JP6171730B2 - Image inspection apparatus, image inspection method, and image inspection program - Google Patents

Description

  The present invention relates to an image inspection apparatus, an image inspection method, and an image inspection program, and more particularly, to color adjustment between an inspection image used in an image comparison inspection and an image to be inspected.

  Conventionally, inspection of printed matter has been performed manually, but in recent years, an apparatus for performing inspection has been used as post-processing of offset printing. In such an inspection apparatus, a master image serving as a reference is generated by manually selecting and reading a non-defective product from the read image of the printed matter, and a corresponding portion of the master image and the read image of the printed matter to be inspected. And the defect of the printed matter is discriminated by the degree of these differences.

  However, plateless printing devices such as electrophotography, which have become popular in recent years, are good at printing a small number of parts, and there are many cases where the content of printing on each page is different, such as variable printing. In comparison, it is inefficient. In order to cope with this problem, it is conceivable to generate a master image from print data. Thereby, it can respond to variable printing efficiently (for example, refer to patent documents 1).

  In addition, when such a comparative inspection is performed, it is premised that the master image and the read image substantially match if printing is performed accurately. Here, the master image is generated based on the print data. However, the read image is not only printed based on the print data but also affected by the type of paper to be printed.

  As a technique for considering the influence of the paper on the read image, for each tray in which the paper used for printing is stored, information set for the paper stored in each tray is stored and compared. At the time of inspection, a method has been proposed in which a comparative inspection is performed based on information associated with a tray in which a sheet used for printing is stored (see, for example, Patent Document 2).

  In the case of the method disclosed in Patent Document 2, it takes time to start printing as much as the process of reading the stored paper occurs, and when a plurality of different types of paper are stored in the tray, Appropriate correction cannot be performed with information associated with the tray by reading only one sheet.

  In view of this, a mode is conceivable in which the type of paper used for the page to be inspected is detected each time and the color is corrected. In that case, for example, it is conceivable to determine the type of paper based on the reading result of the plain portion of the page to be inspected. However, it is conceivable that the density of the reading result of the scanner changes due to the exposure intensity, light receiving sensitivity, and the influence of external light. As a result, the paper is not accurately discriminated and proper color correction becomes difficult.

  The present invention has been made in view of the above circumstances, and is suitable for an image inspection apparatus that inspects a printed matter by comparing a read image obtained by reading the paper with an image for inspection regardless of the type of the paper used for the printed matter. The purpose is to conduct a proper inspection.

  In order to solve the above-described problem, an aspect of the present invention is an image inspection apparatus that inspects a read image obtained by reading an image printed on a paper surface, and the image printed on the paper surface is read. A read image acquisition unit that acquires the generated read image, an inspection image generation unit that generates an inspection image for inspecting the read image based on information on an image to be printed, and the inspection image; An inspection result acquisition unit that acquires an inspection result obtained by determining a defect of the read image based on a difference from the read image, and a sheet of paper to which no developer is added on the paper surface from the acquired read image. A plain area determination unit that extracts a background color area; a variation value calculation unit that calculates a value indicating a density variation of pixels in the plurality of extracted background color areas; and Shadow on color tone due to density A correction value corresponding to the calculated value indicating the variation is obtained by referring to the correction value association information in which the correction value for correcting the color and the value indicating the variation in density of the pixels in the ground color region are associated with each other And a color tone correction unit that corrects one of the generated inspection image and the read image based on the acquired correction value.

  Another aspect of the present invention is an image inspection method for inspecting a read image obtained by reading an image printed on a paper surface. The read image generated by reading the image printed on the paper surface And generating an inspection image for inspecting the read image based on information on the image to be printed, and determining a defect in the read image based on a difference between the inspection image and the read image The obtained inspection result is extracted, and the ground color area of the paper to which the developer is not added is extracted from the acquired read image, and the plurality of extracted ground color area pixels are extracted. A value indicating density variation is calculated, and a correction value for correcting the influence of the density of the background color region on the color tone for each sheet is associated with a value indicating the density variation of pixels in the background color region. Refer to the correction value association information Acquiring a correction value corresponding to the calculated value indicating the variation, and correcting one of the generated inspection image and the read image based on the acquired correction value. .

  According to still another aspect of the present invention, there is provided an image inspection program for inspecting a read image obtained by reading an image printed on a paper surface, the read image generated by reading the image printed on the paper surface. Obtaining an image; generating an inspection image for inspecting the read image based on information of an image to be printed; and reading the image based on a difference between the inspection image and the read image. A step of acquiring an inspection result for determining an image defect, a step of extracting a ground color region of the paper to which a developer is not added on the paper surface from the acquired read image, and a plurality of extracted Calculating a value indicating a variation in pixel density of the background color area, a correction value for correcting an influence on the color tone due to the density of the background color area for each sheet, and the background color area A step of acquiring correction values corresponding to the calculated value indicating the variation, referring to the correction value association information associated with the value indicating the variation of the elementary density, and the generated inspection image and the reading And causing the information processing apparatus to execute a step of correcting one of the images based on the acquired correction value.

  According to the present invention, in an image inspection apparatus that inspects a printed matter by comparing a read image obtained by reading a sheet with an image for inspection, a suitable inspection can be performed regardless of the type of the sheet used for the printed matter. Become.

1 is a diagram illustrating a configuration of an image forming system including an inspection apparatus according to an embodiment of the present invention. It is a block diagram which shows the hardware constitutions of the test | inspection apparatus which concerns on embodiment of this invention. It is a block diagram which shows the function structure of the engine controller which concerns on embodiment of this invention, a print engine, an inspection apparatus, and a post-processing apparatus. It is a figure which shows the aspect of the comparison test | inspection which concerns on embodiment of this invention. 1 is a diagram illustrating a configuration of a print engine according to an embodiment of the present invention. It is a block diagram which shows the function structure of the test | inspection control part which concerns on embodiment of this invention. It is a figure which shows the content of the table contained in correction value DB which concerns on embodiment of this invention. It is a figure which shows the example of the color conversion table which concerns on embodiment of this invention. It is a figure which shows the function structure of the master image process part which concerns on embodiment of this invention. It is a flowchart which shows the operation | movement of the image test | inspection which concerns on embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the present embodiment, in an image inspection system that inspects an output result by comparing a read image obtained by reading an output result of an image formation output with a master image, a master corresponding to the type of paper used in the image formation output. A control mode for correcting an image will be described. FIG. 1 is a diagram illustrating an overall configuration of an image forming system according to the present embodiment. As shown in FIG. 1, the image forming system according to the present embodiment includes a DFE (Digital Front End) 1, an engine controller 2, a print engine 3, and an inspection device 4.

