JP2014178622A - Image inspection device, image inspection system, and image inspection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce incorrect detection in a defect inspection of printed matters when the type of halftone processing applied in creating print data is different from the type of inverse halftone processing applied in creating a master image.SOLUTION: An image inspection device creates a master image for performing an inspection of read images on the basis of information on an image subjected to inverse halftone processing on print data that is created through halftone processing; acquires the type of the halftone processing performed in creating the print data; acquires setting information corresponding to a combination of the acquired types of the halftone processing and the types of the inverse halftone processing, from predetermined setting information for the inspection of read images according to combinations of the types of the halftone processing and the types of the inverse halftone processing; and changes a reference for determining read images as having defects on the basis of the setting information, and performs an inspection to determine defects in read images on the basis of a difference between a read image and the master image.

Description

  The present invention relates to an image inspection apparatus, an image inspection system, and an image inspection method, and more particularly to reduction of false detection in defect inspection of printed matter.

  In recent years, an inspection apparatus that inspects printed matter generates a master image serving as a reference from print data, and detects defects in the printed matter depending on the degree of difference obtained by comparing the master image with the read image of the printed matter to be inspected. Judging. This image comparison is generally performed by comparing the densities of pixels at corresponding positions with respect to the pixels constituting each image. As a result, if any defect occurs in the image due to the image formation output, it can be detected.

  By the way, there are differences in gloss unevenness, color, density, etc., depending on the type (recycled paper, plain paper, coated paper, etc.) of the paper on which the image is formed and output. Therefore, when the read image of the printed material is compared with the master image, the difference between the two may become large due to the influence of uneven gloss, color, density, etc. in the read image. In this case, the inspection apparatus may erroneously detect that a defect has occurred even though the printed matter is normally printed. In view of this, a method has been proposed in which inspection conditions such as the inspection level and the inspection level indicating the strictness of the inspection are set according to the type of paper (see, for example, Patent Document 1).

  Halftone processing is applied to the generation of print data. When a master image is generated based on print data subjected to halftone processing, reverse halftone processing is applied to the print data. However, if the type of inverse halftone processing applied when generating the master image is predetermined as one type, the type of halftone processing applied when generating the print data and the master image generation May be different from the type of inverse halftoning applied to.

  Further, since the blurring of the image after the halftone process differs depending on the type of the halftone process to be applied, a difference occurs in each pixel value when images subjected to different types of halftone processes are compared. Therefore, if the type of inverse halftone processing applied at the time of master image generation is different from the type of halftone processing applied at the time of print data generation, the difference in pixel value between the read image of the printed material and the master image May become larger. In that case, it may be erroneously detected that a defect has occurred even though the printed matter is normally printed.

  In order to deal with such problems, when the type of applied halftone processing is different, the threshold for determining the defect of the printed matter is uniformly lowered as compared with the case where the type of the halftone is the same, and false detection is performed. It is conceivable to avoid this. However, if the threshold is lowered too much, the defect may not be detected even if the defect that is originally desired to be detected has occurred. Further, the technique of Patent Document 1 only sets the inspection condition according to the type of paper, and cannot solve the above-described problem when the type of halftone processing is different.

  The present invention has been made in order to solve such problems, and the type of halftone processing applied when generating print data and the type of inverse halftone processing applied when generating a master image. The purpose is to reduce false detections due to defect inspection of printed matter in the case of different prints.

