JP6066395B2 - Image inspection apparatus and image inspection method - Google Patents

Description

  The present invention relates to an image inspection apparatus and an image inspection method for automatically inspecting a printed material printed based on print data.

  Conventionally, as this type of apparatus, there is an apparatus that performs bitmap collation between an inspection image obtained by photographing a printed matter printed with print data and a reference image composed of the print data (see, for example, Patent Document 1).

  In such an inspection apparatus, a variable data mask image is generated by performing an expansion process (also referred to as a fattening process) on the image line portion in order to absorb the difference between the reference image and the pattern boundary portion between the inspection images. By using this variable data mask image as an edge mask, overdetection and erroneous detection at the pattern boundary portion between the reference image and the inspection image are reduced.

Japanese Patent No. 4736293

However, the conventional example having such a configuration has the following problems.
In other words, since the conventional apparatus attempts to reduce the sensitivity by using an edge mask, if a fine line-like stain due to ink dripping or the like occurs in an area where a pattern such as a character area is crowded, the reference image Even if there is a difference between the inspection image and the inspection image, the edge mask may cause oversight. In other words, the conventional apparatus has a problem that it is not possible to improve the inspection accuracy of fine linear stains in an area where patterns are crowded.

  The present invention has been made in view of such circumstances, and provides an image inspection apparatus and an image inspection method capable of improving the inspection accuracy of linear stains even in an area where patterns are crowded. The purpose is to do.

In order to achieve such an object, the present invention has the following configuration.
That is, the invention according to claim 1 is an image inspection apparatus that inspects an image obtained by a printing process performed while feeding a print medium in a conveyance direction , wherein the image obtained by the printing process is an inspection image, and the conveyance An inspection image dividing means for generating an inspection block image by dividing the inspection image by a predetermined unit having a short side in the sub-scanning direction corresponding to the direction, and an image based on the print data used in the printing process as a reference image A reference image dividing means for dividing the reference image by a predetermined unit having a short side in the sub-scanning direction to create a reference block image; and a pixel value for the inspection block image and the reference block image Threshold processing means for performing threshold processing to change a pixel above the threshold to the maximum pixel value, and creating a thresholded inspection block image and a thresholded reference block image; and The averaged inspection block image and the thresholded reference block image are subjected to an averaging process for obtaining an average value in the sub-scanning direction for each block image to create an averaged inspection block image and an averaged reference block image. Average processing means, filter processing means for creating a filter processing reference block image by performing filter processing for expanding the image on the averaged reference block image, the filter processing reference block image, and the average value And a difference extracting means for extracting a difference image by comparing with the test block image.

  [Operation / Effect] According to the invention described in claim 1, the threshold processing means performs threshold processing on the inspection block image created by the inspection image dividing means and the reference block image created by the reference image dividing means. To create a thresholded inspection block image and a thresholded reference block image. As a result, the influence of show-through and the gloss level of the print medium can be removed. The average value processing means performs an average value process on the thresholded inspection block image and the thresholded reference block image to create an averaged inspection block image and an averaged reference block image. Thereby, the thresholded inspection block image and the thresholded reference block image can be compressed in the sub-scanning direction while leaving the information for each block. The difference extraction unit compares the filter processing reference block image created by the filter processing unit with the averaged inspection block image and extracts a difference image. Since the filter processing reference block image is an image that is compressed and expanded in the sub-scanning direction, and the averaged inspection block image is an image that is compressed in the sub-scanning direction, Due to these differences, a minute difference in the edge portion of the image can be reduced. Therefore, it is possible to suppress over-detection and erroneous detection of linear stains in the sub-scanning direction even in a region where the pattern is crowded. Further, by adjusting a predetermined unit in the sub-scanning direction in the inspection image dividing unit and the reference image dividing unit, it is possible to adjust the detection sensitivity of the linear stain. Furthermore, by adjusting the application range of the filter processing in the filter processing means, it is possible to suppress over-detection due to fluctuations in the printing state. As a result, it is possible to improve the inspection accuracy of linear stains even in a region where patterns are crowded.

In the present invention, gradation inversion means for performing gradation inversion processing on the thresholded inspection block image and the thresholded reference block image to generate a gradation inversion inspection block image and a gradation inversion reference block image. further comprising the averaging processing means, the gray level inversion test block image and the and processing child gradation inversion reference block image as the thresholding test block image and the threshold value of the reference block image is preferably (claim 2).

