JP4946415B2 - Image inspection device - Google Patents

Description

  The present invention relates to a technique for inspecting the quality of an image formed by an image forming apparatus.

  When an image forming apparatus forms an image, an original image may not be formed due to an unexpected factor or the like. Therefore, some image forming apparatuses have a function of inspecting whether or not an image is normally formed. When such an image forming apparatus forms an image on a sheet (paper), the image is optically read, and the image on the sheet is inspected by comparing with the image data on which the image is based.

By the way, an image representing characters such as items and amounts may be superimposed on a sheet on which images such as ruled lines, frames, and shading are printed in advance, such as a form. In such a case, the techniques described in Patent Documents 1 to 3 are used. Patent Documents 1 to 3 describe a technique for inspecting based on an image obtained by removing an image printed on a sheet in advance from a read image.
Further, particularly in a form or the like, an image forming apparatus generally forms an image such as a character using black. In this case, in order to make it easy for the user to visually recognize the contents, a color that is not similar to black is often used for an image printed in advance on a sheet. Therefore, in such a case, for example, as described in Patent Document 4, it is possible to perform an inspection intended by the image forming apparatus using a technique for removing a non-black color from an image.
JP-A-11-78183 JP 2003-108921 A JP 2003-196292 A Japanese Patent No. 2882273

  However, in any of the above-described techniques, the processing for extracting only the target image is complicated, and thus high processing capability is required. In particular, when the color of the image formed by the image forming apparatus is similar to the color of the image printed in advance on the sheet, only the image formed by the image forming apparatus is accurately extracted or the image printed in advance It is extremely difficult to accurately remove only.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to remove unnecessary images more easily and quickly than in the past.

To solve the above problem, this invention provides an image which absorbs light in the infrared wavelength region, a first image, the original image data in based rather the first second image brightness is lower than the image irradiating means for irradiating a light of infrared wavelength region on a sheet bets are formed, obtaining means for obtaining the original image data which is the basis of the image formed on the sheet, the light emitted by the irradiation unit Generation means for receiving reflected light in the infrared wavelength region reflected by the sheet and generating read image data having a gradation corresponding to the amount of received light with a predetermined number of gradations, and generated by the generation means A threshold value corresponding to the brightness between the brightness of the first image and the brightness of the second image is calculated for each of the pixel data according to the gradation value of the pixel data constituting the read image data. A calculating means; and the read image data The gradation value of each pixel data constituting the data, and comparing each with the threshold calculated for each corresponding pixel data by said calculation means, a subtrahend means reducing the number of gradations of the read image data, by the meiotic means And inspection means for comparing gradation values of pixel data at corresponding positions between the read image data with the reduced number of gradations and the document image data and outputting data representing the comparison result. An image inspection apparatus is provided.

  According to the present invention, unnecessary images can be easily and quickly removed as compared with the case where the present configuration is not provided.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(1) First Embodiment FIG. 1 is a block diagram showing a configuration of an image forming apparatus 1. As shown in FIG. 1, the image forming apparatus 1 includes an image forming unit 10, an infrared reading unit 20, a control unit 30, a storage unit 40, a UI (User Interface) unit 50, and a communication unit 60. I have.
The image forming unit 10 forms an image on a sheet based on the supplied image data. The infrared reading unit 20 emits light from an infrared light source, optically reads an image formed on the sheet, and generates image data. The control unit 30 includes a central processing unit (CPU) that controls the entire apparatus, a random access memory (RAM) that provides a work area for work, and a read only memory (ROM) that stores various control programs. Arithmetic processing is performed according to the described procedure. The storage unit 40 includes a storage device such as an HDD (Hard Disk Drive) and stores various data. The UI unit 50 includes a touch panel and various buttons, accepts an operation from the user, and notifies information by an image or sound. The communication unit 60 is an interface device for performing communication via a network, and receives image data from an external terminal such as a computer (not shown) via a network such as a LAN (Local Area Network).

