JP2008060922A - Method of correcting measured printing darkness value, printing method, corrected value calculation method, and method of manufacturing printing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correctly correct a measured value of printing darkness. <P>SOLUTION: In this method of correcting a measured printing darkness value, inks are discharged from a plurality of nozzles which move in the moving direction to form a dot string in each row region along the moving direction, and a pattern composed of a plurality of dots formed in the plurality of row regions which are arranged in a direction crossing the moving direction is formed on a medium. Then, the pattern formed on the medium is read by a scanner, and the printing darkness of each row region of the pattern is measured. By taking an average of the measured values of the printing darkness of the dots in a predetermined number of row regions which are arranged in the direction crossing the moving direction, the printing darkness of dots is calculated corresponding to each row region. Based on the calculated printing darkness corresponding to each row region, the measured value of the printing darkness is corrected in each row region. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a measured density value correction method, a printing method, a correction value calculation method, and a printing apparatus manufacturing method.

  Prints a print image on a medium by alternately repeating a dot forming operation to form dots on a medium (paper, cloth, OHP paper, etc.) by ejecting ink from a head that moves in the moving direction, and a transport operation to transport the medium. A printing apparatus is known. A print image printed by such a printing apparatus is configured by an infinite number of image pieces including dot rows arranged in the transport direction.

  The dot row constituting each image piece is formed by ink droplets ejected from the head nozzle landing on the medium. If an ink droplet of an ideal size lands on an ideal position, a dot row is formed in a predetermined region (row region), and an image piece having an ideal density is formed in that region. However, in practice, due to the influence of variations in processing accuracy and the like, shading occurs in the image piece formed in that region. As a result, striped density unevenness occurs in the printed image.

Therefore, a technique for suppressing such density unevenness and improving the image quality of a printed image has been proposed (see, for example, Patent Document 1).
In the density unevenness correction method of Patent Document 1, a density unevenness detection pattern is printed, and density unevenness correction is performed based on density data of the density unevenness detection pattern (also referred to as a correction pattern). The density data is obtained by reading the correction pattern with an image sensor and measuring the density of the read correction pattern.
JP-A-6-166247

  However, when the image sensor cannot correctly read the density of the correction pattern, there is a possibility that the measured value of the density of the column area of the correction pattern measured after the reading becomes an inappropriate value.

  The present invention has been made in view of such a problem, and an object of the present invention is to correctly correct the measured value of the density of the row region of the correction pattern.

In order to solve the above problems, the main present invention is:
By ejecting ink from a plurality of nozzles moving in the moving direction and forming dot rows in the row region along the moving direction, a plurality of rows formed in the plurality of row regions arranged in a direction crossing the moving direction Forming a pattern composed of the dot rows on the medium;
Read the pattern formed on the medium with a scanner,
Measure the density of each row area of the read pattern,
By calculating an average of the density measurement values of a predetermined number of the row regions arranged in a direction intersecting the moving direction, respectively, a calculated density value corresponding to each row region is obtained,
The measured density value correcting method is characterized in that the measured density value of each row area is corrected based on the calculated density value corresponding to each row area.

  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.

By ejecting ink from a plurality of nozzles moving in the moving direction and forming dot rows in the row region along the moving direction, a plurality of rows formed in the plurality of row regions arranged in a direction crossing the moving direction Forming a pattern composed of the dot rows on the medium;
Read the pattern formed on the medium with a scanner,
Measure the density of each row area of the read pattern,
By calculating an average of the density measurement values of a predetermined number of the row regions arranged in a direction intersecting the moving direction, respectively, a calculated density value corresponding to each row region is obtained,
A measured density value correction method, wherein the measured density value of each row area is corrected based on the calculated density value corresponding to each row area.
Based on the calculated density value corresponding to each row area, when correcting the measured value of density in each row area, even if the measured value of density in each row area of the read pattern becomes an inappropriate value It becomes possible to correct the measured value correctly.

  Further, in the measured density value correction method, a correction value corresponding to each column region is calculated according to a difference between the calculated density value corresponding to each column region and a predetermined reference density value, It is desirable to correct the measured values of the density in each row region based on the correction values. In such a case, the measurement value of each row region can be easily corrected based on the correction value.

  Further, in the measured density value correction method, the reference density value is an average value of the measured values of the density of the plurality of row regions that are larger than the predetermined number arranged in a direction intersecting the moving direction, and is calculated. The correction value is preferably a difference between the calculated density value and the average value. In such a case, the density of the pattern row region is directly reflected, and the correction value can be calculated easily.

  Further, in this measured density value correction method, when the calculated density value corresponding to one row region is obtained, the predetermined number of the one row region including the one row region is located between It is desirable that an average value of the measured values of the density in the row region is calculated, and the calculated average value is used as the calculated density value corresponding to the one row region.

  Further, in this measured density value correction method, when the calculated density value corresponding to the end row region located at the end of the plurality of row regions arranged in the direction intersecting the moving direction is obtained. It is preferable that the calculated density value of the row area where the calculated density value is obtained by calculating the average value is the calculated density value corresponding to the end row area. In such a case, the calculated density value of the end row region can be obtained easily and accurately.

  Further, in this measured density value correction method, when the pattern is formed on the medium, a dot forming process for forming the dot row, and the medium in a direction crossing the moving direction by a predetermined transport amount. Medium transport processing to be transported is repeated, and the predetermined transport amount is the same as the interval between one row region and another row region separated from the one row region by the predetermined number. It is desirable that In such a case, the measured value can be corrected without being affected by the density unevenness that occurs in the cycle of the transport amount of the medium. Thereby, in the density correction process, a correction value corresponding to the density unevenness can be calculated.

Further, the ink is ejected from a plurality of nozzles moving in the moving direction to form dot rows in the row region along the moving direction, thereby forming the plurality of row regions arranged in a direction intersecting the moving direction. Forming a pattern composed of a plurality of the dot rows on the medium;
Read the pattern formed on the medium with a scanner,
Measure the density of each row area of the read pattern,
By calculating an average of the density measurement values of a predetermined number of the row regions arranged in a direction intersecting the moving direction, respectively, a calculated density value corresponding to each row region is obtained,
Based on the calculated density value corresponding to each row area, modify the density measurement value of each row area,
Based on the corrected measurement value of the density of each row area, a correction value corresponding to each row area is calculated,
When forming a print image on a medium, a printing method comprising forming a dot row constituting the print image based on the correction value corresponding to the row region where the dot row is to be formed.
According to such a printing method, the correction value is appropriately calculated based on the measured value corrected based on the calculated density value, so that the gradation value is appropriately corrected. A suppressed print image can be formed on the medium.

  Further, in this printing method, when forming the pattern on the medium, a dot forming process for forming the dot row, and a medium for transporting the medium by a predetermined transport amount in a direction crossing the moving direction Transporting process is repeated, and the predetermined transport amount is the same as the interval between one row region and another row region separated from the one row region by the predetermined number. Is desirable. In such a case, the measurement value can be corrected without being affected by density unevenness (also referred to as transport cycle unevenness) that occurs in the cycle of the transport amount of the medium, and as a result, transport cycle unevenness is less likely to occur in the printed image.

  Further, in this printing method, the correction value corresponding to one row region is a measured value obtained by correcting the density of the one row region and an integral multiple of the predetermined transport amount from the one row region. Calculated by averaging the measured values of the density of another row area separated by a distance, and based on a correction value corresponding to the one row area when the print image is formed on the medium. Forming a dot row to be formed in the one row region and forming a dot row to be formed in another row region separated from the one row region by an integral multiple of the predetermined transport amount. It is desirable to form. In such a case, when the print image is formed on the medium, the correction value of one row area also serves as the correction value of the other row area, so that correction value data can be reduced.

  Further, in this printing method, when the pattern is formed on the medium, the medium is transported in a direction intersecting the moving direction by a dot forming process for forming the dot row and a medium transport roller. The processing is repeated, and the circumference of the medium transport roller has the same size as the interval between one row region and another row region separated from the one row region by the predetermined number. It is desirable. In such a case, the measurement value can be corrected without being affected by the density unevenness that occurs in the period of the circumference of the medium transport roller due to the eccentricity of the medium transport roller, and as a result, the correction corresponding to the density unevenness. The value can be calculated.

  Further, in this printing method, the plurality of nozzles are respectively provided at a constant interval in a direction intersecting the moving direction, and the fixed interval includes one row region and the one row region. It is desirable that the distance is smaller than the distance between the second row region and the other row region that is a predetermined number away from the second row region.

Further, the ink is ejected from a plurality of nozzles moving in the moving direction to form dot rows in the row region along the moving direction, thereby forming the plurality of row regions arranged in a direction intersecting the moving direction. Forming a pattern composed of a plurality of the dot rows on the medium;
Read the pattern formed on the medium with a scanner,
Measure the density of each row area of the read pattern,
By calculating an average of the density measurement values of a predetermined number of the row regions arranged in a direction intersecting the moving direction, respectively, a calculated density value corresponding to each row region is obtained,
Based on the calculated density value corresponding to each row area, modify the density measurement value of each row area,
A correction value calculation method, comprising: calculating a correction value corresponding to each column region based on the corrected measurement value of the density of each column region.
According to such a correction value calculation method, the correction value can be appropriately calculated by correctly correcting the measurement value based on the calculated density value.

In addition, a printing device having a memory is prepared,
A plurality of the rows arranged in a direction intersecting the moving direction by ejecting ink from a plurality of nozzles moving in the moving direction using the printing apparatus to form dot rows in a row region along the moving direction. Forming a pattern composed of a plurality of dot rows formed in a region on a medium;
Read the pattern formed on the medium with a scanner,
Measure the density of each row area of the read pattern,
By calculating an average of the density measurement values of a predetermined number of the row regions arranged in a direction intersecting the moving direction, respectively, a calculated density value corresponding to each row region is obtained,
Based on the calculated density value corresponding to each row area, modify the density measurement value of each row area,
Based on the corrected measurement value of the density of each row area, a correction value corresponding to each row area is calculated,
Information on the calculated correction value is stored in the memory.
According to such a printing apparatus manufacturing method, it is possible to manufacture a printing apparatus that stores correction values corresponding to the characteristics of individual printing apparatuses.

=== Configuration of Printing System ===
<Printing system>
FIG. 1 is a diagram illustrating the configuration of the printing system 100. The printing system is a system including at least a printing apparatus and a printing control apparatus that controls the operation of the printing apparatus. The printing system 100 according to the present embodiment includes a printer 1 as an example of a “printing apparatus”, a computer 110, a display device 120, an input device 130, a recording / reproducing device 140, and a scanner 150.

  The printer 1 prints an image on a “medium” such as paper, cloth, film, or OHP paper. The computer 110 is communicably connected to the printer 1. In order to cause the printer 1 to print an image, the computer 110 outputs print data corresponding to the image to the printer 1. Computer programs such as application programs and printer drivers are installed in the computer 110. The computer 110 is installed with a scanner driver for controlling the scanner 150 and receiving image data of a document read by the scanner 150.

<Printer>
FIG. 2 is a block diagram of the overall configuration of the printer 1. FIG. 3A is a schematic diagram of the overall configuration of the printer 1. FIG. 3B is a cross-sectional view of the overall configuration of the printer 1. Hereinafter, the basic configuration of the printer of this embodiment will be described.