  The DFE 1 generates image data to be printed out based on the received print job, that is, bitmap data that is an output target image, and outputs the generated bitmap data to the engine controller 2. The engine controller 2 controls the print engine 3 based on the bitmap data received from the DFE 1 to execute image formation output. Further, the engine controller 2 according to the present embodiment is a source of an inspection image for referring to the bitmap data received from the DFE 1 when the inspection apparatus 4 inspects the result of the image formation output by the print engine 3. Information is transmitted to the inspection device 4.

  The print engine 3 is an image forming apparatus that executes image forming output based on bitmap data in accordance with control of the engine controller 2. The inspection device 4 generates a master image based on the bitmap data input from the engine controller 2. The inspection device 4 is an image inspection device that inspects an output result by comparing a read image generated by reading a sheet output from the print engine 3 with a reading device with the generated master image.

  When the inspection device 4 determines that the output result is defective by comparing the master image and the read image, the inspection device 4 notifies the engine controller 2 of information indicating a page that is recognized as a defect. Thereby, reprint control of the defective page is executed by the engine controller 2.

  Here, the hardware configuration constituting the functional blocks of the engine controller 2, the print engine 3, and the inspection apparatus 4 according to the present embodiment will be described with reference to FIG. FIG. 2 is a block diagram illustrating a hardware configuration of the inspection apparatus 4 according to the present embodiment. In FIG. 2, the hardware configuration of the inspection apparatus 4 is shown, but the same applies to the engine controller 2 and the print engine 3.

  As shown in FIG. 2, the inspection apparatus 4 according to the present embodiment has the same configuration as an information processing apparatus such as a general PC (Personal Computer) or a server. That is, the inspection apparatus 4 according to the present embodiment includes a CPU (Central Processing Unit) 10, a RAM (Random Access Memory) 20, a ROM (Read Only Memory) 30, an HDD (Hard Disk Drive) 40, and an I / F 50. Connected through. Further, an LCD (Liquid Crystal Display) 60, an operation unit 70, and a dedicated device 80 are connected to the I / F 50.

  The CPU 10 is a calculation means and controls the operation of the entire inspection apparatus 4. The RAM 20 is a volatile storage medium capable of reading and writing information at high speed, and is used as a work area when the CPU 10 processes information. The ROM 30 is a read-only nonvolatile storage medium and stores a program such as firmware. The HDD 40 is a non-volatile storage medium that can read and write information, and stores an OS (Operating System), various control programs, application programs, and the like.

  The I / F 50 connects and controls the bus 90 and various hardware and networks. The LCD 60 is a visual user interface for the user to check the state of the inspection apparatus 4. The operation unit 70 is a user interface such as a keyboard and a mouse for the user to input information to the inspection apparatus 4.

  The dedicated device 80 is hardware for realizing a dedicated function in the engine controller 2, the print engine 3, and the inspection apparatus 4. In the case of the print engine 3, a transport mechanism that transports a sheet that is an image formation output target, A plotter device that executes image formation output on a paper surface. Further, the engine controller 2 and the inspection device 4 are dedicated arithmetic devices for performing image processing at high speed. Such an arithmetic unit is configured as an ASIC (Application Specific Integrated Circuit), for example. Also included is a reading device that reads an image output on paper.

  In such a hardware configuration, a program stored in a recording medium such as the ROM 30, the HDD 40, or an optical disk (not shown) is read into the RAM 20, and the CPU 10 performs calculations according to those programs, thereby configuring a software control unit. The A functional block that realizes the functions of the engine controller 2, the print engine 3, and the inspection apparatus 4 according to the present embodiment is configured by a combination of the software control unit configured as described above and hardware.

  FIG. 3 is a block diagram showing functional configurations of the engine controller 2, the print engine 3, and the inspection apparatus 4 according to the present embodiment. In FIG. 3, data transmission / reception is indicated by a solid line, and the flow of paper is indicated by a broken line. As shown in FIG. 3, the engine controller 2 according to the present embodiment includes a data acquisition unit 201, an engine control unit 202, and a bitmap transmission unit 203. The print engine 3 includes a print processing unit 301. The inspection device 4 includes a reading device 400, a read image acquisition unit 401, a master image processing unit 402, an inspection control unit 403, and a comparative inspection unit 404.

  The data acquisition unit 201 acquires bitmap data input from the DFE 1 and operates the engine control unit 202 and the bitmap transmission unit 203, respectively. Bitmap data is information of each pixel constituting an image to be imaged and output. The engine control unit 202 causes the print engine 3 to execute image formation output based on the bitmap data transferred from the data acquisition unit 201. The bitmap transmission unit 203 transmits the bitmap data acquired by the data acquisition unit 201 to the inspection apparatus 4 for generating a master image.

  The print processing unit 301 is an image forming unit that acquires bitmap data input from the engine controller 2, executes image formation output on printing paper, and outputs printed paper. The print processing unit 301 according to the present embodiment is realized by a general electrophotographic image forming mechanism, but other image forming mechanisms such as an ink jet method can also be used.

  The reading device 400 is an image reading unit that reads an image formed on a sheet of printing paper that has been printed and output by the print processing unit 301 and outputs read data. The reading device 400 is, for example, a line scanner installed in a conveyance path inside the inspection device 4 for printing paper output by the print processing unit 301. The scanning device 400 scans the paper surface of the printing paper to be conveyed on the paper surface. Read the formed image.

  The read image generated by the reading device 400 is an inspection target by the inspection device 4. Since the read image is an image generated by reading the paper surface of the paper output by the image forming output, the read image is an image indicating the output result. In the inspection apparatus 4 according to the present embodiment, the read image is also used to determine the type of paper used for image formation output (hereinafter referred to as “paper type”).

  The read image acquisition unit 401 acquires information of a read image generated by reading the paper surface of the printing paper by the reading device 400. The information of the read image acquired by the read image acquisition unit 401 is input to the inspection control unit 403 for the above-described paper type determination and comparison inspection. Note that the input of the read image to the comparison inspection unit 404 is executed under the control of the inspection control unit 403. At that time, the inspection control unit 403 obtains the read image and inputs it to the comparison inspection unit 404.

