JP2008093851A - Correction value setting method, correction value setting system and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately set many kinds of correction values from limited kinds of densities of a test pattern. <P>SOLUTION: The following processes (A)-(F) are carried out. (A) On the basis of a plurality of tone command values, the test pattern with a plurality of regions of different densities is printed. (B) For each of the plurality of regions and for a non printing region, a measured value of the density is acquired. (C) A target density is set for the region printed by the lowest tone command value. (D) At the time of setting the correction value for the lowest tone command value, a group of measured values to be referred to is specified according to a size relationship between the measured value of the region printed by the lowest tone command value and the target density. (E) By referring to the specified group of measured values, the correction value for the lowest tone command value is set. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a correction value setting method, a correction value setting system, and a program.

In a printing apparatus such as an ink jet printer, a measured value is obtained by measuring the density of a test pattern printed by the printing apparatus, and ink ejection adjustment is performed based on the obtained measured value (for example, Patent Documents). 1).
Japanese Patent Laid-Open No. 2-54676

  In this type of printing apparatus, further improvement in image quality is always required. In order to meet the recent demand for higher image quality, it is conceivable that correction values for ink ejection adjustment are determined for a plurality of command gradation values. For this reason, it is conceivable to print a test pattern having a plurality of areas having different densities with typical command gradation values and to determine a correction value from the measured values of the density in each area. Here, if the number of types of representative command gradation values is increased, the correction accuracy can be increased, and the image quality can be improved. However, as the command gradation value is increased, it is necessary to print the corresponding area, which requires more time for printing or more time for processing.

  The present invention has been made in view of such circumstances, and it is an object of the present invention to obtain many types of correction values with high accuracy from limited types of density regions of a test pattern.

The main invention for solving the above-mentioned problems is:
(A) printing a test pattern having a plurality of regions with different densities on a medium based on a plurality of command gradation values;
(B) measuring a density for each of the plurality of areas and a non-printing area on the medium to obtain a measured value of the density;
(C) setting a target density for an area printed with the lowest command gradation value among the plurality of command gradation values;
(D) When the measured value of the area printed with the lowest command gradation value is larger than the target density, the measured value of the area printed with the lowest command gradation value and the non-printed area of the non-printed area Identify a set of measurements,
When the measured value of the area printed with the lowest command gradation value is smaller than the target density, the measured value of the area printed with the lowest command gradation value is higher than the lowest command gradation value. Identifying the set of measured values in other areas printed with the command gradation value;
(E) setting a correction value for the minimum command gradation value with reference to the specified set of measurement values;
This is a correction value setting method for performing (F).

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

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

That is, (A) printing a test pattern having a plurality of areas with different densities on a medium based on a plurality of command gradation values; (B) non-printing on each of the plurality of areas and on the medium Measuring the density of the area and obtaining a measured value of the density; (C) setting a target density for the area printed with the lowest command gradation value among the plurality of command gradation values; (D) When the measured value of the area printed with the lowest command gradation value is larger than the target density, the measured value of the area printed with the lowest command gradation value and the measured value of the non-printed area When the measured value of the area printed with the lowest command gradation value is smaller than the target density, the measured value of the area printed with the lowest command gradation value and the lowest command floor are specified. Command gradation value higher than the key value Identifying the set of measured values in other printed areas; (E) setting a correction value for the minimum command tone value with reference to the identified set of measured values; It is apparent that a correction value setting method for performing () can be realized.
According to such a correction value setting method, when the correction value for the minimum command gradation value is set, the measured density value is referred to for the non-printing area on the medium. Many types of correction values can be obtained from the obtained types of densities, and the accuracy of the correction value for the minimum command gradation value can be increased.

In this correction value setting method, a target density is set for an area printed with an intermediate command tone value among the plurality of command tone values, and an area printed with the intermediate command tone value is set. When the measured value is larger than the target density, the measured value of the area printed with the intermediate command tone value and the other area printed with the command tone value lower than the intermediate command tone value. Specifying the set of measured values, and when the measured value of the area printed with the intermediate command gradation value is smaller than the target density, the measured value of the area printed with the intermediate command gradation value; Identifying the set of measurement values in other areas printed with a command tone value higher than the intermediate command tone value, referring to the specified set of measurement values, the intermediate command tone value It is preferable to set a correction value.
According to such a correction value setting method, when a correction value for an intermediate command gradation value is set, a set of measurement values to be referred to is specified according to the magnitude relationship between the measurement value and the target density. . For this reason, the accuracy of the correction value for the intermediate command gradation value can be increased.

In this correction value setting method, a target density is set for an area printed with the highest command tone value among the plurality of command tone values, and an area printed with the highest command tone value is set. Regardless of the magnitude relationship between the measured value and the target density, the set of the measured value of the area printed with the highest command gradation value and the measured value of the other area printed with another command gradation value It is preferable to specify and to set a correction value for the highest command gradation value with reference to the specified set of measurement values.
According to such a correction value setting method, when setting a correction value for the maximum command gradation value, a set of measurement values to be referred to is specified regardless of the magnitude relationship between the measurement value and the target density. . For this reason, many types of correction values can be obtained from limited types of density.

This correction value setting method is a print head having a nozzle group composed of a plurality of nozzles for ejecting the same type of ink in printing the test pattern, and the ink of the ink that can eject the nozzle group. An operation of ejecting ink from the nozzles toward the medium while moving a plurality of print heads according to the type in the movement direction, and an operation of conveying the medium in a conveyance direction intersecting the movement direction, It is preferable to repeat the process.
According to such a correction value setting method, the image density can be corrected for each type of ink to be ejected.

The correction value setting method includes a plurality of sub-patterns printed with different nozzle groups in the test pattern printing, the lowest density region printed with the lowest command gradation value, and the plurality of commands. A plurality of sub-patterns each having an intermediate density region printed with an intermediate command tone value in the tone value and a highest density region printed with the highest command tone value in the plurality of command tone values, It is preferable to print a test pattern arranged in the moving direction.
According to such a correction value setting method, the test pattern can be printed quickly, and the processing efficiency can be improved.

In this correction value setting method, in the printing of the test pattern, a ruled line along the moving direction, and a ruled line used when detecting a range of the corresponding subpattern is used in the corresponding subpattern. Printing on each of the one end and the other end in the transport direction, and when acquiring the measurement value of the density, a certain ruled line printed on one end in the transport direction and another ruled line printed on the other end in the transport direction It is preferable to measure the density of the sandwiched non-printing area to obtain a measured value of density.
According to such a correction value setting method, it is possible to effectively use a non-printing region generated by printing ruled lines, that is, a region where a sub-pattern cannot be printed.

In this correction value setting method, in the acquisition of the measurement value of the density, the density of the test pattern and the density of the non-printing area are measured for each of a plurality of row areas arranged in the transport direction, It is preferable to acquire the measured value of the density for each row region.
According to such a correction value setting method, the density measurement value can be obtained for each of the row regions, so that the correction value corresponding to the density variation in the transport direction can be set.

In this correction value setting method, in the target density setting, the measurement values are referred to for a plurality of the row regions belonging to the region printed with the same command gradation value, and an average value of the respective reference measurement values Is preferably set as the target concentration.
According to such a correction value setting method, the set correction value can be made more suitable.

It is also clarified that the following correction value setting system can be realized.
That is, (A) a scanner that measures the density of a test pattern printed on a medium using a printing device that is a correction value setting target, and (A1) a plurality of command gradation values that the test pattern has A scanner that measures the density of each of a plurality of areas with different printed densities and a non-printed area on the medium; and (B) a controller, (B1) the density from the scanner. (B2) setting a target density for an area printed with the lowest command tone value among the plurality of command tone values; and (B3) printing with the lowest command tone value. When the measured value of the printed area is larger than the target density, a set of the measured value of the area printed with the lowest command gradation value and the measured value of the non-printed area is specified, and the lowest command When the measured value of the area printed with the tone value is smaller than the target density, the measured value of the area printed with the lowest command tone value and the command tone value higher than the minimum command tone value (B4) referring to the specified measurement value set, and setting a correction value for the lowest command gradation value, It is also clarified that the correction value setting system having the controller to perform and (C) can be realized.

It is also revealed that the following program can be realized.
That is, a program used in a correction value setting system that sets a correction value in a target printing apparatus, and a test pattern having a plurality of regions with different densities based on a plurality of command gradation values is stored in the printing apparatus. Printing, causing each of the plurality of regions and the non-printing region of the medium to measure the density, obtaining a measured value of the density from the scanner, and determining the lowest of the plurality of command gradation values Setting a target density for the area printed with the command gradation value, and if the measured value of the area printed with the minimum command gradation value is larger than the target density, the minimum command gradation value A set of the measured value of the printed area and the measured value of the non-printed area is specified, and the measured value of the area printed with the minimum command gradation value is smaller than the target density A set of the measurement value of the area printed with the lowest command gradation value and the measurement value of the other area printed with a command gradation value higher than the lowest command gradation value. It is also clarified that a program for causing the controller to set the correction value for the minimum command gradation value can be realized with reference to the specified set of measurement values.

=== Printing System 10 ===
Prior to the description of the correction value setting system, the printing system 10 will be described. The printing system 10 is for printing an image on paper, and includes an inkjet printer 100 (hereinafter also simply referred to as a printer 100) as a printing apparatus and a host computer 200 as shown in FIG. .

<Printer 100>
The printer 100 includes a paper transport mechanism 110, a carriage moving mechanism 120, a head unit 130, a detector group 140, and a printer-side controller 150.

  The paper transport mechanism 110 corresponds to a medium transport unit that transports a medium in the transport direction. This transport direction is a direction that intersects the carriage movement direction described below. As shown in FIGS. 2 and 3, the paper transport mechanism 110 includes a paper feed roller 111 disposed at a predetermined position above the paper stocker SS, a platen 112 that supports the paper S from the back side, and a platen 112. A conveyance roller 113 disposed on the upstream side in the conveyance direction, a discharge roller 114 disposed on the downstream side in the conveyance direction with respect to the platen 112, and a conveyance motor 115 serving as a drive source for the conveyance roller 113 and the discharge roller 114 are provided. . In the paper transport mechanism 110, the paper S held by the paper stocker SS is fed one by one by the paper feed roller 111. Then, the paper S is sent to the platen 112 side by the transport roller 113, and the printed paper S is sent in the transport direction by the paper discharge roller 114.

