direction illustrated in FIG. 12 appears as horizontal stripes parallel to the carriage movement direction. Such horizontal stripe-shaped density unevenness occurs due to, for example, variations in the ink discharge amount for each nozzle, but also due to variations in the processing accuracy of the nozzles. In other words, the flying direction of the ink ejected by the nozzles varies due to variations in nozzle processing accuracy. Due to the variation in the flight direction, the dot formation position by the ink that has landed on the paper S may shift in the transport direction with respect to the target formation position. In this case, the raster line formation position formed by these dots is inevitably shifted from the target formation position in the transport direction. For this reason, the interval between the raster lines adjacent in the transport direction is periodically vacated or clogged. When viewed macroscopically, it appears as horizontal stripe-shaped density unevenness. That is, when the interval between adjacent raster lines is relatively widened or narrowed, a row region in which more dots or a part of dots are formed in a row region is macroscopically formed. When the dots appear dark and dots or a part of the dots that should be originally formed in the row areas are formed in adjacent row areas, the row areas appear macroscopically thin. Here, the raster line indicates a dot row formed along the carriage movement direction by intermittently ejecting ink while moving the carriage 31.

  The cause of density unevenness is also applicable to other ink colors. If this tendency is observed even in one color of CMYK, density unevenness appears in a multicolor image.

=== Regarding the Image Printing Method According to the Present Embodiment ==
FIG. 13 is a flowchart showing a flow of processes and the like related to the image printing method according to the present embodiment. Hereinafter, the outline of each process will be described with reference to this flowchart. First, the printer 1 is assembled on the production line (S110). Next, correction values corresponding to some specific densities are set as adjustment information for correcting the density for each row area, and the processing stored in the printer 1 is executed by an operator in charge of inspection. (S120). This correction value is a value set for each row region in which a raster line is formed in order to correct the gradation value corresponding to each unit region supplied as image data to be printed.

  In the present embodiment, a correction pattern having a sub-pattern to be printed based on gradation values associated with five types of specific densities is printed for each ink color, and each printed sub-pattern of the correction pattern is printed. The density of each row area is detected by detecting the density of each row area in which the raster lines constituting the image are formed, calculating the average value of the density detected for each row area, and using the calculated density average value as the target density By correcting the gradation value of the image data so that becomes the target density, density unevenness between the row regions is suppressed. For this reason, first, correction values for correcting gradation values indicating some specific densities among the five types of specific densities are obtained. That is, the correction pattern is printed only at a specific density, and based on the read density data obtained by reading the density of the actually printed correction pattern, a correction value corresponding to any one of the printed specific densities is obtained. Ask. For other densities other than the specific density corresponding to the correction value, the corrected gradation corresponding to each density is obtained by linearly interpolating the corrected gradation value of the specific density obtained based on the correction value. The value is to be obtained.

  Next, the printer 1 is shipped (S130). The user who has purchased the printer 1 performs the actual printing of the image. At the time of the actual printing, the printer 1 corrects the density of the image data based on the stored correction value for each row area. Then, an image is printed on the paper S based on the corrected image data (S140). Here, the main printing refers to printing of a desired image such as a natural image performed by a user or the like for printing a predetermined test pattern such as a correction pattern. The correction value setting (step S120) according to the present embodiment will be described in detail.

<Step S120: Setting Correction Value for Suppressing Density Unevenness>
FIG. 14 is a flowchart illustrating a procedure of processing for setting a correction value. Hereinafter, the correction value setting procedure will be described with reference to this flowchart.

  The method for setting the correction value is as follows. First, the correction pattern CP is printed by the printer for which the correction value is to be set (S200), the scanner for reading the correction pattern is initially set (S210), and printing. A step of reading the corrected correction pattern CP (S220), a step of detecting the inclination of the read data (S230), a step of adjusting the inclination of the read data (S240), and the extreme end of the desired area in the adjusted data. The step of detecting the position of the raster line (S250), the step of detecting the edge of the correction pattern in the sub-scanning direction (S260), and the data corresponding to the data corresponding to the detected endmost raster line and the column region. Converting (S270), each column region based on the converted data A step of calculating an average value of density (S280), a step of calculating a correction value of a specific density based on the calculated average value of density (S290), and a step of storing the calculated correction value in a memory (S300) Have. Hereinafter, each step will be described. In the present embodiment, the specific gradation values indicating the specific density to be printed as the correction pattern are, for example, five kinds of gradation values corresponding to densities of 10%, 30%, 50%, 70%, and 100%. Here, the settable density range is density 0 to density 100%, the gradation value corresponding to density 0 is the lowest value “0”, and the gradation value corresponding to density 100% is the highest value. “255”.

(1) Step S200: Printing Correction Pattern CP In step S200, the correction pattern CP is printed on the paper S for each ink color. Here, an operator in charge of inspection connects the printer 1 to a communicable state with a computer 720 installed on the inspection line, and prints the correction pattern CP by the printer 1. That is, the operator performs an operation for printing the correction pattern CP via the user interface of the computer 720. By this operation, the computer 720 outputs the print data of the correction pattern CP stored in the memory to the printer 1. The printer 1 prints the correction pattern CP on the paper S based on the print data. Note that the printer 1 that prints the correction pattern CP is the printer 1 for which correction values are set. That is, the correction value is set for each printer 1.

<< Correction pattern >>
FIG. 15 is a diagram for explaining an example of the printed correction pattern CP. As shown in the drawing, four correction patterns CP of this embodiment are printed for each color on one sheet. Each correction pattern CP has a plurality of sub-patterns SP having different densities, and is printed for each ink color. In this example, the sub patterns SP are printed based on the specific gradation values indicating the above-described five specific densities for each ink color. Here, among the five types of specific densities, the sub pattern SP is a specific density pattern based on a specific gradation value indicating any one of the specific densities, and the other sub patterns SP are different in density from the specific density pattern. It corresponds to a specific density pattern.

  In the print data for printing each sub-pattern SP of the correction pattern CP, a specific gradation value corresponding to each density is assigned to all of the virtual areas, that is, the unit areas for forming one dot on the paper. This is print data generated when the assumed CMYK image data is assumed and the assumed CMYK image data is subjected to halftone processing and rasterization processing by a printer driver. For this reason, the print data of the correction pattern CP stored in the memory is printed when each band-shaped sub-pattern SP is printed by an ideal printer based on the gradation value indicating each density. The density is set to be uniform. That is, each sub-pattern SP printed by an ideal printer is printed at a substantially constant density along the transport direction. Here, the ideal printer is a printer that is processed and manufactured as designed, and indicates a printer in which dots are formed at target positions by ink droplets ejected from nozzles. In FIG. 15, for the sake of convenience of explanation, characters indicating the ink color printed for each correction pattern CP are printed, but the characters indicating the ink color need not be printed. In the following description, the correction pattern is the raster line side that is printed first, that is, the leading end side during conveyance of the printed paper is also referred to as the leading end side in the correction pattern, and the last printed raster line side. That is, the rear end side when the printed paper is conveyed is also referred to as the rear end side in the correction pattern.

  The difference between the correction patterns CP for each ink color having the five sub-patterns SP is basically only the ink color. Therefore, in the following, the correction pattern CPk having the five sub patterns SP of black (K) will be described as a representative of the four correction patterns CP.

  As shown in FIG. 15, four correction patterns CP of this embodiment are printed on one sheet for each of K, C, M, and Y colors. Each correction pattern CP is printed with a strip-shaped sub-pattern SP that is long in the paper transport direction at five different densities based on the five specific gradation values. Are arranged in the carriage movement direction and adjacent to each other. That is, each correction pattern CP has a sub pattern group composed of five sub patterns SP.