  In order to solve the above problems, one embodiment of the present invention is an image inspection apparatus that inspects a read image obtained by reading an image formed and output on a paper surface, and each pixel has a first gradation number. Generated by gradation conversion processing that converts a multi-value image expressed by pixel values into a low-value image in which each pixel is expressed by a second number of gradations smaller than the first number of gradations. A reverse gradation conversion process for converting the low-value image into the multi-value image with respect to the image forming output target image, which is a scanned image, and the reading is performed based on the information of the image subjected to the reverse gradation conversion process. An image generation unit for inspection that generates an image for inspection for inspecting an image, a type acquisition unit that acquires a type of the gradation conversion process performed when generating the image to be imaged and output, and Combination of the type of gradation conversion processing and the type of inverse gradation conversion processing The setting corresponding to the combination of the type of the gradation conversion process and the type of the reverse gradation conversion process acquired from the setting information for the inspection of the read image predetermined for each combination according to A setting information acquisition unit that acquires information, and an image inspection unit that performs an inspection to determine a defect of the read image based on a difference between the read image and the inspection image, and the image inspection unit is acquired In addition, based on the setting information, a reference for determining the read image as a defect is changed.

  According to another aspect of the present invention, there is provided an image inspection system for inspecting a read image obtained by reading an image formed and output on a paper surface, wherein each pixel is represented by a pixel value having a first gradation number. An image generated by performing gradation conversion processing for converting the multi-valued image into a low-value image in which each pixel is expressed by a second number of gradations smaller than the first number of gradations A reverse gradation conversion process for converting the low-value image into the multi-value image is performed on the image to be formed and output, and the read image is inspected based on the information of the image subjected to the reverse gradation conversion process. An inspection image generation unit that generates an image for inspection, a type acquisition unit that acquires a type of the gradation conversion process performed when generating the image to be imaged and output, and the gradation conversion process Depending on the combination of the type of color and the type of the reverse gradation conversion process A setting for acquiring setting information corresponding to a combination of the acquired gradation conversion processing type and the reverse gradation conversion processing type from setting information for inspection of the read image predetermined for each combination An information acquisition unit; and an image inspection unit that performs an inspection for determining a defect in the read image based on a difference between the read image and the inspection image, and the image inspection unit includes the acquired setting information. Based on this, the reference for determining the read image as a defect is changed.

  According to still another aspect of the present invention, there is provided an image inspection method for inspecting a read image obtained by reading an image formed and output on a paper surface, wherein each pixel is represented by a pixel value having a first gradation number. An image generated by performing gradation conversion processing for converting the multi-valued image into a low-value image in which each pixel is expressed by a second gradation number smaller than the first gradation number. An inverse gradation conversion process for converting the low-value image into the multi-value image is performed on the image to be imaged and output, and the read image is inspected based on the information of the image subjected to the inverse gradation conversion process. An image for inspection to be generated is generated, the type of the gradation conversion process performed at the time of generating the image of the image formation output target is acquired, and the type of the gradation conversion process and the inverse gradation conversion process Before the predetermined for each combination according to the combination with the type Based on the acquired setting information, setting information corresponding to a combination of the acquired gradation conversion processing type and the reverse gradation conversion processing type is acquired from setting information for inspection of the read image. And changing the reference for determining the read image as a defect, and performing an inspection for determining a defect in the read image based on a difference between the read image and the inspection image. Method.

  According to the present invention, false detection due to defect inspection of printed matter when the type of halftone processing applied when generating print data and the type of inverse halftone processing applied when generating a master image are different is reduced. can do.

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, and an inspection 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 master image process part which concerns on embodiment of this 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 aspect of the comparison test | inspection based on the test | inspection conditions which concern on embodiment of this invention. It is a figure which shows the halftone table which concerns on embodiment of this invention. It is a flowchart which shows the test | inspection setting process 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 including an inspection apparatus that inspects an output result by comparing a read image obtained by reading an output result of image formation output with a master image, the read image and the master image are applied. The configuration is characterized in that the inspection condition is set according to the combination of the types of halftone processing. 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. Bitmap data is generated by applying one or more halftone processes. Halftone processing is gradation conversion processing that executes multi-value / low-value conversion processing on multi-tone multi-value images to generate binary images expressed as colored / colorless, which are low-value images. It is. Note that the low-value image is not limited to the binary image, and may be an image having fewer gradations than the multi-value image according to the performance of the print engine 3.