  A gradation inversion means performs gradation inversion of the thresholded inspection block image and the thresholded reference block image to create a gradation inversion inspection block image and a gradation inversion reference block image. Then, the average value processing means processes the gradation inversion inspection block image and the gradation inversion reference block image as a thresholded inspection block image and a thresholded reference block image.

  In the present invention, it is preferable that the filter processing means executes a minimum value filter as the filter processing.

  The filter processing means can compare adjacent pixels and expand the image using a minimum value filter that matches the pixel value to a pixel having a smaller pixel value.

  In the present invention, it is preferable that the filter processing means executes a maximum value filter as the filter processing.

  The filter processing means can compare adjacent pixels and expand the image using a maximum value filter that matches a pixel value to a pixel having a larger pixel value.

  In the present invention, it is preferable that the threshold processing means performs threshold processing with a maximum pixel value of 255 (claim 5).

  The threshold processing means can remove the influence of the show-through and the glossiness of the print medium by setting the pixels whose pixel values are equal to or larger than the predetermined value to 255. The threshold value may be changed according to the type of paper that is the printing medium, and may be a different value on the front and back sides in double-sided printing.

  In the present invention, it is preferable that the printing process is performed by an ink jet printer.

  The ink jet printer is suitable for the inspection because there is a possibility that a defect which is a linear stain in the sub-scanning direction may occur.

According to a seventh aspect of the present invention, in the image inspection method for inspecting an image obtained by a printing process performed while feeding a print medium in the transport direction, the image obtained by the printing process is used as an inspection image, and the printing is performed. An inspection block image and a reference block image obtained by dividing the inspection image and the reference image in a predetermined unit having a short side in the sub-scanning direction corresponding to the transport direction , using an image based on the print data used for processing as a reference image An image dividing step of generating a threshold value inspection block image and a reference block image, a threshold value processing for changing a pixel value equal to or greater than a predetermined threshold value to a maximum pixel value, A threshold processing step of creating a thresholded reference block image, and the thresholded inspection block image and the thresholded reference block image Performing an averaging process for obtaining an average value in the sub-scanning direction to create an averaged inspection block image and an averaged reference block image, and the averaged reference block image A filter processing step of performing a filter processing for expanding an image to create a filter processing reference block image, and a difference extraction step of comparing the filter processing reference block image and the averaged inspection block image to extract a difference image It is characterized by having.

  [Operation / Effect] According to the invention described in claim 7, in the threshold processing step, the threshold processing is performed on the inspection block image created in the image dividing step and the reference block image created in the reference image dividing step. The thresholded inspection block image and the thresholded reference block image are generated. As a result, the influence of show-through and the gloss level of the print medium can be removed. In the averaging process step, an averaging process is performed on the thresholded inspection block image and the thresholded reference block image to create an averaged inspection block image and an averaged reference block image. Thereby, the thresholded inspection block image and the thresholded reference block image can be compressed in the sub-scanning direction while leaving the information for each block. In the difference extraction step, the filter processing reference block image created in the filter processing step and the averaged inspection block image are compared to extract a difference image. Since the filter processing reference block image is an image that is compressed and expanded in the sub-scanning direction, and the averaged inspection block image is an image that is compressed in the sub-scanning direction, Due to these differences, a minute difference in the edge portion of the image can be reduced. Therefore, it is possible to suppress over-detection and erroneous detection of linear stains in the sub-scanning direction even in a region where the pattern is crowded. Further, by adjusting a predetermined unit in the sub-scanning direction in the inspection image dividing step and the reference image dividing step, it is possible to adjust the detection sensitivity for linear stains. Furthermore, by adjusting the application range of the filter processing in the filter processing step, it is possible to suppress over-detection due to fluctuations in the printing state. As a result, it is possible to improve the inspection accuracy of linear stains even in a region where patterns are crowded.

The invention according to claim 13 is the image inspection method for detecting linear ink dripping in the sub-scanning direction generated in the print image obtained by the printing process performed while feeding the print medium in the transport direction. An image obtained by the printing process is used as an inspection image, an image based on the print data used in the printing process is used as a reference image, and the inspection image and a predetermined unit having a short side in the sub-scanning direction corresponding to the transport direction An image dividing step of dividing the reference image to create an inspection block image and a reference block image, and for the inspection block image and the reference block image, those having a pixel value equal to or greater than a predetermined threshold are set to the maximum pixel value Threshold processing step of performing threshold processing to be changed to create a thresholded inspection block image and a thresholded reference block image, the thresholded inspection block image and the threshold For the averaged reference block image, an average value processing step for performing an average value process for obtaining an average value in the sub-scanning direction for each block image to create an averaged inspection block image and an averaged reference block image, and A filtering process for creating a filtered reference block image by performing a filtering process for expanding the image on the averaged reference block image, and comparing the filtered reference block image with the averaged inspection block image And an ink dripping detection step of detecting ink dripping.

