JP5940818B2 - Correction value acquisition method and image recording apparatus - Google Patents

Description

  The present invention relates to a correction value acquisition method and an image recording apparatus, and more particularly to a technique for acquiring a correction value of a recording element by reading a test pattern recorded by a recording head having a plurality of recording elements.

  2. Related Art Ink jet recording apparatuses that record an image by ejecting ink onto a recording medium using a recording head in which a plurality of nozzles that eject ink are arranged are known. In such an ink jet recording apparatus, it is important to make the ejection amount of ink from each nozzle uniform from the viewpoint of stabilizing the printing quality.

  Therefore, the amount of ink discharged from each nozzle is measured by measuring the amount of ink discharged from each nozzle when a predetermined value is input, and correcting the input value of each nozzle based on the measured amount of discharge. It is made uniform. The measurement of the discharge amount of each nozzle is performed, for example, by reading the output test pattern with a scanner and analyzing the read test pattern.

  In such a test pattern analysis, in order to calculate the density of each nozzle from the scanned image of the scanner, it is necessary to convert the resolution of the scanned image of the test pattern from the scanning resolution of the scanner to the recording resolution of the test pattern. There is. Even when the reading resolution is set to a predetermined integer multiple of the recording resolution, accurate resolution conversion may not be possible even if divided by this predetermined integer due to the effect of deviations during test pattern recording or reading. Occur.

  In order to deal with such a problem, Patent Document 1 discloses a reading resolution by analyzing position information of a ruled line formed together with a test pattern when acquiring a correction value of each nozzle from a reading gradation value of the test pattern. Describes a technique for performing resolution conversion from recording resolution to recording resolution.

JP 2010-269573 A

  In the technique of Patent Document 1, since the reading resolution of the scanner is set higher than the recording resolution of the test pattern, the position information of the ruled line can be accurately calculated. However, as shown in FIG. 17, when the ruled line on the test pattern is read by a scanner having a reading resolution lower than the recording resolution, an error occurs in the reading position information of the ruled line. For this reason, the resolution conversion accuracy deteriorates, and there is a drawback in that an accurate correction value cannot be calculated for each nozzle.

  The present invention has been made in view of such circumstances, and a correction value acquisition method and image recording that can acquire a correction value for each recording element using a reading device having a resolution lower than the resolution of the recording element. An object is to provide an apparatus.

To achieve the above object, one aspect of the correction value acquisition method, while relatively moving the recording head and the recording medium having a plurality of recording elements in a first direction, a dot row along the first direction A plurality of row regions formed in a second direction orthogonal to the first direction, and a ruled line group in which a plurality of ruled lines along the first direction are formed at equal intervals in a second direction orthogonal to the first direction A test pattern recording step of recording a test pattern having a first resolution on the recording medium, and reading the recorded test pattern to obtain a read gradation value of a second resolution lower than the first resolution. A reading gradation value acquisition step, a reading average position calculation step for calculating a reading average position in the second direction of the ruled line group based on the acquisition result of the reading gradation value acquisition step, and the calculated reading average position and recording medium Test pattern recorded on The resolution conversion step of converting the read gradation value of the second resolution into the read gradation value of the first resolution by associating with the average position of the ruled line group, and the read gradation value after the resolution conversion And a correction value acquisition step of acquiring a density unevenness correction value for each printing element .

  According to this aspect, a test pattern having a ruled line group in which a plurality of ruled lines along the first direction are formed at equal intervals in a second direction orthogonal to the first direction is recorded at a first resolution, Based on the reading result by the second resolution, the average reading position of the ruled line group is calculated, and the calculated reading average position is associated with the average position of the ruled line group on the test pattern recorded on the recording medium. Since the resolution read gradation value is converted into the first resolution read gradation value, the read gradation value of the resolution can be reduced even when a reader having a resolution lower than the resolution of the recording element is used. Since the data can be converted into the resolution of the recording element, a correction value for each recording element can be obtained.

  The test pattern recording process records the test pattern in a first size, and the read gradation value acquisition process includes a first area which is a part of the recorded test pattern and a part of the recorded test pattern. A second area including at least a part of the first area is read at a second size smaller than the first size, and the test pattern is read into the first area and the second area. It is preferable to have a ruled line group.

  Thereby, even if it is a case where the test pattern of 1st size is divided | segmented into several by 2nd size smaller than 1st size, each area | region can carry out resolution conversion.

  The test pattern has a first ruled line group in a first area that is not included in the second area, and a second pattern in the second area that is not included in the first area. The ruled line group has a third ruled line group in a first area that is included in the second area, and the reading average position calculating step includes a first reading average position of the first ruled line group. And a second reading average position of the second ruled line group and a third reading average position of the third ruled line group, and the resolution conversion step calculates the calculated first reading average position and the third reading average position. On the basis of the distance between the reading average position and the average position of the first ruled line group and the average position of the third ruled line group on the test pattern recorded on the recording medium. The resolution of the read gradation value of the area of the image is converted, the calculated distance between the second read average position and the third read average position, and the recorded test pattern Based on the distance between the average position of the second ruled line average position and a third ruled line group of the group above, it is preferable that the read-out gray scale value of the second region to the resolution conversion.

  Thereby, even if a deviation occurs during recording or reading of the test pattern, the resolution of each area can be appropriately converted.

In the correction value acquisition step, the density unevenness correction value of the first area and the area included in the second area is obtained by calculating the average value of the reading gradation value in the first area and the reading gradation value in the second area. It is preferable to calculate based on

  Thereby, it is possible to appropriately calculate the correction value in the area overlapping the first area and the second area.

  By associating the calculated read average position with the average position of the ruled line group on the test pattern recorded on the recording medium and specifying the position of the row area according to the ratio of the first resolution and the second resolution, The resolution of the read gradation value having the second resolution may be converted into the read gradation value having the first resolution. Even when a reader having a resolution lower than the resolution of the recording element is used, the resolution can be appropriately converted.

  The interval d between the plurality of ruled lines in the ruled line group is set such that the first resolution is R1, the second resolution is R2, k is an integer greater than 1, and h is an integer satisfying the condition of 0 <h <R1 / R2. D = R1 / R2 × k + h is preferably satisfied. The number N of the plurality of ruled lines in the ruled line group preferably satisfies N = R1 / R2 × k + 1.

  By configuring the ruled line group in this way, it is possible to appropriately calculate the reading average position.

  In the reading gradation value acquisition step, the first area is set in the flat bed scanner in a state in which one end in the second direction of the recording medium on which the test pattern is recorded is aligned with the reference portion of the flat bed scanner. Reading, causing the flatbed scanner to read the second area in a state where the recording medium on which the test pattern is recorded is reversed and the other end in the second direction of the recording medium is aligned with the reference portion It is preferable to provide a process.

