Printing apparatus and printed image inspection method

Abstract

To provide a print image inspection device and the like that can faithfully image print images and accurately inspect the print images, even if printing continues for a long time.SOLUTION: A printing device is provided with a colorimeter 40 for calibrating imaging by an inline scanner 30 for inspecting a print image. The printing device updates a correction coefficient LUT for imaging calibration based on imaging data and colorimetric data for calibration obtained by imaging by the inline scanner 30 for a test pattern image 51 formed on a paper 5 and colorimetry by the colorimeter 40 during printing operation, and calibrates imaging by the inline scanner 30 in real time based on the correction coefficient LUT.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a printed image inspection apparatus for inspecting a printed image and a printing apparatus including the same.

Background Art

[0002] There are known a printed image inspection apparatus that inspects a printed image formed on a substrate such as printing paper in a printing apparatus based on imaging data obtained by imaging the printed image with an imaging unit such as a CIS (Contact Image Sensor), and a printing apparatus including such a printed image inspection apparatus. In such a printed image inspection apparatus, in order to maintain good inspection accuracy of the printed image, it is necessary to appropriately calibrate imaging by the CIS as the imaging unit.

[0003] On the other hand, in a conventional printed image inspection apparatus, the white paper portion of the paper as a substrate is used before printing, and imaging is performed on the white paper portion with the light source turned off and with the light source turned on, and thereby calibration of the CIS is performed.

[0004] In addition, in relation to the printed image inspection apparatus and the like disclosed in the present application, the following Patent Document 1 (Japanese Patent Application Laid-Open No. 2013-184442) discloses a recording apparatus including a first sensor unit including a density sensor and a holding unit that detachably holds a second sensor unit including a spectrocolorimetric sensor, and having a function of performing color calibration. The control unit in this recording apparatus enables execution of calibration using the second sensor unit when the second sensor unit is held, and enables execution of calibration using the first sensor unit when the second sensor unit is not held by the holding unit. In this document, the color calibration function is defined as a function of recording a color patch on a recording medium by a print head, then performing color measurement of the color patch, and performing color correction processing of input image data based on the color measurement result (paragraph

[0003] ).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] When performing calibration of imaging by an imaging unit (CIS) for printed image inspection by turning off and on the light source as described above, printed image inspection cannot be performed during the period when the light source is off. Also, when imaging a paper white portion for calibration during printing, there is no paper white portion large enough to cover the CIS serving as an in-line scanner. From such a situation, it is not practical to perform calibration of imaging by the CIS during printing.

[0007] On the other hand, the imaging sensitivity of the CIS is affected by factors such as temperature. Therefore, when printing continues for a long time, the imaging sensitivity of the CIS may change due to environmental changes such as temperature changes, and in some cases, a printed image may not be captured faithfully.

[0008] Therefore, it is desired to provide a printed image inspection apparatus or the like that can capture a printed image faithfully and inspect the printed image accurately even when printing continues for a long time.

Means for Solving the Problems

[0009] A first aspect of the present invention is A printing apparatus having a function of inspecting a printed image as follows, A printing mechanism for forming a printed image, an imaging unit that captures the printed image, a colorimeter that measures the color of all or part of the printed image, a calibration unit that calibrates the imaging by the imaging unit, a determination unit that determines the quality of the printed image, The printing mechanism, controlling the imaging unit, the colorimeter, and the calibration unitA control unit and comprises The printing mechanism includes A transport mechanism for transporting a substrate, A print head for printing on the printing surface of the substrate, The control unit is Controls the print head and the transport mechanism so that a printed image is formed on the substrate, When a test pattern image for calibrating the imaging by the imaging unit is formed as part or all of the printed image, the imaging unit captures the test pattern image to generate test pattern imaging data, the colorimeter measures the color of the test pattern image to generate color measurement data, and the calibration unit generates imaging calibration data based on the test pattern imaging data and the color measurement data. The imaging unit, the colorimeter, and the calibration unit are controlled, and after the generation of the imaging calibration data, the calibration unit is controlled so as to correct target imaging data generated by the imaging unit capturing a target printed image formed based on print data representing an input image to be printed, based on the imaging calibration data, the determination unit determines the quality of the target printed image based on the target imaging data corrected by the calibration unit And The control unit During the printing operation from the start of printing on the substrate by the printing mechanism to the end of printing on the substrate, The imaging unit newly generates the test pattern imaging data at predetermined time intervals, The colorimeter newly generates the color measurement data at predetermined time intervals, The calibration unit newly generates the imaging calibration data at predetermined time intervals based on the newly generated test pattern imaging data and the color measurement data, and updates the imaging calibration data for correcting the target imaging data, Controls the print head, the transport mechanism, the imaging unit, the colorimeter, and the calibration unit .

[0010] A second aspect of the present invention is In a first aspect of the present invention, the transport mechanism includes first and second transport rollers around which the substrate on which the printed image is formed is wound so as to change the transport direction, the imaging unit is arranged such that the imaging surface of the imaging unit faces the printed surface of the portion of the substrate in contact with the first transport roller, The colorimeter is arranged such that the color detection surface of the colorimeter faces the printed surface of the portion of the base material that is in contact with the second conveying roller.

[0011] A third aspect of the present invention is a printed image inspection method for inspecting a printed image formed by a printing apparatus, an imaging step of imaging the printed image, a color measurement step of measuring all or part of the printed image, the In the imaging step a calibration step of calibrating the imaging, a determination step of determining the quality of the printed image and comprising, when a test pattern image for calibrating the imaging in the imaging step is formed as part or all of the printed image, in the imaging step, test pattern imaging data is generated by imaging the test pattern image, in the color measurement step, color measurement data is generated by measuring the test pattern image, in the calibration step, imaging calibration data is generated based on the test pattern imaging data and the color measurement data, after the generation of the imaging calibration data, in the calibration step, target imaging data generated by imaging a target printed image formed based on print data representing an input image to be printed in the imaging step is corrected based on the imaging calibration data, in the determination step, the quality of the target printed image is determined based on the target imaging data corrected in the calibration step, the printing apparatus Of the substrate during the printing operation from the start of printing on the printing apparatus to the end of printing on the base material, at predetermined time intervals, the imaging step of generating test pattern imaging data by imaging the test pattern image is executed, at predetermined time intervals, the color measurement step of generating the color measurement data by measuring the test pattern image is executed, At a predetermined time interval, the calibration step in which imaging calibration data is generated based on the test pattern imaging data and the colorimetric data is executed, and the imaging calibration data for correcting the target imaging data is updated.

[0012] Other aspects of the present invention will be apparent from the above aspects of the present invention and the descriptions of the embodiments and their modifications described below, and thus the description thereof will be omitted.

Advantages of the Invention

[0013] In the first aspect of the present invention, when a test pattern image for calibrating imaging by an imaging unit is formed as part or all of a printed image, the imaging unit captures the test pattern image to generate test pattern imaging data, and a colorimeter measures the color of the test pattern image to generate colorimetric data, and imaging calibration data is generated based on the test pattern imaging data and the colorimetric data. After the generation of this imaging calibration data, when a target printed image formed based on print data representing an input image to be printed is captured by the imaging unit to generate target imaging data, the target imaging data is corrected based on the imaging calibration data, and the quality of the target printed image is determined based on the corrected target imaging data. More specifically, during the printing operation from the start of printing on the substrate by the printing mechanism to the end of printing on the substrate, the imaging unit newly generates the test pattern imaging data at predetermined time intervals, the colorimeter newly generates the color measurement data at predetermined time intervals, the imaging calibration data is newly generated at predetermined time intervals based on the newly generated test pattern imaging data and the color measurement data, and the imaging calibration data for correcting the target imaging data is updated. According to such a configuration, even during the printing operation, when the test pattern image is formed as a printed image, by calibrating the imaging by the imaging unit using the colorimetric data, even if the imaging sensitivity of the imaging unit fluctuates due to environmental changes such as temperature changes during the printing operation, accurate imaging calibration corresponding to the fluctuation can be performed in real time. As a result, when the density of the target printed image formed on the substrate fluctuates during the printing operation, the density fluctuation can be accurately detected based on the imaging data of the target printed image by the imaging unit.

[0014] In a second aspect of the present invention, in a printing apparatus having a function of inspecting a printed image, a transport mechanism for transporting a substrate includes first and second transport rollers around which the substrate having the printed image formed thereon is wound so as to change the transport direction. An imaging unit for inspecting the printed image is arranged such that an imaging surface of the imaging unit faces a printed surface of a portion of the substrate that is in contact with the first transport roller. A colorimeter for imaging calibration is arranged such that a color detection surface of the colorimeter faces a printed surface of a portion of the substrate that is in contact with the second transport roller. According to such an arrangement configuration of the imaging unit and the colorimeter, fluctuations in the imaging position and color measurement position due to fluttering or cockling during the transport of the substrate are prevented, and stable and good imaging and color measurement are performed on the printed image formed on the substrate. As a result, the imaging by the imaging unit can be calibrated more accurately and the target printed image can be imaged more faithfully, so that the effects obtained by the first aspect of the present invention can be enhanced.

