JP2006007533A - Setting method of correction value, and test pattern for density correction - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce effects onto a correction value as much as possible even when skewing occurs at the time of printing of a test pattern. <P>SOLUTION: In a setting method of the correction value H for correcting a density of an image printed by every unit region adjacent to each other in a predetermined direction (transfer direction)(region of pixels corresponding to a raster line), the setting method includes a printing step (S121) of printing the test pattern (pattern for correction CP), density data acquiring steps (S122 and S123) of acquiring density data of the test pattern for a predetermined range in the predetermined direction from a reference position SP by setting the reference position between one end and the other end of the other predetermined direction (carriage movement direction) which intersects the predetermined direction of the test pattern, and a correction value setting step (S124) of setting the correction value for each of the unit regions on the basis of the density data. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a correction value setting method for correcting the density of an image printed for each unit area adjacent in a predetermined direction, and a test pattern for density correction.

  As an apparatus for printing an image, an ink jet printer (hereinafter simply referred to as a printer) that forms dots by ejecting ink onto a medium (paper, cloth, OHP sheet, etc.) is known. For example, this printer is connected to be able to communicate with a personal computer in which a printer driver is installed. The printer then performs a dot forming operation for forming dots on the paper by ejecting ink from a plurality of nozzles that move with the carriage. By this dot forming operation, a raster line composed of a plurality of dots along the nozzle movement direction (hereinafter also referred to as the carriage movement direction) is printed on the paper. In addition, the printer performs a transport operation for transporting paper in a crossing direction (hereinafter also referred to as a transporting direction) that intersects the moving direction of the nozzles by the transporting unit. When these dot forming operation and transport operation are repeated, a plurality of raster lines are printed on the paper in a state adjacent to the transport direction. As a result, an image is printed on the paper. That is, it can be said that this printer prints a raster line for each unit area adjacent in the transport direction.

In this type of printer, ink droplet ejection characteristics such as the amount of ink droplets and flight direction vary from nozzle to nozzle. This variation in the ejection characteristics is not preferable because it causes density unevenness in the printed image. Therefore, in a conventional printer, a correction value is set for each nozzle, and the amount of ink is adjusted based on the set correction value (see, for example, Patent Document 1). In this conventional method, an output characteristic coefficient indicating the characteristic of the ink ejection amount for each nozzle is stored in the head characteristic register. Then, by using the output characteristic coefficient when ejecting ink droplets, density unevenness of the printed image is prevented.
Japanese Patent Laid-Open No. 2-54676 (2nd page, FIG. 4)

  By the way, the above-described printer corrects the ejection amount for each nozzle, and does not take into account density unevenness due to the flying curve of ink droplets. This density unevenness is caused by the deviation of the landing position of the ink droplet ejected from the nozzle from the normal position in the transport direction. That is, this density unevenness occurs when the interval between adjacent raster lines becomes narrower or wider than a prescribed interval.

  In order to prevent such density unevenness of the image, it is conceivable to set a correction value for each unit area. That is, the density unevenness of the entire image can be suppressed by correcting the density of the image for each unit area. In this case, the correction value is set based on a correction pattern as a test pattern. Here, the correction value is desirably set as accurately as possible. However, in this type of printer, there is a case in which the paper is fed in an uneven manner and the printing direction of the raster line with respect to the paper is gradually shifted (hereinafter also referred to as skew). If the correction pattern is distorted by this skew, the accuracy of the correction value may be impaired.

  The present invention has been made in view of such problems, and its purpose is to print a high-quality image using a correction value for each unit area, even when skew occurs during printing of a test pattern. The purpose is to minimize the influence on the correction value.

  A main invention is a correction value setting method for correcting the density of an image printed for each unit region adjacent in a predetermined direction, the printing step for printing a test pattern, and the predetermined direction in the test pattern. Provides a reference position between one end and the other end of another predetermined direction that intersects, a density data acquisition step for acquiring density data of the test pattern for a predetermined range in the predetermined direction from the reference position; and the density data And a correction value setting step for setting a correction value for each of the unit areas.

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

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

  A correction value setting method for correcting the density of an image to be printed for each unit region adjacent in a predetermined direction, wherein a printing step for printing a test pattern and the predetermined direction in the test pattern intersect A reference position is provided between one end and the other end of the predetermined direction, and a density data acquisition step of acquiring density data of the test pattern for a predetermined range in the predetermined direction from the reference position, and based on the density data, A correction value setting method including a correction value setting step for setting a correction value for each of the unit areas can be realized.

  According to such a correction value setting method, even if a so-called skew occurs and an image forming a test pattern, specifically, an image formed in a unit area is printed with an inclination with respect to a sheet, Measurement errors due to tilt can be reduced. This is because a reference position is provided between one end and the other end in another predetermined direction in the test pattern.

  That is, the density data acquisition target is a test pattern in a predetermined range from the reference position in a predetermined direction. For this reason, the amount of deviation of the unit image from the normal position (the amount of deviation in the predetermined direction) increases as the distance from the reference position in the other predetermined direction increases. Therefore, by providing the reference position between one end and the other end of the test pattern in another predetermined direction, the amount of deviation from the reference position to one end of the test pattern and the amount of deviation from the reference position to the other end of the test pattern Both can be made smaller than the maximum value. In other words, the amount of deviation can be made smaller than when the end of another predetermined direction in the test pattern is used as a reference. As a result, the influence on the skew correction value can be minimized.

In this correction value setting method, the test pattern includes a measurement target pattern in which a plurality of sub-patterns having different densities are arranged along the other predetermined direction. In the correction value setting step, A correction value is set for each density of the sub-pattern based on the density data corresponding to the pattern.
According to such a correction value setting method, the influence on the correction value due to the skew can be reduced for each density.

In this correction value setting method, the reference position is provided between adjacent sub-patterns.
According to such a correction value setting method, the reference position can be easily recognized based on the sub-pattern density difference.

In this correction value setting method, the test pattern has a setting mark formed in a mode different from the sub-pattern between adjacent sub-patterns provided with the reference position.
According to such a correction value setting method, since the reference position is recognized based on the setting mark, the reference position can be reliably recognized.

In this correction value setting method, the adjacent sub-patterns are formed by being spaced apart from each other in the predetermined direction.
According to such a correction value setting method, the data for forming the setting mark can be reduced with respect to the test pattern print data. Therefore, the data amount of the test pattern print data can be reduced.

In this correction value setting method, the setting mark has an index indicating the reference position.
According to such a method for setting the correction value, it is possible to easily determine a predetermined range to be a density measurement target based on the index indicating the reference position.

In this correction value setting method, the reference position is provided between the one end and the other end in the other predetermined direction in the test pattern.
According to such a correction value setting method, the amount of deviation from the reference position due to skew to one end of the test pattern can be made equal to the amount of deviation from the reference position to the other end of the test pattern. . As a result, the influence on the correction value due to the skew can be further reduced.

In this correction value setting method, in the density data acquisition step, density data of the test pattern is acquired at a resolution higher than the print resolution of the test pattern, and the acquired density data is a resolution corresponding to the print resolution. To convert to.
According to such a correction value setting method, the correction value can be obtained with high accuracy.

In this correction value setting method, the test pattern includes a measurement target pattern in which a plurality of sub-patterns having different densities are arranged along the other predetermined direction. In the density data acquisition step, Pattern density data is acquired together with coordinate information, and a plurality of density data belonging to a specific unit region are associated with each other using the coordinate information.
Such a correction value setting method can easily cope with variations in the degree of skew.

In this correction value setting method, the test pattern has another index for associating the density data of the test pattern, and in the density data acquisition step, the other index, and the Using the coordinate information, a plurality of density data belonging to a specific unit region are associated with each other.
According to such a correction value setting method, it is possible to easily associate density data based on another index.

In this correction value setting method, the image is printed for each unit area by ejecting ink from a nozzle selected from a nozzle group. In the correction value setting step, the image is assigned to the unit area. The correction value is set at a set cycle determined based on a combination of nozzles.
According to such a correction value setting method, it is sufficient to set the correction value for a part of the unit area, and therefore the required memory capacity can be reduced.

In this correction value setting method, in the density data acquisition step, the predetermined range is determined so that a plurality of the setting periods are included, and in the correction value setting step, density data of corresponding unit regions of different periods The correction value is set based on
According to such a correction value setting method, the correction value is set based on the density data of the corresponding unit region having a different period, so that the accuracy can be improved.

  A correction value setting method for correcting the density of an image printed for each unit region adjacent in a predetermined direction by ejecting ink from a nozzle selected from a nozzle group, and having a plurality of different densities A sub-pattern having a measurement target pattern arranged along another predetermined direction intersecting the predetermined direction, a printing step of printing a test pattern, and one end and the other end of the other predetermined direction in the test pattern A reference position is provided in between, and a density data acquisition step for acquiring density data of the test pattern for a predetermined range in the predetermined direction from the reference position, and based on the density data corresponding to the sub-pattern, A correction value setting step for setting a correction value for each density of the sub-pattern for each, and the reference position is The test pattern is provided between the adjacent sub-patterns between the one end and the other end in the other predetermined direction, and the test pattern is another parameter for determining the correction amount for the density data of the test pattern. And a setting mark formed in a mode different from the sub-pattern between the adjacent sub-patterns provided with the reference position, and the setting mark indicates a reference position A setting having an index and formed by arranging the adjacent sub-patterns apart from each other in the predetermined direction, and in the correction value setting step, a setting determined based on a combination of the unit region and the nozzle in charge The correction value is set in a cycle, and the correction value is set based on the density data of the corresponding unit region in a different cycle. In the data acquisition step, the density data of the test pattern is acquired at a resolution higher than the print resolution of the test pattern, the acquired density data is converted into a resolution corresponding to the print resolution, and the density data of the test pattern is converted into coordinates. The predetermined information so that a plurality of density data belonging to a specific unit region are associated with each other and a plurality of the set cycles are included using the other index and the information of the coordinates. It is also possible to realize a correction value setting method for defining the range.

  According to such a correction value setting method, almost all the effects described above can be obtained, and therefore the object of the present invention can be achieved most effectively.

  In addition, a measurement target pattern in which a plurality of sub-patterns printed in unit areas adjacent to each other in a predetermined direction and having different densities along another predetermined direction intersecting with the predetermined direction and the adjacent sub-patterns In the meantime, it is possible to realize a density correction test pattern having a density data acquisition range setting mark formed in a mode different from the sub-pattern.

=== Configuration of Printing System ===
Next, an embodiment of a printing system will be described with reference to the drawings.