  In the reading step, when it is determined that the read data acquired from the flatbed scanner is a result of reading the second area, it is preferable to invert the read data.

  As described above, the correction value for each recording element can be obtained by reading the test pattern recorded on the recording medium with the flatbed scanner.

  In the reading gradation value acquisition step, the first area may be read by the first scanner, and the second area may be read by the second scanner.

  In this way, the correction value for each recording element can be obtained by reading the test pattern recorded on the recording medium with the two scanners.

To achieve the above object, one aspect of the image recording apparatus, a density unevenness correction value acquired by the correction value acquisition method, density nonuniformity correction of the recording elements corresponding to each pixel constituting the image data The gradation value indicated by each pixel is corrected by the value, and an image is recorded on the recording medium by the recording element while relatively moving the recording element and the recording medium in the first direction based on the corrected gradation value.

  According to this aspect, since the gradation value can be corrected based on the appropriate correction value, an image with an appropriate gradation can be recorded.

  According to the present invention, it is possible to obtain a correction value for each printing element even when a reading device having a resolution lower than that of the printing element is used.

Overall configuration diagram showing an embodiment of an inkjet recording apparatus Plane perspective view showing a structural example of the head and an enlarged view of a part thereof The figure which shows the aspect which comprises a line head with a short head module. Head cross section Schematic diagram showing a configuration example of the imaging unit Schematic diagram showing another configuration example of the imaging unit Block diagram showing schematic configuration of control system of inkjet recording apparatus Block diagram showing the internal configuration of the correction value acquisition unit Flow chart showing correction value calculation processing The figure which shows the test pattern for density correction for 1 color (for 1 head) The figure which shows the reading area by each line sensor in the test pattern recorded on the paper The figure which shows the read image read by each line sensor The figure for explaining average position calculation processing The figure which shows an example of the method of reading the test pattern recorded on the paper with a flatbed scanner The figure which shows the other example of the method of reading the test pattern recorded on the paper with a flatbed scanner The figure which shows an example of the method of dividing the test pattern recorded on the paper into three times with a flatbed scanner The figure for explaining the case where the ruled line on the test pattern is read with the scanner whose reading resolution is lower than the recording resolution

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

<Overall configuration of inkjet recording apparatus>
FIG. 1 is an overall configuration diagram showing an embodiment of an ink jet recording apparatus (corresponding to an image recording apparatus) according to the present embodiment.

  The inkjet recording apparatus 10 is a single-pass inkjet printer that forms a desired color image by ejecting ink of a plurality of colors from an inkjet head onto a sheet P (corresponding to a recording medium). A paper feeding unit (not shown) that feeds paper, an image recording unit 100 that records an image on a front surface (printing surface) of paper P fed from the paper feeding unit using water-based ink, and an image recording unit 100 And a paper discharge section (not shown) for discharging the paper P on which the image is recorded.

<Image recording part>
The image recording unit 100 draws ink droplets of each color of C, M, Y, and K (water-based ink) on the printing surface of the paper P, and draws a color image on the printing surface of the paper P. The image recording unit 100 mainly presses the image recording drum 110 that transports the paper P and the paper P that is transported by the image recording drum 110, so that the paper P is brought into close contact with the peripheral surface of the image recording drum 110. A roller 112 and an inkjet head (corresponding to a recording head, hereinafter simply referred to as a head) 120C that ejects ink droplets of cyan (C), magenta (M), yellow (Y), and black (K) on the paper P; 120M, 120Y, 120K, an imaging unit 130 that reads an image recorded on the paper P, a mist filter 140 that captures ink mist, and a drum temperature adjustment unit 142.

  The image recording drum 110 is a conveyance unit for the paper P in the image recording unit 100. The image recording drum 110 is formed in a cylindrical shape and is driven to rotate by a motor (not shown). A gripper 110A is provided on the outer peripheral surface of the image recording drum 110, and the leading edge of the paper P is gripped by the gripper 110A. The image recording drum 110 conveys the paper P while winding the paper P around the peripheral surface by gripping and rotating the leading end of the paper P with the gripper 110A. Further, the image recording drum 110 has a large number of suction holes (not shown) formed in a predetermined pattern on the peripheral surface thereof. The paper P wound around the peripheral surface of the image recording drum 110 is conveyed while being sucked and held on the peripheral surface of the image recording drum 110 by being sucked from the suction holes. Thereby, the paper P can be conveyed with high smoothness.

  The suction from the suction hole acts only within a certain range, and acts only between a predetermined suction start position and a predetermined suction end position. The suction start position is set to the installation position of the sheet pressing roller 112, and the suction end position is set to the downstream side of the installation position of the imaging unit 130 (for example, at the position where the sheet is delivered to the transport drum 30 at the next stage). Set). That is, at least at the ink droplet ejection positions by the heads 120C, 120M, 120Y, and 120K and the image reading position by the imaging unit 130, the adsorption area is set so that the paper P is adsorbed and held on the peripheral surface of the image recording drum 110. Is set.

  Note that the mechanism for attracting and holding the sheet P on the peripheral surface of the image recording drum 110 is not limited to the attracting method based on the negative pressure, and a method based on electrostatic attracting can also be employed.

  Further, the image recording drum 110 of this example is provided with grippers 110A at two positions on the outer peripheral surface so that two sheets of paper P can be conveyed by one rotation. The rotation of the transport drum 20 and the image recording drum 110 that transport the paper P from the paper feeding unit to the image recording unit 100 is controlled so that the timing of receiving and delivering the paper P is matched. That is, it drives so that it may become the same peripheral speed, and it drives so that the position of a mutual gripper may match.

  The sheet pressing roller 112 is disposed in the vicinity of the sheet receiving position of the image recording drum 110 (the position where the sheet P is received from the transport drum 20). The sheet pressing roller 112 is composed of a rubber roller, and is installed in press contact with the peripheral surface of the image recording drum 110. The paper P transferred from the transport drum 20 in the previous stage to the image recording drum 110 is nipped by passing through the paper pressing roller 112 and is brought into close contact with the peripheral surface of the image recording drum 110.

  The four heads 120 </ b> C, 120 </ b> M, 120 </ b> Y, and 120 </ b> K are arranged at regular intervals along the conveyance path of the paper P by the image recording drum 110. The heads 120C, 120M, 120Y, and 120K are composed of line heads corresponding to the paper width. Each of the heads 120C, 120M, 120Y, and 120K is disposed so as to be substantially orthogonal to the conveyance direction of the paper P by the image recording drum 110, and the nozzle surface thereof is disposed to face the peripheral surface of the image recording drum 110. Is done. Each of the heads 120C, 120M, 120Y, and 120K ejects ink droplets from the nozzle row formed on the nozzle surface toward the image recording drum 110, whereby an image is printed on the paper P conveyed by the image recording drum 110. Record.

