JP2012166415A - Pattern reading method, correction value obtaining method and test sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately read a test pattern used for obtaining a correction value.SOLUTION: The pattern reading method includes: an image forming step of forming a test pattern, a scale, a first ruled line formed parallel to graduations of the scale, and a second ruled line formed vertically to graduations of the scale; an image data obtaining step of reading the scale, the test pattern, and the respective ruled lines by an image input device to obtain each piece of the image data; a reading original point obtaining step of obtaining a reading original point based on positions of the image data in the first ruled line and the image data in the second ruled line; a position information obtaining step of obtaining position information indicating positions of the respective graduations based on a relative position from the obtained reading original point; and a reading step of reading the image data of the test pattern based on the obtained position information.

Description

  The present invention relates to a test sheet used when acquiring a correction value for correcting the density for each dot row, a pattern reading method for reading a test pattern formed on the test sheet, and the pattern reading method. The present invention relates to a correction value acquisition method for acquiring a correction value based on a pattern.

  As a printing apparatus that transports a medium (for example, paper or cloth) in the transport direction and performs printing on the medium, for example, an inkjet printer is known. When density unevenness (for example, white stripes or black stripes) occurs in the printed image when printing is performed by such a printing apparatus, the image quality of the image deteriorates. Therefore, as a method for solving this problem, a test sheet formed on a medium is read by a scanner, and a density correction value for each dot row (or also called a raster line) calculated based on the read image data is used. A method of correcting the density of an image based on the known method is known (for example, see Patent Document 1).

  A test sheet used in the above-described density unevenness correction method includes a test pattern composed of each color and a scale for specifying the reading position of the test pattern. That is, the scale indicates the position in the image data read by the scanner, so that the position of each dot row constituting the test pattern can be determined.

JP 2009-226802 A

The above-described scale can acquire the position information of the test pattern more accurately as the resolution is higher. Here, the resolution refers to the ability to recognize adjacent dots formed on a medium as different ones. In the present invention, in particular, dpi (dots per inch) indicating the resolution of dots formed in a predetermined area is used. And evaluate the value. Therefore, when the resolution of the scale is 1080 dpi rather than 760 dpi, the position information of the test pattern can be obtained more accurately.
On the other hand, when a test sheet is read by an image input device such as a scanner, the distance from the scanner reading start position (hereinafter also referred to as the scanner origin) to the scale reading position changes according to the test sheet setting mode. . Therefore, when reading the image data related to the scale, it is necessary to determine the reading position and the like while considering the above-described change in distance as an error. In particular, it is expected that the higher the resolution of the scale, the greater the influence of the error given by the test sheet setting mode.

  The present invention has been made in view of the above problems. A pattern reading method capable of reading a test pattern more accurately even when the resolution of the scale is increased, and a pattern read by this pattern reading method. An object of the present invention is to provide a correction value acquisition method for acquiring a correction value and a test sheet.

  In order to solve the above problem, in the present invention, a plurality of dot rows along a predetermined direction are arranged in a crossing direction intersecting the predetermined direction, and two or more test patterns having different colors are arranged between the test patterns. A scale formed by arranging a plurality of scales in the predetermined direction, a first ruled line formed in parallel to the scale marks, and a first line formed perpendicular to the scale marks. An image forming step for forming a second ruled line, and the scale, the test pattern, and the ruled line are read by an image input device, and the image data of the scale, the image data of the test pattern, and the ruled line An image data acquisition step for acquiring image data, and reading based on the positions of the image data of the first ruled line and the image data of the second ruled line A reading origin acquisition step for acquiring a point; a position information acquisition step for acquiring position information indicating a position of each scale based on a relative position from the acquired reading origin; and the acquired position information. And a reading step for reading the image data of the test pattern.

1 is a block configuration diagram of a printing system. FIG. 4 is an explanatory diagram showing the arrangement of nozzles on the lower surface of a head 41. It is explanatory drawing of normal printing. It is explanatory drawing of front end printing and rear end printing. 2 is a diagram illustrating a configuration of a scanner 150. FIG. It is a figure for demonstrating density nonuniformity. It is a figure explaining the error of the reading position resulting from the setting mode of test sheet TS. It is a flowchart of the whole flow of this embodiment. It is a flowchart of the acquisition process of a BRS correction value. It is the schematic diagram which showed a mode that the test pattern and the scale were formed in test sheet TS. It is a figure for demonstrating a scale. It is a flowchart explaining the process performed in step S203 in detail. It is a figure explaining the acquisition method of the reading origin on image data. It is a flowchart explaining the process performed in step S204. It is a figure explaining specification of the reading position of a scale. It is a graph of one-dimensional image data. It is explanatory drawing of the pixel data of a calculation range. It is a figure for demonstrating correction of the image data which concerns on a test pattern. It is explanatory drawing of the mode of the calculation of the pixel data equivalent to a density | concentration calculation position. It is the acquisition value table which put together the acquisition result of the density | concentration of five types of strip | belt-shaped patterns of cyan. It is a graph of the acquired value of the strip | belt-shaped pattern of density 30%, density 40%, and density 50% of cyan. It is a figure explaining the relationship between a command gradation value and a target command gradation value. It is explanatory drawing of the correction value table of cyan. It is explanatory drawing of the density correction process of the nth row | line area | region of cyan. It is a graph of the error of the reading position of a scanner. It is a figure for demonstrating the error of the reading position of a scanner.

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

Hereinafter, a first embodiment of an image processing apparatus according to the present invention will be described with reference to the drawings.
1. First embodiment:
1.1. Printing system configuration:
1.2. Density unevenness (banding):
1.3. Reading position error due to setting of test sheet TS:
1.4. BRS correction value acquisition method:
1.5. Scanner reading position error:
2. Other embodiments:

1. First embodiment:
1.1. Printing system configuration:
FIG. 1 is a block diagram of the printing system. The printing system 100 includes a printer 1, a computer 110, a display device 120, an input device 130, a recording / reproducing device 140, and a scanner 150 as an example of an image input device. The printer 1 is a printing apparatus that prints an image on a medium such as paper, cloth, or film. The computer 110 is communicably connected to the printer 1 and outputs print data corresponding to the image to be printed to the printer 1 in order to cause the printer 1 to print an image.

  A printer driver is installed in the computer 110. The printer driver is a program for causing the display device 120 to display a user interface and converting image data output from the application program into print data. This printer driver can also be downloaded to the computer 110 via the Internet. In addition, this program is comprised from the code | cord | chord for implement | achieving various functions.

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

The transport unit 20 is for transporting a medium (for example, paper S) in the transport direction. The transport unit 20 includes a paper feed roller, a transport motor, a transport roller, a platen, and a paper discharge roller (not shown).
The carriage unit 30 is for moving (also referred to as “scanning”) the head in a predetermined direction (hereinafter also referred to as a moving direction). The carriage unit 30 includes a carriage (not shown) and a carriage motor. The carriage can reciprocate in the moving direction and is driven by a carriage motor. The carriage detachably holds an ink cartridge that stores ink as an example of liquid.