  The master image processing unit 402 acquires the bitmap data input from the engine controller 2 as described above, and generates a master image that is an inspection image for comparison with the inspection target image. That is, the master image processing unit 402 functions as an inspection image generation unit that generates a master image, which is an inspection image for inspecting the read image, based on the output target image.

  In addition, the master image processing unit 402 according to the present embodiment corrects the color tone according to the determination result of the sheet by the inspection control unit 403 when generating the master image as described above. This process is one of the processes according to the gist of the present embodiment. Details will be described later.

  The inspection control unit 403 is a control unit that controls the operation of the entire inspection apparatus 4, and each component included in the inspection apparatus 4 operates according to the control of the inspection control unit 403. In addition, as a process according to the gist of the present embodiment, the inspection control unit 403 analyzes the read image acquired from the read image acquisition unit 401, and provides correction value information for correcting the master image based on the analysis result. Input to the master image processing unit 402.

  The comparison inspection unit 404 compares the read image input from the read image acquisition unit 401 with the master image generated by the master image processing unit 402 according to the control of the inspection control unit 403, and the intended image formation output is executed. Judge whether or not. The comparison inspection unit 404 is configured by an ASIC as described above in order to quickly process a huge amount of calculation.

  In the comparison inspection unit 404, as described above, the 200 dpi read image and the master image expressed in 8 bits for each RGB color are compared for each corresponding pixel, and the difference value of the 8 pixel values for each RGB color described above for each pixel. Is calculated. Based on the magnitude relationship between the difference value thus calculated and the threshold value, the inspection control unit 403 determines the presence or absence of a defect in the read image.

  When comparing the read image and the master image, the comparison inspection unit 404 superimposes the master image divided for each predetermined range on the read image corresponding to the divided range, as shown in FIG. The pixel value of the pixel, that is, the density difference is calculated. Further, while shifting the position where the divided range is superimposed on the read image vertically and horizontally, the position where the calculated difference value is the smallest is determined as the accurate overlapping position, and the difference value calculated at that time is determined. Adopted as a comparison result. By such processing, the difference value is calculated after the read image and the master image are aligned.

  In addition, instead of calculating the difference value by superimposing the entire master image on the read image, the calculation amount can be reduced as a whole by calculating the difference value for each divided range. Furthermore, even if there is a difference in scale between the entire master image and the entire read image, it is possible to reduce the influence of the difference in scale by dividing and positioning for each range as shown in FIG. It is.

  As a comparison method of the magnitude relationship between the difference value and the threshold value, the inspection control unit 403 according to the present embodiment compares the difference value calculated by the comparison inspection unit 404 for each pixel with a preset threshold value. . As a result, the inspection control unit 403 acquires information indicating whether the difference between the master image and the read image exceeds a predetermined threshold for each pixel. That is, it is possible to inspect whether each pixel constituting the read image is a defect. In addition, the size of each division range illustrated in FIG. 4 is determined based on a range in which the comparison / inspection unit 404 configured by the ASIC can compare pixel values at a time as described above, for example.

  In the above embodiment, the comparison inspection unit 404 calculates and outputs a difference value between the pixels constituting the master image and the pixels constituting the read image, and the inspection control unit 403 compares the difference value with the threshold value. The case of doing is taken as an example. In addition, the comparison / inspection unit 404 compares the difference value with the threshold value, and the comparison result, that is, for each pixel constituting the read image, whether or not the difference from the corresponding pixel in the master image exceeds a predetermined threshold value. Such information may be acquired by the inspection control unit 403.

  Next, the mechanical configuration of the print engine 3 and the inspection apparatus 4 and the paper conveyance path will be described with reference to FIG. As shown in FIG. 5, the print processing unit 301 included in the print engine 3 according to this embodiment includes photosensitive drums 102 </ b> Y, 102 </ b> M, 102 </ b> C, and 102 </ b> K (hereinafter referred to as “photosensitive drums”) along the conveying belt 101 that is an endless moving unit. In general, the photosensitive drum 102 is arranged in a line, and is called a so-called tandem type. That is, along the conveyance belt 101 which is an intermediate transfer belt on which an intermediate transfer image to be transferred to a sheet (an example of a recording medium) fed from the sheet feed tray 103 is formed, A plurality of photosensitive drums 102Y, 102M, 102C, and 102K are arranged in order from the upstream side.

  Each color image developed with toner on the surface of the photosensitive drum 102 of each color is superimposed on the conveyor belt 101 and transferred to form a full color image. The full-color image formed on the conveyance belt 101 in this manner is the surface of the sheet conveyed on the path by the function of the transfer roller 104 at a position closest to the sheet conveyance path indicated by a broken line in the drawing. Transcribed above.

  The paper on which the image is formed on the paper surface is further transported, the image is fixed by the fixing roller 105, and then transported to the inspection device 4. In the case of duplex printing, the sheet on which an image is formed and fixed on one side is conveyed to the reversing path 106, reversed, and conveyed again to the transfer position of the transfer roller 104.

  The reading device 400 is configured by an information processing device inside the inspection device 4 by reading each surface of the paper conveyed from the print processing unit 301 in the paper conveyance path inside the inspection device 4 and generating a read image. The image is output to the read image acquisition unit 401. Further, the paper whose surface is read by the reading device 400 is further conveyed through the inside of the inspection device 4 and discharged to the paper discharge tray 410. 5 shows an example in which the reading device 400 is provided only on one side of the paper in the paper transport path in the inspection device 4, but in order to enable inspection of both sides of the paper, The reading device 400 may be arranged on each of both sides.

  In such a configuration, the gist of the present embodiment resides in a master image correction process corresponding to the type of paper determined based on the read image. As a configuration related to the gist of the present embodiment, first, a functional configuration of the inspection control unit 403 according to the present embodiment will be described. FIG. 6 is a block diagram illustrating a functional configuration of the inspection control unit 403 according to the present embodiment. As shown in FIG. 6, the inspection control unit 403 according to the present embodiment includes a plain area determination unit 431, a correction value DB 432, a reference point extraction unit 433, an alignment unit 434, a defect determination unit 435, and a printer interlocking unit 436. .