  The imaging unit 130 is an imaging unit that captures an image recorded by the heads 120C, 120M, 120Y, and 120K, and is installed on the downstream side of the head 120K located at the end in the conveyance direction of the paper P by the image recording drum 110. Has been. The imaging unit 130 includes a line sensor made of a solid-state imaging device such as a CCD or a CMOS, and a fixed focus imaging optical system, for example.

  The mist filter 140 is disposed between the rearmost head 120K and the imaging unit 130, and sucks air around the image recording drum 110 to capture ink mist. In this way, by sucking the air around the image recording drum 110 and capturing the ink mist, it is possible to prevent the ink mist from entering the imaging unit 130. As a result, it is possible to prevent occurrence of reading failure and the like.

  The image recording unit 100 is configured as described above. The paper P delivered from the transport drum 20 is received by the image recording drum 110. The image recording drum 110 conveys the paper P by gripping the leading end of the paper P with the gripper 110A and rotating. The paper P delivered to the image recording drum 110 is first brought into close contact with the peripheral surface of the image recording drum 110 by passing through the paper pressing roller 112. At the same time, it is sucked from the suction hole of the image recording drum 110 and sucked and held on the outer peripheral surface of the image recording drum 110. The sheet P is conveyed in this state and passes through the heads 120C, 120M, 120Y, and 120K. Then, during the passage, ink droplets of the respective colors C, M, Y, and K are ejected from the heads 120C, 120M, 120Y, and 120K onto the printing surface, and a color image is drawn on the printing surface.

  The paper P on which an image is recorded by the heads 120C, 120M, 120Y, and 120K then passes through the imaging unit 130. Then, an image recorded on the printing surface at the time of passing through the imaging unit 130 is read. The recorded image is read as necessary, and inspection such as density correction is performed from the read image. When reading is performed, reading is performed in a state of being held by suction on the image recording drum 110, so that reading can be performed with high accuracy.

  Thereafter, the suction of the paper P is released and the paper P is delivered to the transport drum 40 that transports the paper P to the paper discharge unit.

<Inkjet head configuration example>
Next, the structure of the inkjet head will be described. Since the structures of the heads 120C, 120M, 120Y, and 120K corresponding to the respective colors are common, the heads are represented by the reference numeral 120 in the following.

  2A is a plan perspective view showing an example of the structure of the head 120, and FIG. 2B is an enlarged view of a part thereof. FIG. 3 is a plan perspective view showing another example of the structure of the head 120. FIG. 4 is a three-dimensional configuration of one-channel droplet ejection elements (ink chamber units corresponding to one nozzle 251) serving as recording element units. FIG.

  As shown in FIG. 2, the head 120 of this example includes a plurality of ink chamber units (droplet discharge elements) 253 including nozzles 251 that are ink discharge ports and pressure chambers 252 corresponding to the nozzles 251. In this way, a substantial nozzle interval (projection nozzle pitch) projected (orthogonally projected) so as to be aligned along the longitudinal direction of the head (direction perpendicular to the transport direction of the paper P). ) Is achieved.

  Form in which nozzle rows having a length corresponding to the entire width Wm of the drawing region of the paper P are configured in a direction (arrow M direction, main scanning direction) substantially orthogonal to the transport direction (arrow S direction, sub-scanning direction) of the paper P Is not limited to this example. For example, instead of the configuration of FIG. 2A, as shown in FIG. 3A, a short head module 120 ′ in which a plurality of nozzles 251 are two-dimensionally arranged is arranged in a staggered manner and connected. Then, there is an aspect in which a line head having a nozzle row having a length corresponding to the entire width of the paper P is formed, or an aspect in which the head modules 120 ″ are connected in a line as shown in FIG.

  In addition, not only when the entire surface of the paper P is set as the drawing range, but when a part of the surface of the paper P is a drawing area (for example, when a non-drawing area is provided around the paper), Nozzle rows necessary for drawing in a predetermined drawing area may be formed.

  The pressure chamber 252 provided corresponding to each nozzle 251 has a substantially square planar shape (see FIGS. 2A and 2B), and the nozzle 251 is provided at one of the diagonal corners. An outlet for supplying ink (supply port) 254 is provided on the other side. Note that the shape of the pressure chamber 252 is not limited to this example, and the planar shape may have various forms such as a quadrangle (rhombus, rectangle, etc.), a pentagon, a hexagon, other polygons, a circle, and an ellipse.

  As shown in FIG. 4, the head 120 has a structure in which a nozzle plate 251A in which nozzles 251 are formed and a flow path plate 252P in which flow paths such as a pressure chamber 252 and a common flow path 255 are formed are laminated and joined. The nozzle plate 251A constitutes a nozzle surface (ink ejection surface) 250A of the head 120, and a plurality of nozzles 251 communicating with the pressure chambers 252 are two-dimensionally formed.

  The flow path plate 252P forms a side wall of the pressure chamber 252 and a flow path that forms a supply port 254 as a narrowed portion (most narrowed portion) of an individual supply path that guides ink from the common flow path 255 to the pressure chamber 252. It is a forming member. For convenience of explanation, the flow path plate 252P has a structure in which one or a plurality of substrates are stacked, although it is illustrated in a simplified manner in FIG.

  The nozzle plate 251A and the flow path plate 252P can be processed into a required shape by a semiconductor manufacturing process using silicon as a material.

  The common flow channel 255 communicates with an ink tank (not shown) as an ink supply source, and ink supplied from the ink tank is supplied to each pressure chamber 252 via the common flow channel 255.

  A piezoelectric actuator 258 including an individual electrode 257 is joined to a diaphragm 256 that constitutes a part of the pressure chamber 252 (the top surface in FIG. 4). The diaphragm 256 of this example is made of silicon (Si) with a nickel (Ni) conductive layer functioning as a common electrode 259 corresponding to the lower electrode of the piezoelectric actuator 258, and is arranged corresponding to each pressure chamber 252. It also serves as a common electrode for the actuator 258. It is also possible to form the diaphragm with a non-conductive material such as resin. In this case, a common electrode layer made of a conductive material such as metal is formed on the surface of the diaphragm member. Moreover, you may comprise the diaphragm which serves as a common electrode with metals (conductive material), such as stainless steel (SUS).

  By applying a driving voltage to the individual electrode 257, the piezo actuator 258 is deformed and the volume of the pressure chamber 252 is changed, and ink is ejected from the nozzle 251 due to the pressure change accompanying this. When the piezo actuator 258 returns to its original state after ink ejection, new ink is refilled into the pressure chamber 252 from the common channel 255 through the supply port 254.