  Further, as described above, suppression of density unevenness in multicolor printing is performed for each ink color used for the multicolor printing, but the method used for the suppression is the same. For this reason, the following description will be made on behalf of black (K). In the following description, there is a place where only one color of black (K) is described, but other C, M, and Y inks are used. The same applies to the color.

  In the black (K) correction pattern CPk, five types of density sub-patterns SPka, SPkb, SPkc, SPkd, and SPke are arranged along the carriage movement direction. That is, each of the sub-patterns SPka, SPkb, SPkc, SPkd, and SPke has a plurality of raster lines (dot rows) formed along the carriage movement direction and a plurality of them along the conveyance direction that intersects the carriage movement direction. It is arranged side by side. A raster line composed of dots formed at the same position in the transport direction in each of the sub-patterns SPka, SPkb, SPkc, SPkd, and SPke receives ink from the same nozzle during the same movement operation of the carriage 31. It is formed by being discharged.

  Incidentally, the printer 1 alternately repeats the operation of moving the carriage 31 while ejecting ink and the operation of transporting paper when printing an image. For this reason, printing is performed with the set nozzles for each block having a predetermined width determined by the amount of paper transport and the number of nozzles used. That is, the image is basically formed by connecting a plurality of blocks having a predetermined width in the transport direction, and when the image is printed on one sheet, the dots formed by the nozzles are the same. There are a plurality of blocks arranged in. Therefore, the correction pattern CP is set so as to include at least one block in which each raster line is formed by different nozzles.

  In addition, in the correction pattern CP formed for each color, the outermost raster line located at the end of the plurality of raster lines arranged along the paper conveyance direction is another raster line in the carriage movement direction. It has an extended portion L with a width of 1 dot extending over a wider area. In the extended portion L, the outermost raster line Ls located on the front end side of the correction pattern CP and the outermost raster line Le located on the rear end side are extended longer than the other raster lines, and the density is 100%. It is formed with the density | concentration of. Here, in the extreme end raster line Ls on the front end side and the extreme end raster line Le on the rear end side, an extended portion L and a portion (hereinafter referred to as a main portion) M constituted by five sub patterns SP, Are not necessarily connected, and in the same movement operation as the movement of the carriage 31 when printing the main part M, ink is ejected from the nozzles forming the outermost raster line, and the extension part L is formed. It only has to be. In other words, the extending portion L is a ruled line formed along the moving direction of the carriage 31 to detect the inclination of each correction pattern CP. The extended portion L of the end raster line Ls corresponds to a detected portion for detecting the inclination of the image.

  Furthermore, the correction pattern CP for each color is connected between the extended portion L on the front end side and the extended portion L on the rear end side, is arranged in parallel with the sub-pattern SP, and dots are arranged in one row. A single dot line J as a ruled line is provided at a distance from the sub-pattern SP.

  In the present embodiment, an example is shown in which four correction patterns CP formed for each color are printed on one sheet of paper. However, the correction pattern CP is used for each printing method such as an interlace method or a band feeding method. Accordingly, printing is performed on one sheet for each printing method by changing the sheet conveyance amount and the ink discharge timing of each nozzle. That is, since the raster lines of the image printed by the interlace method, the band feeding method, and the like and the nozzles that form each raster line are different from each other depending on the printing method, the density unevenness for each row region in which the raster line is to be formed is reduced. It is desirable that the correction pattern for suppression is printed in the paper conveyance amount actually used in the main printing and the ink ejection timing of each nozzle, that is, in each printing method and each printing processing mode. For example, in the case of the band feeding method, the paper is conveyed by the length of the nozzle row, and printing is performed for at least one block in a print processing mode in which raster lines having the same pitch as the nozzle pitch are formed. If the interlace method is used, the leading and trailing edge portions of the paper are printed in the main printing, the processing mode in which a small amount of the paper is conveyed and printed with a specific few nozzles, and the portions other than the leading and trailing edges. Printing is performed at least for one block at a time with a print processing mode in which raster lines are formed using as many nozzles as possible while quantitatively conveying paper. In the case of so-called borderless printing for printing without margins, printing is performed in the same manner as the leading and trailing edge portions of the sheet using only the nozzles facing the grooves 24a (see FIG. 6) provided in the platen 24. The mode and the print processing mode in which raster lines are formed using as many nozzles as possible while quantitatively transporting the paper at portions other than the front end and the rear end are printed at least one block at a time. In this way, correction is performed by correcting the density using the correction value obtained based on each printed correction pattern in each print mode in which printing is performed with the same paper conveyance amount and ink ejection timing of each nozzle as in the main printing. Therefore, it is possible to reliably suppress uneven density.

  In the present embodiment, an example of using a correction pattern printed based on gradation values corresponding to five types of specific densities of each color has been described. However, the specific density of each color, that is, the types of gradation values, are five types. Not exclusively. If the number of gradation values is increased, more appropriate density correction can be performed, but the time spent for the process of printing the correction pattern, the process of reading the correction pattern and setting the correction value, and the correction process increases. On the other hand, if the number of gradation values is reduced, appropriate correction may not be performed. Therefore, it is desirable that the gradation value of a specific density be about five kinds.

(2) Step S210: Step of Initializing Scanner In the scanner 400 for reading the printed correction pattern CP, an initial setting operation is executed. The initial setting operation may be executed when the power of the scanner 400 is turned on. The scanner 400 detects the position of the reading carriage 16 by moving the reading carriage 16 in a predetermined direction. Further, the exposure lamp 7 is turned on to stabilize the light emission amount, and a reference density original is read, and the output of the CCD image sensor 14 is detected to check the necessary light amount and adjust the gain. Then, the reading carriage 16 is moved to the home position to enter a standby state. Such initial setting processing of the scanner 400 may be performed in parallel when the correction pattern CP is printed by the printer 1.

(3) Step S220: Step of Reading Correction Pattern CP The density of each correction pattern shown in FIG.
The reading resolution of the scanner 400 of this embodiment is higher than the printing resolution of the printer 1, and the width of the unit area in the printed correction pattern in the sub-scanning direction is the width read by one photodiode of the CCD image sensor 14. Is set to about 4 times. That is, an ideal raster line corresponds to about four widths in the sub-scanning direction of the minimum reading area, which is the minimum unit that can be read by the scanner 400.

FIG. 16 is a diagram for explaining a reading reference position and a reading area when reading a correction pattern.
When reading the correction pattern, the front end of the paper (hereinafter referred to as a correction document) on which the correction pattern CP is printed by the printer 1 is abutted against the document abutting portion 11a of the document restriction plate 11, and One corner of the leading edge of the correction document is positioned at the reference position in the main scanning direction, and the correction document is placed on the document table glass 12. Here, the position where one corner of the leading edge of the correction document is positioned is defined as an absolute reference position P.

  Then, while moving the reading carriage 16 in the sub-scanning direction, the output of the CCD image sensor 14 in an area of a predetermined size including each correction pattern is stored in the memory 117 together with position information. In the present embodiment, the cyan correction pattern has a distance SX1 in the main scanning direction with respect to the absolute reference position P, the distance SY1 in the sub-scanning direction, and the magenta correction pattern has a position in the main scanning direction with respect to the absolute reference position P. The distance SX2 is the position of the distance SY1 in the sub-scanning direction, the yellow correction pattern is relative to the absolute reference position P, the distance SX1 in the main scanning direction is the position of the distance SY1, and the black correction pattern is With respect to the absolute reference position P, the position of distance SY1 in the main scanning direction and the distance SY1 in the sub-scanning direction is set as reference positions (hereinafter referred to as reading reference positions) Pc, Pm, Py, and Pk for reading each correction pattern. Each is set to read an image of an area having a length SH1 in the main scanning direction and a width SW1 in the sub-scanning direction. In other words, the scanner 400 moves the reading carriage 16 in the sub-scanning direction, and after the reading carriage 16 reaches the position where the position (reading position) of the image formed on the CCD image sensor 14 becomes the document abutting portion 11a. When the distance SY1 moves, the output of the CCD image sensor 14 starts to be captured. At this time, the output of the photodiode arranged in the range of the width SW1 in the main scanning direction from the reading reference position Pc is used as reading density data as a measured value of the cyan correction pattern CPc, and from the reading reference position Pm. The output of the photodiode arranged in the range of the width SW1 in the scanning direction is periodically read as reading density data as a measurement value of the magenta correction pattern CPm, and is associated with position information of each minimum reading region. Stored in the memory 117. The cyan and magenta correction patterns CPc and CPm are continuously read while the reading carriage 16 moves from the reading reference position Pc and the reading reference position Pm by the length SH1.