  FIG. 1 is an explanatory diagram showing an external configuration of the printing system 1000. The printing system 1000 includes a printer 1, a computer 1100, a display device 1200, an input device 1300, and a recording / reproducing device 1400. In this example, the printer 1 and the computer 1100 constitute a printing apparatus. That is, the printer 1 corresponds to a printing apparatus main body, and its operation is controlled by a computer 1100 as a printing control apparatus. The printer 1 prints an image on a medium such as paper, cloth, or film. In addition, regarding the medium, in the following description, a sheet S (see FIG. 9) which is a typical medium will be described as an example. The computer 1100 is communicably connected to the printer 1. In order to cause the printer 1 to print an image, the computer 1100 outputs print data corresponding to the image to the printer 1. The display device 1200 has a display. The display device 1200 displays a user interface such as an application program 1104 or a printer driver 1110 (see FIG. 2). The input device 1300 is, for example, a keyboard 1300A or a mouse 1300B. The recording / reproducing device 1400 is, for example, a flexible disk drive device 1400A or a CD-ROM drive device 1400B.

  A printer driver 1110 is installed in the computer 1100. The printer driver 1110 is a program for realizing a function of converting image data output from the application program 1104 into print data, and includes codes for realizing various functions. The printer driver 1110 is provided in a state where it is recorded on a recording medium (computer-readable recording medium) such as a flexible disk or a CD-ROM. The printer driver 1110 can also be downloaded to the computer 1100 via the Internet.

=== Printer driver ===
<About the printer driver 1110>
FIG. 2 is a schematic explanatory diagram of basic processing performed by the printer driver 1110. In addition, about the component already demonstrated, since the same code | symbol is attached | subjected, description is abbreviate | omitted.

  In the computer 1100, programs such as a video driver 1102, an application program 1104, and a printer driver 1110 are operating under an operating system installed in the computer 1100. The video driver 1102 has a function of causing the display device 1200 to display a user interface, for example, in accordance with a display command from the application program 1104 or the printer driver 1110. The application program 1104 has a function of performing image editing, for example, and creates data related to an image (image data). The user can give an instruction to print an image edited by the application program 1104 via the user interface of the application program 1104. When the application program 1104 receives a print instruction, the application program 1104 outputs image data to the printer driver 1110.

  When the user instructs printing on the user interface of the application program 1104, the printer driver 1110 receives image data from the application program 1104. The printer driver 1110 converts this image data into print data, and outputs the print data to the printer 1. The image data has pixel data as data relating to the pixels of the image to be printed. The pixel data is converted in gradation value and the like according to each processing stage described later. The pixel data is converted into data relating to dots formed on the paper (data such as dot color and size) in the final print data stage. Note that a pixel is a square grid that is virtually defined on a sheet in order to define a position where ink is landed to form a dot. An image is formed for each unit region composed of a plurality of pixels arranged in the nozzle movement direction (carriage movement direction). This unit region is defined adjacent to the conveyance direction that intersects the moving direction of the nozzle. Therefore, the image is composed of a plurality of unit images (corresponding to raster lines to be described later) printed for each unit area.

  The print data is data in a format that can be interpreted by the printer 1 and includes pixel data and various command data. The command data is data for instructing the printer 1 to execute a specific operation. For example, the command data is data for instructing paper feeding, data indicating the transport amount, and data for instructing paper ejection. The printer driver 1110 performs resolution conversion processing, color conversion processing, halftone processing, rasterization processing, and the like in order to convert image data output from the application program 1104 into print data. Accordingly, the printer driver 1110, in other words, the computer 1100 in which the printer driver 1110 is installed functions as a print control apparatus and corresponds to a part of the controller. Hereinafter, each process performed by the printer driver 1110 will be described.

  The resolution conversion process is the resolution when printing the image data (text data, image data, etc.) output from the application program 1104 on the paper S (the interval between dots when printing), and is also called the print resolution. ). For example, when the print resolution is specified as 720 × 720 dpi, the image data received from the application program 1104 is converted into image data having a resolution of 720 × 720 dpi. Examples of this conversion method include interpolation and thinning of pixel data. For example, when the resolution of the image data is lower than the designated printing resolution, new pixel data is generated between adjacent pixel data by performing linear interpolation or the like. On the contrary, when the resolution of the image data is higher than the print resolution, the resolution of the image data is made equal to the print resolution by thinning out pixel data at a certain rate. In this resolution conversion process, the size of the print area (referred to as an area where ink is actually ejected) is also adjusted based on the image data.

  Note that each pixel data in the image data is data having multi-level (for example, 256 levels) gradation values represented by an RGB color space. Hereinafter, the pixel data having RGB gradation values is referred to as RGB pixel data, and image data composed of the RGB pixel data is referred to as RGB image data.

  The color conversion process is a process of converting each RGB pixel data of the RGB image data into data having multi-level (for example, 256 levels) gradation values represented by the CMYK color space. This CMYK is the color of the ink that the printer 1 has. That is, C means cyan. M represents magenta, Y represents yellow, and K represents black. Hereinafter, the pixel data having CMYK gradation values is referred to as CMYK pixel data, and the image data composed of these CMYK pixel data is referred to as CMYK image data. This color conversion processing is performed by the printer driver 1110 referring to a table (color conversion lookup table LUT) in which RGB gradation values and CMYK gradation values are associated with each other.

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

  For such halftone processing, for example, a dither method or the like is used, and 2-bit CMKY pixel data is created so that the printer 1 can form dots dispersedly. The halftone process using the dither method will be described later. Further, the method used for the halftone process is not limited to the dither method, and a γ correction method, an error diffusion method, or the like may be used. In this embodiment, pixel data conversion processing based on correction values is performed in this halftone processing (described later).

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

<About halftone processing by dither method>
Here, the halftone process by the dither method will be described in detail. FIG. 3 is a flowchart for explaining halftone processing by the dither method. The printer driver 1110 (in other words, the computer 1100 on which the printer driver 1110 is installed) executes the following steps according to the flowchart.

  First, in step S300, the printer driver 1110 acquires CMYK image data. The CMYK image data is composed of, for example, image data represented by 256 levels of gradation values for each ink color of C, M, Y, and K. That is, the CMYK image data includes C image data related to cyan (C), M image data related to magenta (M), Y image data related to yellow (Y), and K image data related to black (K). These C, M, Y, and K image data are respectively composed of C, M, Y, and K pixel data indicating the gradation value of each ink color. Since the following description applies to any of C, M, Y, and K image data, K image data will be described as a representative of these.

  The printer driver 1110 executes the processing from step S301 to step S311 for all the K pixel data in the K image data while sequentially changing the processing target K pixel data. Through these processes, the K image data is converted into 2-bit data indicating the above-described four gradation values for each K pixel data.

  This conversion process will be described in detail. First, in step 301, large dot level data LVL is set according to the gradation value of the K pixel data to be processed. For this setting, for example, a generation rate table is used.

  Here, FIG. 4 is a diagram showing a generation rate table used for setting level data for large, medium, and small dots. In the figure, the horizontal axis is the gradation value (0 to 255), the left vertical axis is the dot generation rate (%), and the right vertical axis is the level data. The level data refers to data obtained by converting the dot generation rate into 256 levels from 0 to 255. The “dot generation rate” means the ratio of pixels in which dots are formed among pixels in a region when a uniform region is reproduced according to a certain gradation value. For example, the dot generation rate at a certain gradation value is 65% large dots, 25% medium dots, and 10% small dots. With this dot generation rate, 10 pixels in the vertical direction and 10 pixels in the horizontal direction. Suppose that the area of 100 pixels is printed. In this case, of the 100 pixels, 65 pixels are formed with large dots, 25 pixels are formed with medium dots, and 10 pixels are formed with small dots. A profile SD indicated by a thin solid line in FIG. 4 indicates a small dot generation rate. A profile MD indicated by a thick solid line indicates a medium dot generation rate, and a profile LD indicated by a broken line indicates a large dot generation rate.

  In step S301, level data LVL corresponding to the gradation value is read from the large dot profile LD. For example, as shown in FIG. 4, if the gradation value of the K pixel data to be processed is gr, the level data LVL is obtained as 1d from the intersection with the profile LD. Actually, this profile LD is stored in a memory (not shown) such as a ROM provided in the computer 1100 in the form of a one-dimensional table, for example. Then, the printer driver 1110 obtains level data by referring to this table.

  In step S302, it is determined whether or not the level data LVL set as described above is larger than the threshold value THL. Here, dot on / off determination is performed by the dither method. The threshold value THL is set to a different value for each pixel block of a so-called dither matrix. In this embodiment, a dither matrix in which values from 0 to 254 appear in a 16 × 16 square pixel block is used.

  FIG. 5 is a diagram showing dot on / off determination by the dither method. For convenience of illustration, FIG. 5 shows ON / OFF determination results for some K pixel data. The outline of the operation in the on / off determination of this example is as follows.

  First, the printer driver 1110 compares the level data LVL of each K pixel data with the threshold value THL of the pixel block on the dither matrix corresponding to the K pixel data. When the level data LVL is larger than the threshold value THL, the dot is turned on (that is, a dot is formed), and when the level data LVL is smaller, the dot is turned off (that is, the dot is changed). Do not form). In the figure, the pixel data in the shaded area in the dot matrix is K pixel data for turning on the dots. That is, in step S302, if the level data LVL is larger than the threshold value THL, the printer driver 1110 proceeds to step S310, otherwise proceeds to step S303.

  Here, when the process proceeds to step S310, the printer driver 1110 records the value “11” in association with the K pixel data to be processed as pixel data (2-bit data) indicating a large dot, The process proceeds to step S311. In step S311, it is determined whether or not the process has been completed for all the K pixel data. If the process has been completed, the halftone process is terminated. On the other hand, if not completed, the processing target is moved to unprocessed K pixel data, and the process returns to step S301.

  In step S303, the printer driver 1110 sets medium dot level data LVM. The medium dot level data LVM is set by the above-described generation rate table based on the gradation value. The setting method of the medium dot level data LVM is the same as the setting of the large dot level data LVL. That is, in the example of FIG. 4, the level data LVM corresponding to the gradation value gr is obtained as 2d indicated by the intersection with the profile MD indicating the medium dot generation rate.

  Next, in step S304, the medium dot level data LVM and the threshold value THM are compared, and a medium dot on / off determination is performed. The on / off determination method is the same as that for large dots. Here, in the ON / OFF determination of medium dots, the threshold THM used for the determination is set to a value different from the threshold THL in the case of large dots. That is, when on / off determination is performed using the same dither matrix for large dots and medium dots, the pixel blocks where the dots are likely to be turned on coincide with each other. That is, when a large dot is turned off, there is a high possibility that a medium dot is also turned off. As a result, the medium dot generation rate may be lower than the desired generation rate. In order to avoid such a phenomenon, in this embodiment, the dither matrix is changed between large dots and medium dots. That is, by changing the pixel block that is likely to be turned on between large dots and medium dots, each dot is appropriately formed.

  6A and 6B are diagrams illustrating a relationship between a dither matrix used for large dot determination and a dither matrix used for medium dot determination. In this embodiment, the first dither matrix TM of FIG. 6A is used for large dots. For medium dots, the second dither matrix UM in FIG. 6B is used. This second dither matrix UM is obtained by moving each threshold value in the first dither matrix TM symmetrically with the center in the transport direction (corresponding to the vertical direction in the figure) as the center. In the present embodiment, a 16 × 16 matrix is used as described above, but for convenience of illustration, FIG. 6 shows a 4 × 4 matrix. Also, dither matrices that are completely different for large dots and medium dots may be used.