  The plain area determination unit 431 determines a plain part of the scanned image input from the scanned image acquisition unit 401, that is, a part where the developer is not fixed and the sheet surface is exposed, and information corresponding to the determination result. Is obtained from the correction value DB 432. The information acquired by the plain area determination unit 431 is input to the master image processing unit 402 as information for correcting the above-described color tone in the master image processing unit 402 (hereinafter referred to as “tone correction information”).

  The correction value DB 432 stores the determination result by the plain area determination unit 431 and the above-described color tone correction information in association with each other. FIG. 7 shows an example of information stored in the correction value DB 432. As shown in FIG. 7, the correction value DB 432 includes a “paper type ID” for identifying the type of paper, a “plain region average value” that is an average value of reading values of the plain portion of each paper, and each paper. Information associated with “color conversion table ID” for identifying a paper color conversion table, which is color tone correction information generated for each sheet, is stored. ing. The information shown in FIG. 7 is used as correction value association information.

As shown in FIG. 7, “plain area average value” and “plain area standard deviation” are RGB as “(Rm ₀₀₁ , Gm ₀₀₁ , Bm ₀₀₁ )” and “(Rs ₀₀₁ , Gs ₀₀₁ , Bs ₀₀₁ )”. It is a value specified by each value. If it is “plain area average value”, the average value of the pixel values of each pixel constituting the read image read in a state where no image is formed on the paper is used. If it is “plain area standard deviation”, the standard deviation of the pixel values of each pixel constituting the read image read in a state where no image is formed on the paper is used.

  It is conceivable that the density of the read image generated by reading the gist by the scanner changes due to the exposure intensity, light receiving sensitivity, and the influence of external light. In other words, it is conceivable that the pixel values of the pixels constituting the read image vary depending on the reading conditions. On the other hand, among the “plain region average value” and the “plain region standard deviation”, the “plain region standard deviation” is a standard deviation of the whole plain region, that is, a value indicating variation in density. The fluctuation amount due to is reduced. In other words, the “plain area standard deviation” can be considered as a feature value of the plain area of the paper according to the type without depending on the reading condition.

  On the other hand, since the “plain area average value” is an average value of the entire plain area, it is a value that directly reflects the amount of variation due to the reading conditions, and is therefore used alone as a feature value of the plain area of the paper according to the type. It is difficult. On the other hand, there is a possibility that there are multiple papers showing similar values when only “plain area standard deviation” is used, but the paper type is determined by the combination of “plain area standard deviation” and “plain area average value”. By narrowing down, it is possible to suitably narrow down the paper type based on information acquired from the read image.

  In order to enable such determination, the plain area determination unit 431 according to the present embodiment analyzes each pixel constituting the read image input from the read image acquisition unit 401, and each pixel is a plain part. And a function of calculating an average value and a standard deviation based on a pixel value of a pixel determined to be a plain part. That is, the plain area determination unit 431 according to the present embodiment functions as a variation value calculation unit and an average value calculation unit.

  Then, the plain area determination unit 431 obtains a difference between the average value calculated based on the read image and the “plain area average value” in this way, and calculates the difference between the calculated standard deviation and the “plain area standard deviation”. The difference is obtained, and one of the records stored in FIG. 7 is selected based on each difference. When selecting this record, for example, based on the difference between the standard deviation calculated first and the “plain area standard deviation”, the top several records or the records whose difference is less than a predetermined threshold are narrowed down For the resulting record, the record with the smallest difference between the calculated average value and the “plain area average value” can be selected, that is, the paper type can be determined.

  Alternatively, a record having the smallest difference between the calculated average value and the “plain region average value” and the difference between the calculated standard deviation and the “plain region standard deviation” may be selected. In this embodiment, the paper type is determined based on the “plain area average value” and the “plain area standard deviation”, but as described above, the “plain area standard deviation” is read. Regardless of the conditions, it can be considered as a feature value of the plain area of the paper according to the type. Accordingly, the paper type may be determined based only on the difference between the calculated standard deviation and the “plain area standard deviation”.

  When one of the plurality of records shown in FIG. 7 is selected in this way, the plain area determination unit 431 refers to the “color conversion table ID” associated with the record and identifies the paper type color identified thereby. Get conversion table. That is, the plain area determination unit 431 functions as a correction value acquisition unit. In the present embodiment, the correction value DB 432 stores the paper type color conversion table corresponding to each paper type together with the information shown in FIG. With reference to FIG. 8, an example of a paper type color conversion table according to the present embodiment is shown. FIG. 8 is a diagram illustrating an example of a paper type color conversion table according to the present embodiment. As shown in FIG. 8, the paper type color conversion table according to the present embodiment shows the correspondence between “input” indicating the gradation value before conversion and “output” indicating the gradation value after conversion for each color. It is a table shown in FIG.

  As described above, in the paper type color conversion table according to the present embodiment, the master image processing unit 402 changes the color tone of the master image generated based on the bitmap data according to the ground color of the paper used for printing. Used to correct. The influence of the background color of the paper on the color tone of the image becomes smaller as the density of the output image is higher, that is, closer to black, and becomes smaller as the density is lower, that is, closer to white.

  Therefore, in the paper type color conversion table according to the present embodiment, as shown in FIG. 8, the gradation value of the original bitmap data and the gradation value after correction are associated for each color of RGB. Generated as a table. The master image processing unit 402 according to the present embodiment corrects the color of the master image generated from the bitmap data based on the paper type color conversion table as shown in FIG. Details of functions included in the master image processing unit 402 according to the present embodiment will be described with reference to FIG.

  FIG. 9 is a block diagram illustrating an internal configuration of the master image processing unit 402. As shown in FIG. 6, the master image processing unit 402 includes a small-value / multi-value conversion processing unit 421, a resolution conversion processing unit 422, a color conversion processing unit 423, and an image output unit 424. Note that the master image processing unit 402 according to the present embodiment is realized by the dedicated device 80 described in FIG. 2, that is, hardware and software that controls the hardware.