  The head unit 40 is for ejecting ink onto paper. The head unit 40 includes a head having a plurality of nozzles. Since the head is provided in the carriage unit 30, when the carriage unit 30 moves in the movement direction, the head also moves in the movement direction. Then, by intermittently ejecting ink while the head is moving in the moving direction, dot rows (raster lines) along the moving direction are printed on the paper.

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

  FIG. 2 is an explanatory diagram showing the arrangement of nozzles on the lower surface of the head 41. On the lower surface of the head 41, a black ink nozzle group K, a cyan ink nozzle group C, a magenta ink nozzle group M, and a yellow ink nozzle group Y are formed. Each nozzle group includes a plurality of nozzles that are ejection ports for ejecting ink of each color in an intersecting direction (conveying direction) intersecting a predetermined direction (moving direction), and includes 90 nozzles. .

  The plurality of nozzles of each nozzle group are aligned at a constant interval (nozzle pitch: k · D) along the transport direction. Here, D is the minimum dot pitch in the carrying direction (that is, the interval at the highest resolution of dots formed on the paper S). K is an integer of 1 or more. For example, when the nozzle pitch is 90 dpi (1/90 inch) and the dot pitch in the transport direction is 360 dpi (1/360 inch), k = 4.

  The nozzles in each nozzle group are assigned a smaller number as the nozzles on the downstream side (# 1 to # 90). That is, the nozzle # 1 is located downstream of the nozzle # 90 in the transport direction. Each nozzle is provided with an ink chamber (not shown) and a piezoelectric element. By driving the piezo element, the ink chamber expands and contracts, and ink droplets are ejected from the nozzle.

<<< Printing Operation of Printer 1 >>>
When printing on the paper S, the printer 1 ejects ink from the nozzles of the head 41 moving in the movement direction to form dots on the paper, and conveys the paper S in the conveyance direction by the conveyance unit 20. The transfer operation is repeated alternately. In the dot forming operation, ink is intermittently ejected from the nozzles, and a dot row composed of a plurality of dots along the moving direction is formed. This dot row is also called a “raster line”.

  First, normal printing will be described. Normal printing is performed by a printing method called interlaced printing. Here, “interlaced printing” means printing in which unrecorded raster lines are sandwiched between raster lines recorded in one pass. “Pass” refers to dot formation processing, and “pass n” in the following description means n-th dot formation processing.

  FIG. 3 is an explanatory diagram of normal printing. FIG. 3A shows the head position and dot formation in pass n to pass n + 3, and FIG. 3B shows the head position and dot formation in pass n to pass n + 4.

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

  In the figure, nozzles indicated by black circles are nozzles that can eject ink, and nozzles indicated by white circles are nozzles that cannot eject ink. Further, in the figure, the dot indicated by a black circle is a dot formed in the last pass, and the dot indicated by a white circle is a dot formed in the previous pass.

  In this interlaced printing, each time the paper is transported at a constant transport amount F in the transport direction, each nozzle records a raster line immediately above the raster line recorded in the immediately preceding pass. However, there are places where raster lines cannot be formed continuously in the transport direction only by this normal printing. Therefore, printing methods called leading edge printing and trailing edge printing are performed before and after normal printing.

FIG. 4 is an explanatory diagram of leading edge printing and trailing edge printing. The first five passes are leading edge printing, and the last five passes are trailing edge printing.
In front-end printing, when the vicinity of the front end of a print image is printed, the paper is transported by a transport amount (1 · D or 2 · D) smaller than the transport amount (7 · D) during normal printing. In front-end printing, the nozzles that eject ink are not constant. In the trailing edge printing, as in the leading edge printing, when the vicinity of the trailing edge of the print image is printed, the conveying amount (1 · D or 2 · D) is smaller than the conveying amount (7 · D) during normal printing. Then, the paper is conveyed. In the rear end printing, as in the front end printing, the nozzles that eject ink are not constant. As a result, a plurality of raster lines arranged continuously in the transport direction can be formed between the first raster line and the last raster line.

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

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

<<< Scanner configuration >>>
FIG. 5 is a diagram for explaining the configuration of the scanner 150. FIG. 5A is a cross-sectional view of the scanner 150. FIG. 5B is a top view of the scanner 150 with the upper lid 151 removed.
The scanner 150 includes an upper cover 151, a document table glass 152 on which the document 5 is placed, a reading carriage 153 that moves in the sub-scanning direction while facing the document 5 through the document table glass 152, and sub-scans the reading carriage 153. A guide unit 154 for guiding in the direction, a moving mechanism 155 for moving the reading carriage 153, and a scanner controller (not shown) for controlling each unit in the scanner 150 are provided. The reading carriage 153 includes an exposure lamp 157 for irradiating the document 5 with light, a line sensor 158 as an example of a reading unit that detects a line image in the main scanning direction (a direction perpendicular to the paper surface in FIG. 5A), and the document. And an optical system 159 for guiding the reflected light from the line sensor 158 to the line sensor 158. A broken line inside the reading carriage 153 in the drawing indicates a locus of light.

1.2. Density unevenness (banding):
When the printer performs printing, density unevenness occurs. Here, for the sake of simplification of description, the cause of density unevenness occurring in an image printed in a single color will be described. In the case of multicolor printing, the cause of density unevenness described below occurs for each color.

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

  Further, in the following description, “row region” refers to a region constituted by a plurality of unit regions arranged in the moving direction. For example, when the printing resolution is 360 dpi × 360 dpi, the row region is a band-like region having a width of 70.56 μm (≈ 1/360 inch) in the transport direction. When ink droplets are ideally ejected intermittently from the nozzle moving in the moving direction, a raster line is formed in this row region. A plurality of pixels arranged in the movement direction are associated with the row area.

FIG. 6 is a diagram for explaining density unevenness. FIG. 6A is an explanatory diagram of a state when dots are ideally formed. In the figure, since dots are ideally formed, each dot is accurately formed in the unit region, and the raster line is accurately formed in the row region. In the figure, the row region is shown as a region sandwiched between dotted lines, and here is a region having a width of 1/360 inch. In each row region, an image piece having a density corresponding to the coloring of the region is formed. Here, for simplification of explanation, it is assumed that an image having a constant density is printed so that the dot generation rate is 50%.
FIG. 6B is an explanatory diagram of density unevenness. Here, the amount of ink droplets ejected toward the fifth row region is small, and the dots formed in the fifth row region are small.

Originally, even though image pieces having the same density should be formed in each row area, the image pieces are shaded according to the row area. For example, the image piece in the fifth row region is relatively light.
When the print image composed of such raster lines is viewed macroscopically, stripe-shaped density unevenness along the moving direction of the carriage is visually recognized. This density unevenness causes a reduction in image quality of the printed image.