  The carriage movement mechanism 120 is for moving the carriage CR in the carriage movement direction. The carriage CR is a member to which the ink cartridge IC and the head unit 130 are attached. The 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. Here, the head unit 130 includes a head 131 (corresponding to a print head, see FIG. 4). For this reason, the carriage moving mechanism 120 corresponds to a head moving unit, and the carriage moving direction corresponds to the moving direction of the print head. The carriage moving mechanism 120 includes a timing belt 121, a carriage motor 122, a guide shaft 123, a drive pulley 124, and an idler pulley 125. The timing belt 121 is connected to the carriage CR and is spanned between the drive pulley 124 and the idler pulley 125. The carriage motor 122 is a drive source that rotates the drive pulley 124. The guide shaft 123 is a member for guiding the carriage CR in the carriage movement direction. In the carriage movement mechanism 120, the carriage CR can be moved in the carriage movement direction by operating the carriage motor 122.

  The head 131 included in the head unit 130 ejects ink toward the paper S. The head 131 faces the platen 112 when attached to the carriage CR. As shown in FIG. 4, a nozzle Nz for ejecting ink is provided on a surface (nozzle surface) facing the platen 112 in the head 131. The nozzles Nz are grouped for each type of ink to be ejected, and a nozzle row is configured by each group. That is, the nozzle row corresponds to a nozzle group including a plurality of nozzles Nz that eject the same type of ink. The illustrated head 131 includes a black ink nozzle row Nk, a yellow ink nozzle row Ny, a cyan ink nozzle row Nc, a magenta ink nozzle row Nm, a light cyan ink nozzle row Nlc, and a light magenta ink nozzle row Nlm. . Each nozzle row includes n (for example, n = 90) nozzles Nz. The plurality of nozzles Nz belonging to one nozzle row are provided at a constant interval (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 interval) and the dot pitch in the transport direction is 720 dpi (1/720 inch), k = 4. In addition, each nozzle Nz can eject different amounts of ink (droplet ink).

  The detector group 140 is for monitoring the status of the printer 100. As shown in FIGS. 2 and 3, the detector group 140 includes a linear encoder 141, a rotary encoder 142, a paper detector 143, and a paper width detector 144.

  The printer-side controller 150 controls the printer 100 and includes a CPU 151, a memory 152, a control unit 153, and an interface unit 154. The CPU 151 is an arithmetic processing device for performing overall control of the printer 100. The memory 152 is for securing an area for storing a program of the CPU 151, a work area, and the like, and is configured by a storage element such as a RAM, an EEPROM, or a ROM. The CPU 151 controls each control target unit via the control unit 153 in accordance with the computer program stored in the memory 152. Therefore, the control unit 153 outputs various signals based on commands from the CPU 151. A partial area of the memory 152 is used as the correction value storage unit 155. The correction value storage unit 155 stores a correction value (described later) used when correcting the density of the printed image for each row region.

<Host computer 200>
The host computer 200 includes a host-side controller 210, a recording / reproducing device 220, a display device 230, and an input device 240. Among these, the host-side controller 210 includes a CPU 211, a memory 212, a first interface unit 213, and a second interface unit 214. The CPU 211 is an arithmetic processing unit for performing overall control of the computer. The memory 212 is for securing an area for storing a computer program used by the CPU 211, a work area, and the like. The CPU 211 performs various controls according to the computer program stored in the memory 212. The first interface unit 213 exchanges data with the printer 100, and the second interface unit 214 exchanges data with an external device (for example, a scanner) other than the printer 100.

  Examples of computer programs stored in the memory 212 of the host-side controller 210 include an application program 215, a printer driver 216, and a video driver 217 as shown in FIG. The application program 215 causes the host computer 200 to perform a desired operation. The printer driver 216 is for controlling the printer 100. For example, the printer driver 216 generates print data based on image data from the application program 215 and transmits the print data to the printer 100. The video driver 217 is for causing the display device 230 to display display data from the application program 215 and the printer driver 216.

  Here, print data transmitted from the printer driver 216 will be described. This print data is data in a format that can be interpreted by the printer 100, and includes various command data and dot formation data. The command data is data for instructing the printer 100 to execute a specific operation. The command data includes, for example, paper feed data instructing paper feed, transport amount data indicating a transport amount, and paper discharge data instructing paper discharge. The dot formation data is data relating to dots formed on the paper S (data such as dot color and size). This dot formation data is composed of a plurality of dot gradation values determined for each unit area. The unit area refers to a rectangular area virtually defined on a medium such as the paper S, and the size and shape are determined according to the printing resolution. For example, when the printing resolution is 720 dpi (carriage moving direction) × 720 dpi (conveying direction), the unit area is a square shape having a size of about 35.28 μm × 35.28 μm (≈ 1/720 inch × 1/720 inch). It becomes the area of. The dot gradation value indicates the size of dots formed in the unit area. In the printing system 10, the dot gradation value is composed of 2-bit data. Therefore, it is possible to control the formation of dots with four gradations for one unit region.

=== Printing operation ===
<Operation on the host computer 200>
The printing operation is performed, for example, when the user executes a print command in the application program 215. When the print command of the application program 215 is executed, the host-side controller 210 generates image data to be printed. This image data is converted into print data by the host-side controller 210 that executes the printer driver 216. Conversion to print data is performed by resolution conversion processing, color conversion processing, halftone processing, and rasterization processing. Accordingly, the printer driver 216 has a code for performing these processes.

  The resolution conversion process is a process for converting the resolution of image data into a print resolution. The print resolution is the resolution when printing on the paper S. The color conversion process is a process of converting each RGB pixel data of the RGB image data into CMYK pixel data having multi-level (for example, 256 levels) gradation values represented by the CMYK color space. This color conversion processing is performed by referring to a table (color conversion lookup table LUT) in which RGB gradation values and CMYK gradation values are associated with each other. The printer 100 performs printing using six colors of ink of cyan (C), light cyan (LC), magenta (M), light magenta (LM), yellow (Y), and black (K). For this reason, in the color conversion process, data is generated for each of these colors. The correction value stored in the correction value storage unit 155 is used in the color conversion process (described later).

  The halftone process is a process of converting CMYK pixel data having multi-stage gradation values into dot gradation values having small-stage gradation values that can be expressed by the printer 100. Specifically, for each unit area, any one of the four gradation values of “no dot formation”, “small dot formation”, “medium dot formation”, and “large dot formation” is selected. A key value is defined. The generation rate of these dots is determined according to the gradation value. For example, as shown in FIG. 6, in the unit region in which the gradation value gr is designated, the formation probability of large dots is 1d, the formation probability of medium dots is 2d, and the formation probability of small dots is 3d. For such halftone processing, for example, a dither method, a γ correction method, an error diffusion method, or the like is used. The rasterizing process is a process of changing the dot gradation value obtained by the halftone process in the order of data to be transferred to the printer 100. Thereby, dot formation data is generated for each color. The dot formation data constitutes print data together with the command data described above, and is transmitted to the printer 100.

<Operation on Printer 100>
On the printer 100 side, the printer-side controller 150 performs various processes based on the received print data. Note that each process on the printer 100 side described below is performed by the printer-side controller 150 executing a computer program stored in the memory 152. Therefore, this computer program has a code for executing each process.

  As shown in FIG. 7, when the printer controller 150 receives a print command in the print data (S010), the paper feed operation (S020), the dot formation operation (S030), the transport operation (S040), and the paper discharge determination ( S050), a paper discharge operation (S060), and a print end determination (S070). The paper feeding operation is an operation of moving the paper S to be printed and positioning it at a printing start position (so-called cueing position). In this paper feeding operation, the printer-side controller 150 drives the carry motor 115 to rotate the paper feed roller 111 and the carry roller 113. The dot forming operation is an operation for forming dots on the paper S. In this dot forming operation, the printer-side controller 150 drives the carriage motor 122 or outputs a control signal to the head 131. The transport operation is an operation for moving the paper S in the transport direction. In this transport operation, the printer-side controller 150 drives the transport motor 115 to rotate the transport roller 113 and the paper discharge roller 114. By this transport operation, dots can be formed at positions different from the dots formed by the previous dot formation operation. The paper discharge determination is an operation for determining whether or not it is necessary to discharge the paper S to be printed. The paper discharge operation is a process of discharging the paper S, and is performed on the condition that “discharge” is determined in the previous paper discharge determination. In this paper discharge process, the printer-side controller 150 drives the carry motor 115 to rotate the carry roller 113 and the paper discharge roller 114. The print end determination is a determination as to whether or not to continue printing.

  The printing of the image on the paper S is performed by repeatedly performing the dot formation operation (S030) and the conveyance operation (S040). In the dot formation process, ink is intermittently ejected from the head 131 (nozzle Nz) that moves in the carriage movement direction. That is, the printer-side controller 150 ejects ink from the nozzles Nz based on the dot formation data (dot gradation value) included in the print data while moving the carriage CR by driving the carriage motor 122. Then, when the ink ejected from the nozzle Nz lands on the paper S, dots are formed on the paper S. Since ink is intermittently ejected while the head 131 is moving, dots are formed on the surface of the paper S in a state of being aligned along the carriage movement direction. That is, on the surface of the paper S, a dot row (hereinafter also referred to as a raster line) composed of a plurality of dots along the carriage movement direction is formed. Since the dot forming operation and the carrying operation are repeated, a plurality of raster lines are formed in the carrying direction. From the above, it can be said that the image printed on the paper S is composed of a plurality of raster lines adjacent in the transport direction.