  The low-value / multi-value conversion processing unit 421 generates a multi-value image by performing low-value / multi-value conversion processing on a binary image expressed in colored / colorless. The variable data according to the present embodiment is information to be input to the print engine 3, and the print engine 3 executes image formation output based on CMYK (Cyan, Magenta, Yellow, blackK) color binary images. On the other hand, the read image, which is the image to be inspected, is a multi-valued image of RGB (Red, Green, Blue) multi-gradation, so that the binary image is first converted into a multi-value by the low-value multi-value conversion processing unit 421. Converted to an image. As the multivalued image, for example, an image expressed by 8 bits for each of CMYK can be used.

  In this embodiment, the print engine 3 executes image formation output based on CMYK binary images, and the master image processing unit 402 includes a low-value multi-value conversion processing unit 421. Is an example. That is, when the print engine 3 executes image formation output based on a multi-value image, the low-value multi-value conversion processing unit 421 can be omitted.

  The resolution conversion processing unit 422 performs resolution conversion so that the resolution of the multi-value image generated by the small-value multi-value conversion processing unit 421 matches the resolution of the read image that is the image to be inspected. In the present embodiment, since the reading device 400 generates a 200 dpi read image, the resolution conversion processing unit 422 converts the resolution of the multi-valued image generated by the small-value multi-value conversion processing unit 421 to 200 dpi.

  The color conversion processing unit 423 acquires the image whose resolution has been converted by the resolution conversion processing unit 422 and performs color conversion. As described above, since the read image according to the present embodiment is an RGB format image, the color conversion processing unit 423 converts the CMYK format image after the resolution conversion by the resolution conversion processing unit 422 into the RGB format. . As a result, a 200 dpi multi-valued image expressed in 8 bits (total 24 bits) for each color of RGB is generated for each pixel, and this image is used as a master image of variable data.

  In addition, the color conversion processing unit 423 adjusts the color to match the color of the variable data that is digital data with the color of the image generated by reading the paper surface by the reading device 400. As described above, this color adjustment processing is performed by referring to a table in which RGB values of variable data as input are associated with RGB values corresponding to the color of an image generated by the reading device 400. This is executed by converting pixel values of variable data converted from CMYK to RGB. This table also has the same configuration as the paper type color conversion table as described in FIG.

  The table described above, that is, the table in which the RGB values of the variable data as input and the RGB values according to the color of the image generated by the reading device 400 are associated (hereinafter, “normal color conversion table”) For example, a gradation correction image including a plurality of color patches having various colors, that is, different densities, is output to the paper by the print processing unit 301, and a reading device is provided on the surface of the paper on which the gradation correction image is formed. The pixel value at the position of each color patch in the read image for gradation correction, which is the read image of the color patch generated by 400, and the pixel value that is the premise of each color patch are stored in association with each other. Is generated. Such processing is executed by the inspection control unit 403. That is, the inspection control unit 403 functions as a color conversion information generation unit.

  The paper color conversion table generation operation described above is also a normal color conversion table generation operation, that is, a read image obtained by outputting a gradation correction image including a color patch to a registration target paper and reading the output result. This is done by analyzing The paper type color conversion table shown in FIG. 8 is generated by the same processing as the normal color conversion table generation operation described above. Further, the table shown in FIG. 7 shows the average value and standard deviation of the plain portion extracted from the read image obtained by reading the paper on which the gradation correction image is formed, and the paper type color generated based on the read image. It is generated by storing in association with a color conversion table ID for identifying a conversion table.

  The normal color conversion table generation operation using such color patches is executed, for example, when a single print job is started. As a result, a table reflecting the printing conditions and reading conditions when the print job is executed is generated. Further, the above-described gradation correction read image includes a solid portion where no patch is displayed. The pixel value of the plain portion in the read image for gradation correction is used in the plain determination process described later.

  Furthermore, the color conversion processing unit 423 according to the present embodiment performs color correction based on the paper type color conversion table described with reference to FIG. 8 in addition to color conversion based on the table generated based on the color patch, that is, Then, color correction processing according to the type of paper is performed. That is, the color conversion processing unit 423 also functions as an inspection image correction unit. Therefore, the paper type color conversion table acquired from the correction value DB 432 by the plain area determination unit 431 is input to the color conversion processing unit 423.

  Note that color conversion based on the table generated based on the color patch described above (hereinafter referred to as “normal color conversion”) is suitably performed, and is used for the paper used at that time and the page to be inspected. If the printed paper is the same type of paper, the color correction corresponding to the ground color of the paper is also performed by normal color conversion. Therefore, color tone correction using the paper type color conversion table as shown in FIG. 8 is not necessary. On the other hand, if the type of paper used to form the color patch is different from the type of paper used for the page to be inspected, the color of the master image is changed to the color of the read image in normal color conversion. Since it cannot be made to correspond, color conversion for each paper type according to the present embodiment is required.

  In order to enable such an aspect, the inspection control unit 403 according to the present embodiment performs paper type determination by the plain area determination unit 431 even in the above-described color patch reading, and is selected as the determination result. The “paper type ID” indicating one of the records shown in FIG. 7 is stored as reference paper type information. Then, the master image processing is performed so that the color conversion based on the paper type color conversion table shown in FIG. 8 is performed only when the paper type determination result in the actual scanned image inspection and the reference paper type information are different. The unit 402 is controlled. With such a process, even when a plurality of different types of paper are used together in one print job, the color of the master image is set according to the color of the paper used for the page to be inspected. It becomes possible to correct.

  The image output unit 424 inputs the master image generated by the processing up to the color conversion processing unit 423 to the reference point extraction unit 433 of the inspection control unit 403. The reference point extraction unit 433 extracts a reference point serving as a reference for alignment from the master image input from the master image processing unit 402. The reference points here are markings displayed at the four corners of the area inside the document to be imaged and output. Even if there is no such marking, pixels that can be marked may be extracted from the image using an image filter such as a corner extraction filter.

  The alignment unit 434 performs alignment between the master image and the reference point input from the reference point extraction unit 433 and the read image input from the read image acquisition unit 401, and the amount of positional deviation between the read image and the master image Ask for. The alignment unit 434 extracts an image around the reference point extracted from the master image for a predetermined range as described in FIG. 4 and also extracts an image at a position corresponding to the image in the predetermined range extracted from the master image. By extracting from the read image and inputting it to the comparison inspection unit 404, the difference value between the two pixel values is acquired as described in FIG.