  FIG. 6C is an explanatory diagram showing a state when dots are formed by the printing method of the present embodiment. In the present embodiment, the gradation value of the pixel data (CMYK pixel data) of the pixel corresponding to the row region is corrected so that a dark image piece is formed in the row region that is dark and easily visible. Further, the gradation value of the pixel data of the pixel corresponding to the row region is corrected so that a dark image piece is formed in a row region that is easily viewed. For example, the gradation value of the pixel data of the pixel corresponding to each row region is corrected so that the dot generation rate in the fifth row region is increased. As a result, the dot generation rate of the raster lines in each row area is changed, the density of the image pieces in the row area is corrected, and density unevenness of the entire print image is suppressed. That is, in the present embodiment, the gradation value of the pixel data is corrected based on a correction value (BRS correction value (correction value for correcting density unevenness) described later) set for each row region.

1.3. Reading position error due to setting of test sheet TS:
FIG. 7 is a diagram for explaining an error in the reading position due to the setting mode of the test sheet TS. FIG. 7A shows the image data of the test sheet TS read by the scanner 150. The position of the image data read by the scanner 150 can be specified by a distance with the origin (also referred to as the scanner origin) defined when the scanner 150 reads an image as the origin. Here, the ideal setting mode of the test sheet TS is that the vertex of the test sheet TS is set at the scanner origin of the scanner 150, and the predetermined direction and the intersecting direction of the test sheet TS are set in the main scanning direction and the sub scanning direction. To be parallel. When the test sheet TS is read by the scanner 150 in this state, as shown by the dotted lines in FIG. 7A, the test sheet TS is in the x direction (direction corresponding to the main scanning direction) and the y direction (direction corresponding to the sub scanning direction). The distance between each image data constituting the TS and the scanner origin is equivalent to the position of the image on the actual test sheet TS.

  On the other hand, when the vertex of the test sheet TS is set with a deviation from the scanner origin, an error occurs between the scanner origin and the image by this deviation. Therefore, it is necessary to reset the image reading position and the like in consideration of this error amount. For example, in the image data (position shown by a solid line) read in the set mode shown in FIG. 7A, the amount of deviation (Gx, Gy) is generated between the scanner origin and the test sheet TS. It is necessary to offset by the shift amount (Gx, Gy). For this reason, the position of the pixel A constituting a part of the image is offset in the x direction by an offset amount (G1, G2) from the position separated by Xa pixels in the x direction and by Ya pixels in the y direction. The position is indicated by Xa + Gx pixels and Ya + Gy pixels in the y direction.

  FIG. 7B is a diagram for explaining the reading range of the scanner 150. In addition, since the reading range is fixed with respect to the test sheet TS on which the scanner 150 is set, if the amount of deviation is too large, a part of the image formed on the test sheet TS may not be read. . In FIG. 7B, since the setting position of the test sheet TS is too shifted from the scanner origin, a part of the image of the test sheet TS is not read (area indicated by a dotted line in FIG. 7B).

  Therefore, in this embodiment, an origin (also referred to as a reading origin) for reading each image in the image data is calculated so that the error in the set position of the test sheet TS can be eliminated within a predetermined range. The reading position of each image is determined based on the relative position. For this reason, if the test sheet TS is within a predetermined shift amount range with respect to the scanner origin, the test sheet TS can be read without considering an error relating to the set position.

1.4. BRS correction value acquisition method:
FIG. 8 is a flowchart of the overall flow of this embodiment. These processes are performed in the inspection process of the printer manufacturing factory.

First, the inspector attaches the printer 1 to be inspected to the computer 110 (S100, see FIG. 1).
After the printer is attached, the computer 110 performs a BRS correction value acquisition process for correcting density unevenness (S200). In the BRS correction value acquisition process, the scanner 150 reads a BRS correction test pattern (described later) and also reads a scale (described later).
If another printer is to be inspected further (YES in S300), the processes of S100 and S200 are repeated.
The BRS correction value is stored in the memory 63 of the printer that has been inspected, and this printer is shipped from the factory and delivered to the user who purchased the printer. When the user performs printing, density unevenness is corrected by the BRS correction value, and a high-quality printing result is obtained.
Hereinafter, the BRS correction value acquisition process of S200 will be described in detail.

=== BRS Correction Value Acquisition Process (S200) ===
FIG. 9 is a flowchart of BRS correction value acquisition processing. The BRS correction value is a density correction value used when correcting the density (density unevenness) of an image. Each process is realized by a BRS correction program installed in the computer 110.

  First, the computer 110 transmits print data to the printer 1, and the printer 1 forms a test pattern for BRS correction (hereinafter simply referred to as a test pattern) on a test sheet TS as an example of a medium, and the scale is A plurality of scales and ruled lines are formed (S201). Next, the inspector sets the test sheet TS on the scanner 150, reads an image, and acquires test pattern, scale, and ruled line image data (S202). Further, the computer 110 obtains the reading origin based on the ruled line image data (S203). Then, the computer 110 acquires position information indicating the position of the scale in the image data based on the acquired reading origin (S204). Further, the computer 110 calculates a BRS correction value for each dot row (each row region) based on the position information and the image data of the test pattern (S205). Then, the computer 110 transmits the correction data to the printer 1 and stores the BRS correction value in the memory 63 of the printer 1 (S205). The BRS correction value stored in the printer reflects the density unevenness characteristics of each printer.

The printer storing the BRS correction value is packed and delivered to the user. When the user prints an image with the printer, the printer corrects the image data of the image to be printed based on the BRS correction value, and performs printing based on the corrected image data. Thereby, the printed image becomes an image with reduced density unevenness.
Hereinafter, each process in the BRS correction value acquisition process will be described.

<<< Image Forming Step (S201) >>>
FIG. 10 is a schematic diagram showing a state in which test patterns, scales, and ruled lines are formed on the test sheet TS. FIG. 11 is a diagram for explaining the scale. Note that, in FIG. 10, in order to make the drawing easy to understand, a scale in which the interval between the scales is wider than the actual interval is shown.

  In this step, a plurality of dot rows formed with a resolution V1 (720 dpi in the present embodiment) along a predetermined direction are arranged in the transport direction, and are formed between the test patterns and aligned in the predetermined direction. A scale array having scales, and a scale in which the interval between the scales in the predetermined direction is an interval of (1 / V1), and a vertical that defines the reading origin for reading the scales of each scale array S A ruled line (first ruled line) and a horizontal ruled line (second ruled line) are formed on the test sheet TS.

  More specifically, as shown in FIG. 10, each test pattern includes dot rows (raster lines) along the moving direction at intervals of 1/720 inch in the transport direction. It is formed by printing a plurality of lines.

As such test patterns, two or more test patterns having different colors are arranged so that the four test patterns are arranged in the moving direction (in this embodiment, from left to right, yellow, magenta, cyan, and black). The test sheets TS are arranged in order.
Then, the scale is divided into one test pattern (in this embodiment, a magenta test pattern) of the two or more test patterns (four test patterns) and another test pattern (this embodiment). In FIG. 2, it is formed so as to be positioned between the cyan test pattern). In the present embodiment, the scale is formed so that the scale is positioned between the two test patterns. In other words, the scale is adjusted so that the number of test patterns located upstream of the scale in the movement direction (for example, the movement direction from left to right in FIG. 10) is the same as the number of test patterns located downstream. Form.