  As shown in FIG. 2B, the ink chamber units 253 having such a structure are arranged in a fixed manner along a row direction along the main scanning direction and an oblique column direction having a constant angle θ that is not orthogonal to the main scanning direction. By arranging a large number of patterns in a lattice pattern, the high-density nozzle head of this example is realized.

  In this matrix arrangement, when the interval between adjacent nozzles in the sub-scanning direction is Ls, in the main scanning direction, each nozzle 251 is substantially equivalent to a linear arrangement with a constant pitch P = Ls / tan θ. It can be handled. In the nozzle arrangement of the present embodiment, the number of nozzle rows projected so as to be aligned in the main scanning direction is 1200 per inch (1200 dpi).

  In the implementation of the present invention, the arrangement form of the nozzles 251 in the head 120 is not limited to the illustrated example, and various nozzle arrangement structures can be applied. For example, instead of the matrix arrangement described in FIG. 2, a V-shaped nozzle arrangement, a zigzag nozzle arrangement (such as a W-shape) having a V-shaped arrangement as a repeating unit, or the like is also possible. .

  The means for generating the discharge pressure (discharge energy) for discharging the droplets from each nozzle in the inkjet head is not limited to the piezo actuator (piezoelectric element), but the thermal method (the pressure of film boiling due to the heating of the heater) Various pressure generating elements (energy generating elements) such as heaters (heating elements) and other actuators based on other systems can be applied. Corresponding energy generating elements are provided in the flow path structure according to the ejection method of the head.

<Configuration example of imaging unit>
Next, the imaging unit 130 will be described. FIG. 5 is a schematic diagram illustrating a configuration example of the imaging unit 130. As shown in the figure, the imaging unit 130 includes two line sensors 130a and 130b (corresponding to a first scanner and a second scanner). The line sensors 130a and 130b have a large number of solid-state imaging devices arranged along the main scanning direction. In the present embodiment, the line sensors 130a and 130b are arranged so that the reading resolution in the main scanning direction is 500 dpi. Note that the reading resolution in the sub-scanning direction is determined by the reading speed of the image sensor and the conveyance speed of the paper P.

  The sheet P is conveyed to a position facing the imaging unit 130 by an image recording drum 110 (not shown in FIG. 5). As shown in FIG. 5, the line sensor 130a is arranged to read the left side area of the paper P and the line sensor 130b is arranged to read the right side area of the paper P with the leading end in the conveyance direction of the paper P facing upward. Note that the reading area of the line sensor 130a and the reading area of the line sensor 130b are arranged so as to partially overlap. For this reason, the line sensor 130a and the line sensor 130b are not arranged in parallel to the conveyance direction of the paper P, and the line sensor 130b is arranged downstream of the line sensor 130a in the conveyance direction of the paper P. .

  In the example shown in FIG. 5, two line sensors are used, but one line sensor may be used. For example, as shown in FIG. 6, the line sensor 130a is configured to be movable in a state of facing the paper P, and the right side area and the left side area of the paper P are read by the line sensor 130a so as to partially overlap each other. May be. In addition, a mode in which three or more line sensors are used so as to partially overlap each other, and a mode in which one line sensor reads each of three or more regions so as to partially overlap each other are possible.

<Control system>
FIG. 7 is a block diagram showing a schematic configuration of a control system of the inkjet recording apparatus 10 of the present embodiment.

  As shown in the figure, the inkjet recording apparatus 10 includes a system controller 160, a communication unit 162, an image memory 164, a conveyance control unit 166, an image recording control unit 168, an operation unit 170, a display unit 172, a correction value acquisition unit 200, and the like. Is provided.

  The system controller 160 functions as a control unit that performs overall control of each unit of the inkjet recording apparatus 10 and also functions as a calculation unit that performs various calculation processes. The system controller 160 includes a CPU, a ROM, a RAM, and the like, and operates according to a predetermined control program. The ROM stores a control program executed by the system controller 160 and various data necessary for control.

  The communication unit 162 includes a required communication interface, and transmits and receives data to and from the host computer 190 connected to the communication interface.

  The image memory 164 functions as a temporary storage unit for various data including image data, and data is read and written through the system controller 160. Image data captured from the host computer 190 via the communication unit 162 is stored in the image memory 164.

  The conveyance control unit 166 controls the conveyance system of the paper P in the inkjet recording apparatus 10. In other words, in addition to the image recording drum 110 in the image recording unit 100, the driving of the transport drum 20 and the transport drum 30 is controlled.

  The conveyance control unit 166 controls the conveyance system in accordance with a command from the system controller 160 so that the paper P is conveyed without any delay.

  The image recording control unit 168 controls the image recording unit 100 in response to a command from the system controller 160. Specifically, the driving of the heads 120C, 120M, 120Y, and 120K is controlled so that a predetermined image is recorded on the paper P conveyed by the image recording drum 110.

  The operation unit 170 includes necessary operation means (for example, operation buttons, a keyboard, a touch panel, and the like), and outputs operation information input from the operation means to the system controller 160. The system controller 160 executes various processes according to the operation information input from the operation unit 170.

  The display unit 172 includes a required display device (for example, an LCD panel or the like), and displays required information on the display device in response to a command from the system controller 160.

  The correction value acquisition unit 200 functions as a density correction value acquisition unit that acquires a density correction value for each nozzle based on the test pattern data read by the imaging unit 130, and details thereof will be described later.

  As described above, the image data to be recorded on the paper P is taken into the inkjet recording apparatus 10 from the host computer 190 via the communication unit 162. Here, it is assumed that multi-value gradation image data for each ink color (for example, 256 gradation image data for each color corresponding to four colors of CMYK) is acquired. The captured image data is stored in the image memory 164.

  The system controller 160 performs necessary signal processing on the image data stored in the image memory 164 to generate dot data. The image recording control unit 168 controls the driving of each head 120C, 120M, 120Y, 120K of the image recording unit 100 according to the generated dot data, and records the image represented by the image data on the printing surface of the paper P.

  The dot data is generally generated by performing color conversion processing and halftone processing on image data. The color conversion process is a process of converting image data expressed in sRGB or the like (for example, RGB 8-bit image data) into ink amount data of each color of ink used in the inkjet recording apparatus 10 (in this example, C, It is converted into ink amount data for each color of M, Y, and K.) The halftone process is a process of converting the ink amount data of each color generated by the color conversion process into dot data of each color by a process such as error diffusion.

