JP4635818B2 - Determining whether image density correction can be performed - Google Patents

Description

  The present invention relates to a method for determining whether or not to perform image density correction.

2. Description of the Related Art Inkjet printers that form dots by ejecting ink onto a medium such as paper are conventionally known as printing apparatuses that print images.
The ink jet printer ejects ink from the nozzles while moving a plurality of nozzle groups in which a plurality of nozzles are aligned along a predetermined direction in a direction intersecting the predetermined direction (hereinafter also referred to as a moving direction). The dot forming operation for forming dots on the medium and the transport operation for transporting the medium in the predetermined direction (hereinafter also referred to as the transport direction) are repeated. Thereby, a dot row composed of dots along the moving direction is formed for each row region arranged in the transport direction, and an image is printed.
Here, the “row region” refers to a region constituted by a plurality of “unit regions” arranged in the moving direction. The “unit area” refers to a rectangular area virtually defined on the medium, and ink is landed on the unit area to form the dots.

By the way, in an image composed of such a large number of row regions, density unevenness may be seen in parallel along the moving direction. In other words, there are row regions that appear macroscopically dark and row regions that appear thin, and the image may look poor.
Therefore, in order to suppress the density unevenness, a printer is proposed that stores density correction values in association with the row areas and performs density correction for each row area based on the correction values when printing an image. (See Patent Document 1).
Japanese Patent Application Laid-Open No. 2005-224977

The correction value is set to the printer before the printer is shipped. In this case, it is desirable to confirm whether density unevenness is improved by density correction based on the set correction value.
As this confirmation method, there is a method in which a confirmation pattern when density correction is not performed and a confirmation pattern when density correction is performed are printed, and the magnitude of the density variation between the two is relatively compared. .

However, when the absolute value of the density variation of the confirmation pattern is small, it may be larger when the density variation is not performed than when the density correction is not performed. There is a possibility that the density correction cannot be executed even for a printer that does not have a problem of density unevenness and is not problematic, and the shipment is canceled.
In other words, there is a risk that the quality of the printer will be reduced due to excessive quality in terms of density unevenness determination, and even a printer having a level that is not problematic in practice may be rejected in the inspection process.

  The present invention has been made in view of such a problem, and an object of the present invention is to avoid determining that density correction cannot be performed and canceling shipment even for a printing apparatus having no practical problem. The object is to realize a method for determining whether or not to perform density correction of an obtained image.

The main invention for solving the above problems is:
A method for determining whether or not to perform image density correction,
Printing a confirmation pattern when density correction is not performed and a confirmation pattern when density correction is performed on a medium;
A step of reading the density of each confirmation pattern;
Obtaining a variation in density of each of the confirmation patterns based on the density reading;
Based on the comparison result of the density variation between the respective confirmation patterns and the comparison result with respect to the predetermined threshold value of the density variation of the confirmation pattern when the density correction is performed, whether or not the density correction of the image can be executed is determined. A determining step;
Bei to give a,
In the step of determining whether or not to perform density correction of the image,
When the density variation is smaller or equal in the confirmation pattern when the density correction is performed than when the density correction is not performed, it is determined that the density correction can be performed,
Even if the density variation of the confirmation pattern when the density correction is performed is larger than when the density correction is not performed, the density variation of the confirmation pattern when the density correction is performed In the method of determining whether or not to execute density correction of an image, it is determined that the density correction can be performed when the density is equal to or less than a threshold value .

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

  At least the following matters will become clear from the description of the present specification and the accompanying drawings.

A method for determining whether or not to perform image density correction,
Printing a confirmation pattern when density correction is not performed and a confirmation pattern when density correction is performed on a medium;
A step of reading the density of each confirmation pattern;
Obtaining a variation in density of each of the confirmation patterns based on the density reading;
Based on the comparison result of the density variation between the respective confirmation patterns and the comparison result with respect to the predetermined threshold value of the density variation of the confirmation pattern when the density correction is performed, whether or not the density correction of the image can be executed is determined. A determining step;
A determination method for determining whether image density correction can be performed.

According to such a method for determining whether or not to perform density correction of an image, even a printing apparatus that has been determined to be unable to execute density correction based on a relative comparison of density variations between respective confirmation patterns. There is a possibility that it is determined that the density correction can be executed by an absolute comparison of the density variation of the confirmation pattern when the density correction is performed.
Therefore, it is possible to avoid canceling the shipment by determining that the density correction cannot be performed even for a printing apparatus in which the absolute value of the density variation is small and has no practical problem.

A method for determining whether or not to perform density correction of an image,
In the step of determining whether or not to perform density correction of the image,
When the density variation is smaller or equal in the confirmation pattern when the density correction is performed than when the density correction is not performed, it is determined that the density correction can be performed,
Even if the density variation of the confirmation pattern when the density correction is performed is larger than when the density correction is not performed, the density variation of the confirmation pattern when the density correction is performed If it is less than or equal to the threshold, it may be determined that the density correction can be executed.

A method for determining whether or not to perform density correction of an image,
The moving direction is repeated by repeating a dot forming operation for ejecting ink from a plurality of nozzles moving in the moving direction to form dots on the medium and a conveying operation for conveying the medium in a crossing direction intersecting the moving direction. Each check pattern is printed by forming a row of dots along each of the row regions arranged in the intersecting direction,
Preferably, the reading value is generated for each row region.
According to such a determination method for determining whether or not image density correction can be performed, a reading value is generated for each row region, so that it is possible to increase the number of parameters used for confirming the effect of improving density unevenness, and Whether or not density correction can be executed can be determined more accurately.

A method for determining whether or not to perform density correction of an image,
The plurality of nozzles are aligned along the intersecting direction to form a nozzle group,
The nozzle group is provided for each color of ink ejected when printing an image,
Each confirmation pattern is preferably divided into regions for each nozzle group with respect to the movement direction, and the variation in density is obtained for each of the divided regions.
According to such a determination method for determining whether or not image density correction can be performed, variations are compared for each of the regions corresponding to each of the confirmation patterns. The influence of the difference on the variation can be eliminated, and whether or not image density correction can be performed can be determined more accurately.

A method for determining whether or not to perform density correction of an image,
Each confirmation pattern is printed based on image data,
The image data includes gradation value data of density for forming the dot row in a row region included in a region divided for each nozzle group in each check pattern,
It is desirable that the gradation value data is the same over all the row regions included in the partitioned region.
According to such a method for determining whether or not image density correction can be performed, dot rows are formed based on the same gradation value over all row regions of the confirmation pattern. Therefore, it becomes easier to make the density unevenness that becomes apparent due to the change in the interval between adjacent dot rows easier, and as a result, it is possible to more accurately determine whether or not image density correction can be performed.

A method for determining whether or not to perform density correction of an image,
In the step of determining whether or not to perform density correction of the image,
Compare the variations between the regions printed by the same nozzle group in each confirmation pattern,
For any of the above areas, when density variation is smaller or equal when density correction is performed than when density correction is not performed, a determination is made that the density correction can be performed. ,
Even if there is the region where the density variation is larger when the density correction is performed than when the density correction is not performed, the average value of the density variation of the region when the density correction is performed If the value is equal to or smaller than the threshold value, it may be determined that the density correction can be performed.

A method for determining whether or not to perform density correction of an image,
The moving direction is repeated by repeating a dot forming operation for ejecting ink from a plurality of nozzles moving in the moving direction to form dots on the medium and a conveying operation for conveying the medium in a crossing direction intersecting the moving direction. Forming a dot row along each of the row regions arranged in the crossing direction, and printing a correction pattern,
Reading the density for each row region from the correction pattern, and obtaining a correction value for each row region based on the read value of the density,
When it is determined that the density correction can be performed, it is desirable to perform density correction for each row area based on the correction value when printing an image.
According to such a method for determining whether or not image density correction can be performed, whether or not to execute density correction for suppressing density unevenness in an image formed by repeating the dot formation operation and the conveyance operation is more determined. Accurate determination is possible.