<Interlaced printing>
The printer 100 prints an image by ejecting ink from the nozzles Nz while moving the head 131. By the way, each part such as the nozzle Nz varies due to processing and assembly. Due to this variation, characteristics such as ink flight trajectory and ejection amount (hereinafter also referred to as ejection characteristics) vary. In order to alleviate such variations in ejection characteristics, printing by an interlace method (hereinafter also referred to as interlaced printing) is performed. Interlaced printing means printing in which raster lines that are not recorded are sandwiched between raster lines that are recorded in one pass. The pass means a one-time dot formation operation, and the pass n means an n-th dot formation operation.

  In the example of interlaced printing shown in FIG. 8, there are three processing units including a front end processing unit, a normal processing unit, and a rear end processing unit. The normal processing unit is a part where a raster line is formed only by normal processing as a reference of processing. The leading edge processing portion is a portion that is defined on the leading edge side of the paper S relative to the normal processing portion, and is a portion where a raster line is formed by the leading edge processing and the normal processing. In the leading edge processing, the nozzles Nz for discharging ink and the transport amount are determined in order to form a raster line that cannot be formed by the normal processing. The rear end processing unit is a portion that is defined on the rear end side of the sheet S relative to the normal processing unit, and is a portion where a raster line is formed by the normal processing and the rear end processing. Even in this rear end process, the nozzles Nz for discharging ink and the transport amount are determined so as to form a raster line that cannot be formed by the normal process. The normal processing unit can be said to be an intermediate part sandwiched between the front end processing unit and the rear end processing unit. For this reason, the normal processing unit corresponds to an intermediate processing unit, and the normal processing corresponds to an intermediate processing.

  In the example of FIG. 8, for convenience, only one nozzle row of the plurality of nozzle rows of the head 131 is shown. The number of nozzles Nz included in one nozzle row is also reduced. In the example of FIG. 8, the head 131 (nozzle row) is depicted as moving with respect to the paper S, but the relative positional relationship between the head 131 and the paper S is depicted. . That is, in the actual printer 100, the paper S is moved in the transport direction. In addition, a large number of dots are formed in a state of being aligned along the carriage movement direction by the ink ejected intermittently from each nozzle Nz. In this case, depending on the dot gradation value, the dot may not be formed. In addition, the nozzle Nz indicated by a black circle is a nozzle Nz that can eject ink, and the nozzle Nz indicated by a white circle is a nozzle Nz that does not eject ink.

  In this interlaced printing, the first five passes correspond to leading edge processing, and the last five passes correspond to trailing edge processing. An intermediate path corresponds to normal processing. In normal processing, each nozzle Nz records a raster line immediately above the raster line recorded in the immediately preceding pass every time the paper S is transported in the transport direction by a constant transport amount. Thus, in order to perform recording with a constant conveyance amount, it is required to satisfy the following conditions. That is, (1) the number N (integer) of nozzles that can eject ink is coprime to the coefficient k, and (2) the carry amount F is N · D (D: interval at the highest resolution in the carry direction). It is required to satisfy the condition of being set to. Here, N = 7, k = 4, and F = 7 · D are set to satisfy these conditions (D = 720 dpi). And regarding the raster line group formed by the normal process, the combination of the nozzles Nz in charge of each raster line has periodicity. That is, raster lines formed by the combination of the same nozzles Nz appear every predetermined number of lines. On the other hand, in the leading edge processing, the paper S is transported by a transport amount (1 · D or 2 · D) smaller than the transport amount (7 · D) of the normal process. In this tip processing, the nozzles Nz that eject ink are not constant. In the trailing edge process, similarly to the leading edge process, the sheet S is conveyed with a conveyance amount (1 · D or 2 · D) smaller than the conveyance amount (7 · D) of the normal process. In the front end process and the rear end process, it is difficult to find regularity in the combination of the nozzles Nz.

=== Correction value ===
<Density unevenness of printed image>
As described above, the printer 100 prints an image by repeatedly performing a dot formation operation and a conveyance operation. By performing interlaced printing, the ejection characteristics for each nozzle Nz are relaxed, and the image quality is improved. However, there is a high demand for high image quality in recent years, and further improvement in quality is demanded for images obtained by interlaced printing. Here, the density unevenness (banding) of the printed image which causes the quality deterioration will be described. This density unevenness appears as stripes parallel to the carriage movement direction (also referred to as horizontal stripes for convenience). That is, the density unevenness occurs in the transport direction of the paper S.

  In the example of FIG. 9A, since the ejection characteristics are ideal, the ink ejected from the nozzles Nz lands on the unit area virtually determined on the paper S with high positional accuracy. That is, the center of the unit area and the center of the dot are aligned. The raster line is composed of a plurality of dots arranged in the carriage movement direction. In this example, when the image density is compared for the printed image in units of row areas, the image density in each row area is uniform. Here, the row region refers to a region constituted by a plurality of unit regions arranged in the movement direction (carriage movement direction) of the nozzle Nz. For example, when the print resolution is 720 dpi × 720 dpi, the row region is a band-like region having a width of 35.28 μm (≈ 1/720 inch) in the transport direction. Since the image is composed of a plurality of raster lines adjacent in the transport direction, a plurality of row regions are also defined in the transport direction of the paper S (direction intersecting the carriage movement direction). For convenience, in the following description, each image divided in the row region is also referred to as an image piece. Here, the raster line is a row of dots obtained by ink landing. On the other hand, an image piece is a printed image cut out in units of row regions. In this respect, the raster line is different from the image piece.

  In the example of FIG. 9B, the raster line corresponding to the (n + 1) th row region is formed at a position closer to the (n + 2) th row region side (lower side in FIG. 9B) than the normal position due to the influence of ejection characteristics. Has been. As a result, the density of each image piece varies. For example, the density of the image piece corresponding to the (n + 1) th row region is lighter than the density of the image piece corresponding to a standard row region (for example, the nth row region or the (n + 3) th row region). Further, the density of the image piece corresponding to the (n + 2) th row area is higher than the density of the image piece corresponding to the standard row area.

  Then, as shown in FIG. 10, the variation in the density of the image piece is viewed macroscopically as a horizontal stripe-shaped density unevenness. That is, an image piece having a relatively wide interval between adjacent raster lines looks macroscopically thin, and an image piece having a relatively narrow interval between raster lines appears macroscopically dark. This density unevenness causes a reduction in image quality of the printed image. Note that the cause of the density unevenness is also applicable to other ink colors. If even one of the six colors of ink described above has a tendency to vary, density unevenness appears in the image of multicolor printing.

<Outline of correction value>
In order to correct such density unevenness for each row area, the printer 100 stores a correction value for each row area where a raster line is formed, and corrects the density of the print image for each row area. Yes. For example, for a row area that tends to be viewed darker than the reference, a correction value that is set so that an image piece of the row area is formed light is stored. On the other hand, for a row area that tends to be viewed lighter than the reference, a correction value set so that an image piece of the row area is formed dark is stored. This correction value is referred to in processing based on the printer driver 216, for example. For example, the CPU 211 of the host computer 200 corrects multi-tone CMYK pixel data based on the correction value in the color conversion process. Then, halftone processing is performed on the corrected CMYK pixel data. In short, the gradation value is corrected based on the correction value. Thereby, the ink ejection amount is adjusted so as to suppress the density variation in each image piece. In the example of FIG. 9B, the reason why the image piece corresponding to the (n + 2) th row region is dark is that the interval between adjacent raster lines is narrower than the regular interval. Specifically, since the (n + 1) th raster line to be originally formed at the center in the transport direction in the (n + 1) th row region is closer to the (n + 2) th row region, the corresponding image piece Is darker. For this reason, when an image piece is considered as a reference, it is necessary to consider raster lines formed in adjacent row regions.

  The correction value for each row region is set based on the measured density value by the scanner 300 (see FIG. 11). For example, in an inspection process at a printer manufacturing factory, first, the printer 100 is caused to print a test pattern CP (see FIG. 16), and the density of the printed test pattern CP is read by the scanner 300. Then, a correction value is acquired for each row region based on the measurement value (read density) corresponding to each image piece. The acquired correction value is stored in the correction value storage unit 155 of the printer-side controller 150. The printer 100 in which the correction value is stored is used by the user. At that time, the host computer 200 connected to the printer 100 (specifically, the host-side controller 210 executing the printer driver 216) uses the correction value read from the correction value storage unit 155, and uses multi-tone pixels. Data is corrected for each row area. Furthermore, the host-side controller 210 generates print data based on the corrected gradation value. This print data is transmitted to the printer 100. As a result, the image printed by the printer 100 has high image quality with reduced horizontal stripe density unevenness.

  By the way, the printer 100 ejects six colors of ink. These inks are ejected from the corresponding nozzle rows (black ink nozzle row Nk to light magenta ink nozzle row Nlm). For this reason, it is necessary to print a correction pattern HP (see FIG. 16) for obtaining a correction value for each nozzle row. This is because the ejection characteristics are different for each nozzle Nz. Therefore, the test pattern CP printed by each printer 100 has six correction patterns HP. Here, these six correction patterns HP are preferably printed side by side in the width direction of the paper S (carriage movement direction). If the correction pattern HP printed by a certain nozzle row and the correction pattern HP printed by another nozzle row are printed at different positions in the transport direction, N of the certain correction pattern HP is included. Strictly speaking, the printing conditions of the Nth row area of the first row area and the other correction patterns HP are not the same. This difference in printing conditions causes a shift in correction values between a certain nozzle row and other nozzle rows. In addition, since a plurality of correction patterns HP are printed at different positions in the transport direction, there is a problem that printing takes time. As described above, the correction value is set in the process. For this reason, if it takes time to print the correction pattern HP, the manufacturing efficiency deteriorates. In the present embodiment, each test pattern CP has three different types of command gradation values, in other words, three types of density regions belonging to a halftone. Specifically, a strip pattern having a density of 30% corresponding to the command gradation value 77, a strip pattern having a density of 50% corresponding to the command gradation value 128, and a strip pattern having a density of 70% corresponding to the command gradation value 179. It has a pattern (described later).

