JP2008044275A - Setting method of correction value, correction value setting system, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain 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) The test pattern with a plurality of regions different in density is printed on the basis of a plurality of instruction tone values. (B) A measured value of the density is acquired for each of the plurality of regions. (C) A target density is set for each of the region of a middle density and the region of a highest density. (D) For setting the correction value for the instruction tone value corresponding to the middle density, a set of the measured values which should be referred to is specified according to a size relationship between the measured value corresponding to the region of the middle density and the target density. (E) For setting the correction value for the instruction tone value corresponding to the highest density, a set of the measured values which should be referred to is specified regardless of a size relationship between the measured value corresponding to the region of the highest density and the target density. (F) With reference to the specified sets of measured values, the correction value for the instruction tone value corresponding to the middle density and the correction value for the instruction tone value corresponding to the highest density are 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 to set a correction value for adjusting the ejection of ink for each density of the print image. For this reason, it is conceivable to form a test pattern with a representative density and to determine a correction value from the measured value of the representative density. Here, if the number of representative density types is increased, the types of correction values to be obtained are increased, so that the accuracy of correction can be increased and the image quality can be improved. However, the more the types of density in the test pattern, the longer it takes to print and the more time it takes to process.

  The present invention has been made in view of such circumstances, and an object thereof is to obtain many types of correction values from limited types of densities of test patterns.

The main invention for solving the above-mentioned problems is:
(A) printing a test pattern having a plurality of regions having different densities based on a plurality of command gradation values;
(B) measuring a concentration for each of the plurality of regions to obtain a measured value of the concentration;
(C) setting a target density for each of the intermediate density area and the highest density area;
(D) In order to set the correction value for the command gradation value corresponding to the intermediate density, the reference value should be referred to according to the magnitude relationship between the measured value and the target density corresponding to the intermediate density region. Identifying a set of measurements,
(E) In order to set the correction value for the command gradation value corresponding to the highest density, the reference value to be referred to is irrespective of the magnitude relationship between the measured value and the target density corresponding to the highest density region. Identifying a set of measurements,
(F) With reference to the specified set of measurement values, the correction value for the command gradation value corresponding to the intermediate density and the correction value for the command gradation value corresponding to the highest density are set. thing,
This is a correction value setting method for performing (G).

  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 based on a plurality of command gradation values, and (B) measuring the density for each of the plurality of areas, (C) setting a target density for each of the intermediate density area and the highest density area, and (D) setting a correction value for the command gradation value corresponding to the intermediate density. Specifying a set of the measurement values to be referred to according to the magnitude relationship between the measurement value and the target density corresponding to the intermediate density region; and (E) for the command gradation value corresponding to the highest density. In order to set a correction value, regardless of the magnitude relationship between the measured value and the target density corresponding to the region of the highest density, the set of measured values to be referred to is specified, (F) specified With reference to the set of measurements, The correction value for the command gradation value corresponding to the intermediate density, the correction value for the command gradation value corresponding to the highest density, and the correction value setting method for performing (G) can be realized. It becomes clear.
According to such a correction value setting method, many types of correction values can be obtained from the limited types of densities printed by the test pattern.

In this correction value setting method, in specifying the measurement value set to be referred to for setting the correction value for the command gradation value corresponding to the intermediate density, it corresponds to the intermediate density region. When the measured value is larger than the target density, the set of measured values to be referred to is the measured value corresponding to the intermediate density area and the measurement corresponding to the density area lower than the intermediate density. When the measured value corresponding to the intermediate density region is smaller than the target density, the set of measured values to be referred to is the measured value corresponding to the intermediate density region, and It is preferable that the set of measurement values correspond to a region having a density higher than the intermediate density.
According to such a correction value setting method, the set correction value can be made more suitable.

In this correction value setting method, in specifying the measurement value set to be referred to for setting the correction value for the command gradation value corresponding to the intermediate density, it corresponds to the intermediate density region. When the measured value is larger than the target concentration, the set of measured values to be referred to is the measured value corresponding to the intermediate density region and the next lower density region corresponding to the intermediate density. When the measurement value corresponding to the intermediate density area is smaller than the target density, the measurement value set to be referred to is the measurement value corresponding to the intermediate density area; It is preferable that the set of measurement values corresponding to a region having the next highest density after the intermediate density is used.
According to such a correction value setting method, the set correction value can be made more suitable.

In this correction value setting method, in specifying the measurement value set to be referred to for setting the correction value for the command gradation value corresponding to the highest density, the measurement value set to be referred to Is preferably a set of the measurement value corresponding to the highest density region and the measurement value corresponding to a density region lower than the highest density.
According to such a correction value setting method, the set correction value can be made more suitable.

In this correction value setting method, in specifying the measurement value set to be referred to for setting the correction value for the command gradation value corresponding to the highest density, the measurement value set to be referred to Is preferably a set of the measurement value corresponding to the highest density region and the measurement value corresponding to the next lowest density region of the highest density.
According to such a correction value setting method, the set correction value can be made more suitable.

In this correction value setting method, in the setting of the correction value for the command gradation value corresponding to the intermediate density and the correction value for the command gradation value corresponding to the highest density, the specified measurement A command tone value corresponding to the target density is obtained with reference to a set of values and the corresponding command tone value, and a command tone value corresponding to the intermediate density is obtained using the obtained command tone value. It is preferable to set a correction value for use and a correction value for a command gradation value corresponding to the highest density.
According to such a correction value setting method, the correction value can be set by a simple calculation such as linear interpolation.

In this correction value setting method, in printing the test pattern, the medium is transported in a transport direction that intersects the movement direction and the operation of ejecting ink toward the medium while moving the print head in the movement direction. It is preferable to repeat the operation.
According to such a correction value setting method, a highly accurate correction value can be obtained for a printing apparatus that repeatedly performs the operation of ejecting ink while moving the print head and the operation of transporting the medium.

In this correction value setting method, in acquiring the density measurement value, the density of the test pattern is measured for each of a plurality of row regions arranged in the transport direction, and the plurality of regions and the row regions are measured. It is preferable to obtain the measured value of the concentration corresponding to both.
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 setting of the target density, the measurement values for the plurality of row regions belonging to the same density region are referred to, and an average value of each of the referenced measurement values is used as the target density. It is preferable to set.
According to such a correction value setting method, the set correction value can be made more suitable.

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. It is preferable to perform an operation of ejecting ink from the nozzles toward the medium while moving a plurality of print heads corresponding to the type in the moving direction.
According to such a correction value setting method, the image density can be corrected for each type of ink to be ejected.

In this correction value setting method, in the test pattern printing, it is preferable to print a test pattern in which a plurality of sub-patterns printed by different nozzle groups are arranged in the moving direction.
According to such a correction value setting method, the test pattern can be printed promptly.