[0015] According to a third aspect of the present invention, the same effects as those of the first aspect of the present invention can be obtained.

[0016] Regarding the effects of other aspects of the present invention, since they are clear from the description of the effects of the above aspects of the present invention and the effects of the following embodiments and their modifications, the description is omitted.

Brief Description of the Drawings

[0017]

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Embodiments for Carrying Out the Invention

[0018] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0019] <1. First Embodiment> <1.1 Overall Configuration> FIG. 1 is a schematic diagram showing the configuration of an inkjet printing apparatus 10 according to a first embodiment of the present invention. This printing apparatus 10 includes a paper feeding unit 202 that unwinds and supplies a recording paper (hereinafter simply referred to as "paper") 5 as a long substrate from a roll-shaped printing substrate (hereinafter simply referred to as "substrate"), a first drive roller 203 for transporting the paper 5 into the printing mechanism 200, a plurality of support rollers 204 for transporting the paper 5 inside the printing mechanism 200, a recording unit 205 that discharges ink onto the paper 5 for printing, a drying unit 206 that dries the printed paper 5, a second drive roller 207 for outputting the paper 5 from inside the printing mechanism 200, and a paper winding unit 208 that winds up the printed paper 5. In addition, an imaging support roller 204a and a colorimetric support roller 204b are provided to enable stable and good imaging and colorimetry of the printed image formed on the paper 5 by the recording unit 205 while having the function of a support roller (details will be described later).

[0020] The first drive roller 203, the support rollers 204, 204a, 204b, and the second drive roller 207 constitute a transport mechanism for moving the paper 5. The recording unit 205 includes first to fourth print head rows 205k, 205c, 205m, 205y that discharge K (Black), C (Cyan), M (Magenta), and Y (Yellow) inks, respectively. Inside the printing mechanism 200, an in-line scanner 30 as an imaging unit that images the printed image formed on the paper 5 by the recording unit 205 and a colorimeter 40 that measures the color of a predetermined portion in the printed image are included. The imaging data obtained from the in-line scanner 30 and the colorimetric data obtained from the colorimeter 40 are sent to the control unit 100.

[0021] <1.2 Configuration of Control Unit> FIG. 2 is a block diagram showing the hardware configuration of the control unit 100 in the inkjet printing apparatus 10. The control unit 100 includes a main body 11, an auxiliary storage device 12, a display unit 14, and an operation unit 15. The main body 11 includes a CPU 111, a memory 112, a disk interface unit 113, a display control unit 115, an input interface unit 116, an image processing unit 117, a print execution control unit 118, an imaging colorimetry control unit 119, and a network interface unit 120. The CPU 111, the memory 112, the disk interface unit 113, the display control unit 115, the input interface unit 116, the image processing unit 117, the print execution control unit 118, the imaging colorimetry control unit 119, and the network interface unit 120 are connected to each other via a system bus. The auxiliary storage device 12 is connected to the disk interface unit 113. The display unit 14 is connected to the display control unit 115. The operation unit 15 including a keyboard, a mouse, etc. is connected to the input interface unit 116. The network 3 is connected to the network interface unit 120, and the control unit 100 is connected to a host device or the like via this network 3. The auxiliary storage device 12 is a magnetic disk device or the like. The display unit 14 is a liquid crystal display or the like. The display unit 14 is used to display information desired by the operator. The operation unit 15 is used for the operator to input instructions to the inkjet printing apparatus 10.

[0022] The auxiliary storage device 12 stores a control program 17 for generating print data from the input manuscript data received via the network 3 and causing the printing mechanism 200 to print the image represented by the print data. As described above, the printing mechanism 200 is provided with an in-line scanner 30 and a colorimeter 40 as imaging units for respectively imaging and measuring the color of the printed image formed on the paper 5. In addition to the print control process 18a for generating print data and causing the printing mechanism 200 to print an image as described above, the control program 17 is a program for performing an inspection control process 18b for determining the quality of the printed image using the in-line scanner 30 and the colorimeter 40. The auxiliary storage device 1 also stores a correction coefficient LUT 19, which will be described later, used in the inspection control process 18b. The CPU 111 reads and executes the control program 17 stored in the auxiliary storage device 12 in the memory 112, thereby realizing the function of forming a printed image on the paper 5 and the function of determining the quality of the printed image in the inkjet printing device 10. The memory 112 includes a RAM (Random Access Memory) and a ROM (Read Only Memory). The memory 112 functions as a work area for the CPU 111 to execute the control program 17. Also, when the control program 17 is executed, the correction coefficient LUT 19 is also stored in the memory 112 as a work area and accessed in the inspection control process 18b. The details of the correction coefficient LUT 19 will be described later.

[0023] The image processing unit 117 generates bitmap-formatted print data by performing rasterization processing on the input manuscript data described in the page description language under the control of the CPU 111 that executes the control program 17. The print execution control unit 118 functions as an interface for the CPU 111 that executes the control program 17 to control each part of the printing mechanism 200. The imaging color measurement control unit 119 functions as an interface for the CPU 111 that executes the control program 17 to control the in-line scanner 30 and the colorimeter 40 that respectively image and measure the color of the printed image formed on the paper 5.

[0024] <1.3 In-line Scanner, Colorimeter, and Their Arrangement Configurations> FIG. 3 is a plan view for explaining the arrangement configuration of the in-line scanner 30 and the colorimeter 40 as imaging units in the present embodiment, and FIG. 4 is a side view (seen from the left side in FIG. 3) for explaining the arrangement configuration of the in-line scanner 30 and the colorimeter 40 in the present embodiment.

[0025] The in-line scanner 30 includes a plurality of imaging elements 31 arranged over a length corresponding to the full width of the paper 5 in the width direction of the paper 5 as a base material (the width direction perpendicular to the conveyance direction of the paper 5, hereinafter referred to as the "paper width direction") (see FIG. 5 described later). In the present embodiment, a CIS (Contact Image Sensor) is used as the in-line scanner 30, but it is not limited to CIS such as a CCD (Charge Coupled Device). An in-line scanner such as CIS uses a color filter to acquire RGB luminance values and outputs imaging data consisting of the RGB luminance values.

[0026] On the other hand, the colorimeter 40 outputs values such as CMYK density values and Lab values as colorimetric values, and can output absolute color information conforming to standards such as CIE (International Commission on Illumination) as colorimetric values without being affected by the environment such as temperature. Further, this colorimeter 40 spot-measures a small area at a predetermined position in the printed image, and is provided with a moving mechanism 45 for moving the colorimeter to the position to be colorimetrically measured in the printed image. This moving mechanism 45 is configured such that the colorimeter 40 can move at least over the full width of the paper 5 in the paper width direction. This moving mechanism 45 is composed of, for example, a guide member for guiding the colorimeter 40, a feed mechanism such as a rack and pinion or a feed screw for moving the colorimeter 40, and a motor or the like as a drive source for the feed mechanism.

[0027] As described above, the conveyance mechanism includes the imaging support roller 204a and the color measurement support roller 204b. As shown in FIG. 4, the sheet 5 is wound around such that the conveyance direction of the sheet 5 on which a printed image is formed by the recording unit 205 changes at each of the imaging support roller 204a and the color measurement support roller 204b. That is, the conveyance mechanism is configured such that the conveyance direction of the sheet 5 switches from the vertical direction to the horizontal direction at the imaging support roller 204a and switches from the horizontal direction to the vertical direction at the color measurement support roller 204b. Instead of this, the conveyance mechanism may be configured such that, conversely, the conveyance direction of the sheet 5 switches from the horizontal direction to the vertical direction at the imaging support roller 204a and switches from the vertical direction to the horizontal direction at the color measurement support roller 204b.

[0028] In the present embodiment, the in-line scanner 30 as the imaging unit is arranged such that the imaging surface of the in-line scanner 30 faces the printed surface of the portion of the sheet 5 that is in contact with the imaging support roller 204a, and the colorimeter 40 is arranged such that the color detection surface of the colorimeter 40 faces the printed surface of the portion of the sheet 5 that is in contact with the color measurement support roller 204b. Here, the printed surface refers to the surface of the two surfaces of the sheet 5 on which a printed image is formed by the recording unit 205. According to such an arrangement configuration, fluctuations in the imaging position and the color measurement position due to fluttering or cockling during sheet conveyance are prevented, and stable and good imaging and color measurement of the printed image formed on the sheet 5 become possible.