  Each test pattern is composed of a band-shaped pattern having five different densities. The belt-like patterns are each generated from image data having a constant gradation value, and the gradation values 76 (density 30%), 102 (density 40%), and 128 (density 50%) are sequentially from the left belt-like pattern. , 153 (density 60%) and 179 (density 70%), and the patterns are darker in order. These five types of gradation values (density) are referred to as “command gradation values (command density)” and are represented by symbols Sa (= 76), Sb (= 102), Sc (= 128), Sd (= 153) and Se (= 179).

  As shown in FIG. 11, in the scale according to the present embodiment, each of the scale columns S1 to S8 has a scale of resolution V2 (90 dpi in the present embodiment), and each scale column S adjacent in the moving direction has each scale. The scale is printed with a predetermined width shifted so that the scale can obtain the desired resolution in the transport direction. That is, eight scale rows S having a scale width of 90 dpi (1/90 inch) are arranged in the movement direction, and each scale row S1 to S8 is printed so that the scale is shifted every 1/720 inch. Yes. Therefore, the scale is theoretically provided with the same resolution (720 dpi) as the raster line by combining the scales of the scale rows S1 to S8 in ascending order in the transport direction. The length of the scale according to this embodiment in the moving direction is 4 mm.

  In addition to the above example, if the scale requires a resolution of 1080 dpi, 12 scale rows with a resolution of 90 dpi are arranged in the movement direction, and 12 scales are displaced in the movement direction so that each scale shift is (1080 dpi = 90 × 12). What is necessary is just to arrange. Of course, the resolution of the scale column S is not limited to 90 dpi, and if the resolution of each scale column S is 180 dpi and the number of scale columns is 6, the same resolution (1080 dpi = 180 dpi × 6) may be obtained. it can.

  The vertical ruled lines and the horizontal ruled lines according to the present embodiment are formed at the end portion (left end in FIG. 10) of the test sheet TS. The vertical ruled line is composed of line segments parallel to the scale extending direction (moving direction) of the scale row S1. Further, the horizontal ruled lines are constituted by line segments perpendicular to the scale extending direction (moving direction) of the scale row S1.

  Each pattern formed on the test sheet TS is formed by the above-described printing method (the method described with reference to FIGS. 3A and 3B in the section <<<< Printing Operation of Printer 1 >>). That is, the test pattern, the scale, and each ruled line are dots (dots) on the test sheet TS by ejecting ink from the nozzle group while moving the relative positions of the nozzle group of the head 41 and the test sheet TS in the moving direction. Dot formation processing (more specifically, while moving the head 41 (nozzle group thereof) in the moving direction, ink is ejected from the nozzle group to form dots (dot rows) on the test sheet TS. Dot formation process to be formed) and the conveyance process of conveying the test sheet TS in the conveyance direction by the conveyance unit 20 are alternately repeated, and the above-described leading edge printing, normal printing, and trailing edge printing are performed in order. Is done. As a result, there are thousands of dot rows (raster lines) from the first dot row (raster line) to the last dot row (raster line) counted from the top (30 raster lines for leading edge printing, normal printing) A test pattern is formed by arranging them in a row (thousands of units are formed and 30 are formed by rear end printing).

<<< Image Data Acquisition Step (S202) >>>
After the test sheet TS is formed, the inspector sets the test sheet TS on the scanner 150. Then, the computer 110 causes the scanner 150 to read the test pattern, the scale, and each ruled line, and acquires each image data. That is, the scanner 150 crosses the line sensor 158 of the scanner 150 in the intersecting direction (the direction in which the dot rows formed on the test sheet TS are arranged) intersecting the predetermined direction (the direction along the dot rows formed on the test sheet TS). While moving, the line sensor 158 reads the test pattern, the scale, and each ruled line, and each image data is acquired.

  In this embodiment, the reading resolution at this time is 2880 dpi (predetermined direction (also referred to as main scanning direction)) × 2880 dpi (crossing direction (also referred to as sub-scanning direction)). The image data is composed of pixel data of pixels arranged in two dimensions in the x direction (direction corresponding to the main scanning direction) and the y direction (direction corresponding to the sub scanning direction). However, if there is an error in the reading position of the scanner 150, the corresponding length in the sub-scanning direction of each pixel becomes longer or shorter. As a result, due to an error in the reading position, the test pattern image indicated by the image data is distorted in the sub-scanning direction (y direction), and the scale marks indicated by the image data are not equally spaced. , Different from the actual scale.

<<< Reading Origin Acquisition Step (S203) >>>
In this step, the reading origin for determining the reading position and the like of the scale image data is obtained. Here, the reading origin is a point formed in the image data related to the test sheet TS, and is a point for specifying an area where the scale image data is located. The scanner 150 is used for reading the image data. It is different from the origin. In the present embodiment, the reading origin is acquired based on the image data relating to the vertical ruled lines and the horizontal ruled lines formed on the test sheet TS.

  FIG. 12 is a flowchart for explaining in detail the processing executed in step S203. FIG. 13 is a diagram for explaining a method for obtaining a reading origin on image data. Note that the test pattern of the image data shown in FIG. 13 is omitted for convenience.

  In step S2031, the computer 110 searches for a vertical ruled line and a horizontal ruled line within a predetermined area from the scanner origin. The area in which each ruled line is searched is set according to the ideal set mode of the test sheet TS. In other words, if each ruled line does not exist in this area, it means that some test patterns or the like have not been read as shown in FIG. 7B. For example, the computer 110 has a position that is moved by Nx1 pixels in the x direction and Ny1 pixels in the y direction from the scanner origin, and has Nx2 pixels in the x direction and Ny2 pixels in the y direction from this vertex. Search for vertical ruled lines within the enclosed rectangular area. Similarly, the computer 110 uses the position moved from the scanner origin by Nx3 pixels in the x direction and Ny3 pixels in the y direction as a vertex, and Nx4 pixels in the x direction and Ny4 pixels in the y direction from this vertex. A horizontal ruled line is searched for in a rectangular area surrounded by sides. Then, the computer 110 determines that a pixel whose gradation value is a predetermined value or more in each rectangular area is a vertical ruled line or a horizontal ruled line.

  When the computer 110 determines that there are no vertical ruled lines and horizontal ruled lines in each rectangular area designated in step S2031 (step S2032: NO), it displays an error message or the like notifying that the test sheet TS is not set properly. The information is displayed on the device 120 (step S2033), and the process is stopped. That is, the fact that each ruled line does not exist within a predetermined area indicates that the setting mode of the test sheet Ts is not preferable. In this embodiment, the test sheet TS is again transferred to the scanner 150 in such a case. Encourage the inspector to set it again.

  Therefore, when the inspector resets the test sheet TS to the scanner 150 again and performs an operation indicating the inspection resumption (step S2034: YES), the computer 110 resumes the process of step S2031. With this configuration, when the test sheet TS is set at a position outside the allowable range with respect to the scanner 150, this set error can be automatically detected.