  If the medium dot level data LVM is larger than the medium dot threshold value THM in step S304, the printer driver 1110 determines that the medium dot should be turned on, and proceeds to step S309. Advances to step S305. When the process proceeds to step S309, the printer driver 1110 records the pixel data “10” indicating the medium dot in association with the K pixel data to be processed, and the process proceeds to step S311. In step 311, it is determined whether or not the process has been completed for all the K pixel data. If the process has been completed, the halftone process is terminated. On the other hand, if not completed, the processing target is moved to unprocessed K pixel data, and the process returns to step S301.

  When the process proceeds to step S305, the small dot level data LVS is set in the same manner as the setting of the level data for large dots and medium dots. The dither matrix for small dots is preferably different from that for medium dots and large dots as described above in order to prevent a decrease in the generation rate of small dots.

  In step S306, the printer driver 1110 compares the level data LVS with the small dot threshold THS. If the level data LVS is larger than the small dot threshold THS, the printer driver 1110 proceeds to step S308, otherwise. Then, the process proceeds to step S307. If the process proceeds to step S308, pixel data “01” indicating a small dot is recorded in association with the K pixel data to be processed, and the process proceeds to step S311. In step 311, it is determined whether or not the processing has been completed for all the K pixel data. If not, the processing target is moved to unprocessed K pixel data, and the process returns to step S 301. On the other hand, if it has been completed, the halftone process is terminated.

  When the process proceeds to step S307, the printer driver 1110 records the pixel data “00” indicating no dot in association with the K pixel data to be processed, and the process proceeds to step S311. In step S311, it is determined whether or not the processing has been completed for all the K pixel data. If the processing has not been completed, the processing target is moved to unprocessed K pixel data, and the process returns to step S301. On the other hand, if it has been completed, the halftone process is terminated.

<Settings of Printer Driver 1110>
FIG. 7 is an explanatory diagram of a user interface of the printer driver 1110. The user interface of the printer driver 1110 is displayed on the display device 1200 via the video driver 1102. A user can make various settings of the printer driver 1110 using the input device 1300. As basic settings, settings of margin form mode and image quality mode are prepared, and as paper settings, settings of paper size mode and the like are prepared. Then, the printer driver 1110 recognizes the print resolution and the size of the paper S based on the setting by the user interface.

=== Printer ===
<About the configuration of the printer 1>
FIG. 8 is a block diagram of the overall configuration of the printer 1 of the present embodiment. FIG. 9 is a schematic diagram of the overall configuration of the printer 1 of the present embodiment. FIG. 10 is a cross-sectional view of the overall configuration of the printer 1 of the present embodiment. FIG. 11 is a diagram illustrating the arrangement of the nozzles Nz on the lower surface of the head. Hereinafter, the basic configuration of the printer 1 of the present embodiment will be described with reference to these drawings.

  The printer 1 includes a paper transport mechanism 20, a carriage moving mechanism 30, a head unit 40, a sensor group 50, and a printer controller 60.

  The printer 1 (printing apparatus main body) that has received a print signal from the computer 1100 that is an external apparatus controls the control target unit, that is, the paper transport mechanism 20, the carriage moving mechanism 30, and the head unit 40 by the printer controller 60. At this time, the printer controller 60 corresponds to a part of the controller, and prints an image on the paper S based on the print data received from the computer 1100. At this time, each sensor of the sensor group 50 monitors the status in the printer 1. Each sensor outputs a detection result to the printer controller 60. Upon receiving the detection results from the sensors, the printer controller 60 controls the control target unit based on the detection results.

  The paper transport mechanism 20 is a transport mechanism that feeds the paper S as a medium to a printable position, or transports the paper S by a predetermined transport amount in the transport direction. Here, the transport direction is a direction that intersects the carriage movement direction described below, and corresponds to a “predetermined direction”. The paper transport mechanism 20 includes a paper feed roller 21, a transport motor 22, a transport roller 23, a platen 24, and a paper discharge roller 25. The paper feed roller 21 is a roller for automatically feeding the paper S inserted into the paper insertion opening into the printer, and has a D-shaped cross-sectional shape in this example. The carry motor 22 is a motor for carrying the paper S in the carrying direction, and is constituted by, for example, a DC motor. The operation of the carry motor 22 is controlled by the printer controller 60. The transport roller 23 is a roller for transporting the paper S sent by the paper feed roller 21 to a printable area. The operation of the transport roller 23 is also controlled by the transport motor 22. The platen 24 is a member that supports the paper S being printed from the back side of the paper S. The paper discharge roller 25 is a roller for transporting the paper S that has been printed.

  The carriage moving mechanism 30 is a mechanism for moving the carriage CR to which the head unit 40 is attached in the carriage moving direction (corresponding to another predetermined direction). This carriage movement direction includes a movement direction from one side to the other side and a movement direction from the other side to the one side. A head 41 included in the head unit 40 is provided with a nozzle Nz for ejecting ink. For this reason, as the carriage CR moves, the nozzle Nz also moves in the carriage movement direction.

  The carriage moving mechanism 30 includes a carriage motor 31, a guide shaft 32, a timing belt 33, a driving pulley 34, and a driven pulley 35. The carriage motor 31 corresponds to a drive source for moving the carriage CR. The operation of the carriage motor 31 is controlled by the printer controller 60 described above. A drive pulley 34 is attached to the rotation shaft of the carriage motor 31. The drive pulley 34 is disposed on one end side in the carriage movement direction. A driven pulley 35 is disposed on the other end side in the carriage movement direction on the opposite side to the drive pulley 34. The timing belt 33 is connected to the carriage CR and is spanned between a driving pulley 34 and a driven pulley 35. The guide shaft 32 is a member that supports the carriage CR in a movable state. The guide shaft 32 is attached along the carriage movement direction. Accordingly, when the carriage motor 31 operates, the carriage CR moves along the guide shaft 32 in the carriage movement direction.

  The head unit 40 is for ejecting ink onto the paper S. The head unit 40 has a head 41. As shown in FIG. 11, a nozzle Nz as an ejection unit that ejects ink is provided on the lower surface of the head 41. The nozzles Nz are grouped for each type of ink to be ejected, and a nozzle row is configured by each group (hereinafter also referred to as a nozzle group). The illustrated head 41 includes a black ink nozzle row Nk, a cyan ink nozzle row Nc, a magenta ink nozzle row Nm, and a yellow ink nozzle row Ny. Each nozzle row includes n (for example, n = 180) nozzles Nz. In each nozzle row, the nozzle groups are provided at regular intervals (nozzle pitch: k · D) along the transport direction. Here, D is a minimum dot pitch in the transport direction, that is, an interval at the highest resolution of dots formed on the paper S. K is a coefficient representing the relationship between the minimum dot pitch D and the nozzle pitch, and is set to an integer of 1 or more. For example, when the nozzle pitch is 180 dpi (1/180 inch) and the dot pitch in the transport direction is 720 dpi (1/720 inch), k = 4. In the example shown in the figure, the nozzles Nz of each nozzle row are assigned a lower number as the nozzles Nz on the downstream side (# 1 to # 180). That is, the nozzle Nz (# 1) is located downstream of the nozzle Nz (# 180) in the transport direction, that is, on the upper end side of the sheet S.

  In the printer 1, a plurality of types of ink having different amounts can be individually ejected from each nozzle Nz. For example, from each nozzle Nz, there are three types of ink consisting of large ink droplets capable of forming large dots, medium ink droplets capable of forming medium dots, and small ink droplets capable of forming small dots. Drops can be jetted. Therefore, in this example, the non-formation of dots corresponding to the pixel data “00”, the formation of small dots corresponding to the pixel data “01”, the formation of medium dots corresponding to the pixel data “10”, and the pixel data “11”. 4 types of control such as formation of a large dot corresponding to "." That is, four gradation recording is possible.

  The sensor group 50 is for monitoring the status of the printer 1. The sensor group 50 includes a linear encoder 51, a rotary encoder 52, a paper detection sensor 53, a paper width sensor 54, and the like. The linear encoder 51 is for detecting the position of the carriage CR (head 41, nozzle Nz) in the carriage movement 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 leading end position of the paper S to be printed. The paper width sensor 54 is for detecting the width of the paper S to be printed.

  The printer controller 60 controls the printer 1. The printer controller 60 includes an interface unit 61, a CPU 62, a memory 63, and a control unit 64. The interface unit 61 is interposed between the computer 1100, which is an external device, and the printer 1, and transmits and receives data. The CPU 62 is an arithmetic processing unit for controlling the entire printer. The memory 63 is for securing an area for storing a program of the CPU 62, a work area, and the like, and is configured by a storage element such as a RAM, an EEPROM, or a ROM. The CPU 62 controls each control target unit via the control unit 64 in accordance with a program stored in the memory 63. In the present embodiment, a partial area of the memory 63 is used as a correction value storage unit 63a for storing a correction value H (described later).

<About printing operation>
FIG. 12 is a flowchart of the operation during printing. Each operation described below is executed by the printer controller 60 controlling each control target unit in accordance with a program stored in the memory 63. This program has code for executing each operation.

  Print command reception (S001): The printer controller 60 receives a print command from the computer 1100 via the interface unit 61. This print command is included in the header of print data transmitted from the computer 1100. Then, the printer controller 60 analyzes the contents of various commands included in the received print data, controls each control target unit, and performs the following paper feed operation, dot formation operation, transport operation, paper discharge processing, and the like. .

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

  Dot Forming Operation (S003): Next, the printer controller 60 performs a dot forming operation. The dot forming operation is an operation of forming dots on the paper S by intermittently ejecting ink from the nozzles Nz moving along the carriage movement direction. In the following description, the operation of moving the nozzle Nz once from one side of the carriage movement direction to the other side or from the other side to one side while ejecting ink is referred to as “pass”. To do.

  In this dot forming operation, the printer controller 60 drives the carriage motor 31 to move the carriage CR in the carriage movement direction. Further, the printer controller 60 ejects ink from the nozzles Nz based on the print data while the carriage CR is moving. The ink ejected from the nozzles Nz lands on the paper, thereby forming dots on the paper. Therefore, when this dot forming operation is performed, dots are appropriately formed in the unit area along the moving direction of the carriage CR. In other words, raster lines (corresponding to unit images) of these dots are printed in the unit area.

  Transport Operation (S004): Next, the printer controller 60 performs a transport operation. The transport operation is a process of moving the paper S relative to the head 41 along the transport direction. The printer controller 60 drives the carry motor 22 and rotates the carry roller 23 to carry the paper S in the carrying direction. By this carrying operation, the relative position between the nozzle Nz and the paper S changes, and it is possible to form dots at positions (that is, different unit areas) different from the positions of the dots formed by the previous dot forming operation. become. Accordingly, by repeating the dot forming operation and the carrying operation, a plurality of the raster lines described above are formed in the carrying direction, and an image is printed on the paper S.