In this correction value setting method, the sub-pattern is printed at the intermediate density and is long in the transport direction, is printed at the maximum density, is printed at the maximum density and is long in the transport direction, and the lowest It is preferable to have a minimum density region that is long in the transport direction printed with density.
According to such a correction value setting method, it is possible to print a large number of sub-patterns arranged in the moving direction.

It is also clarified that the following correction value setting method can be realized.
That is, (A) a print head having a nozzle group composed of a plurality of nozzles that eject the same type of ink, and a plurality of print heads corresponding to the type of ink that can eject the nozzle group, By repeatedly performing the operation of ejecting ink toward the medium while moving the ink and the operation of transporting the medium in a transport direction that intersects the moving direction, based on a plurality of command gradation values. A plurality of sub-patterns printed by different nozzle groups, the intermediate density region being printed at the intermediate density and being long in the transport direction, the highest pattern A sub-pattern having a maximum density area printed in the density and long in the transport direction and a sub-pattern having a minimum density area long in the transport direction printed in the minimum density is the transfer pattern. Printing a test pattern arranged in a direction; (B) measuring the density of the test pattern for each of the plurality of regions and each of a plurality of row regions arranged in the transport direction; Obtaining a density measurement value corresponding to both the area and the row area, and (C) setting a target density for each of the intermediate density area and the highest density area, and having the same density area. Referring to the measurement values for a plurality of the row regions belonging to, and setting an average value of each of the referenced measurement values as the target density, (D) a correction value for the command gradation value corresponding to the intermediate density To set the measurement value to be referred to, and when the measurement value corresponding to the intermediate density region is larger than the target concentration, the intermediate density region is determined. A set of the measurement values corresponding to the second lowest density region after the measurement value corresponding to the intermediate density is identified as the measurement value set to be referred to, and the measurement value corresponding to the intermediate density region A set of the measurement values to be referred to is a set of the measurement value corresponding to the intermediate density region and the measurement value corresponding to the next highest density region of the intermediate density. And (E) specifying the set of measurement values to be referred to in order to set a correction value for the command gradation value corresponding to the highest density, and corresponding to the region of the highest density Identifying the set of measured values corresponding to the region of the next lowest density after the measured value and the highest density as the set of measured values to be referred to; (F) the set of identified measured values; And referring to the corresponding command gradation value, A command gradation value corresponding to the intermediate density, and a correction value for the command gradation value corresponding to the highest density, using the determined command gradation value. It is also clarified that a correction value setting method for performing (G) can be realized.
According to such a correction value setting method, almost all the effects described above can be obtained, and therefore the object of the present invention can be achieved most effectively.

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 printing apparatus that is a correction value setting target, and (A1) the test pattern has different densities based on a plurality of command gradation values. A scanner that performs density measurement for each of a plurality of areas, and (B) a controller, (B1) obtains a measured value of the density from the scanner, and (B2) an intermediate density area; In order to set a target density for each of the highest density areas, and (B3) to set a correction value for the command gradation value corresponding to the intermediate density, the measured value and the target corresponding to the intermediate density area In order to specify the set of measurement values to be referred to according to the magnitude relationship of density, and (B4) to set a correction value for the command gradation value corresponding to the maximum density, the maximum density is marked. Regardless of the magnitude relationship between the measured value corresponding to the region and the target concentration, (B5) referring to the specified set of measured values, A controller for setting a correction value for the command gradation value corresponding to the intermediate density and a correction value for the command gradation value corresponding to the maximum density; and a correction value setting system having (C) It is also revealed that 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 the scanner to measure the density for each of the plurality of areas, obtaining a density measurement value from the scanner, setting a target density for each of the intermediate density area and the highest density area, In order to set a correction value for the command gradation value corresponding to the intermediate density, a set of the measurement values to be referred to is determined according to the magnitude relationship between the measurement value corresponding to the intermediate density region and the target density. Specifying the measured value and the target corresponding to the region printed at the highest density to identify and set a correction value for the command tone value corresponding to the highest density Regardless of the magnitude relationship, specifying the measurement value set to be referred to, referring to the specified measurement value set, a correction value for the command gradation value corresponding to the intermediate density, and It is also clarified that a program for causing the controller to set the correction value for the command gradation value corresponding to the highest density can be realized.

=== 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 stocker 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). 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 unit 130 includes a head 131 that 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 the flight trajectory and discharge amount of ink (hereinafter also referred to as discharge 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 single dot forming operation, and the pass n means the nth dot forming 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. 8 illustrates the head 131 (nozzle row) as moving with respect to the paper S, the relative positional relationship between the head 131 and the paper S is illustrated. 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 is printed with three types of densities belonging to a halftone. Specifically, each test pattern CP has a strip pattern with a density of 30%, a strip pattern with a density of 50%, and a strip pattern with a density of 70% (described later).

<Outline of correction value setting method>
In this case, if a correction value is determined using a plurality of actually measured values having different densities, only a correction value for a density of 50% can be obtained. Briefly, when the target density in a certain row area is lower than the actually measured density of 50% in that row area, the density for 50% is calculated from the actually measured density of 50% density and the actually measured density of 30% density. A correction value is obtained. On the other hand, when the target density in a certain row area is higher than the actually measured density of 50% in that row area, the correction value for 50% density is obtained from the actually measured density of 50% and the actually measured density of 70%. Is required. However, it is difficult to obtain a sufficient correction effect with only a correction value for one density. In order to obtain a sufficient correction effect, it is desirable to acquire correction values for a plurality of densities. In view of such circumstances, this embodiment employs the following method when setting correction values for a plurality of densities.

  First, the relationship between the intermediate density and the minimum density is as follows. That is, (1) printing a test pattern CP having a plurality of areas with different densities based on a plurality of command gradation values, and (2) measuring the density for each of the plurality of areas, and measuring the density (3) setting a target density for each of the intermediate density area and the minimum density area, and (4) setting a correction value for a command gradation value corresponding to the intermediate density. Specifying a set of the measurement values to be referred to according to the magnitude relationship between the measurement value corresponding to the intermediate density region and the target density; and (5) a correction value for the command gradation value corresponding to the minimum density. (6) specifying the set of measurement values to be referred to regardless of the magnitude relationship between the measurement value corresponding to the area printed at the minimum density and the target density, Refer to the set of measured values Te, the correction value for the instructed tone value corresponding to the intermediate density, and is performed to set a correction value for the instructed tone value corresponding to the lowest concentration.