Next, the configuration of the image forming unit 10 and the infrared reading unit 20 will be described with reference to FIG.
The image forming unit 10 includes a plurality of trays 11, a plurality of transport rolls 12, an image forming unit 13, and a fixing device 14.
The tray 11 accommodates sheets of a predetermined size. Images are formed in advance on the sheets accommodated in the tray 11. That is, the sheet in the present embodiment is so-called preprinted paper. Note that an image formed in advance on a sheet is hereinafter referred to as a “pre-printed image”.

Here, the preprinted image will be described. FIG. 3 is a diagram illustrating a sheet on which a preprinted image is formed. The preprinted image is formed on a white plain sheet S using a color material such as ink. FIG. 3 shows the preprinted image A1 and the preprinted image A2. The preprinted images A1 and A2 are composed of ruled lines and shaded images. A halftone image is a halftone image represented by a halftone dot or the like, and in FIG. 3, this is indicated by hatching.
The preprinted image A1 is formed of a color material other than black. On the other hand, the pre-printed image A2 is formed of a low-lightness gray color material, that is, a color material containing black color material to some extent. The reason why the pre-printed image A2 is gray with low brightness is that it does not hinder the visibility (ease of viewing) of images such as characters that are formed overlapping the pre-printed image A2.
In the following description, the preprinted images A1 and A2 are collectively referred to as “preprinted image A” as necessary.

  Each of the plurality of transport rollers 12 transports the sheet S on which the above-described preprinted image A is formed in accordance with image formation. The image forming unit 13 forms an image by electrophotography. That is, the image forming unit 13 includes a photosensitive drum, a charging unit, an exposure unit, a developing unit, a transfer unit, and the like, and forms an image on the sheet S with toner. Note that the image forming unit 13 forms an image with black toner. The photosensitive drum is a drum-like member that rotates around a shaft at a predetermined speed. The charging unit charges the surface of the photosensitive drum to a predetermined potential. The exposure unit irradiates the charged photosensitive drum with a beam to form an electrostatic latent image. The developing unit develops the image by attaching toner to the electrostatic latent image formed on the photosensitive drum. The fixing device 14 includes a roll member for heating and pressing the sheet, and fixes the image transferred to the sheet S. Under such a configuration, the image forming unit 10 forms an image using black toner based on the supplied image data. The image formed by the image forming unit 10 is hereinafter referred to as “original image”.

  Here, the document image will be described. FIG. 4 is a diagram illustrating a sheet S on which a document image B, which is an example of a document image, is formed. As described above, the document image B includes a plurality of characters and symbols and is formed of black toner. An area of the sheet S where the original image B is not formed is white because the sheet S is exposed as it is. In the following, an area of the sheet S where the original image B is formed is referred to as an “image area”, and an area where the original image B is not formed is referred to as a “background area”.

The document image data representing the document image is configured by a set of pixel data having a gradation number of “256”. The pixel data indicates black when the gradation value is “0”, white when it is “255”, and indicates halftone, that is, gray when the gradation value is “255”.
In the following description, the upper left corner of the document image represented by the document image data is set as the origin, the orthogonal coordinates based on the X axis and the Y axis shown in FIG. 3 are defined, and the coordinates of the pixel data are expressed as (x1, y1). .

  Next, the configuration of the infrared reading unit 20 will be described. As shown in FIG. 2, the infrared reading unit 20 is provided on the downstream side of the fixing device 14 of the image forming unit 10, and optically reads a sheet on which a document image is formed by the image forming unit 10. . FIG. 5 is a diagram illustrating a device configuration of the infrared reading unit 20. As shown in FIG. 5, the infrared reading unit 20 includes an infrared light source 21, an imaging lens 22, and an image sensor 23.

The infrared light source 21 is a light source that emits light in the infrared wavelength region. The infrared light source 21 irradiates light at a predetermined position on the conveyed sheet. The light emitted from the infrared light source 21 only needs to include an infrared wavelength region as a component, and may include other components. The imaging lens 22 images the reflected light from the sheet at the position of the image sensor 23. The image sensor 23 has an image sensor having sensitivity in the infrared wavelength region. The image sensor 23 receives the imaged light, and generates and outputs image data corresponding to the amount of received light. The image data generated by the infrared reading unit 20 is composed of pixel data having a gradation number of “256”. That is, the infrared reading unit 20 represents the density of the original image formed on the sheet based on the magnitude of the pixel data value represented by 8 bits (256 gradations). In the present embodiment, the lightness is higher (brighter) as the gradation value is larger, and the lightness is lower (darker) as the gradation value is smaller.
In the following, the image data generated by the infrared reading unit 20 is referred to as “read image data” and is distinguished from other image data. In addition, with the upper left corner of the read image represented by the read image data as the origin, orthogonal coordinates similar to those of the original image are determined, and the coordinates of the pixel data are expressed as (x2, y2).