[0029] Specifically, as shown in FIG. 4, the in-line scanner 30 is arranged on a vertical line passing through the central axis of the imaging support roller 204a such that its imaging surface is perpendicular to the vertical line. Preferably, the in-line scanner 30 is arranged such that its imaging surface faces the printing surface at the central portion in the circumferential direction of the imaging support roller 204a in the portion of the sheet 5 that is in contact with the imaging support roller 204a. Also, the colorimeter 40 is arranged such that its color detection surface faces the printing surface at the central portion in the circumferential direction of the color measurement support roller 204b in the portion of the sheet 5 that is in contact with the color measurement support roller 204b. From this perspective, as shown in FIG. 4, the colorimeter 40 is arranged on an oblique line that extends in an oblique direction with respect to the vertical direction from the central axis within a plane perpendicular to the central axis of the color measurement support roller 204b. It is preferable that the angle formed by the oblique line and the vertical direction is in the range of 30 degrees to 60 degrees.

[0030] In the examples shown in FIGS. 1 and 4, the conveyance direction of the sheet 5 switches between the vertical direction and the horizontal direction for each of the imaging support roller 204a and the color measurement support roller 204b. However, even if the configuration is not such that the conveyance direction of the sheet 5 switches between the vertical direction and the horizontal direction, it suffices if the conveyance direction of the sheet 5 switches for each of the imaging support roller 204a and the color measurement support roller 204b. Assuming such a configuration of the conveyance mechanism, the imaging surface of the in-line scanner 30 is arranged to face the printing surface in the portion of the sheet 5 that is in contact with the imaging support roller 204a, and the colorimeter 40 is arranged such that its color detection surface faces the printing surface in the portion of the sheet 5 that is in contact with the color measurement support roller 204b. In this way, basically the same effects as described above can be obtained.

[0031] <1.4 Test Pattern Image for Imaging Calibration> As described above, the printing apparatus 10 according to the present embodiment includes an in-line scanner 30 and a colorimeter 40, and performs not only printing control processing 18a but also inspection control processing 18b based on a control program 17. Thereby, the printed image formed on the sheet 5 in the printing control processing 18a is imaged by the in-line scanner 30 to generate imaging data, and the quality of the printed image is determined based on the imaging data. In order to maintain good accuracy (inspection accuracy) of such determination of the quality of the printed image, imaging by the in-line scanner 30 is calibrated using color measurement data by the colorimeter 40. For this calibration, imaging by the in-line scanner 30 and color measurement by the colorimeter 40 are performed on a test pattern image for calibration, such as a calibration patch. Hereinafter, such a test pattern image will be described with reference to FIGS. 5 to 8. Note that among the test pattern images shown in FIGS. 5 to 8, the test pattern images shown in FIGS. 5 and 7 can be used in the present embodiment, while the test pattern images shown in FIGS. 6 and 8 are used in a second embodiment described later.

[0032] FIG. 5 is a schematic diagram showing a first example of a test pattern image to be read for calibration of imaging by the in-line scanner 30 (hereinafter also simply referred to as "imaging calibration") together with the in-line scanner 30 and the colorimeter 40. In this example, after a predetermined test pattern image 51 as shown in FIG. 5 is formed as a printed image on the sheet 5 by the recording unit 205, the in-line scanner 30 images a predetermined portion of the primary color in the test pattern image 51 as a calibration patch, thereby generating test pattern imaging data, and the colorimeter 40 measures the color of the calibration patch, thereby generating colorimetric data. Based on these test pattern imaging data and colorimetric data, imaging calibration data for calibrating the imaging by the in-line scanner 30 is generated (details will be described later). The primary colors are Y (yellow), M (magenta), and C (cyan) as the primary colors in subtractive color mixing. As shown in FIG. 5, this primary color test pattern image 51 is arranged in order (51a, 51b,..., 51n) from the image with the highest density, with the images formed by the recording unit 205 at the same density across the entire width direction. Note that a secondary color or tertiary color patch may be used instead of the primary color patch as the calibration patch. However, in this case, a color space conversion is required in the generation of the imaging calibration data and the calibration of the imaging based on the imaging calibration data (details will be described later).

[0033] FIG. 6 is a schematic diagram showing a second example of a test pattern image to be read for calibration of imaging by the in-line scanner 30 together with the in-line scanner 30 and the colorimeter 40. In this example, from among print images (hereinafter referred to as “target print images”) formed on the sheet 5 by the recording unit 205 based on print data generated from input data, for example, a target print image 50 as shown in FIG. 6, a test pattern image for calibration of imaging by the in-line scanner 30 is selected (hereinafter, this selected image is referred to as “selected partial image” or simply “partial image”). This target print image 50 consists of a partial image 511 and a real image 512 (an image to be a printed matter after the partial image 511 is cut out from the sheet 5). The partial image 511 selected from among the target print images 50 is imaged by some imaging elements in the in-line scanner 30 as a calibration patch, and the colorimeter 40 is moved to a position where color measurement of the partial image 511 is possible to perform color measurement, whereby test pattern imaging data and color measurement data are generated. Based on these test pattern imaging data and color measurement data, imaging calibration data for calibrating imaging by the in-line scanner 30 is generated. Here, the partial image 511 selected from the target print image 50 needs to satisfy the following two conditions. (1) It is a pattern having a width wider than the minimum reading width of the in-line scanner 30 and the colorimeter 40 (2) Ensure a number of solid patterns corresponding to the number of patches required for calibration (calibration) of the CIS as the in-line scanner 30 as the partial image 511 Note that the selection of the partial image 511 may be automatically performed according to a predetermined algorithm based on the print data, or may be performed based on a predetermined input operation.

[0034] FIG. 7 is a schematic diagram showing a third example of a test pattern image to be read for calibration of imaging by the in-line scanner 30 together with the in-line scanner 30 and the colorimeter 40. In this example, after a test pattern image 51 for shading correction as shown in FIG. 7 is formed as a printed image on the sheet 5 by the recording unit 205, the in-line scanner 30 images the test pattern image 51 to generate test pattern imaging data. Further, correction data for shading correction is generated based on this test pattern imaging data. Here, shading correction is to correct print data and the like according to the characteristics of each print head so as to suppress density unevenness of the printed image due to variations in the ink ejection amount ejected from each print head in the recording unit 205. Note that variations in imaging sensitivity among the imaging elements included in the in-line scanner 30 are eliminated by a calibration process performed using the paper white before the start of printing, as will be described later (see step S14 in FIG. 9). The calibration here is a relative calibration for eliminating differences in characteristics among the elements, and is hereinafter referred to as "inter-element calibration". As shown in FIG. 7, the test pattern image 51 is an image formed at the same density over the entire width direction by the recording unit 205 and is arranged in order from the image with the highest density (51a', 51b',..., 51n'). In the present embodiment, density data as absolute color information is acquired as colorimetric data by measuring the color of a predetermined position of the test pattern image 51 in FIG. 7 with the colorimeter 40, and the shading correction is performed based on this colorimetric data. Thereby, the ink ejection amount of each print head is adjusted to correspond to an absolute density. Further, imaging calibration data for calibrating imaging by the in-line scanner 30 is also generated based on the test pattern imaging data and the colorimetric data obtained as described above.

[0035] FIG. 8 is a schematic diagram showing a fourth example of a test pattern image to be read for calibration of imaging by the in-line scanner 30 together with the in-line scanner 30 and the colorimeter 40. When performing shading correction up to halftone in real time during the printing operation using the test pattern image 51 (FIG. 7) of the third example, it is necessary to form a halftone test pattern image as a printed image, and accordingly waste paper is generated. On the other hand, when only a solid image (image with a density of 100%) is used as the test pattern image 51 for shading correction, as shown in FIG. 8, the test pattern image 51 is arranged outside the area of the target printed image 50, that is, outside the page area, and thereby shading correction can be performed in real time. However, when shading correction using the halftone test pattern image 51 is not performed, imaging calibration cannot be performed with sufficiently high accuracy. Therefore, in this example, as shown in FIG. 8, the same colors as the intermediate colors and specific colors included in the target printed image 50 are arranged as representative color patches 52 in the unused area of the target printed image 50. Based on the test pattern imaging data and color measurement data obtained by performing imaging by the in-line scanner 30 and color measurement by the colorimeter 40 using this representative color patch 52 as a calibration patch, imaging calibration data for calibrating the imaging by the in-line scanner 30 is generated.

[0036] <1.5 Operation of the printing apparatus> In this embodiment, the control unit 100 controls the recording unit 205 and the conveyance mechanism in the printing mechanism 200 to print on the paper 5, and controls the in-line scanner 30 and the colorimeter 40 to capture the printed image formed on the paper 5, and determines whether the printed image is a good product based on the captured image data of the printed image, by the CPU 111 reading out the control program 17 from the auxiliary storage device 12 to the memory 112 and executing it (see FIG. 2). That is, in the printing apparatus 10 according to this embodiment, in addition to the original function of the printing apparatus of forming a printed image on the paper 5 in the printing mechanism 200, the CPU 111 executes the printing control process 18a and the inspection control process 18b based on the control program 17, and a inspection function of the printed image for inspecting the printed image formed on the paper 5 using the in-line scanner 30 or the like is realized. That is, in the printing apparatus 10 according to this embodiment, the in-line scanner 30 as an imaging unit, the colorimeter 40, the moving mechanism 45 of the colorimeter (see FIG. 3 described later), the recording unit 205, the conveyance mechanism, and the control unit 100 that executes the inspection control process 18b realize a printed image inspection apparatus.