  Paper discharge determination (S005): Next, the printer controller 60 determines whether or not to discharge the paper S being printed. At the time of this determination, if data for printing on the paper S being printed remains, the paper is not discharged. That is, a dot forming operation is performed. Then, the printer controller 60 alternately repeats the dot formation operation and the conveyance operation until there is no data to be printed, and gradually prints an image composed of dots on the paper S.

  When there is no more data for printing on the paper S being printed, the printer controller 60 performs a paper discharge process. Note that whether or not to perform the paper discharge process may be determined based on a paper discharge command included in the print data.

  Paper Discharge Process (S006): When it is determined that “paper discharge” is made in the paper discharge determination described above, the printer controller 60 performs a paper discharge process for discharging the paper S that has been printed. In this paper discharge process, the printer controller 60 rotates the paper discharge roller 25 to discharge the printed paper S to the outside.

  Determination of printing end (S007): Next, the printer controller 60 determines whether or not to continue printing. If printing is to be performed on the next sheet S, the process returns to the above-described sheet feeding operation to continue printing, and the sheet feeding operation for the next sheet S is started. If printing is not performed on the next sheet S, the printing operation is terminated.

=== Printing method ===
<About the interlace method>
In the printer 1 of this embodiment having such a configuration, printing by an interlace method can be performed. By using this interlace method, individual differences such as ink ejection characteristics for each nozzle are dispersed on the printed image so as not to stand out. Here, FIG. 13A and FIG. 13B are explanatory diagrams of the interlace method. That is, FIG. 13A shows the nozzle position and the state of dot formation in the first to fourth passes. FIG. 13B is a diagram for explaining the relationship between a raster line and the nozzle Nz in charge of the raster line.

In FIG. 13A, the nozzle row shown instead of the head 41 is depicted as moving with respect to the paper S. However, this drawing is drawn for convenience in order to show the relative positional relationship between the nozzle row and the paper S. Therefore, in the actual printer 1, the paper S is moved in the transport direction.
In this figure, the nozzle Nz indicated by a black circle is a nozzle that actually ejects ink, and the nozzle Nz indicated by a white circle is a nozzle that does not eject ink.

  In the interlace method illustrated in FIGS. 13A and 13B, each time the sheet S is transported at a constant transport amount F in the transport direction, each nozzle Nz is immediately above the raster line formed in the immediately preceding pass. A raster line is formed. In order to form each raster line with the carry amount F kept constant in this way, the number of nozzles N (integer) from which ink is actually ejected is required to be relatively prime to the coefficient k described above. . In this case, the carry amount F is set to N · D.

  In the example of the figure, the nozzle row has four nozzles Nz arranged along the transport direction, but in order to form each raster line with a constant transport amount F, the nozzle array is interlaced using three nozzles Nz. Printing is performed using this method. Further, since the three nozzles Nz are used, the paper S is transported with a transport amount of 3 · D. As a result, for example, dots are formed on the paper S at a dot interval of 720 dpi (= D) using a nozzle row having a nozzle pitch of 180 dpi (4 · D).

  In the example shown in the drawing, the first raster line R1 is formed by the nozzle Nz (# 1) in the third pass, and the second raster line R2 is formed by the nozzle Nz (# 2) in the second pass. The nozzle Nz (# 3) is formed in the first pass for the raster line R3, and the nozzle Nz (# 1) is formed in the fourth pass for the fourth raster line R4.

<About the overlap method>
14A and 14B and FIGS. 15A and 15B are explanatory diagrams of the overlap method. That is, FIG. 14A and FIG. 14B show an example in which there are two nozzles Nz in charge of one raster line. 15A and 15B show an example in which there are four nozzles Nz in charge of one raster line.

  In the overlap method, as in the interlace method, each time the paper S is transported in the transport direction by a constant transport amount F, ink is ejected from a predetermined nozzle Nz, and dots are formed on the paper S. Here, in the overlap method, ink is intermittently ejected from each nozzle Nz in one pass, and dots are formed on the paper at intervals of several dots. In another pass, ink is intermittently ejected from other nozzles Nz, and other dots are formed at positions where the gaps between already formed dots are filled. By repeating such an operation, one raster line is completed by a plurality of passes. In the following description, for convenience, when one raster line is completed by M dot forming operations, the number of overlaps is M.

  In the example of FIGS. 14A and 14B, each dot is formed every other dot in one dot forming operation. That is, one raster line is completed by two dot formation operations. For this reason, the overlap number is 2 (M = 2). In the example of FIGS. 15A and 15B, each dot is formed every three dots in one dot forming operation. That is, one raster line is completed by four dot forming operations. For this reason, the number of overlaps is 4 (M = 4). In such an overlap method, in order to perform recording with the carry amount F being constant, it is required to satisfy the following conditions. That is, (1) N / M is an integer, (2) N / M is coprime to the coefficient k, and (3) the transport amount F is set to (N / M) · D. It is necessary to satisfy each condition.

  In the example of FIG. 14A, the nozzle row has eight nozzles Nz arranged along the transport direction. However, in order to satisfy the above-described condition, printing with six nozzles Nz is performed. In this case, N / M is 3, which is a prime relationship with the coefficient k (= 4). The transport amount F of the paper S is set to 3 · D. Thereby, one raster line can be completed by two dot forming operations. That is, in this example, the first raster line R1 is formed by the nozzle Nz (# 4) in the third pass and the nozzle Nz (# 1) in the seventh pass. The second raster line R2 is formed by the nozzle Nz (# 5) in the second pass and the nozzle Nz (# 2) in the sixth pass. Similarly, the third raster line R3 is generated by the nozzle Nz (# 6) in the first dot formation operation (pass 1) and the nozzle Nz (# 3) in the fifth dot formation operation (pass 5). It is completed by two dot forming operations.

  In the example of FIG. 15A, the nozzle row has 12 nozzles Nz arranged along the transport direction. Here, since the coefficient k is 4 and the number of overlaps is 4 (M = 4), even if 12 nozzles Nz (N = 12) are used, this is a condition for performing overlap printing. “N / M and k are relatively prime”. For this reason, printing is performed using 12 nozzles Nz. Further, since N / M = 3, the transport amount F of the sheet S is set to 3 · D. Thereby, one raster line can be completed by four dot forming operations. In this example, the first raster line R1 includes the third pass nozzle Nz (# 10), the seventh pass nozzle Nz (# 7), the eleventh pass nozzle Nz (# 4), and the fifteenth pass. Nozzle Nz (# 1). The second raster line R2 includes the second pass nozzle Nz (# 11), the sixth pass nozzle Nz (# 8), the tenth pass nozzle Nz (# 5), and the fourteenth pass. It is formed by the nozzle Nz (# 2). Similarly, the third raster line R3 includes the first pass nozzle Nz (# 12), the fifth pass nozzle Nz (# 9), the ninth pass nozzle Nz (# 6), and the thirteenth pass. Nozzle Nz (# 3).

<Relationship between nozzle Nz and raster line>
As shown in each of these examples, the arrangement order of assigned nozzles Nz for each raster line (for each unit region) does not necessarily match the arrangement order of the nozzles Nz in the head 41. For example, in the interlace method shown in FIG. 13, the raster line R3 is printed by the nozzle Nz (# 3), and the next raster line R4 is printed by the nozzle Nz (# 1). Similarly, in the overlap method shown in FIG. 14, regarding raster line R1 and raster line R2, raster line R1 is printed by nozzle Nz (# 1) and nozzle Nz (# 4), and raster line R2 is nozzle Nz. (# 2) and the nozzle Nz (# 5).

  The combination of the raster line and the nozzle in charge of the raster line changes periodically. For example, in the examples shown in FIGS. 13 to 15, the same nozzle combination appears every three cycles. This is the same when the number of nozzles Nz used increases. Here, FIG. 16 shows that the number of nozzles Nz constituting one nozzle row is 180 (the number of nozzles Nz ejecting ink is 178 (N = 178)), and the number of overlaps is 2 (M = 2). FIG. 6 is a diagram schematically illustrating an example in which the interval between adjacent nozzles is four times the printing resolution (D) in the transport direction (coefficient k = 4).

  In this example, N / M = 89. Therefore, the transport amount of the sheet S at one time is 89 · D. As shown in this figure, the combination of nozzles responsible for each raster line appears periodically every 89 lines. For example, raster line R1 and raster line R90 are both printed by nozzle Nz (# 156) and nozzle Nz (# 67). Similarly, the raster line R2 and the raster line R91 are both printed by the nozzle Nz (# 134) and the nozzle Nz (# 45). Then, it is considered that the density unevenness of the image appears in the same manner for the raster lines having the same combination of nozzles in charge.

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

  In the following, the cause of density unevenness occurring in a monochrome printed image will be described. Here, FIG. 17 is a diagram schematically illustrating density unevenness that occurs in an image printed in a single color and that occurs in the transport direction of the paper S. FIG. This figure shows density unevenness of an image printed with one ink color of CMYK, for example, black ink.

  The density unevenness in the conveyance direction illustrated in FIG. 17 appears as stripes parallel to the carriage movement direction (also referred to as horizontal stripes for convenience). Such horizontal stripe-shaped density unevenness occurs due to, for example, variations in the amount of ink ejected from nozzle to nozzle, but also due to variations in the flight direction of ink. That is, when the variation in the flight direction occurs, the dot formation position by the ink landed on the paper S is shifted in the transport direction with respect to the target formation position. In this case, the formation position of the raster line formed by these dots also deviates from the target formation position in the transport direction. For this reason, the raster lines adjacent to each other in the transport direction are spaced apart or clogged. When viewed macroscopically, it appears as horizontal stripe density unevenness. That is, raster lines having relatively wide intervals between adjacent raster lines appear macroscopically thin, and raster lines having relatively narrow intervals appear macroscopically dark. Note that the variation in the flying direction of the ink is caused by, for example, variation in the processing accuracy of the nozzles Nz.

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

<Method of Reference Example for Controlling Density Unevenness>
A method of a reference example for suppressing such density unevenness will be described. In the method of this reference example, first, a correction pattern as a test pattern is printed on a sheet, and the density of each raster line constituting the correction pattern is measured. Next, a correction value for the raster line is acquired based on the density of each raster line. In other words, in this reference example, the correction value is set for each unit area corresponding to the raster line. Then, during the actual printing of the image, the density of the raster line is adjusted using the acquired correction value. For example, if the density of a certain raster line in the correction pattern is lighter than specified, the ink ejection amount is increased for the nozzle Nz in charge of the raster line during the actual printing. On the other hand, if the density of a certain raster line is higher than the standard in the correction pattern, the ink ejection amount is reduced for the nozzle Nz in charge of the raster line during the actual printing.