Further, the control unit 30 executes various image processes applied to the image data in addition to the arithmetic process for controlling each unit of the image forming apparatus 1. A part of the image processing executed by the control unit 30 is illustrated in FIG. 6, for example. FIG. 6 is a functional block diagram illustrating functions realized by the control unit 30 executing a control program stored in the ROM. The arrows in the figure schematically show the flow of data.
The control unit 30 realizes an image inspection function by comparing original image data with read image data generated by reading an image formed on a sheet based on the original image data. This function is realized by the reduction processing unit 31 and the collation unit 32.

  The reduction processing unit 31 acquires read image data and document image data to be compared, and performs a process of reducing the number of gradations of each pixel data based on a predetermined threshold value. In the present embodiment, the reduction processing unit 31 performs a so-called binarization process in which the number of gradations of pixel data is reduced from 256 gradations to 2 gradations. When the reduction processing unit 31 performs binarization processing on the read image data and the document image data, the gradation value of the pixel data becomes either “0” or “1”. In the following, a pixel whose gradation value of pixel data is “0” is referred to as “black pixel”, and a pixel whose gradation value of pixel data is “1” is referred to as “white pixel”. The collation unit 32 acquires the read image data and the document image data that have been binarized by the reduction processing unit 31, and compares these image data to obtain the degree of coincidence. In this collation process, the collation unit 32 determines whether or not the tone values match for each pixel data using, for example, a residual sequential test method or the like. The collation unit 32 determines each pixel data, and then generates and outputs data indicating the degree of matching between the read image data and the document image data.

With the above configuration, the image forming apparatus 1 forms an image based on the document image data on a sheet. Further, the image forming apparatus 1 inspects the sheet on which the image is formed by the image forming unit 10 using the infrared reading unit 20 as necessary. The timing at which the image forming apparatus 1 performs the inspection may be when instructed by the user or may be a predetermined cycle. Of course, the inspection may be performed every time the image forming unit 10 forms an image.
FIG. 7 is a flowchart showing a procedure of an operation in which the image forming apparatus 1 inspects an image. Below, operation | movement of the image forming apparatus 1 is demonstrated along this flowchart.

  First, when the image forming apparatus 1 is instructed to form the document image B, the control unit 30 performs a reduction process, that is, a binarization process on the document image data representing the document image B (step SA1). ). Then, the control unit 30 stores the binarized document image data in the storage unit 40.

  Next, the control unit 30 supplies the received document image data to the image forming unit 10 and instructs to form an image. In response to this instruction, the image forming unit 10 forms the document image B based on the supplied document image data. At this time, the original image B and the pre-printed image A are superimposed on the sheet. The infrared reading unit 20 reads such an image as an inspection target. Therefore, hereinafter, the image in this state is referred to as “inspection image”. FIG. 8 is a diagram illustrating an inspection image C formed on the sheet S. The inspection image C is an image formed by superimposing the original image B shown in FIG. 4 on the sheet S on which the preprinted image A shown in FIG. 3 is formed.

  Subsequently, the control unit 30 causes the infrared reading unit 20 to generate read image data obtained by reading the inspection image C (step SA2). FIG. 9 is a diagram showing a read image Ca represented by the read image data. 9, the read image Ca represented by the read image data is an image obtained by removing the shaded image A1 from the inspection image C. This is because the infrared reading unit 20 generates read image data according to the reflected light in the infrared wavelength region from the sheet S.