  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, a hardware configuration constituting 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.

  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 comparison inspection unit 404 for 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. The master image generation processing by the master image processing unit 402 will be described in detail 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. 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, and determines whether or not the intended image formation output is being executed. . 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 present embodiment, the inspection control unit 403 functions as an image inspection unit by controlling the comparative inspection unit 404 and also functions as an inspection result acquisition unit that acquires an inspection result by the comparative inspection unit 404.

  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 between the 8 bit 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 sheet whose paper surface has been read by the reading device 400 is further conveyed inside the inspection device 4, conveyed to the stacker 5, and discharged to the paper discharge tray 501. 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.

  Next, details of functions included in the master image processing unit 402 will be described with reference to FIG. FIG. 6 is a block diagram illustrating an internal configuration of the master image processing unit 402. As illustrated 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 processing unit 424. Note that the master image processing unit 402 according to the present embodiment is realized by operating the dedicated device 80 described in FIG. 2, that is, hardware configured as an ASIC, according to software control.

  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 bitmap data according to the present embodiment is information to be input to the print engine 3, and the print engine 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), which is the basic three primary colors, and is a multi-valued image. The image is converted into a multi-valued 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 low-value image is not limited to a value image, and may be an image having fewer gradations than the multi-value image according to the performance of the print engine 3.

  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 by 8 bits (total 24 bits) of each RGB color is generated for each pixel. That is, in the present embodiment, the small-value / multi-value conversion processing unit 421, the resolution conversion processing unit 422, and the color conversion processing unit 423 function as an inspection image generation unit.

  The image output processing unit 424 performs a scaling process on the RGB 8-bit, 200 dpi image generated by the processing up to the color conversion processing unit 423, and is input from the reading device 400 of the print engine 3 to the inspection device 4. The size of the read image to be mastered and the master image are matched to reduce image misregistration.

  In such a system, the gist of the present embodiment is that the type of the reverse halftone process applied when generating the master image and the image data to be printed (hereinafter referred to as “print data”) are generated. The inspection condition is set according to the combination with the type of applied halftone processing. The inverse halftone process is an inverse gradation conversion process that performs an inverse process of the halftone process. Hereinafter, processing of the system according to the present embodiment will be described.

  In the present embodiment, the DFE 1 outputs to the engine controller 2 the type information of the halftone process applied at the time of generating the bitmap data in addition to the generated bitmap data. The type of halftone processing refers to the types of halftone processing methods such as the dither method and error diffusion method, and the types of parameters used for each method (for example, dither pattern values and error diffusion methods in the dither method). Pixel processing order and the number of peripheral pixels to be processed).

  The engine controller 2 outputs the type information of the halftone process received from the DFE 1 to the inspection device 4. The small-value multi-value conversion processing unit 421 generates a multi-value image by applying inverse halftone processing to the binary image. Note that the type of reverse halftone processing to be applied is one predetermined type (for example, reverse halftone processing suitable for a character region in an image).

  Next, processing in which the inspection control unit 403 sets inspection conditions according to the combination of the type of inverse halftone processing applied when generating the master image and the type of halftone processing applied when generating print data Will be described. FIG. 7 is a diagram illustrating a functional configuration for setting an inspection condition among the functions included in the inspection control unit 403. As shown in FIG. 7, the inspection control unit 403 according to the present embodiment includes a halftone type acquisition unit 431, a halftone table 432, and an inspection condition setting unit 433.

  Here, the inspection conditions in the present embodiment will be described. FIG. 8 illustrates four pixels of each of the read image and the master image expressed in 8 bits for each RGB color compared by the comparison inspection unit 404, and FIG. 8A compares both images in units of one pixel. FIG. 8B is a diagram illustrating a case where both images are compared in units of 2 × 2 pixels. Note that the comparison between the two images in units of 2 × 2 pixels means that a difference value between pixel values (for example, the sum or average of four pixel values) calculated in units of 2 × 2 pixels in each image is calculated. This means that the difference value is compared with the threshold value. In FIG. 8, pixels shown in white (hereinafter referred to as “white pixels”) indicate values close to white, and pixels shown in diagonal lines (hereinafter referred to as “hatched pixels”). ) Indicates a value close to black.