  By the way, in this type of printer 1, a paper feed curve called skew may occur. When the correction pattern is printed in a state where the skew is generated, the correction pattern itself is distorted and printed. However, in the method of the reference example, the distortion of the correction pattern due to the skew is not taken into consideration. In this type of printer 1, it is difficult to completely remove the skew. Therefore, the printed correction pattern may have distortion due to skew. Since the correction value is determined based on the density of the correction pattern, it is desirable to reduce the influence of distortion of the correction pattern as much as possible when determining the correction value.

=== Printing by the Printer of this Embodiment ===
<Outline of this embodiment>
In view of such circumstances, in the present embodiment, the correction value H (for example, see FIG. 21) for correcting the density in the conveyance direction in the image is set for each raster line, in other words, for each unit area in which the raster line is printed. Stipulated in This unit area is an area formed by a plurality of pixels arranged in the carriage movement direction, on which one raster line is printed. In determining the correction value H, first, a correction pattern CP (test pattern, for example, see FIG. 24) is printed on the paper S. Next, the density of the printed correction pattern CP is measured to obtain density data. In acquiring this density data, a reference position SP is provided between one end and the other end of the correction pattern CP in the carriage movement direction (raster line direction, other predetermined direction). Then, the density of the correction pattern CP is measured to obtain density data for a predetermined range from the reference position SP in the transport direction (direction adjacent to the unit area), and a correction value is set based on the obtained density data.

  When the correction value H is set by such a method, the influence on the correction value H when a skew occurs can be reduced. That is, even if a raster line (corresponding to a unit image) constituting the correction pattern CP is printed with an inclination with respect to the paper S due to the occurrence of the skew, a measurement error due to the inclination is reduced. can do. This is because the reference position SP is between the one end and the other end in the carriage movement direction in the correction pattern CP. That is, in the above-described method, the density data measurement target is the correction pattern CP in a predetermined range from the reference position SP in the transport direction (predetermined direction). For this reason, with respect to the carriage movement direction (another predetermined direction), the amount of deviation of the raster line from the normal position, that is, the degree of inclination, increases as the distance from the reference position SP in the carriage movement direction increases. Therefore, by setting the reference position SP in the middle of the carriage movement direction in the correction pattern CP, the amount of deviation from the reference position SP to one end of the correction pattern CP, and from the reference position SP to the other end of the correction pattern CP. Both deviation amounts can be made smaller than the maximum value. As a result, the influence on the correction value H due to skew can be reduced.

<Image printing method>
FIG. 18 is a flowchart showing a flow of processes and the like related to the image printing method according to the present embodiment. Hereinafter, the outline of these steps and the like will be described with reference to this flowchart. First, the printer 1 is assembled on the production line (S110). Next, the correction value H for each unit area (area where the raster line is printed) is set in the printer 1 by the operator of the inspection line (S120). In this step, these correction values H are stored in the memory 63 of the printer 1, more specifically, in the correction value storage unit 63a (see FIG. 8). Next, the printer 1 is shipped (S130). Next, the user who purchases the printer 1 performs the actual printing of the image. At the time of the actual printing, an image is formed for each raster line at a density determined based on the correction value H. That is, the printer 1 prints an image on the paper S so as to obtain the corrected density (S140).

  The image printing method according to the present embodiment is characterized by the correction value H setting step (step S120) and the actual image printing (step S140). Therefore, the following description will be given with respect to step S120 and step S140. For the sake of convenience, the following description is given by taking the correction value H used in the normal processing operation as an example.

  Here, the normal processing operation is a kind of printing processing operation. In addition to the normal processing operation, the print processing operation includes an upper end processing operation and a lower end processing operation. The normal processing operation is a printing processing operation that focuses on the transport amount of the paper S. In other words, in this normal processing operation, conditions such as the nozzle to be used and the amount of conveyance are determined so that the amount of conveyance can be increased as much as possible and a large number of raster lines can be efficiently printed with a small number of passes under a predetermined printing method. . In the upper end processing operation and the lower end processing operation, as many nozzles Nz as possible are used for the upper and lower end portions of the paper S under a predetermined printing method (that is, each nozzle Nz is not protruded from the paper S as much as possible). The conditions such as the nozzle used and the transport amount are determined so that the raster line can be printed.

  For this reason, the normal processing operation can be expressed as an upper end processing operation and a lower end processing operation and a printing processing operation in which the combination of the nozzles Nz to be used and the carry amount is different. In general, the number of rasters in the upper and lower ends of the paper S is smaller than the number of rasters in an intermediate portion sandwiched between these upper and lower ends, that is, a portion printed by a normal processing operation. In this case, the normal processing operation can be said to be a printing processing operation that is most frequently used when printing on the paper S.

  Note that the number of correction values H required in this normal processing operation is determined according to the combination of the raster line (unit region) and the nozzle in charge. For example, in the example shown in FIG. 16, a combination of nozzles is arranged every 89 raster lines. For this reason, the correction value H may be 89 lines from H01 to H89. For this reason, the amount of memory used can be reduced as compared with the case where the correction value H is individually set for all raster lines. In the present embodiment, ten different densities are set for each raster line. The correction value H is set for each density.

<Step S120: Setting Correction Value H>
First, a device used for setting the correction value H will be described. FIG. 19 is a block diagram illustrating this device. In addition, about the component already demonstrated, since the same code | symbol is attached | subjected, description is abbreviate | omitted. In this figure, a computer 1100A is a computer installed on the inspection line, and a process correction program 1120 is operating. This process correction program 1120 is a program for realizing correction value acquisition processing and the like, and has codes for realizing various processes.

  In the correction value acquisition processing, a density data group (for example, a gray scale of 256 gradations with a predetermined resolution) obtained by reading the correction pattern CP (see FIG. 24) printed on the paper S by the scanner device 100. Based on the data, a correction value H for each density is acquired for the raster line to be processed. The correction value H acquisition process will be described later. The application program 1104 operating on the computer 1100A outputs image data for printing the correction pattern CP to the printer driver 1110. Then, the printer driver 1110 outputs print data for printing the correction pattern CP to the printer 1 by performing a series of processes from the resolution conversion process to the rasterization process described above.

  FIG. 20 is a conceptual diagram of a recording table provided in the memory of the computer 1100A. This recording table is prepared for each ink color.

  In this recording table, density measurement values in each raster line, that is, density data obtained by the scanner device 100 reading the correction pattern CP are recorded. Therefore, each recording table has a field for measured density data. In this figure, fields are shown for the black (K) recording table.

  In this embodiment, each record is associated with a raster line, and is recorded in a record having a smaller number in order from the raster line formed on the upper end side of the sheet. Each record is also associated with a reference density. This reference density corresponds to the density of the correction pattern CP. In the correction pattern CP of this embodiment, as will be described later, one raster line is printed at a plurality of different densities. In other words, in the correction pattern CP, a plurality of sub patterns having different densities are arranged along the moving direction of the carriage CR. The density data is acquired for each raster line for each density. In this example, density data (d10 to d100) is acquired for each sub-pattern having a density command value of 10% to 100% (also referred to as density 10% to density 100% for convenience). Thereby, the correction value H is also set for each density (for every h10 to h100) for each raster line.

  FIG. 21 is a conceptual diagram of the correction value storage unit 63 a provided in the memory 63 of the printer 1. As shown in this figure, a correction value table is prepared in the correction value storage unit 63a. The correction value table is prepared for each ink color as in the recording table described above. In this drawing, the fields of the correction value table for black are shown as representative of these correction value tables. The correction value table stores the correction value H for each raster line. This correction value table also has a plurality of records, and a corresponding correction value H is stored in each record. Since the correction pattern CP of this embodiment is drawn with a plurality of densities as described above, the correction value H is also acquired for each density and stored in the corresponding field. In this example, the correction value H (H01 to H89) of each raster line is 10 in total for every 10% density from the correction value h10 corresponding to the density 10% to the correction value h100 corresponding to the density 100% (solid). It consists of step correction values.

  FIG. 22 is a diagram for explaining the scanner device 100 that is communicably connected to the computer 1100A. 22A is a longitudinal sectional view of the scanner device 100, and FIG. 22B is a plan view of the scanner device 100. The scanner device 100 is a type of density measuring device that measures the density of the correction pattern CP. This scanner device 100 can read an image printed on an original 101 (for example, a correction pattern CP printed on a paper S) as a data group in units of pixels, and acquires density data together with coordinate information. it can. The scanner apparatus 100 includes an original table glass 102 on which an original 101 is placed, a reading carriage 104 that moves in a predetermined movement direction while facing the original 101 via the original table glass 102, a reading carriage 104, and the like. A controller (not shown) for controlling each part of the above is provided. The reading carriage 104 is mounted with an exposure lamp 106 that irradiates light on the original 101 and a linear sensor 108 that receives reflected light from the original 101 over a predetermined range in a direction orthogonal to the moving direction. . In the scanner device 100, the linear sensor 108 receives the reflected light while moving the reading carriage 104 in the moving direction with the exposure lamp 106 emitted. As a result, the scanner device 100 reads an image printed on the document 101 with a predetermined reading resolution. The scanner device 100 according to the present embodiment can read an image with a resolution higher than the print resolution of the image. For example, an image printed at a resolution of 720 dpi can be read at a reading resolution of 1800 dpi. Note that the broken line in FIG. 22A indicates the locus of light at the time of image reading.

  FIG. 23 is a flowchart showing the procedure of step S120 in FIG. Hereinafter, a procedure for storing the correction value H in the correction value storage unit 63a will be described with reference to this flowchart.

  This procedure includes a printing step (S121) for printing a correction pattern CP (test pattern), a step for reading the correction pattern CP (S122), a step for obtaining density data for setting (S123), and correction for each raster line. A correction value setting step (S124) for setting the value H for each density; Of these steps, the step of reading the correction pattern CP in S122 and the step of acquiring the density data for setting in S123 correspond to the density data acquisition step of acquiring the density data of the test pattern. . Hereinafter, each step will be described in detail.

(1) Regarding printing of correction pattern CP (S121):
First, the correction pattern CP is printed on the paper S in step S121. Here, the operator of the inspection line connects the printer 1 to a state in which the printer 1 can communicate with the computer 1100A of the inspection line. Then, the correction pattern CP is printed by the printer 1. That is, the operator gives an instruction to print the correction pattern CP via the user interface of the computer 1100A. At this time, a print mode, a paper size mode, and the like are set from this user interface. In response to this instruction, the computer 1100A reads the image data of the correction pattern CP stored in the memory, and performs the above-described resolution conversion processing, color conversion processing, halftone processing, and rasterization processing. As a result, print data for printing the correction pattern CP is output from the computer 1100A to the printer 1. Then, the printer 1 prints the correction pattern CP on the paper S based on the print data. That is, the printer 1 prints the correction pattern CP by an operation similar to that at the time of image printing (main printing described later). The printer 1 that prints the correction pattern CP is the printer 1 for which the correction value H is set. That is, the correction value H is set for each printer.