  [Operation / Effect] According to the invention described in claim 13, in the threshold processing step, the threshold processing is performed on the inspection block image created in the inspection image division step and the reference block image created in the reference image division step. To create a thresholded inspection block image and a thresholded reference block image. As a result, the influence of show-through and the gloss level of the print medium can be removed. In the averaging process step, an averaging process is performed on the thresholded inspection block image and the thresholded reference block image to create an averaged inspection block image and an averaged reference block image. Thereby, the thresholded inspection block image and the thresholded reference block image can be compressed in the sub-scanning direction while leaving the information for each block. In the ink dripping detection step, ink dripping is detected by comparing the filter processing reference block image created in the filter processing step with the averaged inspection block image. The filter processing inspection block image is an image that has been compressed and expanded in the sub-scanning direction, and the averaged reference block image is an image that has been compressed in the sub-scanning direction. Due to these differences, a minute difference in the edge portion of the image can be reduced. Accordingly, it is possible to suppress over-detection and erroneous detection of ink dripping in the sub-scanning direction even in an area where the patterns are crowded. Further, the ink dripping detection sensitivity can be adjusted by adjusting a predetermined unit in the sub-scanning direction in the inspection image dividing step and the reference image dividing step. Furthermore, by adjusting the application range of the filter processing in the filter processing step, it is possible to suppress over-detection due to fluctuations in the printing state. As a result, the ink dripping inspection accuracy can be improved even in a region where the patterns are crowded.

  According to the image inspection apparatus of the present invention, the threshold processing means performs threshold processing on the inspection block image created by the inspection image dividing means and the reference block image created by the reference image dividing means, thereby generating a threshold value. An inspection block image and a thresholded reference block image are created. As a result, the influence of show-through and the gloss level of the print medium can be removed. The average value processing means performs an average value process on the thresholded inspection block image and the thresholded reference block image to create an averaged inspection block image and an averaged reference block image. Thereby, the thresholded inspection block image and the thresholded reference block image can be compressed in the sub-scanning direction while leaving the information for each block. The difference extraction unit compares the filter processing reference block image created by the filter processing unit with the averaged inspection block image and extracts a difference image. Since the filter processing reference block image is an image that is compressed and expanded in the sub-scanning direction, and the averaged inspection block image is an image that is compressed in the sub-scanning direction, Due to these differences, a minute difference in the edge portion of the image can be reduced. Therefore, it is possible to suppress over-detection and erroneous detection of linear stains in the sub-scanning direction even in a region where the pattern is crowded. Further, by adjusting a predetermined unit in the sub-scanning direction in the inspection image dividing unit and the reference image dividing unit, it is possible to adjust the detection sensitivity of the linear stain. Furthermore, by adjusting the application range of the filter processing in the filter processing means, it is possible to suppress over-detection due to fluctuations in the printing state. As a result, it is possible to improve the inspection accuracy of linear stains even in a region where patterns are crowded.

1 is a block diagram illustrating an overall configuration of an inkjet printing system according to an embodiment. It is a flowchart which shows operation | movement of an image inspection apparatus. (A) is a schematic diagram showing an inspection block image and a reference block image obtained by dividing an inspection image and a reference image, and (b) is a threshold processing for the inspection block image and the reference block image, and then a gradation inversion process is performed. It is a schematic diagram which shows a gradation inversion test | inspection block image and a gradation inversion block image. (A) is a schematic diagram showing that the gradation inversion inspection block image is compressed by averaging, and (b) is an average value obtained by averaging the gradation inversion inspection block image and the gradation inversion reference block image. It is a schematic diagram which shows an inspection block image and an averaged reference block image. (A) is a schematic diagram showing an averaged inspection block image, an averaged reference block image, and a filtered reference block image obtained by performing filter processing on the averaged reference block image, and (b) is an average value It is a schematic diagram which shows the difference image of an optimization inspection block image and a filter process reference block image. The modification of an image process is shown, (a) is a schematic diagram which shows the test | inspection block image and reference block image which divided | segmented the test | inspection image and the reference image, (b) is the threshold value which carried out threshold processing of the test | inspection block image and the reference block image It is a schematic diagram which shows an inspection block image and a thresholding reference block image. (A) is the averaged inspection block image and averaged reference block image obtained by averaging the thresholded inspection block image and the thresholded reference block, and the filter reference block image obtained by filtering the averaged reference block image (B) is a schematic diagram which shows the difference image of an averaged test | inspection block image and a filter process reference block image.

An embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram illustrating an overall configuration of an inkjet printing system according to an embodiment.

  The ink jet printing system according to the embodiment includes a paper feed unit 1, an ink jet printer 3, and a paper discharge unit 5.

  The paper supply unit 1 holds the roll-shaped continuous paper WP so as to be rotatable about a horizontal axis, and unwinds and supplies the continuous paper WP to the inkjet printer 3. The inkjet printer 3 performs printing on the continuous paper WP. The paper discharge unit 5 winds the continuous paper WP printed by the inkjet printer 3 around the horizontal axis. When the supply side of the continuous paper WP is the upstream side and the discharge side of the continuous paper WP is the downstream side, the paper feed unit 1 is disposed on the upstream side of the ink jet printer 3, and the paper discharge unit 5 is on the downstream side of the ink jet printer 3. Is arranged.

  The ink jet printer 3 includes a driving roller 7 for taking in the continuous paper WP from the paper supply unit 1 on the upstream side. The continuous paper WP unwound from the paper feeding unit 1 by the driving roller 7 is conveyed along the plurality of conveying rollers 9 toward the paper discharge unit 5 on the downstream side. A driving roller 11 is arranged between the most downstream conveying roller 9 and the paper discharge unit 5. The drive roller 11 feeds the continuous paper WP conveyed on the conveyance roller 9 toward the paper discharge unit 5.

  The inkjet printer 3 includes a front surface printing unit 13, a front surface drying unit 15, a front surface inspection unit 17, a reversing unit 19, a back surface printing unit 21, and a back surface drying unit between the driving roller 7 and the driving roller 11. 23 and a back surface inspection unit 25 are provided in that order. In the present embodiment, “front surface” and “back surface” refer to the printing surface of the continuous paper WP printed first as “front surface”, and the printing surface of the continuous paper WP printed next as “back surface”. .

  The front surface printing unit 13 includes a print head 27 that ejects ink droplets. In general, a plurality of front surface printing units 13 are provided along the conveyance direction of the continuous paper WP. For example, four printing units 13 are individually provided for black (K), cyan (C), magenta (M), and yellow (Y). However, in the present embodiment, in order to facilitate understanding of the invention, it is assumed that only one printing unit 13 is provided. This also applies to the back surface printing unit 21 described later.

  The surface drying unit 15 dries the surface of the continuous paper WP on which an image is printed by ejecting ink droplets. The front surface drying unit 15 includes, for example, a heat drum (not shown), and dries ink droplets deposited on the front surface of the continuous paper WP by bringing the back surface of the continuous paper WP into contact with the heat drum.

  The surface inspection unit 17 inspects the image printed on the surface of the continuous paper WP for dirt or missing. The surface inspection unit 17 includes a camera and an optical system, images the continuous paper WP conveyed directly under the surface inspection unit 17, and outputs it as a surface inspection image.

  The reversing unit 19 reverses the continuous capital increase WP that has been transported with the surface facing upward. That is, the continuous paper WP is turned over so that the back surface of the continuous paper WP faces upward.

  Similar to the front surface printing unit 13, the back surface printing unit 21 includes a print head 29. The print head 29 is the same as the print head 27 of the front surface printing unit 13.

  The back surface drying unit 23 has the same configuration as the front surface drying unit 15 and dries the back surface of the continuous paper WP. The back surface inspection unit 25 has the same configuration as that of the front surface inspection unit 17 and inspects the back surface of the continuous paper WP for dirt or missing. Specifically, the back surface inspection unit 25 includes a camera and an optical system, images the continuous paper WP conveyed directly under the back surface inspection unit 25, and outputs the continuous paper WP as a back surface inspection image.

  The ink jet printer 3 includes a print control unit 31 and an image inspection device 33. The print control unit 31 receives print data corresponding to an image to be printed by the inkjet printer 3 from an external computer or the like, and performs an operation corresponding to printing of the front surface print image data and the back surface print image data with the drive roller 7, 11 for the front surface printing unit 13 and the back surface printing unit 21. In addition, the print control unit 31 receives an inspection result of an image inspection device 33 described later, and notifies the operator of the inspection result, or causes the operation of the inkjet printer 3 to be temporarily stopped.