  As shown in FIG. 8A, when the two images are compared in units of one pixel, for example, the lower left pixel has a large difference value because the master image is a white image and the read image is a hatched image. There is a high possibility that both images are judged to be defective. On the other hand, as shown in FIG. 8B, when the two images are compared in units of 2 × 2 pixels, the number of white pixels and the number of hatched pixels in the four pixels are the same in both images. The value is small, and it is highly possible that both images are judged to be free of defects.

  In this way, if the number of unit pixels for comparing both images is increased, it is possible to reduce the influence of differences in image blurring and the like caused by applying different types of halftone processing when generating both images. it can. However, on the other hand, if the number of unit pixels is increased too much, it may be determined that there is no defect although the image actually has a defect. The inspection condition in the present embodiment indicates the number of unit pixels (hereinafter referred to as “comparison unit”) that serves as a reference when comparing both images in consideration of such a situation.

  The halftone type acquisition unit 431 acquires the type information of the halftone process input from the engine controller 2 and the type information of the reverse halftone process applied in the master image processing unit 402.

  FIG. 9A is a diagram illustrating a halftone table stored in the halftone table 432 in the case where the type of inverse halftone processing applied when generating the master image is determined as halftone A. Similarly, FIG. 9B, FIG. 9C, and FIG. 9D show that the types of inverse halftone processing applied when generating a master image are halftone B, halftone C, and halftone D, respectively. It is a figure which illustrates the halftone table which the halftone table 432 memorize | stores in the case where it is defined.

  As shown in FIG. 9, in the halftone table, table values are set when different types of halftone processes are applied when generating bitmap data than when generating master images. The table value indicates the above-described comparison unit that is an inspection condition, and is set in advance by a setting manager or the like of the inspection apparatus 4.

  For example, as shown in FIG. 9A, when the type of halftone processing applied when generating bitmap data is halftone B, a comparison unit of 3 × 3 pixels is set as an inspection condition, and halftone processing is performed. In the case of tone C, a comparison unit of 2 × 2 pixels is set as an inspection condition. Also, for example, as shown in FIG. 9C, the type of inverse halftone processing applied when generating the master image is halftone C, and the type of halftone processing applied when generating bitmap data. Is a halftone D, a comparison unit of one pixel is set as an inspection condition. Note that the inspection condition for the comparison unit of one pixel is an inspection condition that is initially set.

  FIG. 10 is a diagram illustrating a flowchart in which the inspection condition setting unit 433 performs inspection condition setting processing. As shown in FIG. 10, the inspection condition setting unit 433 that has acquired the type information of the halftone process and the type information of the reverse halftone process input from the halftone type acquisition unit 431 has different types of information acquired. (S1001 / YES), the halftone table stored in the halftone table 432 is acquired (S1002). For example, when the reverse halftone process applied when generating the master image is defined as halftone A, the inspection condition setting unit 433 stores the halftone shown in FIG. 9A stored in the halftone table 432. Get the table.

  On the other hand, if the acquired type information is the same (S1001 / NO), the inspection condition setting unit 433 ends the process without setting the inspection condition. That is, the comparative inspection unit 404 performs a comparative inspection using inspection conditions that are preset in advance (for example, a comparison unit of one pixel).