If a vertical ruled line and a horizontal ruled line exist in each rectangular area in step S2032 (step S2032: YES), the computer 110 acquires the reading origin SP_y in the y direction from the image data related to the vertical ruled line in step S2035. The reading origin SP_x in the x direction is acquired from the image data relating to the horizontal ruled line.
Here, since the accuracy required for the reading origin is on the order of mm (millimeters), the computer 110 calculates the reading origin SP_y by averaging the number of pixels constituting the vertical ruled line arranged in the y direction. In addition, the computer 110 calculates the reading origin SP_x by averaging the number of vertical ruled lines arranged in the x direction. Hereinafter, the calculated reading origin (SP_x, SP_y) is used when reading the scale of the scale in step S204.

<<< Scale Scale Position Information Acquisition Step (S204) >>>
In this step, based on the scale image data (pixel data), position information indicating the position of the scale in the image data in the intersecting direction is acquired. Here, since the scale is composed of a plurality of scale columns S arranged in the moving direction, the position information of the entire scale is obtained by combining the scale position information of each scale column S according to the position in the y direction. To do.

  FIG. 14 is a flowchart illustrating the process executed in step S204. FIG. 15 is a diagram for explaining the specification of the scale reading position. Here, the reading position means an area of a pixel that is trimmed to read each scale on the scale. Therefore, a process for acquiring the scale position is executed for the pixel designated by the reading position. In the image data related to the test sheet TS shown in FIG. 15, the test pattern is not shown for convenience.

  In step S2041, the computer 110 specifies the reading position with the reading origin (SP_x, SP_y) as a base point. In the present embodiment, the computer 110 records relative distances Rd1 to Rd4 from the reading origin to each vertex of the reading position in the memory. Specifically, as shown in FIG. 15, when the relative distance Rd1 from the reading origin (SP_x, SP_y) to one vertex of the reading position (rectangular region) is (nx_rd1, nx_rd2), this vertex is , A pixel moved rightward by the nx_rd-th pixel in the x direction from the reading origin (SP_x, SP_y), and a pixel moved upward by the nx_rd-th pixel in the y direction. Similarly, the other vertices that define the reading position are also obtained from the relative distances Rd2 to Rd4 from the reading origin.

  In step S2042, the computer 110 calculates position information indicating the position of the scale for a predetermined scale row S belonging to the reading position. Therefore, the computer 110 first averages the gradation values of the pixel data of pixels arranged in the x direction with respect to the image data related to the first scale of the scale column S1 belonging to the scale reading position. Thereby, one-dimensional image data in the y direction is created. This one-dimensional image data is composed of pixel data of pixels arranged in 2880 dpi in the y direction.

  FIG. 16 is a graph of one-dimensional image data. The vertical axis of the graph represents the gradation value, and the horizontal axis represents the position in the y direction of the pixel belonging to the reading position. In FIG. 16, for convenience, the first pixel in the y direction of the reading position is described as the 0th pixel in the y direction in the image data. Therefore, the position in the y direction of a pixel 100 pixels away from this pixel is 100. Since a scale composed of scales with an interval of 1/90 inch is read at a resolution of 2880 dpi, a peak indicating the position of the scale appears on the graph every about 32 pixels. However, since there is an error in the reading position of the scanner 150, the peak interval is not necessarily 32 pixels. Therefore, the computer calculates the position of the scale in the image data in consideration of the reading position error of the scanner 150 by the following processing. A detailed description of the reading position error of the scanner 150 will be described later. An explanation will be given based on the error of the reading position of the scanner.

First, the computer 110 takes out pixel data of 32 pixels before and after the first peak (the range of the dotted line in FIG. 16) as a calculation range.
FIG. 17 is an explanatory diagram of pixel data in the calculation range. FIG. 17A is an explanatory diagram of pixel data in the calculation range acquired every 32 pixels. Pixel data (tone values) are discretely located at integer positions in the y direction. The computer 110 obtains the minimum value of these pixel data and subtracts each pixel data by the minimum value. As a result, the minimum value of the pixel data becomes zero.
Next, the computer normalizes the pixel data. Normalization is realized by calculating the sum of the gradation values of 32 pieces of pixel data and dividing the gradation value of each pixel data by the total value. As a result, the sum of the gradation values of the 32 pixel data after normalization is 1.

FIG. 17B is an explanatory diagram of pixel data after normalization. The computer 110 calculates the center position of the normalized pixel data as the scale position. The barycentric position of the pixel data is obtained by multiplying the gradation value of the pixel data by the position in the y direction for each pixel and calculating the sum.
Then, the computer 110 stores the calculated barycentric position as a scale position. The pixel data corresponds to the integer position in the y direction, but the barycentric position is not necessarily an integer position.

  The computer 110 repeats the above processing, calculates all positions in the y direction of the scale in the image data, and acquires position information indicating the positions. Note that the next calculation range is pixel data of 32 pixels before and after the position that is 32 pixels away from the position of the center of gravity calculated immediately before.

  If there is no error in the reading position of the scanner 150, the calculated scale position interval should be 32 (pixels). However, since there is an error in the reading position, the calculated scale position interval does not become 32 (pixels). However, the position information indicating the calculated scale position is information reflecting an error in the reading position of the scanner 150.

  Next, if scale position information is not acquired for all scale columns (step S2043: NO), in step S2044, the scale column S for acquiring position information is changed, and the scale column S is changed to this scale column S. Also, the scale position information is acquired.

  When scale position information is acquired for all scale columns S (step S2043: YES), in step S2045, the position information acquired for all scale columns is sorted in ascending order according to the y-direction position. Then, the position information is synthesized. For example, in the scale shown in FIG. 11, each scale row S is shifted in the transport direction by 1/720 dots with respect to the adjacent scale row S. Scale information in column S2 ... Position information is recorded in the order of the scale in scale column S8.

By this step, the scale of each scale row S is synthesized as a virtual scale scale having a resolution of 720 dpi. That is, theoretically, the scale position of the virtual scale with the resolution as the amount of scale shift between the adjacent scale rows S is calculated.
The calculated scale position is stored in the computer 110 and used in a BRS correction value acquisition step (S205) described later.

<<<< BRS Correction Value Acquisition Step (S205) >>
In this step, a BRS correction value is acquired for each dot row (raster line) based on the position information acquired in S204 and the image data of the test pattern. In the present embodiment, first, the image data of the test pattern is corrected based on the position information. Then, based on the corrected image data, a BRS correction value is acquired for each dot row (raster line).

First, the computer 110 calculates a “density calculation position” based on the position information acquired in S204. “Density calculation position” indicates where the actual 1/2880 inch interval (equal interval) is on the image data. The position of the scale calculated in S204 indicates which position on the image data the positions of 1/720 inch intervals created by combining the position information of the scale of the scale row S are present. Is calculated by dividing the position of the scale calculated in S203 into four. That is, the density calculation position is obtained by interpolating the positions of the three points between the scale marks.
If there is no error in the reading position of the scanner 150, the calculated density calculation position interval should be 1 (pixel). However, since there is actually an error in the reading position, the calculated density calculation position interval does not become 1 (pixel). In most cases, the concentration calculation position is not an integer.