  The printer 1 includes a transport unit 20, a carriage unit 30, a head unit 40, a detector group 50, and a controller 60. The printer 1 that has received print data from the computer 110, which is an external device, controls each unit (the conveyance unit 20, the carriage unit 30, and the head unit 40) by the controller 60. The controller 60 controls each unit based on the print data received from the computer 110 and prints an image on paper. The situation in the printer 1 is monitored by a detector group 50, and the detector group 50 outputs a detection result to the controller 60. The controller 60 controls each unit based on the detection result output from the detector group 50.

  The transport unit 20 transports a medium such as paper in a predetermined direction (hereinafter referred to as a transport direction). 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 as an example of a “medium transport roller”, a platen 24, and a paper discharge roller 25. The paper feed roller 21 is a roller for feeding the paper inserted into the paper insertion slot into the printer. 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. The paper discharge roller 25 is a roller for discharging the paper S to the outside of the printer, and is provided on the downstream side in the transport direction with respect to the printable area. The paper discharge roller 25 rotates in synchronization with the transport roller 23.

  The carriage unit 30 is for moving (also referred to as “scanning”) the head in a predetermined direction (hereinafter referred to as a moving direction). The carriage unit 30 includes a carriage 31 and a carriage motor 32 (also referred to as a CR motor). The carriage 31 can reciprocate in the moving direction. Further, the carriage 31 detachably holds an ink cartridge that stores ink. The carriage motor 32 is a motor for moving the carriage 31 in the movement direction.

  The head unit 40 is for ejecting ink onto paper. The head unit 40 has a head 41. The head 41 has a plurality of nozzles, and ejects ink intermittently from each nozzle. The head 41 is provided on the carriage 31. Therefore, when the carriage 31 moves in the movement direction, the head 41 also moves in the movement direction. Then, by intermittently ejecting ink while the head 41 is moving in the moving direction, dot rows (raster lines) along the moving direction are formed on the paper.

  FIG. 4 is an explanatory diagram showing the arrangement of nozzles on the lower surface of the head 41. On the lower surface of the head 41, a black ink nozzle group K, a cyan ink nozzle group C, a magenta ink nozzle group M, and a yellow ink nozzle group Y are formed. Each nozzle group includes a plurality of nozzles that are ejection openings for ejecting ink of each color. The plurality of nozzles of each nozzle group are aligned at a constant interval (nozzle pitch: k · D) along the transport direction. Here, D is the minimum dot pitch in the carrying direction (that is, the 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. The nozzles of each nozzle group are assigned a smaller number as the nozzles on the downstream side (# 1 to # 180). Each nozzle is provided with an ink chamber (not shown) and a piezo element (not shown). The ink chamber is expanded and contracted by driving the piezo element, and ink droplets are ejected from the nozzle.

  The detector group 50 includes a linear encoder 51, a rotary encoder 52, a paper detection sensor 53, an optical sensor 54, and the like. The linear encoder 51 is for detecting the position of the carriage 31 in the moving direction. The rotary encoder 52 is for detecting the rotation amount of the transport roller 23. The paper detection sensor 53 is for detecting the position of the leading edge of the paper to be printed. The optical sensor 54 is attached to the carriage 31. The optical sensor 54 detects the presence or absence of paper by the light receiving unit detecting reflected light of light irradiated on the paper from the light emitting unit.

  The controller 60 is a control unit for controlling the printer. The controller 60 includes an interface unit 61, a CPU 62, a memory 63, and a unit control circuit 64. The interface unit 61 is for transmitting and receiving data between the computer 110 which is an external device and the printer 1. The CPU 62 is an arithmetic processing unit for controlling the entire printer. The memory 63 is for securing an area for storing a program of the CPU 62, a work area, and the like, and includes storage elements such as a RAM and an EEPROM. The CPU 62 controls each unit via the unit control circuit 64 in accordance with a program stored in the memory 63.

<Scanner>
FIG. 5A is a longitudinal sectional view of the scanner 150. FIG. 5B is a top view of the scanner 150 with the upper lid 151 removed.

  The scanner 150 includes an upper cover 151, a document table glass 152 on which the document 5 is placed, a reading carriage 153 that moves in the sub-scanning direction while facing the document 5 through the document table glass 152, and a sub-scanning of the reading carriage 153. A guide member 154 for guiding in a direction, a moving mechanism 155 for moving the reading carriage 153, and a scanner controller (not shown) for controlling each part in the scanner 150 are provided. The reading carriage 153 receives an exposure lamp 157 for irradiating the original 5 with light, a line sensor 158 for detecting an image of a line in the main scanning direction (direction perpendicular to the paper surface in FIG. 5A), and reflected light from the original 5. An optical system 159 for guiding to the line sensor 158 is provided. A broken line inside the reading carriage 153 in the drawing indicates a locus of light.

  When reading the image of the document 5, the operator opens the upper cover 151, places the document 5 on the document table glass 152, and closes the upper cover 151. Then, the scanner controller moves the reading carriage 153 along the sub-scanning direction with the exposure lamp 157 emitting light, and reads the image on the surface of the document 5 by the line sensor 158. The scanner controller transmits the read image data to the scanner driver of the computer 110, whereby the computer 110 acquires the image data of the document 5.

=== Printing method ===
<About printing operation>
FIG. 6 is a flowchart of processing during printing. Each process described below is executed by the controller 60 controlling each unit in accordance with a program stored in the memory 63. This program has a code for executing each process.

  Print command reception (S001): First, the controller 60 receives a print command from the computer 110 via the interface unit 61. This print command is included in the header of print data transmitted from the computer 110. Then, the controller 60 analyzes the contents of various commands included in the received print data, and performs the following paper feed processing / conveyance processing / dot formation processing using each unit.

  Paper Feed Process (S002): The paper feed process is a process for supplying paper to be printed into the printer and positioning the paper at a print start position (also referred to as a cue position). The controller 60 rotates the paper feed roller 21 and the transport roller 23 to position the paper at the print start position.

  Dot Formation Process (S003): The dot formation process is a process for forming dots on the paper by intermittently ejecting ink from the head 41 that moves along the movement direction. The controller 60 drives the carriage motor 32 to move the carriage 31 in the movement direction, and ejects ink from the head 41 based on the pixel data included in the print data while the carriage 31 is moving. When ink droplets ejected from the head 41 land on the paper, dots are formed on the paper. Since ink is intermittently ejected from the moving head 41, a dot row (raster line) composed of a plurality of dots along the moving direction is formed on the paper.

  Conveyance process (S004): The conveyance process is a process of moving the paper relative to the head in the conveyance direction. The controller 60 rotates the transport roller 23 to transport the paper in the transport direction. By this carrying process, the head 41 can form dots in the next dot forming process at a position different from the position of the dots formed by the previous dot forming process.

  Paper discharge determination (S005): The controller 60 determines whether or not to discharge the paper being printed. If data to be printed remains on the paper being printed, no paper is discharged. Then, the controller 60 alternately repeats the dot formation process and the conveyance process until there is no more data to be printed, and gradually prints an image composed of dots on paper.

  Paper Discharge Process (S006): When there is no more data to be printed on the paper being printed, the controller 60 discharges the paper by rotating the paper discharge roller. The determination of whether or not to discharge paper may be based on a paper discharge command included in the print data.

  Print end determination (S007): Next, the controller 60 determines whether or not to continue printing. If printing is to be performed on the next paper, printing is continued and the paper feeding process for the next paper is started. If printing is not performed on the next paper, the printing operation is terminated.

<Raster line formation>
First, normal printing will be described. Normal printing in this embodiment is performed by a printing method called interlaced printing. Here, “interlaced printing” means printing in which unrecorded raster lines are sandwiched between raster lines recorded in one pass. “Pass” refers to dot formation processing, and “pass n” refers to n-th dot formation processing. A “raster line” is a row of dots arranged in the moving direction, and is also called a dot line.

  7A and 7B are explanatory diagrams of normal printing. FIG. 7A shows the head position and dot formation in pass n to pass n + 3, and FIG. 7B shows the head position and dot formation in pass n to pass n + 4.

For convenience of explanation, only one nozzle group of a plurality of nozzle groups is shown, and the number of nozzles in the nozzle group is also reduced. Although the head 41 (or nozzle group) is depicted as moving with respect to the paper, this figure shows the relative position of the head 41 and the paper, Is moved in the transport direction. Also, for convenience of explanation, each nozzle is shown as having only a few dots (circles in the figure), but in reality, ink droplets are ejected intermittently from nozzles that move in the direction of movement. Therefore, a large number of dots are arranged in the moving direction (the row of dots is a raster line). Of course, the dot may not be formed depending on the pixel data.
In the figure, nozzles indicated by black circles are nozzles that can eject ink, and nozzles indicated by white circles are nozzles that cannot eject ink. Further, in the figure, the dot indicated by a black circle is a dot formed in the last pass, and the dot indicated by a white circle is a dot formed in the previous pass.

  In this interlaced printing, each time the paper is transported at a constant transport amount F in the transport direction, each nozzle records a raster line immediately above the raster line recorded in the immediately preceding pass. In order to perform recording with a constant carry amount in this way, (1) the number N (integer) of nozzles that can eject ink is relatively prime to k, and (2) the carry amount F is N · The condition is that it is set to D. Here, N = 7, k = 4, F = 7 · D (D = 1/720 inch).

  However, there are places where raster lines cannot be formed continuously in the transport direction only by this normal printing. Therefore, printing methods called leading edge printing and trailing edge printing are performed before and after normal printing.

  FIG. 8 is an explanatory diagram of leading edge printing and trailing edge printing. The first five passes are leading edge printing, and the last five passes are trailing edge printing.

  In front-end printing, when the vicinity of the front end of a print image is printed, the paper is transported by a transport amount (1 · D or 2 · D) smaller than the transport amount (7 · D) during normal printing. In front-end printing, the nozzles that eject ink are not constant. In the trailing edge printing, as in the leading edge printing, when the vicinity of the trailing edge of the print image is printed, the conveying amount (1 · D or 2 · D) is smaller than the conveying amount (7 · D) during normal printing. Then, the paper is conveyed. Further, in the rear end printing, the nozzles that eject ink are not constant, as in the front end printing. As a result, a plurality of raster lines arranged continuously in the transport direction can be formed between the first raster line and the last raster line.

  An area where a raster line is formed only by normal printing is called a “normal printing area”. An area located on the leading edge side (downstream in the transport direction) of the paper from the normal printing area is referred to as a “leading edge printing area”. An area located on the rear end side (upstream side in the transport direction) of the normal print area is referred to as a “rear end print area”. Thirty raster lines are formed in the leading edge printing area. Similarly, 30 raster lines are also formed in the trailing edge printing area. On the other hand, approximately several thousand raster lines are formed in the normal print area, although it depends on the size of the paper.

  The arrangement of raster lines in the normal print area has regularity for each number of raster lines (here, 7) corresponding to the carry amount. The first to seventh raster lines in the normal printing region in FIG. 8 are formed by nozzle # 3, nozzle # 5, nozzle # 7, nozzle # 2, nozzle # 4, nozzle # 6, and nozzle # 8, respectively. The next eight and subsequent raster lines are also formed by the nozzles in the same order. On the other hand, it is difficult to find regularity in the arrangement of raster lines in the leading edge printing area and the trailing edge printing area as compared with the raster lines in the normal printing area.