[0037] FIG. 9 is a flowchart showing a control process (hereinafter simply referred to as "control process") of the printing apparatus 10 including the printing control process 18a and the inspection control process 18b realized by the CPU 111 executing the control program 17 in this embodiment. In the printing apparatus 10 according to this embodiment, in order to print the input image represented by the print data generated from the input manuscript data, the control unit 100 controls the printing mechanism 200 and the paper feeding unit 202 and the paper winding unit 208 according to the procedure shown in FIG. 9 (see FIGS. 1 and 2). For this purpose, the CPU 111 reads out the control program 17 from the auxiliary storage device 12 to the memory 112 and executes it. As a result, the control process shown in FIG. 9 is activated, and the CPU 111 operates as follows according to the control program 17. As can be understood from the following description, the inspection control process 18b is realized by steps S14 to S18, S220, and S22 to S28 in the control process of FIG. 9.

[0038] First, the image processing unit 117 is controlled to perform rasterization processing on the input manuscript data given from the outside via the network 3, and print data in bitmap format is generated (step S12). This print data includes data of the target image which is the input image indicated by the input manuscript data.

[0039] Next, before starting the printing of the target image based on the generated print data, processing for calibration of imaging by the in-line scanner 30 is performed (step S14). Specifically, first, processing for eliminating variations in the imaging element 31 in the in-line scanner 30 (variations in the imaging sensitivity of the imaging element 31, also referred to as "sensitivity unevenness" hereinafter) is performed (for example, setting a sensitivity unevenness correction coefficient to be multiplied by the output value of each imaging element in the in-line scanner 30).

[0040] Thereafter, calibration of the colorimeter 40 (calibration of color measurement by the colorimeter 40) is performed (step S16). FIG. 10 is a diagram for explaining this calibration of the colorimeter 40. In the present embodiment, a white reference plate 42 for calibration of the colorimeter 40 is provided in the printing mechanism 200. This white reference plate 42 is arranged at a predetermined position (for example, an end position of the movable range) outside the range of the position where color measurement of the printed image on the sheet 5 is performed within the movable range of the colorimeter 40 in the paper width direction, such that its color detection surface faces the white reference plate 42 when the colorimeter 40 is placed at that position. In step S16, the colorimeter 40 is moved to the predetermined position by the moving mechanism 45 to measure the white reference plate 42, thereby calibrating the colorimeter 40.

[0041] Next, a generation process of imaging calibration data (hereinafter, also simply referred to as "calibration data") for calibrating imaging by the in-line scanner 30 as the imaging unit is performed (step S18). FIG. 11 is a flowchart showing the calibration data generation process in the present embodiment. In this calibration data generation process, the CPU 111 operates as follows.

[0042] First, the recording unit 205 and the conveyance mechanism are controlled so that a calibration patch is formed as a printed image on the sheet 5 by the recording unit 205 (step S182). Here, the printed image of the calibration patch is, in the first and third examples (Figs. 5 and 7) above, the printed image of a test pattern formed separately from the target printed image or a part thereof, in the fourth example (Fig. 8) above, the printed image formed outside the area of the target printed image simultaneously with the target printed image, and in the second example (Fig. 6) above, a part (partial image) of the target printed image is treated as the printed image of the calibration patch (including the test pattern). Therefore, the printed image of the calibration patch formed in this step S182 corresponds to the first and third examples (Figs. 5 and 7) above, and the printed images of the calibration patches shown in the second and fourth examples (Figs. 6 and 8) above are formed by image printing processing (step S210) in the second embodiment described later (see Figs. 22 and 23 described later).

[0043] Next, as shown in Fig. 6 and the like, the colorimeter 40 is moved by the moving mechanism 45 to the reading position of the calibration patch, that is, the position for measuring the printed image of the calibration patch (step S184).

[0044] Thereafter, the printed image of the calibration patch is read by the in-line scanner 30 and the colorimeter 40 (step S186). That is, the printed image of the calibration patch is imaged by the in-line scanner 30 to generate calibration patch imaging data (since this is the imaging data of the printed image of the test pattern or a part thereof, it is also referred to as "test pattern imaging data" hereinafter), and the printed image of the calibration patch is color-measured by the colorimeter to generate color measurement data. In the imaging of the printed image of the calibration patch, the imaging element 31 corresponding to the position of the calibration patch in the paper width direction among the plurality of imaging elements 31 arranged in the paper width direction in the in-line scanner 30 (the imaging element 31 marked with diagonal lines in Figs. 5 to 7) is used.

[0045] When the imaging data of the calibration patch (calibration imaging data) and the colorimetric data are obtained in this way, imaging calibration data is generated based on these data (step S188). This imaging calibration data consists of correction coefficients to be multiplied by the output values of the respective imaging elements 31 included in the inline scanner 30. Each correction coefficient is determined such that the value obtained by multiplying the correction coefficient by the output value of the corresponding imaging element corresponds to the colorimetric value measured by the colorimeter 40 for the calibration patch. In the present embodiment, a look-up table including such correction coefficients is prepared in advance. That is, in the print image inspection process (FIG. 13) described later, as calibration data for calibrating imaging by the inline scanner 30, correction coefficients for the imaging data of the target print image are prepared for each of the imaging elements 31 in the inline scanner 30. For example, if the inline scanner 30 includes n imaging elements 31 and these are distinguished by the symbol "31-k" (k = 1 to n), a look-up table (hereinafter referred to as the "correction coefficient LUT") 19 that associates the correction coefficient Ck of the imaging element 31-k with an integer k such that 1 ≦ k ≦ n is prepared in advance (see FIG. 2). When new correction coefficients C1 to Cn are generated as imaging calibration data in step S188, this correction coefficient LUT 19 is updated with the new correction coefficients C1 to Cn (step S188). Hereinafter, it is assumed that the inline scanner 30 as the imaging unit includes n imaging elements 31-1 to 31-n, and the imaging calibration data consists of correction coefficients C1 to Cn.

[0046] When the correction coefficient LUT19 for imaging calibration is updated in this way, the calibration data generation process ends, and the process proceeds to step S20. In step S20, an image printing process (step S210) and a printed image inspection process (step S220) are executed in parallel. In the example shown in FIG. 9, steps S210 and S220 are assumed to be executed on a per-page basis. When steps S210 and S220 are executed for one page, it is determined in step S22, which will be described later, whether the page is the last page of the print data. Also, in the present embodiment, in the process until the image printing process (S210) and the printed image inspection process (S220) on a per-page basis are sequentially executed up to the last page in the print data, the timing for performing imaging calibration by the in-line scanner 30 (hereinafter referred to as "imaging calibration timing"), and the timing for performing colorimetric calibration by the colorimeter 40 (hereinafter referred to as "colorimetric calibration timing") are set in advance at least one by one each (see steps S24 and S28 described later). These timings are specified in advance, for example, by the elapsed time from the start of printing or the number of printed pages.

[0047] FIG. 12 is a flowchart showing the image printing process in the present embodiment. In this image printing process, the CPU 111 operates as follows.

[0048] First, correction is performed on the print data generated in step S12 (step S212). This correction is for properly recording the image represented by the print data on the paper 5 (forming the printed image on the paper 5). Here, it is assumed that shading correction is performed to prevent density unevenness of the printed image caused by variations in the ink ejection amount from each print head, but other corrections may be included.

[0049] Next, by controlling each part such as the printing mechanism 200 based on the corrected print data, an image represented by the print data, that is, a target image, is formed on the paper 5 as a target printed image (step S214). Specifically, in order to record the image represented by the print data on the paper 5, together with the recording unit 205, the paper feed unit 202, the drive rollers 203 and 207, the drying unit 206, the in-line scanner 30, the colorimeter 40, and the paper take-up unit 208 are controlled (see FIG. 1). As a result, the target image is sequentially recorded on the paper 5 that is unwound and conveyed from the paper feed unit 202 by the recording unit 205. That is, the target printed image is sequentially formed on the paper 5. The paper 5 on which the target printed image is sequentially formed in this way is dried by the drying unit 206, and further, after passing through imaging by the in-line scanner 30, it is wound up by the paper take-up unit 208. Note that the imaging by the in-line scanner 30 and the processing based on the imaging data obtained by the imaging will be described below as print image inspection processing.

