Image processing device, image processing method, and program

Abstract

To provide a technique capable of suppressing wasting of a recording medium.SOLUTION: This image processing system comprises: reading means for acquiring a read image obtained by reading a printed matter having an image printed on a recording medium; and detection means for detecting a defect of the printed matter on the basis of a difference between the read image and a reference image serving as a reference for examination. The detection means performs a first detection process for detecting the defect of the printed article using a first sensitivity and a second detection process for maintaining the printing means for printing on the recording medium using a second sensitivity different from the first sensitivity.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to a technique for inspecting printed matter. [Background technology]

[0002] Since the image forming characteristics of a printer (image forming device) change over time, printer maintenance, such as updating the density gamma correction table and cleaning the recording elements, is essential to maintain the quality of printed matter. Normally, maintenance is performed periodically, but techniques for adaptively starting the maintenance have also been disclosed. Patent Document 1 discloses a technique for reading an image of a printed matter on which a user image has been printed, determining the quality of the image, and starting maintenance if it is determined that the image quality is NG. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-4690 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the technology of Patent Document 1, even if the image formation characteristics of the printer deteriorate, maintenance is not initiated until a quality judgment is made that is NG. In this case, in a sheet-fed printer that prints on sheets of paper, printed matter that is judged to be NG in the quality judgment is discharged to a dedicated tray that is different from the normal tray, and is wasted as so-called waste paper. In addition, in a continuous feed printer that prints on roll paper, even if the quality judgment is made that is NG, it takes time to stop the transport of the roll paper, so the paper (recording medium) that was transported from the time the quality judgment was made that is NG until the transport was stopped is wasted as waste paper.

[0005] In view of the above, an object of the present disclosure is to provide a technique for preventing recording media from going to waste. [Means for solving the problem]

[0006] An image processing device according to one aspect of the present disclosure has a reading means for acquiring a read image obtained by reading a printed matter on which an image is printed on a recording medium, and a detection means for detecting defects in the printed matter based on a differential image between the read image and a reference image that serves as a reference for inspection, wherein the detection means performs a first detection process for detecting defects in the printed matter using a first sensitivity, and performs a second detection process for maintenance of a printing means that prints on the recording medium using a second sensitivity different from the first sensitivity. Effect of the Invention

[0007] According to the present disclosure, it is possible to prevent recording media from being wasted. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram of an inkjet printer. [Diagram 2] FIG. 2 is a block diagram showing an example of a hardware configuration of the image forming system. [Diagram 3] 13 is a flowchart showing the flow of image processing. [Figure 4] FIG. 2 is a block diagram showing the functional configuration of a host PC. [Diagram 5] FIG. 13 is a diagram illustrating an example of defect detection sensitivity. [Figure 6] FIG. 13 is a diagram for explaining the relationship between defect detection sensitivity and area. [Figure 7] FIG. 11 is a diagram for explaining the relationship between printing and maintenance and sensitivity. [Figure 8] FIG. 2 is a block diagram showing the functional configuration of a host PC. [Figure 9] FIG. 13 is a diagram illustrating an example of defect detection sensitivity. [Figure 10] FIG. 13 is a diagram for explaining the relationship between defect detection sensitivity and area. [Figure 11]FIG. 11 is a diagram for explaining the relationship between printing and maintenance and sensitivity. [Figure 12] 13 is a flowchart showing the flow of image processing. [Figure 13] FIG. 2 is a block diagram showing the functional configuration of a host PC. [Figure 14] FIG. 13 is a diagram illustrating an example of defect detection sensitivity. [Figure 15] FIG. 13 is a diagram for explaining the relationship between defect detection sensitivity and area. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the following embodiments do not limit the present invention, and not all of the combinations of features described in each embodiment are necessarily essential to the solution of the present invention. In addition, various forms that do not deviate from the gist of the present invention are also included in the present invention, and parts of the following embodiments can be appropriately combined.

[0010] (Printer configuration) FIG. 1 is a schematic diagram of an inkjet printer as an image forming apparatus assumed in this embodiment. The printer 10 includes a recording head 100 in its housing. The recording head 100 is a so-called full-line type recording head, and has four head sets 101-104 corresponding to the ink colors of black, cyan, magenta, and yellow. The head sets 101-104 are each connected to two nozzle rows (101a and 101b in the case of black) that eject black, cyan, magenta, and yellow inks so that they overlap each other. In each nozzle row, nozzles that eject ink are arranged at regular intervals in the X direction. For example, in the case of a nozzle row in which the length of the recording head is 15 inches and the recording resolution is 1200 dpi, approximately 18000 (=15×1200) nozzles are arranged in the x direction.

[0011] Paper 105 as a recording medium is conveyed in the Y direction by conveyance roller 106 (and other rollers, not shown) rotating due to the driving force of a motor (not shown). The Y direction in FIG. 1 is referred to as the paper conveyance direction. While paper 105 is being conveyed, each nozzle (recording element) in each nozzle row in head sets 101 to 104 ejects ink in accordance with recording data, thereby forming an image on the paper surface. In the following description, the recording resolution in the paper conveyance direction is 1200 dpi.

[0012] An in-line sensor 107 is provided at a position downstream of the recording head 100 in the Y direction. The in-line sensor 107 optically reads the colors of the image on the print using optical reading elements arranged at intervals of 1200 dpi in the X direction, and outputs a scanned image (read image) in which the colors are expressed in the RGB color space. In the following description, the reading resolution in the paper transport direction is 1200 dpi.

[0013] The printer to which the present embodiment can be applied is not limited to a full-line type inkjet printer. For example, it may be a so-called serial type inkjet printer that scans a recording head in a direction intersecting the paper transport direction to form an image. In addition, the interval between nozzles in each nozzle row and the recording resolution in the paper transport direction are not limited to 1200 dpi. Similarly, the interval between optical reading elements of the in-line sensor 107 and the reading resolution in the paper transport direction are not limited to 1200 dpi. In addition, the method of recording an image is not limited to the inkjet method, and it can be applied to a printer that uses LEDs or heating elements as recording elements. Specifically, it can be applied to an electrophotographic printer that uses an LED array as a light source for exposure, and a dye-sublimation printer that uses a thermal head in which minute heating elements are arranged as a heat source for vaporizing solid ink.

[0014] (Configuration of Image Forming System) 2 is a diagram showing an example of the hardware configuration of an image forming system including the above-mentioned printer 10 according to this embodiment. The image forming system 30 has the printer (image forming device) 10 shown in FIG. 1 and a personal computer (PC) 20 as its host device (image processing device).

[0015] The host PC 20 is a device that controls the printer 10, and includes, for example, a smartphone, a tablet, a PC, and the like.

[0016] The host PC 20 has a CPU 201, a RAM 202, a HDD 203, a display I / F 204, a keyboard and mouse I / F 205, and a data transfer I / F 206. The CPU 201 executes a predetermined process according to a program stored in the RAM 202 or the HDD 203. The RAM 202 is a volatile storage device, and temporarily stores programs and data. The HDD 203 is a non-volatile storage device, and similarly stores programs and data. The display I / F 204 is an interface that controls a display device (not shown) such as an LCD monitor. The keyboard and mouse I / F 205 controls a HID (Human Interface Device) such as a keyboard or a mouse. The data transfer I / F 206 is an interface that controls the transmission and reception of data to and from the printer 10. A USB or a LAN is used as a connection method for this data transmission and reception.

[0017] The printer 10 includes a CPU 211, a RAM 212, a ROM 213, a head controller 214, a sensor controller 215, and a data transfer I / F 216. The CPU 211 executes a predetermined process according to a program stored in the RAM 212 or the ROM 213. The RAM 212 is a volatile storage device, and temporarily stores programs and data. The ROM 213 is a non-volatile storage device, and similarly stores programs and data. The head controller 214 controls the ink ejection operation of each nozzle array of the print head 100 based on a halftone image, for example, quantized to a binary value, stored in the RAM 212. The sensor controller 215 controls each optical reading element of the in-line sensor 107. The data transfer I / F 216 is an interface that controls the transmission and reception of data to and from the host PC 20.

[0018] All image processing described in each embodiment below is performed by the host PC 20. The host PC 20 may be equipped with a GPU, and all or part of the image processing executed by the CPU 211 may be executed by the GPU. Similarly, all or part of the image processing may be executed by the CPU 211 of the printer 10.

[0019] (Printer Maintenance) Since the image forming characteristics of a printer change over time, printer maintenance is essential to maintain the quality of printed matter. An example of such maintenance is described below.

[0020] (Maintenance example 1: Updating density gamma correction table) In an inkjet printer as shown in FIG. 1, the amount of ink discharged from each nozzle (each recording element) changes over time. When the amount of discharge changes, the gamma characteristics of the printed matter change, and in particular, when printing a photograph, the impression of the photograph changes. In this case, by updating the density gamma correction table as maintenance, the gamma characteristics can be maintained in the same state even if the amount of discharge changes over time. When updating the density gamma correction table, a test image consisting of uniform patches of multiple gradations is printed and read by the in-line sensor 107. Then, the density gamma correction table is updated based on the gradation values ​​of the uniform patches and the read values ​​of the in-line sensor 107. Note that, since the gamma characteristics also change over time in electrophotographic printers, the density gamma correction table is updated as maintenance.