=== Density Density Correction (Outline) ===
<About density unevenness (banding)>
Here, for the sake of simplification of description, the cause of density unevenness occurring in an image printed in a single color will be described. In the case of multicolor printing, the cause of density unevenness described below occurs for each color.

  In the following description, the “unit area” refers to a rectangular area virtually defined on a medium such as paper, and the size and shape are determined according to the printing resolution. For example, when the printing resolution is 720 dpi (moving direction) × 720 dpi (conveying direction), the unit area has a square shape with a size of about 35.28 μm × 35.28 μm (≈ 1/720 inch × 1/720 inch). Become an area. When the print resolution is 360 dpi × 720 dpi, the unit area is a rectangular area having a size of about 70.56 μm × 35.28 μm (≈ 1/360 inch × 1/720 inch). When an ink droplet is ideally ejected, the ink droplet lands on the center position of the unit region, and then the ink droplet spreads on the medium to form a dot in the unit region. One unit area corresponds to one pixel constituting image data. In addition, since a pixel is associated with each unit area, pixel data of each pixel is also associated with each unit area.

  Further, in the following description, “row region” refers to a region constituted by a plurality of unit regions arranged in the moving direction. For example, when the print resolution is 720 dpi × 720 dpi, the row region is a band-like region having a width of 35.28 μm (≈ 1/720 inch) in the transport direction. When ink droplets are ideally intermittently ejected from the nozzle moving in the moving direction, a raster line is formed in this row region. A plurality of pixels arranged in the movement direction are associated with the row area.

  FIG. 9A is an explanatory diagram of a state when dots are ideally formed. In the figure, since dots are ideally formed, each dot is accurately formed in the unit region, and the raster line is accurately formed in the row region. In the figure, the row region is shown as a region sandwiched between dotted lines, and here is a region having a width of 720 dpi. In each row region, an image piece having a density corresponding to the coloring of the region is formed. Here, for simplification of explanation, it is assumed that an image having a constant density is printed so that the dot generation rate is 50%.

FIG. 9B is an explanatory diagram of the influence of variations in nozzle processing accuracy. Here, a raster line formed in the second row region is formed closer to the third row region side (upstream in the transport direction) due to variations in the flight direction of the ink droplets ejected from the nozzles. Further, the amount of ink droplets ejected toward the fifth row region is small, and the dots formed in the fifth row region are small.
Although the image pieces having the same density should be formed in each row area originally, the image pieces are shaded according to the row areas due to variations in processing accuracy. For example, the image piece in the second row region is relatively light and the image piece in the third row region is relatively dark. Further, the image piece in the fifth row region becomes relatively light.
When the print image composed of such raster lines is viewed macroscopically, stripe-shaped density unevenness along the moving direction of the carriage is visually recognized. This density unevenness causes a reduction in image quality of the printed image.

  FIG. 9C is an explanatory diagram showing a state when dots are formed by the printing method of the present embodiment. In the present embodiment, the gradation value of the pixel data (CMYK pixel data) of the pixel corresponding to the row region is corrected so that a dark image piece is formed in the row region that is dark and easily visible. Further, the gradation value of the pixel data of the pixel corresponding to the row region is corrected so that a dark image piece is formed in a row region that is easily viewed. For example, the dot generation rate of the second row region in the figure is increased, the dot generation rate of the third row region is decreased, and the dot generation rate of the fifth row region is increased. The gradation value of the pixel data of the pixel corresponding to the column area is corrected. As a result, the dot generation rate of the raster lines in each row area is changed, the density of the image pieces in the row area is corrected, and density unevenness of the entire print image is suppressed.

  Incidentally, in FIG. 9B, the reason why the density of the image piece formed in the third row region is high is not due to the influence of the nozzles forming the raster line in the third row region, but the adjacent second row. This is due to the influence of nozzles that form raster lines in the region. For this reason, when a nozzle that forms a raster line in the third row region forms a raster line in another row region, the image piece formed in that row region is not always dark. That is, even if the image pieces are formed by the same nozzle, the density may be different if the nozzles that form adjacent image pieces are different. In such a case, the density unevenness cannot be suppressed with the correction value simply associated with the nozzle. Therefore, in this embodiment, the gradation value of the pixel data is corrected based on the correction value set for each row area.

  For this reason, in this embodiment, in the inspection process of the printer manufacturing factory, the printer prints a correction pattern, reads the correction pattern with a scanner, and determines each column area based on the density of each column area in the correction pattern. Is stored in the memory of the printer. The correction value stored in the printer reflects the density unevenness characteristic of each printer.

  Then, under the user who purchased the printer, the printer driver reads the correction value from the printer, corrects the gradation value of the pixel data based on the correction value, and generates print data based on the corrected gradation value Then, the printer performs printing based on the print data.

<About processing at printer manufacturing plants>
FIG. 10 is a flowchart of the correction value acquisition process performed in the inspection process after manufacturing the printer.

First, the inspector connects the printer 1 to be inspected to the computer 110 in the factory (S101). The computer 110 in the factory is also connected to the scanner 150, and in advance a printer driver for causing the printer 1 to print a test pattern, a scanner driver for controlling the scanner 150, and a correction read from the scanner. A correction value acquisition program for performing image processing, analysis, and the like on the pattern image data is installed.

Next, the printer driver of the computer 110 causes the printer 1 to print a test pattern (S102).
FIG. 11 is an explanatory diagram of a test pattern. FIG. 12 is an explanatory diagram of a correction pattern. In the test pattern, four correction patterns are formed for each color. Each correction pattern is composed of a band-shaped pattern of five types of density, an upper ruled line, a lower ruled line, a left ruled line, and a right ruled line. The belt-like patterns are each generated from image data having a constant gradation value, and the gradation values 76 (density 30%), 102 (density 40%), and 128 (density 50%) are sequentially from the left belt-like pattern. , 153 (density 60%) and 179 (density 70%), and the patterns are darker in order. These five types of gradation values (density) are referred to as “command gradation values (command density)” and are represented by symbols Sa (= 76), Sb (= 102), Sc (= 128), Sd (= 153) and Se (= 179). Since each belt-like pattern is formed by leading edge printing, normal printing, and trailing edge printing, it is composed of a raster line in the leading edge printing area, a raster line in the normal printing area, and a raster line in the trailing edge printing area. In normal printing, thousands of raster lines are formed in the normal printing area, but in printing the correction pattern, raster lines for eight cycles are formed in the normal printing area. Here, for simplification of explanation, it is assumed that the correction pattern is printed by the printing of FIG. 8, and the belt-like pattern has 30 raster lines in the front-end printing region and 56 normal printing regions (7 × 8 cycles). , And a total of 116 raster lines including 30 raster lines in the trailing edge printing area. The upper ruled line is formed by the first raster line (raster line on the most downstream side in the transport direction) constituting the belt-like pattern. The lower ruled line is formed by the final raster line (raster line on the most upstream side in the transport direction) constituting the belt-like pattern.

  Next, the inspector places the test pattern printed by the printer 1 on the platen glass 152 of the scanner 150, closes the upper cover 151, and sets the test pattern on the scanner 150. Then, the scanner driver of the computer 110 causes the scanner 150 to read the correction pattern (S103). Hereinafter, reading of a cyan correction pattern will be described (the reading of correction patterns for other colors is performed in the same manner).

  FIG. 13 is an explanatory diagram of the reading range of the cyan correction pattern. The range of the alternate long and short dash line surrounding the cyan correction pattern is the reading range when reading the cyan correction pattern. Parameters SX1, SY1, SW1, and SH1 for specifying this range are set in advance in the scanner driver by the correction value acquisition program. If the scanner 150 reads this range, the entire cyan correction pattern can be read even if the test pattern is set to the scanner 150 with a slight shift. By this processing, the image in the reading range in the drawing is read by the computer 110 as rectangular image data having a resolution of 2880 × 2880 dpi.

  Next, the correction value acquisition program of the computer 110 detects the inclination θ of the correction pattern included in the image data (S104), and performs a rotation process on the image data according to the inclination θ (S105).

FIG. 14A is an explanatory diagram of image data at the time of tilt detection. FIG. 14B is an explanatory diagram of detection of the position of the upper ruled line. FIG. 14C is an explanatory diagram of the image data after the rotation process. The correction value acquisition program includes KX1 pixel data from the left and KH pixel data from the top, and KX2 pixel data from the left and KH pixels from the top among the read image data. Retrieve the data. The parameters KX1, KX2, and KH are determined in advance so that the pixels extracted at this time include the upper ruled line and do not include the right ruled line and the left ruled line. Then, the correction value acquisition program obtains the gravity center positions KY1 and KY2 of the gradation values of the extracted KH pieces of pixel data in order to detect the position of the upper ruled line. Then, the correction value acquisition program calculates the inclination θ of the correction pattern based on the parameters KX1 and KX2 and the barycentric positions KY1 and KY2, and the rotation of the image data based on the calculated inclination θ. Process.
θ = tan ⁻¹ {(KY2-KY1) / (KX2-KX1)}

Next, the correction value acquisition program of the computer 110 trims unnecessary pixels from the image data (S106).
FIG. 15A is an explanatory diagram of image data at the time of trimming. FIG. 15B is an explanatory diagram of a trimming position on the upper ruled line. Similar to the processing in step S104, the correction value acquisition program includes pixel data of KX1 pixels from the left and KH pixels from the top, and pixel data of KX2 from the left, from the rotated image data. Thus, pixel data of KH pixels are extracted from the top. Then, in order to detect the position of the upper ruled line, the correction value acquisition program obtains the centroid positions KY1 and KY2 of the gradation values of the extracted KH pixel data, and calculates the average value of the two centroid positions. Then, the nearest pixel boundary is determined as a trimming position at a position that is ½ the width of the row area from the center of gravity position. In this embodiment, since the resolution of the image data is 2880 dpi and the width of the row area is 720 dpi, ½ of the width of the row area corresponds to the width of two pixels. Then, the correction value acquisition program cuts out the pixels above the determined trimming position and performs trimming.

  FIG. 15C is an explanatory diagram of the trimming position at the lower ruled line. As in the upper ruled line side, the correction value acquisition program includes KX1 pixel data from the left, KH pixel data from the bottom, and KX2 pixels from the left, among the rotated image data. Then, the pixel data of KH pixels are taken out from the bottom, and the barycentric position of the lower ruled line is calculated. Then, the nearest pixel boundary is determined as the trimming position at a position that is ½ the width of the row area from the center of gravity position. Then, the correction value acquisition program cuts out pixels below the trimming position and performs trimming.

  Next, the correction value acquisition program of the computer 110 converts the resolution of the trimmed image data so that the number of pixels in the Y direction is 116 (the same number as the number of raster lines constituting the correction pattern) (S107). ).