  The image inspection apparatus 33 includes an inspection image division unit 35, a reference image division unit 37, a threshold processing unit 39, a gradation inversion unit 41, an average value processing unit 43, a filter processing unit 45, and a difference extraction unit. 47. In the following description, the image inspection device 33 is described as receiving the back surface inspection image from the back surface inspection unit 25 and inspecting the inspection image. However, the image inspection device 33 receives the surface inspection image from the surface inspection device 17 and inspects the inspection image. This is the same even when the inspection is performed.

  The inspection image dividing unit 35 corresponds to the “inspection image dividing unit” in the present invention, the reference image dividing unit 37 corresponds to the “reference image dividing unit” in the present invention, and the threshold processing unit 39 corresponds to the “threshold value in the present invention. The gradation inversion unit 41 corresponds to the “gradation inversion unit” in the present invention, the average value processing unit 43 corresponds to the “average value processing unit” in the present invention, and the filter processing unit. 45 corresponds to the “filter processing unit” in the present invention, and the difference extraction unit 47 corresponds to the “difference extraction unit” in the present invention.

  The inspection image dividing unit 35 receives from the back surface inspection unit 25 a back surface inspection image of the continuous paper WP that has been printed on the front and back sides based on the print data as an inspection image. Then, the inspection image is divided into strips in a predetermined unit having a short side in the sub-scanning direction (conveying direction of the continuous paper WP), and an inspection block image is created. The predetermined unit that defines the length of the short side is set in advance by the operator as the detection sensitivity of the linear dirt.

  The reference image dividing unit 37 receives the print data used for the back side printing process from the print control unit 31 as a reference image. Then, the inspection image dividing unit 35 divides the reference image into strips in the sub-scanning direction (conveying direction of the continuous paper WP) in a predetermined unit used for the division, and creates a reference block image.

  Note that the division in the inspection image dividing unit 35 and the reference image dividing unit 37 described above corresponds to setting an area for obtaining an average value in the following averaging process.

  The threshold processing unit 39 receives the inspection block image from the inspection image dividing unit 35 and receives the reference block image from the reference image dividing unit 37. Then, threshold processing is performed on the inspection block image and the reference block image, a thresholded inspection block image is generated from the inspection block image, and a thresholded reference block image is generated from the reference block image. The thresholding process is a process of changing a pixel value equal to or greater than a predetermined threshold value to the maximum pixel value. For example, when the minimum pixel value is 0 (black) and the maximum pixel value is 255 (white), the pixel value is set to 255 (white), which is the maximum value, for pixels that are above a certain pixel value. change. The threshold value at this time is determined to be a value that can remove the influence of the show-through and the glossiness of the continuous paper WP after various experiments, and is set in advance.

  The gradation inversion unit 41 receives the thresholded inspection block image and the thresholded reference block image from the threshold processing unit 39. Then, gradation inversion processing is performed on the thresholded inspection block image and the thresholded reference block image to create a gradation inverted inspection block image from the thresholded inspection block image, and gradation inversion reference from the thresholded reference block image Create a block image.

  The average value processing unit 43 receives the gradation inversion inspection block image and the gradation inversion reference block image from the gradation inversion unit 41. Then, the gradation inversion inspection block image and the gradation inversion reference block image are averaged to create an averaged inspection block image from the gradation inversion inspection block image, and from the gradation inversion reference block image Create an averaged reference block image. The averaging process is to obtain an average value of pixel values in the sub-scanning direction for each block image for the gradation inversion inspection block image and the gradation inversion reference block image. As a result, the gradation inversion inspection block image and the gradation inversion reference block image are compressed in the sub-scanning direction while the information for each block remains.

The filter processing unit 45 receives only the averaged reference block image from the averaged processing unit 43. Filtering unit 4 5 performs a filtering process on averaging the reference block image to create a filtered reference block image. The filter process is an expansion process (also referred to as a fattening process) of an image. In this embodiment, since the gradation of the averaged reference block image is inverted by the gradation inversion process and the image is changed to a large pixel value (white side), the maximum value filter is applied. Become. The maximum value filter compares pixel values of adjacent pixels and changes a pixel having a small pixel value to a pixel value of a pixel having a large pixel value.

The difference extraction unit 47 receives the averaged inspection block image FC2 from the average processing unit 43 and also receives the filter processing reference block image from the filter processing unit 45. The difference extraction unit 47 compares the averaged inspection block image FC2 with the filter processing reference block image FR3, and extracts a difference image. This difference image is an image that should not exist in the print data. Therefore, if any image exists in the extracted image, it indicates that a defect exists in the image of the continuous paper WP that has been subjected to the printing process. The defect is, for example, a linear stain in the sub-scanning direction such as ink dripping generated during the printing process.