[0021] (Maintenance example 2: Nozzle cleaning) In inkjet printers, nozzle (recording element) failure or drying of ink inside the nozzle (recording element) can cause non-ejecting nozzles that are unable to eject ink droplets, resulting in white streaks on printed matter. If the nozzle is not broken, cleaning the nozzle by suction, wiping, or other means can be performed as maintenance, which will restore the non-ejecting nozzle to a normal state and eliminate the white streaks. Even if the nozzle is not broken, continuing to send ink ejection signals to the nozzle when a non-ejecting nozzle has occurred can cause the nozzle to break. For this reason, if a non-ejecting nozzle occurs, it is advisable to immediately start maintenance such as nozzle cleaning by suction or wiping.

[0022] (Maintenance example 3: Updating non-discharge compensation parameters) In an inkjet printer, when a white streak occurs on an image due to a non-discharge nozzle, the occurrence of the white streak is eliminated by performing a non-discharge complement process in which ink droplets that should be formed by the non-discharge nozzle are complemented by other nozzles. However, when a new non-discharge nozzle occurs due to changes over time, a new white streak occurs on the printed matter. On the other hand, the condition of a nozzle that was unable to discharge ink droplets may improve and become able to discharge ink droplets, at which time unnecessary non-discharge complement process is performed, causing a black streak to occur on the printed matter. In this case, by updating the non-discharge complement parameters as a maintenance, the image quality can be maintained even if the non-discharge state changes over time. The non-discharge complement parameters are information on the position of the nozzle that performs the non-discharge complement. When updating the non-discharge complement parameters, a test image consisting of a line pattern is printed and read by the in-line sensor 107. Then, the non-discharge complement parameters are updated by identifying the recording element where the non-discharge occurs from the position where the line pattern is missing.

[0023] (Maintenance example 4: Updating head shading parameters) In an inkjet printer, the ink ejection amount and landing position vary between nozzles (printing elements), causing striped density unevenness in the printed matter. This striped density unevenness can be improved by performing head shading. However, the degree of variation in the ink ejection amount and landing position changes over time, and the striped density unevenness becomes noticeable as printing is repeated. In this case, the striped density unevenness can be improved by updating the head shading parameters as maintenance. When updating the head shading parameters, a test image consisting of uniform patches of multiple gradations, having the same width as the headsets 101 to 104, is printed and read by the in-line sensor 107. Then, the head shading parameters are updated based on the gradation values ​​of the uniform patches and the read values ​​of the in-line sensor 107. The head shading parameters are a collection of density gamma correction tables, and are generated in the same number as the number of printing elements. By applying these density gamma correction tables to each position in the nozzle row direction, density fluctuations in the nozzle row direction, that is, stripe-like density unevenness, are reduced.

[0024] (Outline of this embodiment) Here, the prevention of the generation of waste paper, which is an overview of this embodiment, will be described, including the problems involved. Printer maintenance includes periodic startup and adaptive startup.

[0025] For example, in the technology of Patent Document 1, a quality judgment is performed on an image that is printed and scanned from a user's image, and maintenance is initiated if a defective product is detected. In the quality judgment, defects in the printout, such as streaks and stains, are detected by image processing. Maintenance is adaptively initiated based on the results of the defect detection at this time. Printouts that are judged to be OK in the quality judgment are discharged to a normal tray, and printouts that are judged to be NG are discharged to a dedicated tray as waste paper.

[0026] However, in the technology of Patent Document 1, even if the image forming characteristics of the printer deteriorate, maintenance is not started until the quality judgment is NG. In this case, in a sheet-fed printer that prints on sheets, the printouts that are judged to be NG in the quality judgment are discharged to a dedicated tray that is different from the normal tray, and are wasted as so-called waste paper. In addition, in a continuous feed printer that prints on roll paper, even if the quality judgment is NG, it takes time to stop the transport of the roll paper, so the paper that is transported from the time the quality judgment is NG to the time the transport is stopped is wasted as waste paper. For example, in an inkjet printer as shown in FIG. 1, as described above, even if head shading is performed, the degree of variation in the ink ejection amount and landing position changes over time, and streaky density unevenness becomes noticeable as printing is repeated. In this case, if maintenance is started before the quality judgment is NG, the generation of waste paper can be prevented. Specifically, if the above-mentioned update of the head shading parameters is started as maintenance, the streaky density unevenness is reduced, and the generation of waste paper can be prevented. However, when the technology of Patent Document 1 is used, maintenance is not initiated until a quality judgment results in an NG.

[0027] Therefore, in this embodiment, two types of judgments are made based on the defect detection results of an image obtained by printing and scanning a user image: a judgment of the quality of the printed matter and a judgment of whether maintenance is necessary. At this time, different defect detection sensitivities are used when making the judgment of the quality of the printed matter and when making the judgment of whether maintenance is necessary. Specifically, a first sensitivity is used when judging whether the quality of the printed matter meets the quality expected by the user. On the other hand, a second sensitivity different from the first sensitivity is used when judging whether maintenance is necessary. The first sensitivity is set by the user according to the level of quality expected by the user for the printed matter. On the other hand, the second sensitivity is set separately from the first sensitivity.

[0028] If a defect is detected using the first sensitivity, the user is notified that the quality of the print does not meet the user's expectations and that a NG quality judgment has occurred. At this time, maintenance is not initiated. In other words, the defect detection results when the first sensitivity is used are not used as the criterion for determining whether or not to initiate maintenance. Prints that have a NG quality judgment are discharged to a waste paper tray that is different from the normal tray. Note that in printers that do not have a waste paper tray, a mark indicating that the paper is waste may be additionally printed. Such waste paper is usually discarded.

[0029] On the other hand, if a defect is detected with the second sensitivity, maintenance is initiated. Note that the content of the notification to the user regarding the quality of the printed matter does not depend on the defect detection result when the second sensitivity is used, but only on the result when the above-mentioned first sensitivity is used. In other words, the defect detection result when the second sensitivity is used is not used as a criterion for determining whether the quality of the printed matter meets the quality expected by the user. Therefore, if a defect is detected with the second sensitivity but not with the first sensitivity, maintenance is initiated, but the printed matter is not considered to be waste paper and is discharged to the normal tray.

[0030] In this way, by using different defect detection sensitivities for judging the quality of the printed matter and for judging whether maintenance is necessary, maintenance can be started before a NG result is generated in the quality judgment, and the generation of waste paper can be prevented. In other words, by using the second sensitivity to capture signs of deterioration in the printer's image formation characteristics, maintenance can be started before a NG result is generated in the quality judgment using the first sensitivity. On the other hand, with the technology of Patent Document 1, maintenance is not started until a NG result is generated, so the generation of waste paper is unavoidable when the printer's image formation characteristics deteriorate due to changes over time.

[0031] <<Embodiment 1>> In this embodiment, a configuration is described with reference to figures in which a second sensitivity that is slightly higher than a first sensitivity set by the user is used in conjunction with the first sensitivity in order to detect signs of deterioration in the printer's image forming characteristics.

[0032] (Image Processing) Image processing (detection processing) in this embodiment will be described below with reference to Figs. 3 and 4. Fig. 3 is a flowchart showing the flow of image processing executed by the host PC of this embodiment. Fig. 4 is a block diagram showing the functional configuration (software configuration) of the host PC of this embodiment. Each module shown in Fig. 4 can be realized by the CPU 201 of the host PC 20 executing a program stored in the HDD 203. In Fig. 3, "S" stands for "step."

[0033] In S301, the CPU 201 of the host PC 20 sets a first sensitivity based on a user instruction input from the input UI unit 401. The set first sensitivity is stored in the storage unit 402.

[0034] In S302, the sensitivity setting unit 403 sets a sensitivity slightly higher than the first sensitivity as the second sensitivity based on the first sensitivity stored in the storage unit 402. The set second sensitivity is stored in the storage unit 404. Details of the sensitivity will be described later.

[0035] In S303, the CPU 201 of the host PC 20 prints a user image 421 with the image forming unit 405 and scans it with the image reading unit 406. The image forming unit 405 is a module for forming an image on a recording medium, and examples of the image forming unit 405 include the headsets 101 to 104 and the conveyor roller 106 in the printer 10. The image reading unit 406 is a module for reading an image formed on a recording medium, and examples of the image reading unit 406 include the in-line sensor 107 in the printer 10.

[0036] In S304, the defect detection unit 410 detects defects with the first sensitivity. In this embodiment, the defects to be detected are stripe-like density unevenness caused by variations in the ink ejection amount and landing position between nozzles (between recording elements). Note that the image forming unit 405 performs the head shading described above, and it is assumed that the stripe-like density unevenness is reduced immediately after the head shading parameters are updated as maintenance. It is also assumed that the degree of variation in the ink ejection amount and landing position changes over time, so that the stripe-like density unevenness becomes noticeable as printing is repeated even if head shading is performed. Note that the present invention is applicable even if the defects to be detected are white stripes caused by non-ejecting nozzles, changes in gamma characteristics, and the like.