  The alignment unit 434 repeats the difference value calculation result acquisition processing by the comparison inspection unit 404 a plurality of times while shifting the range of the image extracted from the read image vertically and horizontally, and reads when the sum of the difference values is the smallest. The image extraction range is determined as a position corresponding to the master image extraction range. The misregistration amount between the read image extraction range and the master image extraction range determined as described above is determined as the misregistration amount of the reference point corresponding to the image.

  The alignment unit 434 repeats the same processing for a plurality of reference points extracted from the master image, and the final displacement between the master image and the read image based on the amount of displacement calculated for each reference point. Find the amount. As a process for obtaining the final misregistration amount, for example, an aspect that employs an average value of misregistration amounts calculated for each reference point, or an image based on the misregistration amount calculated for each reference point is used. A mode in which the amount of positional deviation of each part is obtained linearly can be used.

  The defect determination unit 435 inputs the master image and the read image input from the alignment unit 434 to the comparison inspection unit 404, and performs defect determination by the process described with reference to FIG. That is, the defect determination unit 435 functions as an inspection result acquisition unit. It should be noted that the defect determination unit 435 considers the amount of misalignment obtained by the alignment unit 434 when extracting the images in the inspection range from the master image and the read image and inputting them to the comparison inspection unit 404. An inspection range image is extracted from the image and the read image.

  That is, when the defect determination unit 435 according to the present embodiment extracts a read image range corresponding to one inspection range of the divided master image as illustrated in FIG. 4, the position obtained by the alignment unit 434 is obtained. An image is extracted from the read image in consideration of the shift amount. Accordingly, when performing the comparative inspection while shifting the extraction range vertically and horizontally as described in FIG. 4, the comparative inspection is started in a state where the alignment between the master image and the read image has already been performed. It is possible to perform calculation in an appropriate alignment state by the number of calculations.

  When the page to be inspected is determined to be defective by the defect determination unit 435, the printer interlocking unit 436 determines whether to stop the print job or reprint, and sends a print job stop request to the engine control unit 202 of the engine controller 2. Send a reprint request. When transmitting a reprint request, the printer interlocking unit 436 notifies the number of pages to be reprinted and a job identification number indicating a print job. Thereby, the engine control unit 202 executes processing for reprinting. That is, the printer interlocking unit 436 functions as a reprint command unit.

  Next, the operation of the entire inspection apparatus 4 when one print job is executed in the image inspection system according to the present embodiment will be described. FIG. 10 is a flowchart showing the operation of the entire inspection apparatus 4 according to this embodiment. As shown in FIG. 10, when executing one print job, first, the above-described output and reading of the color patch are executed (S1001).

  As a result, the read image acquisition unit 401 acquires a read image obtained by reading a sheet on which a color patch is formed, and inputs the read image to the inspection control unit 403. In the inspection control unit 403, the plain area determination unit 431 performs the paper type determination process as described above based on the read image of the color patch, and acquires and stores the “paper type ID” from the table described in FIG. (S1002). This “paper type ID” functions as a reference paper identifier. The plain area determination unit 431 generates the above-described paper type color conversion table based on the read image of the color patch (S1003).

  Subsequently, image formation output of each page included in the print job is started, and the master image processing unit 402 acquires the bitmap data transmitted by the bitmap transmission unit 203 (S1004), and as described in FIG. A master image generation process is executed by the small-value / multi-value conversion processing unit 421, the resolution conversion processing unit 422, and the color conversion processing unit 423 (S1005).

  On the other hand, when the print processing unit 301 of the print engine 3 is controlled by the engine control unit 202 and image formation output is executed on the paper, the paper surface of the paper is read by the reading device 400 to generate a read image. . The read image acquisition unit 401 waits until a read image for each page is acquired (S1006 / NO). When the read image is acquired (S1006 / YES), the acquired read image is input to the inspection control unit 403. As a result, the plain area determination unit 431 performs the paper type determination based on the read image as described above (S1007), and acquires the “paper type ID” associated with the record as the inspection target paper identifier.

  As a result of the determination in S1007, if the acquired paper type ID is the same as the paper type ID stored in S1002 (S1008 / YES), the color correction corresponding to the ground color of the paper is also performed by the normal color conversion. It will be. Therefore, since the tone correction using the paper type color conversion table as shown in FIG. 8 is unnecessary, the inspection control unit 403 causes the master image processing unit 402 to output the master image generated by the normal color conversion (S1009). ). As a result, the reference point extraction unit 433 extracts a reference point serving as a reference for alignment from the master image as described above.

  On the other hand, as a result of the determination in S1007, if the acquired paper type ID is different from the paper type ID stored in S1002 (S1008 / NO), the color correction according to the paper type is not performed in the normal color conversion. The plain area determination unit 431 acquires the paper type color conversion table associated with the determined paper type from the correction value DB 432 and inputs it to the master image processing unit 402 (S1013).

  The master image processing unit 402 that has acquired the paper type color conversion table from the plain area determination unit 431 performs color tone correction of the master image based on the acquired paper type color conversion table (S1014). When the color tone correction based on the paper type color conversion table is completed, the master image processing unit 402 outputs a master image whose color tone conversion has been completed in accordance with the control of the inspection control unit 403 (S1009). As a result, the reference point extraction unit 433 extracts a reference point serving as a reference for alignment from the master image as described above.

  Subsequently, the alignment unit 434 executes the alignment process as described above based on the master image and the reference point input from the reference point extraction unit 433 and the read image input from the read image acquisition unit 401 (S1010). ). Then, the defect determination unit 435 inputs the inspection range image extracted from the master image and the read image based on the result of the alignment process by the alignment unit 434 to the comparison inspection unit 404, and performs defect determination (S1011). As a result, the defect determination unit 435 causes the printer interlocking unit 436 to execute control such as print stop or reprint request according to the result of the defect determination.

  The inspection control unit 403 repeats the processing from S1004 until output of all pages is completed for one print job (S1012 / NO), and ends output when all pages are output and inspected (S1012 / YES). To do. By such processing, the operation of the entire inspection apparatus 4 according to the present embodiment is completed.

  As described above, in the inspection apparatus 4 according to the present embodiment, the paper type color which is the standard deviation of the pixel value of the plain portion and the color tone correction value corresponding to the paper type for each paper type as described in FIG. Information associated with the conversion table is prepared, the paper type is determined based on the standard deviation of the pixel value of the plain portion extracted from the read image, and an appropriate correction value is selected. Then, by correcting the master image with the correction value thus selected, it is possible to perform a comparative inspection with a color tone according to the type of paper used in the image forming output, and to reduce erroneous detection of defects. It becomes possible.