  The print control unit 31 determines whether or not the printed matter has a defect based on the difference image of the difference extraction unit 47, notifies the operator of the inspection result, or temporarily stops the operation of the ink jet printer 3. Or let the action be performed.

  Next, the operation of the above-described image inspection apparatus 33 will be described with reference to FIGS. FIG. 2 is a flowchart showing the operation of the image inspection apparatus. FIG. 3A is a schematic diagram showing an inspection block image and a reference block image obtained by dividing the inspection image and the reference image. FIG. 3B is a diagram after threshold processing is performed on the inspection block image and the reference block image. FIG. 4A is a schematic diagram showing a gradation inversion inspection block image and a gradation inversion block image that have been subjected to gradation inversion processing, and FIG. 4A shows that the gradation inversion inspection block image is compressed by averaging. FIG. 4B is a schematic diagram showing an averaged inspection block image and an averaged reference block image obtained by averaging the gradation inversion inspection block image and the gradation inversion reference block image. FIG. 5A is a schematic diagram illustrating an averaged inspection block image, an averaged reference block image, and a filtered reference block image obtained by performing filtering on the averaged reference block image. (B) is a schematic diagram showing a differential image between the average value of the inspection block image and filtering the reference block image.

Step S1 (image division processing)
The inspection image dividing unit 35 receives the inspection image and divides it in a predetermined unit having a short side in the sub-scanning direction to create an inspection block image FC. In FIG. 3A, a character string is printed as an image on the inspection image, and show-through by surface printing occurs on both sides of the character string image. In addition, the character string is overlapped with linear stains (ink dripping) in the sub-scanning direction. In addition, a plurality of block images are divided by a one-dot chain line. The reference image dividing unit 37 performs the same division on the reference image to create a reference block image FR. In FIG. 3A, only a character string exists as an image in the reference image FR.

Step S2 (threshold processing)
The threshold processing unit 39 performs threshold processing on the inspection block image FC and the reference block image FR to create a thresholded inspection block image and a thresholded reference block image.

Step S3 (gradation inversion process)
As shown in FIG. 3B, the gradation inversion unit 41 performs gradation inversion processing on the thresholded inspection block image to create a gradation inversion inspection block image FC1. Similarly, gradation inversion reference block image FR1 is generated by performing gradation inversion processing on the thresholded reference block image.

Step S4 (averaging process)
The average value processing unit 43 performs an averaging process on the gradation inversion inspection block image FC1 and the gradation inversion reference block image FR1, and creates an average inspection block image FC2 and an averaged reference block image FR2. To do. The averaging process will be described taking the gradation inversion inspection block image FC1 as an example. As shown in FIG. 4A, for each block image of the gradation inversion inspection block image FC1, an average value is obtained for the pixel values of all the pixels that are arranged in the sub-scanning direction, and this average value is obtained as a sub-image of the block image. The pixel value in the scanning direction is used. Therefore, the gradation inversion inspection block image FC1 is compressed in the sub-scanning direction while the block image information remains. Similarly, the gradation value reference block image FR1 is averaged to create an averaged reference block image FR2. FIG. 4B shows an averaged inspection block image FC2 and an averaged reference block image FR2.

Step S5 (filter processing)
The filter processing unit 45 performs filter processing (maximum value filter) on the averaged reference block image FR2, performs expansion processing on the image in the averaged reference block image FR2, and is shown in FIG. Thus, the filter processing reference block image FR3 is created.

Step S6 (difference extraction process)
As shown in FIGS. 5A and 5B, the difference extraction unit 47 compares the averaged inspection block image FC2 with the filter processing reference block image FR3 and extracts a difference image FD. In this example, an image corresponding to linear stains (ink dripping) is extracted from the difference image FD in the sub-scanning direction. Therefore, the print control unit 27 can determine that a defect has occurred based on the difference image FD.