  The system controller 160 performs color conversion processing and halftone processing on the image data to generate dot data for each color. Then, the image represented by the image data is recorded on the paper P by controlling the driving of the corresponding inkjet head according to the generated dot data of each color.

  FIG. 8 is a block diagram illustrating an internal configuration of the correction value acquisition unit 200. As shown in the figure, the correction value acquisition unit 200 includes a test pattern storage unit 201, an image data storage unit 202, an average position calculation unit 204, a resolution conversion unit 205, a density data conversion unit 203, a density calculation unit 206, a correction value. A calculation unit 207 and the like are provided.

  The test pattern storage unit 201 stores various test patterns in addition to the density correction test pattern according to the present embodiment. The test pattern storage unit 201 transmits the selected test pattern to the image recording control unit 168 in response to a command from the system controller 160. The image recording control unit 168 controls driving of the heads 120 </ b> C, 120 </ b> M, 120 </ b> Y, and 120 </ b> K and outputs the test pattern on the printing surface of the paper P. That is, the image recording control unit 168 functions as a test pattern recording unit.

  The length of the test pattern in the conveyance direction is the reading speed based on the resolution of the image sensor, that is, the paper P body, so that the area from the front end to the end of the test pattern is completely and clearly imaged when the image capturing unit 130 captures an image. Is set in consideration of the transport speed.

  The test pattern recorded by the image recording unit 100 is captured by the imaging unit 130 and stored as inspection image data in the image data storage unit 202.

  The density data conversion unit 203 converts the inspection image data read from the image data storage unit 202 into a read image including density data.

  The average position calculation unit 204 functions as an average position calculation unit that calculates the average position of the ruled line group formed together with the test pattern, and the resolution conversion unit 205 converts the resolution of the read image based on the average position of the ruled line group. It functions as a resolution conversion means. Details of operations of the average position calculation unit 204 and the resolution conversion unit 205 will be described later.

  The density calculation unit 206 calculates an average value of density data for each pixel column (nozzle column) from the resolution-converted read image. This calculation is performed for all pixel columns.

  The correction value calculation unit 207 calculates a density unevenness correction value H for each nozzle based on the density data for each pixel column calculated by the density calculation unit 206. For example, for a nozzle region that is dark and easily visible, a density unevenness correction value H for correcting a gradation value indicated by pixel data corresponding to the nozzle region is calculated so that a light image piece is formed. Further, for a nozzle region that is faint and easily visible, a density unevenness correction value H for correcting the gradation value indicated by the pixel data corresponding to the nozzle region is calculated so that a dark image piece is formed.

  The density unevenness correction value H calculated in this way is stored in the correction value storage unit 208. The system controller 160 reads the density unevenness correction value H of each nozzle stored in the correction value storage unit 208 at the time of image output, and corrects the density of the output image data.

<First Embodiment>
FIG. 9 is a flowchart showing correction value calculation processing in the present embodiment.

  First, a density correction test pattern is printed by each of the heads 120C, 120M, 120Y, and 120K (corresponding to step ST1, a test pattern recording process). As described above, the density correction test pattern is stored in the test pattern storage unit 201. FIG. 10 is a diagram showing a density correction test pattern for one color (for one head). As shown in the figure, the density correction test pattern is composed of strip patterns PT1, PT2, and PT3 having three types of density, and ruled line groups LA, LB, and LC each including a plurality of ruled lines.

In each of the strip patterns PT1, PT2, and PT3, a dot row along the sub-scanning direction (corresponding to the first direction) formed by all the nozzles 251 of one head is the main scanning direction (corresponding to the second direction). Are formed side by side. The gradation values for forming each strip pattern are called command gradation values. In the example shown in FIG. 10, the strip pattern PT1 is the command gradation value Sa, the strip pattern PT2 is the command gradation value Sb, and the strip pattern PT3 is Depending on the command gradation value, band-like patterns having densities of 30%, 50%, and 70% are formed. Note that the type, arrangement order, command gradation value, and the like of the belt-like pattern are not limited to the example in FIG. 10 and may be determined as appropriate.

  Each ruled line group LA, LB, LC is composed of a plurality of ruled lines, and is formed on the upstream side of the strip pattern PT1 in the transport direction. In the example shown in FIG. 10, the ruled line group LA is formed on the left side in the main scanning direction with the upstream side in the transport direction up, the ruled line group LB is formed on the right side in the main scanning direction, and the ruled line group LC is formed in the main scanning direction. It is formed at the center. The ruled line groups LA, LB, and LC may be formed on the downstream side in the transport direction of the belt-like pattern, or may be formed on both the upstream side and the downstream side.

  Each ruled line constituting each ruled line group LA, LB, LC is arranged at equal intervals in the main scanning direction. Each ruled line is formed by one nozzle, and is recorded by a nozzle selected from all the nozzles 251. A mode in which one ruled line is formed by a plurality of adjacent nozzles is also possible.

  The system controller 160 reads the density correction test pattern stored in the test pattern storage unit 201 and outputs it to the image recording control unit 168. The image recording control unit 168 controls the driving of the heads 120C, 120M, 120Y, and 120K according to the input test pattern, and records the test pattern on the printing surface of the paper P.

  The density unevenness correction value H needs to be calculated for each ink color (here, cyan, magenta, yellow, and black). Therefore, the test pattern shown in FIG. 10 is printed for each ink color (each head).

  Next, the recorded density correction test pattern is read by the imaging unit 130, and test pattern data is acquired (step ST2, corresponding to a read gradation value acquisition step).

  As described with reference to FIG. 5, the imaging unit 130 includes two line sensors 130a and 130b.

  The line sensor 130a reads an area on the left side of the sheet P (a broken line area shown in FIG. 11A) with the leading end of the sheet P in the transport direction facing up. Further, the line sensor 130b reads the area on the right side of the paper P (the broken line area shown in FIG. 11B). The read test pattern data is stored in the image data storage unit 202. Also, the density data conversion unit 203 generates density data (read gradation value data) from the test pattern data and uses it as a read image.

  FIG. 12 is a diagram illustrating a read image A read by the line sensor 130a and a read image B read by the line sensor 130b. As shown in the figure, the read image A is data of the left region of the paper P including the ruled line group LA and the ruled line group LC, and the read image B is the paper P including the ruled line group LB and the ruled line group LC. This is the data of the area on the right side of As described above, the entire test pattern is read by the two line sensors 130a and 130b by overlapping the area of the ruled line group LC as a common area.

  Next, the average position calculation unit 204 calculates the average position of the ruled line group (step ST3, corresponding to the reading average position calculation step).

  FIG. 13 is a diagram for explaining the average position calculation processing in the average position calculation unit 204, and is a diagram illustrating an example of a ruled line group LA and a read image of the ruled line group LA.