  FIG. 16 is an explanatory diagram of resolution conversion. If the printer 1 ideally forms a correction pattern including 116 raster lines of 720 dpi, and the scanner 150 ideally reads the correction pattern at 2880 dpi (4 times the resolution of the correction pattern), trimming is performed. The number of pixels in the Y direction of the subsequent image data should be 464 (= 116 × 4). However, in actuality, there are cases where the number of pixels in the Y direction of the image data does not become 464 due to the influence of misalignment during printing or reading. Here, the number of pixels in the Y direction of the image data after trimming is 470. The correction value acquisition program of the computer 110 uses the magnification of 116/470 (= [number of raster lines constituting the correction pattern] / [number of pixels in the Y direction of the trimmed image data]) for this image data. To perform resolution conversion (reduction processing). Here, the bicubic method is used for resolution conversion. As a result, the number of pixels in the Y direction of the image data after resolution conversion becomes 116. In other words, the image data of the correction pattern of 2880 dpi is converted into the image data of the correction pattern of 720 dpi. As a result, the number of pixels arranged in the Y direction and the number of column regions are the same, and the pixel columns and column regions in the X direction have a one-to-one correspondence. For example, the pixel column in the X direction positioned at the top corresponds to the first column region, and the pixel column positioned below corresponds to the second column region. In this resolution conversion, since the purpose is to set the number of pixels in the Y direction to 116, resolution conversion (reduction processing) in the X direction may not be performed.

  Next, the correction value acquisition program of the computer 110 measures the density of each of the five types of belt-like patterns in each row region (S108). Hereinafter, the measurement of the density of the left band-shaped pattern formed with the gradation value 76 (density 30%) in the first row area will be described (note that the measurement in the other row areas is performed in the same manner. The density of the belt-like pattern is also measured in the same manner).

  FIG. 17A is an explanatory diagram of image data when the left ruled line is detected. FIG. 17B is an explanatory diagram of detection of the position of the left ruled line. FIG. 17C is an explanatory diagram of the measurement range of the density of the band-like pattern having a density of 30% in the first row region. The correction value acquisition program extracts pixel data of KX pixels from the left, which are H2 pixels from the top, from the resolution-converted image data. The parameter KX is determined in advance so that the left ruled line is included in the pixels extracted at this time. Then, the correction value acquisition program obtains the barycentric position of the gradation value of the pixel data of the extracted KX pixels in order to detect the position of the left ruled line. It is known from the shape of the correction pattern that a strip-shaped pattern having a width of W3 and having a density of 30% exists on the right side by X2 from the position of the center of gravity (the position of the left ruled line). Therefore, the correction value acquisition program extracts pixel data in a dotted line range excluding the left and right W4 ranges of the belt-like pattern with reference to the barycentric position, and calculates an average value of gradation values of the pixel data in this range as 1 The measured value of the density in the second row region is 30%. Note that when measuring the density of a strip-like pattern having a density of 30% in the second row region, pixel data in a range one pixel below the dotted line range in the figure is extracted. In this way, the correction value acquisition program measures the density of the five types of belt-like patterns for each row region.

  FIG. 18 is a measurement value table summarizing the measurement results of the densities of the five types of cyan belt-like patterns. As described above, the correction value acquisition program of the computer 110 creates a measurement value table by associating the measurement values of the density of the five types of belt-like patterns for each row region. A measurement value table is also created for other colors. In the following description, the measured values of the band-shaped pattern of the gradation values Sa to Se are set to Ca to Ce for a certain row region, respectively.

  FIG. 19 is a graph of measured values of a band-like pattern having a cyan density of 30%, a density of 40%, and a density of 50%. Although each belt-like pattern is uniformly formed with each command gradation value, shading is generated for each row region. The density difference for each row area is a cause of density unevenness in the printed image.

  In order to eliminate the density unevenness, it is desirable that the measured value of each strip pattern is constant. Therefore, a process for making the measurement value of the belt-like pattern having the gradation value Sb (density 40%) constant will be considered. Here, the average value Cbt of the measurement values of all the row regions of the strip-like pattern having the gradation value Sb is determined as a target value of 40% density. In the row region i where the measurement value is lighter than the target value Cbt, in order for the density measurement value to approach the target value Cbt, it is considered that the gradation value should be corrected to be darker. On the other hand, in the row region j where the measured value is darker than the target value Cbt, in order for the measured value of density to approach the target Cbt, it is considered that the gradation value should be corrected to be lighter.

  Therefore, the correction value acquisition program of the computer 110 calculates a correction value corresponding to the row region (S109). Here, calculation of the correction value for the command gradation value Sb in a certain row region will be described. As will be described below, the correction value for the command gradation value Sb (density 40%) in the row region i of FIG. 19 is calculated based on the measured values of the gradation value Sb and the gradation value Sc (density 50%). Is done. On the other hand, the correction value for the command gradation value Sb (density 40%) of the row region j is calculated based on the measured values of the gradation value Sb and the gradation value Sa (density 30%).

FIG. 20A is an explanatory diagram of the target command tone value Sbt with respect to the command tone value Sb in the row region i. In this row area, the measured value Cb of the density of the strip pattern formed with the command tone value Sb shows a tone value smaller than the target value Cbt (in this row area, the average density of the strip pattern having a density of 40%. Paler). If the printer driver causes the printer to form a density pattern of the target value Cbt in this row area, the printer driver is instructed based on the target instruction gradation value Sbt calculated by the following equation (linear interpolation based on the straight line BC). That's fine.
Sbt = Sb + (Sc−Sb) × {(Cbt−Cb) / (Cc−Cb)}

FIG. 20B is an explanatory diagram of the target command tone value Sbt with respect to the command tone value Sb in the row region j. In this row area, the measured value Cb of the density of the strip pattern formed with the command tone value Sb shows a tone value larger than the target value Cbt (in this row area, the average density of the strip pattern having a density of 40%. Darker). If the printer driver causes the printer to form a density pattern of the target value Cbt in this row area, the printer driver is instructed based on the target instruction gradation value Sbt calculated by the following equation (linear interpolation based on the straight line AB). That's fine.
Sbt = Sb− (Sb−Sa) × {(Cbt−Cb) / (Ca−Cb)}

After calculating the target command tone value Sbt in this way, the correction value acquisition program calculates a correction value Hb for the command tone value Sb in this row region by the following equation.
Hb = (Sbt−Sb) / Sb

  The correction value acquisition program of the computer 110 calculates a correction value Hb for the gradation value Sb (density 40%) for each row region. Similarly, the correction value acquisition program calculates the correction value Hc for the gradation value Sc (density 50%) for each column region based on the measurement value Cc of each column region and the measurement value Cb or Cd. To do. Similarly, the correction value acquisition program calculates the correction value Hd for the gradation value Sd (density 60%) for each column region based on the measurement value Cd of each column region and the measurement value Cc or Ce. To do. For other colors, three correction values (Hb, Hc, Hd) are calculated for each row region.

  By the way, although there are 56 raster lines in the normal print area, there is regularity for every 7 raster lines. This regularity is taken into account when calculating the correction value for the normal printing area.

  When the correction value acquisition program calculates a correction value in the first row area of the normal print region (the 31st row region of the entire print region), the above-described measurement value Ca includes the values 1, 8, and The average value of the measured values of the density of 30% in the 15th, 22th, 29th, 36th, 43rd, and 50th eight row regions is used. Similarly, when calculating the correction value in the first row region of the normal print region (the 31st row region of the entire print region), the above-described measured values Cb to Ce include 1, 8, 15 of the normal print region. , 22, 29, 36, 43, and 50, the average values of the measured values of the respective densities in the row regions of the eight row regions are used. Then, as described above, the correction values (Hb, Hc, Hd) of the first row area of the normal print area are calculated based on the measured values Ca to Ce. As described above, the correction value of the row region of the normal print region is calculated based on the average of the measured values of the respective densities of every eighth row region. As a result, in the normal print region, correction values are calculated only for the first to seventh row regions, and correction values are not calculated for the eighth to 56th row regions. In other words, the correction values for the first to seventh seven row regions of the normal print region also become correction values for the eighth to 56th row regions.

  Next, the correction value acquisition program of the computer 110 stores information on the calculated correction value in the memory 63 of the printer 1 (S110).

  FIG. 21 is an explanatory diagram of a cyan correction value table. There are three types of correction value tables, one for the front end print area, one for the normal print area, and one for the rear end print area. In each correction value table, three correction values (Hb, Hc, Hd) are associated with each row region. For example, three correction values (Hb_n, Hc_n, Hd_n) are associated with the nth raster line in each row region. The three correction values (Hb_n, Hc_n, Hd_n) correspond to the command gradation values Sb (= 102), Sc (= 128), and Sd (= 153), respectively. The same applies to correction value tables for other colors.

  After the correction value is stored in the memory 63 of the printer 1, the correction value acquisition process ends. Thereafter, the connection between the printer 1 and the computer 110 is disconnected, the other inspections for the printer 1 are finished, and the printer 1 is shipped from the factory. The printer 1 also includes a CD-ROM that stores a printer driver.

<About processing under the user>
FIG. 22 is a flowchart of processing performed under the user.
The user who purchased the printer 1 connects the printer 1 to the computer 110 owned by the user (of course, a computer different from the computer at the printer manufacturing factory) (S201, S301). Note that the scanner 150 may not be connected to the user's computer 110.

  Next, the user sets the enclosed CD-ROM in the recording / reproducing apparatus 140 and installs the printer driver (S202). The printer driver installed in the computer requests the computer 110 to transmit correction values to the printer 1 (S203). In response to the request, the printer 1 transmits the correction value table stored in the memory 63 to the computer 110 (S302). The printer driver stores the correction value sent from the printer 1 in the memory (S204). Thereby, a correction value table is created on the computer side. After completing the processing so far, the printer driver enters a standby state until a print command is received from the user (NO in S205).

  Upon receiving a print command from the user (YES in S205), the printer driver generates print data based on the correction value (S206) and transmits the print data to the printer 1. The printer 1 performs a printing process according to the print data (S303).

FIG. 23 is a flowchart of print data generation processing. These processes are performed by the printer driver.
First, the printer driver performs resolution conversion processing (S211). The resolution conversion process is a process for converting image data (text data, image data, etc.) output from an application program into a resolution for printing on paper. For example, when the resolution when printing an image on paper is specified as 720 × 720 dpi, the image data received from the application program is converted into image data having a resolution of 720 × 720 dpi. Note that the image data after the resolution conversion process is 256-gradation data (RGB data) represented by an RGB color space.

  Next, the printer driver performs a color conversion process (S212). The color conversion process is a process for converting RGB data into CMYK data represented by a CMYK color space. This color conversion process is performed by the printer driver referring to a table (color conversion lookup table LUT) in which the gradation values of RGB data and the gradation values of CMYK data are associated with each other. Through this color conversion process, RGB data for each pixel is converted into CMYK data corresponding to the ink color. The data after the color conversion processing is CMYK data with 256 gradations represented by the CMYK color space.

  Next, the printer driver performs density correction processing (S213). The density correction process is a process for correcting the gradation value of each pixel data based on the corresponding correction value of the column region to which the pixel data belongs.

  FIG. 24 is an explanatory diagram of density correction processing for the nth row region of cyan. This figure shows how the gradation value S_in of the pixel data of the pixels belonging to the nth row region of cyan is corrected. Note that the corrected gradation value is S_out.

  If the gradation value S_in of the pixel data before correction is the same as the command gradation value Sb, the printer driver corrects the gradation value S_in to the target instruction gradation value Sbt, and the corresponding unit of the pixel data. An image having the target density Cbt can be formed in the region. That is, if the gradation value S_in of the pixel data before correction is the same as the command gradation value Sb, the gradation value S_in (= Sb) is set to Sb × using the correction value Hb corresponding to the command gradation value Sb. It is good to correct to (1 + Hb). Similarly, if the gradation value S of the pixel data before correction is the same as the command gradation value Sc, the gradation value S_in (= Sc) is preferably corrected to Sc × (1 + Hc).