  Then, when the reading carriage 16 moves from the absolute reference position P by the distance SY2, the output of the CCD image sensor 14 is started again. At this time, the output of the photodiode arranged in the range of the width SW1 in the main scanning direction from the reading reference position Py is used as reading density data as a measurement value of the yellow correction pattern CPy, and from the reading reference position Pk. The output of the photodiode arranged in the range of the width SW1 in the scanning direction is periodically read as read density data as a measurement value of the black correction pattern CPk, and is associated with the position information of each minimum reading region. Stored in the memory 117. Reading of the correction patterns CPy and CPk for yellow and black is continuously executed while the reading carriage 16 moves the reading reference position Py and the reading reference position Pk by the length SH1. In this way, the data of the area including each correction pattern CP includes the size of the photodiode of the CCD image sensor 14, the moving speed of the reading carriage 16, the projection magnification in the optical system, and the reading speed of the CCD image sensor 14. Is stored in the memory 117 in association with the position information of each minimum reading area. In the present embodiment, the reading resolution of the scanner 400 is, for example, 2880 dpi, and the minimum reading area is an area having a side of 1/2880 inches.

  In the read density data read at this time, the maximum value (white level) of the photodiode output in each ink color is associated with the read density “0”, and the minimum output value (maximum density level) is the read density “255”. Is stored.

(4) Step S230: A step of detecting the inclination of the read data Since the correction pattern CP is a pattern printed by the printer 1, the correction pattern CP is not necessarily inclined to the paper due to the paper conveyance characteristics of the printer 1. Not necessarily. Even if the correction pattern is printed without tilting on the correctly conveyed paper, the correction pattern is tilted when it is not placed correctly when placed on the platen glass. There is a fear of being read in.

  By the way, the correction executed by the correction value generated based on the read density data of the correction pattern CP is a correction for suppressing density unevenness between the column regions where the raster lines are formed. Generated for each area. For this reason, when the correction pattern CP in the tilted state is read by the scanner 400, the read density data is spread over a plurality of different row regions even if it is intended to read one row region along the sub-scanning direction. There is a possibility that reading is performed, and erroneous reading density data is handled as reading density data of one row region, and a correct correction value may not be obtained.

  Therefore, using the read density data of the black correction pattern CPk read in step S220, the inclination of the black correction pattern CPk is detected and adjusted so that the inclination disappears.

FIG. 17 is a diagram for explaining processing for detecting the inclination of the black correction pattern.
As shown in the figure, it is assumed that the black correction pattern CPk is read with an inclination. A one-dot chain line in the figure indicates the entire read area.

  In the present embodiment, when detecting the inclination of the correction pattern, the extended portion L of the outermost raster line located at the end in the sub-scanning direction among the raster lines constituting each correction pattern is detected. Since the extension L is printed at a portion where no other raster line is printed in the sub-scanning direction, the center of gravity position in the density distribution is detected as the position of the extension L from the read density data in the sub-scanning direction. Is possible. Here, the position of the outermost raster line located on the leading end side of the correction document in the sub-scanning direction is detected at two positions spaced apart in the main scanning direction, and the inclination is determined by the difference between the two detected positions. Is detected. That is, the CCD image sensor 14 has read density data read by two photodiodes spaced apart from each other, and the read reference data Pk in the sub-scanning direction of the extracted read density data at two locations is extracted. In the density distribution in the sub-scanning direction, the inclination is detected by comparing the distance to the center of gravity position.

  The process of detecting the inclination of the correction pattern is performed by a predetermined program executed by the computer 720 connected to the scanner 400.

  When the computer 720 executes a program for detecting the inclination of the correction pattern, the reading density data read in step S220 stored in the memory 117 of the scanner 400 is referred to, and the main data is read from the reading reference position Pk. The reading density data read by the photodiodes arranged at the distances KX1 and KX2 in the scanning direction is extracted from the reading reference position Pk by the distance KY0 in the sub-scanning direction.

  At this time, when the correction pattern is tilted and read as shown in FIG. 17, in the read density data read by the photodiode corresponding to the position of the distance KX1 and the photodiode corresponding to the position of the distance KX2. The distance from the reading reference position Pk in the sub-scanning direction to the barycentric position in the density distribution in the sub-scanning direction is different.

FIG. 18 is a diagram for explaining a difference in distance from the reading reference position Pk to the center of gravity position in the density distribution in the sub-scanning direction at the distance KX1 and the distance KX2.
The read density data read by the photodiodes corresponding to the position of the distance KX1 and the position of the distance KX2 is a graph as shown in FIG. 18, and the center of gravity in the density distribution in the sub-scanning direction from the read reference position Pk. The distance to the position is different.

That is, the center-of-gravity position in the density distribution in the sub-scanning direction differs from the distance (KX2-KX1) in the main scanning direction by the distance (KY1-KY2). For this reason, the inclination angle θ of the correction pattern is obtained by (Equation 1).
θ = tan ⁻¹ {(KY1−KY2) / (KX2−KX1)} (Formula 1)
At this time, the computer 720 detects that the read correction pattern is inclined by the angle θ.

(5) Step 240: Step of adjusting the inclination of the read data The computer 720 that has detected that the read density data that has been read is tilted changes the read density data stored in the memory 117 to the detected angle θ. Based on the position information associated with the read density data, so-called image data rotation processing is performed to process the data with an image that rotates the image so as to eliminate the inclination.
FIG. 19 is a diagram illustrating an image of the read density data after the image data rotation process is executed based on the detected inclination.
As shown in the drawing, by executing the image data rotation process on the read reading density data, it is possible to adjust the inclination of the correction pattern as if the image based on the read image data was rotated. As described above, the read density data adjusted in inclination is formed by data corresponding to the direction of each raster line constituting the correction pattern and the column region in which the corresponding raster line is to be formed in the read read density data. The direction of the raster line to be coincided with.

(6) Processing for extracting data of desired area of tilt-adjusted data For data whose tilt has been adjusted, that is, read density data equivalent to that read when correction pattern CP is correctly arranged without tilting, correction is performed. In addition to the read density data of the pattern for use, the read density data of the blank portion is also included, and the position of the row area constituting the correction pattern is not clear. Further, since the width in the sub-scanning direction of the row area in the printed correction pattern is four times the minimum reading area (reading resolution) of the scanner 400, the number of data in the sub-scanning direction in the read density data and the correction It does not match the number of column regions in the pattern. Furthermore, since the correction pattern read by the scanner 400 is printed, the width of the raster line in the sub-scanning direction is not always printed due to ink bleeding or the like. Further, due to the speed of the reading carriage when reading the correction document, the error of the data capture timing of the CCD image sensor 14, etc., the width corresponding to four times the minimum reading area when the correction pattern is read is a raster line. This does not necessarily match the width in the sub-scanning direction. For this reason, the read density data corresponding to the main portion M of the correction pattern CP in the read density data adjusted in inclination is extracted, and the extracted read density data is associated with each row area constituting the correction pattern CP. Execute the process.

  First, the read density data of the main part M of the correction pattern CP is extracted from the read density data whose inclination has been adjusted.