A method for determining whether or not to perform density correction of an image,
The correction pattern may be printed for each nozzle group.

A method for determining whether or not to perform image density correction,
Printing a confirmation pattern when density correction is not performed and a confirmation pattern when density correction is performed on a medium;
A step of reading the density of each confirmation pattern;
Obtaining a variation in density of each of the confirmation patterns based on the density reading;
Based on the comparison result of the density variation between the respective confirmation patterns and the comparison result with respect to the predetermined threshold value of the density variation of the confirmation pattern when the density correction is performed, whether or not the density correction of the image can be executed is determined. A determining step;
With
The moving direction is repeated by repeating a dot forming operation for ejecting ink from a plurality of nozzles moving in the moving direction to form dots on the medium and a conveying operation for conveying the medium in a crossing direction intersecting the moving direction. Are formed for each row region arranged in the intersecting direction, and each check pattern is printed, and the reading value is generated for each row region,
The plurality of nozzles are aligned along the intersecting direction to form a nozzle group, and the nozzle group is provided for each color of ink ejected when printing an image, and each confirmation pattern is moved as described above. The area is divided for each nozzle group with respect to the direction, and the variation in density is obtained for each of the divided areas,
Each confirmation pattern is printed based on image data, and the image data has a density for forming the dot row in a row region included in a region divided for each nozzle group in each confirmation pattern. Gradation value data, and the gradation value data is the same over all the column regions included in the partitioned region,
In the step of determining whether or not to perform density correction of the image, the variation is compared between the areas printed by the same nozzle group in each of the confirmation patterns, and density correction is not performed for any of the areas. When the density correction is smaller than or equal to the case where the density correction is performed, it is determined that the density correction can be performed, while the density correction is performed more than when the density correction is not performed. Even if there is the region where the variation in density is larger when the density correction is performed, the density is not corrected if the average value of the density variation in the area when the density correction is performed is equal to or less than the threshold value. A decision is made that correction can be performed,
The moving direction is repeated by repeating a dot forming operation for ejecting ink from a plurality of nozzles moving in the moving direction to form dots on the medium and a conveying operation for conveying the medium in a crossing direction intersecting the moving direction. Are formed for each row region arranged in the intersecting direction, a correction pattern is printed, the density is read for each row region from the correction pattern, and the row is read based on the read density value. When a correction value is obtained for each area, and it is determined that the density correction can be performed, density correction is performed for each row area based on the correction value when an image is printed,
The method for determining whether or not image density correction can be performed, wherein the correction pattern is printed for each nozzle group.
According to such a method for determining whether or not image density correction can be performed, all of the effects described above can be achieved, and thus the object of the present invention can be achieved more effectively.

=== Configuration of Printing System 100 ===
<Printing system 100>
FIG. 1 is an explanatory diagram of 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 this embodiment includes a printer 1, 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. Further, the computer 110 is installed with a scanner driver for controlling the scanner 150 and receiving image data of the original 5 read by the scanner 150.

<Printer 1>
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, a basic configuration of the printer 1 of the present 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, 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 1. The transport roller 23 is a roller that transports the paper 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 being printed. The paper discharge roller 25 is a roller for discharging paper to the outside of the printer 1 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 a later-described head 41 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 33 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, a dot row along the moving direction is formed on the paper.

  FIG. 4 is an explanatory diagram of 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). 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.

  Ink supply to each nozzle group is performed by ink cartridges 33 (C), 33 (M), 33 (Y), and 33 (K) of each ink color mounted on the carriage 31 (see FIG. 3). reference). That is, the carriage 31 is provided with an ink cartridge mounting portion (not shown) for mounting these ink cartridges 33 (C), 33 (M), 33 (Y), and 33 (K) for each ink color. Yes. The ink supply ports of the ink cartridges 33 (C), 33 (M), 33 (Y), and 33 (K) that store the inks of the respective colors are mounted on the corresponding ink cartridge mounting portions, thereby Ink of the corresponding ink color is supplied to the nozzles of the nozzle group.

  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 1. 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 1. 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 150>
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. The dotted line inside the reading carriage 153 in the drawing indicates the 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.

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

  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 feeding operation / conveying operation / dot forming operation using each unit.

  Paper Feed Operation (S002): The paper feed operation is an operation for supplying paper to be printed into the printer 1 and positioning the paper at a predetermined position (also referred to as a cueing position) where printing is possible. The controller 60 rotates the paper feed roller 21 and the transport roller 23 to position the paper at the cueing position.

  Dot Forming Operation (S003): The dot forming operation is an operation in which ink is intermittently ejected from the head 41 moving along the moving direction to form dots on the paper. 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 composed of a plurality of dots along the moving direction is formed on the paper.

  Transport Operation (S004): The transport operation is an operation of moving the paper relative to the head 41 along the transport direction. The controller 60 rotates the transport roller 23 to transport the paper in the transport direction perpendicular to the moving direction. With this carrying operation, the head 41 can form dots at the next dot forming operation at a position different from the position of the dots formed by the previous dot forming operation.

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

  Paper Discharge Operation (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 25. 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 next paper feeding operation is started. If printing is not performed on the next paper, the printing operation is terminated.

<Dot row 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 non-recorded dot rows are sandwiched between dot rows recorded in one pass. “Pass” refers to a dot formation operation, and “pass n” refers to the nth dot formation operation. A “dot row” is a row of dots arranged in the moving direction.

  7A and 7B are explanatory diagrams of normal printing. 7A shows the position of the head 41 and how dots are formed in pass n to pass n + 3, and FIG. 7B shows the position of the head 41 and how dots are formed in pass n to pass n + 4.

  7A and 7B, for convenience of explanation, only one nozzle group is shown instead of the head 41, and the number of nozzles in the nozzle group is also reduced. Although the nozzle group is depicted as moving with respect to the paper, this figure shows the relative position between the nozzle group (head 41) and the paper. It 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 to form a dot row. 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 dot row immediately above the dot row 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 dot rows 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. Thereby, a plurality of dot rows that are continuously arranged in the transport direction can be formed between the first dot row and the last dot row.

  An area (intermediate area) in which a dot row is formed only by normal printing is called a “normal printing area”. In addition, a region (downstream end region) located on the front end side (downstream in the transport direction) of the paper with respect to the normal print region is referred to as a “leading end print region”. Further, a region (upstream end region) located on the rear end side (upstream side in the transport direction) from the normal print region is referred to as a “rear end print region”. Thirty dot rows are formed in the leading edge printing area. Similarly, 30 dot rows are also formed in the trailing edge print region. On the other hand, in the normal printing area, although it depends on the size of the paper, approximately several thousand dot rows are formed.

  The arrangement of the nozzles assigned to each row region of the normal print region (refers to a region where a dot row is to be formed and the details of the definition and the like will be described later) is a predetermined number P corresponding to the carry amount (here There are regularities in each of the 7) row regions. That is, the arrangement of the nozzles assigned to the row region changes with seven row regions as one cycle.

  For example, the first to seventh row regions of the normal print region in FIG. 8 are respectively represented by nozzle # 3, nozzle # 5, nozzle # 7, nozzle # 2, nozzle # 4, nozzle # 6, and nozzle # 8. A dot row is formed, and dot rows are also formed in the next eight and subsequent seven row regions by the nozzles in the same order.

  On the other hand, it is difficult to find regularity in the arrangement of nozzles assigned to each row area of the leading edge printing area and the trailing edge printing area as compared with the dot line of the normal printing area. However, the nozzles assigned to the respective row regions of the front end print region and the rear end print region are also determined in advance corresponding to each row region. For example, each time the leading edge printing is performed, as shown in FIG. 8, dot rows are formed by the nozzle # 2 in the first to fourth row regions in the leading edge printing region, and the nozzles are formed in the fifth row region. In # 3, a dot row is formed by nozzle # 2 in the sixth row region, nozzle # 3 in the seventh and eighth row regions, and nozzle # 4 in the ninth row region (hereinafter omitted). ) The arrangement of the nozzles does not change every time the leading edge printing is executed.