  As described above, according to the image inspection apparatus 33 according to the present embodiment, the thresholded inspection block image and the thresholded reference block image are generated, and the influence of the show-through and the gloss level of the printing medium is removed, and the average value is obtained. An inspection block image FR2 and an averaged reference block image FC2 are created, and compressed in the sub-scanning direction while leaving information for each block in the gradation inversion inspection block image and the gradation inversion reference block image, and averaged An inspection block image FC2 and an averaged reference block image FR2 are created. Then, the filter processing reference block image FR3 and the averaged inspection block image FC2 are compared to extract the difference image FD. The filter processing reference block image FR3 is an image that is compressed and expanded in the sub-scanning direction, and the averaged inspection block image FC2 is an image that is compressed in the sub-scanning direction. Therefore, the minute difference in the edge portion of the image can be reduced by the difference between them. Therefore, it is possible to suppress over-detection and erroneous detection of linear stains in the sub-scanning direction even in a region where the pattern is crowded. In addition, by adjusting a predetermined unit in the sub-scanning direction, it is possible to adjust the detection sensitivity for linear stains. Furthermore, by adjusting the application range of the filter processing, it is possible to suppress overdetection due to a change in the printing state. As a result, it is possible to improve the inspection accuracy of linear stains even in a region where patterns are crowded.

<Modification>
The present invention may be configured such that the gradation inversion unit 41 and step S3 are omitted from the image inspection apparatus 33 described above. Processing in this case will be described with reference to FIGS.

  FIG. 6 shows a modification of image processing, (a) is a schematic diagram showing an inspection block image and a reference block image obtained by dividing the inspection image and the reference image, and (b) is an inspection block image and a reference block. It is a schematic diagram which shows the thresholding test | inspection block image and thresholding reference block image which threshold-processed the image. In FIG. 7A, the averaged inspection block image and the averaged reference block image obtained by averaging the thresholded inspection block image and the thresholded reference block, and the averaged reference block image are subjected to filter processing. It is a schematic diagram which shows a filter reference block image, (b) is a schematic diagram which shows the difference image of an averaged test | inspection block image and a filter process reference block image.

  The inspection image dividing unit 35 and the reference image dividing unit 37 create an inspection block image FC and a reference block image FR, respectively (FIG. 6A). The threshold processing unit 39 performs threshold processing on the inspection block image FC and the reference block image FR, and creates a thresholded inspection block image FC0 and a thresholded reference block image FR0 (FIG. 6B).

  The average value processing unit 43 performs an average value process on the thresholded inspection block image FC0 and the thresholded reference block image FR0, and creates an averaged inspection block image FC2 and an averaged reference block image FR2. (FIG. 7A).

The filter processing unit 45 performs filter processing (minimum value filter) on the thresholded reference block image FR2 to create a filter processing reference block image FR3 (FIG. 7A).

  The difference extraction unit 47 compares the filter processing reference block image FR3 and the averaged inspection block image FC2 to extract a difference image FD (FIG. 7B).

  Even with such a configuration, the same effects as those of the above-described embodiment can be obtained.

  The present invention is not limited to the above embodiment, and can be modified as follows.

  (1) In the above-described embodiment, the defect inspection in the ink jet printer 3 is performed. However, the present invention can also be applied to inspect defects in a printer using another method.

  (2) In the above-described embodiments, the description has been made by taking the image of the monochrome gradation as an example.

  (3) In the above-described embodiment, the maximum pixel value is set to 255 in the threshold processing, but the present invention is not limited to such threshold processing.

WP: Continuous paper 3 ... Inkjet printer 31 ... Print control unit 33 ... Image inspection device 35 ... Inspection image dividing unit 37 ... Reference image dividing unit 39 ... Threshold processing unit 41 ... Tone reversing unit 43 ... Average value processing unit 45 … Filter processing unit 47… Difference extraction unit FC… Inspection block image FR… Reference block image

Claims (14)