<Extraction of reading density data corresponding to main part of correction pattern>
When reading density data corresponding to the main part M of the correction pattern CP is extracted from the read density data adjusted in inclination, two edges in the sub-scanning direction are detected in the main part M of the correction pattern CP. Read density data corresponding to between the edges is extracted as read density data of the main portion M of the correction pattern CP. The detection of the edge in the main part M of the correction pattern CP is performed by detecting the edge of the outermost raster line located at the extreme end in the sub-scanning direction in the main part M of the correction pattern CP from the read density data whose inclination has been adjusted. Is realized. In this embodiment, the edge of the endmost raster line is detected using the extended portion L of the endmost raster line of the correction pattern.

[First embodiment]
Step S250: Step for Detecting the Position of the Endmost Raster Line FIG. 20 is a diagram for explaining a first embodiment of processing for detecting an edge using the extended portion of the endmost raster line of the correction pattern. is there.

  For example, as shown in FIG. 19, the processing for detecting the position of the most extreme raster line corresponds to the positions of the distance KX1 and the distance KX2 in the main scanning direction from the reading reference position Pk in the read density data whose inclination is adjusted. This is executed using read density data read by a photodiode. Here, since the correction pattern has two endmost raster lines in the sub-scanning direction, the position of the endmost raster line is detected for each endmost raster line. That is, reading density data corresponding to the distance KY0 in the sub-scanning direction is extracted from the reading reference position Pk as reading density data for detecting the position of the most extreme raster line Ls on the leading end side of the correction document. As reading density data for detecting the position of the most recent raster line Le on the trailing edge side of the document, it corresponds to a distance KY0 in the sub-scanning direction from a position separated by a distance KY3 in the sub-scanning direction from the reading reference position Pk. Reading density data is extracted.

  The central portion of FIG. 20 shows an image of the read density data around the outermost raster line L read by the photodiode corresponding to the position of the distance KX1 and the distance KX2, and on the left side is the read at the distance KX1. An image of density data is shown in a graph, and on the right side, an image of read density data at a distance KX2 is shown in a graph.

  In the example of FIG. 20, eight minimum reading regions r having a density different from the blank portion are detected in the reading density data around the endmost raster line in the sub-scanning direction. Since the extending portion L is one raster line (raster line formed in one row region), it should be originally detected as the four minimum reading regions arranged in the sub-scanning direction. That is, of the eight minimum reading regions r1 to r8 in which the density is detected, the four minimum reading regions r are data indicating the extension L, and the remaining four minimum reading regions r should not exist originally. . For this reason, the four minimum reading areas indicating the extended portion L are specified, and the edge outside the minimum reading area located outside the correction pattern CP among the four minimum reading areas is the main of the correction pattern CP. Detect as an edge in part M. In the following explanation, the processing for detecting the edge of the most extreme raster line on the front end side will be mainly described, and the difference in processing between the extreme end raster line on the front end side and the extreme end raster line on the rear end side will be described. Each will be described.

  The computer 720 stores information indicating the printing resolution when the correction pattern is printed and the reading resolution when the printed correction pattern is read by the scanner 400. The computer 720 calculates the number of continuous minimum reading areas included in the width of the extending portion L in the sub-scanning direction based on the stored printing resolution and reading resolution. In the present embodiment, “4” is calculated. Further, when the calculated number of minimum reading areas is an even number, in order to obtain the distance from the center of the width in the sub-scanning direction of the extending portion L to the edge, half of the calculated number of the minimum reading areas is also calculated. calculate. In the present embodiment, “2” is calculated.

  The computer 720 reads the reading density data corresponding to the distance KY0 in the sub-scanning direction from the reading reference position Pk in the minimum reading area located at the distance KX1 and the distance KX2 in the main scanning direction (hereinafter referred to as leading edge side reading density data). ), And reading density data corresponding to the distance KY0 in the sub-scanning direction (hereinafter referred to as rear-end side reading density data) is extracted from a position separated by the distance KY3 in the sub-scanning direction from the reading reference position Pk.

  Based on the extracted front end side read density data, the center of gravity position in the density distribution in the sub-scanning direction is detected for each of the distance KX1 and the distance KX2. In the example of FIG. 20, the position g1 on the lower end side from the center of the fourth minimum reading region r4 is detected as the barycentric position in the density distribution in the sub-scanning direction at the distance KX1, and the barycentric position in the density distribution in the sub-scanning direction at the distance KX2 As a result, a position g2 on the upper end side from the center of the fifth minimum reading region r5 is detected.

  When two barycentric positions in the density distribution in the sub-scanning direction are detected, the computer 720 detects the center position between them. In the example of FIG. 20, the boundary portion between the fourth minimum reading region r4 and the fifth minimum reading region r5 is detected as the center position of the outermost raster line L. At this time, when the position detected as the center position of the outermost raster line L is not the boundary portion between the two minimum reading areas, for example, the position g3 on the lower end side from the center of the fifth minimum reading area r5 is detected. In this case, the edge near the position g3 of the minimum reading area including the position g3, that is, the boundary portion between the fifth minimum reading area r5 and the sixth minimum reading area r6 is the center position of the outermost raster line L. It is set to be detected.

Step 260: Step of detecting the edge of the correction pattern in the sub-scanning direction The computer 720 detects the position information of the boundary portion between the two detected minimum reading areas r4 and r5, and the sub-scan of the calculated extension portion L. An edge in the main portion M of the correction pattern CP is detected from “2”, which is half the number of minimum reading areas included in the width in the direction.
For example, in the case of FIG. 20, the boundary between the fourth minimum reading region r4 and the fifth minimum reading region r5 from the front end side in the sub-scanning direction is the highest among the eight minimum reading regions r1 to r8 in which the density is detected. Since the center position of the end raster line L, that is, the center of the extension portion L is detected, the edge of the minimum reading area two outside the correction pattern CP from the center of the extension portion L is used as the correction pattern CP. Detected as an edge.

  Then, if FIG. 20 is read density data when the extended portion L located on the leading end side of the correction pattern is read, the fourth minimum reading region r4 detected as the center position of the outermost raster line Ls and An edge on the leading end side of the third minimum reading region r3 located second in the outward direction of the correction pattern CP from the boundary portion of the fifth minimum reading region r5 is detected as an edge on the leading end side of the correction pattern CP. Then, a trimming process is performed to delete the data in the minimum reading area column outside the third minimum reading area r3 from the reading density data corresponding to the correction pattern CP.

  Further, if FIG. 20 is read density data when the extension portion L located on the rear end side of the correction pattern is read, the fourth minimum reading region r4 detected as the center position of the outermost raster line Le. The edge of the rear end side of the sixth minimum reading region r6 located second in the outward direction of the correction pattern CP from the boundary portion between the correction pattern CP and the fifth minimum reading region r5 is detected as the rear end side edge of the correction pattern CP. To do. Then, a trimming process is performed to delete the data in the minimum reading area column outside the sixth minimum reading area r6 from the reading density data corresponding to the correction pattern CP.

Next, a process for detecting an edge using the extension when the number of continuous minimum reading areas included in the width of the extension in the sub-scanning direction is an odd number will be described.
If the number of consecutive minimum reading areas included in the calculated width of the extending portion in the sub-scanning direction is an odd number, half the number is calculated by one less than the calculated number of minimum reading areas. For example, when the number of consecutive minimum reading areas included in the calculated width of the extending portion in the sub-scanning direction is “3”, “1” is calculated. Then, based on the gravity center position in the density distribution in the sub-scanning direction at the distance KX1 and the gravity center position in the density distribution in the sub-scanning direction at the distance KX2, the center position of the outermost raster line L is a position g1 shown in FIG. (Step: S250). In this case, the minimum reading area including the center position g1 of the detected endmost raster line L, that is, the fourth minimum reading area r4 is the center minimum reading located at the center in the sub-scanning direction in the extending portion. Detected as a region.