[0050] The print image inspection process is executed in parallel with the above-described image printing process. FIG. 13 is a flowchart showing the print image inspection process in the present embodiment. In this print image inspection process, the CPU 111 operates as follows.

[0051] First, during the printing operation in which the target printed image is sequentially formed on the paper 5 by the above-described image printing process, the target printed image formed on the paper 5 is sequentially imaged by the in-line scanner 30 (step S222). However, as described above, in the example shown in FIG. 9, since step S220 is executed in units of one page, when imaging data is generated by imaging the target printed image for one page, the process proceeds to the next step S224.

[0052] In step S224, the imaging data for one page generated in step S222 is corrected using the correction coefficient LUT 19 updated in step S18. This correction corresponds to calibration of imaging by the in-line scanner 30 (imaging calibration).

[0053] Thereafter, the captured image data corrected as described above (hereinafter referred to as "corrected captured image data") is compared with, for example, the print data at the time of submission to determine the quality of the target printed image captured in step S222 (step S226). Regarding this determination result, it is stored and / or displayed, etc. in the control unit 100, but the details are omitted because they are not directly related to the present invention.

[0054] When the quality of the printed image of one page is determined as described above, the process of step S220 of the printed image inspection process ends, and the process proceeds to step S22.

[0055] In step S22, it is determined whether printing and inspection have been completed for all pages of the print data by forming and inspecting the target printed image in steps S210 and S220 above (step S22). As a result of the determination, if there are still pages in the print data for which printing and inspection have not been completed, the process proceeds to step S24, and it is determined whether it is the imaging calibration timing (imaging calibration timing) by the in-line scanner 30.

[0056] As a result of the determination in step S24, if it is not the imaging calibration timing, the process proceeds to step S28, and it is determined whether it is the color measurement calibration timing (color measurement calibration timing) by the colorimeter 40. As a result of the determination, if it is not the color measurement calibration timing, the process returns to step S20, and the steps after step S20 are executed as described above.

[0057] Thereafter, until printing and inspection are completed for all pages of the print data, if it is determined in step S24 that it is not the imaging calibration timing and it is determined in step S28 that it is not the color measurement calibration timing, steps S20 (steps S210, S220) → step S22 → step S24 → step S28 are repeatedly executed. During the execution of these steps S20 to S28, when it is determined in step S24 that it is the imaging calibration timing, the process returns to step S18, and after updating the correction coefficient LUT19 by the calibration data generation process ( Figure 11Refer to it and execute the steps after step S20.

[0058] During the execution of steps S20 to S28 above, when it is determined in step S28 that it is the color measurement calibration timing, return to step S16, calibrate the colorimeter 40, and update the correction coefficient LUT19 (Fig. 11) by the calibration data generation process. After that, execute the steps after step S20.

[0059] During the execution of steps S20 to S28 above, when it is determined in step S22 that printing and inspection have been completed for all pages of the print data, the control process of the printing apparatus 10 for the print data generated from one input data ends (end of the printing operation).

[0060] <1.6 Update of Correction Coefficient LUT and Correction of Imaging Data> As described above, in this embodiment, the correction coefficient LUT19 for imaging calibration is prepared in advance. When the imaging calibration timing arrives during the printing operation, the correction coefficient LUT19 is updated by the imaging calibration data generated in the calibration data generation process (step S18) (step S24 → S18 in Fig. 9). Also, in the print image inspection process (step S220), imaging calibration is realized by correcting the imaging data of the print image using the correction coefficient LUT19 (step S224 in Fig. 13). Hereinafter, the update of such a correction coefficient LUT19 and the correction of imaging data using the correction coefficient LUT19 will be described by focusing on the generation of related data.

[0061] Fig. 14 is a flowchart showing a first example of the update procedure of the correction coefficient LUT in this embodiment. In Fig. 14, rectangles represent hardware or software (processing routines included in the control program 17) that perform predetermined processing, and octagons represent data (including look-up tables). Such a graphical representation is also adopted in Figs. 16 to 21 described later.

[0062] As shown in FIG. 14, in the present embodiment, in the calibration data generation process (S18), a printed image of a test pattern including calibration patches formed on the sheet 5 is imaged by the in-line scanner 30, thereby generating TP imaging luminance data Lsc as calibration imaging data (steps S182 to S186 in FIG. 11). The printed image of this calibration patch is also colorimetrically measured by the colorimeter 40, thereby generating TP colorimetric data Dcm as calibration colorimetric data (step S186 in FIG. 11). Since the TP imaging luminance data Lsc is RGB luminance data and the TP colorimetric data Dcm is CMY density data, it is necessary to match the color spaces of these data Lsc and Dcm in order to generate imaging calibration data from these data Lsc and Dcm. Therefore, in this example, a color space conversion process P10 for converting the TP imaging luminance data Lsc into density data is performed. This color space conversion process P10 is performed by a previously prepared look-up table (LUTsc). Thereby, TP imaging density data Dsc is obtained.

[0063] Next, a process P30 for updating the correction coefficient LUT151 for imaging calibration is performed (step S188 in FIG. 11). In order to distinguish the correction coefficient LUT19 updated in this example from the correction coefficient LUT updated in another example, the symbol "151" is used instead of the symbol "19". In the update process P30, the difference between the TP imaging density data Dsc and the TP colorimetric data Dcm obtained as described above is obtained, and the correction coefficients C1 to Cn described above are obtained so that this difference is eliminated or at least reduced. For example, when the test pattern image including the calibration patches is a printed image recorded at the same density in the paper width direction (see FIG. 7), for each of the imaging elements 31-1 to 31-n, the value of the TP imaging density data Dsc corresponding to the output value of the imaging element 31-k is multiplied by the correction coefficient Ck so that it becomes equal to the value of the colorimetric data Dcm of the calibration patch, and the correction coefficient Ck is obtained (k = 1 to n). The correction coefficient LUT151 is updated with the newly obtained correction coefficients C1 to Cn in this way.

[0064] FIG. 15 is a diagram for explaining a second example of the update procedure of the correction coefficient LUT19. In this example, in order to distinguish the correction coefficient LUT19 updated in this example from the correction coefficient LUT updated in another example, the symbol "152" is used instead of the symbol "19". In this example, in advance, imaging by the in-line scanner 30 and colorimetry by the colorimeter 40 are performed on patches of various densities of primary colors, and colorimetric values for the luminance values obtained from the in-line scanner 30 are obtained for each RGB channel. Thereby, for each of CMY (cyan, magenta, yellow), a table as shown in FIG. 15 showing the relationship between the luminance value in the corresponding complementary color RGB (red, green, blue) channel in the in-line scanner 30 and the density value by the colorimeter 40 is created in advance. Thereafter, the correction coefficient LUT152 is created according to the degree to which the correspondence between the value (luminance value) of the calibration imaging data and the value (density value) of the colorimetric data obtained by imaging the calibration patch by the in-line scanner 30 and colorimetry by the colorimeter 40 deviates from the relationship between the luminance value and the density value shown in the table of FIG. 15. Further, after the creation of the correction coefficient LUT152, the correction coefficient LUT152 is updated by performing imaging of the calibration patch by the in-line scanner 30 and colorimetry by the colorimeter 40 during the printing operation.

[0065] FIG. 16 is a flowchart showing a first example of the correction procedure of imaging data for imaging calibration in the present embodiment. When a target printed image is formed on the sheet 5 based on print data in the printing mechanism 200, this target printed image is imaged by the in-line scanner 30, and thereby target imaging luminance data LOsc is generated as target imaging data (step S222 in FIG. 13). This target imaging luminance data LOsc is converted into target imaging density data DOsc by the color space conversion process P10. Thereafter, imaging correction processing P40 is performed on this target imaging density data DOsc. In this imaging correction processing P40, the target imaging density data DOsc is corrected by the correction coefficient LUT151 updated as shown in FIG. 14, and thereby corrected imaging data DOcsc is generated (step S224 in FIG. 13). This correction corresponds to imaging calibration.

[0066] FIG. 17 is a flowchart showing a third example of the update procedure of the correction coefficient LUT 19. In this example, the look-up table (LUTsc) for the color space conversion process P10 in the first example shown in FIG. 14 and the correction coefficient LUT are integrated into one look-up table (hereinafter referred to as "conversion / correction coefficient LUT") 153. For the creation and update of this conversion / correction coefficient LUT, as shown in FIG. 17, based on the TP imaging luminance data Lsc generated by the in-line scanner 30 and the TP colorimetric data Dcm obtained by the colorimeter 40, the update process P32 of the conversion / correction coefficient LUT 153 is performed. By the update process P32 of the conversion / correction coefficient LUT 153, the conversion / correction coefficient LUT 153 is created and updated as a look-up table for performing imaging correction without converting the RGB luminance data as the imaging data generated by the in-line scanner 30 into density data.