<Outline of correction value setting method>
In this case, if a correction value is set using measurement values in a plurality of density regions, only a correction value for a specific command gradation value can be obtained. In the above-described example, only the correction value for the command tone value corresponding to the density of 50% (the correction value for the intermediate command tone value in the plurality of command tone values) can be obtained. Briefly, when the target density in a certain row area is lower than the measured value of 50% density in that row area, the density corresponds to 50% from the measured value of 50% density and the measured value of 30% density. A correction value for the command gradation value to be obtained is obtained. On the other hand, when the target density in a certain row region is higher than the measured value of 50% density in that row region, the density corresponds to 50% from the measured value of 50% density and the measured value of 70% density. A correction value for the command gradation value is obtained.

  However, it is difficult to obtain a sufficient correction effect with only one correction value for the command gradation value. In order to obtain a sufficient correction effect, it is desirable to set a plurality of correction values for command gradation values. In view of such circumstances, this embodiment employs the following method when setting correction values for a plurality of densities.

  First, the following method is adopted for the minimum command gradation value among the plurality of command gradation values. That is, (1) printing a test pattern CP having a plurality of areas with different densities on a sheet S based on a plurality of command gradation values; (2) each of the plurality of areas and non-printing on the sheet S Measuring the density of the print area and obtaining a measurement value of the density; (3) setting a target density for the area printed with the lowest command gradation value among the plurality of command gradation values; (4) When the measured value of the area printed with the lowest command gradation value is larger than the target density, the set of the measured value of the area printed with the lowest command gradation value and the measured value of the non-printed area is specified, and the lowest command When the measured value of the area printed with the gradation value is smaller than the target density, the measured value of the area printed with the minimum command gradation value and the command gradation value higher than the minimum command gradation value were printed. Identify the set of measurements in other areas, (5) special With reference to the set of measurement values is performed to set a correction value for the lowest tone value.

  In addition, the following method is adopted for intermediate command tone values among a plurality of command tone values. That is, (1) printing a test pattern CP having a plurality of areas with different densities on a sheet S based on a plurality of command gradation values; (2) each of the plurality of areas and non-printing on the sheet S Measuring the density of the print area and obtaining a measurement value of the density; (3) setting a target density for an area printed with an intermediate command tone value among a plurality of command tone values; (4) When the measured value of the area printed with the intermediate command tone value is larger than the target density, the measured value of the area printed with the intermediate command tone value and the command tone value lower than the intermediate command tone value Measured values for the area printed with the intermediate command tone value when the set of measured values for the other printed area is specified and the measured value for the area printed with the intermediate command tone value is smaller than the target density Printed with a command gradation value higher than the intermediate command gradation value. It was to identify a set of measurements of other regions, (5) with reference to the set of specified measurements performed to set a correction value for the intermediate tone value.

  Further, for the highest command tone value among the plurality of command tone values, the following method is adopted. That is, (1) printing a test pattern CP having a plurality of areas with different densities on a sheet S based on a plurality of command gradation values; (2) each of the plurality of areas and non-printing on the sheet S Measuring the density of the print area and obtaining a measured value of the density; (3) setting a target density for the area printed with the highest command tone value among the plurality of command tone values; (4) Regardless of the relationship between the measured value of the area printed with the highest command tone value and the target density, the measured value of the area printed with the highest command tone value and other areas printed with other command tone values (5) The correction value for the highest command gradation value is set with reference to the specified measurement value set.

  By adopting such a setting method, with respect to the minimum command gradation value, the minimum command gradation value is measured when the measured value of the area printed with the minimum command gradation value is larger than the target density. A set of measurement values of the area printed with the gradation value and measurement values of the non-print area is specified. On the other hand, if the measured value of the area printed with the lowest command tone value is smaller than the target density, the measured value of the area printed with the lowest command tone value and the command tone higher than the minimum command tone value A set of measurements for other regions printed with values is identified. As described above, since the measurement value of the non-printing area is used, a combination suitable for the combination of the measurement values can be specified according to the magnitude relationship between the target density and the measurement value. As for the intermediate command gradation value, a combination suitable for the combination of measurement values can be specified according to the magnitude relationship between the target density and the measurement value. Further, for the maximum command gradation value, a predetermined combination is specified regardless of the magnitude relationship between the target density and the measured value. Thereby, a correction value can be set for each of the densities in the test pattern CP. As a result, the image quality of the printed image can be improved.

=== Correction Value Setting System 20 ===
In describing the setting of the correction value, first, the correction value setting system 20 used for setting the correction value will be described. As shown in FIG. 11, the correction value setting system 20 includes a scanner 300 and a process host computer 200 ′.

<Scanner 300>
The scanner 300 includes a scanner-side controller 310, a reading mechanism 320, and a moving mechanism 330. The scanner-side controller 310 includes a CPU 311, a memory 312, and an interface unit 313. The CPU 311 performs overall control of the scanner 300. A reading mechanism 320 and a moving mechanism 330 are communicably connected to the CPU 311. The memory 312 is used to secure an area for storing a computer program, a work area, and the like, and includes a RAM, an EEPROM, a ROM, and the like. The interface unit 313 exchanges data with the process host computer 200 ′. In this embodiment, the interface unit 313 included in the scanner 300 is connected to the second interface unit 214 included in the process host computer 200 ′.

  As illustrated in FIGS. 12A and 12B, the reading mechanism 320 includes a document table glass 321, a document table cover 322, and a reading carriage 323. The reading carriage 323 faces the reading target surface of the original (the sheet S on which the test pattern CP is printed) via the original table glass 321 and is moved in a predetermined direction along the original table glass 321. In the reading carriage 323, the image density is measured by the CCD image sensor 324. The CCD image sensor 324 includes a plurality of CCDs arranged corresponding to the reading width along a direction intersecting the moving direction of the reading carriage 323 (a direction orthogonal in this embodiment). Then, the light from the exposure lamp 325 is reflected on the document, and the reflected light is guided by a plurality of mirrors 326. Then, the light is condensed by the lens 327 and input to each CCD. Thereby, density data indicating the density of the image is obtained. That is, the density of the image is measured.

  The moving mechanism 330 is for moving the reading carriage 323. The moving mechanism 330 includes a support rail 331, a regulation rail 332, a drive motor 333, a drive pulley 334, an idler pulley 335, and a timing belt 336. The support rail 331 supports the reading carriage 323 in a movable state. The restriction rail 332 restricts the moving direction of the reading carriage 323. The drive pulley 334 is attached to the rotation shaft of the drive motor 333. The idler pulley 335 is disposed at the end opposite to the drive pulley 334. The timing belt 336 is bridged between a driving pulley 334 and an idler pulley 335, and a part of the timing belt 336 is fixed to the reading carriage 323.

  In the scanner 300 having such a configuration, the reading carriage 323 is moved along the platen glass 321 (that is, the original reading surface), and the voltage output from the CCD image sensor 324 is acquired at a predetermined cycle. As a result, it is possible to measure the density of the original corresponding to the distance moved by the reading carriage 323 during one cycle.

<Process Host Computer 200 '>
The process host computer 200 ′ is configured in the same manner as the host computer 200 included in the printing system 10. For this reason, the same code | symbol is attached | subjected to the same part and description is abbreviate | omitted. The major difference between the process host computer 200 'and the host computer 200 is the installed computer program. That is, a process program is installed in the process host computer 200 ′ as an application program. The process program includes, for example, a function for causing the printer 100 to be a correction value setting target to print the test pattern CP, a function for controlling the scanner 300 to obtain a density measurement value in the test pattern CP, and A function for setting a correction value for each row region from the density measurement value is realized in the process host computer 200 '. These functions will be described later.

  A printer driver for controlling the printer 100 and a scanner driver for controlling the scanner 300 are also installed in the process host computer 200 ′. Further, as shown in FIG. 13, the memory 212 of the process host computer 200 ′ is used as a data table in which a part of the memory 212 stores density data (measurement values). Further, the process host computer 200 ′ stores the obtained correction value in the correction value storage unit 155 of the target printer 100. As shown in FIG. 14, the correction value storage unit 155 stores an area for storing the correction value for the front end processing unit, an area for storing the correction value for the normal processing unit, and the correction value for the rear end processing unit. An area to be provided is provided. In addition to the correction value storage unit 155, the memory 152 of the printer 100 stores an area for storing the number of row areas of the front end processing unit, an area for storing the number of row areas of the normal processing unit, and a rear end processing unit. An area for storing the number of column areas is also provided.

=== Processing at the printer manufacturing factory ===
<Print test pattern CP>
Next, processing performed at the printer manufacturing factory will be described. The correction value setting process described below is realized by a computer program installed in the process host computer 200 ′, that is, a correction value setting program, a scanner driver, and a printer driver. Therefore, these computer programs have codes for performing correction value setting processing.

  Prior to the correction value setting process, an operator in the factory connects the printer 100 to which correction values are set to the process host computer 200 '. The correction value setting program installed in the process host computer 200 ′ causes the CPU 212 to perform correction value setting processing and related processing. As this processing, for example, processing for causing the printer 100 to print the test pattern CP, processing for performing image processing or analysis on the density data acquired from the scanner 300, and setting the correction value to the correction value of the printer 100 Processing for storing in the storage unit 155 is included.

  After the printer 100 is connected, the test pattern CP is printed as shown in FIG. 15A (S100). This printing step is performed according to an operator's instruction. In this printing step, the CPU 212 of the process host computer 200 ′ generates print data for the test pattern CP. The print data generated by the CPU 212 is transmitted to the printer 100. The printer 100 prints the test pattern CP on the paper S based on the print data from the process host computer 200 ′. This printing operation is performed in accordance with the processing described above (see FIG. 7). Briefly, the dot formation operation (S030) and the transport operation (S040) are performed repeatedly according to the print data. That is, in the dot forming operation, ink is ejected toward the paper S while moving the head 131 in the carriage movement direction. In the transport operation, the paper S is transported in the transport direction. At this stage, the correction value storage unit 155 stores no correction value. For this reason, the test pattern CP to be printed reflects the ejection characteristics for each nozzle Nz.