=== 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.

  FIG. 9A is an explanatory diagram of a state when dots are ideally formed. While the carriage 31 moves in the moving direction, ink is ejected from each nozzle, and ink is landed on the paper to form dots. Since each nozzle intermittently ejects ink during movement, a row of dots (dot row) is formed along the movement direction. Each dot row forms a long and narrow image piece along the moving direction, and a large number of image pieces are arranged in the carrying direction to form a printed image. 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%.

  In the figure, since dots are ideally formed, each dot is accurately formed in a unit region defined on the paper, and a dot row is accurately formed in the row region.

  Here, the “unit area” refers to a rectangular area virtually defined on a medium such as paper, and is an area corresponding to a pixel that is a minimum constituent unit of a print image. The size and shape are determined according to the print 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 at the center position of the unit region, and then the ink droplet spreads on the medium to form a dot in the unit region.

  Further, “row region” refers to a region composed of a plurality of unit regions arranged in the movement direction, and in the drawing, “row region” is shown as a region sandwiched between dotted lines. For example, when the printing resolution is 720 dpi × 720 dpi, the row region is a band-like region having a width of 30.28 μm (≈ 1/720 inch) in the transport direction. When ink droplets are ideally ejected intermittently from the nozzle moving in the moving direction, a dot row is formed in this row region, whereby each row region has a plurality of densities according to the coloration of that region. An image piece composed of the pixels is formed.

  FIG. 9B is an explanatory diagram of the influence of variations in nozzle processing accuracy. Here, due to variations in the flight direction of the ink droplets ejected from the nozzles, the dot row formed in the second row region is formed closer to the third row region side (upstream side in the transport direction). 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 dot rows is viewed macroscopically, striped density unevenness along the moving direction of the carriage 31 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. Thereby, the dot generation rate of the dot row in each row region is changed, the density of the image pieces in the row region is corrected, and the density unevenness of the entire print image is suppressed.

  By the way, 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 nozzle forming the dot row in the third row region, but the adjacent second row. This is due to the influence of nozzles that form dot rows in the region. For this reason, when a nozzle that forms a dot row in the third row region forms a dot row in another row region, an 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 the present embodiment, in the inspection process of the printer manufacturing factory, the printer 1 is caused to print a correction pattern, the correction pattern is read by the scanner 150, and each correction is performed based on the density of each row region in the correction pattern. The correction value corresponding to the row area is stored in the memory of the printer 1. The correction value stored in the printer 1 reflects the density unevenness characteristics of each printer 1.

  Then, under the user who purchased the printer 1, the printer driver reads the correction value from the printer 1, corrects the gradation value of the pixel data based on the correction value, and print data based on the corrected gradation value. And the printer 1 performs printing based on the print data.

<About processing at printer manufacturing plants>
FIG. 10A is a flowchart of processing performed in the inspection process after manufacturing the printer 1. In this inspection process, a “correction value setting process (S100)” for setting a correction value in the printer 1 and a “density correction effect confirmation process (S100) for confirming the effect of improving density unevenness due to the set correction value ( S150) ". Here, the correction value setting process in step S100 will be described in detail, and the density correction effect confirmation process in step S150 will be described later.

  FIG. 10B is a flowchart of the correction value setting process. FIG. 10C is an explanatory diagram of the inspection ink cartridge 35 included in the inspection kit.

  First, the inspector sets the printer 1 to be inspected in an inspection kit that is always provided in the inspection process of the factory. This inspection kit includes an inspection computer 110 having a scanner 150 and an inspection ink cartridge 35. The printer 1 is connected to the inspection computer 110 (S101), and the inspection ink cartridge 35 is mounted on the ink cartridge mounting portion of the printer 1 as shown in FIG. 10C.

  The inspection ink cartridge 35 contains inspection ink for printing a test pattern. When the inspection ink cartridge 35 is attached to the ink cartridge attachment portion of the carriage 31 of the printer 1, the inspection ink is supplied to the printer 1. The head 41 can be supplied.

  In addition, the inspection computer 110 previously stores a printer driver for causing the printer 1 to print a test pattern, a scanner driver for controlling the scanner 150, and image data of a correction pattern read from the scanner 150. A correction value setting program for performing image processing and analysis is installed.

  Next, the printer driver of the inspection computer 110 causes the printer 1 to print a test pattern for setting correction values (S102). FIG. 11 is an explanatory diagram of a test pattern for setting a correction value, and FIG. 12 is an explanatory diagram of a correction pattern included in the test pattern. This test pattern is printed at a print resolution of, for example, 720 × 720 dpi, and has a correction pattern for each nozzle group. 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.

  However, here, all of the four correction patterns are printed in the same color. This is because only one kind of the inspection ink is prepared from the viewpoint of simplifying the inspection process, that is, the correction pattern for the black ink nozzle group (K), the cyan ink nozzle group (C). The correction pattern of magenta ink nozzle group (M) and the correction pattern of yellow ink nozzle group (Y) are different in the nozzle group from which ink is ejected, but the same type of ink Printed by. More specifically, the inspection ink cartridge 35 has a total of four ink supply ports corresponding to all ink cartridge mounting portions provided in the carriage 31 of the printer 1 for each nozzle group. These ink supply ports are respectively mounted on the ink cartridge mounting portions of the respective nozzle groups, whereby one type of inspection ink is supplied to all four nozzle groups. As the inspection ink, an ink having the same hue as one of the inks that can be ejected by the printer 1 and a lighter tone is desirable from the viewpoint of facilitating the manifestation of density unevenness. Here, the light magenta Ink of the same color as magenta but lighter in tone than magenta is used.

  Each of the belt-like patterns is generated from image data having a constant gradation value in the conveyance direction, and gradation values 76 (density 30%), 102 (density 40%), 128 (density 50%), 153 (density 60%), and 179 (density 70%), which are patterns of dark density 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 leading edge printing region dot row, a normal printing region dot row, and a trailing edge printing region dot row. In normal printing, thousands of dot rows are formed in the normal printing region, but in printing the correction pattern, eight cycles of dot rows are formed in the normal printing region. Here, for the sake of simplification of explanation, it is assumed that the correction pattern is printed by printing in FIG. 8. ) × 8 cycles) and a total of 116 dot rows including 30 dot rows in the trailing edge printing area. The upper ruled line is formed by the first dot row (dot row on the most downstream side in the transport direction) constituting the belt-like pattern. The lower ruled line is formed by the last dot row (dot row on the most upstream side in the transport direction) constituting the belt-like pattern.

  Incidentally, it goes without saying that when this test pattern is printed, density correction processing (see step S213 in FIG. 23) based on correction values described later is not performed.

  Next, the inspector places the paper on which the test pattern is printed by the printer 1 on the platen glass 152 of the scanner 150, closes the upper lid 151, and sets the test pattern on the scanner 150. Then, the scanner driver of the inspection computer 110 causes the scanner 150 to read the correction pattern, for example, in gray scale (tone value data that has no color information and is created only by brightness) (S103). Hereinafter, only reading of the correction pattern for the cyan ink nozzle group will be described, but reading of the correction pattern for the nozzle group relating to other ink colors is similarly performed.

  FIG. 13 is an explanatory diagram of the reading range of the correction pattern for the cyan ink nozzle group. In the figure, the range surrounded by the alternate long and short dash line is a reading range when reading a correction pattern related to the cyan ink nozzle group (hereinafter, the term “cyan ink nozzle group” may be simply referred to as “cyan”). It is. Parameters SX1, SY1, SW1, and SH1 for specifying this range are set in advance in the scanner driver by the correction value setting 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 inspection computer 110 as rectangular image data having a reading resolution of 2880 × 2880 dpi.