  The inspection condition setting unit 433 that has acquired the halftone table refers to the acquired halftone table, acquires a table value corresponding to the type of halftone processing applied at the time of bitmap data generation, and sets a comparison unit. Setting is made (S1003). For example, referring to the halftone table shown in FIG. 9A, when the type of halftone processing applied at the time of generating bitmap data is halftone B, the inspection condition setting unit 433 has 3 × 3 pixels. Are set as inspection conditions. That is, the inspection condition setting unit 433 functions as a setting information acquisition unit that acquires setting information to be set as an inspection condition. The comparative inspection unit 404 performs a comparative inspection between the read image and the master image using the inspection conditions set by the inspection condition setting unit 433.

  As described above, in the present embodiment, when the type of halftone processing applied at the time of generating bitmap data is different from the predetermined type of reverse halftone processing applied at the time of generating a master image In addition, a comparison unit for comparison inspection is set in accordance with the combination of both types of halftone processing. As a result, the difference between the master image and the read image is calculated in a comparison unit in which the influence due to the difference between the master image and the read image generated according to the combination of the applied halftone processing types is reduced. Misdetection of defect inspection due to different types of halftone processing is reduced.

  In the above-described embodiment, a case where the combination of the type of inverse halftone processing applied when generating a master image and the type of halftone processing applied when generating bitmap data is 1: 1 will be described. However, it may be one-to-many. In that case, the inspection condition setting unit 433 acquires and refers to the halftone table as described above, and acquires a comparison unit corresponding to each of a plurality of types of halftone processes applied when generating bitmap data. . Then, the inspection condition setting unit 433 sets the largest comparison unit among the acquired comparison units as the inspection condition.

  That is, when the type of inverse halftone processing applied when generating a master image is halftone A, and the halftone processing applied when generating bitmap data is halftone B and halftone C The inspection condition setting unit 433 sets a comparison unit of 3 × 3 pixels as the inspection condition with reference to the halftone table shown in FIG. As a result, even when multiple types of halftone processing different from the master image generation are applied when generating bitmap data, erroneous detection of defect inspection due to different types of halftone processing is prevented. Reduced.

  Further, when the DFE 1 outputs halftone application region information indicating which type of halftone processing is applied to which region of the image when generating bitmap data to the engine controller 2, the inspection condition setting unit 433. The following processing can be performed. First, the engine controller 2 outputs the halftone application area information input from the DFE 1 to the inspection apparatus 4. In this case, for example, the halftone type acquisition unit 431 also functions as an area information acquisition unit that acquires halftone application area information.

  The inspection condition setting unit 433 acquires a comparison unit corresponding to the type of halftone process included in the halftone application area information input from the engine controller 2 from the halftone table. The inspection condition setting unit 433 acquires an area to which the halftone process is applied from the halftone application area information, and sets the acquired comparison unit as an inspection condition for the acquired application area.

  In addition, the inspection condition setting unit 433 sets an initially set comparison unit as an inspection condition, except for an area to which a different type of halftone process from that used when generating a master image is applied. In addition, when a plurality of types of halftone processing are applied at the time of generating bitmap data, the inspection condition setting unit 433 acquires a comparison unit and an application area for each type, and performs a comparison corresponding to each application area. Set the unit as the inspection condition. Then, the comparison inspection unit 404 performs a comparison inspection between the read image and the master image using the inspection conditions set for each application region.

  With such a configuration, the comparison inspection unit 404 uses the inspection conditions set for each region in accordance with the type of halftone processing applied to each region when generating bitmap data, and uses the read image and the master image. Can be compared. Therefore, it is possible to perform defect inspection of printed matter more efficiently and accurately. In the above embodiment, the comparison unit is separate from the division range determined based on the range in which the comparison inspection unit 404 configured by the ASIC described in FIG. 4 can compare pixel values at a time. However, as long as it is a range that can be handled by the ASIC, the division range may be changed according to the inspection condition, and the difference may be obtained in units of the division range.

  In the above embodiment, the case where the comparison unit when comparing the read image and the master image is set as the inspection condition has been described as an example. However, a threshold for determining a defect may be set as the inspection condition. . When the type of inverse halftone processing applied when generating a master image is different from the type of halftone processing applied when generating bitmap data, the difference is greater than when the types are the same due to differences in image blurring, etc. The value may be large.