  Here, FIG. 24A is a diagram for explaining an example of the printed correction pattern CP (test pattern), and is a diagram for explaining the correction pattern CPk for black. FIG. 24B is an enlarged view of the setting mark CPkm.

  As shown in these drawings, the correction pattern CPk has a measurement target pattern and a setting mark CPkm. The measurement target pattern is a portion used for measuring density data. In the measurement target pattern of the present embodiment, a plurality of sub-patterns CPk1 to CPk10 are arranged along the carriage movement direction (another predetermined direction). These sub-patterns CPk1 to CPk10 have different concentrations. The sub-patterns CPk1 to CPk10 of the present embodiment are gradually increased in density from the left side to the right side in FIG. Specifically, the leftmost sub-pattern CPk1 is printed with a density of 10% (that is, a density command value of 10%), and the rightmost sub-pattern CPk10 is printed with a density of 100% (that is, a density command value of 100%). ) Is printed. The intermediate sub-patterns CPk2 to CPk9 are printed with a density command value that is 10% higher than the sub-pattern on the left.

  The setting mark CPkm is used to set the reading range of the correction pattern CP when acquiring density data. The setting mark CPkm in the present embodiment is a ground color portion of the paper S. The setting mark CPkm is formed, for example, by printing adjacent sub-patterns apart in the carriage movement direction. In the present embodiment, the fifth sub-pattern CPk5 (sub-pattern with a density of 50%) from the first sub-pattern CPk1 (sub-pattern with a density of 10%) from the left is grouped into one group, and the sixth sub-pattern CPk6 from the left The tenth sub-pattern CPk10 (sub-pattern with 100% density) from (sub-pattern with 60% density) is made into one group. Both groups are printed so that the sub-pattern CPk5 and the sub-pattern CPk6 are separated by about 10 to 20 pixels in the carriage movement direction. Thus, the setting mark CPkm is formed between the fifth sub-pattern and the sixth sub-pattern from the left side, in other words, approximately in the center of the correction pattern CP in the carriage movement direction, along the transport direction. .

  The setting mark CPkm may be formed by printing. For example, the setting mark CPkm may be formed by printing with different densities or with different colors. And, when forming the setting mark CPkm as in the present embodiment, when printing is performed with the adjacent sub-patterns spaced apart in the carriage movement direction, the image data for the correction pattern CP can be reduced. It is advantageous. This is because the setting mark CPkm can be formed by designating the printing position of the sub-pattern.

  Even when printing is performed with the sub-patterns adjacent to each other, the boundary can be recognized based on the density difference between the sub-patterns. That is, a boundary (a line recognized by a density difference) between adjacent sub-patterns may be used as a setting mark. Therefore, the setting mark only needs to be formed in a mode different from the sub-patterns CPk1 to CPk10.

  In addition, the setting mark CPkm of the present embodiment is provided with a reference position SP in the transport direction, in other words, an index CPki (hereinafter also referred to as a range index CPki) indicating a reading start position. The range index CPki is provided at the same position as the reference raster line in the transport direction. That is, the reference raster line number can be recognized based on the range index CPki. The range index CPki is, for example, a line printed along the carriage movement direction, and is printed at predetermined intervals (for example, every 1 inch) in the transport direction.

  In addition, the correction pattern CP is also provided with an inclination correction index CPka (hereinafter also referred to as a correction index CPka). The correction index CPka is paired with a left portion (also referred to as a left correction index CPkL) and a right portion (also referred to as a right correction index CPkR). The left-side correction index CPkL is, for example, linear, and is printed along the carriage movement direction on the left side of the leftmost sub-pattern (sub-pattern with a density of 10%). The right correction index CPkR is also linear, for example, and is printed on the right side of the right end sub-pattern (sub-pattern with 100% density) along the carriage movement direction. Then, regarding the position in the transport direction, the left correction index CPkL and the right correction index CPkR are provided at the same position. Further, the left correction index CPkL and the right correction index CPkR are provided at the same position as the range index CPki. Therefore, the left correction index CPkL, the right correction index CPkR, and the range index CPki are provided side by side along the same raster line.

(2) Reading the correction pattern CP (step S122):
Next, the printed correction pattern CP is read by the scanner device 100 to obtain density data. In this step S122, first, the operator on the inspection line places the paper S on which the correction pattern CP is printed on the platen glass 102. At this time, as shown in FIG. 22B, the sheet S is loaded so that the direction of the raster line in the correction pattern CP and the orthogonal direction in the scanner device 100 (that is, the arrangement direction of the linear sensors 108) are the same direction. Put. If the paper S is loaded, the operator designates the reading conditions via the user interface of the computer 1100A, and then instructs the start of reading.

  Here, it is desirable that the reading resolution in the moving direction of the reading carriage 104 is finer than half of the interval (pitch) of the raster lines. This is based on the sampling theorem that “the sampling frequency must be at least twice the maximum frequency included in the sampling target”. In the present embodiment, since the raster line interval is 720 dpi, the scanner device 100 reads an image at a reading resolution of 1800 dpi, which is finer than half (1440 dpi). Thereby, the computer 1100A can calculate the density of the raster line based on the measured value (described later). Upon receiving a reading start instruction, a controller (not shown) of the scanner apparatus 100 reads the correction pattern CP printed on the paper S by controlling the reading carriage 104 and the like, and obtains it at a reading resolution of 1800 dpi. The obtained density data (measurement result) is transferred to the computer 1100A. Then, the computer 1100A stores this density data in the memory. As described above, since the density data is acquired together with the coordinate information, it is stored in the computer 1100A together with the coordinate information.

(3) Acquisition of setting density data (step S123):
Next, the computer 1100A acquires setting density data used for setting the correction value H for each raster line and each density. The acquisition of the density data for setting is performed based on the density data transferred from the scanner device 100. Here, FIG. 25 is a flowchart showing the procedure of the setting density data acquisition operation. FIG. 26A to FIG. 26C are schematic diagrams for explaining the operation of acquiring setting density data. 26A to 26C show images based on density data for convenience.

  FIG. 26A is a diagram showing an image transferred from the scanner device 100. FIG. That is, FIG. 26A shows density data that is printed in a state where the right correction index CPkR is lowered to the downstream side of the sheet S by about 1 to 2 rasters from the density data of the left correction index CPkL, and is taken in as it is. Yes. FIG. 26B is a diagram illustrating a state in which the inclination of the image is corrected at the position of the correction index CPka. That is, FIG. 26B shows a state in which the density data is rotated leftward by about 1 to 2 rasters with respect to the density data of FIG. 26A. FIG. 26C is a diagram for explaining a target range X from which density data is acquired.

  First, the computer 1100A corrects the inclination of the density data transferred from the scanner device 100 (S123a). The inclination is corrected based on data corresponding to the correction index CPka in the density data. That is, the computer 1100A selects the correction index CPka, and transfers the data so that the density data of the corresponding left correction index CPkL and the density data of the right correction index CPkR are aligned in the X-axis direction on the coordinate system. Rotate the entire density data. That is, coordinate conversion is performed on the density data.

  In other words, the computer 1100A associates these density data with respect to density data belonging to a specific raster line (unit region) at the same position as the correction index CPka. More specifically, the computer 1100A selects the correction index CPka (CPkL, CPkR) drawn on the upper side, and density data belonging to the same unit area as the correction index CPka is displayed in the reference direction (X on the coordinate system). The entire density data is rotated so that it is aligned in the axial direction. By this correction processing, the density data is in the state shown in FIG. 26B. That is, in this example, the image is rotated to the left by about 1 to 2 rasters compared to the image in FIG. 26A.

  Next, the computer 1100A sets a target range for acquiring setting density data for the rotated density data (S123b). The target range is set based on the range index CPki. Here, the computer 1100A recognizes the coordinates of the range index CPki belonging to the same raster line as the correction index CPka used as a reference when correcting the inclination from the corrected density data. If the coordinates of the range index CPki are recognized, the computer 1100A sets the coordinates as the reference position SP. At this time, in this embodiment, the setting mark CPkm is the ground color portion of the paper S, and the range mark CPki is provided in the setting mark CPkm. For this reason, the computer 1100A can easily recognize the coordinates of the range index CPki.

  Then, the computer 1100A sets a predetermined range in the transport direction (predetermined direction) from the reference position SP as a target range X from which density data is acquired, as indicated by a one-dot chain line in FIG. 26C. As shown in this figure, the target range X is defined as a range surrounding the correction pattern CP. The predetermined range is determined so as to include a plurality of periods based on the nozzles Nz in charge of each raster line (unit region). When the correction pattern CPk is printed by the printing method shown in FIG. 16, the predetermined range is set to 1 inch, for example. In this case, since one cycle is composed of 89 raster lines (unit areas) and the printing resolution in the transport direction is 720 dpi, density data for about eight cycles can be obtained.

  If the target range X is set, the computer 1100A acquires density data for the target range X (S123c). Here, based on the coordinates of the target range X, for example, density data is acquired based on the coordinates of the four vertices of the target range X. If the density data is acquired for the target range X, the computer 1100A converts the resolution of the acquired density data into the print resolution (S123d). The conversion to the print resolution is performed by an interpolation process (also an enlargement / reduction process). Examples of the interpolation processing method include a nearest neighbor method, a bilinear method, and a bicubic method. In the nearest neighbor method, the measurement value closest to the position where the density is to be obtained becomes the density at the position where the density should be obtained as it is. In the bilinear method, linear interpolation is performed based on the gradient of density in the vicinity of 2. Since these methods are simple to calculate, there is an advantage that the processing by the computer 1100A can be performed in a short time. The bicubic method is a kind of cubic interpolation. According to this bicubic method, the acquired density data is reflected deeply in the converted density data, so that the conversion can be performed with high accuracy.

  In these steps, in the present embodiment, since the target range X from which density data is acquired is set to a predetermined range from the reference position SP, a skew occurs when the correction pattern CPk (test pattern) is printed, and correction is performed. Even if the pattern CPk is distorted and printed, the influence can be reduced. For example, even if the raster lines constituting the correction pattern CPk are printed with an inclination with respect to the paper S, the influence can be reduced.

  This is because the reference position SP is determined at the center in the carriage movement direction of the correction pattern CPk when determining the target range X for acquiring density data. In this case, regarding the acquired density data, a deviation amount in the transport direction from the reference position SP to one end of the correction pattern CPk (one end in the carriage movement direction), and from the reference position SP to the other end of the correction pattern CPk. Both deviation amounts in the transport direction can be made smaller than the maximum value. That is, the amount of shift in the transport direction can be made smaller than when the correction pattern CPk is based on the end in the carriage movement direction. As a result, the influence on the skew correction value H can be reduced.

  This will be specifically described based on the example of FIG. 26C. Here, the raster line is printed to the lower right due to the skew, and at the position of the lower end of the sheet in the acquisition range (the position of the lower end of the target range X in FIG. 26C), 4 in the transport direction between the left end and the right end of the raster line. Assume that raster deviation has occurred.