  Next, the correction value setting program of the inspection computer 110 detects the inclination θ of the correction pattern included in the image data (S104), and performs rotation processing according to the inclination θ on the image data (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. From the read image data, the correction value setting 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. 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 setting program obtains the gravity center positions KY1 and KY2 of the gradation values of the extracted KH pixel data in order to detect the position of the upper ruled line. Then, the correction value setting program calculates the inclination θ of the correction pattern based on the parameters KX1 and KX2 and the barycentric positions KY1 and KY2, and rotates the image data based on the calculated inclination θ. Process.
θ = tan ⁻¹ {(KY2-KY1) / (KX2-KX1)}
Next, the correction value setting program of the inspection 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 setting program includes pixel data of KX1 pixels from the left, KH pixels from the top, and KX2 pixels 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 setting program obtains the gravity center positions KY1 and KY2 of the gradation values of the extracted KH pixel data, and calculates the average value of the two gravity center 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 setting program cuts out 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 setting 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 setting program cuts out pixels below the trimming position and performs trimming.

  Next, the correction value setting program of the inspection 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 dot rows constituting the correction pattern). (S107).

  FIG. 16 is an explanatory diagram of resolution conversion. If the printer 1 ideally forms a correction pattern consisting of 116 dot rows 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 setting program of the inspection computer 110 uses 116/470 (= [number of dot rows constituting the correction pattern] / [number of pixels in the Y direction of the trimmed image data]) for this image data. Resolution conversion (reduction processing) is performed at a magnification of. 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 setting program of the inspection computer 110 measures the respective densities 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 region will be described. Measurements in other row regions are performed in the same manner. In addition, the measurement of the density of other band-like patterns is performed 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 setting program extracts pixel data of HX pixels from the top and KX pixels from the left 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 setting 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 setting 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 first 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 setting 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 setting program of the inspection 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 strip pattern is uniformly formed with gradation values Sa (= 76), Sb (= 102), and Sc (= 128), 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 j1 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 j2 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 setting program of the inspection computer 110 calculates a correction value corresponding to the row area (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 j1 in 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 j2 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 j1. In this row region, 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 region, the average density of the strip pattern having a density of 30%. Paler). If the printer driver causes the printer 1 to form a density pattern of the target value Cbt in this row area, the command is based on the target command tone value Sbt calculated by the following equation (linear interpolation based on the straight line BC). do it.
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 j2. 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 30%. Paler). If the printer driver causes the printer 1 to form a density pattern of the target value Cbt in this row region, the command is based on the target command tone value Sbt calculated by the following equation (linear interpolation based on the straight line AB). do it.
Sbt = Sb− (Sb−Sa) × {(Cbt−Cb) / (Ca−Cb)}

After calculating the target command tone value Sbt in this way, the correction value setting 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 setting program of the inspection computer 110 calculates a correction value Hb for the gradation value Sb (density 40%) for each row region. Similarly, the correction value setting program sets the correction value Hc for the gradation value Sc (density 50%), the measurement value Cc for each row region, the measurement value Cb or Cd, and the command gradation value Sb or Sd. Based on the above, calculation is performed for each row region. Similarly, the correction value setting program sets the correction value Hd for the gradation value Sd (density 60%), the measurement value Cd of each row region, the measurement value Cc or Ce, and the command gradation value Sc or Se. Based on the above, calculation is performed for each row region. For other colors, three correction values (Hb, Hc, Hd) are calculated for each row region.

  By the way, as shown in FIG. 12, there are 56 row areas in the normal print area. As described above, the arrangement of the nozzles assigned to these row areas is 7 cycles as one period. Change. That is, as shown in FIG. 8, nozzle # 3, nozzle # 5, nozzle # 7, nozzle # 2, nozzle # 4, nozzle # 6, nozzle # 3 are arranged in the first to seventh row areas of the normal printing area, respectively. Dot rows are formed by the nozzle # 8, and dot rows are also formed by the nozzles in the same order in the next eight and subsequent seven row regions. Therefore, this regularity is taken into account in the calculation of the correction value for the normal printing area shown in FIG.

When the correction value setting program calculates the correction value in the first row area of the normal printing area (the 31st row area of the entire printing area), the above-described measurement value Ca is the nozzle # 3 in the normal printing area. The average value Ca _ave of the measured values of the 30% density of the first, eighth, fifteen, twenty-second, twenty-ninth, thirty-six, forty-third, and fifty eighth row regions is used. Similarly, when calculating a correction value in the first row region of the normal print region (the 31st row region of the entire print region), nozzle # 3 is assigned to the above-described measurement values Cb to Ce in the normal print region. The average values Cb _{ave to} Ce _ave of the measured values of the respective densities of the first, eighth, fifteenth, twenty-second, twenty-ninth, thirty-sixth, thirty-fourth, and fifty eighth row regions are used. Then, as described above, the correction values (Hb, Hc, Hd) for the first row area of the normal printing area are calculated based on the average values Ca _{ave to} Ce _ave instead of the above-described measured values Ca to Ce. The As described above, the correction value of the row region of the normal print region is calculated based on the average value 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 setting program of the inspection computer 110 stores the correction value in the memory 63 of the printer 1 (S110).

  FIG. 21A is an explanatory diagram of a cyan correction value table. There are three types of correction value tables for the leading edge printing area, the normal printing area, and the trailing edge printing 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 dot row 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.

The normal print area correction value calculation method described above obtains the average values Ca _{ave to} Ce _ave of the density measurement values Ca _{ave to} Ce _ave of the eight row areas to which the same nozzle is assigned, and calculates the average value Ca using _{ave ~Ce ave,} 3 one correction value for each row region (Hb, Hc, Hd) but was to calculate the timing of averaging, even without the time of measurement Ca~Ce It may be performed after calculating the correction values (Hb, Hc, Hd).

  In other words, using a cyan correction value table as an example, first, three correction values (Hb, Hc, Hd) are calculated for each of the 56 row regions included in the normal print region (left in FIG. 21B). (See diagram). Then, the correction values (Hb, Hc, Hd) are averaged for each set of row regions in which the assigned nozzles are the same among the 56 row regions, and finally shown in the right diagram of FIG. 21B. As described above, correction values (Hb, Hc, Hd) corresponding to the first to seventh seven row regions may be obtained.

  For example, the row region to which nozzle # 3 is assigned is the first, eighth, fifteenth, twenty-second, twenty-ninth, thirty-sixth, thirty-sixth, and fifty eighth row regions, as indicated by the bold lines in the left diagram of FIG. However, correction values (Hb, Hc, Hd) are obtained for these row regions, respectively. Then, as shown in the middle formula of FIG. 21B, the eight correction values Hb_1, Hb_8, Hb_15, Hb_22, Hb_29, Hb_36, Hb_43, and Hb_50 obtained are averaged to obtain a correction value Hb_1. The eight correction values Hc_1, Hc_8, Hc_15, Hc_22, Hc_29, Hc_36, Hc_43, Hc_50 are averaged to obtain a correction value Hc_1, and the eight correction values Hd_1, Hd_8, Hd_15, Hd_22, Hd_29, Hd_36, Hd_43 are obtained. , Hd_50 is averaged to obtain a correction value Hd_1. Then, these correction values (Hb_1, Hc_1, Hd_1) are stored in the correction value table as correction values for the first row region as shown in the right diagram of FIG. 21B. The same applies to the correction values (Hb_2, Hc_2, Hd_2) to (Hb_7, Hc_7, Hd_7) of the remaining second to seventh row regions.

  After the correction value is stored in the memory 63 of the printer 1 in this way, the correction value setting process (step S100 in FIG. 10A) ends.