  On the other hand, when the gradation value S_in before correction is different from the command gradation value, the gradation value S_out to be output is calculated by linear interpolation as shown in the figure. In the linear interpolation in the figure, linear interpolation is performed between the corrected gradation values S_out (Sbt, Sct, Sdt) corresponding to the command gradation values (Sb, Sc, Sd). However, the present invention is not limited to this. For example, the correction value H corresponding to the gradation value S_in is calculated by linearly interpolating between the correction values (Hb, Hc, Hd) corresponding to each command gradation value, and the correction value H is calculated based on the calculated correction value H. The corrected gradation value may be calculated as S_in × (1 + H).

  For the pixel data in the first to thirty-th column areas of the leading edge printing area, the printer driver corresponds to the first to thirty-th column areas stored in the correction value table for the leading edge printing area. Based on the correction value, density correction processing is performed. For example, for the pixel data in the first row area of the leading edge printing area, the printer driver uses the correction values (Hb_1, Hc_1, Hd_1) of the first row area in the correction value table for leading edge printing. Density correction processing is performed.

  Similarly, for pixel data in each of the first to seventh column regions (the 31st to 37th column regions of the entire print region) of the normal print region, the printer driver corrects the correction value for the normal print region. Density correction processing is performed based on the correction values corresponding to the first to seventh row regions stored in the table. However, although there are thousands of row regions in the normal print region, only the correction values corresponding to the seven row regions are stored in the correction value table for the normal print region. Therefore, for the pixel data in the eighth to fourteenth row areas of the normal print area, the printer driver stores the first to seventh row areas stored in the correction value table for the normal print area. Based on the corresponding correction value, density correction processing is performed. As described above, for the row region of the normal print region, the printer driver repeatedly uses the correction values corresponding to the first to seventh row regions for every seven row regions. Since the regular printing area has regularity for every seven row areas, the density unevenness characteristic is considered to be repeated in the same cycle. Therefore, the correction value data to be stored can be stored by repeatedly using the correction value in the same cycle. The amount is reduced.

Although the number of normal print areas of the correction pattern is 56, the number of the normal print areas of the print image printed by the user is larger than this, reaching several thousand. . A trailing edge printing area composed of 30 row areas is formed on the upstream side of the normal printing area in the transport direction (the trailing edge side of the paper).
In the trailing edge printing area, similarly to the leading edge printing area, the printer driver stores the pixel data in the first to thirty-th column areas of the trailing edge printing area in the correction value table for the trailing edge printing area. The density correction processing is performed based on the correction values corresponding to the first to thirty-th row regions.

  With the above-described density correction processing, a column area that is easily visually recognized as dark is corrected so that the gradation value of the pixel data (CMYK data) of the pixel corresponding to the column area becomes low. On the other hand, for a column region that is faint and easily visible, correction is performed so that the gradation value of the pixel data of the pixel corresponding to the column region is high. Note that the printer driver performs the correction process in the same manner for other row regions of other colors.

  Next, the printer driver performs halftone processing (S214). The halftone process is a process for converting high gradation number data into gradation number data that can be formed by a printer. For example, data representing 256 gradations is converted into 1-bit data representing 2 gradations or 2-bit data representing 4 gradations by halftone processing. In the halftone process, pixel data is created by using a dither method, γ correction, error diffusion method, or the like so that the printer can form dots dispersedly. When performing halftone processing, the printer driver refers to the dither table when performing the dither method, refers to the gamma table when performing γ correction, and stores the diffused error when performing the error diffusion method. Refer to the error memory. The data subjected to the halftone process has a resolution (for example, 720 × 720 dpi) equivalent to the RGB data described above.

  In the present embodiment, the printer driver performs halftone processing on the pixel data of the gradation value corrected by the density correction processing. As a result, in a row region that is dark and easily visible, the tone value of the pixel data in the row region is corrected to be low, so the dot generation rate of the dots that make up the raster line in the row region is low. On the other hand, the dot generation rate is high in the row region that is easily recognized visually.

  Next, the printer driver performs rasterization processing (S215). The rasterization process is a process of changing matrix image data in the order of data to be transferred to the printer. The rasterized data is output to the printer as pixel data included in the print data.

  If the printer performs a printing process based on the print data generated in this way, as shown in FIG. 9C, the dot generation rate of the raster line in each row area is changed, and the density of the image pieces in the row area is corrected. Thus, density unevenness of the entire printed image is suppressed.

  In the above description, the number of nozzles and the number of row regions (number of raster lines) are reduced for the sake of simplicity of description, but in practice, the number of nozzles is 180, for example, the row region of the leading edge print region Will be 360. However, the processing performed by the correction value acquisition program, printer driver, and the like is substantially the same.

=== About correction of measured value or target value ===
<<< About the effect when the measured value of concentration is inappropriate >>>
As described in the section “Problems to be Solved by the Invention”, the scanner 150 cannot correctly read the density of the correction pattern (specifically, the row area in which the dot row constituting the correction pattern is formed). In this case, the measured value of the density of the row area measured after reading is an inappropriate value. As a result, the density correction process is not performed correctly, and there is a possibility that uneven density in the printed image cannot be suppressed appropriately.

  In this section, the effect of the measurement of the density of the row area measured after reading becomes an inappropriate value will be described in detail, taking as an example the case where the measured density of the read correction pattern is tilted. To do.

FIG. 25A is a graph of measured values of the density of each row region of a 30% density belt-like pattern when the scanner is normal. When the scanner is normal, the measurement values are distributed in the vicinity of the average value Cbt of the measurement values.
FIG. 25B is a graph of the measured values of the density of each row region of the belt-like pattern having a density of 30% when the scanner is abnormal. For example, if the guide member 154 (see FIG. 5A) of the scanner 150 is attached obliquely, or if the upper cover 151 is not closed sufficiently and the document 5 is floating, the reading carriage 153 is moved according to the position in the sub-scanning direction. The optical distance between the document 5 and the line sensor 158 varies. As a result, when the output result of the line sensor 158 changes according to the position of the reading carriage 153 in the sub-scanning direction, the measurement value changes according to the position of the row region, and the measurement value may be inclined overall. Yes (in FIG. 25B, the graph of measured values is tilted so as to be generally slanted). In FIG. 25A and FIG. 25B, the measurement value of each row region of the normal print region is periodically changed every seven row regions.

As described above, when the measurement value is tilted according to the position of the row region, the correction value calculated based on the measurement value is also tilted according to the position of the row region. For example, in the row region on the front end side, since the density is measured to be higher than the actual density, a correction value that sets the gradation value S_in lower than necessary is set. On the other hand, in the row region on the rear end side, since the measurement is lighter than the actual density, a correction value that sets the gradation value S_in higher than necessary is set.
As described above, as a result of the inclination of the correction value depending on the position of the row area, the density-corrected print image is printed so as to gradually become darker from the front end side toward the rear end side, and the shading in the print image is thus increased. Unevenness cannot be suppressed appropriately.

<<<< Regarding Calculation Process of Correction Value Accompanying Correction of Measured Value or Target Value >>>>
In this embodiment, in order to prevent an adverse effect caused by an inappropriate measurement value, the measurement value or the target value is corrected, and each column region is corrected based on the corrected measurement value or the target value. The value is calculated.

<Correction value calculation process when correcting measurement values>
First, correction value calculation processing when correcting a measurement value will be described. In this calculation process, the calculated density value corresponding to each row region is calculated by calculating the average of the density measurement values of a predetermined number of row regions (specifically, seven row regions) arranged in the transport direction. Ask for each. Here, the calculated density value means an average value of the measured values of the density of the seven row regions arranged in the transport direction. Then, based on the calculated density value corresponding to each column area, the density measurement value of each column area is corrected, and the correction value for each column area is calculated based on the corrected density value of each column area. calculate.

  FIG. 26A is a graph of measured values and target values before correction processing. The graph of the measured value here is the same as the graph of FIG. 25B.

  First, the correction value acquisition program takes the fourth to 113th column regions as the calculation target range, and extracts the measured values of the density of the column regions in this range. Here, the reason why the first to third row regions and the 114th to 116th row regions are excluded from the calculation target range is that these row regions are located on the downstream side in the transport direction and on the upstream side in the transport direction, respectively. This is because the density of these row regions may be measured lightly by being positioned in the vicinity of the margin.

  Next, the correction value acquisition program calculates an approximate curve indicated by a thick line in FIG. 26A based on the measured value of the density of the row region within the calculation target range. This approximate curve is obtained by connecting calculated density values corresponding to the respective row regions, and a method for calculating the calculated density value will be described later. Further, the correction value acquisition program calculates the average value Cbt based on the measured value of the density of the row region within the calculation target range. This average value Cbt is the above-mentioned target value Cbt, and is not limited to the column region within the calculation target range, and is the target value for all the column regions.

  Here, the calculation method of the calculated density value will be described by taking the calculation method of the calculated density value of the nth and (n + 1) th row regions as an example.

  FIG. 27A is a schematic diagram for explaining a method of calculating the calculated density value of the nth row region. FIG. 27B is a schematic diagram for explaining a calculation method of the calculated density value of the (n + 1) th row region. Note that n is an integer of 7 or more and 110 or less.

  The correction value acquisition program calculates the calculated density value of the nth column region by averaging the measured values of the densities of the seven column regions from the (n−3) th column region to the (n + 3) th column region. In other words, the average value obtained by averaging the measured values of the densities of the seven row regions that are row regions within the averaging range is the nth row that is the row region located in the middle of the seven row regions. This is the calculated density value of the area. Similarly, the correction value acquisition program calculates the calculated density value of the (n + 1) th column region by averaging the measured values of the densities of the seven column regions from the (n-2) th column region to the (n + 4) th column region. calculate. In this way, the calculated density values corresponding to the seventh to 110th row regions are sequentially calculated. For example, the calculated density value corresponding to the 10th row region is an average value of the measurement values of 7 row regions from the 7th row region to the 13th row region.

  In other words, the calculated density values of the seventh to 110th row regions are sequentially calculated by the so-called moving average of the measurement values of the fourth to 113th row regions in the cycle of the seven row regions (moving average cycle). The That is, the aforementioned approximate curve is a moving average line.

  On the other hand, the fourth to sixth and 111th to 113th row regions are row regions within the calculation target range. When the correction value acquisition program obtains the calculated density values of these row regions, Do not perform the above averaging. This is because, for example, when the calculated density value of the sixth row region is obtained by averaging, the measurement value of the third row region outside the calculation target range is required. Therefore, when the correction value acquisition program obtains the calculated density values of these row areas, the calculated density of the row areas (that is, the seventh to 110th row areas) in which the calculated density values have already been calculated by averaging. Apply the value. Specifically, for the calculated density values corresponding to the fourth to sixth row areas, the calculated density value of the seventh row area closest to these row areas is applied, and the 111th to 113th row areas are applied. For the calculated density value, the calculated density value of the 110th row region is applied.

  Further, the calculated density values of the first to third column areas that are outside the calculation target range are the same as the calculated density values of the fourth to sixth column areas, that is, the calculated density of the seventh column area. Value is applied. Similarly, for the calculated density values of the 114th to 116th row regions, the same calculated density value as the 111th to 113th row regions, that is, the calculated density value of the 110th row region is applied.