  Since the standard deviation is a value indicating the variation in the pixel value of the plain portion, the value variation due to the reading condition when the reading device 400 reads the document is small. Therefore, by determining the paper type based on the standard deviation value of the plain portion, it is possible to appropriately perform the paper type determination regardless of the reading conditions.

  In this embodiment, in addition to the standard deviation of the pixel values of the plain portion, the average value of the pixel values of the plain portion is associated with each paper color conversion table. In determining the paper type, the average value of the plain portion is referred to in addition to the standard deviation of the plain portion. As a result, even if there are papers with different paper types and similar standard deviation values for the plain part, it is possible to identify the paper based on the gradation value of the plain part and perform the paper type determination appropriately. It becomes.

  Note that the above embodiment has been described on the assumption that the paper type determination is successful in S1007. However, information about the paper used for image formation output is not necessarily registered in the correction value DB 432 as shown in FIG. In such a case, if a record having the smallest difference value between the plain area standard deviation and the plain area average value is selected, an incorrect paper type color conversion table is selected.

  In order to avoid such an adverse effect, in the paper type determination processing by the plain area determination unit 431, it is preferable to provide a threshold for the difference values of the plain area standard deviation and the plain area average value. That is, the plain area determination unit 431 calculates the standard deviation and the average value calculated based on the pixel value of the plain part extracted from the read image, and the “plain area standard deviation” and “plain area average value” shown in FIG. As a result of calculating the difference value, if the calculated difference value is greater than or equal to the predetermined threshold value for any record, the paper used for the page to be inspected is registered in the correction value DB 432. If it is not determined, the process ends due to an error.

  When the process is terminated due to an error in this way, the gradation correction image including the color patch is output to the target sheet in the sheet registration mode, that is, as described above, and the read image obtained by reading the output result is analyzed. It is preferable to display a message prompting registration of the paper type color conversion table for the paper on the display device depending on the mode.

  Note that such a determination as to whether or not a sheet has been registered can also be made in S1002 of FIG. That is, also in S1002, the plain area determination unit 431 performs paper type determination based on the pixel value of the plain part extracted from the read image. As a result, the difference value between the calculated average value and the “plain region average value” shown in FIG. 7 or the difference value between the calculated standard deviation and the “plain region standard deviation” shown in FIG. 7 exceeds a predetermined threshold. If it is, it is determined that the sheet is unregistered.

  In this case, the average value and the standard deviation calculated at that time are registered as “solid color area average value” and “solid color area standard deviation”, respectively, and the normal color conversion table generated in S1003 is converted to paper type color conversion. By registering as a table, new data can be registered in the correction value DB 432 without performing a separate paper registration process.

  Further, in the above-described embodiment, the description has been made by using the RGB value as an example for the “plain area average value” and the “plain area standard deviation”. This is effective in that the value space can be directly used because the color space of the read image is generally an RGB space. However, this is an example, and the paper type may be determined using another color space.

  For example, the pixel values constituting the read image read in the RGB color space may be converted into values of other color spaces such as the Lab color space, the CIE 1976 color space, the Munsell color system, and the values may be used. In this case, as a value used for the plain color determination, it is conceivable to make a determination based on the standard deviation or the average value as described above by using a luminance value that is considered to have the greatest influence on human vision.

  In the above embodiment, as described with reference to FIG. 7, a case where one record is generated for each paper type is taken as an example. In this embodiment, the standard deviation of the pixel value of the plain portion is calculated in order to enable the paper type determination with the influence of the reading condition reduced as much as possible, but the color tone of the read image depends on the reading condition. Therefore, even if the paper type is suitably determined, depending on the reading conditions, there may be cases where color conversion using the paper type color conversion table associated with the paper type is not appropriate.

  The difference in color tone depending on the reading condition appears in the “plain area average value” rather than the “plain area standard deviation”. Therefore, even if the same sheet is used, by registering the record shown in FIG. 7 while changing the exposure intensity and light receiving sensitivity at the time of scanning by the reading device 400, a record having a different “plain area average value” is generated. At the same time, as the paper type color conversion table shown in FIG.

  As described above, by registering a plurality of records under different reading conditions even for the same sheet, the determination result in S1007 of FIG. 10 includes not only the determination of the paper type but also the determination including the reading conditions. That is, it is possible to determine which paper type is read under what reading condition, and it is possible to acquire a paper type color conversion table corresponding to the determination result. As a result, it is possible to correct the master image including not only the paper type but also the reading condition of the read image of the page to be inspected.

  In the above embodiment, the case where the master image processing unit 402 corrects the color tone of the master image based on the paper type color conversion table acquired from the plain area determination unit 431 has been described as an example. In this case, the function of the color conversion processing unit 423 originally included in the master image processing unit 402 can be used as it is, and a module for color tone correction based on the paper type color conversion table is newly configured. It is effective in that it is not necessary.

  However, the gist of the present case is to match the color tone of the master image and the read image in accordance with the type of paper used for the page to be inspected. Therefore, the read image may be corrected not only when the master image is corrected. In this case, it can be easily realized by applying the values of “input” and “output” shown in FIG. 8 in reverse.

  In the above embodiment, the standard deviation of the pixel value of the plain area is used as information for specifying the paper type regardless of the reading conditions. However, the purpose of using the standard deviation is to use a value that indicates the variation in density of the plain portion and that suppresses the influence of the magnitude of each density value. Therefore, the value to be used is not limited to the standard deviation, and any other value may be used as long as the value meets such a purpose.

  As another example of the value indicating the variation in density of the plain portion and suppressing the influence of the magnitude of each density value, for example, a dispersion value can be used. Further, as a technique for suppressing the influence of the magnitude value of each density, it is conceivable to divide the value of variance or standard deviation by the average value.

  In the above embodiment, the case where the master image is generated including the normal color conversion processing by the color conversion processing unit 423 in S1005 of FIG. 10 has been described as an example. However, a mode in which the color conversion process using the paper type color conversion table is performed instead of the normal color conversion is also possible. Therefore, in S1005 of FIG. 10, the processing up to the resolution conversion processing unit 422 may be performed.