Next, the computer 110 calculates pixel data (tone value) of the test pattern corresponding to the density calculation position, and corrects the image data of the test pattern based on the calculated pixel data.
FIG. 18 is a diagram for explaining correction of image data related to a test pattern. FIG. 18A is an explanatory diagram of image data before correction of a test pattern. The horizontal axis in the figure indicates the position of the pixel in the y direction. The scale on the horizontal axis indicates the integer position in the y direction, and indicates the corresponding position of each pixel. Note that the position in the y direction of the first pixel is 0, and the position in the y direction of a pixel 100 pixels away from this pixel is 100. The vertical axis in the figure indicates the gradation value indicated by the pixel data. Here, the gradation values of the pixel data of the pixels arranged in the y direction of the two-dimensional image data are shown as black circles as discrete data.

  FIG. 18B is an explanatory diagram of a method of calculating pixel data corresponding to the density calculation position. The position of the arrow in the figure indicates the density calculation position. As already described, due to an error in the reading position, the interval between the density calculation positions is not 1, and the density calculation position is not an integer. The computer 110 calculates a gradation value corresponding to the density calculation position by linear interpolation.

  Then, the gradation value at the first density calculation position is set as pixel data of the first pixel in the y direction, and the gradation value at the nth density calculation position is set as pixel data of the nth pixel in the y direction. The data is corrected. As a result, the distortion in the sub-scanning direction (y direction) of the image of the image data is corrected. That is, distortion in the sub-scanning direction (y direction) of the test pattern image is corrected.

  FIG. 19 is an explanatory diagram of how pixel data corresponding to the density calculation position is calculated. For example, when the 22nd density calculation position is “22.264”, the density calculation position is determined based on the pixel data of the pixel A whose position in the y direction is “22” and the pixel data of the pixel B of “23”. The gradation value is calculated by linear interpolation, and the calculated gradation value becomes pixel data of the pixel C. Note that the pixel data of the pixel immediately adjacent to the pixel C is calculated by linear interpolation based on the pixel data of the pixel adjacent to the right of the pixel A and the pixel data of the pixel adjacent to the right of the pixel B. .

  Then, the computer 110 converts the resolution so that the image of the 2880 dpi test pattern becomes an image of 720 dpi. By this resolution conversion, the number of pixels arranged in the y direction is equal to the number of raster lines constituting the test pattern. As a result, the column of pixels arranged in the x direction on the image data after resolution conversion corresponds to the column region. For example, the pixel column in the x direction located at the top corresponds to the first row region, and the pixel row located below corresponds to the second row region.

  Next, the computer 110 acquires the density of each of the five types of belt-like patterns in each row region. Since each pixel column arranged in the x direction includes portions of five types of density patterns, for example, when acquiring the density of a pattern having a density of 30% in a certain column region, the computer 110 includes the column region in that column region. The density is calculated by averaging the tone values of the pixels constituting the 30% density pattern image in the corresponding pixel row.

  FIG. 20 is an acquisition value table that summarizes the acquisition results of the density of the five types of belt-like patterns of cyan. As described above, the computer 110 creates an acquired value table by associating the acquired values of the density of the five types of belt-shaped patterns for each row region. An acquisition value table is also created for other colors. In the following description, the acquired values of the band-shaped patterns of the gradation values Sa to Se are set to Ma to Me for a certain row region, respectively.

  FIG. 21 is a graph of the acquired values of the band-like pattern having a cyan density of 30%, a density of 40%, and a density of 50%. Although each belt-like pattern is uniformly formed with the command gradation value, shading is generated for each row region. The density difference in the row area is a cause of density unevenness in the printed image.

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

  Therefore, the computer 110 calculates a correction value for each row region. Here, calculation of the correction value for the command gradation value Sb in a certain row region will be described. As will be described below, the correction value for the command gradation value Sb (density 40%) in the row region i of FIG. 21 is calculated based on the acquired values of the gradation value Sb and the gradation value Sc (density 50%). Is done. On the other hand, the correction value for the command gradation value Sb of the row region j is calculated based on the acquired values of the gradation value Sb and the gradation value Sa (density 30%).

FIG. 22 is a diagram for explaining the relationship between the command tone value and the target command tone value. FIG. 22A is an explanatory diagram of the target command tone value Sbt with respect to the command tone value Sb in the row region i. In this row area i, the obtained density value Mb of the belt-like pattern formed with the command gradation value Sb shows a gradation value smaller than the target value Mbt (the density of this row area is lighter than the average density). . If the printer is to form a density pattern of the target value Mbt in this row area, the printer driver is commanded based on the target command tone value Sbt calculated by the following equation (linear interpolation based on the straight line BC). I think it would be good.
Sbt = Sb + (Sc−Sb) × {(Mbt−Mb) / (Mc−Mb)}

FIG. 22B is an explanatory diagram of the target command tone value Sbt with respect to the command tone value Sb in the row region j. In this row region j, the obtained density value Mb of the belt-like pattern formed with the command tone value Sb shows a tone value larger than the target value Mbt (the density of this row region is higher than the average density). . If the printer is to form a density pattern of the target value Mbt in this row area, the printer driver is commanded based on the target command tone value Sbt calculated by the following equation (linear interpolation based on the straight line BC). I think it would be good.
Sbt = Sb− (Sb−Sa) × {(Mbt−Mb) / (Ma−Mb)}

After calculating the target command tone value Sbt in this way, the computer 110 calculates a correction value Hb for the command tone value Sb in this row region by the following equation.
Hb = (Sbt−Sb) / Sb

  The computer 110 calculates a correction value Hb for the gradation value Sb (density 40%) for each row region. Similarly, a correction value Hc for the gradation value Sc (density 50%) is calculated for each row region based on the acquired value Mc of each row region and the acquired value Mb or Md. Similarly, the correction value Hd for the gradation value Sd (density 60%) is calculated for each row region based on the acquired value Md of each row region and the acquired value Mc or Me. For other colors, three correction values (Hb, Hc, Hd) are calculated for each row region.

By the way, there are thousands of raster lines in the normal print region, but there is regularity for every seven raster lines. This regularity is taken into account when calculating the correction value for the normal printing area.
When the computer 110 calculates the correction value in the first row area (the 31st row area of the entire print area) of the normal print area, the acquired value Ma includes the normal print areas 1, 8, 15, The average value of the acquired values of the density of 30% in the 22, 29, 36, 43, 50,. Similarly, when calculating the correction value in the first row region of the normal print region (the 31st row region of the entire print region), the acquired values Mb to Me include the values 1, 8, 15 of the normal print region. , 22, 29, 36, 43, 50,..., The average value of the acquired values of each density in the first row region is used. Based on such acquired values Ma to Me, the correction values (Hb, Hc, Hd) of the first row area of the normal print area are calculated as described above. As described above, the correction value of the row region of the normal print region is calculated based on the average of the acquired values of the respective densities of every seventh row region. As a result, in the normal printing area, correction values are calculated only for the first to seventh column areas, and correction values are not calculated for the eighth and subsequent column areas. In other words, the correction values for the first to seventh column regions in the normal print region also become correction values for the eighth and subsequent column regions. These correction values become BRS correction values for correcting density unevenness.