  In general, in color materials such as toner and ink, black color materials absorb light in the infrared wavelength region, while color materials of other colors almost reflect light in the infrared wavelength region. Further, since the surface of the sheet S is also white, most of the light in the infrared wavelength region is reflected. In other words, light in the infrared wavelength region is absorbed only in a region where an image is formed with a substantially black color material. In the present embodiment, all of the document images B are formed with black toner, whereas the preprinted image A is preliminarily formed with a color material other than black. The print image A2 is formed of a color material including a black color material. Therefore, the read image Ca is an image obtained by removing the preprinted image A1 from the inspection image C.

  Subsequently, when the read image data is supplied from the infrared reading unit 20, the control unit 30 performs binarization processing on the read image data based on a predetermined threshold (step SA3). That is, the control unit 30 compares the gradation value of each pixel data of the read image data with a predetermined threshold value, converts the gradation value of pixel data whose gradation value is equal to or greater than the threshold value to “1”, and The gradation value of the pixel data whose value is less than the threshold value is converted to “0”. That is, the number of gradations of the read image data is reduced from “256” to “2”.

  Here, the threshold value determination method used in step SA3 will be described. As described above, black toner is used for the image area of the original image B, and low-lightness gray ink or the like is used for the preprinted image A2. Therefore, the threshold value may be set based on the gradation value corresponding to gray used for the preprinted image A2 and the gradation value of the document image data. Specifically, the threshold value is set to an intermediate gradation value between the gradation value of the pixel data corresponding to the preprinted image A2 and the gradation value of the pixel data corresponding to the image area of the document image B. In this embodiment, it is assumed that this threshold value is the same for all pixel data constituting the read image data.

Next, the control unit 30 reads the document image data binarized in step SA1 from the storage unit 40, and performs collation processing for comparison with the binarized read image data (step SA4). In this collation process, the control unit 30 performs template pattern matching on a pixel basis using, for example, a residual successive test method. Then, the control unit 30 compares the gradation values of the pixel data at the corresponding positions with respect to these image data, and identifies them as pixels that do not match. Thereafter, the control unit 30 determines whether or not the non-matching pixels exceed a predetermined allowable amount based on the number and position of the non-matching pixels, and generates and outputs data indicating that ( Step SA5). If the control unit 30 determines that the mismatched pixels exceed the allowable amount based on the determination result indicated by the data, for example, the control unit 30 displays a message “printing failure” on the UI unit 50. Then, the user is notified. On the other hand, if the control unit 30 determines that the pixel that does not match is within the allowable amount, the control unit 30 generates and outputs data indicating that fact, and based on the determination result indicating, for example, “Normally printed. Is displayed on the UI unit 50 to notify the user.
Note that when the control unit 30 determines that the mismatched pixels exceed the allowable amount, the control unit 30 causes a character image such as “printing failure” to be superimposed on the corresponding sheet S and used by the user by mistake. This may be prevented.

  According to the first embodiment described above, the image forming apparatus 1 removes the preprinted image formed of the color material other than black in the inspection image by irradiating the inspection image with the light of the infrared light source 21. Read image data is generated. Further, the image forming apparatus 1 binarizes the read image data, and removes a pre-printed image formed with a color material other than black included in the read image. In this way, the image forming apparatus 1 can inspect the read image data representing the image obtained by removing only the preprinted image from the inspection image and the original image data after the binary comparison. That is, according to the image forming apparatus 1 of the present embodiment, the pre-printed image can be quickly generated from the inspection image using a relatively simple method of performing the binarization process (decrease process) using the infrared light source 21. The removed image can be generated and inspected with high accuracy.

(2) Second Embodiment Next, a second embodiment of the present invention will be described. The present embodiment is the same as the apparatus configuration although the operation is different from that of the first embodiment described above. Therefore, in this embodiment, the operation will be described.