  As a reference example, a case is assumed in which a predetermined range in the transport direction is defined with reference to the left end of the correction pattern CPk, and resolution conversion is performed. In this case, with respect to the left end of the correction pattern CPk (that is, the sub-pattern CPk1 having a density of 10%), the number of raster lines actually drawn is equal to the number of raster lines recognized for control. As a result, the density of the correction pattern CPk after the resolution conversion (the density of each raster line) accurately reflects the density of the drawn raster line. On the other hand, at the right end of the correction pattern CPk (that is, the sub-pattern CPk10 having a density of 100%), the number of raster lines actually drawn and the number of raster lines recognized in the control are the most different, and the amount of four raster lines It becomes a gap. As a result, the density of the correction pattern CPk after resolution conversion reflects this shift. Accordingly, the accuracy is deteriorated accordingly.

  On the other hand, when the predetermined range is defined with reference to the center of the correction pattern CPk and resolution conversion is performed as in the present embodiment, the center of the correction pattern CPk (that is, the density 50% or the density 60%). In the sub-patterns CPk5 and CPk6), the number of raster lines actually drawn is equal to the number of raster lines recognized in the control. Thereby, the density of the correction pattern CPk after resolution conversion accurately reflects the density of the drawn raster line. On the other hand, for the sub-patterns CPk1 and CPk10 at the left end and right end of the correction pattern CPk, the number of raster lines actually drawn deviates from the number of raster lines recognized in the control, but the shift amount is equivalent to two raster lines. That's okay. In other words, the raster line shift amount can be dispersed throughout. As a result, the overall accuracy can be improved, and the influence on the skew correction value H can be reduced.

  In the present embodiment, before the target range X is determined, the gradient of the density data transferred from the scanner device 100 is corrected (S123a). Thereby, the density data of the raster line to which the reference position SP belongs are in a state of being associated with each other. As a result, the density data of the raster line to which the reference position SP belongs can be in a constant state regardless of the degree of skew and the inclination of the paper S when acquiring the density data. Thereby, it is possible to easily cope with the skew degree and the difference in the inclination of the sheet S when acquiring the density data, and the correction value H can be acquired with high accuracy.

  When the resolution conversion is completed, the computer 1100A acquires density data for each raster line (each unit area) (S123e). In this embodiment, the density data is acquired in the transport direction for each of the sub-patterns CPk1 to CPk10, and the density data of corresponding raster lines having different periods is averaged. In the example of FIG. 16, since there are 89 raster lines, density data is acquired for the first raster line, the 90th raster line, the 179th raster line,. The average value is calculated. Then, the average value of the density data is acquired as the density data of the first raster line and recorded in the corresponding field of the recording table. Similarly, for the second raster line, density data is acquired for the second raster line, the 91st raster line, the 180th raster line,..., The 625th raster line, and the average value of each density data is obtained. calculate. Then, the average value of the density data is acquired as the density data of the second raster line and recorded in the corresponding field of the recording table. If such a process is performed up to the raster line corresponding to the end of the cycle, for example, the 89th raster line, the same process is repeated for the next sub-pattern (density). When the density data has been acquired for all the sub patterns, the density data acquisition process ends.

(4) Setting of the correction value H for each raster line (step S124):
Next, the computer 1100A sets a correction value H according to the calculated density of the raster line. Here, the computer 1100A calculates the correction value H based on the density of each raster line acquired for each density. Then, the computer 1100A stores the correction value H in the correction value storage unit 63a of the printer 1.

  The correction value H is obtained, for example, in the form of a correction ratio indicating the ratio of correction with respect to the density gradation value. Specifically, it is calculated as follows. First, an average value dav of density data of all raster lines is calculated for sub-patterns having the same density. Then, for each raster line, a deviation Δd (= dav−d) between the density data d of the raster line and the average value dav is calculated, and a value obtained by dividing the deviation Δd by the average value dav is set as a correction value H.

That is, if the correction value H is expressed by a mathematical expression, it is as follows.
Correction value H = Δd / dav
= (Dav-d) / dav
For example, when the density d of the acquired raster line is 95 and the average value of the density in each raster line is 100, the correction value H is calculated by (100−95) / 100) +0.05. When the density d of the acquired raster line is 105 and the average value of the density in each raster line is 100, the correction value H is calculated by (100−105) / 100) -0.05.

  As described above, when the density d in the raster line is smaller than the average value dav, that is, when the density is lower than the specified value, the correction value H is positive. On the other hand, when the density d in the raster line is larger than the average value dav, that is, when the density is higher than the specified value, the correction value H is negative. As will be described later, when the correction value H is positive, correction is performed so as to increase the density of the raster line. When the correction value H is negative, correction is performed so as to reduce the density of the raster line.

  The density data used for setting the correction value H is, as described above, for a predetermined range set based on the reference position SP (position of the range index CPki) set in the middle of the carriage movement direction. Has been acquired. For this reason, with respect to the correction value H, it is possible to alleviate the density measurement error caused by the bending of the raster line. Further, since the correction value H is used in the above-described normal processing operation, the correction value H is set using the average value of density data for a plurality of corresponding raster lines. In this respect also, the influence of the skew of the correction value H can be reduced.

  Further, the density data used for setting the correction value H is an average value of density data of corresponding raster lines having different periods as described above. For this reason, it is possible to suppress density variation due to skew, density variation due to paper feeding accuracy, and the like, and to increase the accuracy of the correction value H that is set.

<Step S140: Full-printing the image while correcting the density for each raster line>
The density correction value H is set in this way, and the shipped printer 1 is used by the user. That is, the main printing is performed under the user. In this actual printing, the printer driver 1110 and the printer 1 cooperate to perform density correction for each raster line, and execute printing that suppresses density unevenness. Here, the printer driver 1110 refers to the correction value H stored in the correction value storage unit 63a in the printer 1 and corrects the pixel data so that the density is corrected based on the correction value H. That is, the printer driver 1110 changes multi-tone pixel data based on the correction value H when converting RGB image data into print data. Then, print data based on the corrected image data is output to the printer 1. The printer 1 forms corresponding raster line dots based on the print data. Hereinafter, the printing procedure will be described in detail.

  FIG. 27 is a flowchart showing the density correction procedure for each raster line according to step S140 in FIG. The density correction procedure will be described below with reference to this flowchart. In this procedure, first, the printer driver 1110 performs resolution conversion processing (step S141). Then, the printer driver 1110 sequentially performs color conversion processing (step S142), halftone processing (step S143), and rasterization processing (S144). These processes are performed in a state where the user connects the printer 1 to the computer 1100 so as to be communicable and sets the state of the printing system 1000 described in FIG. Specifically, it is performed on the condition that a print execution operation has been performed from the user interface screen of the printer driver 1110 in a state where necessary information such as an image quality mode and a paper size mode has been input. Hereinafter, the processing of each step will be described.

  Resolution Conversion Processing (S141): First, the printer driver 1110 performs resolution conversion processing on the RGB image data output from the application program 1104. That is, the resolution of the RGB image data is converted into a print resolution corresponding to the input image quality mode. Furthermore, by appropriately processing the RGB image data such as trimming processing, the number of pixels in the RGB image data is adjusted to match the number of dots in the print area corresponding to the specified paper size and margin form mode. To do.

  Color Conversion Process (S142): Next, the printer driver 1110 executes the color conversion process described above to convert RGB image data into CMYK image data. As described above, the CMYK image data includes C image data, M image data, Y image data, and K image data, and has a data amount corresponding to the print area.

  Halftone processing (S143): Next, the printer driver 1110 executes halftone processing. This halftone process is a process of converting 256 gradation values indicated by each pixel data in C, M, Y, and K image data into 4 gradation values that can be expressed by the printer 1. In this embodiment, density correction for each raster line is executed in this halftone process. That is, the process of converting each pixel data constituting each image data from a 256-step gradation value to a 4-step gradation value is performed while correcting based on the correction value H described above. This density correction is performed for each of the C, M, Y, and K image data based on the correction value table for each ink color.

  In the present embodiment, in this halftone process, the 256 gradation values are temporarily replaced with level data and then converted into four gradation values. Therefore, at the time of this conversion, the 256 gradation values are changed by the correction value H, thereby correcting the pixel data of the gradation values of 4 steps, thereby correcting the pixel data based on the correction value H. It is carried out. In brief, the printer driver 1110 acquires, for example, the density of the raster line (for example, the average density of the printed image). Then, the computer 1100 selects the correction value H having the density closest to the density of the raster line and sets it as the correction value H of the raster line. When the correction value H is obtained in this way, the gradation value is changed by the amount of the obtained correction value H, and the level data is read. That is, Δgr is calculated by multiplying the gradation value gr of the pixel data by the correction value H, and the gradation value gr of the pixel data is changed to gr + Δgr. Then, the printer driver 1110 reads the level data based on the gradation value gr + Δgr.

  Referring to the example of FIG. 4, when the gradation value gr changes by + Δgr, the large dot level data LVL is 11d, the medium dot level data LVL is 12d, and the small dot level data LVL is 13d. Each is required. Such arithmetic processing can be performed easily and at high speed. Accordingly, the processing can be simplified and it is possible to cope with high frequency ejection of ink.

  Rasterization processing (S144): Next, the printer driver 1110 performs rasterization processing. The rasterized print data is output to the printer 1, and the printer 1 prints an image on the paper S according to the pixel data included in the print data.

  Note that, as described above, since the density of the pixel data is corrected for each raster line, the density unevenness of the image can be effectively suppressed in the printed image. That is, as described above, since the influence of the skew during printing of the correction pattern CP on the correction value H is reduced, correction can be performed with high accuracy.

=== Other Embodiments ===
Each of the above-described embodiments is mainly described for the printer 1, which includes disclosure of a printing apparatus, a printing method, a printing system 1000, and the like. Further, the printer 1 as one embodiment has 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.

<Regarding correction pattern CP>
In the above-described embodiment, the reference position SP is provided at the center in the carriage movement direction, but the present invention is not limited to this. That is, the reference position SP may be provided between one end and the other end of the correction pattern CP in the carriage movement direction, that is, in the middle of the carriage movement direction. In this case, it is preferable that the reference position SP is provided adjacent to a sub-pattern having a density where density unevenness is most noticeable. This is because the subpattern closer to the reference position SP is less affected by the skew. From this point of view, as shown in FIG. 28, in the black correction pattern CP, the reference position SP is provided between the sub-pattern CPk3 having the density of 30% and the sub-pattern CPk4 having the density of 40%, and the setting mark CPkm. The structure which forms is preferable.