[0037] A method for detecting defects in S304 will be described with reference to FIG. 4. The difference image generating unit 411 subtracts the reference image 422 from the scan image 423 to generate a difference image. Before generating the difference image, a known alignment process may be performed so that the scan image 423 and the reference image 422 are aligned. The scan image 423 is an image of an inspection target that may have a defect such as a streaky density unevenness. The reference image 422 is a reference image that serves as a reference in the inspection, and is an image that is assumed to have no defects. Therefore, a difference image between the scan image 423 and the reference image 422 is generated, and if a place (pixel) where the absolute value of the difference is greater than a predetermined value exists in the difference image, it can be determined that the image of the inspection target has a defect.

[0038] A user image 421 is used as the reference image 422. Note that, taking into consideration the characteristics of the printer, an image obtained by processing the user image 421 based on the printer characteristics so that the color becomes close to that of the scanned image 423 may be used as the reference image 422. For example, the reference image 422 may be generated by applying a known printer simulator to the user image 421. Also, an image that has been printed and scanned in the past may be used as the reference image 422. In this case, an image that has been visually confirmed to be free of defects is used.

[0039] The filter processing unit 412 convolves a predetermined filter coefficient with the difference image output by the difference image generating unit 411 to emphasize the defect to be detected. In this embodiment, in order to detect streaky density unevenness, a filter coefficient having a shape similar to that of the streaky density unevenness is used. For example, the pixel value of the area where the streaky density unevenness occurs in the scanned image is used as the filter coefficient. In this way, by using a filter coefficient having a strong correlation with the streaky density unevenness, the difference image is emphasized at the position where the streaky density unevenness occurs. Note that the type of defect to be detected is not limited to streaky density unevenness. For example, if it is desired to detect dot-shaped stains, an isotropic filter coefficient corresponding to the dot-shaped stains may be used.

[0040] The threshold processing unit 413 finds the absolute value of the difference image enhanced by the filter processing unit 412 and generates an absolute difference image. Then, threshold processing is applied to the absolute difference image to generate a binary image made up of pixels of 0 and 1. In the absolute difference image, pixels that exceed the threshold are regarded as defective pixels and the pixel value of the binary image is set to 1. On the other hand, pixels that are equal to or smaller than the threshold are regarded as non-defective pixels and the pixel value of the binary image is set to 0.

[0041] The presence / absence determination unit 414 searches the binary image for the presence of a pixel whose pixel value is 1. If the presence / absence determination unit 414 obtains a search result indicating that a pixel whose pixel value is 1 exists, it determines that there is a defect. If the presence / absence determination unit 414 obtains a search result indicating that there is no pixel whose pixel value is 1, it determines that there is no defect.

[0042] As described above, in S304, the first sensitivity is used as the threshold value. Therefore, in S304, the first sensitivity stored in the storage unit 402 is used as the threshold value in the threshold processing unit 413. In this manner, in this embodiment, the threshold value is adjusted in order to adjust the sensitivity of defect detection. When it is desired to increase the sensitivity, the threshold value is lowered, and when it is desired to decrease the sensitivity, the threshold value is raised. The same applies to the second sensitivity. The same applies to the third sensitivity used in the embodiment 3 described below.

[0043] When the second sensitivity is used, the second sensitivity stored in the storage unit 404 is used as a threshold value. When this is used in the threshold processing unit 413, the connection destination of the switching unit 415 is switched to the storage unit 404. That is, by switching the connection destination using the switching unit 415, the sensitivity when detecting defects in the defect detection unit 410 can be switched. In this manner, in this embodiment, the process of detecting defects using the first sensitivity and the process of detecting defects using the second sensitivity are performed in the same defect detection unit 410. When the third sensitivity is used as in the third embodiment described later, the sensitivity used in the process is switched to perform defect detection using the third sensitivity in the same defect detection unit 410. Hereinafter, the process of detecting defects using the first sensitivity is referred to as the first detection process. Moreover, the process of detecting defects using the second sensitivity is referred to as the second detection process. Similarly, the process of detecting defects using the third sensitivity described later is referred to as the third detection process. These processes may be performed in separate defect detection units.

[0044] Returning to the description of Fig. 3, in S305, the quality reporting unit 417 judges whether or not a defect is detected when the first sensitivity is used. If the judgment result indicates that a defect is not detected (NO in S305), the first detection process using the first sensitivity is terminated. If the judgment result indicates that a defect is detected (YES in S305), the process proceeds to S306.

[0045] In S306, the quality notification unit 417 notifies the user, via the output UI unit 418, that the quality of the printed matter does not meet the quality expected by the user. If no defects are detected, the user may or may not be notified that the quality expected by the user is met. When the process of S306 ends, the first detection process using the first sensitivity ends.

[0046] In S307, the defect detection unit 410 detects defects at the second sensitivity. At this time, the threshold processing unit 413 uses the threshold stored in the storage unit 404. The content of the process for detecting defects is the same as that of S304 described above, except that a different sensitivity is used. As described above, the switching unit 415 is used to select the sensitivity to be used in the process.

[0047] In S308, the maintenance activation unit 416 judges whether or not a defect is detected when the second sensitivity is used. If the determination result indicates that a defect is not detected (NO in S308), the maintenance is not activated and the second detection process using the second sensitivity is terminated. If the determination result indicates that a defect is detected (YES in S308), the process proceeds to S309.

[0048] In S309, the maintenance startup unit 416 starts maintenance. As the maintenance, the update of the head shading parameters described above is started. This makes it possible to reduce streaky density unevenness that becomes noticeable as printing is repeated.

[0049] As described above, a sensitivity slightly higher than the first sensitivity is used as the second sensitivity in conjunction with the first sensitivity set by the user. Therefore, in cases where streaky density unevenness becomes noticeable after repeated printing, a defect will be detected with the second sensitivity before it is detected with the first sensitivity, and maintenance will be initiated. In other words, maintenance will be initiated before a NG is generated in the quality judgment using the first sensitivity. This makes it possible to prevent the generation of paper waste due to NG.

[0050] 5A is a diagram showing an example of sensitivity used in the detection process of this embodiment. For example, when a user requires a medium quality for a printed matter, in the input UI unit 401, the user selects "3", which is a medium sensitivity for defect detection, as the "user setting" 511 for quality judgment. In this case, the threshold value applied to the absolute difference image as the first sensitivity 512 is 60. In this embodiment, the range of the image output by the inline sensor 107 and the range of the absolute difference image are from 0 to 255.

[0051] In this way, when the threshold value is set to 60 as the first sensitivity 512, the sensitivity setting unit 403 sets the second sensitivity 513 to a sensitivity slightly higher than the first sensitivity 512 as described above. In order to increase the sensitivity, the threshold value can be lowered, so the threshold value is set to 50 as the second sensitivity 513. In this way, the sensitivity margin 514 is provided, and the threshold value used as the second sensitivity 513 is set to 10 smaller than the threshold value used as the first sensitivity 512. The sensitivity margin 514 may be, for example, about 1% to 5% of the lower limit of the first sensitivity 512. In FIG. 6(a), the user image 610 shows a state in which the threshold value of the first sensitivity 611 is set to 60 over the entire surface. Also, the user image 620 shows a state in which the threshold value of the second sensitivity 621 is set to 50 over the entire surface.

[0052] As another example, when a user desires the highest quality for a printed matter, the highest sensitivity for defect detection, "5", is selected as the "user setting" 511 for quality judgment in the input UI unit 401. In this case, the threshold value applied to the difference absolute value image as the first sensitivity 512 is 15. In this case, the threshold value is set to 5 as the second sensitivity 513 by the sensitivity setting unit 403. That is, the second sensitivity 513 is set to a sensitivity higher than the first sensitivity 512 by a sensitivity margin 514. In FIG. 6(b), the user image 630 shows a state in which 15 is set as the threshold value for the first sensitivity 631 over the entire surface. The user image 640 shows a state in which 5 is set as the threshold value for the second sensitivity 641 over the entire surface.

[0053] In this way, by using a second sensitivity that is slightly higher than the first sensitivity in conjunction with the first sensitivity set by the user, defects are detected with the second sensitivity and maintenance is initiated before a quality judgment using the first sensitivity results in an NG, thereby preventing the generation of waste paper.

[0054] Fig. 7 is a diagram for explaining the relationship between printing and maintenance and sensitivity. In Fig. 7(a), Fig. 7(b), and Fig. 7(c), the vertical axis indicates the maximum absolute difference value in the absolute difference image, and the horizontal axis indicates time. In all of Fig. 7(a) to (c), it is assumed that head shading parameters are updated as maintenance, and streaky density unevenness becomes noticeable as printing is repeated.