[0067] FIG. 18 is a flowchart showing a second example of the correction procedure of the imaging data for imaging correction in the present embodiment. In this example, the corrected imaging data DOcsc is generated using the above conversion / correction coefficient LUT 153. That is, when the target printed image is imaged by the in-line scanner 30 to generate the target imaging luminance data LOsc as the target imaging data (step S222 in FIG. 13), for this target imaging luminance data LOsc, by the imaging correction process P42 using the conversion / correction coefficient LUT 153, the conversion into density data and the correction for imaging correction are performed simultaneously. Thereby, the corrected imaging data DOcsc is generated (see step S224 in FIG. 13).

[0068] FIG. 19 is a flowchart showing a fourth example of the update procedure of the correction coefficient LUT19. In this example, in order to distinguish the correction coefficient LUT19 updated in this example from the correction coefficient LUT updated in another example, the symbol "154" is used instead of the symbol "19". In this example, the colorimeter 40 has a look-up table (LUTfl) that takes into account the characteristics of the color filter used in the in-line scanner 30. That is, in this example, as shown in FIG. 19, the TP colorimetric original data Dcm1 is generated as the colorimetric data for calibration by the colorimeter 40, and this TP colorimetric original data Dcm1 is converted into the TP colorimetric prepared data Dcm2 by the filter-corresponding conversion process P20. This filter-corresponding conversion process P20 is a process for correcting colorimetric data in consideration of the characteristics of the color filter in the in-line scanner 30 in order to enable appropriate imaging calibration in a wider color reproduction area, and a look-up table (LUTfl) corresponding to the process is used. On the other hand, the TP imaging luminance data Lsc generated by the in-line scanner 30 is converted into the TP imaging density data Dsc by the color space conversion process P10 in the same manner as in the first example (FIG. 14) of the update procedure of the correction coefficient LUT. Based on the thus obtained TP imaging density data Dsc and the TP colorimetric prepared data Dcm2, the correction coefficient LUT154 is updated with the correction coefficients C1 to Cn obtained in the same manner as in the first example by the correction coefficient LUT update process P34.

[0069] FIG. 20 is a flowchart showing a fifth example of the update procedure of the correction coefficient LUT19. In this example, in order to distinguish the correction coefficient LUT19 updated in this example from the correction coefficient LUT updated in another example, the symbol "155" is used instead of the symbol "19". The correction coefficients constituting the correction coefficient LUTs 151 to 154 described above are correction coefficients for imaging data expressed in density, but may also be correction coefficients for imaging data in other color spaces. In this example, a correction coefficient LUT155 composed of correction coefficients for imaging data in the CIE1976 (L*a*b*) color space is used. By using such a correction coefficient LUT155, imaging calibration can be performed even when secondary color or tertiary color patches are used as calibration patches. Hereinafter, the update procedure of the correction coefficient LUT155 in this example will be described.

[0070] In this example, the printed image of the calibration patch or the test pattern including the same is imaged by the in-line scanner 30, thereby generating the TP imaging luminance data Lsc. The TP imaging luminance data Lsc is converted into the TP imaging L*a*b* data Dsc2 which is imaging data in the CIE1976 (L*a*b*) color system by the color space conversion process P12 using the look-up table (LUTsc2) (steps S182 to S186 in FIG. 11). The printed image of this calibration patch is also color-measured by the colorimeter 40, thereby generating the TP color-measured L*a*b* data Dcm3 which is color-measured data in the CIE1976 (L*a*b*) color system as calibration color-measured data (step S186 in FIG. 11). Thereafter, a process P36 for updating the correction coefficient LUT155 for imaging calibration is performed (step S188 in FIG. 11).

[0071] FIG. 21 is a flowchart showing a third example of the correction procedure of imaging data for imaging calibration in the present embodiment. When the target printed image is formed on the sheet 5 based on the print data in the printing mechanism 200, the target printed image is imaged by the in-line scanner 30, thereby generating the target imaging luminance data LOsc as the target imaging data (step S222 in FIG. 13). The target imaging luminance data LOsc is converted into the target imaging L*a*b* data DOsc2 by the color space conversion process P12 using the look-up table (LUTsc2).

[0072] Thereafter, the imaging calibration process P46 is performed on the target imaging L*a*b* data DOsc2. In this imaging calibration process P46, as shown in FIG. 20, the target imaging L*a*b* data DOsc2 is corrected by the updated correction coefficient LUT155, thereby generating the corrected imaging L*a*b* data DOcsc1 (step S224 in FIG. 13). This correction corresponds to the imaging calibration. In the printed image inspection process (FIG. 13), the quality of the target printed image is determined based on the corrected imaging L*a*b* data DOcsc1 (step S226 in FIG. 13).

[0073] <1.7 Effect> As described above, in this embodiment, the calibration of imaging by the in-line scanner 30 as the imaging unit is performed not only before the start of printing using the blank portion of the paper, but also during the printing operation, the imaging by the in-line scanner 30 is calibrated at a predetermined timing (step S24 → S18 in FIG. 9). That is, during the printing operation, at least a part of the printed image formed on the paper 5 is used as an image of a calibration patch, and imaging by the in-line scanner 30 and colorimetry by the colorimeter 40 are performed on the calibration patch (see FIGS. 5, 7, and 9). Thereby, imaging calibration data and colorimetry data for calibration are acquired, imaging calibration data is generated based on these data, and the correction coefficient LUT is updated based on the imaging calibration data (see FIGS. 11, 14, 17, 19, and 20). In the printed image inspection process (FIG. 13) in this embodiment, based on this correction coefficient LUT, the paper 5 In the imaging data of the target printed image formed by the in-line scanner 30 Is supplemented is corrected, and imaging calibration is achieved by this correction (see steps S224 in FIG. 13, FIGS. 16, 18, and 21). Based on this corrected imaging data (corrected imaging data), the quality of the target printed image is determined (see step S226 in FIG. 13).

[0074] According to such an embodiment, even during the printing operation, imaging calibration is performed using the colorimetric data of the calibration patch. Therefore, even if the imaging sensitivity of the in-line scanner 30 fluctuates due to environmental changes such as temperature changes during the printing operation, the imaging calibration corresponding to the fluctuation can be accurately performed in real time. Therefore, when the density of the printed image formed on the paper 5 fluctuates during the printing operation, the density fluctuation can be accurately detected by the printed image inspection process based on the imaging data by the in-line scanner 30 (see step S220 in FIG. 9 and FIG. 13). That is, it is possible to accurately monitor the density of the printed image during the printing operation while eliminating the influence of the characteristic change of the printed image inspection apparatus due to environmental fluctuations such as temperature. According to this embodiment, since high-precision imaging calibration data can be obtained by imaging and colorimetry of the calibration patch including intermediate colors and secondary colors, accurate imaging calibration is possible by correcting the inspection target image with the correction coefficient LUT based on the data.

[0075] Also, in this embodiment, as described above, the in-line scanner 30 and the colorimeter 40 for obtaining the imaging data and colorimetric data for calibration necessary for the above imaging calibration are arranged as shown in FIG. 4 with respect to the imaging support roller 204a and the colorimetric support roller 204b, respectively. Thereby, fluctuations in the imaging position and colorimetric position due to fluttering or cockling in paper conveyance are prevented, and stable and good imaging and colorimetry can be performed on the printed image formed on the paper 5. Therefore, according to this embodiment, the arrangement configuration of the in-line scanner 30 and the colorimeter 40 as shown in FIG. 4 also contributes to accurate imaging calibration.

[0076] <2. Second Embodiment> Next, the printing apparatus 10 according to the second embodiment of the present invention will be described. In the present embodiment, as a test pattern image for calibration of imaging by the in-line scanner 30 as an imaging unit, the test pattern images shown in FIGS. 6 and 8, that is, the test pattern images included in the target printed image formed on the sheet 5 based on the print data, or the test pattern images arranged outside the area of the target printed image are used. Hereinafter, the same reference numerals are given to the same or corresponding parts of the configuration of the printing apparatus 10 according to the present embodiment as those of the first embodiment, and detailed description thereof will be omitted.

[0077] FIG. 22 is a flowchart showing a control process (hereinafter simply referred to as "control process") of the printing apparatus 10 including a print control process 18a and an inspection control process 18b realized by the CPU 111 executing the control program 17 in the present embodiment. In the printing apparatus 10 according to the present embodiment, in order to print the input image represented by the print data generated from the input manuscript data, the control unit 100 controls the printing mechanism 200, the sheet feeding unit 202, and the sheet winding unit 208 according to the procedure shown in FIG. 22 (see FIGS. 1 and 2). For this purpose, the CPU 111 reads the control program 17 from the auxiliary storage device 12 into the memory 112 and executes it. As a result, the control process shown in FIG. 9 is activated, and the CPU 111 operates as shown in FIG. 22 according to the control program 17.