  The following method is used for the relationship between the intermediate density and the maximum density. That is, (1) printing a test pattern CP having a plurality of areas with different densities based on a plurality of command gradation values, and (2) measuring the density for each of the plurality of areas, and measuring the density (3) setting a target density for each of the intermediate density area and the highest density area, and (4) setting a correction value for the command gradation value corresponding to the intermediate density. Specifying the set of measured values to be referred to according to the magnitude relationship between the measured value and the target density corresponding to the intermediate density region; and (5) for the command gradation value corresponding to the highest density. (6) specifying a set of the measurement values to be referred to regardless of the magnitude relationship between the measurement value and the target density corresponding to the region of the highest density. Refer to the set of measured values. , The correction value for the instructed tone value corresponding to the intermediate density, and is performed to set a correction value for the instructed tone value corresponding to the maximum concentration.

  By adopting such a setting method, for the intermediate density, a combination suitable for the combination of the measurement values is selected according to the magnitude relationship between the target density and the measurement value. On the other hand, for the minimum density and the maximum density, a predetermined combination is selected regardless of the magnitude relationship between the target density and the actually measured density. 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 strip patterns BD, an upper ruled line UL, a lower ruled line DL, a left ruled line LL, and a right ruled line. It is comprised by RL. The band-shaped pattern BD corresponds to areas printed at different densities and has a long band shape in the transport direction. The belt-like pattern BD of the present embodiment is composed of three types of patterns printed with different density command values. Therefore, it can be said that the test pattern CP has a plurality of sets of strip patterns BD (groups of regions) printed with different command gradation values corresponding to the nozzle rows.

  For example, the correction pattern (Y) printed by the yellow ink nozzle row Ny includes a strip pattern BD (Y30) printed at a density of 30%, a strip pattern BD (Y50) printed at a density of 50%, and a density. And a belt-like pattern BD (Y70) printed at 70%. 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-shaped pattern BD is described without specifying the nozzle row in charge, the band-shaped pattern BD (30) for the density 30%, the band-shaped pattern BD (50) for the density 50%, Those having a density of 70% are shown as a strip pattern BD (70).

  These band-like patterns BD (30) to BD (70) are band-like regions that are long in the transport direction, and are arranged in a state of being aligned in the carriage movement direction. Specifically, in order from the strip pattern BD at the left end, there are a command gradation value 77 (density 30%), a command gradation value 128 (density 50%), and a command gradation value 179 (density 70%). It is printed with a larger command gradation value as it is located on the right side. The strip pattern BD (30) printed at a density of 30% corresponds to the lowest density area, and the strip pattern BD (50) printed at a density of 50% corresponds to the intermediate density area. The strip pattern BD (70) printed at a density of 70% corresponds to the highest density area. Moreover, these strip | belt-shaped patterns BD (30) -BD (70) are printed in the mutually adjacent state.

  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 convenience, a command gradation value corresponding to a density of 30% is indicated by a symbol Sa, a command gradation value corresponding to a density of 50% is indicated by a symbol Sb, and a command gradation value corresponding to a density of 70% is indicated. It 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. In the correction pattern HP, as shown in FIG. 17, the upper ruled line UL is formed by the first row region in the strip pattern BD. Similarly, the lower ruled line DL is formed by the last row region in the strip pattern BD.

<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 belt-like pattern BD. 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 θ of the correction pattern HP included in the image data (S220), and performs rotation processing according to the inclination θ 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 θ 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). In obtaining the density for each row region, the host-side controller 210 obtains the barycentric position of the reference vertical ruled line (in this example, the left ruled line LL), and uses the barycentric position of the ruled line as a reference for each band-like pattern BD. A pixel to be configured is specified. And pixel density data is acquired about the specified pixel. 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 other row regions and other strip patterns BD. This measurement value corresponds to the density measurement value by the scanner 300. 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 of the pattern, and the row area number. Note that the density 1 to density 3 in FIG. 13 mean the density of each strip pattern BD. For example, density 1 corresponds to density 30%, density 2 corresponds to density 50%, and density 3 corresponds to density 70%. 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 BD 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 a strip pattern BD printed at different predetermined densities. 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 at a predetermined density). Accordingly, the correction value is set for each different color, each different density, and each row region.

<Setting correction value at 50% density>
Hereinafter, the setting of the correction value will be described in detail. First, setting of correction values for 50% density (command gradation value Sb, gradation value 128) will be described. The command gradation value Sb corresponds to an intermediate density command gradation value. First, the host-side controller 210 determines a target density for the density for which the correction value is set (that is, the density corresponding to the command gradation value Sb). In the present embodiment, the average value of the measurement values in each row region is set as the target density for the band-shaped pattern BD (50) of the density to be 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 Cbt 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 30%, density 70%).

  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 is set to a density of 50% (command gradation value Sb), the measurement value of the row area constituting the strip pattern BD 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 having a density of 70% is selected. Note that the row area selected with the low-side density or the high-side density has the same position as the row area to be set. For example, when the correction value is set for the first row region at the density of 50%, the measurement value of the first row region at the density of 30% and the measurement value of the first row region at the density of 70% are selected. Is done.

  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 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 30% is X1, the measurement result of the row area at the density of 50% is Y1, and the row area at the density of 70%. The measurement result is Z1. Here, the measurement result Y1 of 50% density is plotted below the target density Cbt 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 Y1 of the row region LAn at the density of 50% is higher than the target density Cbt. For this reason, the host-side controller 210 specifies the measurement value corresponding to the 50% density row region and the measurement value corresponding to the 30% density row region as a set of measurement values to be referred to. In a certain row area indicated by the symbol LAm, the measurement result of the row area at a density of 30% is X2, the measurement result of the row area at a density of 50% is Y2, and the measurement result of the row area at a density of 70% is Z2. . In this case, the density of the row region LAm at a density of 50% is lower than the target density Cbt. For this reason, the host-side controller 210 specifies the measurement value corresponding to the 50% density row region and the measurement value corresponding to the 70% density row region 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. 19A, 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, a correction value is set based on the command gradation value Sb and measurement value Cb1 in the measurement result Y1 and the command gradation value Sa and measurement value Ca1 in the measurement result X1. Specifically, the host-side controller 210 performs primary interpolation shown in the following equation (1) to calculate a command gradation value Sbt1 corresponding to the target density, and performs an operation shown in the following equation (2) for correction. The value Hb1 is set.
Sbt1 = Sa + (Sb−Sa)
X {(Cbt-Ca1) / (Cb1-Ca1)} (1)
Hb1 = (Sbt1-Sb) / Sb (2)

In the case of the row area LAm, as shown in FIG. 19B, a set of a measurement result Y2 of 50% row area LAm and a measurement result X2 of 70% row area LAm is used. Then, the correction value is set based on the command gradation value Sb2 and the measurement value Cb2 in the measurement result Y2 and the command gradation value Sc2 and the measurement value Cc2 in the measurement result Z2. Specifically, the host-side controller 210 performs primary interpolation shown in the following equation (3) to calculate a command gradation value Sbt2 corresponding to the target density, and performs correction shown in the following equation (4). The value Hb2 is set.
Sbt2 = Sb + (Sc-Sb)
X {(Cbt-Cb2) / (Cc2-Cb2)} (3)
Hb2 = (Sbt2-Sb) / Sb (4)

  The host-side controller 210 performs the above calculation for each column region, and sets a correction value Hb for the command gradation value Sb (density 50%) for each column region. The correction value Hb 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 Hb1 obtained by the equation (2) is represented by a difference with respect to the coefficient 1.00. For example, when the command gradation value Sb is the value [128] and the command gradation value Sbt1 corresponding to the target density is the value [124], the correction value Hb1 is the value [−0.03]. 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 Hb1 is the value [−0.03], the correction value to be stored is the value [0.97]. The same applies to the correction value Hb2 obtained by Expression (4).