  The correction value acquisition program calculates, for each column region, the difference between the approximate value (that is, the calculated density value) of the approximate curve corresponding to each column region and the average value Cbt, and uses this value as the correction value for that column region. And Then, the correction value acquisition program corrects the measurement value of each column region by adding or subtracting the correction value to the density measurement value of each column region. For example, the correction value acquisition program corrects the measurement value by adding the difference (correction value) between the calculated density value of the tenth row region and the average value Cbt to the measurement value of the tenth row region. .

  As described above, the correction value acquisition program calculates the correction value corresponding to each column area according to the difference between the calculated density value corresponding to each column area and the average value Cbt, and the density of each column area is calculated. Are corrected based on the correction values. FIG. 26B is a graph of measured values after correction processing. In the graph of measured values after correction, the measured value in each row region is a value near the average value Cbt as compared to FIG. 26A.

  The approximate curve (moving average line) indicates the tendency of fluctuation of each density value that is the target of calculation of the calculated density value of each row region. Here, the characteristics of the moving average line in this processing are as follows. explain.

  FIG. 26C is a schematic diagram enlarging a portion A of the leading edge print region shown in FIG. 26A. Unlike the case where the scanner 150 is normal, the measurement values before correction shown in FIG. 26A and FIG. 26C include a variation in density value due to the abnormality of the scanner 150. For this reason, the measured values in the normal printing area are inclined downward as a whole (note that the measured values move up and down in the seven row areas), and the leading edge printing area and trailing edge printing The fluctuation state of the measured value of the area is irregular as compared with the normal printing area. However, the variation of the measured value is not limited to this, and for example, the measured value may be curved as a whole.

  The moving average line in this process is a moving average of measured values (density values targeted for the calculated density value) including fluctuations in density values due to the abnormality of the scanner 150. For this reason, the tendency of fluctuation of the measurement value including the fluctuation of the density value due to the abnormality of the scanner 150 is indicated by the moving average line. Therefore, based on the moving average line of this processing, by adding or subtracting the variation of the density value caused by the abnormality of the scanner 150 to the measurement value of each row region, as shown in FIG. It is possible to correct the measurement value from which the fluctuation of the resulting density value has been removed (that is, correct the measurement value of each row region to be a value close to the target value).

  By the way, density unevenness having a predetermined cycle may occur in the printed correction pattern. In such a case, the measurement value of each row region also varies with a predetermined cycle (as shown in FIG. 25B, the predetermined cycle). Will move up and down). As this density unevenness, there is a density unevenness that occurs when a correction pattern is printed on a paper every predetermined transport amount (this density unevenness is also referred to as a transport amount periodic unevenness). If there is a change in the measurement value due to the conveyance amount period unevenness, the influence is reflected on the moving average line, and the correction of the measurement value may not be performed effectively.

  Therefore, in the present embodiment, the amount of paper transport {specifically, the amount of paper transport during normal printing (= 7 · D)} is seven from the nth row region and the nth row region. This is the same size as the space between the row regions (= 7 · D) between the n + 7th row regions that are separated from each other. For example, the amount of paper transport during normal printing is the same as the distance between the 50th row area and the 57th row area. As a result, a moving average line in which the conveyance amount period unevenness is difficult to be reflected can be calculated, and as a result, a measurement value including a variation in density value due to an abnormality of the scanner 150 can be corrected more correctly.

  In the above description, the paper conveyance amount during normal printing is described as 7 · D. For example, when the conveyance amount is 10 · D (that is, the paper conveyance amount and the row region interval). When the transport amount is different), the moving average line reflecting the transport amount cycle unevenness is calculated as compared with the case where the transport amount is 7 · D. As a result, the correction of the variation of the density value due to the abnormality of the scanner 150 is not appropriately performed on the measurement value.

  The description of the correction value calculation process will be continued. The correction value acquisition program calculates a correction value corresponding to each row region based on the corrected measurement value (S109). Here, the correction value of the row area of the normal print region is different from the correction value of the row region of the front end print region and the rear end print region, and every eight row regions (for example, 31, 38, 45,. 52, 59, 66, 73, and 80th (eight column regions) are calculated based on the average of the measured values after correction of each density. As a result, correction values are calculated only for the first to seventh seven row regions (31st to 37th row regions of the entire print region) of the normal print region, and the eighth to 56th normal print region. Correction values are not calculated for the first row area (the 38th to 86th row areas of the entire print area).

  Next, as shown in FIG. 21, the correction value acquisition program stores information on the calculated correction value in the memory 63 of the printer 1 (S110). Under the user, the printer driver performs density correction processing based on the correction value calculated based on the corrected measurement value to generate print data, and the printer performs printing based on the print data.

  By executing the correction value calculation process accompanied by the correction of the measurement value described above, the following effects can be obtained. That is, as described above, based on the moving average line, a measurement value from which the fluctuation of the density value due to the abnormality of the scanner 150 has been removed is obtained (the corrected measurement value is a value near the target value). Therefore, the correction value, which is the difference between the corrected measurement value and the target value, is a value from which the fluctuation of the density value due to the abnormality of the scanner 150 is removed. Therefore, even when the scanner 150 is abnormal, a correction value that can appropriately eliminate the density unevenness can be calculated for each row region, and as a result, the density unevenness in the printed image can be appropriately suppressed.

  Further, as described above, since the transport amount during normal printing is the same as the interval between the nth row region and the n + 7th row region (row region interval), the corrected measurement value (after correction) In this measurement value, the correction value corresponding to the conveyance amount period unevenness can be calculated by calculating the correction value based on the influence of the conveyance amount period unevenness). This makes it difficult for the conveyance amount cycle irregularity to occur.

<Regarding correction value calculation processing when the target value is corrected>
The correction value calculation process when correcting the measurement value has been described above, but the correction value calculation process when correcting the target value without correcting the measurement value will be described below. In this calculation process, by calculating the average of the measured values of the density of a predetermined number of row areas (seven row areas) arranged in the transport direction, the calculated density value corresponding to each row area is obtained, respectively. Based on the calculated density value corresponding to the area, a target value for calculating the correction value corresponding to the density of each column area, and a predetermined target value is corrected for each column area. Then, based on the corrected target value of each row area, a correction value corresponding to each row area is calculated.

  FIG. 28A is a graph of target values and measured values before correction processing. The graph of the measured value here is the same as the graph of FIG. 25B (graph of FIG. 27A).

  First, the correction value acquisition program in this process uses the fourth to 113th column areas as calculation target ranges as in the case of the “correction value calculation process with correction of measurement values”, and sets the column area in this range. Take the concentration measurement. The reason why the first to third column regions and the 114th to 116th column regions are excluded from the calculation target range is as described above.

  Next, the correction value acquisition program calculates an approximate curve indicated by a thick line in FIG. 28A (same as the approximate straight line shown in FIG. 27A) based on the measured value of the density of the row region within the calculation target range. This approximate curve (moving average line) is obtained by connecting the calculated density values corresponding to the respective row regions, and the calculation method of the calculated density value is the same as in the case of “correction value calculation process with correction of measured value”. The same is true (see FIGS. 27A and 27B). Further, the correction value acquisition program calculates the average value Cbt based on the measured value of the density of the row region within the calculation target range. This average value Cbt is a target value for all the column regions, not limited to the column region within the calculation target range.

  Next, for each row region, the correction value acquisition program calculates the approximate value (ie, calculated density value) of the approximate curve corresponding to each row region, and the target value (ie, average value Cbt) determined in advance before correction. ) Is calculated, and this value is used as the correction value for the row region. Then, the correction value acquisition program corrects the target value Cbt of each column region by adding or subtracting the correction value to the target value Cbt determined in advance before the correction of each column region. For example, the correction value acquisition program adds the difference between the calculated density value of the tenth row region and the average value Cbt to the corresponding target value (average value Cbt) of the tenth row region, thereby obtaining the target value. Correct it.

  FIG. 28B is a graph of the target value Cbt ′ after the correction process, and this graph matches the approximate curve. The target value Cbt before correction is the same value in all the column regions, but the target value Cbt ′ after correction is a value corresponding to each column region. Thus, in this process, the target value is corrected to the calculated density value.

  Next, the correction value acquisition program calculates a correction value corresponding to each row region based on the corrected target value Cbt ′ (S109). Here, in the “calculation of correction values accompanied by correction of measured values”, the first to seventh seven row regions of the normal print region (the seventh to thirty seventh row regions of the entire print region). In this process, the correction values for all the row regions (31st to 86th row regions) of the normal print region are the same as in the case of the front end print region and the rear end print region. Calculation is performed.

  Next, the correction value acquisition program stores information on the calculated correction value in the memory 63 of the printer 1 (S110). Here, the correction values of the row areas of the normal print area stored in the memory 63 are not the correction values of all the row areas of the normal print area, but every eighth row area (for example, 31, 38, 45, 52, 59, 66, 73, and 80 (the eight column regions) are averaged correction values (see FIG. 21).

  Under the user, the printer driver performs density correction processing based on the correction value calculated based on the corrected target value Cbt ′ to generate print data, and the printer performs printing based on the print data. Do.

  By executing the correction value calculation process involving the correction of the target value described above, the same effect as in the case of the “correction value calculation process involving the correction of the measurement value” can be obtained. That is, by correcting the target value (Cbt) based on the moving average line obtained by moving and averaging the measurement values including the variation of the density value caused by the abnormality of the scanner 150, the density value caused by the abnormality of the scanner 150. The target value (Cbt ′) including the fluctuation amount is obtained (the corrected target value becomes a value in the vicinity of the measured value). For this reason, the correction value, which is the difference between the corrected target value and the measured value including the variation in the density value due to the abnormality of the scanner 150, has a variation in the density value due to the abnormality in the scanner 150. The removed value. Therefore, even when the scanner 150 is abnormal, a correction value that can appropriately eliminate the density unevenness can be calculated for each row region, and as a result, the density unevenness in the printed image can be appropriately suppressed.

  Further, since the calculation method of the moving average line in this process is “correction value calculation process with correction of measured value”, it is possible to calculate the correction value corresponding to the conveyance amount period unevenness, and as a result, the print image This makes it difficult for the conveyance amount cycle irregularity to occur.

=== Summary ===
In the above embodiment, (1) by ejecting ink from a plurality of nozzles moving in the moving direction and forming “dot rows” (raster lines) in the row region along the moving direction, A “pattern” (correction pattern) composed of a plurality of raster lines formed in a plurality of row regions arranged in the “crossing direction” (conveying direction) is formed on “medium” (paper), and (2) the medium The formed correction pattern is read by the scanner 150, (3) the density of each row area of the read correction pattern is measured, and (4) a predetermined number of row areas (seven row areas) arranged in the transport direction. ) By calculating the average of the measured density values, respectively, to obtain a calculated density value corresponding to each row area, and (5) measuring the density of each row area based on the calculated density value corresponding to each row area. Modify each value We are and. Thereby, the following effects are produced.