  If it does so, it will transfer to step S150 of FIG. 10A, "Confirmation process of a density correction effect" will be performed, and the presence or absence of the improvement of the density non-uniformity as an effect of the density correction based on the said correction value will be confirmed. After completion of the density correction effect confirmation process, the printer 1 is disconnected from the inspection computer 110, but the printer 1 determined to have no density unevenness improvement effect, that is, density correction cannot be executed. The determined printer 1 is sent to a predetermined investigation process for the purpose of investigating the cause. On the other hand, the printer 1 that has been determined to have an improvement effect, that is, the printer 1 that has been determined to be capable of performing density correction, is shipped from the factory after completion of other inspections on the printer 1. 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 inspection computer in 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 110 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 correction value corresponding to 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 FIG. 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 the pixel data in the first to seventh column regions (the 31st to 38th 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 of converting high gradation number data into gradation number data that can be formed by the printer 1. For example, 8-bit data indicating 256 gradations is converted into 1-bit data indicating 2 gradations or 2-bit data indicating 4 gradations by halftone processing. In the halftone process, pixel data is created using the dither method, γ correction, error diffusion method, and the like so that the printer 1 can form dots dispersedly. When performing halftone processing, the printer driver refers to the dither table when performing dithering, refers to the gamma table when performing γ correction, and stores diffused errors when performing error diffusion. 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 that row region is corrected to be low, so the dot generation rate of the dots that make up the dot row in that 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 rasterizing process is a process of changing matrix image data in the order of data to be transferred to the printer 1. The rasterized data is output to the printer 1 as pixel data included in the print data.

  If the printer performs print processing based on the print data generated in this way, as shown in FIG. 9C, the dot generation rate of the dot row in each row region is changed, and the density of the image pieces in the row region 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 (the number of dot rows) are reduced for the sake of simplification. However, in actuality, 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 setting program, the printer driver, etc. is almost the same.

=== Concerning Density Correction Effect Confirmation Process (S150) ===
The “density correction effect confirmation processing” in step S150 of FIG. 10A is a pattern for confirming whether or not the correction value set in the printer 1 actually exhibits the effect of improving the desired density unevenness. Is confirmed by printing. Therefore, the printer 1 for which the correction value has been set is the object of this confirmation process. If it is determined that there is no correction effect based on the confirmation pattern, the printer 1 regards that the density correction cannot be performed, and notifies the inspector of the inspection process to that effect. Cancel the shipment of 1 and send it to the specified investigation process.

FIG. 25 is a flowchart of the density correction effect confirmation process.
First, the inspector checks whether the processing target printer 1 is set in the inspection kit (S151). Since this time is immediately after the end of the correction value setting process shown in FIG. 10B, the printer 1 to be processed is set in the inspection kit unless there are special circumstances. That is, the printer 1 remains connected to the inspection computer 110 and the inspection ink cartridge 35 of the inspection kit. In addition, the inspection computer 110 of this inspection kit performs a confirmation process for quantitatively improving the density unevenness based on the image data of the confirmation pattern read from the scanner 150 in addition to the printer driver and the scanner driver. The correction effect confirmation program is installed.

Next, the printer driver of the inspection computer 110 causes the printer 1 to print a test pattern for checking the correction effect (S152).
FIG. 26 is an explanatory diagram of a test pattern for confirming a correction effect, and FIG. 27 is an explanatory diagram of a confirmation pattern included in the test pattern. As shown in FIG. 26, two confirmation patterns are formed as test patterns on one sheet of paper. One confirmation pattern is a pattern in which density correction is performed based on the above-described correction value (hereinafter, also referred to as a confirmation pattern with correction), and the other confirmation pattern formed thereunder is density These patterns are not corrected (hereinafter also referred to as “uncorrected confirmation patterns”), and are all printed at a print resolution of 720 × 720 dpi as in the above-described correction patterns.

  The image data used for printing these two confirmation patterns is the same as each other. The difference between these confirmation patterns is that the density correction process in step S213 is performed in the print data generation process of FIG. 23 performed by the printer driver. It is only in terms of whether or not it is done. That is, when printing a check pattern with correction, the image data is processed according to the flow of FIG. 23 to generate print data. When a check pattern without correction is printed, FIG. Step S213 of the density correction process is skipped, and steps S211, S212, S214, and S215 are performed to generate print data from the image data.

  Therefore, these two confirmation patterns have no apparent difference except for the density unevenness, and both of the two confirmation patterns have four types of strips arranged in parallel in the moving direction as shown in FIG. The pattern includes an upper ruled line, a lower ruled line, a left ruled line, and a right ruled line.

  Each belt-like pattern is generated from image data having a constant gradation value in the transport direction, and is formed by ejecting ink from only the cyan ink nozzle group (C) in order from the left. A belt-shaped pattern formed by ejecting ink only from the nozzles of the magenta ink nozzle group (M), a belt-shaped pattern formed by ejecting ink only from the nozzles of the yellow ink nozzle group (Y), and Band-shaped patterns formed by ejecting ink only from the nozzles of the black ink nozzle group (K) are arranged.

  Here, the above-described inspection ink cartridge 35 is mounted on the carriage 31 of the printer 1. Therefore, light magenta ink is ejected as inspection ink from any of the four nozzle groups, and therefore, any belt-like pattern is colored with light magenta.

  In addition, since it is desirable that the gradation value is set to a gradation value at which density unevenness is likely to be manifested, in this example, halftone gradation values (= 102 (density 30) are obtained for all strip patterns. %)). Therefore, on the actual confirmation pattern, the boundary between the band-shaped patterns is not visible, but here, for convenience of explanation, the density is changed for each band-shaped pattern as shown in FIGS. .

  As shown in FIG. 27, the belt-like pattern of each nozzle group is formed by leading edge printing, normal printing, and trailing edge printing, respectively, similarly to the belt-like pattern in the correction pattern described above. For this reason, each belt-like pattern includes 30 dot rows in the front-end print region, 56 dot rows in the normal print region (= 7 (pieces / cycle) × 8 cycles), and 30 dots in the rear-end print region. It consists of a dot row. The upper ruled line is formed by the first dot row (dot row on the most downstream side in the carrying direction) constituting the belt-like pattern, and the lower ruled line is the last dot row (dot on the most upstream side in the carrying direction) constituting the belt-like pattern. The point formed by the column) is the same as that of the correction pattern described above.

  Next, the inspector places the paper on which the test pattern is printed by the printer 1 on the platen glass 152 of the scanner 150 and sets it on the scanner 150. Then, the scanner driver of the inspection computer 110 causes the scanner 150 to read each confirmation pattern (S153). In the following, reading of one confirmation pattern will be mainly described, but the other confirmation pattern is read in the same manner.

  FIG. 28 is an explanatory diagram of the reading range of the confirmation pattern. The range of the alternate long and short dash line surrounding the confirmation pattern is the reading range of the confirmation pattern. This reading is performed by the same method as step S103 (reading the correction pattern) described above. As a result, the image in the reading range in the figure is rectangular image data with a reading resolution of 2880 × 2880 dpi, and the inspection computer. 110 is read.

  Next, the correction effect confirmation program of the inspection computer 110 detects the inclination θ of the confirmation pattern included in the image data as shown in FIG. 29A (S154), and as shown in FIG. Then, a rotation process corresponding to the inclination θ is performed (S155). It should be noted that the inclination detection and rotation processing of the confirmation pattern are also achieved by applying the same method as in step S104 (correction pattern inclination selection) and step S105 (rotation processing) described above.

  Next, the correction effect confirmation program trims unnecessary pixel data from the image data (S156). Unnecessary pixel data is pixel data located above the upper ruled line in the Y direction and below the lower ruled line in the image data indicated by the one-dotted line in FIG. 30A. Is processed into image data as shown in FIG. This trimming is also achieved by applying the same method as step S106 (trimming) described above.

  Next, the correction effect confirmation program converts the resolution of the image data so that the number of pixels in the Y direction of the trimmed image data is the same as the number of dot rows constituting the confirmation pattern (S157). This resolution conversion is also performed by the same method as step S107 (resolution conversion) described above. As a result, the image data before the resolution conversion shown in FIG. 30B has the number of pixels in the Y direction confirmed as shown in FIG. 30C. The number of dot rows that make up the pattern for use is converted to the same number. As a result, the pixel rows in the X direction of the image data correspond to the row regions on a one-to-one basis.