  As described above, for the strip pattern BD having a density of 50%, which is an intermediate density, when the measured value of the row region is higher than the target density Cbt, the measured value of the row region having the density of 50% and the row region having the density of 30%. A correction value is set using a set of measured values. Further, when the measured value of the column region having the density of 50% is lower than the target concentration Cbt, the correction value is set using a set of the measured value of the column region to be set and the measured value of the high-side density. In this way, the target concentration Cbt belongs within a range defined by one measurement value and the other measurement value. Therefore, when setting a correction value for a row region having a density of 50%, a suitable set is used according to the magnitude relationship between the measured value of the row region and the target density Cbt. As a result, the set correction value can be made more suitable. In the example of FIG. 19A, the slope of the straight line passing through the measurement result Y1 and the measurement result X1 is different from the slope of the straight line passing through the measurement result Z1 and the measurement result Y1, but linear interpolation can be performed with a straight line on a suitable side.

  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, using the obtained command gradation value, a correction value for the command gradation value corresponding to the density of 50% is set. 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 also applies to other densities, that is, a density of 30% (pattern minimum density) and a density of 70% (pattern maximum density).

<Setting correction value at 30% density>
Next, the setting of correction values for a density of 30% (command gradation value Sa, gradation value 77) will be described. The command tone value Sa corresponds to the command tone value of the lowest density in the correction pattern HP. Also in this case, the host-side controller 210 first sets a target density for the density for which a correction value is set. The method for setting the target density is the same as the method for the density 50% (command gradation value Sb). 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.

  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 30%, which is the lowest density in the correction pattern HP. For this reason, there is no measured value with a concentration lower than 30%. Therefore, the host-side controller 210 specifies the second highest density measurement value. As a result, the measurement value of the row region having a density of 30% and the measurement value of the row region having a 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 30% and the target concentration Cat. Note that the row area specified by the density of 50% is at the same position as the row area for which the correction value is set. For example, when the correction value is set for the first row region at the density of 30%, the measurement value of the first row region at the density of 50% is specified.

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. 19A and 19B, a set of measurement results X1 of 30% row regions LAn and a measurement result Y1 of 50% row regions LAn are used. Here, in the row region LAn, as shown in FIG. 19A, the target density Cat is lower than the measured value of the density 30%. In this case, the host-side controller 210 performs the primary interpolation shown in the following formula (5) to calculate the command gradation value Sbt1 corresponding to the target density Cat, and performs the calculation shown in the following formula (6) to correct the correction value. Set Ha1.
Sat1 = Sa− (Sb−Sa)
× {(Cb1-Cat) / (Cb1-Ca1)} (5)
Ha1 = (Sat1-Sa) / Sa (6)

In the case of the row region LAm, as shown in FIG. 19B, the target density Cat is higher than the measured value of density 30%. In this case, the host-side controller 210 performs the primary interpolation shown in the following equation (7) to calculate the command gradation value Sbt2 corresponding to the target density Cat, and performs the calculation shown in the following equation (8) to correct the correction value. Ha2 is set.
Sat2 = Sa + (Sb-Sa)
X {(Cbt-Ca2) / (Cb2-Ca2)} (7)
Ha2 = (Sat2-Sa) / Sa (8)

  The host-side controller 210 performs the above calculation for each column region, and sets a correction value Ha for a density of 30% (command gradation value Sa) for each column region. The correction value Ha set in this way is stored in the correction value storage unit 155 of the printer 100 in the same procedure as the correction value Hb.

  As described above, regarding the strip pattern BD having the minimum density of 30%, when the measured value of the row region is higher than the target density Cat, the measured value of the row region having the density of 50% and the row region having the density of 30%. A correction value is set using a set of measured values. Even when the measured value of the row region having the density of 50% is lower than the target density Cbt, the correction value is set using the set of the measured value of the row region having the density of 50% and the measured value of the row region having the density of 30%. Is done. That is, when setting a correction value for a row region having a density of 30%, a set of a measured value of the lowest density and a measured value of the second lowest density is obtained regardless of the magnitude relationship between the measured value of the row region and the target density Cbt. Used. As a result, a correction value for 30% density can be set with one set of measurement values. Here, when the measured value of the density 30% is lower than the target density Cat, the target density Cat is higher than the low-side density obtained by the measurement (for example, the measurement result X2), and the high-side density obtained by the measurement ( For example, it becomes lower than the measurement result Y2). Thus, since the correction value can be set based on the straight line connecting the two points obtained by the measurement, the accuracy of the correction value can be increased.

  It is also possible to set the correction value using the measured value of the row region having a density of 30% and the measured value of the row region having a density of 70%. Then, as in this embodiment, it is considered that a more suitable correction value can be set by using the measurement value of the row region having the lightest density of 30% and the measurement value of the row region having the next lightest density of 50%. . This is because it is considered that the measured values in the row region closer in density reflect the characteristics more faithfully.

<Setting correction value at 70% density>
Next, the setting of the correction value for the command gradation value Sc (density 70%, gradation value 179) will be described. This command tone value Sc corresponds to the command tone value of the highest density in the correction pattern HP. Also in this case, the host-side controller 210 first sets a target density for the density for which a correction value is set. The method for setting the target density is the same as the method using the command gradation values Sb and Sa. That is, the density of the last row area is added from the density of the first row area, and a value obtained by dividing the added density by the number of row areas is set as the target density. 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. Note that the row area specified by the density of 50% is at the same position as the row area for which the correction value is set. For example, when a correction value is set for the first row region at a density of 70%, the measurement value of the first row region at a density of 50% is specified.