[0078] As can be seen by comparing FIG. 22 with FIG. 9, in the first embodiment, the calibration data generation process (S18) is performed before the execution of the image printing process (S210), whereas in the second embodiment, the calibration data generation process (S26) is performed after the execution of the image printing process (S210). In the present embodiment, the test pattern images shown in FIGS. 6 and 8 are used, and at the same time as the formation of the target printed image on the sheet 5 based on the print data, the test pattern image including the calibration patch is formed as a part of the target printed image or as a printed image outside the area of the target printed image.

[0079] FIG. 23 is a flowchart showing the calibration data generation process (S26) in the present embodiment. In this calibration data generation process (S26), the CPU 111 operates as follows.

[0080] As described above, in the present embodiment, since the test pattern image including the calibration patch is formed on the sheet 5 simultaneously with the formation of the target printed image (see FIGS. 6 and 8), in the calibration data generation process (S26), first, the image of the calibration patch is selected from the printed image including the target printed image formed on the sheet 5 (step S183). However, in the case of the test pattern image as shown in FIG. 8, since the test pattern image (including the calibration patch) has been specified in advance, the process proceeds to the next step S184 without performing substantial processing in step S183. The processing after step S184 in the calibration data generation process (S26) is the same as the calibration data generation process (S18, FIG. 11) in the first embodiment, and thus the description thereof is omitted.

[0081] As shown in FIG. 22, in the present embodiment, until printing and inspection are completed for all pages of the print data, if it is determined in step S24 that it is the imaging calibration timing, the above-described calibration data generation process (S26) is executed to update the correction coefficient LUT. If it is determined in step S24 that it is not the imaging calibration timing, the process proceeds to step S28. The processing after step S28 is the same as the control process (FIG. 9) in the first embodiment.

[0082] Also in the present embodiment as described above, similar to the first embodiment, during the printing operation, imaging and colorimetry of the calibration patch are performed at a predetermined timing, whereby the imaging by the in-line scanner 30 is calibrated (see steps S24 and S26 in FIG. 22 and step S224 in FIG. 13). As a result, the same effects as those of the first embodiment can be obtained, and the density of the printed image during the printing operation can be accurately monitored while eliminating the influence of changes in the characteristics of the printed image inspection apparatus due to environmental variations such as temperature. In this embodiment, since the test pattern image for imaging calibration is formed as part of the target printed image or outside the target printed image area (FIGS. 6 and 8), the occurrence of waste paper due to imaging calibration is suppressed.

[0083] <3. Third Embodiment> Next, the printing apparatus 10 according to the third embodiment of the present invention will be described. In this embodiment, as the test pattern image for calibrating the imaging by the in-line scanner 30 as the imaging unit, the test pattern images shown in FIGS. 7 and 8 are used, that is, the test pattern image for shading correction regarding the ink ejection amount in the recording unit 205 (hereinafter referred to as "shading correction TP image"). When the test pattern image shown in FIG. 7 is used, the entire printing apparatus operates according to the procedure shown in FIG. 9, and when the test pattern image shown in FIG. 8 is used, the entire printing apparatus operates according to the procedure shown in FIG. 22. In this embodiment, in relation to shading correction, there are differences in the calibration data generation process from the calibration data generation processes in the first and second embodiments in the calibration data generation process. Regarding the parts other than the calibration data generation process in the configuration of the printing apparatus 10 according to this embodiment, since they are the same as those in the first and second embodiments, the same reference numerals are assigned to the same or corresponding parts and detailed description thereof is omitted. Hereinafter, the calibration data generation process in this embodiment will be described assuming that the test pattern image shown in FIG. 7 is used. This test pattern image has a configuration in which strip-shaped images extending in the paper width direction based on print data showing the same color and the same density are arranged in a plurality in the conveyance direction with different colors and densities.

[0084] FIG. 24 is a flowchart showing the calibration data generation process (S18) in the present embodiment. In this calibration data generation process (S18), the CPU 111 operates as follows.

[0085] First, a test pattern image (shading correction TP image) as shown in FIG. 7 is printed (step S192). Thereafter, in the same manner as the calibration data generation process (S18, FIG. 11) in the first embodiment, a part of the test pattern image is used as a calibration patch, and calibration imaging data and colorimetric data are generated by imaging the calibration patch with the in-line scanner 30 and colorimetry with the colorimeter 40, and the correction coefficient LUT is updated based on these data (steps S194 to S198). Actually, test pattern imaging data is generated by imaging the test pattern image (shading correction TP image) in FIG. 7 with the in-line scanner 30, and a portion corresponding to the calibration patch is used as the calibration imaging data. Next, shading correction data is generated by correcting the test pattern imaging data with the updated correction coefficient LUT (step S199).

[0086] In the image printing process (step S220 in FIG. 9, FIG. 12) after the execution of such a calibration data generation process (S18), the shading correction data is used when correcting the print data. Thereby, density unevenness in the printed image formed on the sheet 5 by the recording unit 205 is suppressed.

[0087] According to the present embodiment as described above, similar to the first embodiment, during the printing operation, by imaging and color measurement of the calibration patch at a predetermined timing, the imaging by the in-line scanner 30 is calibrated (see step S18 in FIG. 9 and step S224 in FIG. 13). In this embodiment, in the imaging of the calibration patch, a shading correction TP image including the calibration patch is imaged by the in-line scanner 30 to generate test pattern imaging data, and the test pattern imaging data is corrected by a correction coefficient LUT to generate shading correction data. In this way, the imaging of the test pattern image (shading correction TP image) for shading correction also serves as the imaging of the test pattern image (calibration patch included therein) for imaging calibration. Thereby, shading correction and imaging calibration during the printing operation can be efficiently performed.

[0088] <4. Modifications and Application Examples> The present invention is not limited to the above embodiments, and various further modifications can be made without departing from the scope of the present invention. For example, although the above embodiments apply the present invention to an inkjet printing apparatus, the present invention can also be applied to a printing apparatus using a method other than the inkjet method by appropriately modifying the configuration of the above embodiments as necessary.

[0089] Further, in the second embodiment, when a partial image (see FIG. 6) that can be used as a calibration patch cannot be found in the target printed image based on the print data, as shown in FIG. 25, a test pattern image including the calibration patch may be arranged outside the layout such as the upper end that is finally cut off in the sheet 5. In the example shown in FIG. 25, a test pattern image of a color that is desired to be accurately monitored is arranged outside the upper layout of the target printed image 50 as a patch of a size that can be imaged by the in-line scanner 30 and color-measured by the colorimeter 40.

[0090] In each of the above-described embodiments, during the printing operation, imaging by the in-line scanner 30 is calibrated based on the colorimetric data obtained by the colorimeter 40, so that imaging data with correct density values is generated by the in-line scanner 30. Therefore, when it is desired to maintain a specific color in the target printed image 50 based on the print data, for example, as shown in FIG. 26, a strip-shaped patch 54 for density adjustment of the print head is arranged outside the area of the target printed image 50 in the printed image formed on the paper 5. Thereby, by correcting the print data given to the print head based on the read data of this patch 54, a specific color (color of interest) can be stably maintained in the target printed image 50.

[0091] FIG. 27 is a block diagram for explaining a correction operation of density variation by control of a print head using such a strip-shaped patch 54 for density adjustment.

[0092] As shown in FIG. 27, an embodiment corresponding to this application example includes a sub-block SB1 that calculates a correction coefficient from a calibration patch 52 read by the in-line scanner 30 and the colorimeter 40, a sub-block SB2 that reads the strip-shaped patch 54 for density adjustment and performs the above-described imaging calibration on the read signal, a correction data calculation unit P55 that generates a color correction coefficient of the print data based on the image data after imaging calibration and the reference data of the color of interest, and a second multiplier 60 that multiplies the color correction coefficient by the CMYK print data for correction and gives the corrected print data to each of the CMYK print heads 21.

[0093] Since the configuration and operation of the sub-block SB1 are the same as those of the embodiment according to FIG. 14 described above, the description thereof is omitted.

[0094] The sub-block SB2 includes an in-line scanner 30 that outputs the strip-shaped patch 54 for density adjustment as imaging luminance data Lsc, a color conversion unit P51 that converts the imaging luminance data Lsc into CMYK density data Dsc, and a first multiplier P52 that multiplies the correction coefficient generated by the sub-block SB1 by the density data Dsc for correction.

[0095] For the imaging luminance data Lsc of the strip-shaped patch 54 for density adjustment output by the in-line scanner 30, imaging correction is performed by the sub-block SB2. Therefore, even if the imaging sensitivity of the in-line scanner 30 varies during the printing operation, the sub-block SB2 can output the density data Dsc of the strip-shaped patch 54 for density adjustment in response to the variation.

[0096] The correction data calculation unit P55 calculates, for each of CMYK, a color correction coefficient capable of minimizing the color difference between the printing result of the target color by the print head 21 and the reference data of the target color based on the density data Dcsc after imaging correction and the reference data of the target color in this way.