[0055] FIG. 7(a) shows the operation of an image forming system to which the first and second sensitivity setting methods according to this embodiment are applied. In this embodiment, a sensitivity slightly higher than the first sensitivity is used as the second sensitivity. Therefore, before a quality judgment using the first sensitivity results in NG, a defect is detected at the second sensitivity and maintenance is started, thereby preventing the generation of waste paper. In the case of FIG. 7(a), 60 is set as the threshold value of the first sensitivity 731, and 50 is set as the threshold value of the second sensitivity 732. As described above, the smaller the threshold value, the higher the sensitivity, so the second sensitivity is set higher than the first sensitivity. In this case, when the threshold value of the second sensitivity 732 is reached in the second detection process during the printing 711, the maintenance 721 is executed. After the maintenance 721 is completed, the printing 712 is executed. That is, the printing and maintenance are repeated as in the following order: printing 711, maintenance 721, printing 712, maintenance 722, printing 713, maintenance 723, and printing 714.

[0056] On the other hand, Fig. 7(b) shows the operation of an image forming system to which the technology of Patent Document 1 is applied. Patent Document 1 can be said to disclose a configuration that has only a first sensitivity used for quality judgment, and starts maintenance when a defect is detected with the first sensitivity. Therefore, since maintenance is not started until a quality judgment results in NG, waste paper is generated. In other words, print 741, waste paper generation 761, maintenance 751, print 742, waste paper generation 762, maintenance 752, print 743, waste paper generation 763, maintenance 753 are repeated.

[0057] FIG. 7(c) shows a configuration in which maintenance is not adaptively started, but is started periodically. Printing and maintenance before the first sensitivity is reached are repeatedly executed. That is, printing 771, maintenance before the first sensitivity is reached 731 781, printing 772, maintenance before the first sensitivity is reached 731 782, printing 773, and maintenance before the first sensitivity is reached 731 783 are executed. Then, each process is executed in the order of printing 774, maintenance before the first sensitivity is reached 731 784, printing 775, maintenance before the first sensitivity is reached 731 785, and printing 776. This configuration is common in normal printers. In this case, maintenance is started before the difference on the vertical axis reaches the first sensitivity 731. That is, if the user sets 60 as the threshold value of the first sensitivity 731, which is required as a standard for quality judgment, maintenance is started more frequently than necessary, and the time during which printing cannot be performed due to maintenance increases. In contrast, in Fig. 7(a), maintenance is adaptively started based on the criteria desired by the user, so the number of maintenances is reduced and the time during which printing is unavailable is shortened compared to the case of Fig. 7(c). Note that if the user desires a high standard for quality judgment, the second sensitivity will also be high in conjunction with the set first sensitivity, and the frequency of maintenance will increase.

[0058] As described above, according to this embodiment, by using different defect detection sensitivities for judging the quality of the printed matter and for judging whether maintenance is required, it is possible to prevent waste paper. In other words, it is possible to suppress the waste of recording media. Maintenance can be started before a quality judgment using the first sensitivity results in an NG result, and the image forming characteristics of the printer can be restored.

[0059] (Modification 1 of the first embodiment) When the second sensitivity is high and the threshold value is close to 0, it is assumed that unnecessary maintenance is frequently started due to accidental factors such as dust on the paper. Therefore, in this modified example, when a sensitivity slightly higher than the first sensitivity is used as the second sensitivity in conjunction with the first sensitivity set by the user, the higher the first sensitivity is, the smaller the margin between the first sensitivity and the second sensitivity is according to its magnitude. Note that unnecessary maintenance means maintenance under a situation where the image quality of the next page and subsequent pages is not improved even if maintenance is performed. For example, immediately after maintenance, image quality is hardly improved even if additional maintenance is performed. Maintenance under such a situation is hereinafter referred to as unnecessary maintenance.

[0060] FIG. 5(b) shows an example in which the higher the first sensitivity 522, the smaller the margin 524 between the first sensitivity 522 and the second sensitivity 523 is. In the case of FIG. 5(a), the sensitivity margin is 10, but in the case of FIG. 5(b), when the sensitivity is high, the sensitivity margin 524 is smaller than 10. Specifically, when the user setting 521 is "4", the sensitivity margin 524 is 5, and when the user setting 521 is "5", the sensitivity margin 524 is "2". As a result, for example, when the user setting 511 is "5", in the case of FIG. 5(a), the threshold value is set to 5 as the second sensitivity, which is a value close to 0, and therefore unnecessary maintenance may be frequently activated due to accidental factors such as dust. On the other hand, in the case of FIG. 5(b), when the user setting 521 is “5”, the sensitivity margin 524 is reduced in size, so that the possibility of unnecessary maintenance being triggered due to accidental factors is lower than in the case of FIG. 5(a).

[0061] (Modification 2 of the first embodiment) In this modified example, a first sensitivity used for quality judgment is set for each partial region. For example, in a photograph or graphic region, the sensitivity used for quality judgment is set higher than in a text region. FIG. 6(c) shows an example in which the sensitivity is different between a graphic region and a text region. In a user image 650, a threshold value of a first sensitivity 651 for a user setting region A is set to 15, and a threshold value of a first sensitivity 652 for a user setting region B is set to 60. The smaller the threshold value, the higher the sensitivity. Therefore, the sensitivity used for quality judgment is higher in the user setting region A, which is a graphic region, than in the user setting region B, which is a text region. The range of the partial region and the first sensitivity corresponding to each partial region are set by the user.

[0062] At this time, a sensitivity slightly higher than the first sensitivity is used as the second sensitivity in conjunction with the first sensitivity for each partial region. That is, a different sensitivity may be used for each reading position. In the user image 660, a threshold value of the second sensitivity 661 for the user setting region A is set to 5, and a threshold value of the second sensitivity 662 for the user setting region B is set to 50. In this way, by providing a sensitivity margin for each partial region, before detecting a defect with the first sensitivity set for each partial region, a defect is detected with the second sensitivity set in conjunction with each partial region, and maintenance is started. That is, even when the first sensitivity is set for each partial region, maintenance is started before a NG occurs in the quality judgment using the first sensitivity, so that waste paper can be prevented.

[0063] That is, when the image forming characteristics of the printer deteriorate, maintenance is initiated before a quality judgment results in an NG, thereby preventing the generation of waste paper.

[0064] <<Embodiment 2>> In this embodiment, a host PC having the same functional configuration as the host PC in the first embodiment is used to prevent failure of an image forming device such as a nozzle (recording element). In this embodiment, a use case is assumed in which the quality of the printed matter is relatively unimportant. That is, a case is assumed in which the user expects a low quality for the printed matter and sets a value close to the lower limit as the sensitivity of the quality judgment. When a value close to the lower limit is set as the sensitivity of the quality judgment, NG hardly occurs in the quality judgment. However, in the technology of Patent Document 1, maintenance is not started unless NG occurs in the quality judgment, so in this case, there is a possibility that the nozzle (recording element) will break down due to the maintenance hardly being started. For example, in the case of an inkjet printer, there is a possibility that the nozzle (recording element) of the inkjet head will break down. That is, under conditions in which maintenance is not started periodically, when a value close to the lower limit is set as the sensitivity of the quality judgment, there is a possibility that maintenance will not be started until the nozzle (recording element) breaks down.

[0065] Therefore, in this embodiment, a mode will be described in which a sensitivity that is close to and higher than the lower limit of the first sensitivity that can be set by the user is used as the second sensitivity. The image processing executed by the host PC in this embodiment is the same as that in the first embodiment, and detailed description thereof will be omitted.

[0066] (Image Processing) Image processing (detection processing) in this embodiment will be described below with reference to FIG. 8. FIG. 8 is a block diagram showing the functional configuration (software configuration) of the host PC of this embodiment. The host PC of this embodiment has modules 401-402, 404-406, 410, and 416-418 that the host PC of the first embodiment shown in FIG. 4 has. That is, the host PC of this embodiment has the same modules as the host PC of the first embodiment shown in FIG. 4, except that the host PC of this embodiment does not have the sensitivity setting unit 403 that the host PC of the first embodiment has. Note that in FIG. 8, the same modules as those shown in FIG. 4 are denoted by the same numbers.

[0067] In this embodiment, a sensitivity that is close to and higher than the lower limit of the first sensitivity that can be set by the user is stored in the storage unit 404 as the second sensitivity.

[0068] FIG. 9 is a diagram showing an example of sensitivity used in the detection process of this embodiment. FIG. 9(a) shows the relationship between the first sensitivity and the second sensitivity and the user setting. It is noted that a smaller number in the user setting indicates a lower sensitivity, and a larger number in the user setting indicates a higher sensitivity. The second sensitivity is constant regardless of the user setting. In this embodiment, as in the first embodiment, the first sensitivity 912, 922 can be set from "1" to "5" as the user settings 911, 921. Meanwhile, in the first embodiment, the second sensitivity is linked to the first sensitivity, but in this embodiment, the second sensitivity 913, 923, 924 is not linked to the first sensitivity 912, 922, but a fixed value is used. As the fixed value, a sensitivity that is close to and higher than the lower limit of the first sensitivity that can be set by the user is used.