<Test pattern CP>
Next, the printed test pattern CP will be described. Note that the test pattern CP includes a plurality of correction patterns HP. One correction pattern HP is a portion drawn by a nozzle row (nozzle group) that can eject the same type of ink, and corresponds to a sub-pattern. The correction pattern HP is used for evaluating density variation. As described above, the head 131 of the printer 100 includes the black ink nozzle row Nk, the yellow ink nozzle row Ny, the cyan ink nozzle row Nc, the magenta ink nozzle row Nm, the light cyan ink nozzle row Nlc, and the light magenta ink nozzle row. It has 6 nozzle rows made of Nlm. Therefore, as shown in FIG. 16, the test pattern CP has six correction patterns HP (Y) to HP (K) corresponding to the respective nozzle rows. These correction patterns HP (Y) to HP (K) are arranged (printed) in a state of being aligned in the carriage movement direction.

  As shown in FIGS. 16 and 17, each of the correction patterns HP (Y) to HP (K) includes a plurality of types of belt-like patterns BD (30) to BD (70), an upper ruled line UL, and a lower ruled line DL. The left ruled line LL and the right ruled line RL. The strip patterns BD (30) to BD (70) correspond to areas printed with different command gradation values, and have a strip shape that is long in the transport direction. Accordingly, the test pattern CP has a plurality of sets of band-like patterns BD (30) to BD (70) (that is, sets of regions) printed with different command gradation values corresponding to the nozzle rows. I can say that.

  For example, the correction pattern (Y) printed with the yellow ink nozzle row Ny includes the belt-like pattern BD (Y30) printed with the command gradation value 77 corresponding to the density 30%, and the command floor corresponding to the density 50%. A belt-like pattern BD (Y50) printed with a tone value 128 and a belt-like pattern BD (Y70) printed with a command gradation value 179 corresponding to a density of 70% are included. For convenience, in the following description, when the correction pattern HP is described without specifying the nozzle row in charge, the correction pattern HP is simply indicated. Similarly, when each band pattern is described without specifying the nozzle row in charge, the band pattern BD (30) for the density 30%, the band pattern BD (50) for the density 50%, and the density A 70% pattern is shown as a strip pattern BD (70).

  These band-like patterns BD (30) to BD (70) are arranged side by side in the carriage movement direction. And it is printed with the command gradation value so large that it is located on the right side. The belt-like pattern BD (30) printed with a density of 30% (command gradation value 77) corresponds to the lowest density region, and the belt-like pattern BD (50 with a density of 50% (command gradation value 128)). ) Corresponds to the intermediate density region. The strip pattern BD (70) printed with a density of 70% (command gradation value 179) corresponds to the highest density area. Moreover, these strip | belt-shaped patterns BD (30) -BD (70) are printed in the mutually adjacent state.

  Corresponding to each correction pattern HP, the upper ruled line UL is printed along the carriage movement direction at the upstream end in the transport direction, and the lower ruled line DL is printed at the downstream end in the transport direction. Are printed along the carriage movement direction. These upper ruled line UL and lower ruled line DL are printed for detecting the range of the corresponding correction pattern HP. By printing the upper ruled line UL and the lower ruled line DL, an area sandwiched between the upper ruled line UL and the lower ruled line DL is generated. Although the belt-like patterns BD (30) to BD (70) cannot be printed in this area, the correction value setting system 20 defines a non-printing area sandwiched between the pair of upper ruled line UL and lower ruled line DL on the sheet S. It is used as an area for measuring the density of the ground color. As a result, the limited area of the paper S is effectively utilized. For convenience, in the following description, the non-printing area adjacent to the belt-like pattern BD (30) is also referred to as a non-printing area BD (0).

  In this embodiment, ink of the same color (hereinafter also referred to as process ink) is ejected from each nozzle row in the process. For example, the process ink is colored light magenta. Even when the correction patterns HP (Y) to HP (K) printed on the paper S are printed in the same color, unevenness occurs in density due to the characteristics of the nozzles Nz constituting the nozzle row. By setting the correction value so as to reduce the density unevenness, it is possible to reduce the density unevenness when the user performs multicolor printing. In the following description, for the sake of convenience, a command gradation value 77 corresponding to a density of 30% is indicated by a symbol Sa, a command gradation value 128 corresponding to a density of 50% is indicated by a symbol Sb, and a command gradation corresponding to a density of 70%. The value 179 is also expressed as symbol Sc.

  As described above, leading edge processing, normal processing, and trailing edge processing are performed during image printing. Each correction pattern HP is also printed by leading edge processing, normal processing, and trailing edge processing. That is, each correction pattern HP includes a front end processing unit, a normal processing unit (corresponding to an intermediate processing unit), and a rear end processing unit. In the image printing performed by the user, the raster lines constituting the normal processing unit are, for example, about several thousand in the case of A4 size. However, the combination of the nozzles Nz in charge of each raster line of the normal processing unit has a periodicity, so it is not necessary to print all of them. Therefore, in the present embodiment, the length in the transport direction of the normal processing unit in each correction pattern HP is set to include raster lines corresponding to a plurality of cycles. For example, the length corresponds to 8 periods. Further, in this correction pattern HP, as shown in FIG. 17, the upper ruled line UL is formed by the first row region in the strip patterns BD (30) to BD (70). Similarly, the lower ruled line DL is formed by the last row region in the belt-like patterns BD (30) to BD (70).

<Initial Settings of Scanner 300>
If the test pattern CP has been printed, a correction value is set and stored in the printer 100 (S200). Hereinafter, this process will be described. As shown in FIG. 15B, in this process, the initial setting of the scanner 300 is first performed (S210). In this initial setting, for example, necessary items such as the reading resolution of the scanner 300 and the type of document are set. Here, the reading resolution of the scanner 300 is required to be higher than the printing resolution. Preferably, it is set to an integral multiple of the print resolution. In this embodiment, since the print resolution of the test pattern CP is 720 dpi, the reading resolution of the scanner 300 is set to 2880 dpi, which is four times that. The document type is a reflective document, the image type is an 8-bit gray scale, and the storage format is a bitmap.

<Reading test pattern CP>
If the initial setting of the scanner 300 is performed, the test pattern CP is read (S215). In this step, in the scanner 300, the scanner-side controller 310 controls the reading mechanism 320 and the moving mechanism 330, and acquires density data of the entire sheet S. Here, density data is acquired along the longitudinal direction of the non-printing region BD (0) and the strip-shaped patterns BD (30) to BD (70). Then, the scanner 300 outputs the acquired density data to the process host computer 200 ′. The density data acquired in this way is data representing density for each pixel (here, a region having a size defined by the reading resolution), and constitutes an image. For this reason, in the following description, the data acquired by the scanner 300 is also referred to as image data. The density data for each pixel constituting the image data is also referred to as pixel density data. This pixel density data is composed of gradation values indicating density.

  When receiving the image data from the scanner 300, the host-side controller 210 of the process host computer 200 ′ cuts out a predetermined range of image data corresponding to each correction pattern HP from the received image data. This predetermined range is defined as a rectangular range that is slightly larger than each correction pattern HP. In the present embodiment, six image data are cut out corresponding to each of the six types of correction patterns HP. For example, for the correction pattern HP (Y) drawn by the nozzle row that discharges yellow ink, image data in the range indicated by the symbol Xa in FIG. 16 is cut out.

<Inclination correction for each correction pattern HP>
Next, the host-side controller 210 detects the inclination of the correction pattern HP included in the image data (S220), and performs rotation processing corresponding to the inclination on the image data (S225). For example, the host-side controller 210 acquires the image density of the upper ruled line UL at a plurality of locations with different positions in the width direction of the paper S, and detects the inclination of the correction pattern HP based on these image densities. Then, based on the detected inclination, the image data is rotated.

<Trimming correction pattern HP>
Next, the host-side controller 210 detects horizontal ruled lines (upper ruled line UL, lower ruled line DL) from the image data of each correction pattern HP (S230), and performs trimming (S235). First, the host-side controller 210 acquires pixel density data for a predetermined range of pixels from the rotated image data. Then, the upper ruled line UL is recognized based on the image density, and a portion above the upper ruled line UL is removed by trimming. Similarly, the lower ruled line DL is recognized based on the image density, and a portion below the lower ruled line DL is removed by trimming.

<Resolution conversion>
If the trimming has been performed, the host-side controller 210 converts the resolution of the trimmed image data (S240). In this processing, the resolution of the image data is converted so that the number of pixels in the Y-axis direction (conveyance direction, array direction of the row area) in the image data is the same as the number of raster lines constituting the correction pattern HP. The Assume that a correction pattern HP printed at a resolution of 720 dpi is read at a resolution of 2880 dpi. In this case, ideally, the number of pixels in the Y-axis direction in the image data is four times the number of raster lines constituting the correction pattern HP. However, in reality, the number of raster lines and the number of pixels may not match due to the influence of errors during printing and reading. Resolution conversion is performed on the image data in order to eliminate such inconsistencies. In this resolution conversion process, the conversion magnification is calculated based on the ratio between the number of raster lines constituting the correction pattern HP and the number of pixels in the Y-axis direction of the trimmed image data. Then, resolution conversion processing is performed at the calculated magnification. Various methods such as a bicubic method can be used for resolution conversion. As a result, the number of pixels arranged in the Y-axis direction is equal to the number of column regions, and the columns of pixels arranged in the X-axis direction correspond to each other in a one-to-one manner.