Therefore, in order to reduce erroneous detection of defects, for example, when it is determined that there is a defect when the difference value between the master image and the read image exceeds the threshold value, it is conceivable to increase the threshold value. However, on the other hand, if the threshold is increased too much, it may be determined that there is no defect even though the image actually has a defect.

  In the present embodiment, in consideration of such a situation, the combination of the type of inverse halftone processing applied at the time of generating the master image and the type of halftone processing applied at the time of generating bitmap data is used. A corresponding threshold value is set. In this case, the table value of the halftone table indicates a threshold value for defect determination. Then, the inspection condition setting unit 433 refers to the halftone table when the type of halftone processing applied when generating the images is different, and refers to the halftone processing applied when generating the bitmap data. A threshold value corresponding to the type is set as an inspection condition.

  When setting the comparison unit as the inspection condition, the difference calculation of both images must be changed according to the set comparison unit, but when setting the threshold as the inspection condition, only the threshold is changed. It is possible to reduce erroneous detection of defects with a simpler configuration.

  In the above embodiment, the case where the table value of the halftone table is a comparison unit or a threshold value has been described as an example. In addition, the table value may be information that can acquire information on the comparison unit or threshold, such as identification information associated with the comparison unit or threshold. Further, the table value related to the threshold value may be a level of detection level for detecting a defect, a level decrease level indicating how much the level is to be decreased from the initially set detection level, and the like.

In the above-described embodiment, the table value of the halftone table has been described as an example in which the setting manager of the inspection apparatus 4 is set. However, the table value is calculated using some index according to the type of halftone processing. Also good. For example, the table value is calculated using a halftone value indicating the degree of blurring of the image by the halftone process as an index. For example, if the halftone value of the reverse halftone process applied when generating the master image is x and the halftone value of the halftone process applied when generating the bitmap data is y, the table value TableValue is as follows: Calculated by equation (1).

  Here, k is a constant and is a positive rational number that is not 0. The table value obtained by the expression (1) becomes lower as the halftone value of the halftone process applied when generating both images is closer. That is, the closer the degree of blur between the master image and the read image (that is, the smaller the difference between the two images), the lower the table value. Therefore, when such a table value is used, the table value is, for example, configured to be associated with an inspection condition having a smaller comparison unit or threshold value as the value is lower.

  Further, when the inspection device 4 displays the inspection result on the LCD 60 or the like, the halftone process type applied when generating the bitmap data and the master image generation among the pages in which the defect is detected are generated. For a page having a different type of applied reverse halftone process, a message to that effect or an area to which a different type of halftone process is applied may be notified. This makes it easier for the user to determine whether the defect is erroneously detected due to the effect of halftone processing.

  In addition, the user can change the inspection conditions set according to the type of inverse halftone processing applied at the time of master image generation and the type of halftone processing applied at the time of bitmap data generation. Also good. Thereby, the user can change according to a situation whether emphasizing false detection of a defect or overlooking a defect.

1 DFE
2 Engine controller 3 Print engine 4 Inspection device 5 Stacker 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 421 Small value multi-value conversion processing unit 422 Resolution conversion processing unit 423 Color conversion processing unit 424 Image output processing unit 431 Halftone Type acquisition unit 432 Halftone table 433 Inspection condition setting unit

JP 2007-148027 A

Claims (6)