Next, the computer 110 stores the correction value in the memory 63 of the printer 1.
FIG. 23 is an explanatory diagram of a cyan correction value table. There are three types of correction value tables, one for the front end print area, one for the normal print area, and one for the rear end print area. In each correction value table, three correction values (Hb, Hc, Hd) are associated with each row region. For example, three correction values (Hb_n, Hc_n, Hd_n) are associated with the nth raster line in each row region. The three correction values (Hb_n, Hc_n, Hd_n) correspond to the command gradation values Sb (= 102), Sc (= 128), and Sd (= 153), respectively. The same applies to correction value tables for other colors.
After the correction value is stored in the memory 63 of the printer 1, the BRS correction value acquisition process ends. Thereafter, the connection between the printer 1 and the computer 110 is disconnected, the other inspections for the printer 1 are finished, and the printer 1 is shipped from the factory. The printer 1 also includes a CD-ROM that stores a printer driver.

<<< Correction of density unevenness (reference) >>>
For reference, a printing method using the BRS correction value will be described. However, the printing method using the BRS correction value is performed at the time of the printing operation under the user, and is not performed at the time of the “BRS correction value acquisition process”.

  The user who purchased the printer 1 connects the printer 1 to the computer 110 owned by the user (of course, a computer different from the computer at the printer manufacturing factory). When the bundled CD-ROM is set in the computer 110, a printer driver is installed in the computer 110. At this time, the printer driver requests the printer 1 to transmit a correction value, and stores the BRS correction value sent from the printer in the memory.

  Upon receiving a print command from the user, the printer driver performs resolution conversion processing, color conversion processing, density correction processing, halftone processing, and rasterization processing. The BRS correction value is used for this density correction process. Hereinafter, these processes will be described.

The resolution conversion process is a process for converting image data (text data, image data, etc.) output from an application program into a resolution for printing on paper. For example, when the resolution when printing an image on paper is specified as 720 × 720 dpi, the image data received from the application program is converted into image data having a resolution of 720 × 720 dpi. Note that the image data after the resolution conversion process is 256-gradation data (RGB data) represented by an RGB color space.
The color conversion process is a process for converting RGB data into CMYK data represented by a CMYK color space. Through this color conversion process, RGB data for each pixel is converted into CMYK data corresponding to the ink color. The data after the color conversion processing is CMYK data with 256 gradations represented by the CMYK color space.
The density correction process is a process for correcting the gradation value of each pixel data based on the corresponding correction value of the column region to which the pixel data belongs.

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

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

  On the other hand, when the gradation value S_in before correction is different from the command gradation value, the gradation value S_out to be output is calculated by linear interpolation as shown in the figure. In the linear interpolation in the figure, linear interpolation is performed between the corrected gradation values S_out (Sbt, Sct, Sdt) corresponding to the command gradation values (Sb, Sc, Sd).

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

  For the pixel data of the first to seventh row areas of the normal print area (31st to 38th row areas of the entire print area), the printer driver stores them in the correction value table for the normal print area. Density correction processing is performed based on the correction values corresponding to the first to seventh row regions. However, although there are thousands of row regions in the normal print region, only the correction values corresponding to the seven row regions are stored in the correction value table for the normal print region. Therefore, for the pixel data in the eighth to fourteenth row areas of the normal print area, the printer driver stores the first to seventh row areas stored in the correction value table for the normal print area. Based on the corresponding correction value, density correction processing is performed. As described above, for the row region of the normal print region, the printer driver repeatedly uses the correction values corresponding to the first to seventh row regions for every seven row regions. Since the regular printing area has regularity for every seven row areas, the density unevenness characteristic is considered to be repeated in the same cycle. Therefore, the correction value data to be stored can be stored by repeatedly using the correction value in the same cycle. The amount is reduced.

  In the trailing edge printing area, similarly to the leading edge printing area, the printer driver stores the pixel data in the first to thirty-th column areas of the trailing edge printing area in the correction value table for the trailing edge printing area. The density correction processing is performed based on the correction values corresponding to the first to thirty-th row regions.

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

  The halftone process is a process for converting high gradation number data into gradation number data that can be formed by a printer. For example, data representing 256 gradations is converted into 1-bit data representing 2 gradations or 2-bit data representing 4 gradations by halftone processing. In the halftone process, pixel data is created using a dither method, an error diffusion method, or the like so that the printer can form dots dispersedly. The data subjected to the halftone process has a resolution (for example, 720 × 720 dpi) equivalent to the RGB data described above. Further, the pixel data subjected to the halftone process represents a dot formation state. When the pixel data after halftone processing is 2-bit data, the pixel data indicates no dot, small dot formation, medium dot formation, and large dot formation.

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

  The rasterizing process is a process of changing matrix image data in the order of data to be transferred to the printer. The rasterized data is output to the printer as pixel data included in the print data.

  If the printer performs printing processing based on the print data generated in this way, the dot generation rate of the raster lines in each row area is changed, the density of the image pieces in the row area is corrected, and the entire print image is corrected. Density unevenness is suppressed.

As described above, in this embodiment, the vertical ruled lines parallel to the scale marks and the scale marks and the vertical formation are formed on the test sheet TS so that the error in the set position of the test sheet TS can be eliminated within a predetermined range. Then, in the image data obtained by reading the test sheet TS, the reading origin is calculated from the image data relating to each ruled line, and the scale reading position and the like are specified by the relative distance from the reading origin. For this reason, if the test sheet TS is within a predetermined shift amount range with respect to the scanner origin, the test sheet TS can be read without considering an error relating to the set position.
Further, by adopting such a pattern reading method, it is not necessary to consider the set deviation of the test sheet TS within a predetermined range, so that the margin (margin) formed on the test sheet TS can be reduced. That is, the conventional test sheet TS is provided with a margin in the outer peripheral portion of the test pattern in preparation for misalignment when set to the scanner 150. However, by adopting the pattern reading method according to the present embodiment, a scale or the like Since the position is specified by the relative position in the image data, the margin can be reduced.

1.5. Scanner reading position error:
Here, the description will be made on the assumption that an image is read at a resolution of 720 dpi (main scanning direction) × 720 dpi (sub-scanning direction). The error in the reading position of the scanner described here is not an error due to the mode of setting the test sheet, but an error due to the movement of the reading carriage 153 being not constant.

  FIG. 25 is a graph of the error in the reading position of the scanner. The horizontal axis of the graph indicates the reading position (theoretical value) (that is, the horizontal axis of the graph indicates the position (theoretical value) of the reading carriage 153). The vertical axis of the graph represents the reading position error (difference between the theoretical value of the reading position and the actual reading position). According to this graph, for example, when the reading carriage 153 is moved 1 inch (= 25.4 mm), an error of about 60 μm occurs.

  If the theoretical value of the reading position matches the actual reading position, a pixel that is 720 pixels away from the pixel indicating the reference position (position where the reading position is zero) in the sub-scanning direction is exactly 1 inch from the reference position. It should show an image at a distant location. However, when an error in the reading position as shown in the graph occurs, a pixel that is 720 pixels away from the pixel that indicates the reference position in the sub-scanning direction is a position that is further 60 μm away from a position that is 1 inch away from the reference position. An image will be shown.