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. 19A and 19B, 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. 19A, 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 (9) to calculate a command gradation value Sct1 corresponding to the target density Cct, and performs an operation shown in the following equation (10) to correct the correction value. Set Hc1.
Sct1 = Sb + (Sc-Sb)
X {(Cct-Cb1) / (Cc1-Cb1)} (9)
Hc1 = (Sct1-Sc) / Sc (10)

In the case of the row region LAm, as shown in FIG. 19B, 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 (11) to calculate a command gradation value Sct2 corresponding to the target density Cct, and performs an operation shown in the following equation (12) to obtain a correction value. Set Hc2.
Sct2 = Sc + (Sc-Sb)
X {(Cct-Cc2) / (Cc2-Cb2)} (11)
Hc2 = (Sct2-Sc) / Sc (12)

  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, regarding the strip pattern BD having the maximum density of 70%, when the measurement value of the row area is higher than the target density Cct, the measurement value of the row area having the density of 70% and the row area having the density of 50%. A correction value is set using a set of measured values. Even when the measured value of the row region with the density of 70% is lower than the target density Cct, the correction value is set using the set of the measured value of the row region with the density of 70% and the measured value of the row region with the density of 50%. Is done. That is, when setting a correction value for a 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 measurement value of the highest density and the measurement value of the second highest density is obtained. Used. As a result, a correction value for 70% density can be set with one set of measurement values. Here, when the measured value of the density 70% is higher than the target density Cct, the target density Cct is higher than the low-side density obtained by the measurement (for example, the measurement result Y1), and the high-side density obtained by the measurement ( For example, it becomes lower than the measurement result Z1). Thus, since the correction value can be set based on the straight line connecting the two points obtained by the measurement, the accuracy of the correction value can be increased.

  In this case as well, it is possible to obtain the correction value using the measurement value of the row region having the density of 70% and the measurement value of the row region having the density of 30%. Then, as in the present embodiment, it is considered that a more appropriate correction value can be set by using the measurement value of the row region having the darkest density 70% and the measurement value of the row region having the next darkest density 50%. . This is because it is considered that the measured values in the row region closer in density reflect the characteristics more faithfully.

<Correction value for density other than pattern density>
By the above-described processing, correction values for each row region are set for the density of 30%, the density of 50%, and the density of 70%. These densities are all the density of the strip pattern BD. By the way, it is preferable that the types of correction values (types of density for setting correction values) are larger. This is because an improvement in image quality can be expected. In view of such circumstances, the correction value setting system 20 sets correction values for other densities (corresponding to densities of other command gradation values). In this case, the correction value setting system 20 performs the following. That is, (1) printing a test pattern CP having a plurality of areas with different densities based on a plurality of command gradation values, and (2) measuring the density for each of the plurality of areas, Acquiring, (3) setting a correction value for each of a plurality of command tone values based on the measured value, and (4) a correction value of another command tone value different from the plurality of command tone values. To determine the ratio of the pre-correction command tone value and the post-correction command tone value for the command tone value closest to the other command tone values among the plurality of command tone values, (5) Setting correction values of other command tone values so that the ratio of the command tone value before correction and the command tone value after correction for the closest command tone value is the same. ing.

  Specifically, correction values are set for each of a density of 10% (command gradation value 26) and a density of 90% (command gradation value 230). Note that the strip pattern BD is not printed for these densities. Therefore, a correction value for 10% density and a correction value for 90% density are set using the previously set correction value. Briefly, first, the correction value of the closest density is selected from the correction values for density corresponding to the strip pattern BD. Then, the ratio between the pre-correction command gradation value and the post-correction command gradation value is obtained using the selected correction value. Next, correction values for 10% density and 90% density are set so as to be the same ratio as the obtained ratio.

  By adopting such a setting method, correction values can be set for densities other than the density of the test pattern CP. That is, more types of correction values can be set than the types of density of the printed test pattern CP. For example, the correction value can be set for a density of 10% or a density of 90% that is not included in each of the strip patterns BD (30) to BD (70) included in the test pattern CP. As a result, the print data can be finely corrected and the image quality can be improved. Hereinafter, a detailed procedure will be described for each concentration.

<Setting of 10% density correction value>
First, the setting of a correction value of 10% density will be described. In this case, the host-side controller 210 specifies a density of 30% as the density of the nearest strip pattern BD. Then, the correction value is acquired for the row region at the same position as the row region having the density of 10%, which is a correction value setting target. For example, when a correction value for 10% density is set for the first row area, the correction value for the first row area at a density of 30% is acquired. Similarly, when a correction value for 10% density is set for the second row area, the correction value for the second row area at a density of 30% is acquired.

If a correction value of 30% density is acquired, the host-side controller 210 sets a correction value of 10% density based on the acquired correction value. At this time, the host-side controller 210 obtains the ratio of the pre-correction command gradation value and the post-correction command gradation value based on the correction value of 30% density, and the density is 10% so that the ratio is the same. The correction value H10 is set. For example, the command gradation value S10 corresponding to the density of 10% is calculated by the following equation (13), and the correction value H10 is set by the following equation (14). FIG. 20 schematically shows the relationship between the pre-correction command tone value and the post-correction command tone value corresponding to each density.
S10 = S10std × (Sat / Sa) (13)
S10std: Standard command gradation value of 10% density
Sat: Command gradation value after correction of density 30%
Sa: command gradation value before correction at a density of 30% H10 = (S10−S10std) / S10std (14)

  Assuming that the standard command gradation value S10std of 10% density is the value [26], the pre-correction command gradation value Sa of 30% density is the value [77], and the post-correction command gradation value Sat of 30% density. Is the value [74]. In this case, the command gradation value S10 is a value [25], and the correction value H10 is a value [−0.04]. Further, if the pre-correction command gradation value Sa with a density of 30% is a value [77] and the post-correction command gradation value Sat with a density of 30% is a value [84], the command gradation value S10 is a value [ 28], and the correction value H10 is the value [0.08].

  The above processing is repeated from the first row area to the last row area, and the correction value H10 is set for each row area. The correction value H10 set in this way is stored in the correction value storage unit 155 of the printer 100 in the same procedure as other correction values.

  The correction value H10 obtained by such a method is the measured value of the strip pattern BD (30) having the closest density of 30% among the plurality of strip patterns BD (30) to BD (70) printed at different densities. Set based on. Thereby, a suitable correction value can be set rather than setting based on other band-like patterns BD (50) and BD (70). That is, since the combination of the nozzles Nz is determined for each row region, the discharge characteristics are the same for all the densities. For this reason, it is considered that a more appropriate correction value can be set by using the measured value of the strip-shaped pattern BD (30) having a close density.