  That is, the above-described calculated density value (moving average line) is a measured value (a density value of a predetermined number of row regions subjected to the calculated density value) including a variation in density value caused by an abnormality of the scanner 150. It is a moving average. For this reason, the tendency of fluctuation of the measured value including the fluctuation of the density value due to the abnormality of the scanner 150 is shown in the calculated density value (the moving average line). Therefore, based on the moving average line of this processing, by adding or subtracting the variation of the density value caused by the abnormality of the scanner 150 to the measurement value of each row region, as shown in FIG. It becomes possible to correct the measurement value from which the fluctuation of the resulting density value has been removed.

  In the above embodiment, the correction value corresponding to each row region is calculated based on the corrected measurement value of the density of each row region. As described above, since the correction value is obtained by the difference between the measured value of the density of the row region and the predetermined target value, if the measured value is correctly corrected based on the calculated density value, the corrected measured value becomes the target value. It becomes a value near (Cbt shown in FIG. 26A etc.), and the correction value can be calculated appropriately.

  In the above-described embodiment, when a print image is formed on paper, a raster line constituting the print image is formed based on a correction value corresponding to a column region where the raster line is to be formed. Yes. As described above, print data is generated based on the gradation value corrected by the correction value, and a print image is formed on paper based on the generated print data. For this reason, if the correction value is appropriately calculated based on the measured value corrected based on the calculated density value, the gradation value is appropriately corrected, and as a result, the printed image in which the density unevenness is suppressed is printed on the paper. Can be formed.

  In the above embodiment, when the “printing apparatus” (printer 1) is manufactured, the information regarding the calculated correction value is stored in the memory 63 of the printer 1. Since the density unevenness may vary depending on the characteristics of the individual printers 1, in the case of the above embodiment, the printer 1 storing the correction values corresponding to the characteristics of the individual printers 1 can be manufactured.

  Furthermore, in the above embodiment, the correction value corresponding to each row area is calculated according to the difference between the calculated density value corresponding to each row area and a predetermined “reference density value” (target value). Then, the measured values of the density in each row region are corrected based on the correction value. Thereby, based on the correction value calculated according to the difference between the calculated density value and the target value (Cbt shown in FIG. 26A and the like), the measurement value of each row region can be easily corrected.

=== Other Embodiments ===
Although the printer 1 and the printing system 100 as one embodiment have been described, the above-described embodiment is for facilitating the understanding of the present invention, and is not intended to limit the present invention. The present invention can be changed and improved without departing from the gist thereof, and it is needless to say that the present invention includes equivalents thereof.

For example, the printer 1 described above is separate from the scanner 150. However, it may be a multifunction device in which a printer and a scanner are integrated.
In the above-described embodiment, the correction value table is created by printing a test pattern in the inspection process at the time of manufacturing the printer 1, but the invention is not limited to this. For example, a user who has purchased the printer 1 may cause the printer 1 to print a test pattern, read the test pattern with the scanner 150, and create a correction value table. In this case, the correction value acquisition program may be included in the printer driver.
In the above-described embodiment, one raster line is formed by one nozzle. However, the present invention is not limited to this. For example, one raster line may be formed by two nozzles.

  In the above embodiment, as shown in FIG. 4, the number of nozzles in each nozzle group is 180 from # 1 to # 180, and the nozzle pitch size of these nozzles is 4 · D. However, the present invention is not limited to this. For example, the number of nozzles in each nozzle group may be 90, and the size of the nozzle pitch may be 8 · D.

Furthermore, in the above-described embodiment, the target value (Cbt shown in FIG. 26A and the like) is an average value of the measured values of the density of a plurality of row regions (fourth to 113th row regions) arranged in the transport direction. The corrected value is a difference between the calculated density value and the average value, but is not limited to this. For example, the target value may be a value obtained by adding or subtracting a certain value to the average value.
However, when the target value is the average value, when correcting the measurement value of each row area, the density of the row area of the correction pattern is directly reflected, and the correction value can be easily calculated. More desirable.

Furthermore, in the above embodiment, when obtaining the calculated density value corresponding to one row region (here, n-th row region), the n-th row region including the n-th row region is An average value of the measured values of the density of the predetermined number 7 of row regions (that is, the (n−3) th to (n + 3) th row region) located between them is calculated, and the calculated average value is used as the nth row region. Although the corresponding calculated density value is set, the present invention is not limited to this. For example, the average value of the density measurement values of the n−3 th to n + 3 th row regions may be set to the calculated density value corresponding to the n−3 th row region.
However, when the average value of the density measurement values of the (n−3) th to (n + 3) th row regions is the calculated density value of the n−3th row region that is not the middle row region, There is a risk that the phase of the moving average line will be shifted by that amount. On the other hand, in the case where the average value is a calculated density value of a column region (for example, the n-th column region) located in the middle, it is possible to prevent the phase of the moving average line from shifting. More desirable.

Furthermore, in the above-described embodiment, end row regions (first to sixth row regions and 111th to 116th row regions) located at the ends of the plurality of row regions arranged in the transport direction, When calculating the calculated density value corresponding to the average density, the calculated density value of the row area from which the calculated density value is obtained by the calculation of the average value is set to the calculated density value corresponding to the end row area. (That is, the calculated density value of the seventh row area is changed to the calculated density value of the first to sixth row areas, and the calculated density value of the 110th row area is changed to the calculated density value of the 111th to 116th row areas. However, the present invention is not limited to this. For example, the calculated density value of the end row region may be obtained by calculation.
However, since the end row region (for example, the first to sixth row regions) is located in the vicinity of the margin, the measurement value of the end row region may be different from the actual density. When the calculated density value of the second row region is calculated and obtained, a calculated density that does not appropriately reflect the actual measurement value may be calculated. On the other hand, when the calculated density value of the row area (for example, the seventh row area) for which the calculated density value is obtained by calculating the average value is used as the calculated density value of the first to sixth row areas. Is more preferable in that the above-described problems are less likely to occur, and the calculated density values of the first to sixth column regions can be obtained easily and accurately.

Furthermore, in the above embodiment, when the correction pattern is formed on the paper, a dot forming process for forming a raster line and a predetermined transport amount of the paper in the transport direction (specifically, a transport amount during normal printing) F) is carried out repeatedly, and the carrying amount F during normal printing is set to one row area (nth row area) and another distance of the predetermined number 7 from the nth row area. Although the size is the same as the space between the row regions (n + 7th row region (also referred to as row region spacing)), the present invention is not limited to this. May be different in size from the column region interval between the nth column region and the n + 7th column region.
However, when the carry amount F during normal printing is the same as the row area interval, the movement is not affected by density unevenness (hereinafter also referred to as carry amount cycle unevenness) that occurs in the paper carry amount cycle. Based on the average line, the measured value can be corrected by the amount of change in the density value due to the abnormality of the scanner 150 (the effect of the unevenness in the conveyance amount remains in the corrected measured value). Then, by calculating the correction value based on the corrected measurement value, it is possible to calculate the correction value corresponding to the conveyance amount periodic unevenness, and as a result, the conveyance amount periodic unevenness hardly occurs in the printed image. Therefore, it is more desirable that the carry amount F during normal printing is the same as the row area interval.

In the above embodiment, the carry amount F during normal printing is the same size as the row region spacing, but the carry amount F during top-end printing and bottom-end printing is the same as the row region spacing. It may be a size. In such a case, based on a moving average line that is not affected by the density unevenness that occurs during the paper conveyance amount period at the time of upper-end printing or lower-end printing, the measurement value is calculated by the amount of change in the density value due to an abnormality in the scanner 150. Further, the circumference of the “medium conveyance roller” (conveyance roller 23) is the same as the interval between one row region and another row region that is a predetermined number away from the one row region. It is good also as being.
In such a case, based on the moving average line that is not affected by the density unevenness that occurs in the period of the circumferential length of the transport roller 23 due to the eccentricity of the transport roller 23, only the variation in the density value due to the abnormality of the scanner 150 occurs. The measured value can be corrected (the effect of the density unevenness remains in the corrected measured value). Then, by calculating the correction value based on the corrected measurement value, it is possible to calculate the correction value corresponding to the density unevenness of the circumference of the transport roller 23. As a result, the density unevenness is added to the print image. Is less likely to occur.

Further, in the above-described embodiment, the plurality of nozzles are provided at regular intervals (nozzle pitch: k · D) in the transport direction, and the nozzle pitch (= 4 · D) is equal to one row region (n Is smaller than the column region interval (= 7 · D) between the nth column region and another column region (n + 7th column region) separated from the nth column region by the predetermined number. . In this case, the row region interval is not an integer multiple of the nozzle pitch, but the nozzle pitch and the row region interval may be determined so that the row region interval is an integer multiple of the nozzle pitch. Good.
In such a case, based on the moving average line that is not affected by the density unevenness that occurs in the nozzle pitch cycle, the measured value can be corrected by the amount of change in the density value due to the abnormality of the scanner 150 (to the corrected measured value Is still affected by the density unevenness). Then, by calculating the correction value based on the corrected measurement value, it is possible to calculate the correction value corresponding to the density unevenness of the nozzle pitch cycle, and as a result, the density unevenness hardly occurs in the printed image. .

1 is a diagram illustrating a configuration of a printing system 100. FIG. 1 is a block diagram of an overall configuration of a printer 1. FIG. FIG. 3A is a schematic diagram of the overall configuration of the printer 1. FIG. 3B is a cross-sectional view of the overall configuration of the printer 1. FIG. 4 is an explanatory diagram showing the arrangement of nozzles on the lower surface of a head 41. FIG. 5A is a longitudinal sectional view of the scanner 150. FIG. 5B is a top view of the scanner 150 with the upper lid 151 removed. It is a flowchart of the process at the time of printing. 7A and 7B are explanatory diagrams of normal printing. FIG. 7A shows the head position and dot formation in pass n to pass n + 3, and FIG. 7B shows the head position and dot formation in pass n to pass n + 4. It is explanatory drawing of front end printing and rear end printing. FIG. 9A is an explanatory diagram of a state when dots are ideally formed. FIG. 9B is an explanatory diagram of the influence of variations in nozzle processing accuracy. FIG. 9C is an explanatory diagram showing a state when dots are formed by the printing method of the present embodiment. It is a flowchart of the correction value acquisition process performed at the inspection process after manufacture of a printer. It is explanatory drawing of a test pattern. It is explanatory drawing of the pattern for a correction | amendment. It is explanatory drawing of the reading range of the pattern for cyan correction. FIG. 14A is an explanatory diagram of image data at the time of tilt detection. FIG. 14B is an explanatory diagram of detection of the position of the upper ruled line. FIG. 14C is an explanatory diagram of the image data after the rotation process. FIG. 15A is an explanatory diagram of image data at the time of trimming. FIG. 15B is an explanatory diagram of a trimming position on the upper ruled line. FIG. 15C is an explanatory diagram of the trimming position at the lower ruled line. It is explanatory drawing of resolution conversion. FIG. 17A is an explanatory diagram of image data when the left ruled line is detected. FIG. 17B is an explanatory diagram of detection of the position of the left ruled line. FIG. 17C is an explanatory diagram of the measurement range of the density of the band-like pattern having a density of 30% in the first row region. It is the measurement value table which put together the measurement result of the density | concentration of five types of strip | belt-shaped patterns of cyan. It is a graph of the measured value of the strip | belt-shaped pattern of density 30%, density 40%, and density 50% of cyan. FIG. 20A is an explanatory diagram of the target command tone value Sbt with respect to the command tone value Sb in the row region i. FIG. 20B is an explanatory diagram of the target command tone value Sbt with respect to the command tone value Sb in the row region j. It is explanatory drawing of the correction value table of cyan. It is a flowchart of the process performed under the user. FIG. 9 is a flowchart of print data generation processing. It is explanatory drawing of the density correction process of the nth row | line area | region of cyan. FIG. 25A is a graph of measured values when the scanner is normal. FIG. 25B is a graph of measured values when the scanner is abnormal. FIG. 26A is a graph of measured values and target values before correction processing. FIG. 26B is a graph of measured values after the correction process. FIG. 26C is a schematic diagram enlarging a portion A of the leading edge print region shown in FIG. 26A. FIG. 27A is a schematic diagram for explaining a method of calculating the calculated density value of the nth row region. FIG. 27B is a schematic diagram for explaining a calculation method of the calculated density value of the (n + 1) th row region. FIG. 28A is a graph of target values and measured values before correction processing. FIG. 28B is a graph of the target value after the correction process.