  If the slope of the graph is zero, images should be read at equal intervals every 1/720 inch. However, when the slope of the graph is positive, images are read at intervals longer than 1/720 inch. Further, when the slope of the graph is negative, images are read at intervals shorter than 1/720 inch.

  FIG. 26 is a diagram for explaining an error in the reading position of the scanner. FIG. 26A is an explanatory diagram of the relationship between a document and image data when the reading position of the scanner is accurate. The reading carriage 153 moves relative to the document in the vertical direction in the drawing. The image indicated by the image data is configured by arranging square pixels having a size of 1/720 inch (main scanning direction) × 1/720 inch (sub-scanning direction) in a matrix.

  Here, for simplification of explanation, the document is assumed to be a regular triangle having a height of about 2000/720 inches. Further, for convenience of explanation, a white line is formed at a position half the height of the regular triangle (a position spaced 1000/720 inches from the apex of the regular triangle). In the following description, the reference in the sub-scanning direction of the reading position is the position of the vertex of the equilateral triangle, and the reference of the pixel position in the image data is the pixel of the apex of the equilateral triangle.

  When the reading position of the scanner 150 is accurate, the document is read at equal intervals each time the reading carriage 153 moves 1/720 inch in the sub-scanning direction (see the left figure). The image data read in this way is as shown in the image of the original (see the right figure). The white line in the document is read at the 1001st reading, and is read as pixel data of a pixel that is 1000 pixels away from the reference pixel.

  FIG. 26B is an explanatory diagram of the relationship between a document and image data when there is an error in the reading position of the scanner. Here, images are read at intervals shorter than 1/720 inch (ie densely) at positions close to the reference position, and images are read at intervals longer than 1/720 inch (ie coarsely) at positions far from the reference position. (See the left figure). The image of the image data read in this way is deformed from the shape indicated by the document (see the right figure). Note that at the 1001st reading, an image at a position above the white line in the document is read (see the left figure). Further, the white line in the original is read at the time of about 1200 reading (see the left figure), and is read as pixel data of a pixel about 1200 pixels away from the reference pixel (see the right figure). As a result, the white line in the image data is positioned relatively below the white line of the document.

  As described above, the image data read by the scanner 150 has a reading position error caused by the mechanism of the scan 150. In this embodiment, the scanner reads the BRS correction test pattern printed by the printer when calculating the BRS correction value for correcting the density unevenness. However, if there is an error in the reading position of the scanner, the test pattern for BRS correction cannot be read accurately, and as a result, the correction value cannot be calculated accurately. Therefore, when the correction value is calculated based on the image data read by the scanner 150, correction is performed in consideration of the characteristics of the scanner 150.

2. Other embodiments:
In the above embodiment, as an example of an ink jet printer, a serial printer in which a head including nozzles moves in the predetermined direction with respect to the medium and ejects ink from the nozzles is described. However, the present invention is not limited thereto. For example, the printer may be a line printer that ejects ink from the nozzles to a medium that moves in the predetermined direction with respect to a non-moving line head that includes nozzles.
That is, in the correction value acquisition method according to the above-described embodiment, the test pattern and the scale are formed by the serial printer in the forming step. However, the present invention is not limited to this. This correction value acquisition method can also be applied to an example where a scale is formed.
Further, in a line head printer, the elongation of a medium such as paper generated during printing tends to be larger than that of an ink jet printer. Here, since the test sheet according to the present embodiment is composed of a plurality of scale rows S arranged in the movement direction, the scale intervals in each scale row S can be widened, and each scale row S Printing can be performed separately in the moving direction. For this reason, it is possible to reduce the influence of the elongation of the medium.

  Needless to say, the present invention is not limited to the above embodiments. That is, the mutually replaceable members and configurations disclosed in the above embodiments are applied by changing their combinations as appropriate. The members and configurations disclosed in the examples can be replaced with the members and configurations interchangeable with each other as appropriate, and the combination thereof is changed and applied. It is one of the present invention that a person skilled in the art can appropriately substitute the members and configurations that can be assumed as substitutes for the members and configurations disclosed in the above-described embodiments based on the above, and change the combination to apply. It is disclosed as an example.

  DESCRIPTION OF SYMBOLS 1 ... Printer, 20 ... Conveyance unit, 30 ... Carriage unit, 40 ... Head unit, 41 ... Head, 50 ... Detector group, 60 ... Controller, 61 ... Interface part, 62 ... CPU, 63 ... Memory, 64 ... Unit control Circuit: 100 ... Printing system 110 ... Computer 120 ... Display device 130 ... Input device 140 ... Recording / reproducing device 150 ... Scanner 151 ... Upper lid 152 ... Platen glass 153 ... Reading carriage 154 ... Guide 155 ... Moving mechanism, 157 ... Exposure lamp, 158 ... Line sensor, 159 ... Optical system

Claims (6)

Two or more test patterns having different colors from each other, wherein a plurality of dot rows along a predetermined direction are arranged in a crossing direction intersecting the predetermined direction;
A scale formed between the test patterns and having a plurality of scales arranged in the predetermined direction;
An image forming step of forming a first ruled line formed parallel to the scale of the scale and a second ruled line formed perpendicular to the scale of the scale;
An image data acquisition step of reading the scale, the test pattern, and the ruled lines with an image input device, and acquiring the scale image data, the image data of the test pattern, and the image data of the ruled lines;
A reading origin acquisition step of acquiring a reading origin based on the position of the image data of the first ruled line and the image data of the second ruled line;
A position information acquisition step of acquiring position information indicating the position of each scale based on the relative position from the acquired reading origin;
A pattern reading method comprising: reading image data of the test pattern based on the acquired position information.   2. The pattern according to claim 1, wherein in the reading origin acquisition step, the first ruled line and the second ruled line are searched within a predetermined range from an origin when the image input device reads image data. Reading method.   3. The pattern reading according to claim 2, wherein in the reading origin acquisition step, the subsequent processing is executed only when the first ruled line and the second ruled line are detected within the predetermined range. Method.   The scale has a scale column in which a scale having a resolution V2 that is a divisor of the resolution V1 is arranged in a predetermined direction over the n columns (where V1 = V2 × n, n is an integer) in the cross direction (1 / The pattern reading method according to any one of claims 1 to 3, wherein the pattern reading method is formed by being shifted by an interval of V1).   The correction value acquisition method according to claim 1, further comprising: a correction value acquisition step of calculating a correction value for correcting the density for each dot row based on the image data of the test pattern read by the pattern reading method. . A test sheet used when calculating a density correction value for each predetermined dot row,
Two or more test patterns having different colors from each other, wherein a plurality of dot rows along a predetermined direction are arranged in a crossing direction intersecting the predetermined direction;
A scale formed between the test patterns and having a plurality of scales arranged in the first direction; and
A test sheet comprising: a first ruled line formed in parallel to the scale of the scale; and a second ruled line formed perpendicular to the scale of the scale.