  The upper part of FIG. 13 shows a ruled line group LA recorded at a recording resolution R1 (here, 1200 dpi). The ruled line group LA shown in the figure is composed of seven ruled lines L1 to L7, and each ruled line is recorded at intervals of 8 pixels (8 nozzle intervals). The average position (average coordinate in the main scanning direction) of the ruled line group LA in the main scanning direction is the position of the ruled line L4 as the center.

  The lower part of FIG. 13 shows an area corresponding to the ruled line group LA shown in the upper part of the read image A of the line sensor 130a with the reading resolution R2 (here, 500 dpi). Here, the position (reading position) of each pixel of the read image in the main scanning direction is 1, 2, 3,. As shown in the figure, the ruled line L1 is the S1 pixel at the reading position 1, the ruled line L2 is the S2 pixel at the reading position 5, the ruled line L3 is the S3 pixel at the reading position 8, and the ruled line L7 is the S7 pixel at the reading position 22. It corresponds to. That is, each ruled line position (read ruled line position) in the main scanning direction of the ruled line group LA in the read image A with the resolution R2 is a position of S1, S2, S3,.

  Here, the average position in the main scanning direction of the ruled line group LA in the read image A at the reading resolution R2 is obtained by averaging the read ruled line positions corresponding to the ruled lines L1 to L7, that is, the positions of the S1 to S7 pixels. . In the example shown in FIG. 13, the average position (reading average position) in the main scanning direction of the ruled line group LA in the read image A is 1, 5, 8, 11, 15, 18 which is the reading positions of the S1 to S7 pixels. , 22 is an average value of 11.429.

  Therefore, the position of the ruled line L4, which is the average position in the main scanning direction of the ruled line group LA on the test pattern, and the read average position of 11.429 can be associated with each other and handled as the same position.

  The average position calculation unit 204 reads the read image A from the image data storage unit 202, and calculates the read average position for the ruled line groups LA and LC as described above.

  Next, the resolution conversion unit 205 converts the resolution of the read image into the recording resolution based on the average reading position calculated in step ST3 (step ST4, corresponding to the resolution conversion process).

  When the image recording unit 100 ideally prints a test pattern and the imaging unit 130 ideally reads the test pattern, the interval (nozzle interval) of one pixel at the recording resolution R1 is R2 at the recording resolution R2. This corresponds to / R1 pixel. Here, since R1 = 1200 dpi and R2 = 500 dpi, it is 0.417 pixels.

  Further, as described above, the position of the ruled line L4, which is the average position in the main scanning direction of the ruled line group LA on the test pattern, can be handled as the same position. Therefore, on the read image, a dot row is recorded (nozzles are arranged) every 0.417 pixels from the read average position 11.429 of the ruled line group LA. By specifying all the nozzle positions in this way, it is possible to convert the read image to the recording resolution.

  However, in actuality, there is an influence of a deviation at the time of printing or reading, and the nozzle interval in the main scanning direction in the read image obtained by reading the test pattern may not be R2 / R1 pixels. Therefore, in this embodiment, resolution conversion is not performed on the read image at the ratio of R2 / R1, but on the basis of the average position of the ruled line groups LA and LC and the ratio of the number of nozzles therebetween.

  Since the average position of the ruled line group LA on the test pattern (recorded average position, the position of the ruled line L4 in the example of FIG. 13) and the record average position of the ruled line group LC are known, pixels existing between these two average positions The number (number of nozzles) can be calculated.

  In step ST3, the average read position of the ruled line groups LA and LC in the read image A in the main scanning direction is calculated. Therefore, the resolution of the read image can be converted into the recording resolution by using the average reading position of the ruled line groups LA and LC and the ratio of the number of nozzles described above.

That is, the read average position of the ruled line group LA in the read image A is AVA, the read average position of the ruled line group LC is AVC, and the nozzle between the average record value of the ruled line group LA and the record average position of the ruled line group LC on the test pattern. When the number is M, the distance L between the nozzles at the reading resolution R2 is
L = (AVC−AVA) / (M + 1) [pixel] (Equation 3)
It can be expressed as.

  Thus, resolution conversion can be performed based on the read average position of the ruled line groups LA and LC in the read image and the ratio of the number of nozzles existing between them.

  Similarly, for the read image B, the average position calculation unit 204 calculates the read average position for the ruled line groups LB and LC (step ST3), and the resolution conversion unit 205 determines each nozzle based on the calculated read average position. The position is calculated by converting the resolution (step ST4).

  Also, as shown in FIG. 12, the read image A and the read image B overlap the area of the ruled line group LC as a common area. Accordingly, by handling the read average position of the ruled line group C of the read image A and the read average position of the ruled line group C of the read image B, the read image A and the read image B are read by one test pattern. It can also be processed as an image.

  As described above, if the nozzle position in the read image can be specified, the correction value may be calculated by a known method.

  In the present embodiment, the density calculation unit 206 calculates an average value of density data (reading gradation values) for each nozzle (step ST5), and the correction value calculation unit 207 calculates a density unevenness correction value H for each nozzle ( Step ST6, corresponding to a correction value acquisition step).

  For the common area of the read image A and the read image B, the density unevenness correction value H can be calculated based on each read image. Accordingly, the density unevenness correction value H in this region may be calculated by averaging the density unevenness correction values calculated based on the respective read images, or a weighted average according to the distance between the read images A and B. You may calculate by performing (slope average).

  As described above, a ruled line group formed by nozzles selected at equal intervals is formed together with a strip-shaped test pattern in which dot rows formed by all nozzles are arranged in the main scanning direction, and reading is performed. By calculating the average position of the ruled line group at the resolution and converting the resolution based on the calculated average position of the ruled line group, each nozzle position can be specified by the recording resolution in the read image having a resolution lower than the recording resolution. .

Here, the interval (nozzle interval) d between the ruled lines forming one ruled line group is:
d = R1 / R2 × k + h (Formula 1)
It is preferable to satisfy. Note that k is an integer greater than 1, and h is an integer that satisfies the condition of 0 <h <R1 / R2.

The number N of ruled lines forming one ruled line group is
N = R1 / R2 × k + 1 (Formula 2)
It is preferable to satisfy. Here, k is the same number as in (Formula 1).

  Further, the position of each ruled line group is not particularly limited as long as it is included in at least one area read at a time. If the test pattern is read by dividing some areas into a plurality of areas, at least two are included in each divided area, and at least one of them is formed in an area overlapping with other areas. Preferably it is. A ruled line group may be formed over the entire range in the main scanning direction.