In an image inspection apparatus that inspects an image obtained by a printing process performed while feeding a print medium in a conveyance direction ,
An image obtained by the printing process as an inspection image, and an inspection image dividing unit that divides the inspection image in a predetermined unit having a short side in a sub-scanning direction corresponding to the transport direction to create an inspection block image;
A reference image dividing means for creating a reference block image by dividing an image based on print data used for the printing process as a reference image and dividing the reference image in a predetermined unit having a short side in the sub-scanning direction;
A thresholded inspection block image and a thresholded reference block image are generated by performing threshold processing on the inspection block image and the reference block image by changing a pixel value equal to or greater than a predetermined threshold value to the maximum pixel value. Threshold processing means;
For the thresholded inspection block image and the thresholded reference block image, an average value processing for obtaining an average value in the sub-scanning direction is performed for each block image to generate an averaged inspection block image and an averaged reference block image Averaging means for performing,
Filter processing means for creating a filtered reference block image by performing filter processing for expanding the image on the averaged reference block image;
A difference extraction means for comparing the filter processing reference block image and the averaged inspection block image to extract a difference image;
An image inspection apparatus comprising: The image inspection apparatus according to claim 1,
Gradation inversion means for performing gradation inversion processing on the thresholded inspection block image and the thresholded reference block image to create a gradation inversion inspection block image and a gradation inversion reference block image;
The average value processing means processes the gradation inversion inspection block image and the gradation inversion reference block image as the thresholded inspection block image and the thresholded reference block image. The image inspection apparatus according to claim 1,
The image processing apparatus, wherein the filter processing unit executes a minimum value filter as the filter processing. The image inspection apparatus according to claim 2,
The image processing apparatus, wherein the filter processing means executes a maximum value filter as the filter processing. In the image inspection apparatus according to any one of claims 1 to 4,
The image processing apparatus according to claim 1, wherein the threshold processing unit performs threshold processing with a maximum pixel value of 255. In the image inspection apparatus according to any one of claims 1 to 5,
The image inspection apparatus, wherein the printing process is performed by an ink jet printer. In an image inspection method for inspecting an image obtained by a printing process performed while feeding a print medium in a conveyance direction ,
The image obtained by the printing process is an inspection image, the image based on the print data used in the printing process is a reference image, and the inspection image is in a predetermined unit having a short side in the sub-scanning direction corresponding to the transport direction. And an image dividing step of dividing the reference image to create an inspection block image and a reference block image;
A thresholded inspection block image and a thresholded reference block image are generated by performing threshold processing on the inspection block image and the reference block image by changing a pixel value equal to or greater than a predetermined threshold value to the maximum pixel value. A threshold processing step;
For the thresholded inspection block image and the thresholded reference block image, an average value processing for obtaining an average value in the sub-scanning direction is performed for each block image to generate an averaged inspection block image and an averaged reference block image An averaging process step,
A filtering process for creating a filtered reference block image by performing a filtering process for expanding the image on the averaged reference block image;
A difference extraction step of comparing the filtered reference block image and the averaged inspection block image to extract a difference image;
An image inspection method comprising: The image inspection method according to claim 7,
Between the threshold value processing step and the average value processing step, gradation inversion processing is performed on the thresholded inspection block image and the thresholded reference block image, and the gradation inversion inspection block image and the gradation inversion reference are performed. It further includes a gradation inversion process for creating a block image,
The average value processing step includes processing the gradation inversion inspection block image and the gradation inversion reference block image as the thresholded inspection block image and the thresholded reference block image. The image inspection method according to claim 7,
In the image processing method, the filter processing step executes a minimum value filter as the filter processing. The image inspection method according to claim 8.
In the image processing method, the filter processing step executes a maximum value filter as the filter processing. The image inspection method according to any one of claims 7 to 10,
An image inspection method, wherein the threshold value processing step performs threshold value processing with a maximum pixel value of 255. The image inspection method according to any one of claims 7 to 11,
An image inspection method, wherein the printing process is performed by an ink jet printer. In an image inspection method for detecting linear ink dripping in a sub-scanning direction generated in a print image obtained by a printing process performed while feeding a print medium in a conveyance direction ,
The image obtained by the printing process is an inspection image, the image based on the print data used in the printing process is a reference image, and the inspection image is in a predetermined unit having a short side in the sub-scanning direction corresponding to the transport direction. And an image dividing step of dividing the reference image to create an inspection block image and a reference block image;
A thresholded inspection block image and a thresholded reference block image are generated by performing threshold processing on the inspection block image and the reference block image by changing a pixel value equal to or greater than a predetermined threshold value to the maximum pixel value. A threshold processing step;
For the thresholded inspection block image and the thresholded reference block image, an average value processing for obtaining an average value in the sub-scanning direction is performed for each block image to generate an averaged inspection block image and an averaged reference block image An averaging process step,
A filtering process for creating a filtered reference block image by performing a filtering process for expanding the image on the averaged reference block image;
An ink dripping detection step of comparing the filter processing reference block image and the averaged inspection block image to detect ink dripping;
An image inspection method comprising: The image inspection method according to claim 13.
Between the threshold value processing step and the average value processing step, gradation inversion processing is performed on the thresholded inspection block image and the thresholded reference block image, and the gradation inversion inspection block image and the gradation inversion reference are performed. It further includes a gradation inversion process for creating a block image,
The average value processing step includes processing the gradation inversion inspection block image and the gradation inversion reference block image as the thresholded inspection block image and the thresholded reference block image.