<Density acquisition for each row area>
Next, the host-side controller 210 acquires the density for each column area in the correction pattern HP (S245). When acquiring the density for each row region, the host-side controller 210 acquires the center of gravity of the reference vertical ruled line (in this example, the left ruled line LL), and uses each bar pattern BD ( 30) to BD (70) are specified. Further, the range of the non-printing area BD (0) is specified. Then, pixel density data is acquired for the specified pixel, and background color density data of the paper S is acquired for the range of the non-printing area BD (0). For example, for the belt-like pattern BD (30) printed at a density of 30%, as shown in FIG. 17, pixel density data is acquired for each pixel belonging to the central range W2 excluding both end portions indicated by reference numeral W1. Then, an average value obtained from each acquired pixel density data is set as a measured value of 30% density for the first row region. Measurement values are obtained in the same manner for the other row regions, the other strip patterns BD (50), BD (70), and the non-printing region BD (0). The acquired measurement values are stored in a data table (see FIG. 13) in the memory 212 of the host-side controller 210. That is, the measured value is stored in an area specified by the type of nozzle row, the print density (command gradation value) of the pattern, and the row area number. Note that the density 0 to density 3 in FIG. 13 mean measured values of the non-printing area BD (0) and the strip patterns BD (30) to BD (70). For example, density 0 is a measurement value of a non-printing area BD (command gradation value 0, background color of paper S), density 1 is a measurement value of density 30% (command gradation value Sa), and density 2 is The density is a measurement value of 50% (command gradation value Sb), and the density 3 is a measurement value of density 70% (command gradation value Sc). Then, when the measurement value stored in the data table is set on the vertical axis and the position of the row region is set on the horizontal axis and plotted, for example, the graph of FIG. 18 is obtained.

<Details of correction value setting>
If the measurement value for each column region is acquired, the host-side controller 210 sets a correction value for each column region (S250). As described above, one strip pattern is printed with the same command gradation value. However, the obtained measurement values for each row region vary. This variation causes density unevenness in the printed image. In order to eliminate this density unevenness, it is required to make the measurement values for each row region as uniform as possible for each strip pattern BD. From such a viewpoint, the correction value is set for each row region based on the measurement value for each row region. As described above, the test pattern CP has a plurality of correction patterns HP (Y) to HP (K) printed for each type of nozzle row, and each of the correction patterns HP (Y) to HP (K). Has strip patterns BD (30) to BD (70) printed with different command gradation values. And each strip | belt-shaped pattern BD (30) -BD (70) has a some row area | region. That is, a plurality of row regions are defined in a state where they are arranged in the transport direction within the belt-like pattern BD (region printed with a predetermined command gradation value). Accordingly, the correction value is set for each different color, for each different command gradation value (for each density), and for each row region. Hereinafter, the setting of the correction value will be described in detail.

<Setting of correction value for density 30% (command gradation value 77)>
First, setting of a correction value for a density of 30% (command gradation value 77 (= Sa)) will be described. The command tone value Sa corresponds to the lowest command tone value among the plurality of command tone values for which correction values are to be set. First, the host-side controller 210 determines a target density for the command gradation value Sa that is a correction value setting target. In the present embodiment, as the target density of the command gradation value Sa to be set, the average value of the measurement values of each row region included in the strip pattern BD (30) is set. That is, each measured value from the first row region to the last row region is added, and a value obtained by dividing the added value by the number of row regions is set as the target density. In the example of FIG. 18, the value indicated by the symbol Cat is set as the target density. A correction value for a certain row region is determined according to a difference from the target density. By setting the correction value for each row region in this way, each correction value becomes more suitable. This is because the image density of each row region is aligned with the average density as the target density. In this regard, the same applies to other densities (density 50%, density 70%).

  Next, the host-side controller 210 selects a low-side density measurement value lower than the density corresponding to the command gradation value for which the correction value is set and a high-side density measurement value higher than the corresponding density. To do. In this embodiment, since the correction value setting target is the command gradation value Sa, a density of 0% lower than the corresponding density of 30% is selected as the low-side density, and measurement of the non-printing area BD (0) is performed. The value is obtained. On the other hand, as the high-side density, a density 50% higher than the corresponding density 30% is selected, and the measured value of the strip pattern BD (50) is acquired.

  It should be noted that in the low-side density and the high-side density, the column region from which the measurement value is acquired is the same position as the column region from which the correction value is set. For example, when the correction value is set for the 10th row region in the strip pattern BD (30), the measurement value of the 10th row region in the non-print region BD (0) and 10 in the strip pattern BD (50). The measurement value of the th column region is obtained.

  Here, regarding the non-printing area BD (0), the upper ruled line UL is printed in a portion corresponding to the first row area. Similarly, a lower ruled line DL is printed on a portion corresponding to the final row region. For this reason, the correction value setting system 20 does not correct the portion corresponding to the first row region and the portion corresponding to the last row region.

  If the low-side density and high-side density measurement values are acquired, the host-side controller 210 responds according to the magnitude relationship between the measurement value corresponding to the 30% density row region for which the correction value is set and the target density Cat. To identify the set of measurements to be referenced. Here, a set of measurement values to be referred to is specified so that the target density falls within the range of the measurement values of the row area to be set and the measurement values of other densities. In other words, if the measured value of the row area to be set is higher than the target concentration, the set of the measured value of the row area to be set and the measured value of the low side concentration is specified as the set of measured values to be referred to. To do. On the other hand, when the measured value of the row area to be set is lower than the target concentration, the set of the measured value of the row area to be set and the measured value of the high-side density is set as the set of measured values to be referred to. Identify.

  For example, in the graph of FIG. 18, in a certain row area indicated by the symbol LAn, the measurement result of the row area at the density of 0% is B1, the measurement result of the row area at the density of 30% is X1, and the measurement of the row area at the density of 50%. The result is Y1, and the measurement result of the row region at a density of 70% is Z1. Here, the measurement result X1 with a concentration of 30% is plotted below the target concentration Cat in the graph. The vertical axis of this graph has a lower density on the upper side and a higher density on the lower side. Therefore, the measurement result X1 of the row region LAn at the density of 30% is higher than the target density Cat. For this reason, the host-side controller 210 specifies the measurement value corresponding to the row region having a density of 30% and the measurement value corresponding to the row region having a concentration of 0% as a set of measurement values to be referred to. Also, in a certain row area indicated by the symbol LAm, the measurement result of the row area at the density of 0% is B2, the measurement result of the row area at the density of 30% is X2, the measurement result of the row area at the density of 50% is Y2, and the density. The measurement result of the row region at 70% is Z2. In this case, the density of the row region LAm at a density of 30% is lower than the target density Cat. For this reason, the host-side controller 210 specifies the measurement value corresponding to the row region with a density of 30% and the measurement value corresponding to the row region with a density of 50% as a set of measurement values to be referred to.

When the set of measurement values to be referred to is specified, the host-side controller 210 sets a correction value for the target row area. The correction value is set by primary interpolation based on the measured value and the command gradation value. In the case of the row region LAn, as shown in FIG. 19, a set of the measurement result X1 of the row region LAn having a concentration of 30% and the measurement result B1 of the row region LAn having a concentration of 0% is used. Then, a correction value is set based on the command gradation value Sa and the measurement value Ca1 in the measurement result X1 and the command gradation value [0] and the measurement value Cd1 in the measurement result B1. Specifically, the host-side controller 210 performs primary interpolation shown in the following equation (1) to calculate the command gradation value Sat1 corresponding to the target density, and performs the calculation shown in the following equation (2) to correct it. The value Ha1 is set.
Sat1 = Sa × {(Cat−Cd1) / (Ca1−Cd1)} (1)
Ha1 = (Sat1-Sa) / Sa (2)

In the case of the row region LAm, as shown in FIG. 20, a set of a measurement result X2 of 30% row region LAm and a measurement result Y2 of 50% row region LAm is used. Then, a correction value is set based on the command gradation value Sa and the measurement value Ca2 in the measurement result X2 and the command gradation value Sb and the measurement value Cb2 in the measurement result Y2. Specifically, the host-side controller 210 performs primary interpolation shown in the following equation (3) to calculate the command gradation value Sat2 corresponding to the target density, and performs the calculation shown in the following equation (4) for correction. The value Ha2 is set.
Sat2 = Sa +
(Sb-Sa) × {(Cat-Ca2) / (Cb2-Ca2)} (3)
Ha2 = (Sat2-Sa) / Sa (4)

  The host-side controller 210 performs the above calculation for each column region, and sets a correction value Ha for the command gradation value Sa (density 30%) for each column region. The correction value Ha set in this way is temporarily stored in the memory 212 (for example, work memory) of the host-side controller 210. Thereafter, the correction value is stored in the correction value storage unit 155 of the printer 100. Here, the correction value Ha1 obtained by the equation (2) and the correction value Ha2 obtained by the equation (4) are represented by a difference with respect to the coefficient 1.00. In the present embodiment, in order to simplify the process under the user, the correction value storage unit 155 stores a correction value taking the coefficient 1.00 into account. For example, when the correction value Ha1 is the value [−0.03], the correction value to be stored is the value [0.97].

  As described above, for the strip pattern BD (30) having a density of 30% printed with the lowest command gradation value, when the measured value of the row area is higher than the target density Cat, the measurement of the row area having the density of 30% is performed. A correction value is set using a set of a value and a measured value of the row area of 0% density. Further, when the measured value of the 30% density row region is lower than the target density Cat, the correction value is set using a set of the measured value of the 30% density row region and the measured value of the 50% density row region. The In this way, the target concentration Cat belongs within a range defined by one measurement value and the other measurement value. Accordingly, when setting a correction value for a row region having a density of 30%, a suitable set is used according to the magnitude relationship between the measured value of the row region and the target density Cat. As a result, the set correction value can be made more suitable. In the example of FIG. 19, the slope of the straight line passing through the measurement result B1 and the measurement result X1 is different from the slope of the straight line passing through the measurement result X1 and the measurement result Y1, but linear interpolation can be performed with the corresponding straight line. . In addition, since the measured value of the non-printing area BD (0), in other words, the density of the ground color of the paper S is used for the density of 0%, the correction value can be set with high accuracy accordingly.