1 DFE
2 Engine controller 3 Print engine 4 Inspection device 10 CPU
20 RAM
30 ROM
40 HDD
50 I / F
60 LCD
70 Operation Unit 80 Dedicated Device 90 Bus 101 Conveying Belts 102, 102Y, 102M, 102C, 102K Photosensitive Drum 103 Paper Feed Tray 104 Transfer Roller 105 Fixing Roller 106 Reverse Path 201 Data Acquisition Unit 202 Engine Control Unit 203 Bitmap Transmission Unit 301 Print processing unit 400 Reading device 401 Read image acquisition unit 402 Master image processing unit 403 Inspection control unit 404 Comparison inspection unit 410 Paper discharge tray 421 Small value multi-value conversion processing unit 422 Resolution conversion processing unit 423 Color conversion processing unit 424 Image processing unit 431 Solid region determination unit 432 Correction value DB
433 Reference point extraction unit 434 Position alignment unit 435 Defect determination unit 436 Printer interlocking unit

JP 2011-114574 A Japanese Laid-Open Patent Publication No. 2005-205703

Claims (9)

An image inspection apparatus for inspecting a read image obtained by reading an image printed on a paper surface,
A read image acquisition unit that acquires a read image generated by reading an image printed on the paper;
An inspection image generation unit for generating an inspection image for inspecting the read image based on information of an image to be printed;
An inspection result acquisition unit for acquiring an inspection result obtained by determining a defect of the read image based on a difference between the image for inspection and the read image;
A plain area determination unit that extracts a ground color area of the paper to which no developer is added on the paper surface from the acquired read image;
A variation value calculation unit that calculates a value indicating a variation in density of pixels of the plurality of extracted ground color regions;
Refer to correction value association information in which a correction value for correcting the influence on the color tone due to the density of the background color area for each sheet is associated with a value indicating a variation in density of pixels in the background color area, A correction value acquisition unit that acquires a correction value corresponding to the calculated value indicating the variation;
An image inspection apparatus comprising: a color correction unit that corrects one of the generated image for inspection and the read image based on the acquired correction value. An average value calculating unit that calculates an average value of the density of pixels of the plurality of extracted ground color regions;
The correction value association information is information in which a combination of a value indicating a variation in density of pixels in the ground color region and an average value of the density of pixels in the ground color region is associated with the correction value,
The image inspection apparatus according to claim 1, wherein the correction value acquisition unit acquires a correction value corresponding to a combination of the calculated variation value and the average value.   The correction value association information includes, for each type of paper, a combination of a value indicating a variation in density of pixels in the background color area and an average value of the density of pixels in the background color area for each different reading condition. The image inspection apparatus according to claim 2, wherein the image inspection apparatus is information associated with the correction value.   The correction value acquisition unit, based on a difference value between a value indicating the variation included in the correction value association information and a value indicating the calculated variation, a correction value corresponding to the calculated value indicating the variation The image inspection apparatus according to claim 1, further comprising:   The correction value acquisition unit is configured to inspect the read image when a difference value between the calculated value indicating variation and a value indicating the variation included in the correction value association information is equal to or greater than a predetermined threshold. The image inspection apparatus according to claim 1, wherein the image inspection apparatus is interrupted. Before the start of the inspection, a color patch read image obtained by reading a sheet on which a plurality of color patches having different densities are printed on a paper surface is obtained, and a density value in each read image of each of the plurality of color patches and the plurality of the plurality of color patches are read. Including a color conversion information generation unit that generates color conversion information by associating with the density value used for printing the color patch;
The color tone correction unit generates one of the inspection image and the read image using the generated color conversion information,
The plain area determination unit extracts a background color area of the paper from the color patch read image,
The variation value calculation unit calculates a value indicating variation in density of pixels in a ground color region extracted from the color patch read image;
The correction value acquisition unit acquires and stores from the correction value association information, as a reference sheet identifier, a sheet identifier corresponding to a value indicating the density variation of the pixels in the ground color region extracted from the color patch read image. And storing the identifier of the sheet corresponding to the value indicating the density variation of the pixel of the ground color area extracted from the read image to be inspected from the correction value association information as the inspection target sheet identifier, 6. The correction value corresponding to a value indicating the variation calculated for the read image is acquired when a reference sheet identifier and the inspection target sheet identifier are different from each other. The image inspection apparatus according to the description,   The correction value acquisition unit, for all values indicating the variation included in the correction value association information, a difference value from a value indicating a variation in density of pixels in the ground color region extracted from the color patch read image Is equal to or greater than a predetermined threshold value, the generated color conversion information is used as a correction value for correcting the influence on the color tone due to the density of the background color region. The image inspection apparatus according to claim 6, wherein the correction value association information is generated in association with a value indicating variation in density of pixels in a region. An image inspection method for inspecting a read image obtained by reading an image printed on a paper surface,
Obtaining a read image generated by reading an image printed on the paper;
Generating an inspection image for inspecting the read image based on information of an image to be printed;
Obtaining an inspection result for determining a defect in the read image based on a difference between the image for inspection and the read image;
From the acquired read image, a ground color region of the paper to which no developer is added is extracted on the paper surface,
Calculating a value indicating a variation in density of pixels of the plurality of extracted ground color regions;
Refer to correction value association information in which a correction value for correcting the influence on the color tone due to the density of the background color area for each sheet is associated with a value indicating a variation in density of pixels in the background color area, Obtain a correction value corresponding to the calculated value indicating the variation,
An image inspection method, wherein either one of the generated inspection image and the read image is corrected based on the acquired correction value. An image inspection program for inspecting a read image obtained by reading an image printed on a paper surface,
Obtaining a read image generated by reading an image printed on the paper;
Generating an inspection image for inspecting the read image based on information of an image to be printed;
Obtaining an inspection result in which a defect of the read image is determined based on a difference between the inspection image and the read image;
Extracting from the acquired read image a ground color region of the paper to which no developer is added on the paper surface;
Calculating a value indicating a variation in density of pixels of the plurality of extracted ground color regions;
Refer to correction value association information in which a correction value for correcting the influence on the color tone due to the density of the background color area for each sheet is associated with a value indicating a variation in density of pixels in the background color area, Obtaining a correction value corresponding to the calculated value indicating the variation;
An image inspection program that causes an information processing apparatus to execute a step of correcting one of the generated image for inspection and the read image based on the acquired correction value.