[0069] In the sensitivity database 910, the user setting 911 is linked to a first sensitivity 912 and a second sensitivity 913. It is assumed that thresholds are set in the first sensitivity 912 and the second sensitivity 913. The user setting 911 "1" is linked to the threshold "240" of the first sensitivity 912 and the threshold "200" of the second sensitivity 913. The user setting 911 "2" is linked to the threshold "120" of the first sensitivity 912 and the threshold "200" of the second sensitivity 913. The user setting 911 "3" is linked to the threshold "60" of the first sensitivity 912 and the threshold "200" of the second sensitivity 913. The user setting 911 "4" is linked to the threshold "30" of the first sensitivity 912 and the threshold "200" of the second sensitivity 913. The value "5" in the user setting 911 is associated with a threshold value "15" in the first sensitivity 912 and a threshold value "200" in the second sensitivity 913 .

[0070] 9(a), the threshold value corresponding to the lower limit of the first sensitivity that can be set by the user is 240. A higher sensitivity in the vicinity of this sensitivity is used as the second sensitivity 913. To increase the sensitivity, the threshold value should be made smaller, so the threshold value corresponding to the second sensitivity 913 is set to 200.

[0071] 10(a), a user image 1010 shows a state in which the threshold value of a first sensitivity 1011 is set to 240 over the entire surface. Also, a user image 1020 shows a state in which the threshold value of a second sensitivity 1021 is set to 200 over the entire surface.

[0072] In this way, by using a sensitivity as the second sensitivity that is close to and higher than the lower limit of the first sensitivity that can be set by the user, failure of the nozzles (printing elements) can be prevented without having to perform maintenance periodically.

[0073] Figure 11 shows the relationship between printing and maintenance and sensitivity. In Figures 11(a) and 11(b), the vertical axis indicates the maximum absolute difference value in the absolute difference image, and the horizontal axis indicates time. In both Figures 11(a) and (b), it is assumed that nozzle (printing element) cleaning is performed as maintenance, and streaky density unevenness becomes noticeable as printing is repeated.

[0074] Fig. 11(a) shows the operation of an image forming system to which the first and second sensitivity setting methods according to this embodiment are applied. In the case of Fig. 11(a), 240, which is the lower limit, is set as the threshold of the first sensitivity 1131. And 200 is set as the threshold of the second sensitivity, which is close to the first sensitivity 1131 and is higher than the first sensitivity. Therefore, maintenance is started before the difference reaches the first sensitivity.

[0075] On the other hand, FIG. 11(b) shows the operation of an image forming system to which the technology described in Patent Document 1 is applied. Patent Document 1 can be said to disclose a configuration that has only a first sensitivity used for quality judgment, and starts maintenance when a defect is detected at the first sensitivity. Therefore, maintenance is not started until a NG occurs in the quality judgment. In this case, if a sensitivity (threshold) close to the lower limit is set as the first sensitivity used for quality judgment, maintenance is hardly started, increasing the possibility of a nozzle (printing element) malfunction. FIG. 11(b) shows a state in which a malfunction occurs when the difference exceeds the second sensitivity 1132 in FIG. 11(a).

[0076] (Modification of the second embodiment) 1 (ends in the X-axis direction), images are more likely to be blurred due to optical aberration than the center of the in-line sensor. Therefore, when detecting defects, defects may occur more frequently in an area read by the end of in-line sensor 107 (for example, an area about 1 cm to 2 cm inward from the end) than in other areas. If the second defect detection sensitivity is set to be the same for such a defect-frequent area and other normal areas outside the defect-frequent area, unnecessary maintenance may be initiated by detecting a defect in the defect-frequent area, even if the possibility of a failure occurring is low.

[0077] In this modified example, therefore, a mode in which the second sensitivity is set for each partial region will be described. Specifically, in the defect-prone region, a lower sensitivity (threshold) is used as the second sensitivity than in the normal region. By lowering the sensitivity, it becomes more difficult to detect defects in the defect-prone region compared to the normal region.

[0078] FIG. 9(b) shows the relationship between the first sensitivity, the second sensitivity (normal region), and the second sensitivity (region where defects frequently occur) and the user settings. A smaller number in the user settings indicates a lower first sensitivity, and a larger number in the user settings indicates a higher first sensitivity. The second sensitivity is constant regardless of the user settings. The "1" in the user settings 921 is associated with the threshold "240" of the first sensitivity 922, the threshold "200" of the second sensitivity (normal region) 923, and the threshold "220" of the second sensitivity (region where defects frequently occur) 924. The "2" in the user settings 921 is associated with the threshold "120" of the first sensitivity 922, the threshold "200" of the second sensitivity (normal region) 923, and the threshold "220" of the second sensitivity (region where defects frequently occur) 924.

[0079] The "3" in the user setting 921 is associated with a threshold value "60" of the first sensitivity 922, a threshold value "200" of the second sensitivity (normal region) 923, and a threshold value "220" of the second sensitivity (region where defects frequently occur) 924. The "4" in the user setting 921 is associated with a threshold value "30" of the first sensitivity 922, a threshold value "200" of the second sensitivity (normal region) 923, and a threshold value "220" of the second sensitivity (region where defects frequently occur) 924. The "5" in the user setting 921 is associated with a threshold value "15" of the first sensitivity 922, a threshold value "200" of the second sensitivity (normal region) 923, and a threshold value "220" of the second sensitivity (region where defects frequently occur) 924.

[0080] The threshold of the second sensitivity 923 in the normal region is the same as the threshold of the second sensitivity 913 shown in Fig. 9(a). On the other hand, the threshold of the second sensitivity 924 in the frequent defect region is set to be higher than the threshold of the second sensitivity 923 in the normal region, thereby making the sensitivity lower than that in the normal region.

[0081] FIG. 10B shows a state where the threshold value of the first sensitivity 1031 is set to 240 over the entire surface of the user image 1030. Also, in the user image 1040, the threshold value of the second sensitivity 1041 for the normal region is set to 200, and the threshold values ​​of the second sensitivities 1042 and 1043 for the frequent defect region are set to 220. In this case, the second sensitivities 1042 and 1043 for the frequent defect region are set to the region corresponding to the end of the in-line sensor 107 in FIG. 1, but they may be set to other regions. For example, in an inkjet printer, defects are likely to occur at a connecting portion where the nozzle rows overlap in the Y direction, such as the connecting portion between the nozzle rows 101a and 101b in FIG. 1. Therefore, the region corresponding to the nozzle connecting portion may be set to the frequent defect region, and other regions outside the frequent defect region may be set to the normal region. In this case, the frequent defect region and the normal region are also separated according to the sensor position of the in-line sensor.

[0082] In this way, by using a lower sensitivity in the defect-prone area than in the normal area as the second sensitivity, it is possible to prevent unnecessary maintenance from being started.

[0083] In addition, not only the second sensitivity but also the first sensitivity used for quality judgment may be set for each partial region. That is, a different sensitivity may be set for each reading position. FIG. 10(c) shows a state in which, in a user image 1050, the threshold value of the first sensitivity 1051 for the user setting region A is set to 15, and the threshold value of the first sensitivity 1052 for the user setting region B is set to 240. On the other hand, in a user image 1060, the threshold value of the second sensitivity 1061 for the normal region is set to 200, and the threshold values ​​of the second sensitivities 1062 and 1063 for the defect-prone regions are set to 220.

[0084] In this way, the partial regions when setting the first sensitivity do not match the partial regions when setting the second sensitivity, because the division of the partial regions when setting the first sensitivity is set by the user, whereas the division of the partial regions when setting the second sensitivity is set depending on whether defects occur frequently or not.

[0085] <<Embodiment 3>> This embodiment is a combination of the first and second embodiments, and provides two advantages: preventing the generation of waste paper and preventing failure of nozzles (recording elements).

[0086] (Image Processing) Image processing (detection processing) in this embodiment will be described below with reference to Fig. 12 and Fig. 13. Fig. 12 is a flowchart showing the flow of image processing executed by the host PC in this embodiment. The explanation will focus on the differences from the flowchart shown in Fig. 3.

[0087] If a determination result indicating that there is no defect is obtained in S308 (NO in S308), the process proceeds to S1201. In S1201, the defect detection unit 410 executes a process of detecting defects at a third sensitivity. At this time, the threshold processing unit 413 uses a threshold value stored in the storage unit 1301. The content of the process for detecting defects is the same as that of S307 described above, except that a different sensitivity is used. As described above, the switching unit 1302 is used to select the sensitivity to be used in the process.

[0088] In S1202, the maintenance startup unit 1303 determines whether or not a defect is detected when the third sensitivity is used. If the determination result indicates that a defect is not detected (NO in S1202), maintenance is not started and the third detection process using the third sensitivity is terminated. If the determination result indicates that a defect is detected (YES in S1202), the process proceeds to S309.

[0089] Fig. 13 is a block diagram showing a functional configuration (software configuration) of the host PC of this embodiment. The CPU 201 of the host PC 20 executes a program stored in the HDD 203 to realize each module shown in Fig. 13. The host PC of this embodiment has a storage unit 1301 that stores a third sensitivity, a switching unit 1302, and a maintenance startup unit 1303 in addition to the modules 401 to 406, 410, 417, and 418 that the host PC of the first embodiment shown in Fig. 4 has. In Fig. 13, the same modules as those shown in Fig. 4 are denoted by the same numbers.

[0090] In this embodiment, the second sensitivity is the same as that in the first embodiment. That is, in this embodiment, a sensitivity slightly higher than the first sensitivity is used as the second sensitivity in conjunction with the first sensitivity set by the user. This makes it possible to prevent the generation of waste paper, as in the first embodiment.

[0091] On the other hand, the second sensitivity in the second embodiment is used as the newly added third sensitivity. That is, in this embodiment, a sensitivity that is close to and higher than the lower limit of the first sensitivity that can be set by the user is used as the third sensitivity. This makes it possible to prevent failure of the nozzles (printing elements) in the same way as in the second embodiment. This third sensitivity is stored in the storage unit 1301.

[0092] The defect detection unit 410 detects defects using each of the first sensitivity, the second sensitivity, and the third sensitivity. A switching unit 1302 is used to switch the sensitivity used in the defect detection unit 410.

[0093] The maintenance startup unit 1303 starts maintenance when a defect is detected with either the second sensitivity or the third sensitivity. Different maintenance may be started when a defect is detected with the second sensitivity and when a defect is detected with the third sensitivity. For example, when a defect is detected with the second sensitivity, image quality recovery maintenance may be started as the maintenance, and when a defect is detected with the third sensitivity, failure prevention maintenance may be started as the maintenance. As image quality recovery maintenance, head shading parameters are updated and non-ejection compensation parameters are updated. As failure prevention maintenance, inkjet nozzle cleaning is performed.

[0094] FIG. 14 is a diagram showing an example of sensitivity used in the detection process of this embodiment. The sensitivity database 1410 shows the relationship between the first sensitivity 1412, the second sensitivity 1413, and the third sensitivity 1414 and the user setting 1411. It is noted that a smaller number in the user setting 1411 indicates a lower first sensitivity 1412, and a larger number in the user setting 1411 indicates a higher first sensitivity 1412. The third sensitivity 1414 is constant regardless of the user setting 1411. The first sensitivity 1412 and the second sensitivity 1413 are the same as the first sensitivity 512 and the second sensitivity 513 shown in FIG. 5(a). The third sensitivity 1414 is the same as the second sensitivity 913 shown in FIG. 9(a). In this way, the second sensitivity 1413 is linked to the first sensitivity 1412, but the third sensitivity 1414 is not linked to the first sensitivity 1412.

[0095] As described above, in this embodiment, by combining the first and second embodiments, two effects can be obtained: the effect of preventing the generation of waste paper, and the effect of preventing failure of nozzles (recording elements).

[0096] (Modification of the third embodiment) In this modified example, the first sensitivity, the second sensitivity, and the third sensitivity are set for each partial region. Fig. 15 is a diagram showing an example of setting the first sensitivity, the second sensitivity, and the third sensitivity in a user image.

[0097] 15(a) shows a state in which 15 is set as the threshold value of a first sensitivity 1511 for a user setting area A in a scanned image 1510, and 240 is set as the threshold value of a first sensitivity 1512 for a user setting area B. User setting area A indicates a graphic area. User setting area B indicates a text area.

[0098] At this time, similarly to the first embodiment, a sensitivity slightly higher than the first sensitivity is used as the second sensitivity in conjunction with the first sensitivity for each partial region. That is, a different sensitivity is used for each reading position. FIG. 15(b) shows a state in which the threshold value of the second sensitivity 1521 for the user setting region A is set to 5, and the threshold value of the second sensitivity 1522 for the user setting region B is set to 230 in the scanned image 1520. The user setting region A indicates a graphic region. The user setting region B indicates a character region. In the case of FIG. 15(b), a defect is detected with the second sensitivity before a defect is detected with the first sensitivity set for each partial region, and maintenance is started, thereby preventing the generation of waste paper.

[0099] On the other hand, as for the third sensitivity, as in the second embodiment, a sensitivity that is close to and higher than the lower limit of the first sensitivity that can be set by the user is set as the third sensitivity, and further, different sensitivities are used for the frequent defect area and the normal area as the third sensitivity. That is, a lower sensitivity is used for the frequent defect area than for the normal area as the third sensitivity. FIG. 15(c) shows a state in which, in a user image 1530, 200 is set as the threshold value of the third sensitivity 1531 for the normal area, and 220 is set as the threshold values ​​of the third sensitivities 1532 and 1533 for the frequent defect area. In the case of FIG. 15(c), it is possible to prevent unnecessary maintenance from being started in the frequent defect area.

[0100] [Other embodiments] If unnecessary maintenance is initiated due to an accidental factor such as dust on the paper, the time during which printing cannot be performed will increase. In particular, in the first embodiment, the second sensitivity is set higher than the first sensitivity, so that there is a possibility that unnecessary maintenance will be initiated due to an accidental factor. To prevent this, when a defect is detected with the second sensitivity, the characteristics of the image area in which the defect was detected may be examined, and whether or not to initiate maintenance may be determined based on the characteristics.

[0101] For example, when a defect is found in white paper, it can be determined that the defect is not caused by inkjet non-discharge. However, when the method of the first embodiment is applied, even in such a case, there is a possibility that maintenance to deal with the non-discharge may be started. Therefore, when the DUTY of the image area where the defect is detected in the second sensitivity does not exceed a predetermined value, maintenance is not started. Note that the density of the image may be used instead of the DUTY. This reduces the possibility of erroneously starting maintenance to deal with the non-discharge when a defect is found in white paper.

[0102] Furthermore, when white streaks are found in flat areas using the second sensitivity, it is highly likely that they are caused by inkjet non-discharge, but when defects are found in character or texture areas, other causes such as the attachment of dirt may be considered. Therefore, if the pixel variation in an area where a defect is detected using the second sensitivity does not fall below a predetermined value and the area is not substantially flat, maintenance is not started. This reduces the possibility of erroneously starting maintenance to deal with non-discharge when a defect is found in a character or texture area.

[0103] Furthermore, when the second sensitivity is used, it is possible to check whether defects are detected consecutively on multiple pages, and if they are not detected consecutively, not to start maintenance, thereby reducing the possibility of starting unnecessary maintenance. At this time, it is also possible to check whether defects are detected at the same location on multiple pages, and if defects are not detected at the same location on multiple pages, not to start maintenance.

[0104] In addition, when detecting defects using the second sensitivity or the third sensitivity, the defect detection result changes depending on the conditions at the time of printing or the conditions at the time of defect detection. However, it is desirable that the judgment of whether or not to start maintenance does not change depending on the conditions at the time of printing or the conditions at the time of defect detection. In particular, in the second embodiment, the necessity of maintenance to prevent failure of the nozzle (recording element) is judged. Therefore, when it becomes difficult to detect defects due to the conditions at the time of printing or the conditions at the time of defect detection, there is a possibility that the nozzle (recording element) will fail without starting maintenance. In order to deal with this, it is effective to change the second sensitivity or the third sensitivity depending on the conditions at the time of printing or the conditions at the time of defect detection. For example, when there are a high-speed mode and a low-speed mode as printing conditions, defects caused by printing are less likely to occur in the low-speed mode than in the high-speed mode, so that the second sensitivity or the third sensitivity is made higher in the low-speed mode than in the high-speed mode. Note that the high-speed mode is a mode in which an image is formed by increasing the paper transport speed and lowering the print resolution. The low-speed mode is a mode in which the paper transport speed is slowed down and the print resolution is increased to form an image.

[0105] In addition, since defects appear differently depending on the paper used for printing, the second sensitivity or the third sensitivity may be changed depending on the type of paper. For example, with thick paper, the distance to the in-line sensor 107 is shorter than with normal paper, and defects are more likely to appear due to the influence of optical blur. Therefore, with thick paper, the second sensitivity or the third sensitivity is made lower than with normal paper.

[0106] In addition, there are a method of using the user image 421 and a method of using an image printed and scanned in the past as the reference image 422. Comparing these, the image printed and scanned in the past contains defects such as non-discharge caused by printer fluctuations, whereas the user image 421 does not contain defects because it is an input image used for print output. Therefore, when an image printed and scanned in the past is used as the reference image 422, defects are less likely to occur compared to when the user image 421 is used. Therefore, when an image printed and scanned in the past (inspection image) is used as the reference image 422, the second sensitivity or the third sensitivity is made higher than when the user image 421 is used. That is, in the special mode in which an inspection image acquired in the past is used as the reference image, a higher sensitivity is used as the second sensitivity or the third sensitivity than in the normal mode in which a user image is used as the reference image.

[0107] Furthermore, in order to reduce the processing load, defect detection using the second sensitivity or the third sensitivity may be performed at a predetermined page interval of two or more pages.

[0108] In addition, in the first to third embodiments, the maintenance is adaptively performed, but the maintenance may be performed periodically and adaptively. For example, the maintenance is periodically performed by starting the maintenance when the counter for the print volume or the elapsed time reaches a specified value. In such a configuration, when a defect is detected using the second sensitivity and the maintenance is started as a result, the counter is reset. This makes it possible to extend the time until the next regular maintenance and reduce the time during which printing cannot be performed. In addition, in such a configuration, in a print job that performs defect detection using the second sensitivity, the maintenance is not started even if the counter reaches a specified value during the execution of the print job. This makes it possible to prevent the maintenance from being started at a timing not desired by the user.

[0109] In addition, in order to adjust the sensitivity of defect detection, the filter coefficient used in the filter processing unit 412 may be adjusted. In addition, a configuration for multiplying a gain by the difference image output by the difference image generating unit 411 may be added, and the sensitivity of defect detection may be adjusted by adjusting the gain. Similarly, a configuration for multiplying a gain by the difference image after filtering output by the filter processing unit 412 may be added, and the sensitivity of defect detection may be adjusted by adjusting the gain. In addition, a configuration for performing an opening process on the binary image output by the threshold processing unit 413 may be added, and the sensitivity of defect detection may be adjusted by adjusting the parameters. That is, the sensitivity of defect detection may be increased or decreased by increasing or decreasing the parameters. The opening process is a process of contracting the same number of times and then expanding.

[0110] The present disclosure can also be realized by a process in which a program for implementing one or more functions of the above-described embodiments is supplied to a system or device via a network or a storage medium, and one or more processors in a computer of the system or device read and execute the program. It can also be realized by a circuit (e.g., ASIC) that implements one or more functions.

[0111] The disclosure of this embodiment includes the following configuration examples.

[0112] (Configuration 1) A reading means for obtaining a read image by reading a printed matter on which an image is printed on a recording medium; a detection means for detecting defects in the printed matter based on a difference image between the read image and a reference image serving as a reference for inspection; having The detection means includes: performing a first detection process to detect defects on the printed matter using a first sensitivity; A second detection process for maintenance of a printing means that prints on the recording medium is executed using a second sensitivity different from the first sensitivity. 13. An image processing device comprising:

[0113] (Configuration 2) a notification unit for notifying a user of the quality of the printed matter; The notifying means notifies the user of the quality of the printed matter when the detecting means executes the first detection process and detects a defect in the printed matter. 2. The image processing device according to claim 1,

[0114] (Configuration 3) The printing apparatus further includes a start-up unit for starting maintenance of the printing unit, The starting means starts maintenance of the printing means when the defect is detected by executing the second detection process by the detection means. 3. The image processing device according to configuration 1 or 2.

[0115] (Configuration 4) The second sensitivity is higher than the first sensitivity. 4. The image processing device according to any one of configurations 1 to 3.

[0116] (Configuration 5) The detection means uses a sensitivity higher than the first sensitivity as the second sensitivity in conjunction with the first sensitivity set by a user. 5. The image processing device according to any one of configurations 1 to 4.

[0117] (Configuration 6) The detection means uses the second sensitivity having a smaller margin between the first sensitivity and the second sensitivity as the first sensitivity is higher. 6. The image processing device according to any one of configurations 2 to 5.

[0118] (Configuration 7) 7. The image processing device according to any one of configurations 2 to 6, wherein the notification means uses a different sensitivity for each partial region of the reference image as the first sensitivity.

[0119] (Configuration 8) The detection means uses a sensitivity higher than the first sensitivity as the second sensitivity in conjunction with the first sensitivity for each partial region of the reference image. 8. The image processing device according to any one of configurations 3 to 7.

[0120] (Configuration 9) 8. The image processing device according to configuration 7, wherein the range of the partial region and the first sensitivity corresponding to the partial region are set by the user.

[0121] (Configuration 10) 9. The image processing device according to configuration 8, wherein the range of the partial region and the first sensitivity corresponding to the partial region are set by a user.

[0122] (Configuration 11) The activation means uses a sensitivity that is close to and higher than a lower limit of the first sensitivity that can be set by a user as the second sensitivity. 11. The image processing device according to any one of configurations 3 to 10.

[0123] (Configuration 12) a notification unit for notifying a user of the quality of the printed matter; When the detection means detects a defect in the print by executing the first detection process using a different sensitivity for each partial area of ​​the reference image as the first sensitivity, the notification means notifies the user of the quality of the print. 12. The image processing device according to claim 11,

[0124] (Configuration 13) 13. The image processing device according to claim 11, wherein the activation means uses a different sensitivity for each reading position of the reading means as the second sensitivity.

[0125] (Configuration 14) The starting means uses, in a defect-prone region where the defect frequently occurs, a sensitivity lower than that of a normal region excluding the defect-prone region as the second sensitivity. 14. The image processing device according to claim 13,

[0126] (Configuration 15) The range of the partial region of the reference image and the first sensitivity corresponding to the partial region are set by a user. 15. The image processing device according to any one of configurations 11 to 14.

[0127] (Configuration 16) The printing apparatus further includes a start-up unit for starting maintenance of the printing unit, the detection unit executes a third detection process for maintenance of the printing unit using a third sensitivity different from the first sensitivity and the second sensitivity; The detection means includes: When the defect is detected by executing the second detection process using a second sensitivity that is linked to the first sensitivity set by a user and is higher than the first sensitivity, or when the defect is detected by executing the third detection process using a sensitivity that is close to and higher than a lower limit of the first sensitivity that can be set by the user as the third sensitivity, The starting means starts the maintenance. 16. The image processing device according to any one of configurations 1 to 15.

[0128] (Configuration 17) a notification unit for notifying the user of the quality of the printed matter; When the detection means detects a defect in the print by executing the first detection process using a different sensitivity for each partial area of ​​the reference image as the first sensitivity, the notification means notifies the user of the quality of the print. 17. The image processing device according to claim 16,

[0129] (Configuration 18) The starting means includes: For each of the partial regions, a sensitivity higher than the first sensitivity is used as the second sensitivity in conjunction with the first sensitivity; A sensitivity that differs for each reading position by the reading means is used as the third sensitivity. 18. The image processing device according to claim 17,

[0130] (Configuration 19) The starting means uses, in a defect-prone region where the defects frequently occur, a sensitivity lower than that of a normal region excluding the defect-prone region as the third sensitivity. 19. The image processing device according to configuration 18.

[0131] (Configuration 20) the printing means is an inkjet type, and forms an image using a head having a connection portion connecting two or more nozzle rows; The defect-prone region is located at a position corresponding to a connection portion of the nozzle rows. 20. The image processing device according to any one of configurations 14 to 19.

[0132] (Configuration 21) The starting means does not start the maintenance when the duty of the area in which the defect is detected in the second detection process does not exceed a predetermined value. 21. The image processing device according to any one of configurations 3 to 20.

[0133] (Configuration 22) The starting means does not start the maintenance when a pixel variation in the area where the defect is detected in the second detection process does not fall below a predetermined value. 22. The image processing device according to any one of configurations 3 to 21,

[0134] (Configuration 23) The starting means does not start the maintenance when the defect is not detected continuously on a plurality of pages in the second detection process. 23. The image processing device according to any one of configurations 3 to 22.

[0135] (Configuration 24) the printing means has a high-speed mode and a low-speed mode, In the low speed mode, the activation means uses a higher sensitivity as the second sensitivity than in the high speed mode. 24. The image processing device according to any one of configurations 11 to 23.

[0136] (Configuration 25) 25. The image processing device according to any one of configurations 11 to 24, wherein the starting means uses a sensitivity that differs depending on the type of the recording medium as the second sensitivity.

[0137] (Configuration 26) the detection means has a normal mode in which the image is used as the reference image, and a special mode in which a previously acquired inspection image is used as the reference image; The activation means uses a higher sensitivity in the special mode than in the normal mode as the second sensitivity. 26. The image processing device according to any one of configurations 11 to 25.

[0138] (Configuration 27) 27. The image processing device according to any one of configurations 3 to 26, wherein the starting means executes the second detection process at a predetermined page interval of two or more pages.

[0139] (Configuration 28) The printing means performs printing by an inkjet method, The maintenance includes any one of updating a head shading parameter, updating a discharge failure compensation parameter, and cleaning a nozzle. 28. The image processing device according to any one of configurations 1 to 27.

[0140] (Configuration 29) The printing apparatus further includes a start-up unit for starting maintenance of the printing unit, the starting means starts the maintenance when a print volume or an elapsed time counter reaches a specified value; When the maintenance is started due to the defect being detected in the second detection process, the counter is reset. 29. The image processing device according to configuration 28.

[0141] (Configuration 30) 30. The image processing device according to claim 29, wherein the starting means does not start the maintenance in a print job that executes the second detection process, even if the counter reaches the specified value during execution of the print job.

[0142] (Configuration 31) the starting means starts different maintenance operations depending on whether the defect is detected in the second detection process or the third detection process; When the defect is detected in the second detection process, image quality recovery maintenance is started as the maintenance, When the defect is detected in the third detection process, a preventive maintenance is started as the maintenance. 31. The image processing device according to any one of configurations 16 to 30.

[0143] (Configuration 32) The detection means includes: a filter processing means for performing a filter process on the difference image to enhance a predetermined defect; a generating means for generating a binary image from the difference image enhanced by the filtering means; having The detection means detects the defect based on the binary image generated by the generation means. 32. The image processing device according to any one of configurations 1 to 31.

[0144] (Configuration 33) The detection means adjusts the sensitivity in accordance with a threshold value used by the generation means. 33. The image processing device according to claim 32,

[0145] (Configuration 34) the detection means has a multiplication means for multiplying the difference image by a gain, The sensitivity is adjusted by adjusting the gain. 34. The image processing device according to claim 33,

[0146] (Configuration 35) the detection means has a multiplication means for multiplying the difference image enhanced by the filter processing means by a gain, The sensitivity is adjusted by adjusting the gain. 33. The image processing device according to claim 32,

[0147] (Configuration 36) the detection means has an opening processing means for performing an opening process on the binary image generated by the generation means, 33. The image processing apparatus according to configuration 32, wherein the detection means detects the defect based on the binary image that has been subjected to the opening process by the opening process means.

[0148] (Configuration 37) a reading step of acquiring a read image by reading a printed matter on which an image is printed on a recording medium; a detection step of detecting defects in the printed matter based on a difference between the read image and a reference image serving as a reference for inspection; Including, In the detection step, performing a first detection process to detect defects on the printed matter using a first sensitivity; performing a second detection process for initiating maintenance of a printing means for printing on the recording medium using a second sensitivity different from the first sensitivity; 13. An image processing method comprising:

[0149] (Configuration 38) 38. A program for causing a computer to execute each step of the image processing method according to claim 37.

Claims

1. A reading means for obtaining a read image by reading a printed matter on which an image is printed on a recording medium; a detection means for detecting defects in the printed matter based on a difference image between the read image and a reference image serving as a reference for inspection; having The detection means includes: performing a first detection process to detect defects on the printed matter using a first sensitivity; A second detection process for maintenance of a printing means that prints on the recording medium is executed using a second sensitivity different from the first sensitivity.

13. An image processing device comprising:

2. a notification unit for notifying a user of the quality of the printed matter; The notifying means notifies the user of the quality of the printed matter when the detecting means executes the first detection process and detects a defect in the printed matter.

2. The image processing device according to claim 1,

3. The printing apparatus further includes a start-up unit for starting maintenance of the printing unit, The starting means starts maintenance of the printing means when the defect is detected by executing the second detection process by the detection means.

2. The image processing device according to claim 1,

4. The second sensitivity is higher than the first sensitivity.

2. The image processing device according to claim 1,

5. The detection means uses a sensitivity higher than the first sensitivity as the second sensitivity in conjunction with the first sensitivity set by a user.

2. The image processing device according to claim 1,

6. The detection means uses the second sensitivity having a smaller margin between the first sensitivity and the second sensitivity as the first sensitivity is higher.

3. The image processing device according to claim 2.

7. 3. The image processing apparatus according to claim 2, wherein the notification means uses a different sensitivity for each partial area of ​​the reference image as the first sensitivity.

8. The detection means uses a sensitivity higher than the first sensitivity as the second sensitivity in conjunction with the first sensitivity for each partial region of the reference image.

4. The image processing device according to claim 3.

9. The image processing device according to claim 7 , wherein the range of the partial region and the first sensitivity corresponding to the partial region are set by the user.

10. The image processing device according to claim 8 , wherein the range of the partial region and the first sensitivity corresponding to the partial region are set by a user.

11. The activation means uses a sensitivity that is close to and higher than a lower limit of the first sensitivity that can be set by a user as the second sensitivity.

4. The image processing device according to claim 3.

12. a notification unit for notifying a user of the quality of the printed matter; When the detection means detects a defect in the print by executing the first detection process using a different sensitivity for each partial area of ​​the reference image as the first sensitivity, the notification means notifies the user of the quality of the print. The image processing device according to claim 11 .

13. 12. The image processing apparatus according to claim 11, wherein the activation means uses a different sensitivity for each reading position of the reading means as the second sensitivity.

14. The starting means uses, in a defect-prone region where the defects frequently occur, a sensitivity lower than that of a normal region excluding the defect-prone region as the second sensitivity. The image processing device according to claim 13 .

15. The range of the partial region of the reference image and the first sensitivity corresponding to the partial region are set by a user. The image processing device according to claim 11 .

16. The printing apparatus further includes a start-up unit for starting maintenance of the printing unit, the detection unit executes a third detection process for maintenance of the printing unit using a third sensitivity different from the first sensitivity and the second sensitivity; The detection means includes: When the defect is detected by executing the second detection process using a second sensitivity that is linked to the first sensitivity set by a user and is higher than the first sensitivity, or when the defect is detected by executing the third detection process using a sensitivity that is close to and higher than a lower limit of the first sensitivity that can be set by the user as the third sensitivity, The starting means starts the maintenance.

2. The image processing device according to claim 1,

17. a notification unit for notifying the user of the quality of the printed matter; When the detection means detects a defect in the print by executing the first detection process using a different sensitivity for each partial area of ​​the reference image as the first sensitivity, the notification means notifies the user of the quality of the print.

17. The image processing device according to claim 16,

18. The starting means includes: For each of the partial regions, a sensitivity higher than the first sensitivity is used as the second sensitivity in conjunction with the first sensitivity; A sensitivity that differs for each reading position by the reading means is used as the third sensitivity.

18. The image processing device according to claim 17,

19. The starting means uses, in a defect-prone region where the defects frequently occur, a sensitivity lower than that of a normal region excluding the defect-prone region as the third sensitivity.

20. The image processing device according to claim 18,

20. the printing means is an inkjet type, and forms an image using a head having a connection portion connecting two or more nozzle rows; The defect-prone region is located at a position corresponding to a connection portion of the nozzle rows.

15. The image processing device according to claim 14.

21. The starting means does not start the maintenance when a duty of the area in which the defect is detected in the second detection process does not exceed a predetermined value.

4. The image processing device according to claim 3.

22. The starting means does not start the maintenance when a pixel variation in the area where the defect is detected in the second detection process does not fall below a predetermined value.

4. The image processing device according to claim 3.

23. The starting means does not start the maintenance when the defect is not detected continuously on a plurality of pages in the second detection process.

4. The image processing device according to claim 3.

24. the printing means has a high-speed mode and a low-speed mode; In the low speed mode, the activation means uses a higher sensitivity as the second sensitivity than in the high speed mode. The image processing device according to claim 11 .

25. 12. The image processing apparatus according to claim 11, wherein the starting means uses a sensitivity that differs depending on the type of the recording medium as the second sensitivity.

26. the detection means has a normal mode in which the image is used as the reference image, and a special mode in which a previously acquired inspection image is used as the reference image; The activation means uses a higher sensitivity in the special mode than in the normal mode as the second sensitivity. The image processing device according to claim 11 .

27. 4. The image processing apparatus according to claim 3, wherein the starting means executes the second detection process at a predetermined page interval of two or more pages.

28. The printing means performs printing by an inkjet method, The maintenance includes any one of updating a head shading parameter, updating a discharge failure compensation parameter, and cleaning a nozzle.

2. The image processing device according to claim 1,

29. The printing apparatus further includes a start-up unit for starting maintenance of the printing unit, the starting means starts the maintenance when a print volume or an elapsed time counter reaches a specified value; When the maintenance is started due to the defect being detected in the second detection process, the counter is reset.

29. The image processing device according to claim 28.

30. 30. The image processing apparatus according to claim 29, wherein the starting means does not start the maintenance in a print job for which the second detection process is executed, even if the counter reaches the specified value during execution of the print job.

31. the starting means starts different maintenance operations depending on whether the defect is detected in the second detection process or the third detection process; When the defect is detected in the second detection process, image quality recovery maintenance is started as the maintenance, When the defect is detected in the third detection process, a preventive maintenance is started as the maintenance.

17. The image processing device according to claim 16,

32. The detection means includes: a filter processing means for performing a filter process on the difference image to enhance a predetermined defect; a generating means for generating a binary image from the difference image enhanced by the filtering means; having The detection means detects the defect based on the binary image generated by the generation means.

2. The image processing device according to claim 1,

33. The detection means adjusts the sensitivity in accordance with a threshold value used by the generation means.

33. The image processing apparatus according to claim 32.

34. the detection means has a multiplication means for multiplying the difference image by a gain, The sensitivity is adjusted by adjusting the gain.

33. The image processing apparatus according to claim 32.

35. the detection means has a multiplication means for multiplying the difference image enhanced by the filter processing means by a gain, The sensitivity is adjusted by adjusting the gain.

33. The image processing apparatus according to claim 32.

36. the detection means has an opening processing means for performing an opening process on the binary image generated by the generation means, 33. The image processing apparatus according to claim 32, wherein said detection means detects said defect based on said binary image that has been subjected to the opening process by said opening process means.

37. a reading step of acquiring a read image by reading a printed matter on which an image is printed on a recording medium; a detection step of detecting defects in the printed matter based on a difference between the read image and a reference image serving as a reference for inspection; Including, In the detection step, performing a first detection process to detect defects on the printed matter using a first sensitivity; performing a second detection process for initiating maintenance of a printing means for printing on the recording medium using a second sensitivity different from the first sensitivity; 13. An image processing method comprising:

38. A program for causing a computer to execute each step of the image processing method according to claim 37.

Images