  Next, the correction effect confirmation program measures the density of each strip pattern for each row region for each strip pattern of the four nozzle groups (S158). The method for measuring the concentration is also substantially the same as step S108 described above. However, since there is a slight difference, the measurement of the density of the row region will be described below using the belt-like pattern of the cyan ink nozzle group among the four nozzle groups as an example.

  As shown in the enlarged view of the confirmation pattern in FIG. 31, first, pixel data in a dotted line area excluding the left and right W4 areas of the cyan belt-like pattern is extracted for each column area. Then, the gradation values of the extracted pixel data in the above range are averaged for each column region, and each obtained average value is used as a measured value of the density of each column region. Up to this point, the process is the same as step S108 described above.

  However, in this step S158, the measured values of the density of each row region are set as “temporary measured values”, and these “temporary measured values” are smoothed in the Y direction by a method similar to the moving average method, A measured value (corresponding to a read value) of the density of each row region is obtained. That is, the average value of “provisional measurement values” of a predetermined number of column regions in the Y direction including the target column region (hereinafter referred to as the target column region) is measured as the concentration of the target column region. Value.

 Here, it is desirable that the predetermined number coincide with the number k that defines the nozzle pitch of the head 41, and the nozzle pitch k · D of the present embodiment is 4 · D. Is set to 4. For example, as shown in FIG. 31, the measured value of the density of the first row region is obtained as an average value of “temporary measurement values” of four row regions in the Y direction from the first row region. In addition, the measured value of the density of the second row region is obtained as an average value of “temporary measurement values” of four row regions in the Y direction from the second row region, and subsequently continues in the Y direction. The measured value of the density of the row region is obtained in the same manner.

 The reason why the measurement value of the density of the row region is obtained by performing the smoothing process in this way is to reduce the influence of the abnormal value of the density and increase the accuracy of the measurement value.

 From the viewpoint of improving the accuracy of the measurement value, it is also effective to remove the column region near the end in the Y direction, which tends to be an abnormal value due to the density of the blank space, from the density measurement target. For example, as shown in FIG. 32, the three row regions located at the front end and the rear end in the Y direction of the belt-like pattern may be excluded from the density measurement targets.

  Next, the correction effect confirmation program calculates the variation in density of each confirmation pattern (S159). The calculation of the density variation (hereinafter referred to as density variation) is performed for each divided region obtained by dividing each confirmation pattern into a grid pattern in the moving direction and the carrying direction, as shown in FIG. Done. In the example shown in the drawing, each confirmation pattern is divided for each band-like pattern for each nozzle group in the movement direction and for each print area in the transport direction. As a result, the number of divided areas for each confirmation pattern is 12 respectively. It has become a piece.

  In the following description, the leading edge printing area relating to the cyan ink nozzle group is designated as the dividing area C-1, the normal printing area is designated as the dividing area C-2, and the trailing edge printing area is designated as the dividing area C-3. The printing area is the divided area M-1, the normal printing area is the divided area M-2, the trailing edge printing area is the dividing area M-3, and the leading edge printing area related to the yellow ink nozzle group is the dividing area Y-1. The normal print area is the divided area Y-2, the rear end print area is the divided area Y-3, the front print area related to the black ink nozzle group is the divided area K-1, and the normal print area is the divided area K-2. Similarly, the trailing edge print area is defined as a divided area K-3.

Here, a so-called standard deviation σ is used as an evaluation index of density variation in the segmented area. That is, the density variation in each segmented region is as follows when the segmented region has n column regions and the measured value of the density of the jth column region included in the segmented region is C _j. Calculated by the formula.
σ = √ {[(C ₁ −C _ave ) ² +... + (C _n −C _ave ) ² ] / n}
Here, C _ave in the above formula is C _ave = (C ₁ +... + C _n ) / n.

  After obtaining the density variation σ of the 12 divided areas for each of the confirmation pattern with correction and the confirmation pattern without correction, the correction effect confirmation program next determines the density correction effect (S160). ).

  FIG. 34 is a flowchart of the density correction effect determination step (S160). In this step S160, first, the density variation σ is compared for each of the corresponding divided areas for the check pattern with correction and the check pattern without correction (S162). Then, if any one of the 12 divided areas has a corrected area with a larger density variation σ, it is determined that there is no correction effect, and the printer 1 regards that the density correction cannot be performed. (S165). On the other hand, if the density variation σ with correction is smaller than or equal to that with no correction for all 12 divided areas, it is not determined that there is no correction effect, and the printer 1 executes density correction. This is considered possible (S164).

  When it is assumed that density correction can be performed, the correction effect confirmation program displays “density correction can be performed” on the display device 120 of the inspection computer 110. On the other hand, when it is assumed that the density correction cannot be executed, the display device 120 displays “density correction cannot be executed”. Preferably, however, the confirmation pattern is displayed together with the display indicating that the density correction cannot be executed. A warning for prompting reprinting or a warning for prompting the recreation of the density correction value may be displayed. Then, the inspector redoes the re-inspection of the printer 1 from the above-described step S150 “confirmation process of density correction effect” or step S100 “correction value setting process”, and the density correction cannot be performed on the printer 1. After confirming the reproducibility of the determination, the printer 1 is sent to the investigation process. As a result, it is possible to reduce the number of printers 1 that are erroneously determined not to be able to execute density correction due to problems such as omission of inspection by the inspector.

=== Regarding the Problem of “Density Correction Effect Determination (S160)” ===
In the above-described “Density Correction Effect Determination (S160)”, the density correction effect determination is performed by relatively comparing the density variation σ of each check pattern with and without correction for each corresponding segment area. I was going. Specifically, if there is even one segmented region where the density variation σ with correction is larger than that without correction, it is determined that there is no correction effect.

However, when the absolute value of the density variation σ is small, the determination result based on the above-mentioned relative comparison can be easily reversed due to a slight difference in the inspection state, and as a result, the density correction is not performed. If this is performed, the density variation σ may become larger (hereinafter referred to as “reversal phenomenon”).
In this case, the above-described method may determine that the density correction cannot be performed even for the printer 1 in which the density unevenness is not visible and has no problem, and the shipment may be canceled.

  FIG. 35A to FIG. 35B are explanatory diagrams of the above-described reversal phenomenon, and all the figures show measured values of the density of the band-like pattern of the confirmation pattern. The horizontal axis represents the position of the row area in the belt-like pattern, and the vertical axis represents the measured value of the density of the row area.

One cause of this reversal phenomenon is, for example, the undulation of density fluctuation that can be caused by density correction. That is, when density correction is performed, undulations of density fluctuations that have not occurred in the uncorrected belt-like pattern shown in the left half of FIG. 35A occur in the belt-like pattern with correction, as shown in the right half of FIG. There is.
However, the amplitude of this swell is generally small as shown in the right half of FIG. 35A. Therefore, as shown in the left half of FIG. 35A, when the absolute value of the density variation σ without correction is large, the amount of reduction in the density variation σ due to the density correction may be large, and the waviness is generated in the density correction. However, the reversal phenomenon that the density variation σ with correction becomes larger than that without correction hardly occurs.

On the other hand, when the density variation σ is already small on the uncorrected band-shaped pattern as shown in the left half of FIG. 35B, the reduction margin of the density variation σ due to the density correction is small. The contribution rate of the increasing effect on the waviness density variation σ is relatively large. As a result, in the density variation σ of the band-shaped pattern with correction shown in the right half surface of FIG. In this case, a reverse phenomenon occurs in which the density variation with correction σ becomes larger than that without correction.
However, as described above, the amplitude of the swell is small, and this swell has a long-period property of changing over a plurality of row regions. For this reason, this swell is hardly recognized as density unevenness by visual observation, and in many cases, it does not actually cause a problem.