  Then, the computer 720 uses the detected position information of the central minimum reading region r4 and the calculated “1” as an edge in the main portion M of the correction pattern CP as an edge on the leading end side of the minimum reading region r3, Then, an edge on the rear end side of the minimum reading area r5 is detected (step: S260).

[Second Embodiment]
Step S250: Step of Detecting the Position of the Endmost Raster Line FIG. 21 is a diagram for explaining a second embodiment of processing for detecting an edge using the extended portion of the endmost raster line of the correction pattern. It is.
The graph on the left side of FIG. 21 shows an image of the read density data around the outermost raster line among the data read by one photodiode in the CCD image sensor 14 in the read density data whose inclination has been adjusted. Show. Further, the diagram on the right side of FIG. 21 is a diagram showing an image of the extending portion L in the read image when the read density data indicates the density as in the graph on the left side. In FIG. 21, as read density data around the endmost raster line, read density data read by a photodiode corresponding to a position at a distance KX1 in the main scanning direction from the read reference position Pk, from the read reference position Pk. Reading density data corresponding to the distance KY0 is shown in the sub-scanning direction.

  The computer 720 stores information indicating the printing resolution when the correction pattern is printed and the reading resolution when the printed correction pattern is read by the scanner 400. The computer 720 stores the information. Calculating the number of consecutive minimum reading areas “4” and the half thereof “2” included in the width of the extending portion L in the sub-scanning direction based on the print resolution and the reading resolution being The same as in the first embodiment.

  The computer 720 sets the reading density data corresponding to the distance KY0 in the sub-scanning direction from the reading reference position Pk, and the distance KY0 in the sub-scanning direction from the position separated by the distance KY3 in the sub-scanning direction from the reading reference position Pk. From the corresponding reading density data, the minimum reading area where the density reaches a peak is detected, and the position information is stored. At this time, when the number of continuous minimum reading areas included in the width of the extending portion L in the sub-scanning direction is an even number, the minimum reading area where the density reaches a peak is the two minimum reading areas from the higher density side. The reading area is detected and the position information is stored. That is, it is detected that the boundary portion that is the middle between the two detected minimum reading regions is the center of the extension L. In the example of FIG. 21, the fourth and fifth minimum reading areas r4 and r5 are detected as the minimum reading areas where the density reaches a peak, and the position information is stored. Then, it is detected that the middle of the detected minimum reading areas r4 and r5 is the center of the extension L.

  Hereinafter, in step 260, the position information of the boundary portion between the two minimum reading areas detected and half the number “2” of the number of the minimum reading areas included in the calculated width of the extending portion L in the sub-scanning direction. Thus, the processing for detecting the edge in the main portion M of the correction pattern CP is the same as that in the first embodiment.

Next, a process for detecting an edge using the extension when the number of continuous minimum reading areas included in the width of the extension in the sub-scanning direction is an odd number will be described.
When the number of consecutive minimum reading areas included in the calculated width of the extending portion in the sub-scanning direction is an odd number, the minimum reading area having the highest density, for example, a fourth reading area as the minimum reading area where the density reaches a peak It is assumed that the minimum reading area r4 is detected. In this case, the fourth minimum reading region r4 having the highest density is detected as the central minimum reading region located at the center in the sub-scanning direction in the extending portion L.
Then, the computer 720 determines the edge of the main portion M of the correction pattern CP from the detected position information of the central minimum reading region r4 and the calculated “1”, the edge on the leading end side of the minimum reading region r3, Then, it is detected as an edge on the rear end side of the minimum reading region r5 (step: S260).

  In the case of the second embodiment, since the position is detected in units of the minimum reading area, the processing for detecting the edge is easy, but the accuracy of the detected position is lowered. In addition, since the center position of the extended portion is specified by the minimum reading area where the density peak is reached, the influence of density variation increases depending on the reading position, and erroneous detection due to dust etc. is likely to occur. It is possible to obtain a more stable result in the first embodiment in which the position of the center of the extending portion is specified by the position of the center of gravity.

(7) Step 270: A step of converting the data so as to correspond to the number of raster lines included in the correction pattern (a step of converting the data so as to associate the data corresponding to the detected endmost raster lines with the row region).
The computer 720 uses the read density data of the minimum reading area having the trailing edge as the reading density data of the correction pattern CP from the read density data of the minimum reading area having the leading edge of the detected correction pattern CP. Extract.
Next, the computer 720 converts the data extracted as the read density data of the correction pattern and the read density data corresponding to each column area based on the number of raster lines included in the correction pattern CP. That is, using all the data extracted as the read density data of the correction pattern CP, conversion is performed so that one read density data corresponds to each row region by, for example, the bicubic method. At this time, in the main scanning direction, four read density data are converted as unit area data corresponding to one unit area. The read density data after the conversion is unit area density data indicating the density corresponding to each unit area constituting the correction pattern CP.

(8) Step 280: Step of calculating the average value of the density of each row area based on the converted data Next, the computer 720 calculates the unit area density corresponding to the main part M of the correction pattern CP of the converted data. From the data, unit area density data of a plurality of unit areas is extracted for each row area included in the sub-pattern SP for each density in the row area where the raster line constituting the main part M of the correction pattern CP is to be formed. The average value is calculated.

  The memory of the computer 720 stores position information indicating the distance in the main scanning direction between the single dot line J of the correction pattern CP and each sub-pattern SP.

  The computer 720 extracts unit area density data of a predetermined row area of the converted data, for example, a unit area of a central row area in the sub-scanning direction, and extracts the unit area density data from the reading reference position side in the main scanning direction. The center position of the single dot line J is detected by referring to and detecting the position of the center of gravity in the density distribution. The method for detecting the center of the single dot line J is the same as the method for detecting the center of the extended portion L in the sub-scanning direction of the correction pattern CP except for the direction.

  Based on the detected position of the single dot line J and position information indicating the distance in the main scanning direction between the single dot line J and each sub pattern SPka, SPkb, SPkc, SPkd, SPke stored in the memory, The unit area density data of a plurality of unit areas of each column area in which the raster lines forming the sub-patterns SPka, SPkb, SPkc, SPkd, and SPke are to be formed are extracted, and the plurality of extracted unit area density data Is obtained as density data for each row region.

  FIG. 22 is a diagram for explaining a process of extracting unit area density data of unit areas included in each column area constituting each subpattern. Here, a description will be given by taking as an example a sub-pattern SPka (sub-pattern having a density of 10%) arranged on the side closest to the single dot line J in the correction pattern CP.

  The computer 720 detects the center position of the single dot line J for each row region, and then uses the detected center position of the single dot line J as a reference based on the position information stored in the memory of the computer 720. Then, unit area density data of a plurality of unit areas as different parts in the central part of the 10% density sub-pattern existing in the area of width W3 from the position separated by X2 in the main scanning direction is extracted. That is, unit area density data of a plurality of unit areas in the central portion excluding unit areas existing in the width W4 on both sides in the main scanning direction from the 10% density sub-pattern. Then, for example, the average value of all the unit area density data included in the extracted central portion is calculated and used as density data of the row area in the 10% density sub-pattern. In this way, density data for each row area of the 10% density sub-pattern SPka is obtained from the front end side row area to the rear end side row area of the correction pattern.

  In addition, the position where the center of the single dot line J is detected, the position where the center of the single dot line J is detected, the sub pattern SPkb having a density of 30% existing in the region of the width W3 from the position separated by X2 + W3 in the main scanning direction with the position where the center of the single dot line J is detected With reference to the position where the center of the single dot line J is detected with the sub-pattern SPkc having a density of 50% present in the area of the width W3 from the position separated by X2 + W3 × 2 in the main scanning direction as a reference, X2 + W3 × 3 in the main scanning direction. A sub-pattern SPkd having a density of 70% and a position where a single dot line J is detected present in a region with a width W3 from a position separated by a distance, and present in a region with a width W3 from a position separated by X2 + W3 × 4 in the main scanning direction. The same applies to the sub pattern SPke having a density of 100%.