An image inspection apparatus for inspecting a read image obtained by reading an image formed and output on a paper surface,
A multi-value image in which each pixel is represented by a pixel value having a first gradation number is converted into a low-value image in which each pixel is represented by a second gradation number that is smaller than the first gradation number. An inverse gradation conversion process for converting the low-value image into the multi-value image is performed on the image forming output target image that is an image generated by the gradation conversion process, and the inverse gradation conversion process is performed. An inspection image generation unit that generates an inspection image for inspecting the read image based on the information of the read image;
A type acquisition unit that acquires a type of the gradation conversion process performed at the time of generating the image of the image formation output target;
The gradation conversion processing acquired from the setting information for the inspection of the read image predetermined for each combination according to the combination of the gradation conversion processing type and the reverse gradation conversion processing type. A setting information acquisition unit that acquires setting information corresponding to a combination of the type of the reverse gradation conversion process and the type of the reverse gradation conversion process;
An image inspection unit that performs an inspection for determining a defect of the read image based on a difference between the read image and the inspection image;
The image inspection unit changes a reference for determining the read image as a defect based on the acquired setting information. The setting information indicates the number of pixels,
The image inspection apparatus according to claim 1, wherein the image inspection unit calculates a difference between the read image and the inspection image in units of the number of pixels indicated by the acquired setting information. The setting information indicates a threshold for determining the defect,
The image inspection unit performs an inspection for determining a defect of the read image based on a magnitude relationship between a difference between the read image and the inspection image and a threshold value indicated by the acquired setting information. The image inspection apparatus according to claim 1 or 2. Area information for acquiring image area information of each of the plurality of types of gradation conversion processing when a plurality of types of gradation conversion processing is performed when generating the image to be output Including the acquisition unit,
The setting information acquisition unit acquires setting information corresponding to a combination of the acquired gradation conversion processing type and the reverse gradation conversion processing type for each of the plurality of types of gradation conversion processing,
The image inspection unit, based on the setting information corresponding to the gradation conversion processing performed in the image region, for an image region indicated by the acquired image region information in the read image and the inspection image. The image inspection apparatus according to claim 1, wherein an inspection for determining a defect of the read image is performed. An image inspection system for inspecting a read image obtained by reading an image formed and output on a paper surface,
A multi-value image in which each pixel is represented by a pixel value having a first gradation number is converted into a low-value image in which each pixel is represented by a second gradation number that is smaller than the first gradation number. An inverse gradation conversion process for converting the low-value image into the multi-value image is performed on the image forming output target image that is an image generated by the gradation conversion process, and the inverse gradation conversion process is performed. An inspection image generation unit that generates an inspection image for inspecting the read image based on the information of the read image;
A type acquisition unit that acquires a type of the gradation conversion process performed at the time of generating the image of the image formation output target;
The gradation conversion processing acquired from the setting information for the inspection of the read image predetermined for each combination according to the combination of the gradation conversion processing type and the reverse gradation conversion processing type. A setting information acquisition unit that acquires setting information corresponding to a combination of the type of the reverse gradation conversion process and the type of the reverse gradation conversion process;
An image inspection unit that performs an inspection for determining a defect of the read image based on a difference between the read image and the inspection image;
The image inspection unit changes a reference for determining the read image as a defect based on the acquired setting information. An image inspection method for inspecting a read image obtained by reading an image formed and output on a paper surface,
A multi-value image in which each pixel is represented by a pixel value having a first gradation number is converted into a low-value image in which each pixel is represented by a second gradation number that is smaller than the first gradation number. An inverse gradation conversion process for converting the low-value image into the multi-value image is performed on the image forming output target image that is an image generated by the gradation conversion process, and the inverse gradation conversion process is performed. Generating an inspection image for inspecting the read image on the basis of the image information obtained,
Obtaining the type of the gradation conversion processing performed at the time of generating the image of the image formation output target;
The gradation conversion processing acquired from the setting information for the inspection of the read image predetermined for each combination according to the combination of the gradation conversion processing type and the reverse gradation conversion processing type. Setting information corresponding to the combination of the type of the image and the type of the reverse gradation conversion process,
Based on the acquired setting information, an inspection for changing the reference for determining the read image as a defect and determining a defect in the read image based on a difference between the read image and the inspection image is performed. An image inspection method characterized by being performed.