  Therefore, it has been determined that the printer 1 cannot perform density correction even for the printer 1 that has caused the reverse phenomenon in the determination of the density correction effect (S160) due to such waviness. In this case, the determination becomes more strict than necessary, and the quality of the density unevenness is deteriorated. That is, there is a possibility that even the printer 1 at a level that has no practical problem is rejected in the inspection process, and the production efficiency of the printer is substantially lowered.

  Therefore, in the determination of the density correction effect according to the present embodiment described below (step S160a), in addition to relatively comparing the density variation σ, the density variation σ is further determined using a predetermined determination threshold. By making a comparison based on values, a final determination without a correction effect is made (see FIG. 36). As a result, it is effectively avoided that the density correction cannot be executed and the shipment is canceled even for the printer 1 which has no practical problem.

=== About “Density Correction Effect Determination Step (S160a)” of this Embodiment ===
FIG. 36 is a flowchart of the “density correction effect determination step (S160a)” according to the present embodiment.

The main difference from the example of the flowchart of FIG. 34 described above is that step S163 is added. That is, in the example of FIG. 34, when it is determined that there is no correction effect in the relative comparison of the density variation σ in step S162, the printer 1 immediately assumes that the density correction cannot be performed and the printer 1 However, in the present embodiment, in step S163, it is determined whether the density variation σ has no practical problem. If it is determined that there is no problem, the printer 1 is regarded as a printer capable of correcting the density, and is shipped as it is without being sent to the investigation process.
Therefore, this step S163 is almost the same as the example of FIG. 34 described above except that step S163 is added, and step S163 will be mainly described below.

In step S163 shown in FIG. 36, determination concentration variation of the printer 1 sigma is either level or not no practical problem, the magnitude of the density variation sigma, performed by comparison with a predetermined determination threshold value sigma _th. That is, the absolute value of the density variation σ is evaluated.

Here, as the density variation σ used for comparison, an average value σ _ave of density variations σ _{ave of} all twelve divided regions of the check pattern with correction is used. Specifically, the density variation σ is calculated by the following equation. .
σ _ave = (σ _C-1 + σ _C-2 + σ _C-3 + σ _M-1 + σ _M-2 + σ _M-3
+ Σ _Y-1 + σ _Y-2 + σ _Y-3 + σ _K-1 + σ _K-2 + σ _K-3 ) / 12
In the above equation, σ _C-1 , σ _C-2 , σ _C-3 , σ _M-1 , σ _M-2 ,..., Σ _K-3 are respectively divided regions C-1, C-2. , C-3, M-1, M-2,...

When the average value σ _ave is equal to or smaller than the determination threshold σ _th, it is determined that the density correction can be performed (S165). On the other hand, when the average value σ _ave exceeds the determination threshold σ _th , the density correction is performed. It is determined that it is impossible (S164).
Incidentally, the determination threshold value σ _th is determined in advance by a method using sensory evaluation as follows. First, a sample of a belt-like pattern that can be discriminated when the density unevenness is visually different is printed over, for example, five levels. Then, these five levels of density unevenness are visually evaluated by a plurality of people using five levels of sensory evaluation values (level 1: none, level 2: small, level 3, medium, level 4: large, level 5: extra large). do that for me. On the other hand, in parallel with this, these five levels of density are read by the scanner 150 to obtain the density variation σ of each level.
Then, the sensory evaluation value of the density unevenness and the density variation σ are graphed as shown in FIG. 37 with respect to the horizontal axis and the vertical axis, respectively, and thereafter, from the graph, the level 1 (corresponding to no density unevenness) is supported. The density variation σ to be read may be read and used as the determination threshold σ _th .

=== Other Embodiments ===
The above-described embodiment has been described mainly for the printing system 100 including the printer 1, but it goes without saying that the disclosure includes a method for determining whether or not image density correction can be performed.
Further, the printer 1 and the like as one embodiment have been described, but the above-described embodiment is for facilitating 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. In particular, the embodiments described below are also included in the present invention.

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

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

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

<About the moving direction of the head 41>
In the above-described embodiment, it is not described whether the ink is ejected when the head 41 moves in the reciprocating direction. However, the ink is ejected only in the forward path, only in the return path, or both in the reciprocal direction. May be.

<Ink colors used for printing>
In the above-described embodiment, multicolor printing in which four inks of cyan (C), magenta (M), yellow (Y), and black (K) are ejected onto paper to form dots has been described as an example. The ink color is not limited to this. For example, in addition to these ink colors, ink such as light cyan (light cyan, LC) and light magenta (light magenta, LM) may be used.

<About inspection ink>
In the above-described embodiment, from the viewpoint of simplifying the inspection process, a test pattern for correction value setting and a test pattern for confirming the correction effect are printed using one kind of ink (light magenta) as the inspection ink. This is not a limitation.
For example, each belt-like pattern of the test pattern may be printed using ink of ink color corresponding to each nozzle group. That is, the band pattern of the cyan nozzle group is printed with cyan ink, the band pattern of the magenta nozzle group is printed with magenta ink, the band pattern of the yellow nozzle group is printed with yellow ink, and the band pattern of the black nozzle group is printed with black ink. May be.

<Subject for “Correction Value Setting Process” and “Density Correction Effect Confirmation Process”>
In the above-described embodiment, the “correction value setting process (S100)” and the “density correction effect confirmation process (S150)” illustrated in FIG. 10A are performed in the factory inspection process. It may be performed under the user who made it. In this case, a user can install a printer driver for causing the printer 1 to print a test pattern, a scanner driver for controlling the scanner, a correction value setting program, and a correction effect confirmation program on his computer 110. Thus, it goes without saying that a CD-ROM or the like storing these programs is attached to the printer 1.
Under this user, the ink cartridges 33 (K), 33 (C), 33 (M), and 33 (Y) corresponding to each nozzle group are mounted on the carriage 31 instead of the inspection ink cartridge 35. Therefore, it goes without saying that each belt-like pattern of the test pattern is printed using the ink color corresponding to each nozzle group as described above.

<Regarding the number of divided areas for which density variation is obtained>
In the above-described embodiment, as shown in FIG. 33, each confirmation pattern is divided into 12 divided areas for each belt-like pattern and for each print area. However, the present invention is not limited to this. For example, instead of dividing each printing area, it is possible to divide each band-like pattern in the moving direction into four divided areas.