<Setting of 90% density correction value>
Next, the setting of a correction value for 90% density will be described. In this case, the host-side controller 210 specifies a density of 70% as the density of the nearest strip pattern BD. Then, the correction value is acquired for the row region at the same position as the row region having the density of 90%, which is a correction value setting target. For example, when a correction value for 90% density is set for the first row area, the correction value for the first row area at a density of 70% is acquired. If the correction value of 70% density is acquired, the host-side controller 210 sets the correction value of 90% density based on the acquired correction value. Also here, the host-side controller 210 obtains the ratio between the pre-correction command gradation value and the post-correction command gradation value based on the correction value of the density 70%, and the density 90% so that the ratio is the same. A correction value H90 is obtained. For example, the command gradation value S90 corresponding to the density of 90% is calculated by the calculation of the following formula (15), and the correction value H90 is set by the calculation of the following formula (16).
S90 = S90std × (Sct / Sc) (15)
S90std: Standard command gradation value of density 90%
Sct: corrected gradation value of 70% density
Sc: command gradation value before correction of density 70% H90 = (S90-S90std) / S90std (16)

  The above processing is repeated from the first row area to the last row area, and the correction value H90 is set for each row area. The correction value H90 obtained by such a method is the measured value of the band-shaped pattern BD (70) having the closest density of 70% among the plurality of band-shaped patterns BD (30) to BD (70) printed at different densities. Set based on. For the same reason as the correction value H10, it is considered that a suitable correction value can be set rather than setting based on the other strip patterns BD (30) and BD (50).

<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. Further, as shown in part in FIG. 21, 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 this correction value setting system 20, a correction value of 30% density, a correction value of 50% density, and a correction value of 70% density set based on the measurement values of the strip patterns BD (30) to BD (70). Then, among these correction values, a total of five types of correction values are stored, consisting of a correction value with a density of 10% and a correction value with a density of 90% set based on the correction value with the closest density. Accordingly, the correction value storage unit 155 stores these correction values for each row region.

=== 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.

=== Second Embodiment ===
In the first embodiment described above, correction values are set for a density of 10% that is lighter than the density of the band-shaped pattern BD and a density of 90% that is darker than the density of the band-shaped pattern BD. In this regard, a correction value may be set for a density between two adjacent densities among the strip-shaped patterns BD (30) to BD (70). Hereinafter, the second embodiment configured as above will be described. In the second embodiment, the following method is adopted when setting the correction value.

  That is, (1) printing a test pattern CP having a plurality of areas with different densities corresponding to different command gradation values, and (2) measuring the density for each of the plurality of areas and measuring the density (3) setting a correction value for each of the plurality of command tone values based on the measured value, (4) being larger than the first command tone value in the plurality of command tone values, In order to set a correction value of another command tone value smaller than the second command tone value corresponding to the next darkest density of the first command tone value, the first command tone value and the second command tone value are set. Among the values, the ratio of the pre-correction command tone value and the post-correction command tone value for the predetermined command tone value is obtained, and (5) the ratio is the same as the ratio for the predetermined command tone value. As described above, correction values for other command gradation values are set.

  By adopting such a setting method, a correction value can be set for a density other than the density of the test pattern CP (the density of each strip pattern BD (30) to BD (70)). For example, correction values can be set for density 40% and density 60% (corresponding to densities corresponding to other command gradation values) that are not included in each strip pattern BD included in the test pattern CP. . As a result, the print data can be finely corrected and the image quality can be improved. Hereinafter, a detailed procedure will be described for each concentration. In the second embodiment, correction values for 10% density, 30% density, 50% density, 70% density, and 90% density are set. Since the procedure for setting is the same as in the first embodiment, description thereof is omitted.

<Setting of 40% density correction value>
First, the setting of the correction value with a density of 40% will be described. In this case, the host-side controller 210 sets a reference density (hereinafter also referred to as a reference density) on the side lower than the density 40% and the closest density 30% and higher than the density 40%. The density on the predetermined side of the nearest 50% is specified. These density 30% and density 50% are equal in absolute value of density difference between density 40%. Therefore, the command gradation value corresponding to the density of 30% corresponds to a certain command gradation value closest to the other command gradation value, and the command gradation value corresponding to the density of 50% This corresponds to the other command gradation value closest to the tone value. In the setting of the correction value of the density 40%, the command gradation value corresponding to the density 30% corresponds to the first command gradation value in the plurality of command gradation values, and the command scale corresponding to the density 50%. The tone value also corresponds to a second command tone value in a plurality of command tone values.

  Various criteria can be used for specifying the reference concentration. For example, with respect to one to several printers 100 selected as samples (corresponding to a printing apparatus as a sample), a belt-like pattern BD having a density of 40% printed based on a correction value having a density of 30% and a density of 50 Compared with the 40% density belt-shaped pattern BD printed using the% correction value, the density on the side where the image quality is good can be specified as the reference density. Specifically, using the first correction value of 40% density set so as to be the same ratio as the ratio of the pre-correction command gradation value and the post-correction command gradation value based on the correction value of 30% density, 40% of the first strip pattern is printed. Further, using the second correction value of 40% density set so as to be the same as the ratio of the command gradation value before correction based on the correction value of 50% density and the command gradation value after correction, the density of 40% A second strip pattern is printed. The density on the side where the image quality is good can be specified as the reference density. In this case, since the reference density is specified based on the actually printed image, the appropriate density can be specified.

  Further, since it can be said that the correction value of 50% density is higher in accuracy than the correction value of 30% density, the reference density may be specified by giving priority to 50% density. This is because the correction value of 50% density is obtained by specifying a set of measurement values to be referred to according to the magnitude relationship between the measurement value at the density and the target density, whereas the density is 30%. This is because the correction value is obtained by specifying a set of measured values to be referred to regardless of the magnitude relationship between the measured value at the density and the target density.

  In other words, the correction value of 50% density is set with reference to three types of measured values of density 30%, density 50%, and density 70%. On the other hand, the correction value of 30% density is set with reference to two kinds of measured values of density 30% and density 50%. As described above, when the correction value is set, the density of 50% is referred to more than the density of 30%, and thus the correction value of 50% density has higher accuracy.

  In the present embodiment, the host-side controller 210 specifies 50% density as the reference density. When such a method is adopted, it is not necessary to print a new test pattern CP when setting a correction value of 40% density, so that the process efficiency can be improved.

  If the reference density is specified, the host-side controller 210 acquires the correction value at the reference density for the row area at the same position as the 40% density row area for which the correction value is to be set. For example, when a correction value for a density of 40% is set for the first row area, the correction value for the first row area at a density of 50% is acquired. Similarly, when setting a correction value for a density of 40% for the second row area, a correction value for the second row area at a density of 50% is acquired.