  That is, out of the width W3 of each sub-pattern SPkb, SPkc, SPkd, SPke, unit area density data of a plurality of unit areas different from each other in the central portion excluding the width W4 from both sides in the main scanning direction is extracted. Based on the unit area density data, an average value of the unit area density data for each row area is calculated. An average value of the calculated unit area density data is set as a read density value. Here, since the reading density value is simply the average value of the unit area density data based on the reading density data read by the scanner 400, the reading density value is the same as the reading density data when the density is the lowest white level. “0” is expressed as “255” when the density is the highest density level.

  In the present embodiment, the example of obtaining the average value of the unit region density data of all the unit regions included in the central portion of each sub-pattern SP has been described. However, the average value of all the unit regions included in the central portion is not necessarily used. It is not necessary. However, particularly in the case of the subpattern SP having a low density, the number of unit areas in which dots are not formed increases, and the difference in unit area density data for each unit area increases, so that the unit area density of as many unit areas as possible. It is desirable to obtain the average value of the data.

(9) Step 290: Step of calculating a correction value of a specific density based on the read density value Calculate a correction value at two specific densities based on the calculated read density value.
In the present embodiment, the print data is set such that the average value of the density of the row areas of the sub-pattern SP is the target density value of the specific density associated with the sub-pattern SP, and the density of each row area is the target density value. By correcting the tone values of the above, density unevenness between the respective row regions is suppressed. For this reason, first, the average value of the densities of the row regions constituting each sub-pattern SP is calculated for each specific density. The average value of the calculated densities is the target density value at each specific density.

  Next, a correction value for each row region is obtained based on the calculated target density value. Here, the correction values do not necessarily have to be obtained for all the specific densities, and it is only necessary to obtain correction values corresponding to some specific densities. In the present embodiment, correction values are calculated for two specific densities, a specific density of 30%, and a specific density of 50%.

FIG. 23 is a diagram for explaining the concept of how to obtain a correction value at a specific density.
As shown in the drawing, the read density value of the predetermined row area at the specific density 3 is compared with the target density value, and when the read density value of the row area A is larger than the target density value as in the row area A, When the read density value of the row area A at a specific density lower than the specific density 3 (here density 1) is used, and the read density value is smaller than the target density value as in the row area B, the density is higher than the specific density 3. The correction value is obtained by using the read density value of the row region B at a specific density with high density (here, density 5).

  For example, the read density value of a predetermined row area at a specific density of 50% is compared with the target density value. If the read density value is larger than the target density value, the read density value of the same row area at the specific density of 10% is set. If the read density value is smaller than the target density value, the correction value is obtained using the read density value of the same row area at the specific density of 100%. This is because the gradation value to be specified for printing the predetermined row area at the target density value in the predetermined row area is such that the read density value of the predetermined row area at a specific density of 50% is larger than the target density value. In such a case, the reading density value exists between the reading density value of the specific density of 50% and the reading density value of the specific density of 10%, and the reading density value of the predetermined row region at the specific density of 50% is smaller than the target density value. This is because a reading density value having a specific density of 50% and a reading density value having a specific density of 100% exist.

The correction value α _{50 at} the specific density of 50% is obtained by (Expression 2) and (Expression 3).
When the reading density value of the specific density 50% is larger than the target density value α ₅₀ = (C ₅₀ −C ₁₀ ) × (T−Z ₅₀ ) / {(Z ₁₀ −Z ₅₀ ) × C ₅₀ }
... (Formula 2)
T: target density value C _50: gradation value C ₁₀ in a concentration of 50% before correction: gradation value Z ₅₀ at a concentration of 10% before correction: concentration of 50% of the read density value Z _10: 10% strength reading density When the read density value of the specific density 50% is smaller than the target density value α ₅₀ = (C ₁₀₀ −C ₅₀ ) × (TZ ₅₀ ) / {(Z ₁₀₀ −Z ₅₀ ) × C ₅₀ }
... (Formula 3)
C ₁₀₀ : gradation value at a density of 100% before correction Z ₁₀₀ : read density value at a density of 100%

In the above-described embodiment, the example in which the read density values of 10% and 100% are used to determine the correction value α ₅₀ at the specific density of 50% has been described. However, the specific density to be used is the specific density to be obtained. Any two specific density values sandwiching the density value may be used. However, it is desirable to determine the specific density to be used so that the correction value can be set so that the output density changes as linearly as possible with respect to the designated gradation value change.

In the present embodiment, the correction value α is obtained for a specific density of 50% and a density of 30% among the five types of specific densities. When calculating the correction value α ₃₀ at a density of 30%, for example, a read density value of 10% density and a read density value of 70% density are obtained by (Equation 4) and (Equation 5).
When the reading density value at a specific density of 30% is larger than the target density value α ₃₀ = (C ₃₀ −C ₁₀ ) × (T−Z ₃₀ ) / {(Z ₁₀ −Z ₃₀ ) × C ₃₀ }
... (Formula 4)
T: target density value C _30: gradation value C ₁₀ in a concentration of 30% before correction: gradation value Z ₃₀ at a concentration of 10% before correction: concentration of 30% of the read density value Z _10: 10% strength reading density When the read density value of the specific density 30% is smaller than the target density value α ₃₀ = (C ₇₀ −C ₃₀ ) × (TZ ₃₀ ) / {(Z ₇₀ −Z ₃₀ ) × C ₃₀ }
... (Formula 5)
C ₇₀ : gradation value at a density of 70% before correction Z ₇₀ : read density value at a density of 70% In this way, correction values for each row region are obtained for each of two types of specific densities and stored in a memory ( S300).

Since the obtained correction value α ₅₀ is printed based on the gradation value given as the image data of the image to be printed, density unevenness occurs between the row regions. The ratio for correcting the obtained gradation value is shown for each row region. In the present embodiment, the image data indicates the density of each unit area with a gradation value of 0 to 255, and is set so that the gradation value of 0 to 100% is expressed with 256 gradations by the gradation value of 0 to 255. ing. That is, the change rate of the gradation value specified by the image data is equal to the change rate of the gradation value indicating the density to be printed. For this reason, when a gradation value designating a density of 50%, for example, “128” is designated by the image data, the corrected gradation value is “128 × (1 + α ₅₀ )”. In the case of a density of 30%, when a gradation value that designates a density of 30% is designated by image data, for example, “77”, the gradation value after correction is “77 × (1 + α ₃₀ ). "

The gradation values after correction for the densities other than the density 30% and the density 50% are the obtained density 30%, the density values corrected based on the correction value of the density 50%, and the gradation values of the density 50%, It is obtained by interpolating gradation values of density 0 and density 100%. At this time, the gradation value designating the density 0 is “0” and the gradation value designating the density 100% is “255”, which are extreme values of the gradation values, and are not corrected. That is, the correction values α ₀ and α _{100 at} the density 0 and 100% are both “0”.

FIG. 24 is a diagram for explaining the concept of processing for correcting image data based on a calculated correction value.
As shown in the figure, for example, when a gradation value F is given as image data, a gradation value “0” with a density of 0 and a gradation value “77 × (1 + α ₃₀ ) after correction with a density of 30% are obtained. Is converted into a corrected gradation value F ′ obtained by linear interpolation. When the gradation value G is given as image data, the gradation value after correction of 30% density “77 × (1 + α ₃₀ )” and the gradation value after correction of density 50 “128 × (1 + α _50). ) ”Is converted into a corrected gradation value G ′ obtained by linear interpolation. When the gradation value H is given as the image data, linear interpolation is performed between the gradation value “128 × (1 + α ₅₀ )” after correction of the density 50 and the gradation value “255” of the density 100%. Converted to the corrected gradation value H ′.