1 is an explanatory diagram of 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, and FIG. 3B is a cross-sectional view of the overall configuration of the printer 1. 4 is an explanatory diagram of an arrangement of nozzles on a lower surface of a head 41. FIG. 5A is a longitudinal sectional view of the scanner 150, and FIG. 5B is a top view of the scanner 150 with the upper cover 151 removed. It is a flowchart of the operation | movement at the time of printing. 7A and 7B are explanatory diagrams of normal printing. 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, and FIG. 9C is obtained by the printing method of the present embodiment. It is explanatory drawing of a mode when a dot is formed. FIG. 4 is a flowchart of processing performed in an inspection process after manufacturing the printer 1. FIG. 10B is a flowchart of the correction value acquisition process shown in FIG. 10A. It is explanatory drawing of the ink cartridge 35 for a test | inspection which an inspection kit comprises. It is explanatory drawing of the test pattern for a correction value setting. 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. 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, and FIG. 14C is an explanatory diagram of image data after the rotation processing. 15A is an explanatory diagram of image data at the time of trimming, FIG. 15B is an explanatory diagram of a trimming position at the upper ruled line, and FIG. 15C is an explanatory diagram of a trimming position at the lower ruled line. It is explanatory drawing of resolution conversion. FIG. 17A is an explanatory diagram of image data at the time of detection of the left ruled line, FIG. 17B is an explanatory diagram of detection of the position of the left ruled line, and FIG. It is explanatory drawing of the measurement range of the density of a pattern. 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. 20A is an explanatory diagram of the target command tone value Sbt with respect to the command tone value Sb in the row region A, and 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 B. is there. It is explanatory drawing of the correction value table of cyan. It is explanatory drawing of the correction value table for normal printing regions 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. 10B is a flowchart of the density correction effect confirmation process shown in FIG. 10A. It is explanatory drawing of the test pattern for a correction effect confirmation. It is explanatory drawing of the pattern for confirmation. It is explanatory drawing of the reading range of the pattern for confirmation. FIG. 29A is an explanatory diagram of image data at the time of tilt detection, and FIG. 29B is an explanatory diagram of image data after the rotation process. 30A is an explanatory diagram of image data before trimming, FIG. 30B is an explanatory diagram of image data after trimming, and FIG. 30C is an explanatory diagram of image data after resolution conversion. It is explanatory drawing of the measurement of the density | concentration of each row area | region from the 1st to the 4th. It is explanatory drawing of the row | line | column area | region which may be excluded from the object of density | concentration measurement. It is explanatory drawing of the division area which is a calculation unit of the density dispersion | variation of each confirmation pattern. FIG. 26 is a flowchart of a density correction effect determination step (S160) shown in FIG. 35A and 35B are explanatory diagrams of a reverse phenomenon that can occur when the density variation σ is small. It is a flowchart of the density correction effect determination step (S160a) according to the present embodiment. It is a graph of the relationship between the sensory evaluation value of density unevenness and density variation σ, which is used to acquire the determination threshold value σ _th .

Explanation of symbols

1 printer, 5 manuscripts,
20 transport unit, 21 paper feed roller, 22 transport motor, 23 transport roller,
24 platen, 25 paper discharge roller,
30 Carriage unit, 31 Carriage, 32 Carriage motor,
33 ink cartridge, 35 inspection ink cartridge,
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 device,
130 input device, 140 recording / reproducing device, 150 scanner,
151 Upper lid, 152 Document platen glass, 153 Reading carriage, 154 Guide member,
155 Movement mechanism, 157 exposure lamp, 158 line sensor, 159 optical system

Claims (8)

A method for determining whether or not to perform image density correction,
Printing a confirmation pattern when density correction is not performed and a confirmation pattern when density correction is performed on a medium;
A step of reading the density of each confirmation pattern;
Obtaining a variation in density of each of the confirmation patterns based on the density reading;
Based on the comparison result of the density variation between the respective confirmation patterns and the comparison result with respect to the predetermined threshold value of the density variation of the confirmation pattern when the density correction is performed, whether or not the density correction of the image can be executed is determined. A determining step;
Bei to give a,
In the step of determining whether or not to perform density correction of the image,
When the density variation is smaller or equal in the confirmation pattern when the density correction is performed than when the density correction is not performed, it is determined that the density correction can be performed,
Even if the density variation of the confirmation pattern when the density correction is performed is larger than when the density correction is not performed, the density variation of the confirmation pattern when the density correction is performed A determination method for determining whether or not to execute density correction of an image , wherein if it is equal to or less than a threshold value, determination is made that the density correction can be executed. A method for determining whether or not to perform density correction of an image according to claim 1 ,
The moving direction is repeated by repeating a dot forming operation for ejecting ink from a plurality of nozzles moving in the moving direction to form dots on the medium and a conveying operation for conveying the medium in a crossing direction intersecting the moving direction. Each check pattern is printed by forming a row of dots along each of the row regions arranged in the intersecting direction,
A method for determining whether or not to perform density correction of an image, wherein the read value is generated for each row region. A method for determining whether or not to perform density correction of an image according to claim 2 ,
The plurality of nozzles are aligned along the intersecting direction to form a nozzle group,
The nozzle group is provided for each color of ink ejected when printing an image,
Each confirmation pattern is divided into regions for each nozzle group with respect to the moving direction, and the variation in density is obtained for each of the divided regions. A method for determining whether or not to perform density correction of an image according to claim 3 ,
Each confirmation pattern is printed based on image data,
The image data includes gradation value data of density for forming the dot row in a row region included in a region divided for each nozzle group in each check pattern,
The gradation value data is the same over all the row areas included in the divided areas, and the determination method of whether or not image density correction can be performed. A method for determining whether or not to perform density correction of an image according to claim 3 or 4 ,
In the step of determining whether or not to perform density correction of the image,
Compare the variations between the regions printed by the same nozzle group in each confirmation pattern,
For any of the above areas, when density variation is smaller or equal when density correction is performed than when density correction is not performed, a determination is made that the density correction can be performed. ,
Even if there is the region where the density variation is larger when the density correction is performed than when the density correction is not performed, the average value of the density variation of the region when the density correction is performed When the value is equal to or smaller than the threshold value, a determination is made that the density correction can be performed. A method for determining whether or not to perform image density correction according to any one of claims 3 to 5 ,
The moving direction is repeated by repeating a dot forming operation for ejecting ink from a plurality of nozzles moving in the moving direction to form dots on the medium and a conveying operation for conveying the medium in a crossing direction intersecting the moving direction. Forming a dot row along each of the row regions arranged in the crossing direction, and printing a correction pattern,
Reading the density for each row region from the correction pattern, and obtaining a correction value for each row region based on the read value of the density,
When it is determined that the density correction can be performed, density correction is performed for each row area based on the correction value when the image is printed. Judgment method. A method for determining whether or not to perform density correction of an image according to claim 6 ,
The method for determining whether or not image density correction can be performed, wherein the correction pattern is printed for each nozzle group. A method for determining whether or not to perform image density correction,
Printing a confirmation pattern when density correction is not performed and a confirmation pattern when density correction is performed on a medium;
A step of reading the density of each confirmation pattern;
Obtaining a variation in density of each of the confirmation patterns based on the density reading;
Based on the comparison result of the density variation between the respective confirmation patterns and the comparison result with respect to the predetermined threshold value of the density variation of the confirmation pattern when the density correction is performed, whether or not the density correction of the image can be executed is determined. A determining step;
With
The moving direction is repeated by repeating a dot forming operation for ejecting ink from a plurality of nozzles moving in the moving direction to form dots on the medium and a conveying operation for conveying the medium in a crossing direction intersecting the moving direction. Are formed for each row region arranged in the intersecting direction, and each check pattern is printed, and the reading value is generated for each row region,
The plurality of nozzles are aligned along the intersecting direction to form a nozzle group, and the nozzle group is provided for each color of ink ejected when printing an image, and each confirmation pattern is moved as described above. The area is divided for each nozzle group with respect to the direction, and the variation in density is obtained for each of the divided areas,
Each confirmation pattern is printed based on image data, and the image data has a density for forming the dot row in a row region included in a region divided for each nozzle group in each confirmation pattern. Gradation value data, and the gradation value data is the same over all the column regions included in the partitioned region,
In the step of determining whether or not to perform density correction of the image, the variation is compared between the areas printed by the same nozzle group in each of the confirmation patterns, and density correction is not performed for any of the areas. When the density correction is smaller than or equal to the case where the density correction is performed, it is determined that the density correction can be performed, while the density correction is performed more than when the density correction is not performed. Even if there is the region where the variation in density is larger when the density correction is performed, the density is not corrected if the average value of the density variation in the area when the density correction is performed is equal to or less than the threshold value. A decision is made that correction can be performed,
The moving direction is repeated by repeating a dot forming operation for ejecting ink from a plurality of nozzles moving in the moving direction to form dots on the medium and a conveying operation for conveying the medium in a crossing direction intersecting the moving direction. Are formed for each row region arranged in the intersecting direction, a correction pattern is printed, the density is read for each row region from the correction pattern, and the row is read based on the read density value. When a correction value is obtained for each area, and it is determined that the density correction can be performed, density correction is performed for each row area based on the correction value when an image is printed,
The method for determining whether or not image density correction can be performed, wherein the correction pattern is printed for each nozzle group.