[0097] The color correction coefficients of CMYK are respectively multiplied by the CMYK print data in the second multiplier 60. The multiplication result is given to the print head 21 of the corresponding color. By such a correction operation for density variation by controlling the print head, the density of the target color in the printed image can be stably maintained.

[0098] Note that the unit of control of the print head may be any of a print head row, a print head, and a nozzle. Also, the ink ejection amount from the print head may be controlled by any of the drive waveform, drive timing, and drive voltage of the print head. Further, instead of controlling the print head, the above CMYK correction density values may be given to other elements capable of adjusting the density of the printed image. For example, correction of density variation may be realized by reflecting the above CMYK correction density values in the processing of print data for shading correction or the screening process for generating print data.

[0099] Also, in the above embodiment, the correction coefficient was a value multiplied by the output value of each imaging element 31. However, the value by which the correction coefficient is multiplied is not limited to this. For example, the correction coefficient may be multiplied by a value obtained by performing color conversion processing on the output value of each imaging element.

[0100] In addition, in FIG. 14, color space conversion processing was performed on the TP imaging luminance data Lsc imaged by the in-line scanner 30. However, the color space conversion processing may be performed on the TP colorimetric data Dcm colorimetrically measured by the colorimeter 40.

[0101] In the above, embodiments and their modifications have been described to disclose the present invention. However, configurations obtained by appropriately combining the embodiments and modifications described above are also included in the scope of the present invention as long as they do not cause contradictions and do not contravene the spirit of the present invention.

Explanation of Reference Numerals

[0102] 5... Paper (base material) 10... Inkjet printing apparatus 17... Control program 18a... Printing control process 18b... Inspection control process 19... Correction coefficient LUT 30... In-line scanner (imaging unit) 31... Image sensor 40... Colorimeter 45... Moving mechanism 50... Target printed image 51... Test pattern image 52... Representative color patch 54... Density adjustment strip patch 100... Control unit 111... CPU 151~155... Correction coefficient LUT 200... Printing mechanism 204a... Imaging support roller 204b... Colorimetric support roller 205... Recording unit 205k,205c,205m,205y... Print head rows

Claims

A printing apparatus having a function of inspecting a printed image, comprising: a printing mechanism for forming a printed image; an imaging unit for imaging the printed image; a colorimeter for measuring the color of all or part of the printed image; a calibration unit for calibrating the imaging by the imaging unit; a determination unit for determining the quality of the printed image; a control unit for controlling the printing mechanism, the imaging unit, the colorimeter, and the calibration unit; and the printing mechanism includes a transport mechanism for transporting a substrate; and a print head for printing on the printing surface of the substrate; the control unit controls the print head and the transport mechanism so that a printed image is formed on the substrate, and when a test pattern image for calibrating the imaging by the imaging unit is formed as part or all of the printed image, the imaging unit captures the test pattern image to generate test pattern imaging data, the colorimeter measures the color of the test pattern image to generate color measurement data, and the calibration unit generates imaging calibration data based on the test pattern imaging data and the color measurement data, and controls the imaging unit, the colorimeter, and the calibration unit; and after the generation of the imaging calibration data, the calibration unit corrects the target imaging data generated by the imaging unit capturing a target printed image formed based on print data representing an input image to be printed based on the imaging calibration data, and controls the calibration unit; the determination unit determines the quality of the target printed image based on the target imaging data corrected by the calibration unit; the control unit during the printing operation from the start of printing on the substrate by the printing mechanism to the end of printing on the substrate, the imaging unit newly generates the test pattern imaging data at predetermined time intervals, the colorimeter newly generates the color measurement data at predetermined time intervals, the calibration unit newly generates the imaging calibration data at predetermined time intervals based on the newly generated test pattern imaging data and the color measurement data, and updates the imaging calibration data for correcting the target imaging data, and controls the print head, the transport mechanism, the imaging unit, the colorimeter, and the calibration unit. A printing apparatus.

2. The calibration unit A conversion unit that performs color space conversion on one or both of the test pattern imaging data and the colorimetric data so that the color space of the test pattern imaging data matches the color space of the colorimetric data; A difference calculation unit that calculates the difference between the test pattern imaging data and the colorimetric data after the color space conversion; A calibration data generation unit that generates the imaging calibration data as calibration data for correcting the target imaging data so that the difference is reduced; The printing apparatus according to claim 1, comprising:

3. The control unit controls the print head and the transport mechanism so that the test pattern image is formed at a position different from the position where the target print image is formed. The printing apparatus according to claim 1 or 2.

4. The imaging unit generates the test pattern imaging data by imaging a partial image selected as the test pattern image from the target print image. The colorimeter generates the colorimetric data by measuring the color of the partial image. The partial image has an area capable of being imaged by the imaging unit and measured by the colorimeter. The printing apparatus according to claim 1 or 2.

5. The printing apparatus further includes a moving mechanism for moving the colorimeter. The imaging unit includes a plurality of imaging elements arranged in a width direction orthogonal to the transport direction of the substrate. The control unit moves the colorimeter in the width direction by the moving mechanism so that the colorimetric data corresponding to the test pattern imaging data generated by the plurality of imaging elements is generated by the colorimeter. The printing apparatus according to any one of claims 1 to 4.

6. The transport mechanism includes first and second transport rollers around which the substrate on which the print image is formed is wound so as to change the transport direction. The imaging unit is arranged such that the imaging surface of the imaging unit faces the printing surface of the portion of the substrate in contact with the first transport roller. The colorimeter is arranged such that the color detection surface of the colorimeter faces the printing surface of the portion of the substrate in contact with the second transport roller. The printing apparatus according to any one of claims 1 to 5.

7. The transport mechanism is configured to be in contact with the first transport roller at a portion where the substrate is being transported in the horizontal direction. The imaging unit is arranged on the vertical line of the first transport roller. The printing apparatus according to claim 6.

8. The colorimeter is arranged such that the color detection surface faces the printing surface at the central portion in the circumferential direction of the second conveying roller in the portion of the base material that is in contact with the second conveying roller, and the printing apparatus according to claim 6.

9. The conveying mechanism is configured such that the conveying direction of the base material is switched from a horizontal direction to a vertical direction or from a vertical direction to a horizontal direction at the second conveying roller. The colorimeter is arranged on an oblique line that extends in an oblique direction with respect to the vertical direction from the central axis within a plane perpendicular to the central axis of the second conveying roller, and the printing apparatus according to claim 8.

10. The colorimeter is arranged such that the angle formed by the oblique line and the vertical direction is in the range of 30 degrees to 60 degrees, and the printing apparatus according to claim 9.

11. The printing apparatus further includes a correction unit that corrects the printing data. The printing head has a plurality of nozzles arranged in a width direction orthogonal to the conveying direction of the base material, and is configured to discharge ink onto the base material from the plurality of nozzles. The control unit controls the printing head and the conveying mechanism such that an image for shading correction that compensates for variations in ink discharge amounts among the plurality of nozzles is formed on the base material as the test pattern image. controls the calibration unit such that the calibration unit corrects the test pattern imaging data obtained by imaging the test pattern image by the imaging unit based on the imaging calibration data, and generates shading correction data based on the corrected test pattern imaging data. The correction unit corrects the printing data based on the shading correction data. The control unit controls the printing head and the conveying mechanism based on the printing data corrected by the correction unit to form the target printed image on the base material, and the printing apparatus according to claim 6.

12. A printed image inspection method for inspecting a printed image formed by a printing apparatus, comprising: an imaging step of imaging the printed image; a color measurement step of measuring all or part of the printed image; a calibration step of calibrating the imaging in the imaging step; a determination step of determining the quality of the printed image and when a test pattern image for calibrating the imaging in the imaging step is formed as part or all of the printed image. In the imaging step, test pattern imaging data is generated by imaging the test pattern image. In the color measurement step, color measurement data is generated by measuring the color of the test pattern image. In the calibration step, imaging calibration data is generated based on the test pattern imaging data and the color measurement data. After the generation of the imaging calibration data, in the calibration step, target imaging data generated by imaging a target printed image formed based on print data representing an input image to be printed in the imaging step is corrected based on the imaging calibration data. In the determination step, the quality of the target printed image is determined based on the target imaging data corrected in the calibration step. During the printing operation from the start of printing on the substrate of the printing apparatus to the end of printing on the substrate, at a predetermined time interval, the imaging step of generating test pattern imaging data by imaging the test pattern image is executed. at a predetermined time interval, the color measurement step of generating the color measurement data by measuring the color of the test pattern image is executed. at a predetermined time interval, the calibration step of generating imaging calibration data based on the test pattern imaging data and the color measurement data is executed, and the imaging calibration data for correcting the target imaging data is updated. A method for inspecting a printed image.

Images