  In this embodiment, the density unevenness correction value H for each nozzle is acquired after resolution conversion of the read image. However, the correction value calculation unit 207 calculates the density unevenness correction value for each reading resolution, and uses the calculated density unevenness correction value. A mode of converting the resolution to the correction value of the recording resolution is also possible.

<Second Embodiment>
In the first embodiment, the test chart is automatically read using an inline sensor. However, a mode in which the user manually reads the test chart using a flatbed scanner or the like after recording the test chart is also possible.

  FIG. 14 is a diagram illustrating an example of a method for reading the test pattern recorded on the paper P by the flatbed scanner 300. The flatbed scanner 300 includes a reading sensor (not shown) that moves in the left-right direction of the drawing while facing the document, and the reading resolution in the direction orthogonal to the moving direction (up-down direction in the drawing) is higher than the recording resolution of the test pattern. It shall be low. FIG. 14 shows a view from the side of the reading sensor, and the reading range is indicated by a broken line 302.

  As shown in FIG. 14A, the paper P on which the test pattern is recorded is set so that the end portion (one end portion in the main scanning direction) matches the reference position of the reading range. A region including the ruled line group LA and the ruled line group LC is read. The read image obtained as a result is data of the left region in the main scanning direction of the paper P including the ruled line group LA and the ruled line group LC. Further, as shown in FIG. 14B, an area including the ruled line group LB and the ruled line group LC in the test pattern is set so that the other end of the paper P is aligned with the opposite side of the reference position of the reading range. Read. The read image obtained as a result is data of the area on the right side in the main scanning direction of the paper P including the ruled line group LB and the ruled line group LC.

  As described above, the two read images obtained by the reading method illustrated in FIG. 14 are the same data as the read image A and the read image B of the first embodiment. Therefore, in order to calculate the density unevenness correction value H of each nozzle, the processing after step ST3 in the flowchart shown in FIG.

  However, in a general flatbed scanner, a cover that covers the document table is provided in order to prevent external light from being reflected in an output image, and the reading method shown in FIG. 14 may not be used.

  FIG. 15 is a diagram illustrating another example of a method for reading the test pattern recorded on the paper P by the flatbed scanner 300.

  As shown in FIG. 15A, the paper P on which the test pattern is recorded is set so that one end thereof matches the reference position of the reading range, and the ruled line group LA and the ruled line group LC in the test pattern are set. Read the containing area. The read image thus obtained is data of the left region in the main scanning direction of the paper P including the ruled line group LA and the ruled line group LC, and is the same data as the read image A of the first embodiment.

  Further, as shown in FIG. 15B, the sheet P is reversed 180 degrees from the state of FIG. 15A, and the other end of the sheet P is set so as to match the reference position of the reading range. An area including the ruled line group LB and the ruled line group LC is read from the pattern. The read image obtained in this way is data of the area on the right side in the main scanning direction of the paper P including the ruled line group LB and the ruled line group LC, and is the data inverted 180 degrees from the read image B of the first embodiment. .

  Therefore, one of the two scanned images obtained by the scanning method shown in FIG. 15 is the same data as the scanned image of the first embodiment, and the other is 180 degrees inverted from the scanned image of the first embodiment. It becomes data. Therefore, in order to calculate the density unevenness correction value H of each nozzle, it is necessary to invert the data inverted by 180 degrees. Thereby, the process after step ST3 of the flowchart shown in FIG. 9 can be used.

  Note that which of the two scanned images is inverted by 180 degrees can be determined from the arrangement of the strip patterns PT1, PT2, and PT3 and the ruled line groups LA, LB, and LC. Therefore, when it is determined that the read data is inverted, the density data conversion unit 203 inverts the read data and converts it into a read image.

  Further, depending on the size of the test pattern, the entire region of the test pattern may not be read by two reading operations. In this case, it is also possible to divide and read three times or more.

  FIG. 16 is a diagram illustrating an example of a method of reading the test pattern recorded on the paper P by the flatbed scanner 300 in three steps. The test pattern in this example includes four ruled line groups LA, LB, LC, and LD.

  As shown in FIG. 16A, the paper P on which the test pattern is recorded is set so that one end in the main scanning direction matches the reference position of the reading range, and the ruled line group LA and the ruled line in the test pattern are set. Read the area containing the group LC. The read image obtained as a result is data of the left region in the main scanning direction of the paper P including the ruled line group LA and the ruled line group LC.

  Also, as shown in FIG. 16B, the paper P is inverted 180 degrees from the state of FIG. 16A, and the other end of the paper P is set so as to match the reference position of the reading range. An area including the ruled line group LB and the ruled line group LD in the pattern is read. The read image obtained as a result is data of the area on the right side in the main scanning direction of the paper P including the ruled line group LB and the ruled line group LD.

  Further, as shown in FIG. 16C, the paper P is rotated 90 degrees from the state of FIG. 16B so that one end of the paper P in the sub-scanning direction matches the reference position of the reading range. And a region including the ruled line group LC and the ruled line group LD in the test pattern is read. The read image obtained as a result is data of a region near the center in the main scanning direction of the paper P including the ruled line group LC and the ruled line group LD.

  In this way, three read images are obtained by the reading method shown in FIG. By unifying the orientations of these three scanned images, the density unevenness correction value H of each nozzle can be calculated by the same processing as before.

  For example, in order to unify the orientation of the read image data in FIG. 16A, the read image data in FIG. 16B is inverted by 180 degrees, and the read image data in FIG. 16C is rotated by 90 degrees. do it. Which of the three scanned images is inverted 180 degrees and which is rotated 90 degrees can be determined from the arrangement of the strip patterns PT1, PT2, PT3 and the ruled line groups LA, LB, LC. it can. Therefore, if the density data conversion unit 203 determines that the read data is inverted 180 degrees or rotated 90 degrees, the density data conversion unit 203 performs rotation processing so that all the read data are in the same direction, and then converts the read data into a read image. .

  Further, by handling the average position of the ruled line group LC of the read image in FIG. 16A and the average position of the ruled line group LC of the read image in FIG. It can be processed as a read image of the test pattern. Similarly, from the average position of the ruled line group LD of the read image in FIG. 16B and the average position of the ruled line group LD of the read image in FIG. 16C, these two read images are read as one test pattern read image. Can be processed as As a result, the read image of FIG. 16A, the read image of FIG. 16B, and the read image of FIG. 16C can be processed as a read image of one test pattern. As described above, even when the test pattern is read in three or more times, it is possible to perform processing as one test pattern data.

  When the user reads the edge of the paper P along the edge of the reading area 302 of the flatbed scanner 300 as in the present embodiment, the test pattern may be read with an inclination. Therefore, it is preferable to perform rotation processing on the read image. For this rotation processing, a ruled line group of test patterns can be used, and the detailed method thereof can be preferably the method described in Patent Document 1.