Explanation of symbols

1 printer, 5 manuscripts,
20 transport unit, 21 paper feed roller, 22 transport motor (PF motor),
23 transport roller, 24 platen, 25 discharge roller,
30 Carriage unit, 31 Carriage,
32 Carriage motor (CR motor),
40 head units, 41 heads,
50 detector groups, 51 linear encoder, 52 rotary encoder,
53 Paper detection sensor, 54 Optical sensor,
60 controller, 61 interface unit, 62 CPU,
63 memory, 64 unit control circuit,
100 printing system, 110 computer,
120 display devices, 130 input devices,
140 recording / reproducing apparatus, 150 scanner,
151 Upper lid, 152 Document platen glass, 153 Reading carriage,
154 guide member, 155 moving mechanism, 157 exposure lamp,
158 Line sensor, 159 optical system

Claims (15)

By ejecting ink from a plurality of nozzles moving in the moving direction and forming dot rows in the row region along the moving direction, a plurality of rows formed in the plurality of row regions arranged in a direction crossing the moving direction Forming a pattern composed of the dot rows on the medium;
Read the pattern formed on the medium with a scanner,
Measure the density of each row area of the read pattern,
By calculating an average of the density measurement values of a predetermined number of the row regions arranged in a direction intersecting the moving direction, respectively, a calculated density value corresponding to each row region is obtained,
A measured density value correction method, wherein the measured density value of each row area is corrected based on the calculated density value corresponding to each row area. The method for correcting a measured density value according to claim 1,
According to the difference between the calculated density value corresponding to each row area and a predetermined reference density value, a correction value corresponding to each row area is calculated,
A measured density value correction method, wherein a measured value of density in each row region is corrected based on the correction value. The method for correcting a measured density value according to claim 2,
The reference density value is an average value of the measured values of the density of the plurality of row regions larger than the predetermined number arranged in a direction intersecting the moving direction,
The calculated correction value is a difference between the calculated density value and the average value. A measurement concentration value correction method according to any one of claims 1 to 3,
When obtaining the calculated density value corresponding to one row region,
Calculating an average value of the measured values of the density of the predetermined number of row regions including the one row region and between which the one row region is located;
The measured density value correction method, wherein the calculated average value is set to the calculated density value corresponding to the one row region. The method of correcting a measured density value according to claim 4,
When obtaining the calculated density value corresponding to an end row region located at an end of the plurality of row regions arranged in a direction intersecting the moving direction,
A method for correcting a measured density value, wherein the calculated density value of the row area for which the calculated density value is obtained by calculating the average value is used as the calculated density value corresponding to the end row area. A measured concentration value correction method according to any one of claims 1 to 5,
When forming the pattern on the medium, a dot formation process for forming the dot row and a medium conveyance process for conveying the medium by a predetermined conveyance amount in a direction crossing the moving direction are repeated.
The predetermined transport amount is the same size as an interval between one row region and another row region separated by the predetermined number from the one row region. Method. (A) By ejecting ink from a plurality of nozzles moving in the moving direction and forming dot rows in the row region along the moving direction, the ink is formed in the plurality of row regions aligned in the direction crossing the moving direction. Forming a pattern composed of a plurality of the dot rows on the medium,
Read the pattern formed on the medium with a scanner,
Measure the density of each row area of the read pattern,
By calculating an average of the density measurement values of a predetermined number of the row regions arranged in a direction intersecting the moving direction, respectively, a calculated density value corresponding to each row region is obtained,
Based on the calculated density value corresponding to each row area, modify the density measurement value of each row area,
(B) calculating a correction value corresponding to each column region according to a difference between the calculated density value corresponding to each column region and a predetermined reference density value;
Correct the measured value of the density of each row region based on the correction value,
(C) The reference density value is an average value of measured values of the density of the plurality of row regions that are larger than the predetermined number arranged in a direction intersecting the moving direction,
The calculated correction value is a difference between the calculated concentration value and the average value,
(D) When obtaining the calculated density value corresponding to one row region,
Calculating an average value of the measured values of the density of the predetermined number of row regions including the one row region and between which the one row region is located;
The calculated average value is set to the calculated density value corresponding to the one row region,
(E) When obtaining the calculated density value corresponding to an end row region located at an end of the plurality of row regions arranged in a direction intersecting the moving direction,
The calculated density value of the row area from which the calculated density value is obtained by calculating the average value is set to the calculated density value corresponding to the end row area,
(F) When forming the pattern on the medium, a dot forming process for forming the dot row and a medium transport process for transporting the medium by a predetermined transport amount in a direction intersecting the moving direction are repeated. And
The predetermined transport amount is the same size as an interval between one row region and another row region separated by the predetermined number from the one row region. Method. By ejecting ink from a plurality of nozzles moving in the moving direction and forming dot rows in the row region along the moving direction, a plurality of rows formed in the plurality of row regions arranged in a direction crossing the moving direction Forming a pattern composed of the dot rows on the medium;
Read the pattern formed on the medium with a scanner,
Measure the density of each row area of the read pattern,
By calculating an average of the density measurement values of a predetermined number of the row regions arranged in a direction intersecting the moving direction, respectively, a calculated density value corresponding to each row region is obtained,
Based on the calculated density value corresponding to each row area, modify the density measurement value of each row area,
Based on the corrected measurement value of the density of each row area, a correction value corresponding to each row area is calculated,
When forming a print image on a medium, a printing method comprising forming a dot row constituting the print image based on the correction value corresponding to the row region where the dot row is to be formed. The printing method according to claim 8, comprising:
When forming the pattern on the medium, a dot formation process for forming the dot row and a medium conveyance process for conveying the medium by a predetermined conveyance amount in a direction crossing the moving direction are repeated.
The printing method according to claim 1, wherein the predetermined conveyance amount has the same size as an interval between one row region and another row region separated by the predetermined number from the one row region. The printing method according to claim 9, comprising:
The correction value corresponding to one row region is
Averaging the corrected measurement value of the density of the one row area and the corrected measurement value of the density of another row area that is separated from the one row area by an integral multiple of the predetermined transport amount; By
Calculated,
When forming the print image on the medium, based on the correction value corresponding to the one row region,
Forming a dot row to be formed in the one row region, and forming a dot row to be formed in another row region separated from the one row region by an integral multiple of the predetermined transport amount,
A printing method characterized by forming. It is the printing method in any one of Claims 8-10, Comprising:
When forming the pattern on the medium, a dot formation process for forming the dot row and a medium conveyance process for conveying the medium in a direction intersecting the moving direction by a medium conveyance roller are repeated.
The circumference of the medium conveying roller is the same size as the interval between one row region and another row region separated from the one row region by the predetermined number. . It is a printing method in any one of Claims 8-11, Comprising:
The plurality of nozzles are respectively provided at regular intervals in a direction intersecting the moving direction,
The printing method according to claim 1, wherein the fixed interval is smaller than an interval between one row region and another row region separated from the one row region by the predetermined number. (A) By ejecting ink from a plurality of nozzles moving in the moving direction and forming dot rows in the row region along the moving direction, the ink is formed in the plurality of row regions aligned in the direction crossing the moving direction. Forming a pattern composed of a plurality of the dot rows on the medium,
Read the pattern formed on the medium with a scanner,
Measure the density of each row area of the read pattern,
By calculating an average of the density measurement values of a predetermined number of the row regions arranged in a direction intersecting the moving direction, respectively, a calculated density value corresponding to each row region is obtained,
Based on the calculated density value corresponding to each row area, modify the density measurement value of each row area,
Based on the corrected measurement value of the density of each row area, a correction value corresponding to each row area is calculated,
When forming a print image on a medium, the dot row constituting the print image is formed based on the correction value corresponding to the row region where the dot row is to be formed,
(B) When forming the pattern on the medium, a dot forming process for forming the dot row and a medium transport process for transporting the medium by a predetermined transport amount in a direction crossing the moving direction are repeated. And
The predetermined transport amount is the same size as an interval between one row region and another row region separated from the one row region by the predetermined number,
(C) The correction value corresponding to one row region is
Averaging the corrected measurement value of the density of the one row area and the corrected measurement value of the density of another row area that is separated from the one row area by an integral multiple of the predetermined transport amount; By
Calculated,
When forming the print image on the medium, based on the correction value corresponding to the one row region,
Forming a dot row to be formed in the one row region, and forming a dot row to be formed in another row region separated from the one row region by an integral multiple of the predetermined transport amount,
Forming,
(D) When forming the pattern on the medium, a dot forming process for forming the dot row and a medium transport process for transporting the medium in a direction crossing the moving direction by a medium transport roller are repeated. ,
The circumferential length of the medium transport roller is the same size as the interval between one row region and another row region that is separated from the one row region by the predetermined number,
(E) The plurality of nozzles are provided at regular intervals in a direction intersecting the moving direction,
The printing method according to claim 1, wherein the fixed interval is smaller than an interval between one row region and another row region separated from the one row region by the predetermined number. By ejecting ink from a plurality of nozzles moving in the moving direction and forming dot rows in the row region along the moving direction, a plurality of rows formed in the plurality of row regions arranged in a direction crossing the moving direction Forming a pattern composed of the dot rows on the medium;
Read the pattern formed on the medium with a scanner,
Measure the density of each row area of the read pattern,
By calculating an average of the density measurement values of a predetermined number of the row regions arranged in a direction intersecting the moving direction, respectively, a calculated density value corresponding to each row region is obtained,
Based on the calculated density value corresponding to each row area, modify the density measurement value of each row area,
A correction value calculation method, comprising: calculating a correction value corresponding to each column region based on the corrected measurement value of the density of each column region. Prepare a printing device with memory,
A plurality of the rows arranged in a direction intersecting the moving direction by ejecting ink from a plurality of nozzles moving in the moving direction using the printing apparatus to form dot rows in a row region along the moving direction. Forming a pattern composed of a plurality of dot rows formed in a region on a medium;
Read the pattern formed on the medium with a scanner,
Measure the density of each row area of the read pattern,
By calculating an average of the density measurement values of a predetermined number of the row regions arranged in a direction intersecting the moving direction, respectively, a calculated density value corresponding to each row region is obtained,
Based on the calculated density value corresponding to each row area, modify the density measurement value of each row area,
Based on the corrected measurement value of the density of each row area, a correction value corresponding to each row area is calculated,
Information on the calculated correction value is stored in the memory.