  When the printer driver detects the print command together with the image data to be printed, the printer driver first executes the resolution conversion process and the color conversion process described above. Then, the gradation value of each unit area of the color-converted image data is obtained by obtaining the corrected gradation value based on the two stored correction values for each row area and each ink color. The image data is converted into image data having a new gradation value. Halftone processing and rasterization processing are executed on the converted image data and output to the printer 1 as print data. The printer 1 prints an image based on the input print data.

  According to the printing system 700 of the present embodiment, when acquiring the correction value, the density of only the central portion in the moving direction of the row area in which each raster line forming the sub-pattern SP as the specific density pattern is formed. Since the reading result is used, the acquired correction value does not include the reading result of the density near the edge of the specific density pattern. For this reason, it is possible to obtain an appropriate correction value based on a reading result of a more appropriate density for correction. In particular, in the present embodiment, a plurality of correction values are acquired based on the reading results of the plurality of sub-patterns SP included in the correction pattern CP. Therefore, the image data is further converted based on the correction values corresponding to the plurality of densities. It is possible to correct appropriately.

  In addition, the correction pattern CP of the present embodiment has a specific density sub-pattern SP and another specific density sub-pattern SP having a density different from that of the sub-pattern SP. It is possible to narrow the area occupied by the CP on the paper S. Even when the sub-patterns SP having different densities are adjacent to each other, when acquiring the correction value, only the central portion in the moving direction of the row region in which each raster line constituting each sub-pattern SP is formed. Therefore, the density of adjacent sub-patterns SP may not affect the read density data of each other. For this reason, it is possible to acquire a more appropriate correction value.

  Further, the reading result for obtaining the correction value is not only the density of one unit area of the central part in the moving direction of the row area where each raster line is formed, but also a plurality of units of different parts in the central part. Since the average value of a plurality of read density data obtained by reading the density of the region, it is possible to obtain a correction value based on a more accurate density as the density of the central portion.

  Further, since the position of each sub-pattern SP is specified with reference to the center position of a single dot line printed in the same manner as each sub-pattern SP, each sub-pattern SP can be accurately detected without including a printing position shift with respect to the paper. It is possible to specify the position of the pattern SP. For this reason, it is possible to acquire an appropriate correction value based on accurate unit area density data corresponding to each row area where each sub-pattern SP is printed.

  Further, the scanner 400 reads the density of the unit area of each sub-pattern SP printed based on the gradation value indicating the specific density as density data for each minimum reading area in the scanner 400, so that it is indicated in the image data. It is possible to read the density in each unit area of the correction pattern CP printed with the gradation value as density data. Therefore, it is possible to associate the gradation value shown in the image data with the density data of the correction pattern CP printed based on this gradation value.

  Further, since the position of the ruled line is detected by detecting the barycentric position in the density distribution in the moving direction based on the density data of the minimum reading area arranged in the moving direction on the ruled line, only the density data of the individual minimum reading area is detected. Since the reliability is higher than when detecting the position of the ruled line, the position of the ruled line can be detected reliably and accurately.

  Further, in the present embodiment, the reading resolution of the scanner 400 is higher than the printing resolution at which the correction pattern CP is printed. Therefore, even if the printed ruled line is a ruled line having a width of 1 dot, for example, Density data exists over a plurality of minimum reading areas in the direction (main scanning direction). For this reason, it is possible to acquire more accurate density data when the ruled line is read.

=== Other Embodiments ===
The above embodiments are mainly described for the printing system, but it goes without saying that the disclosure of the printer 1, the printing apparatus, the printing method, and the like is included therein.
Moreover, although the printing system etc. as one embodiment were demonstrated, said embodiment is for making an understanding of this invention easy, and is not for limiting and interpreting this 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.
In this embodiment, the printing system and the printing method for correcting the density unevenness generated in the paper conveyance direction have been described. However, the printer 1 is configured by the above correction, such as vibration caused by the movement of the carriage on which the head is mounted. This is also applicable to vertical stripe-shaped density unevenness that occurs in the direction along the transport direction due to the mechanism that performs this.

<About the printer>
In the above-described embodiment, the printer 1 has been described as the printing unit. However, the present invention is not limited to this. For example, color filter manufacturing apparatus, dyeing apparatus, fine processing apparatus, semiconductor manufacturing apparatus, surface processing apparatus, three-dimensional modeling machine, liquid vaporization apparatus, organic EL manufacturing apparatus (particularly polymer EL manufacturing apparatus), display manufacturing apparatus, film formation The same technique as that of the present embodiment may be applied to various recording apparatuses to which an ink jet technique is applied such as an apparatus and a DNA chip manufacturing apparatus. These methods and manufacturing methods are also within the scope of application.

<About ink>
In the above-described embodiment, dye ink or pigment ink is ejected from the nozzles of the printer 1 from the nozzles. However, the ink ejected from the nozzle is not limited to such ink.

<About nozzle>
In the above-described embodiment, ink is ejected using a piezoelectric element. However, the method of ejecting ink is not limited to this. For example, other methods such as a method of generating bubbles in the nozzle by heat may be used.

<About the carriage moving direction for ejecting ink>
In the above-described embodiment, unidirectional printing in which ink is ejected only when the carriage 31 moves in the forward direction has been described as an example. However, the present invention is not limited to this, and so-called ink ejection is performed when the carriage 31 reciprocates in both directions. Bidirectional printing may be performed.

<Ink colors used for printing>
In the above-described embodiment, multicolor printing in which dots are formed by ejecting four colors of ink of cyan (C), magenta (M), yellow (Y), and black (K) onto the paper S has been described as an example. However, the ink color is not limited to this. For example, in addition to these ink colors, ink such as light cyan (light cyan, LC) and light magenta (light magenta, LM) may be used.
Conversely, monochrome printing may be performed using only one of the four ink colors.

It is explanatory drawing which showed the external appearance structure of the printing system. It is a block diagram for demonstrating the principal part of a printing system. It is a front view for demonstrating the structure of a scanner. It is a top view for demonstrating the structure of a scanner. 1 is a schematic diagram of an overall configuration of a printer according to an embodiment. 1 is a side sectional view of an overall configuration of a printer according to an embodiment. It is explanatory drawing which shows the arrangement | sequence of the nozzle in the lower surface of a head. It is explanatory drawing of the drive circuit of a head. It is a timing chart explaining each signal. FIG. 3 is a schematic explanatory diagram of basic processing performed by a printer driver. It is a flowchart of the operation | movement at the time of printing. FIG. 6 is a diagram for explaining density unevenness that occurs in a paper transport direction in an image printed in monochrome. 6 is a flowchart showing a flow of processes and the like related to the image printing method according to the embodiment. It is a flowchart which shows the procedure of the process which sets a correction value. It is a figure for demonstrating an example of printed correction pattern CP. It is a figure for demonstrating the reading reference position and reading area at the time of reading the pattern for a correction | amendment. It is a figure for demonstrating the process which detects the inclination of the pattern for a correction | amendment of black. FIG. 6 is a diagram for explaining a difference in distance from a reading reference position Pk to a center of gravity position in a density distribution in the sub-scanning direction at a distance KX1 and a distance KX2. It is a figure which shows the image of the reading density data after performing the rotation process of image data based on the detected inclination. It is a figure for demonstrating the process which detects an edge using the extension part of the most end raster line of the pattern for a correction | amendment. It is a figure for demonstrating the process which detects an edge using an extension part when an odd minimum reading area | region is equivalent to the width | variety of a raster line in a subscanning direction. It is a figure for demonstrating the process which extracts the unit area | region density data of the unit area | region which each row area | region which comprises each sub pattern has. It is a figure for demonstrating the concept of how to obtain | require the correction value in specific density. It is a figure for demonstrating the concept of the process which correct | amends image data based on the calculated correction value.