  Further, from the viewpoint of evenly distributing density unevenness due to skew, it is preferable that the reference position SP is determined in the middle of the carriage movement direction. From this point of view, it is preferable that the setting mark CPkm is provided at the center in the carriage movement direction, and the density is more conspicuous, and the printing is performed at a position closer to the setting mark CPkm. Regarding density unevenness, halftone density (for example, density 30% to 50%) is most noticeable, and dark density (density 70% to 100%) is least noticeable. And at a low density (density 10% to 20%), density unevenness is less noticeable than at a high density. In consideration of such conditions, in the example shown in FIG. 29, the sub-pattern CPk3 having a density of 30% and the sub-pattern CPk4 having a density of 40% are printed close to the setting mark CPkm and outside the sub-patterns ( A sub-pattern CPk2 having a density of 20% and a sub-pattern CPk5 having a density of 50% are printed on the far side from the setting mark CPkm. Furthermore, the 10% density sub-pattern CPk1 outside the 20% density sub-pattern CPk2, the 70% density sub-pattern CPk7 outside the 10% density sub-pattern, and the density outside the 70% density sub-pattern CPk7. 90% of the sub-pattern CPk9 is printed. On the other hand, a sub-pattern CPk6 having a density of 60% outside the sub-pattern CPk5 having a density of 50%, a sub-pattern CPk8 having a density of 80% outside the sub-pattern CPk6 having a density of 60%, and outside the sub-pattern CPk8 having a density of 80%. Each of the sub patterns CPk10 having a density of 100% is printed.

  In the above-described embodiment, the correction pattern CP is printed in the factory before the printer 1 is shipped. The correction pattern CP was measured in the factory. However, it is not limited to this. For example, after the printer 1 is shipped, the printer 1 may print the correction pattern CP under the user. Then, the user may read the correction pattern CP with a scanner, and the printer driver 1110 may store the correction data in the printer 1 based on the measurement value. That is, the process correction program 1120 that was in the computer 1100A in the factory may be incorporated in the printer driver 1110. In this way, even if the flight direction of the ink droplet changes with time, the user can acquire new correction data each time.

<About Printer 1>
In the above-described embodiment, the printer 1 and the scanner device 100 are individually configured, and each is communicably connected to the computer 1100. However, the configuration is not limited to this. For example, it may be a so-called printer / scanner multifunction device having both the function of the printer 1 and the function of the scanner device 100. In addition, in the above-described embodiment, the printer 1 as the printing apparatus main body and the printer driver 1110 (the computer 1100 in which the printer driver 1110 is installed) as the printing control apparatus are individually configured and connected so as to communicate with each other. It was. In this regard, the printer 1 including the printer driver 1110 may be used. In short, a printing apparatus in which the printing apparatus main body and the printing control apparatus are integrated may be used.

  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 embodiment is an embodiment of the printer 1, the dye ink or the pigment ink is ejected from the nozzle Nz. However, the ink ejected from the nozzle Nz is not limited to such ink.

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

<About the printing method>
As a printing method, printing may be performed using only the interlace method, or may be performed using only the overlap method.

<Density correction target>
In the above-described embodiment, the density correction based on the correction value H is performed in the halftone process. However, the present invention is not limited to this method. For example, density correction based on the correction value H may be performed on RGB image data obtained by resolution conversion processing.

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

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

It is explanatory drawing which showed the external appearance structure of the printing system. FIG. 3 is a schematic explanatory diagram of basic processing performed by a printer driver. It is a flowchart explaining the halftone process by a dither method. It is a figure which shows the production | generation rate table utilized for the setting of the level data with respect to each dot of large, medium, and small. It is a figure which shows the ON / OFF determination of the dot by a dither method. 6A and 6B are diagrams illustrating a relationship between a dither matrix used for large dot determination and a dither matrix used for medium dot determination. 3 is an explanatory diagram of a user interface of a printer driver. FIG. 1 is a block diagram of an overall configuration of a printer. 1 is a schematic diagram of an overall configuration of a printer. 1 is a cross-sectional view of the overall configuration of a printer. It is a figure which shows the arrangement | sequence of the nozzle in the lower surface of a head. It is a flowchart of the operation | movement at the time of printing. 13A and 13B are explanatory diagrams of the interlace method. 14A and 14B are explanatory diagrams of the overlap method. 15A and 15B are explanatory diagrams of the overlap method. It is explanatory drawing of an overlap system. FIG. 6 is a diagram schematically illustrating density unevenness that occurs in a paper conveyance direction. It is a flowchart which shows the flow of the process etc. which are related to the printing method of an image. It is a block diagram explaining the apparatus used for the setting of a correction value. It is a conceptual diagram of the recording table provided in the memory of the computer. It is a conceptual diagram of a correction value storage unit. FIG. 22A is a longitudinal sectional view of the scanner device. FIG. 22B is a plan view of the scanner device. It is a flowchart which shows the setting procedure of the density | concentration correction value. FIG. 24A is a diagram illustrating an example of a correction pattern. FIG. 24B is an enlarged view showing a setting mark portion. It is a flowchart which shows the procedure of the acquisition operation of density data for setting. FIG. 26A to FIG. 26C are schematic diagrams for explaining an operation of acquiring setting density data. It is a flowchart which shows the procedure of the density | concentration correction | amendment for every raster line. It is a figure explaining the other example of the pattern for a correction | amendment. It is a figure explaining the further another example of the pattern for a correction | amendment.

Explanation of symbols

1 printer, 20 paper transport mechanism, 21 paper feed roller, 22 transport motor,
23 transport roller, 24 platen, 25 paper discharge roller, 30 carriage moving mechanism,
31 Carriage motor, 32 guide shaft, 33 timing belt,
34 drive pulley, 35 driven pulley, 40 head unit, 41 head,
50 sensor groups, 51 linear encoder, 52 rotary encoder,
53 Paper detection sensor, 54 Paper width sensor, 60 Printer controller,
61 interface unit, 62 CPU, 63 memory, 63a correction value storage unit,
64 control unit, 100 scanner device, 101 document, 102 platen glass,
104 reading carriage, 106 exposure lamp, 108 linear sensor,
1000 printing system, 1100 computer, 1100A computer,
1102 video driver, 1104 application program,
1110 Printer Driver, 1120 Process Correction Program, 1200 Display Device,
1300 input device, 1300A keyboard, 1300B mouse,
1400 recording / reproducing apparatus, 1400A flexible disk drive apparatus,
1400B CD-ROM drive, S paper,
LUT color conversion lookup table, CR carriage, H correction value,
CP correction pattern, CPk1 to CPk10 sub-pattern, CPkm setting mark,
CPki range index, CPka correction index, CPkL left correction index,
CPkR Right side correction index, X Target range for acquiring density data

Claims (14)

A correction value setting method for correcting the density of an image printed for each unit region adjacent in a predetermined direction,
A printing step for printing a test pattern;
A density that provides a reference position between one end and the other end of another predetermined direction that intersects the predetermined direction in the test pattern, and obtains density data of the test pattern for a predetermined range in the predetermined direction from the reference position A data acquisition step;
A correction value setting step for setting a correction value for each of the unit areas based on the density data;
A correction value setting method. The correction value setting method according to claim 1,
The test pattern is
A plurality of sub-patterns having different densities have measurement target patterns arranged along the other predetermined direction,
In the correction value setting step,
A correction value setting method for setting a correction value for each density of the sub-pattern based on the density data corresponding to the sub-pattern. The correction value setting method according to claim 2,
The reference position is
A correction value setting method provided between adjacent sub-patterns. The correction value setting method according to claim 3,
The test pattern is
Between the adjacent sub-patterns where the reference position is provided,
A correction value setting method having a setting mark formed in a different form from the sub-pattern. The correction value setting method according to claim 4,
The setting mark is
A correction value setting method, which is formed by arranging the adjacent sub-patterns apart from each other in the predetermined direction. A correction value setting method according to claim 4 or claim 5, wherein
The setting mark is
A correction value setting method having an index indicating the reference position. A correction value setting method according to any one of claims 1 to 6,
The reference position is
A correction value setting method provided between the one end and the other end in the other predetermined direction in the test pattern. A correction value setting method according to any one of claims 1 to 7,
In the concentration data acquisition step,
A correction value setting method of acquiring density data of the test pattern at a resolution higher than the print resolution of the test pattern, and converting the acquired density data into a resolution corresponding to the print resolution. A correction value setting method according to any one of claims 1 to 8,
The test pattern is
A plurality of sub-patterns having different densities have measurement target patterns arranged along the other predetermined direction,
In the concentration data acquisition step,
Obtain density data of the test pattern together with coordinate information;
A correction value setting method in which a plurality of density data belonging to a specific unit region are associated with each other using the coordinate information. The correction value setting method according to claim 9,
The test pattern is
Having other indicators for associating density data of the test pattern;
In the concentration data acquisition step,
A correction value setting method in which a plurality of density data belonging to a specific unit area are associated with each other using the other index and the coordinate information. A correction value setting method according to any one of claims 1 to 10,
The image is
By ejecting ink from the nozzles selected from the nozzle group, it is printed for each unit area,
In the correction value setting step,
A correction value setting method in which the correction value is set at a set cycle determined based on a combination of the unit area and the nozzle in charge. The correction value setting method according to claim 11,
In the concentration data acquisition step,
The predetermined range is determined so that a plurality of the set periods are included,
In the correction value setting step,
A correction value setting method in which the correction value is set based on density data of corresponding unit areas having different periods. A correction value setting method for correcting the density of an image printed for each unit region adjacent in a predetermined direction by ejecting ink from a nozzle selected from a nozzle group,
A printing step of printing a test pattern, in which a plurality of sub-patterns having different densities have a measurement target pattern arranged along another predetermined direction intersecting the predetermined direction;
A density data acquisition step of providing a reference position between one end and the other end in another predetermined direction in the test pattern, and acquiring density data of the test pattern for a predetermined range in the predetermined direction from the reference position;
A correction value setting step for setting a correction value for each density of the sub-pattern for each of the unit areas based on the density data corresponding to the sub-pattern,
The reference position is
In the middle of one end and the other end of the other predetermined direction in the test pattern, provided between adjacent sub-patterns,
The test pattern is
While having another index for determining the correction amount for the density data of the test pattern,
Between the adjacent sub-patterns where the reference position is provided, there is a setting mark formed in a mode different from the sub-pattern,
The setting mark is
It has an index indicating the reference position,
The adjacent sub-patterns are formed by being spaced apart in the other predetermined direction,
In the correction value setting step,
Set the correction value at a set cycle determined based on the combination of the unit area and the nozzle in charge,
Based on the density data of the corresponding unit area of different period, set the correction value,
In the concentration data acquisition step,
Obtaining density data of the test pattern at a resolution higher than the print resolution of the test pattern;
The acquired density data is converted into a resolution corresponding to the print resolution,
While acquiring the density data of the test pattern together with the coordinate information,
Using the other index and the coordinate information, a plurality of density data belonging to a specific unit region are associated with each other, and
A correction value setting method for determining the predetermined range so that a plurality of the setting periods are included. A measurement target pattern in which a plurality of sub-patterns printed in unit directions adjacent to each other in a predetermined direction and having different densities along other predetermined directions intersecting with the predetermined direction;
Between the adjacent sub-patterns, a mark for setting the density data acquisition range formed in a mode different from the sub-pattern,
A test pattern for correcting the density.

Images