FIG. 10 is a flowchart showing a procedure of an operation in which the image forming apparatus 1 inspects an inspection image in the present embodiment. From FIG. 10, the control unit 30 first calculates a threshold value used for the binarization processing for each pixel data constituting the read image data (step SB1). Since this threshold value is different for each coordinate of the pixel data, it is hereinafter referred to as “threshold value Th _{x2, y2} (p _{x1, y1} )”.
Here, a method of calculating the threshold Th _{x2, y2} (p _{x1, y1} ) will be described. The control unit 30 calculates the pixel data threshold at the coordinates (x1, y1) of the original image data in order to calculate the threshold value Th _{x2, y2} (p _{x1, y1} ) of the pixel data at the coordinates (x2, y2) of the read image data. The calculation shown in the following equation (1) is performed using the adjustment value.
(Equation 1)
_{Th x2, y2 (p x1,} y1) = (T H -T L) * p x1, y1 / 255 + T L ··· (1)

In Expression (1), p _{x1, y1} is a group of nine pixels (three pixels in the X-axis direction and three pixels in the Y-axis direction) with the pixel at the coordinates (x1, y1) of the document image as the target pixel. Hereinafter, it is an average value of gradation values of “neighboring pixel group”. Further, _{T L} is a threshold of the pixel data of the coordinates when the _{p x1, y1 = 0 (x2} , y2), T H is p _{x1, y1} = 255 pixel data of the coordinates (x2, y2) of the time Is the threshold value. T _L and T _H are predetermined values.

FIG. 11 is a graph illustrating the relationship between the gradation value p _{x1, y1} represented by the equation (1) and the threshold Th _{x2, y2} (p _{x1, y1} ). From FIG. 11, the threshold Th _{x2, y2} (p _{x1, y1} ) is specified by a linear function that increases in accordance with the value of p _{x1, y1} . As described above, the threshold value is determined according to the gradation value of the pixel data constituting the document image data, so that when the control unit 30 binarizes the read image data, the preprinted image is more accurately removed. Will be able to. The threshold Th _{x2, y2} (p _{x1, y1} ) calculated for each pixel data will be specifically described below using an example of the gradation value of the document image data.

FIG. 12 shows the gradation value of each pixel data located in this area W by paying attention to the area W of a certain document image data. As shown in FIG. 12, the region W includes an “H” type image region, and this image region is composed of black pixels whose gradation value of pixel data is “0”. When the control unit 30 calculates the threshold Th _{x2, y2} (p _{x1, y1} ) for each pixel data of the read image data based on the formula (1) for the region W including such an image region, the threshold Th _{x2, y2} (p _{x1, y1} ) is as shown in FIG. From FIG. 13, the more black pixels are located in the neighboring pixel group including the target pixel, the smaller the gradation value of the neighboring pixel group and the smaller the threshold corresponding to the target pixel. The small tone value of the neighboring pixel group means that there are pixels having a relatively high density in the neighboring pixel group including the target pixel. Therefore, when the pixel of interest of the read image data is located in the image area, it is not mistakenly removed from the preprinted image even if the threshold is relatively small. On the other hand, when the pixel of interest is located in the background area, the threshold value is small, so that the gray preprinted image is removed even if the density is high to some extent.

On the other hand, the more white pixels are located in the neighboring pixel group including the target pixel, the larger the gradation value of the neighboring pixel group and the larger the threshold for the target pixel. A large tone value of the neighboring pixel group means that a pixel having a relatively low density exists in the neighboring pixel group including the target pixel. Therefore, when the target pixel of the read image data is located in the image area, the threshold value is relatively large, so that it is not mistakenly removed as a preprinted image. On the other hand, when the target pixel is located in the background area, a preprinted image having a certain density or less is removed.
In the above equation (1), the threshold value Th _{x2, y2} (p _{x1, y1} ) is calculated by a linear function (linear function) with the gradation values p _{x1, y1} of the pixel data constituting the document image as variables. However, the function is not limited to this. For example, it may be a curve function represented by a higher order expression than a linear function.

Returning to the description of FIG. After calculating the threshold Th _{x2, y2} (p _{x1, y1} ), the control unit 30 binarizes the document image data (step SB2), and causes the infrared reading unit 20 to generate read image data of the inspection image ( Step SB3). Then, the control unit 30 binarizes the read image data based on the threshold Th _{x2, y2} (p _{x1, y1} ) obtained in step SB1 (step SB4). Then, the control unit 30 performs a collation process between the read image data after binarization and the original image data binarized in step SB2 (step SB5), and the non-matching pixels have a predetermined allowable amount. It is determined whether or not it exceeds, and data indicating that is generated and output (step SB6). The operations in steps SB2, SB3, SB5, and SB6 are the same as the operations in steps SA1, SA2, SA3, and SA5 in the first embodiment described above.