  In this embodiment, when setting the correction value, the command gradation value corresponding to the target density is obtained by referring to the specified set of measured values and the corresponding command gradation value. Then, a correction value for the minimum command tone value corresponding to a density of 30% is set using the obtained command tone value. As described above, since the correlation between the command gradation value, the measured value, and the target density is used, the correction value can be set by a simple calculation such as primary interpolation. As a result, the processing speed can be increased. This is also true for other densities, that is, 50% density (command gradation value 128) and 70% density (command gradation value 179).

<Setting of correction value for density 50% (command gradation value 128)>
Next, setting of a correction value for a density of 50% (command gradation value 128 (= Sb)) will be described. The command tone value Sb corresponds to an intermediate command tone value among a plurality of command tone values for which correction values are to be set. Also in this case, the host-side controller 210 determines the target density for the density for which the correction value is set (that is, the density corresponding to the command gradation value Sb). The target density is set in the same procedure as in the case where the density is 30%.

  First, the average value of the measured values in each row region of the strip pattern BD (50) (the value of the symbol Cbt in FIG. 18) is set as the target density.

  Next, the host-side controller 210 selects a low-side density measurement value that is lower than the density for which the correction value is to be set, and a high-side density measurement value that is higher than this density. In this embodiment, since the correction value setting target is the command gradation value Sb, the measurement value of the row region constituting the strip pattern BD (30) having a density of 30% is selected as the low-side density. Similarly, as the high-side density, the measurement value of the row region constituting the band-shaped pattern BD (70) having the density of 70% is selected.

  If the low-side density and high-side density measurement values are selected, the host-side controller 210 responds to the magnitude relationship between the measurement value corresponding to the 50% density column region for which the correction value is set and the target density Cbt. To identify the set of measurements to be referenced. Here, a set of measurement values to be referred to is specified so that the target density Cbt falls within the range of the measurement values of the row area to be set and the measurement values of other densities. That is, when the measurement value of the row region to be set is higher than the target concentration Cbt, the set of the measurement value of 50% density and the measurement value of 30% density is specified as the set of measurement values to be referred to. On the other hand, when the measured value of the row area to be set is lower than the target density Cbt, the set of the measured value of 50% density and the measured value of 70% density is specified as the set of measured values to be referred to. . This is the same as in the case of a density of 30%.

  When the set of measurement values to be referred to is specified, the host-side controller 210 sets the correction value Hb (Hb1, Hb2) for the target row region. The correction value Hb is set by primary interpolation based on the measured value and the command gradation value. For example, in the case of the row region LAn, as shown in FIG. 19, a set of a measurement result Y1 of 50% row region LAn and a measurement result X1 of 30% row region LAn is used. Then, the correction value Hb1 is set based on the command gradation value Sb and the measurement value Cb1 in the measurement result Y1 and the command gradation value Sa and the measurement value Ca1 in the measurement result X1. This calculation is the same as in the case of a density of 30%. Therefore, the description is omitted.

  As described above, when setting the correction value Hb of the density 50%, which is an intermediate density, the band-like shape is obtained regardless of whether the measured value of the row region is higher than the target density Cbt or lower than the target density Cbt. Measurement values of the patterns BD (30) to BD (70) are used. For this reason, the correction value can be set with high accuracy.

<Setting of correction value at density 70% (command gradation value 179)>
Next, setting of a correction value for a density of 70% (command gradation value 179 (= Sc)) will be described. This command tone value Sc corresponds to the highest command tone value among a plurality of command tone values for which correction values are to be set. Also in this case, the target density is determined for the density for which the correction value is to be set (that is, the density corresponding to the command gradation value Sc). The method for setting the target density is the same as the method using the command gradation values Sb and Sa. In the example of FIG. 18, a value indicated by a symbol Cct is set as the target density.

  Next, the host-side controller 210 specifies a set of measurement values used for primary interpolation. Here, the density for which the correction value is set is 70%, which is the highest density in the correction pattern HP. For this reason, there is no measured value with a density higher than 70%. Therefore, the host-side controller 210 specifies the second highest density measurement value. As a result, the measurement value in the row region having the density of 70% and the measurement value in the row region having the density of 50% are specified as a set of measurement values used for the primary interpolation. That is, these measured values are specified regardless of the magnitude relationship between the measured value at the concentration of 70% and the target concentration Cct.

When the set of measurement values to be referred to is specified, the host-side controller 210 sets a correction value for the target row area. As described above, the correction value is set by primary interpolation based on the measurement value and the command gradation value. In the case of the row region LAn, as shown in FIGS. 19 and 20, a set of measurement results Z1 of the row region LAn having a concentration of 70% and a measurement result Y1 of the row region LAn having a concentration of 50% are used. Here, in the row region LAn, as shown in FIG. 19, the target density Cct is lower than the measured value of the density 70%. In this case, the host-side controller 210 performs primary interpolation shown in the following equation (5) to calculate a command gradation value Sct1 corresponding to the target density Cct, and performs an operation shown in the following equation (6) to correct the correction value. Set Hc1.
Sct1 = Sb +
(Sc-Sb) × {(Cct-Cb1) / (Cc1-Cb1)} (5)
Hc1 = (Sct1-Sc) / Sc (6)

In the case of the row region LAm, as shown in FIG. 20, the target density Cct is higher than the measured value of the density 70%. In this case, the host-side controller 210 performs primary interpolation shown in the following equation (7) to calculate the command gradation value Sct2 corresponding to the target density Cct, and performs the calculation shown in the following equation (8) to correct the correction value. Set Hc2.
Sct2 = Sc +
(Sc-Sb) * {(Cct-Cc2) / (Cc2-Cb2)} (7)
Hc2 = (Sct2-Sc) / Sc (8)

  The host-side controller 210 performs the above calculation for each column region, and sets a correction value Hc for a density of 70% (command gradation value Sc) for each column region. The correction value Hc set in this way is stored in the correction value storage unit 155 of the printer 100 in the same procedure as the correction values Hb and Ha.

  As described above, for the strip pattern BD (70) having a density of 70% corresponding to the highest command gradation value, when the measured value of the row region is higher than the target density Cct, the measured value of the row region having the density of 70%. And a correction value Hc is set using a set of measured values of the row region having a density of 50%. Even when the measurement value of the row region with the density of 70% is lower than the target density Cct, the correction value Hc is set using the set of the measurement value of the row region with the density of 70% and the measurement value of the row region with the density of 50%. Is set. That is, when setting the correction value Hc for the row region having a density of 70%, regardless of the magnitude relationship between the measurement value of this row region and the target density Cct, a set of the highest density measurement value and the second highest density measurement value is set. Is used. That is, the correction value Hc for the density of 70% is set with one set of measurement values.

<Storing correction values>
If the correction value is set, the host-side controller 210 stores the set correction value in the memory 152 (correction value storage unit 155, see FIG. 14) of the printer-side controller 150 (S255). In this case, the host-side controller 210 communicates with the printer 100 so that the correction value can be stored. Then, the host-side controller 210 transfers the correction value stored in the memory 212 and stores it in the memory 212 of the printer-side controller 150. As shown in FIG. 14, the correction value storage unit 155 includes a storage area for correction values for front end processing, a storage area for correction values for normal processing, and a storage area for correction values for rear end processing. A plurality of these storage areas are provided corresponding to the row areas. Note that the number of storage areas of the normal processing unit is a number corresponding to one repetition cycle. In the correction value setting system 20, the correction value for the minimum command tone value Sa and the correction for the intermediate command tone value Sb set based on the measured values of the strip patterns BD (30) to BD (70). Value and the correction value for the maximum command gradation value Sc are stored.

=== Printing by user ===
According to the above-described procedure, the printer 100 in which the correction value is stored in the correction value storage unit 155 undergoes another inspection and is shipped from the factory. A user who has purchased the printer 100 connects the printer 100 to a host computer 200 owned by the user, for example, as shown in FIG. When the power is turned on, the printer 100 waits for print data sent from the host computer 200. When print data is sent from the host computer 200, a printing operation is performed. The printing operation here is as described above. That is, the host computer 200 refers to the correction value in the color conversion process, and corrects the image density (command gradation value) in the row region with the corresponding correction value. Then, the host computer 200 performs halftone processing or the like with the corrected image density to obtain print data. The printer 100 performs printing based on the print data.

  As a result of density correction by the host computer 200, for a column area that is easily visible, the gradation value of the pixel data (CMYK data) in the unit area corresponding to the column area is corrected to be low. On the other hand, for a column region that is faint and easily visible, the gradation value of the pixel data of the unit region corresponding to the column region is corrected so as to be high. By outputting the print data generated in this manner to the printer 100, the density of the image pieces corresponding to each row region of the print image by the printer 100 is corrected, and density unevenness of the entire image is suppressed.

=== Other Embodiments ===
Each of the above-described embodiments is mainly described with respect to the correction value setting system 20 having the printer 100, but the disclosure includes a correction value setting method and a correction value setting device. The above-described embodiments are for facilitating understanding of the present invention, and are not intended to limit the present invention. The present invention can be changed and improved without departing from the gist thereof, and it is needless to say that the present invention includes equivalents thereof. In particular, the embodiments described below are also included in the present invention.

<About test pattern CP>
In each of the embodiments described above, regarding the correction pattern HP for each nozzle row, the minimum command tone value (density 30%), the intermediate command tone value (density 50%), and the maximum command tone value (density 70%). ) Had three types of belt-like patterns printed at different densities. The belt-like pattern included in each correction pattern HP is not limited to these three types, and can be determined as appropriate.

  For example, four types of belt-like patterns printed with command gradation values corresponding to respective densities of 20% density, 40% density, 60% density, and 80% density may be used. In this case, an area having a density of 20% is printed in an area printed with the lowest command gradation value, an area in which density 40% and density 60% are printed with an intermediate command gradation value, and density 80% is the highest command gradation value. Correspond to the areas printed in.

  Further, five types of belt-like patterns BD may be printed in which the density is changed by 10% in the density range of 30% to 70%.