Explanation of symbols

1 printer (inkjet printer), 2 HP sensor, 4 support rails,
4a Support surface, 5 Document, 6 Regulation guide, 7 Exposure lamp, 8 Lens, 9 Mirror,
11 Document restriction plate, 11a Document abutting part, 12 Document platen glass,
12a Document placement surface, 13 Document table cover, 14 CCD image sensor,
15 Guide receiving portion, 16 reading carriage, 16a one end of the reading carriage,
18 drive unit, 20 transport unit, 21 paper feed roller, 22 transport motor,
23 transport roller, 24 platen, 24a groove, 25 paper discharge roller,
30 carriage unit, 31 carriage, 40 head unit, 41 head,
50 sensors, 51 linear encoders, 52 rotary encoders,
53 Paper detection sensor, 54 Paper width sensor, 60 Printer controller,
63 memory, 64 unit control circuit, 644A original drive signal generator,
644B drive signal shaping unit,
90 ink cartridge, 100 controller, 103 scanner controller,
117 memory, 181 timing belt, 182 pulley, 183 pulse motor,
184 idler pulley, 400 scanner, 700 printing system,
704 display device, 708 input device, 708A keyboard, 708B mouse,
710 recording / reproducing apparatus, 710A flexible disk drive apparatus,
710B CD-ROM drive, 720 computer,
721 application program, 722 video driver,
725 Printer driver, CP correction pattern,
CPc Cyan correction pattern, CPk Black correction pattern,
CPm magenta correction pattern, CPy yellow correction pattern, L extension,
Ls Endmost raster line on the front end side, Le Endmost raster line on the rear end side,
M main part of correction pattern, Nc cyan ink nozzle row,
Nk black ink nozzle row, Nm magenta ink nozzle row,
Ny yellow ink nozzle row, J single dot line, P absolute reference position,
Pc Cyan reading reference position, Pk black reading reference position,
Pm Magenta reading reference position, Py yellow reading reference position,
R1 to R4 minimum reading area row, r1 to r8 minimum reading area, S paper,
SP sub-pattern, SPka-SPke sub-pattern

Claims (11)

A plurality of nozzles provided along a predetermined direction, and based on image data for printing an image, ejecting ink while moving in a moving direction intersecting the predetermined direction to form a dot row on the medium;
The density of the central portion in the moving direction in each row region in which each dot row forming a specific density pattern printed by ejecting ink from the nozzles based on image data for printing an image of a specific density is formed Correction information for correcting to suppress density unevenness between the row regions, based on the read result of
A controller for correcting image data for printing an image based on the correction information;
A printing apparatus comprising: The printing apparatus according to claim 1,
The specific density pattern and another specific density pattern having a density different from the specific density pattern are arranged in the moving direction and printed on the medium,
Correction information corresponding to the other specific density pattern is acquired based on the density reading result of the central portion in the moving direction in each row region where each dot row constituting the other specific density pattern is formed. Characteristic printing device. The printing apparatus according to claim 2,
The printing apparatus, wherein the specific density pattern and the other specific density pattern are adjacent to each other. The printing apparatus according to any one of claims 1 to 3,
The printing apparatus according to claim 1, wherein an average value of reading densities of different portions in the central portion is used as the reading result. The printing apparatus according to any one of claims 2 to 4,
The specific density pattern and the other specific density pattern are printed on a medium as a correction pattern, together with the specific density pattern and ruled lines along the predetermined direction arranged at intervals in the moving direction,
The printing apparatus according to claim 1, wherein the central portion is specified based on the ruled line. The printing apparatus according to claim 5, wherein
A reading unit for reading the correction pattern;
The image data indicates a gradation value for each unit area formed on the medium,
The reading unit includes the unit area included in the specific density pattern printed based on the gradation value indicating the specific density and the other specific density pattern printed based on the other gradation value indicating the specific density. The printing apparatus is characterized in that the density is read as density data for each minimum reading area in the reading unit. The printing apparatus according to claim 6.
The controller detects a centroid position in the density distribution in the movement direction based on density data of the minimum reading area arranged in the movement direction on the ruled line, and based on the detected centroid position in the density distribution, A printing apparatus that detects a position of the ruled line in a moving direction. The printing apparatus according to claim 6 or 7,
The printing apparatus according to claim 1, wherein a reading resolution of the reading unit is higher than a printing resolution at which the correction pattern is printed. A plurality of nozzles provided along a predetermined direction, and based on image data for printing an image, ejecting ink while moving in a moving direction intersecting the predetermined direction to form a dot row on the medium;
The density of the central portion in the moving direction in each row region in which each dot row forming a specific density pattern printed by ejecting ink from the nozzles based on image data for printing an image of a specific density is formed Correction information for correcting to suppress density unevenness between the row regions, based on the read result of
A controller for correcting image data for printing an image based on the correction information;
Have
The specific density pattern and another specific density pattern having a density different from the specific density pattern are printed on the medium adjacent to the moving direction,
Based on the reading result of the density of the central portion in the moving direction in each row region where each dot row constituting the other specific density pattern is formed, the correction information corresponding to the other specific density pattern is acquired,
As the reading result, an average value of reading densities of different portions in the central portion is used,
The specific density pattern and the other specific density pattern are printed on a medium as a correction pattern, together with the specific density pattern and ruled lines along the predetermined direction arranged at intervals in the moving direction,
The central portion is identified with reference to the ruled line;
A reading unit for reading the correction pattern;
The image data indicates a gradation value for each unit area formed on the medium,
The reading unit includes the unit area included in the specific density pattern printed based on the gradation value indicating the specific density and the other specific density pattern printed based on the other gradation value indicating the specific density. Is read as density data for each minimum reading area in the reading unit,
The controller detects a centroid position in the density distribution in the movement direction based on density data of the minimum reading area arranged in the movement direction on the ruled line, and based on the detected centroid position in the density distribution, Detect the position of the ruled line in the moving direction,
The reading resolution of the reading unit is higher than the printing resolution at which the correction pattern is printed,
Each having information indicating the reading resolution and the printing resolution;
The controller calculates the number of continuous minimum reading areas included in the width of the ruled line in the moving direction based on the reading resolution and the printing resolution;
When the calculated number of the continuous minimum reading areas is an even number,
Detecting the middle of the minimum reading area having the two density data as the detected peak as the position of the ruled line in the moving direction;
When the calculated number of the consecutive minimum reading areas is an odd number,
A printing apparatus that detects a minimum reading area having the detected density data as the peak as a position of the ruled line in the moving direction. A plurality of nozzles are provided along a predetermined direction, and ejecting ink while moving in a moving direction intersecting with the predetermined direction based on image data for printing an image to form a dot row on a medium. In the printing device,
The density of the central portion in the moving direction in each row region in which each dot row forming a specific density pattern printed by ejecting ink from the nozzles based on image data for printing an image of a specific density is formed Correction information for correcting to suppress density unevenness between each of the row regions based on the read result of
A computer program for realizing a function of correcting image data for printing an image based on the correction information. A plurality of nozzles are provided along a predetermined direction for ejecting ink while moving in a moving direction intersecting the predetermined direction based on image data for printing an image to form a dot row on a medium. A step of printing a specific density pattern printed by ejecting ink from the nozzles based on image data for printing an image of a specific density;
In order to correct the density unevenness between the row regions based on the density reading result of the central portion in the moving direction in each row region where the dot rows constituting the specific density pattern are formed. Obtaining the correction information of
Correcting image data for printing an image based on the correction information;
A printing method characterized by comprising: