Inspection equipment and program

Abstract

To provide an inspection device which generates a reference image used as a reference for defect inspection from print data, and is capable of performing more accurate defect inspection compared with a case where inspection for defects is performed on a print without using information on color of a sheet.SOLUTION: When performing defect inspection by comparing a first image generated from print data used to generate a print and a second image read from the print, a processor of an inspection device provided herein acquires a color difference between sheet portions of the first and second images, sets an inspection threshold according to the acquired color difference, and inspects the print for defects using the set threshold.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an inspection device and a program. [Background technology]

[0002] 2. Description of the Related Art Some printing systems include a process of inspecting printed matter for defects as a post-process of the printing process. In this type of printing system, an image used as a standard for inspection (hereinafter referred to as a "reference image") may be generated from print data corresponding to the printed material. This type of printing system compares an image optically read from the printed material (hereinafter referred to as an "inspection image") with the reference image, and determines that any areas where the pixel values ​​of the different parts exceed a threshold value are defective. Examples of defects include stains and whiteouts. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-255216 Summary of the Invention [Problem to be solved by the invention]

[0004] In reality, the color of paper used for printing is not necessarily limited to white. For example, blue paper may also be used. On the other hand, the reference image is based on the assumption that the image corresponding to the print data will be printed on white paper. For this reason, the color of the paper in the inspection image may cause areas that are not actually problematic to be erroneously detected as defective.

[0005] The present invention aims to improve the accuracy of defect inspection in an inspection device that generates a reference image used as a basis for defect inspection from print data, compared to inspecting printed matter for defects without using paper color information. [Means for solving the problem]

[0006] The invention of claim 1 is an inspection device having a processor, wherein when inspecting for defects by comparing a first image generated from print data used to generate a printed matter with a second image read from the printed matter, the processor obtains a color difference between the paper portions of the first image and the second image, sets a threshold value for inspection according to the obtained color difference, and inspects for defects in the printed matter using the set threshold value. the processor corrects a previously prepared initial value according to the color difference and sets the corrected value as the threshold value; If the corrected value exceeds a predetermined upper limit, the upper limit is set as the threshold. , inspection equipment is. Claim 2 The invention described in an inspection device having a processor, wherein when inspecting for defects by comparing a first image generated from print data used to generate a printed matter with a second image read from the printed matter, the processor acquires a color difference between a paper portion of the first image and the second image, sets a threshold value for inspection according to the acquired color difference, and inspects for defects on the printed matter using the set threshold value, wherein the processor sets a value obtained by correcting a previously prepared initial value according to the color difference as the threshold value; The amount of reflection of the color difference is changed depending on the type of defect to be detected. 、 It is an inspection device. Claim 3 The invention described in an inspection device having a processor, wherein when inspecting for defects by comparing a first image generated from print data used to generate a printed matter with a second image read from the printed matter, the processor acquires a color difference between a paper portion of the first image and the second image, sets a threshold value for inspection according to the acquired color difference, and inspects for defects on the printed matter using the set threshold value, wherein the processor sets a value obtained by correcting a previously prepared initial value according to the color difference as the threshold value; If the paper before printing contains multiple areas with different colors, the color difference is obtained for each area, and the threshold is set for each area. 、 It is an inspection device. Claim 4 The invention described in is a program for causing a computer that inspects defects by comparing a first image generated from print data used to generate a printed matter with a second image read from the printed matter to achieve the following functions: acquiring a color difference between the paper portions of the first image and the second image; setting a threshold value for inspection according to the acquired color difference; and inspecting defects in the printed matter using the set threshold value. and the function of setting the threshold value is a program that corrects a previously prepared initial value according to the color difference and sets the corrected value as the threshold value, and if the corrected value exceeds a predetermined upper limit value, sets the upper limit value as the threshold value. do. The invention described in claim 5 is a program for enabling a computer that inspects defects by comparing a first image generated from printing data used to generate a printed matter with a second image read from the printed matter to achieve the following functions: acquiring the color difference between the paper portions of the first image and the second image; setting a threshold value for inspection according to the acquired color difference; and inspecting defects in the printed matter using the set threshold value; wherein the function of setting the threshold value is a program that sets a value that is a pre-prepared initial value corrected according to the color difference as the threshold value, and changes the amount of reflection of the color difference according to the type of defect to be detected. The invention described in claim 6 is a program for enabling a computer that inspects defects by comparing a first image generated from printing data used to generate a printed matter with a second image read from the printed matter to achieve the following functions: acquiring the color difference between the paper portions of the first image and the second image; setting a threshold value for inspection according to the acquired color difference; and inspecting defects in the printed matter using the set threshold value; wherein the function of setting the threshold value is set to a value obtained by correcting a pre-prepared initial value according to the color difference; and, if the paper before printing contains multiple areas of different colors, acquiring the color difference for each area and setting the threshold value for each area. [Effects of the Invention]

[0007] Claim 1 According to the described invention, it is possible to avoid a decrease in detection accuracy due to an excessively large threshold value. Claim 2 According to the described invention, the accuracy of defect detection can be maintained regardless of the type of defect to be detected. Claim 3 According to the described invention, the accuracy of defect detection can be maintained even when the paper is not monochromatic. According to the invention of claim 4, it is possible to avoid a decrease in detection accuracy due to an excessively large threshold value. According to the invention of claim 5, the accuracy of defect detection can be maintained regardless of the type of defect to be detected. According to the sixth aspect of the present invention, the accuracy of defect detection can be maintained even when the color of the paper is not monochromatic. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of an image printing system used in the first embodiment. [Figure 2] FIG. 2 is a diagram illustrating an example of a hardware configuration of an inspection device. [Figure 3] FIG. 2 is a diagram illustrating an example of a functional configuration of an inspection apparatus. [Figure 4] 5 is a flowchart illustrating an example of an inspection operation for defects by the inspection device used in the first embodiment. [Figure 5] 1A and 1B are diagrams illustrating examples of calculation of the color difference between paper on which an inspection image is printed and white paper on which the reference image is assumed, where (A) shows an example in which the inspection image is printed on white paper, and (B) shows an example in which the inspection image is printed on colored paper. [Figure 6] 10 is a table illustrating an example of setting threshold values ​​according to the type of paper and the presence or absence of an edge. [Figure 7] 1A and 1B are diagrams illustrating examples of threshold settings and judgments used in defect inspection, where (A) shows an example of threshold settings and judgments when the inspection image is printed on white paper, and (B) shows an example of threshold settings and judgments when the inspection image is printed on colored paper. [Figure 8] FIG. 10 is a diagram illustrating components related to a function for a user to specify an area in which the ground color of a sheet is to be detected. [Figure 9] 10A and 10B are diagrams illustrating an example of an operation screen displayed on a display by an area designation UI unit. [Figure 10] 10A and 10B are diagrams illustrating an example of a method for reading out threshold values ​​to be used in an inspection operation by utilizing the operation of selecting paper to be used for printing. (A) shows an example of an operation screen, and (B) shows an example of a table that stores the relationship between the tray containing paper and the set of threshold values. [Figure 11]10A and 10B are diagrams illustrating another example of a method for reading out threshold values ​​to be used in an inspection operation by utilizing the operation of selecting the paper to be used for printing, where (A) shows an example of an operation screen, and (B) shows an example of a table that stores the relationship between paper names and threshold sets. [Figure 12] 10 is a table illustrating an example of setting threshold values ​​according to the type of paper and the presence or absence of an edge. [Figure 13] 10A and 10B are diagrams illustrating an example of an inspection image and threshold settings when one sheet of paper has two background colors. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. <First Embodiment> <System configuration> FIG. 1 is a diagram illustrating an example of the configuration of an image printing system 1 used in the first embodiment. The image printing system 1 shown in FIG. 1 is made up of a print data generating device 20 and a printing system 30 connected to a network 10. For example, a wired LAN (Local Area Network) or a wireless LAN is used as the network 10. However, the Internet or a mobile communication system such as 5G may also be used as the network 10.

[0010] The print data generating device 20 is a processing device that converts document data into print data. The print data generating device 20 is also called, for example, a DFE (Digital Front End) or a RIP (Raster Image Processor). In this embodiment, print data is output as raster format data (hereinafter referred to as "raster data"). Note that document data is text and images, and is provided from a computer operated by a user.

[0011] The printing system 30 comprises a printing device 310 that prints an image corresponding to the printing data on the surface of paper, an inspection device 320 that receives printed paper (hereinafter also referred to as "printed matter") from the printing device 310 and inspects the printing defects, and a post-processing device 330 that processes the printed matter according to a pre-specified output format. The printing device 310 has a processing unit that processes print data and a printing unit that prints an image on paper. The printing device 310 prints an image on the surface of paper using, for example, an electrophotographic method or an inkjet method. In this embodiment, the paper is assumed to be cut paper. However, the paper may also be roll paper.

[0012] The inspection device 320 optically reads the printed matter discharged from the printing device 310 to obtain an inspection image, and inspects the printed matter for defects in real time. The inspection image is an example of a second image. Defects to be detected include, for example, stains and white spots. Inspection device 320 in this embodiment generates a reference image from print data to be used as a reference when inspecting for print defects. The reference image is an example of a first image. The post-processing device 330 is a so-called finisher, and performs, for example, sorting, stapling, folding, and tape binding.

[0013] <Configuration of inspection equipment> FIG. 2 is a diagram illustrating an example of the hardware configuration of the inspection device 320. As shown in FIG. 2 includes a processor 321 that controls the operation of the entire apparatus, a ROM (Read Only Memory) 322 that stores a BIOS (Basic Input Output System) and the like, a RAM (Random Access Memory) 323 that is used as a work area for the processor 321, a display 324 that displays information related to the inspection, an operation reception device 325 that receives user operations, a scanner 326 that reads inspection images from printed materials, a hard disk drive 327 that stores reference images and inspection images, and a communication module 328 that is used for communication with the outside. The processor 321 and each component are connected via a signal line 329 such as a bus.

[0014] The processor 321, ROM 322, and RAM 323 function as a so-called computer. The processor 321 realizes various functions by executing programs. For example, the processor 321 executes a process for detecting defects in printed matter. The display 324 is, for example, a liquid crystal display or an organic EL display. In the present embodiment, the display 324 is integrally provided on the main body of the device, but may be a monitor connected to the inspection device 320.

[0015] The operation reception device 325 is composed of a capacitance type film sensor arranged on the surface of the display 324, and switches, buttons, etc. arranged on the housing. A device that integrates the display 324 and the operation reception device 325 is called a touch panel. The touch panel is used to receive user operations on keys displayed as software (hereinafter also referred to as "soft keys"). The scanner 326 includes a light source that irradiates the surface of the printed material being conveyed with linear illumination light, a line sensor that receives the light reflected from the surface of the printed material, and an optical system that forms an image of the reflected light on the line sensor. In this embodiment, an image of the entire printed material is called an "inspection image." The inspection image is stored in, for example, RAM 323.

[0016] The hard disk drive 327 stores an inspection threshold 327A, an inspection log 327B, etc. The inspection threshold 327A is stored as an initial value (hereinafter referred to as a "reference value"). There may be one or more thresholds 327A as the reference value. The reference values ​​used to detect defects are prepared according to the brightness of the area to be inspected. For example, different reference values ​​are prepared for bright image areas where stains are easily noticeable and dark image areas where white areas are easily noticeable. In addition, different reference values ​​are prepared for edge areas and non-edge areas.

[0017] The reference value is determined assuming that the print data will be printed on white paper, that is, that the background color of the test image is white. The white color assumed in the reference value means, for example, a whiteness of 100%. Hereinafter, paper with a whiteness of 100% will be referred to as white paper. In this embodiment, the threshold value used for the inspection is set according to the color of the paper of the print corresponding to the inspection image. Specifically, the inspection is performed using a value obtained by correcting the reference value. Inspection log 327B records the results of inspections performed for each printed product.

[0018] A reference image generated from the print data may be stored in the hard disk drive 327. The reference image is digitally generated by the processor 321 from the print data. In addition, firmware and application programs used for defect inspection are also stored in the hard disk drive 327. Hereinafter, firmware and application programs will be collectively referred to as "programs." In this embodiment, the hard disk drive 327 is assumed to be the auxiliary storage device, but a semiconductor memory may also be used. The communication module 328 is configured with a communication module that complies with wired or wireless communication standards, and may be, for example, an Ethernet (registered trademark) module, a USB (Universal Serial Bus) module, or a wireless LAN module.

[0019] Fig. 3 is a diagram illustrating an example of the functional configuration of the inspection device 320. Fig. 3 shows functions related to defect inspection. The functions shown in Fig. 3 are realized through the execution of a program by the processor 321 (see Fig. 2). The inspection device 320 shown in FIG. 3 has inspection-related functions, including a reference image generation unit 351, an inspection image generation unit 352, an intra-image edge extraction unit 353, a difference image generation unit 354, a paper color difference acquisition unit 355, a threshold setting unit 356, and a defect extraction unit 357.

[0020] The reference image generation unit 351 is a functional unit that generates a reference image based on print data provided from the print data generation device 20 (see FIG. 1) to the printing device 310. The reference image in this embodiment is generated assuming that the image is printed on white paper. The reference image is provided to an intra-image edge extraction unit 353 , a difference image generation unit 354 , a paper color difference acquisition unit 355 , and a threshold setting unit 356 . The inspection image generating unit 352 is a functional unit that generates an inspection image in real time from an image read in a line by the scanner 326 . The inspection image is also provided to an intra-image edge extraction unit 353 , a difference image generation unit 354 , a paper color difference acquisition unit 355 , and a threshold setting unit 356 . The printed matter that has passed through the scanner 326 is discharged to a post-processing device 330 (see FIG. 1) at the subsequent stage.

[0021] The intra-image edge extraction unit 353 is a functional unit that extracts edges from both the reference image and the test image. Edges are, for example, the contours or features of a subject, and can be extracted using discontinuities in brightness values. The edge images extracted from the reference image and the edge images extracted from the test image are provided to a difference image generation unit 354, a paper color difference acquisition unit 355, and a threshold setting unit 356. The difference image generating unit 354 has a registration unit 354A as a sub-function, and is a functional unit that generates a difference image between the reference image and the inspection image after registration. The alignment unit 354A collates, for example, an edge image of the reference image with an edge image of the inspection image, and aligns the reference image with the inspection image. The difference image generation unit 354 outputs the generated difference image to the defect extraction unit 357.

[0022] The paper color difference acquisition unit 355 is a functional unit that acquires the color of the paper of the printed matter as a color difference with respect to white paper. In this embodiment, the paper color difference acquisition unit 355 uses a portion of the edge-free area in both the reference image and the test image to acquire the paper color. Specifically, the paper color difference acquisition unit 355 detects the edge-free area in both the reference image and the test image, and acquires the difference value between the color information of the reference image and the color information of the test image corresponding to the detected area as the color difference representing the difference in the background color of the paper.

[0023] However, the color information of an edge-free area is not necessarily the same as the background color of the paper. For example, there are areas printed with white toner or white ink, and there are also areas printed with black toner or black ink. Therefore, the paper color difference acquisition unit 355 calculates the color difference using bright areas among areas where no edges exist. This is because information about the background color of the paper is more likely to appear in bright areas than in dark areas. Note that a threshold value may be set for the brightness used to calculate the color difference of the paper, and if the threshold value is not exceeded, the user may be requested to calculate or specify the color difference using another method.

[0024] In addition, the area from which the color of the paper on which the test image is printed is obtained should not only be a continuous area that does not include edges, but should also be as large as possible, because calculating the color difference using the colors of just a few pixels can result in a large error from the actual color of the paper. Furthermore, although the color difference may be calculated from only one area that satisfies the above conditions, it is possible to reduce the error from the actual color of the paper by calculating it as the average value of multiple areas, preferably the average value of distant areas on the paper, such as the top right and bottom left of the paper.

[0025] The paper color difference may be acquired for all printed matter, but if the same type of paper is used, the paper color difference may be acquired only once for the first printed matter, and the first acquired color difference information may be reused for inspection of the second and subsequent printed matters. In other words, for the second and subsequent printed matters, execution of the paper color difference acquisition unit 355 may be skipped when inspecting for defects.

[0026] The threshold setting unit 356 is a functional unit that sets a threshold used for defect inspection. In this embodiment, the threshold setting unit 356 corrects a reference value determined according to a combination of the brightness of the reference image, edge information of the reference image, edge information of the inspection image, etc., using the acquired color difference, and sets the corrected value as a threshold used by the defect extraction unit 357. It should be noted that the color difference information can be reused regardless of the content of the image corresponding to the print data, as long as there is no change in the type of paper to be printed on, etc.

[0027] The defect extraction unit 357 is a functional unit that extracts defects contained in the inspection image by comparing the pixel values ​​of the differential image provided by the differential image generation unit 354 with a threshold value. The extracted defects are recorded in an inspection log as inspection results and are also used to control post-processing. Incidentally, the defect extracting unit 357 determines that a pixel whose pixel value is less than the threshold is normal, and determines that a pixel whose pixel value is equal to or greater than the threshold is defective. The defect extraction unit 357 in this embodiment also evaluates defects in the entire inspection image based on, for example, the number of pixels determined to be defective, the area of ​​a region where pixels determined to be defective are consecutive, etc.

[0028] <Inspection operation> 4 is a flowchart illustrating an example of an inspection operation for defects by the inspection device 320 (see FIG. 1) used in embodiment 1. As described above, the processing operation shown in FIG. 4 is realized through the execution of a program by the processor 321 (see FIG. 2). When the processor 321 receives a new printed matter from the printing device 310 (see FIG. 1), it starts the processing operation shown in FIG.

[0029] First, the processor 321 acquires a reference image (step 1), and then acquires an inspection image (step 2). If the same image is to be printed continuously, the reference image may be acquired only once. Next, processor 321 extracts edges of the reference image (step 3), and then extracts edges of the inspection image (step 4). Processor 321 then aligns the reference image and the inspection image using the two edge images (step 5), although the alignment of the reference image and the inspection image may be performed before extracting the edge images.

[0030] Next, processor 321 calculates the color difference between the paper in the test image and the paper in the reference image (step 6). Next, the processor 321 determines the reference value of the threshold for the pixel to be processed using information on the reference image and the edge image (step 7). For example, the processor 321 determines the reference value of the threshold to be used for determining defects depending on the presence or absence of an edge, etc. Furthermore, the processor 321 corrects the determined reference value of the threshold and sets the threshold to be used for defect extraction (step 8). In this embodiment, the processor 321 sets the threshold to a value obtained by adding the color difference to the reference value of the threshold.

[0031] Once the threshold is set, processor 321 calculates the difference between the pixel values ​​of the reference image and the inspection image for the pixel to be processed (step 9), and determines whether the calculated difference exceeds the threshold (step 10). After this, processor 321 determines whether or not the determination of all pixels has been completed (step 11). If a negative result is obtained in step 11, processor 321 returns to step 7 and repeats the processes of steps 7 to 10 described above for the remaining pixels that have not been inspected. If a positive result is obtained in step 11, processor 321 outputs the result of the test (step 12).

[0032] <Example> A specific example of defect inspection according to this embodiment will be described below with reference to FIGS. 5A and 5B are diagrams illustrating examples of calculating the color difference between paper on which an inspection image is printed and white paper on which the reference image is assumed. (A) shows an example in which the inspection image is printed on white paper, and (B) shows an example in which the inspection image is printed on colored paper.

[0033] In Figures 5(A) and (B), the area near the bottom left corner where no edges exist is selected as the area for calculating the color difference of the paper. Figures 5(A) and (B) show a frame W that surrounds this area. The area surrounded by the frame W is not only a bright area, but also an area where no edges exist in both the reference image and the inspection image.

[0034] In the case of Figure 5(A), the paper on which the test image is printed is white, so the color difference is "0." On the other hand, in the case of Figure 5(B), the paper on which the test image is printed is colored, so there is a color difference. In this example, it is "30." In addition, in both of the inspection images shown in FIGS. 5(A) and 5(B), a circular stain D is attached to the upper right portion. In the case of Figure 5(A), the stain D is noticeable, but in the case of Figure 5(B), the stain D is not noticeable. In the case of Figure 5(B), the color of the stain D is close to the background color of the paper and the surrounding color.

[0035] FIG. 6 is a table illustrating an example of setting the threshold value depending on the type of paper and the presence or absence of an edge. The chart in Figure 6 shows examples of threshold settings for combinations of "edge-present" and "edge-less" areas for the reference image and the test image, depending on the color of the paper on which the test image is printed. In the case of FIG. 6, the threshold value used for colored paper is given as a value obtained by uniformly adding the color difference value to the threshold value for white paper.

[0036] For example, in the case of an area where there are no edges in both the reference image and the inspection image, the threshold value for white paper is 100, and the threshold value for colored paper is 130 (=100+30). In the case of an area where there are no edges in the reference image but there are edges in the inspection image, the threshold for white paper is 50 and the threshold for colored paper is 80 (=50+30). This threshold is used to inspect for stains. The threshold is set to a low value so that stains can be easily detected.

[0037] For areas where the reference image has edges but the inspection image does not, the threshold for white paper is 150 and the threshold for colored paper is 180 (=150+30). These thresholds are used to inspect for white areas. For regions where there are edges in both the reference image and the test image, the threshold for white paper is 150 and the threshold for colored paper is 180 (=150+30). The threshold value for the edge portion is set to a value greater than the threshold value for the non-edge portion.

[0038] 7A and 7B are diagrams illustrating examples of threshold settings and judgments used in defect inspection. (A) shows an example of threshold settings and judgments when the inspection image is printed on white paper, and (B) shows an example of threshold settings and judgments when the inspection image is printed on colored paper. In the case of Figure 7(A) where the color difference is 0, the threshold for the area AR1 where there is an edge only in the inspection image is 50, while the color difference of the inspection image relative to the reference image is 70. Therefore, this area is determined to be stain D.

[0039] In the case of Figure 7(A) where the color difference is 0, the threshold for the area AR2 where there are no edges in both the reference image and the inspection image is 100, and the color difference of the inspection image relative to the reference image is 0. Therefore, this area is determined not to be defective. In the case of Figure 7(A) where the color difference is 0, the threshold for area AR3 where there is an edge in both the reference image and the inspection image is 150, and the color difference of the inspection image relative to the reference image is 0. Therefore, this area is determined not to be defective.

[0040] In the case of Figure 7(B) where the color difference is 30, the threshold for the area AR1 where there is an edge only in the inspection image is 80, whereas the color difference of the inspection image relative to the reference image is 70. Therefore, in this area, stain D is not determined to be a defect. In the case of Figure 7(B) where the color difference is 30, the threshold for the area AR2 where there are no edges in both the reference image and the inspection image is 130, and the color difference of the inspection image relative to the reference image is 0. Therefore, this area is determined not to be defective. In the case of Figure 7(B) where the color difference is 30, the threshold for area AR3 where there is an edge in both the reference image and the inspection image is 180, and the color difference of the inspection image relative to the reference image is 0. Therefore, this area is determined not to be defective.

[0041] <Embodiment 2> The inspection device 320 (see FIG. 1) used in this embodiment differs from the first embodiment in that it has an additional function of specifying an area in which the ground color of the paper is to be detected. Therefore, the hardware configuration and functional configuration of the inspection device 320 used in this embodiment are basically the same as those in the first embodiment.

[0042] Fig. 8 is a diagram illustrating components related to a function for a user to specify an area for detecting the background color of a sheet of paper. In Fig. 8, the same reference numerals are used to denote parts corresponding to those in Figs. 1 and 3. Although not shown in FIG. 8, the functional configuration shown in FIG. This embodiment differs from the first embodiment in that the inspection image read by the scanner 326 is also provided to the area designation UI (=User Interface) unit 360, and information on the area received by the area designation UI unit 360 (hereinafter referred to as "area information") is provided to the paper color difference acquisition unit 355.

[0043] In this embodiment, the paper color difference acquisition unit 355 uses the area specified by the area information provided from the area designation UI unit 360 as the area used to calculate the color difference of the paper. When the area specification by the area specification UI unit 360 is accepted before the start of the inspection, the paper color difference acquisition unit 355 skips the process of selecting the area to be used for calculating the color difference. The paper color difference acquisition unit 355 holds the color difference calculated for the specified area unless it receives a notification of a change in the type of paper to be used for printing.

[0044] The threshold setting unit 356 (see FIG. 3) also holds the color difference information received from the paper color difference acquisition unit 355 unless it receives a notification of a change in the type of paper to be used for printing. The color difference information can be used regardless of differences in the content of the image corresponding to the print data unless there is a change in the type of paper to be used for printing.

[0045] FIG. 9 is a diagram illustrating an example of an operation screen 370 that the area designation UI unit 360 displays on the display 324. As shown in FIG. The operation screen 370 shown in FIG. 9 is provided with a title 371, an explanatory text 372 explaining the operation required of the user, a display field 373 for the examination image, a button 374 to be operated when confirming the area specification, and a button 375 to be operated when canceling the specified area.

[0046] 9 contains a stain D, the user designates an area 376 where no subject is present as the area to be used for acquiring color differences. Area 376 can be designated by dragging cursor K diagonally. Since the user visually specifies the area while avoiding the locations of stains and white spots, stains and white spots may exist in the inspection image used to specify the area used to acquire the color difference, as shown in FIG. Furthermore, since obtaining the paper background color and calculating the color difference only needs to be performed once for the paper used for printing, the test image to be inspected after calculating the color difference may contain stains or white spaces.

[0047] <Third Embodiment> In this embodiment, a case will be described in which an inspection threshold value stored in a previous inspection operation is selectively used in another inspection operation. The hardware configuration and functional configuration of the inspection device 320 (see FIG. 1) used in this embodiment are basically the same as those in the first embodiment. 10A and 10B are diagrams illustrating an example of a method for reading out threshold values ​​to be used in an inspection operation by utilizing the operation of selecting the paper to be used for printing. (A) shows an example of an operation screen 380, and (B) shows an example of a table 390 that stores the relationship between the tray containing the paper and the set of threshold values ​​(hereinafter referred to as the "threshold set").

[0048] The operation screen 380 shown in FIG. 10(A) has a title 381, buttons 382, ​​383, and 384 for specifying the tray containing the paper to be used for printing, a button 385 for confirming the tray specification, and a button 386 for canceling the tray specification. The operation screen 380 shown in Figure 10(A) may be displayed as part of the screen used to set up printing for the printing device 310 (see Figure 1), or may be displayed as part of the screen used to set up inspection by the inspection device 320.

[0049] 10(A), the user knows the types of paper stored in "Tray 1," "Tray 2," and "Tray 3," so information such as paper size, dimensions, and paper orientation is not displayed. However, information related to the types of paper stored may be displayed on or outside the display of buttons 382, ​​etc. In a table 390 shown in FIG. 10B, threshold sets used in previous defect inspections are stored in association with each tray.

[0050] For example, if the paper stored in "Tray 1" is white paper, four values, "100," "50," "150," and "150," are stored as "Threshold Set 1." These values ​​correspond to the four thresholds for white paper shown in FIG. 6. Incidentally, in the case of colored paper, the threshold reference value corrected by the color difference is stored as "threshold set 4."

[0051] In the case of Figure 10(B), the paper stored in "Tray 1" and "Tray 3" has a history of being used for printing. Therefore, threshold sets are stored for "Tray 1" and "Tray 3," but the paper stored in "Tray 2" has no history of being used for printing. Therefore, in the case of Figure 10(B), the threshold set column corresponding to "Tray 2" is blank. The threshold set is read out by, for example, the threshold setting unit 356, so the user does not know the set threshold values. However, information about the set thresholds and threshold set may be displayed on the operation screen 380.

[0052] 11 is a diagram illustrating another example of a method for reading out threshold values ​​to be used in an inspection operation by utilizing the operation of selecting the paper to be used for printing. (A) shows an example of an operation screen 400, and (B) shows an example of a table 410 that stores the relationship between paper names and threshold sets. The operation screen 400 shown in FIG. 11(A) is arranged with a title 401, buttons 402, 403, and 404 for specifying the type of paper to be used for printing, a button 405 that is operated to confirm the specification of the paper type, and a button 406 that is operated to cancel the specification of the paper type.

[0053] 11(A), names indicating the types of paper (hereinafter referred to as "paper names") are displayed on buttons 402 to 404. The paper names are an example of registered names. The operation screen 400 shown in Figure 11 (A) may also be displayed as part of the screen used to set up printing for the printing device 310 (see Figure 1), or as part of the screen used to set up inspection by the inspection device 320. 11(A), the user can identify the type of paper just from "Paper Name 1," "Paper Name 2," and "Paper Name 3," so information such as paper size, dimensions, and paper orientation is not displayed. However, information such as paper size may be displayed on or outside the buttons 402, etc. In a table 410 shown in FIG. 11(B), threshold sets used in previous defect inspections are stored in association with paper names.

[0054] For example, if the paper stored in "Paper Name 1" is white paper, four values, "100," "50," "150," and "150," are stored as "Threshold Set 1." These values ​​correspond to the four thresholds for white paper shown in FIG. 6. Incidentally, in the case of colored paper, threshold values ​​obtained by correcting the reference values ​​of the threshold values ​​by color difference are stored as the threshold value set.

[0055] In the case of Figure 11(B), "Paper Name 1" and "Paper Name 3" have a history of being used for printing. Therefore, threshold sets are stored for "Paper Name 1" and "Paper Name 3," but the paper stored in "Paper Name 2" has no history of being used for printing. Therefore, in the case of Figure 11(B), the threshold set column corresponding to "Paper Name 2" is blank.

[0056] The association between paper names and threshold sets is unrelated to trays. Therefore, table 410 also stores the association between paper names and threshold sets for paper not stored in a tray. In table 410 shown in FIG. 11(B), "threshold set 6" is stored in association with "paper name 5," which is not stored in a tray. The threshold set is read out by, for example, the threshold setting unit 356, so the user does not know the set threshold values. However, information about the set thresholds and threshold set may be displayed on the operation screen 380.

[0057] <Other embodiments> (1) Although the embodiments of the present invention have been described above, the technical scope of the present invention is not limited to the scope of the above-described embodiments. It is clear from the claims that various modifications and improvements to the above-described embodiments are also included in the technical scope of the present invention.

[0058] (2) In the above embodiment, the color difference value between the paper on which the inspection image is printed and white paper is added to the threshold value used when inspecting defects in a printed matter printed on white paper. However, the threshold value used for defect inspection may be corrected with a value different from the calculated color difference. For example, if the color difference is "30," "20" or "40" may be added to the reference value of the threshold.

[0059] (3) In the above embodiment, the threshold values ​​corresponding to the combination of the presence or absence of an edge are uniformly corrected based on the color difference between the paper on which the inspection image is printed and the white paper. However, the amount of color difference reflection may be changed for each combination of the presence or absence of an edge. In other words, the amount of color difference reflection may be changed depending on the type of defect to be detected. 12 is a table illustrating an example of setting threshold values ​​according to the type of paper and the presence or absence of edges. FIG. 12 corresponds to FIG.

[0060] In the example of settings shown in FIG. 12, the color difference of the paper is also "30". However, the threshold value used to detect stains on colored paper is "90", which is set to a value "40" higher than the threshold value used to detect stains on white paper. Furthermore, the color difference of the paper is "30", but the threshold value used to detect whiteouts on colored paper is "170", which is set to a value "20" larger than the threshold value used to detect whiteouts on white paper. The reflection amounts shown in Figure 12 are values ​​used to explain the difference in the reflection amount of color difference for each combination of whether or not an edge is present, and the threshold value for detecting dirt and the threshold value for detecting whiteouts may be greater than the color difference, or conversely, may be smaller than the threshold value.

[0061] (4) In the case of the above-mentioned embodiment 1, the color difference of the paper is calculated from the printed matter to be inspected, but the process of inspecting defects and the process of calculating the color difference of the paper may be separated, and the color difference of the paper used to print the printed matter may be calculated before the inspection for defects. For example, print data corresponding to an entirely colorless image may be provided to the printing device 310 (see FIG. 1), and the paper output from the printing device 310 may be captured as an inspection image to calculate the color difference. In this case, the paper to be used for printing is directly fed into the inspection device 320, so it is possible to accurately calculate the color difference with the background color of the paper to be used for printing.

[0062] (5) In the above-described embodiment, it is assumed that the entire surface of the paper used for printing is one color. However, if paper with multiple color areas, paper with a printed base pattern, or paper with foil stamping or holograms is used, it is sufficient to calculate the color difference for each base area and set a threshold value for judgment. FIG. 13 is a diagram illustrating an example of an inspection image and threshold settings when a single sheet of paper has two background colors. In the case of FIG. 13, the background colors are different between the upper and lower halves of the paper. In the case of FIG. 13, the color difference in the upper half is "30" and the color difference in the lower half is "50". Therefore, the threshold for determining the upper half of the edgeless area is set to "130", and the threshold for determining the lower half is set to "150".

[0063] (6) In the above-described embodiment, the value obtained by adding the calculated color difference to the reference value is used as the judgment threshold value. However, an upper limit may be set for the judgment threshold value. For example, if the reference value is "180," the color difference is "30," and the upper limit is "200," even if adding the color difference to the reference value results in "210," the threshold value used for judgment may be "200." The upper limit is set to prevent a decrease in detection accuracy due to the threshold value being too large. This prevents the threshold value from becoming too large and reducing the accuracy of defect detection.

[0064] (7) In the above embodiment, the white paper is described as paper with a whiteness of 100%, but the whiteness may be other values.

[0065] (8) The processor in each of the above-mentioned embodiments refers to a processor in a broad sense, and includes general-purpose processors (e.g., CPUs, etc.) as well as dedicated processors (e.g., GPUs (Graphical Processing Units), ASICs (Application Specific Integrated Circuits), FPGAs (Field Programmable Gate Arrays), programmable logic devices, etc.). Furthermore, the operations of the processor in each of the above-described embodiments may be performed by a single processor alone, or may be performed by multiple processors located in physically separate locations in cooperation with each other. Furthermore, the order in which the operations of the processors are performed is not limited to the order described in each of the above-described embodiments, and may be changed individually. [Explanation of symbols]

[0066] 1...image printing system, 10...network, 20...printing data generation device, 30...printing system, 310...printing device, 320...inspection device, 330...post-processing device, 351...reference image generation unit, 352...inspection image generation unit, 353...intra-image edge extraction unit, 354...difference image generation unit, 354A...alignment unit, 355...paper color difference acquisition unit, 356...threshold setting unit, 357...defect extraction unit, 360...area designation UI unit

Claims

1. A processor, The processor: When inspecting for defects by comparing a first image generated from print data used to generate a printed matter with a second image read from the printed matter, obtaining a color difference between the paper portions of the first image and the second image; setting a threshold value for inspection according to the acquired color difference; Inspecting the print for defects using the set threshold value; It is an inspection device, The processor: a value obtained by correcting a previously prepared initial value in accordance with the color difference is set as the threshold value; If the corrected value exceeds a predetermined upper limit value, the upper limit value is set as the threshold value. Inspection equipment.

2. A processor, The processor: When inspecting for defects by comparing a first image generated from print data used to generate a printed matter with a second image read from the printed matter, obtaining a color difference between the paper portions of the first image and the second image; setting a threshold value for inspection according to the acquired color difference; Inspecting the print for defects using the set threshold value; It is an inspection device, The processor: a value obtained by correcting a previously prepared initial value in accordance with the color difference is set as the threshold value; changing the amount of reflection of the color difference depending on the type of defect to be detected; Inspection equipment.

3. A processor, The processor: When inspecting for defects by comparing a first image generated from print data used to generate a printed matter with a second image read from the printed matter, obtaining a color difference between the paper portions of the first image and the second image; setting a threshold value for inspection according to the acquired color difference; Inspecting the print for defects using the set threshold value; It is an inspection device, The processor: a value obtained by correcting a previously prepared initial value in accordance with the color difference is set as the threshold value; If the paper before printing includes a plurality of areas with different colors, the color difference is obtained for each area; setting the threshold for each region; Inspection equipment.

4. a computer that inspects for defects by comparing a first image generated from print data used to generate a printed matter with a second image read from the printed matter; a function of acquiring a color difference between the paper portions of the first image and the second image; a function of setting a threshold value for inspection in accordance with the acquired color difference; a function of inspecting a printed matter for defects using the threshold value after the threshold value has been set; It is a program to achieve The function of setting the threshold value is a value obtained by correcting a previously prepared initial value in accordance with the color difference is set as the threshold value; If the corrected value exceeds a predetermined upper limit value, the upper limit value is set as the threshold value. program.

5. a computer that inspects for defects by comparing a first image generated from print data used to generate a printed matter with a second image read from the printed matter; a function of acquiring a color difference between the paper portions of the first image and the second image; a function of setting a threshold value for inspection in accordance with the acquired color difference; a function of inspecting a printed matter for defects using the threshold value after the threshold value has been set; It is a program to achieve The function of setting the threshold value is a value obtained by correcting a previously prepared initial value in accordance with the color difference is set as the threshold value; changing the amount of reflection of the color difference depending on the type of defect to be detected; program.

6. a computer that inspects for defects by comparing a first image generated from print data used to generate a printed matter with a second image read from the printed matter; a function of acquiring a color difference between the paper portions of the first image and the second image; a function of setting a threshold value for inspection in accordance with the acquired color difference; a function of inspecting a printed matter for defects using the threshold value after the threshold value has been set; It is a program to achieve The function of setting the threshold value is a value obtained by correcting a previously prepared initial value in accordance with the color difference is set as the threshold value; If the paper before printing includes a plurality of areas with different colors, the color difference is obtained for each area; setting the threshold for each region; program.

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