  In these test patterns CP, a set of measurement values corresponding to densities that are not adjacent to each other can be selected. In this regard, it is considered that the correction value to be set can be made more suitable by selecting a set of measurement values corresponding to adjacent densities in the test pattern CP as in the above-described embodiments. This is because it is considered that the selection of a density close to the density for which the correction value is set reflects the characteristics faithfully.

<About the printing system 10>
In the above-described embodiment, the printing system 10 has been described in which the printer 100 as a printing apparatus and the computer as a printing control apparatus are separately configured. However, the present invention is not limited to this configuration. The printing system 10 may be one in which a printing apparatus and a print control apparatus are integrated. Further, it may be a combined printer / scanner device in which the scanner 300 is integrated. With this composite apparatus, it is easy for the user to set the correction value again. That is, the correction value setting system 20 can be easily constructed.

<About resetting correction values>
The setting of the correction value in the process has been described above. That is, the setting of the correction value at the time of manufacture has been described. In this regard, the correction value may be reset after shipment.

<About ink>
In the above-described embodiment, six colors of ink are ejected from the head 131. However, the types of ink to be ejected are not limited to these six colors. The types of colors may be different and the number of colors may be increased. For example, red ink, violet ink, and gray ink may be included.

<About the printing method>
In the above-described embodiment, the interlace method is exemplified as the printing method, but the present invention is not limited to this. For example, an overlap method may be used. This overlap method is a printing method in which one raster line is formed by a plurality of different nozzles Nz.

<About other application examples>
In the above-described embodiment, the printer 100 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.

1 is a block diagram illustrating a configuration of a printing system. It is a perspective view explaining the structure of a printer. It is a side view explaining the structure of a printer. It is a figure explaining the nozzle row which a head has. It is a conceptual diagram explaining the computer program memorize | stored in memory of a host computer. It is a figure explaining halftone processing typically. 6 is a flowchart illustrating a printing operation on the printer side. It is a figure explaining the example of interlaced printing. FIG. 9A is a diagram illustrating a dot group formed with ideal ejection characteristics. FIG. 9B is a diagram for explaining the influence of variations in ejection characteristics. It is a conceptual diagram for demonstrating density nonuniformity. It is a block diagram explaining the structure of a correction value setting system. FIG. 12A is a front view illustrating the structure of the scanner. FIG. 12B is a plan view illustrating the structure of the scanner. It is a conceptual diagram of the data table of measured values provided in the process host computer. It is a conceptual diagram of a correction value storage unit provided in the memory of the printer. FIG. 15A is a flowchart for explaining correction value setting processing performed in an inspection process after manufacturing the printer. FIG. 15B is a flowchart illustrating correction value setting and storage steps in the correction value setting process. It is explanatory drawing of a test pattern. It is explanatory drawing which shows a part of correction pattern. It is the figure which showed the measured value of each strip | belt-shaped pattern for every row area. It is a figure explaining the setting of the correction value in a certain row area. It is a figure explaining the setting of the correction value in another row area.

Explanation of symbols

10 printing system, 20 correction value setting system,
100 printer, 110 paper transport mechanism, 111 paper feed roller,
112 platen, 113 transport roller, 114 discharge roller,
115 transport motor, 120 carriage movement mechanism, 121 timing belt,
122 carriage motor, 123 guide shaft, 124 drive pulley,
125 idler pulley, 130 head unit, 131 head,
140 detector groups, 141 linear encoders,
142 rotary encoder, 143 paper detector, 144 paper width detector,
150 printer-side controller, 151 CPU, 152 memory,
153 control unit, 154 interface unit, 155 correction value storage unit,
200 host computer, 200 ′ process host computer,
210 Host side controller, 211 CPU, 212 memory,
213 first interface unit, 214 second interface unit,
220 recording / reproducing device, 230 display device, 240 input device,
300 scanner, 310 scanner side controller,
311 CPU, 312 memory, 313 interface unit,
320 scanning mechanism, 321 platen glass, 322 platen cover,
323 reading carriage, 324 CCD image sensor,
325 exposure lamp, 326 mirror, 327 lens, 330 moving mechanism,
331 support rail, 332 regulation rail, 333 drive motor,
334 Drive pulley, 335 idler pulley, 336 timing belt,
SS paper stocker, S paper, IC ink cartridge, Nz nozzle,
Nk black ink nozzle row, Ny yellow ink nozzle row,
Nc cyan ink nozzle row, Nm magenta ink nozzle row,
Nlc light cyan ink nozzle row, Nlm light magenta ink nozzle row,
CP test pattern, HP correction pattern, BD strip pattern

Claims (10)

(A) printing a test pattern having a plurality of regions with different densities on a medium based on a plurality of command gradation values;
(B) measuring a density for each of the plurality of areas and a non-printing area on the medium to obtain a measured value of the density;
(C) setting a target density for an area printed with the lowest command gradation value among the plurality of command gradation values;
(D) When the measured value of the area printed with the lowest command gradation value is larger than the target density, the measured value of the area printed with the lowest command gradation value and the non-printed area of the non-printed area Identify a set of measurements,
When the measured value of the area printed with the lowest command gradation value is smaller than the target density, the measured value of the area printed with the lowest command gradation value is higher than the lowest command gradation value. Identifying the set of measured values in other areas printed with the command gradation value;
(E) setting a correction value for the minimum command gradation value with reference to the specified set of measurement values;
A correction value setting method for performing (F). The correction value setting method according to claim 1,
Setting a target density for an area printed with an intermediate command tone value among the plurality of command tone values;
When the measured value of the area printed with the intermediate command tone value is larger than the target density, the measured value of the area printed with the intermediate command tone value is lower than the intermediate command tone value Identify the set of measured values in other areas printed with the command gradation value,
When the measured value of the region printed with the intermediate command tone value is smaller than the target density, the measured value of the region printed with the intermediate command tone value is higher than the intermediate command tone value Identifying the set of measured values in other areas printed with the command gradation value;
Referring to the specified set of measured values, and setting a correction value for the intermediate command gradation value;
How to set the correction value. A method for setting a correction value according to claim 1 or claim 2,
Setting a target density for an area printed with the highest command tone value among the plurality of command tone values;
Regardless of the relationship between the measured value of the area printed with the highest command gradation value and the target density, the measurement value of the area printed with the highest command gradation value and another command gradation value are printed. Identifying the set of measurements of the other areas
Referring to the specified set of measured values, and setting a correction value for the highest command gradation value;
How to set the correction value. A correction value setting method according to any one of claims 1 to 3,
In printing the test pattern,
A print head having a nozzle group composed of a plurality of nozzles that eject the same type of ink, the print head having a plurality according to the type of ink that can eject the nozzle group while moving in the moving direction. A correction value setting method in which an operation of ejecting ink from a nozzle toward the medium and an operation of transporting the medium in a transport direction intersecting the moving direction are repeatedly performed. The correction value setting method according to claim 4,
In printing the test pattern,
A plurality of sub-patterns printed by different nozzle groups, the lowest density region printed with the lowest command tone value, and the intermediate density region printed with an intermediate command tone value among the plurality of command tone values And a correction value setting for printing a test pattern in which a plurality of sub-patterns each having a highest density area printed at the highest command tone value among the plurality of command tone values are arranged in the moving direction. Method. The correction value setting method according to claim 5,
In printing the test pattern,
A ruled line along the moving direction, and a ruled line used when detecting a range of the corresponding sub pattern is printed on each of one end and the other end of the corresponding sub pattern in the transport direction,
In obtaining the concentration measurement value,
Correction for measuring the density of the non-printing region sandwiched between a certain ruled line printed at one end in the transport direction and another ruled line printed at the other end in the transport direction, and obtaining a measured value of the density How to set the value. A correction value setting method according to any one of claims 1 to 6,
In obtaining the concentration measurement value,
A correction value setting method for measuring the density of the test pattern and the density of the non-printing area for each of a plurality of row areas arranged in the transport direction, and acquiring the density measurement value for each row area . The correction value setting method according to claim 7,
In setting the target density,
A correction value setting method of referring to the measurement values for a plurality of the row regions belonging to a region printed with the same command gradation value, and setting an average value of each of the referenced measurement values as the target density. (A) a scanner that measures the density of a test pattern printed on a medium using a printing apparatus that is a correction value setting target;
(A1) measuring the density of each of a plurality of areas having different densities printed with a plurality of command gradation values and a non-printing area of the medium, which the test pattern has,
A scanner to do
(B) a controller,
(B1) obtaining a measured value of the density from the scanner;
(B2) setting a target density for an area printed with the lowest command gradation value among the plurality of command gradation values;
(B3) When the measured value of the area printed with the lowest command gradation value is larger than the target density, the measured value of the area printed with the lowest command gradation value and the non-printed area of the non-printed area Identify a set of measurements,
When the measured value of the area printed with the lowest command gradation value is smaller than the target density, the measured value of the area printed with the lowest command gradation value is higher than the lowest command gradation value. Identifying the set of measured values in other areas printed with the command gradation value;
(B4) referring to the specified set of measured values, and setting a correction value for the minimum command gradation value;
A controller to perform
A correction value setting system having (C). A program used in a correction value setting system for setting a correction value in a target printing apparatus,
Causing the printing apparatus to print a test pattern having a plurality of regions having different densities based on a plurality of command gradation values;
Causing the scanner to measure the density of each of the plurality of regions and a non-printing region of the medium;
Obtaining a density measurement from the scanner;
Setting a target density for an area printed with the lowest command gradation value among the plurality of command gradation values;
When the measured value of the area printed with the lowest command gradation value is larger than the target density, the measured value of the area printed with the lowest command gradation value and the measured value of the non-printed area Identify the pair,
When the measured value of the area printed with the lowest command gradation value is smaller than the target density, the measured value of the area printed with the lowest command gradation value is higher than the lowest command gradation value. Identifying the set of measured values in other areas printed with the command gradation value;
Referring to the specified set of measured values, and setting a correction value for the minimum command gradation value;
A program to make the controller perform.