If the reference density correction value is acquired, the host-side controller 210 sets a correction value of 40% density based on the acquired correction value. At this time, the host-side controller 210 obtains the ratio between the pre-correction command gradation value and the post-correction command gradation value based on the correction value of 50% density, and the density is 40% so that the ratio is the same. The correction value H40 is set. For example, the command gradation value S40 corresponding to the density of 40% is calculated by the calculation of the following equation (17), and the correction value H40 is set by the calculation of the following equation (18). FIG. 22 schematically shows the relationship between the pre-correction command tone value and the post-correction command tone value corresponding to each density.
S40 = S40std × (Sbt / Sb) (17)
S40std: Standard command gradation value of density 40%
Sbt: corrected gradation value of 50% density
Sb: command gradation value before correction at a density of 50% H40 = (S40-S40std) / S40std (18)

  Temporarily, the standard command gradation value S40std with a density of 40% is the value [102], the pre-correction command gradation value Sb with the density of 50% is the value [128], and the post-correction command gradation value Sbt with the density of 50%. Is the value [136]. In this case, the command gradation value S40 is a value [108], and the correction value H10 is a value [0.06].

  The above processing is repeated from the first row area to the last row area, and the correction value H40 is set for each row area. The correction value H40 set in this way is stored in the correction value storage unit 155 included in the printer 100 in the same procedure as other correction values. This correction value H40 is the closest density among the plurality of strip patterns BD printed at different densities, and is set based on the measured value of the strip pattern BD on the predetermined side. As a result, it is possible to set a correction value that is more suitable than the setting based on other band-like patterns BD. That is, since the combination of the nozzles Nz is determined for each row region, the discharge characteristics are the same for all the densities. For this reason, it is considered that a more appropriate correction value can be set by using the measured value of the belt-like pattern BD having a close density.

<Setting of 60% density correction value>
Next, setting of a correction value with a density of 60% will be described. Also in this case, the host-side controller 210 first specifies the reference density. The reference density is specified in the same manner as in the case of a density of 40%. In the present embodiment, the host-side controller 210 specifies a density of 50% as a reference density. The subsequent processing is the same as in the case of the density of 40%. In brief, the host-side controller 210 acquires a correction value at the reference density for a row area at the same position as the row area of 60% density that is a correction value setting target. Next, the host-side controller 210 sets a correction value with a density of 60% based on the acquired correction value. For example, the command gradation value S60 corresponding to the density of 60% is calculated by the calculation of the following equation (19), and the correction value H60 is set by the calculation of the following equation (20).
S60 = S60std × (Sbt / Sb) (19)
S60std: standard command gradation value of density 60% H60 = (S60-S60std) / S60std (20)

  The above processing is repeated from the first row area to the last row area, and the correction value H60 is set for each row area. This correction value H60 is also considered to be a value that is more suitable than that set based on other band-like patterns BD. The reason is as described for the correction value of 40% density.

<Storing correction values>
When the correction value is set, the host-side controller 210 stores the set correction value in the memory 152 (correction value storage unit 155) of the printer-side controller 150 in the same procedure as in the first embodiment. 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 152 of the printer-side controller 150. That is, as shown in part in FIG. 23, the correction value storage unit 155 in the second embodiment includes a total of five types of correction values from a correction value of 10% density to a correction value of 90% density. Stored for each area.

<Print by user>
A user who has purchased the printer 100 whose correction value is stored in the correction value storage unit 155 by the procedure described above connects the printer 100 to the host computer 200 owned by the user. At the time of printing by the printer 100, 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. 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 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. As a result, in the print image, the density of the image piece corresponding to each row region 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, three types of belt-like patterns BD having a minimum density (density 30%), an intermediate density (density 50%), and a maximum density (density 70%) are obtained. Had. The strip pattern BD included in each correction pattern HP is not limited to these three types.

  For example, four types of belt-like patterns BD printed at respective densities of 20% density, 40% density, 60% density, and 80% density may be used. In this case, the density 20% corresponds to the minimum density, the density 40% and the density 60% correspond to the intermediate density, and the density 80% corresponds to the maximum density. For setting the correction value for the lowest density, the measurement value of the row area having the lowest density and the measurement value of the row area having the intermediate density (density 40%) next to the lowest density are used. For setting the correction value for the highest density, the measured value of the highest density column area and the measured value of the highest density intermediate density (density 60%) column area are used. Further, for the setting of the correction value for the intermediate density, a measurement value having a density one step lower than the intermediate density and a measurement value having a density one step higher are used. Specifically, when setting a correction value for a density of 40%, a measurement value of a row area having a density of 40%, a measurement value of a row area having a density of 20%, and a measurement value of a row area having a density of 60% Is used.

  Further, it may be five types of belt-like patterns BD in which the density is changed by 10% in the density range of 30% to 70%. In this case, the density of 30% corresponds to the lowest density, the density from 40% to 60% corresponds to the intermediate density, and the density of 70% corresponds to the highest density.

  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. FIG. 19A is a diagram illustrating the setting of correction values in a certain row region. FIG. 19B is a diagram for describing setting of correction values in other row regions. It is a conceptual diagram for demonstrating the setting of the correction value in 1st Embodiment. It is a conceptual diagram for demonstrating the correction value memory | storage part in 1st Embodiment. It is a conceptual diagram for demonstrating the setting of the correction value in 2nd Embodiment. It is a conceptual diagram for demonstrating the correction value memory | storage part in 2nd Embodiment.

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 (15)