<Other variations>
Up to this point, the line head corresponding to the paper width has been described as an example, but a shuttle type head in which the recording head reciprocates in a direction orthogonal to the paper transport direction can also be used. In the shuttle type head, nozzles that form adjacent dot rows may differ depending on the drawing method (scanning method) even if the image pieces are formed by the same nozzle. In such a case, it is necessary to set the density unevenness correction value H for each row region because the density unevenness cannot be suppressed simply by the correction value associated with the nozzles.

  In this case, the density data converter 203 calculates density data for each row area from the inspection image data, the density calculator 206 calculates the average value of the density data for each row area, and the correction value calculator 207 The density unevenness correction value H for each row area may be calculated based on the density data for each row area.

  The technical scope of the present invention is not limited to the scope described in the above embodiment. The configurations and the like in the respective embodiments can be appropriately combined among the respective embodiments without departing from the spirit of the present invention.

  In the above embodiment, the configuration of CMYK standard colors (four colors) is exemplified, but the combination of ink colors and the number of colors is not limited to this embodiment, and light ink, dark ink, and special color ink are used as necessary. May be added. For example, it is possible to add an inkjet head that discharges light-colored ink such as light cyan and light magenta, and the arrangement order of the color heads is not particularly limited.

  In the above embodiment, the case where the present invention is applied to an ink jet recording apparatus has been described. However, the scope of the present invention is not limited to this. That is, the present invention relates to an image recording apparatus of a type other than an ink jet recording apparatus, for example, a thermal transfer recording apparatus including a recording head using a thermal element as a recording element, and an LED electrophotography including a recording head including an LED element as a recording element. The present invention can also be applied to a printer and a silver halide photographic printer having an LED line exposure head.

  DESCRIPTION OF SYMBOLS 10 ... Inkjet recording device, 100 ... Image recording part, 110 ... Image recording drum, 120C, 120M, 120Y, 120K, 120 ... Inkjet head, 130 ... Imaging part, 130a, 130b ... Line sensor, 200 ... Correction value acquisition part, DESCRIPTION OF SYMBOLS 201 ... Test pattern memory | storage part, 202 ... Image data memory | storage part, 204 ... Average position calculation part, 205 ... Resolution conversion part, 251 ... Nozzle, 300 ... Flatbed scanner, 302 ... Reading range, LA, LB, LC, LD ... Ruled line group, P ... paper, PT1, PT2, PT3 ... band pattern

Claims (11)

A plurality of dot rows along the first direction are formed in a second direction orthogonal to the first direction while relatively moving a recording head having a plurality of recording elements and a recording medium in the first direction. A test pattern having a row area and a group of ruled lines in which a plurality of ruled lines along the first direction are formed at equal intervals in a second direction orthogonal to the first direction is formed on the recording medium. A test pattern recording process for recording at a resolution of
A read gradation value acquisition step of reading the recorded test pattern and acquiring a read gradation value of a second resolution lower than the first resolution;
A reading average position calculating step of calculating a reading average position in the second direction of the ruled line group based on an acquisition result of the reading gradation value acquiring step;
By associating the calculated reading average position with the average position of the ruled line group on the test pattern recorded on the recording medium, the reading gradation value of the second resolution is converted to the reading gradation value of the first resolution. A resolution conversion process for converting the resolution to
A correction value acquisition step of acquiring a density unevenness correction value for each recording element based on the read gradation value subjected to resolution conversion;
A correction value acquisition method comprising: The test pattern recording step records the test pattern in a first size,
The reading gradation value acquisition step includes a first area that is a partial area of the recorded test pattern, and a partial area of the recorded test pattern that is at least a part of the first area. And a second area each including a second area smaller than the first size,
The correction value acquisition method according to claim 1, wherein the test pattern includes the ruled line group in the first area and the second area. The test pattern has a first ruled line group in a region that is the first region and not included in the second region, and is the second region and not included in the first region. Having a second ruled line group in the area, and having a third ruled line group in the first area and included in the second area,
The reading average position calculating step includes a first reading average position of the first ruled line group, a second reading average position of the second ruled line group, and a third reading average of the third ruled line group. Position and
In the resolution conversion step, the calculated distance between the first reading average position and the third reading average position, the average position of the first ruled line group on the test pattern recorded on the recording medium, and the first reading The resolution of the read gradation value of the first area is converted based on the distance between the average position of the three ruled line groups and the calculated second read average position and third read average position And the read gradation value of the second area based on the distance between the average position of the second ruled line group and the average position of the third ruled line group on the recorded test pattern. The correction value acquisition method according to claim 2, wherein resolution conversion is performed. In the correction value acquisition step, the density unevenness correction value of the first area and included in the second area is read as the reading gradation value in the first area and the reading in the second area. The correction value acquisition method according to claim 3, wherein the correction value is calculated based on an average value of gradation values.   The calculated reading average position is associated with the average position of the ruled line group on the test pattern recorded on the recording medium, and the position of the row region is specified according to the ratio of the first resolution and the second resolution. The correction value acquisition method according to claim 1, wherein the resolution conversion of the read gradation value of the second resolution into the read gradation value of the first resolution is performed. The interval d between the plurality of ruled lines in the ruled line group is R1 as the first resolution, R2 as the second resolution, k is an integer greater than 1, and h is an integer satisfying the condition of 0 <h <R1 / R2. When
d = R1 / R2 × k + h
The correction value acquisition method according to claim 1, wherein: The number N of the plurality of ruled lines in the ruled line group is:
N = R1 / R2 × k + 1
The correction value acquisition method according to claim 6, wherein:   In the reading gradation value acquisition step, the one end of the recording medium on which the test pattern is recorded in the second direction is aligned with the reference portion of the flat bed scanner. In the state where the first area is read, the recording medium on which the test pattern is recorded is reversed, and the other end of the recording medium in the second direction is aligned with the reference portion. The correction value acquisition method according to any one of claims 2 to 4, further comprising a reading step of causing the flatbed scanner to read the second region.   The correction value acquisition method according to claim 8, wherein the reading step reverses the read data when it is determined that the read data acquired from the flatbed scanner is a result of reading the second area.   5. The correction value acquisition according to claim 2, wherein the reading gradation value acquisition step reads the first area by a first scanner and reads the second area by a second scanner. 6. Method. A the density unevenness correction value acquired by the correction value acquisition method according to any one of claims 1 to 10, wherein the density unevenness correction value of the recording elements corresponding to each pixel constituting the image data To correct the gradation value indicated by each pixel,
An image recording apparatus for recording an image on the recording medium by the recording element while relatively moving the recording element and the recording medium in the first direction based on the corrected gradation value.

Images