(A) printing a test pattern having a plurality of regions having different densities based on a plurality of command gradation values;
(B) measuring a concentration for each of the plurality of regions to obtain a measured value of the concentration;
(C) setting a target density for each of the intermediate density area and the highest density area;
(D) In order to set the correction value for the command gradation value corresponding to the intermediate density, the measurement to be referred to according to the magnitude relationship between the measured value corresponding to the intermediate density region and the target density Identifying value pairs,
(E) In order to set the correction value for the command gradation value corresponding to the highest density, the measurement to be referred to regardless of the magnitude relationship between the measured value corresponding to the highest density region and the target density Identifying value pairs,
(F) With reference to the specified set of measurement values, the correction value for the command gradation value corresponding to the intermediate density and the correction value for the command gradation value corresponding to the highest density are set. thing,
A correction value setting method for performing (G). The correction value setting method according to claim 1,
In specifying the set of measurement values to be referred to in order to set a correction value for a command gradation value corresponding to the intermediate density,
When the measured value corresponding to the intermediate density region is larger than the target density, the set of measured values to be referred to is lower than the measured value corresponding to the intermediate density region and the intermediate density A set of the measurement values corresponding to the concentration area,
When the measured value corresponding to the intermediate density region is smaller than the target density, the set of measured values to be referred to is higher than the measured value corresponding to the intermediate density region and the intermediate density A correction value setting method in which a set of measurement values corresponding to a density region is used. The correction value setting method according to claim 2,
In specifying the set of measurement values to be referred to in order to set a correction value for a command gradation value corresponding to the intermediate density,
When the measurement value corresponding to the intermediate density region is larger than the target concentration, the set of measurement values to be referred to is the measurement value corresponding to the intermediate density region, and the intermediate density next. A set of the measurement values corresponding to the low density region,
When the measured value corresponding to the intermediate density region is smaller than the target density, the set of the measured values to be referred to is the next to the measured value corresponding to the intermediate density region and the intermediate density. A correction value setting method in which the set of measurement values corresponding to a high density region is used. A correction value setting method according to any one of claims 1 to 3,
In specifying the set of measurement values to be referred to in order to set the correction value for the command gradation value corresponding to the highest density,
A correction value setting method, wherein a set of the measurement values to be referred to is a set of the measurement value corresponding to the region of the highest density and the measurement value corresponding to a region of the density lower than the highest density. The correction value setting method according to claim 4,
In specifying the set of measurement values to be referred to in order to set the correction value for the command gradation value corresponding to the highest density,
A correction value setting method, wherein a set of the measurement values to be referred to is a set of the measurement value corresponding to the highest density region and the measurement value corresponding to the next lowest density region. A correction value setting method according to any one of claims 1 to 5,
In the setting of the correction value for the command gradation value corresponding to the intermediate density and the correction value for the command gradation value corresponding to the highest density,
A command tone value corresponding to the target density is obtained by referring to the specified set of measurement values and the corresponding command tone value, and the intermediate density is handled using the obtained command tone value. A correction value setting method for setting a correction value for a command gradation value to be performed and a correction value for the command gradation value corresponding to the highest density. A correction value setting method according to any one of claims 1 to 6,
In printing the test pattern,
A correction value setting method in which an operation of ejecting ink toward a medium while moving a print head in a movement direction and an operation of conveying the medium in a conveyance direction intersecting the movement direction are repeatedly performed. The correction value setting method according to claim 7,
In obtaining the concentration measurement value,
A correction value setting for measuring the density of the test pattern for each of a plurality of row regions arranged in the transport direction, and acquiring the density measurement value in correspondence with both the plurality of regions and the row regions. Method. The correction value setting method according to claim 8,
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 the region having the same density, and setting an average value of each of the referenced measurement values as the target density. A correction value setting method according to any one of claims 7 to 9,
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, and having a plurality of print heads according to the type of ink that can eject the nozzle group while moving in the moving direction A correction value setting method for performing an operation of ejecting ink from the nozzle toward a medium. The correction value setting method according to claim 10,
In printing the test pattern,
A correction value setting method for printing a test pattern in which a plurality of sub-patterns printed by different nozzle groups are arranged in the moving direction. The correction value setting method according to claim 11,
The sub-pattern is
An intermediate density area printed in the intermediate density and long in the transport direction, a maximum density area printed in the maximum density and long in the transport direction, and a minimum density area long in the transport direction printed in the minimum density; How to set the correction value. (A) 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 is moved in the moving direction. By repeating the operation of ejecting ink toward the medium while transporting the medium in the transport direction that intersects the moving direction, the density differs based on a plurality of command gradation values. Printing a test pattern having a plurality of areas,
A plurality of sub-patterns printed by different nozzle groups, the intermediate density region printed in the intermediate density and long in the transport direction, the maximum density region printed in the maximum density and long in the transport direction, and the lowest Printing a test pattern in which a sub-pattern having a minimum density region that is long in the transport direction and printed in the density is arranged in the moving direction;
(B) measuring the density of the test pattern for each of the plurality of regions and each of the plurality of row regions arranged in the transport direction, and corresponding to both the plurality of regions and the row regions; Obtaining a concentration measurement,
(C) setting a target density for each of the intermediate density area and the highest density area,
Referring to the measured values for a plurality of the row regions belonging to the region of the same density, and setting an average value of each of the referenced measured values as the target density,
(D) identifying a set of measurement values to be referred to in order to set a correction value for a command gradation value corresponding to an intermediate density,
If the measured value corresponding to the intermediate density region is greater than the target density, the measured value corresponding to the intermediate density region and the measured value corresponding to the next lower density region are set. Identifying a set as the set of measurements to be referenced;
If the measured value corresponding to the intermediate density region is smaller than the target density, the measured value corresponding to the intermediate density region and the measured value corresponding to the next highest density region are set. Identifying a set as the set of measurements to be referenced;
(E) identifying a set of measurement values to be referred to in order to set a correction value for a command gradation value corresponding to the highest density,
Identifying the set of measurement values corresponding to the highest density region and the measurement value corresponding to the next lowest density region of the highest density as the set of measurement values to be referenced;
(F) A command tone value corresponding to the target density is obtained with reference to the specified set of measured values and the corresponding command tone value, and the command tone value obtained is used to determine the command tone value. Setting a correction value for a command gradation value corresponding to an intermediate density and a correction value for a command gradation value corresponding to the highest density;
A correction value setting method for performing (G). (A) A scanner that measures the density of a test pattern printed on a printing apparatus that is a correction value setting target,
(A1) measuring the density for each of a plurality of regions having different densities based on a plurality of command gradation values included in the test pattern;
A scanner to do
(B) a controller,
(B1) obtaining a measured value of the density from the scanner;
(B2) setting a target density for each of the intermediate density area and the highest density area;
(B3) In order to set a correction value for the command gradation value corresponding to the intermediate density, the measured value to be referred to according to the magnitude relationship between the measured value corresponding to the intermediate density region and the target density Identifying a set of
(B4) In order to set a correction value for the command gradation value corresponding to the highest density, reference is made regardless of the magnitude relationship between the measured value corresponding to the area printed at the highest density and the target density. Identifying the set of said measurement values
(B5) Referring to the specified set of measurement values, a correction value for the command gradation value corresponding to the intermediate density and a correction value for the command gradation value corresponding to the highest density are set. thing,
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 density for each of the plurality of regions;
Obtaining a density measurement from the scanner;
Setting a target density for each of the intermediate density area and the highest density area;
In order to set a correction value for the command gradation value corresponding to the intermediate density, a set of the measurement values to be referred to is determined according to the magnitude relationship between the measurement value corresponding to the intermediate density region and the target density. To identify,
In order to set the correction value for the command gradation value corresponding to the highest density, the measurement to be referred to is irrespective of the magnitude relationship between the measured value corresponding to the area printed at the highest density and the target density. Identifying value pairs,
With reference to the specified set of measured values, setting a correction value for the command gradation value corresponding to the intermediate density and a correction value for the command gradation value corresponding to the highest density,
A program to make the controller perform.