  According to the second embodiment described above, the image forming apparatus 1 obtains the threshold value of each pixel data constituting the read image data according to the gradation value of the pixel data constituting the document image data. As a result, if the pixel of interest in the read image data is an image region, it can be prevented from being mistakenly removed as a preprinted image. If the pixel of interest is a background region, high-density preprinting can be performed to some extent. Even in the case of an image, the preprinted image is accurately removed by binarization.

(3) Modifications Note that the present invention is not limited to the above-described embodiment, and can be implemented in various modes. Specifically, the following modifications are mentioned, for example. These modifications can be combined as appropriate.

  In the above-described embodiment, the image forming apparatus 1 in which the image inspection apparatus is integrally configured has been described as an example. However, for example, only a configuration corresponding to the image inspection apparatus may be configured as a detachable optional apparatus. That is, the image inspection apparatus includes the infrared reading unit 20 and the control unit 30 described above, and acquires document image data from an image forming apparatus that is an external device.

In the first embodiment described above, the user sets the threshold value used for binarization of the read image data. However, the image forming apparatus 1 may set the threshold value according to the preprinted image.
For example, when the user newly accommodates a sheet on which a different pre-printed image is formed in the tray 11, the user operates the UI unit 50 to instruct the image forming apparatus 1 to perform processing for updating the threshold value. . In response to this instruction, the control unit 30 causes the transport roll 12 to transport only one sheet stored in the tray 11. At this time, the image forming unit 13 and the fixing device 14 are stopped without performing the operation at the time of image formation, and only the conveyance of the sheet is performed. When the sheet is conveyed to a predetermined position on the conveyance roll 12, the infrared reading unit 20 generates preprinted image data representing an image obtained by reading the preprinted image. The gradation value of the pixel data constituting the pre-printed image data is a value representing the density of 256 gradations, similar to the read image data described above.
In the following, the upper left corner of the image represented by the preprinted image data is set as the origin, the orthogonal coordinates similar to the original image are defined, and the coordinates of the pixel data are represented as (x3, y3).
Then, the control unit 30 performs the calculation shown in the following equation (2) to calculate the threshold Th _{x2, y2} (p _{x3, y3} ) of the read image data based on the preprinted image data.
(Equation 2)
Th _{x2, y2} (p _{x3, y3} ) ≦ p _{x3, y3} + α _{(x3, y3)} (2)

Expression (2) specifies a range of threshold values Th _{x2, y2} (p _{x3, y3} ) that can be taken by the pixel data at the coordinate address (x2, y2) of the read image data, and the gradation value p of the pixel data _It is made smaller than _{x3, y3} plus offset α _{(x3, y3)} . In this way, when the control unit 30 binarizes the read image data, it is possible to more reliably remove only the preprinted image.
Here, the reason why the offset α _{(x3, y3)} is added to the gradation value p _{x3, y3} of the pixel data will be described. In an image reading unit such as a scanner, if dust adheres to each member such as an image sensor and exists on the optical path, in-plane unevenness in which the density is nonuniform in the surface may occur. Therefore, the gradation values p _{x3 and y3} of the pixel data generated by the infrared reading unit 20 may be different from the original values. In such a case, if the threshold value Th _{x2, y2} (p _{x3, y3} ) only needs to be equal to or smaller than the gradation value p _{x3, y3} , the preprinted image is not removed or the original image is There is a risk of being removed by mistake. Therefore, the infrared reading unit 20 forms an image on the sheet based on the image data whose gradation value is known. And the control part 30 calculates | requires the correction value for correct | amending a gradation value to an original value about each pixel data which comprises the image data produced | generated by reading the said image. Then, if this correction value is used as the offset α _{(x3, y3)} , the control unit 30 can obtain a desired threshold Th _{x2, y2} (p ₎ even if the image representing the preprinted image data is affected by in-plane unevenness. _{x3, y3} ) can be obtained.

In the first embodiment described above, the threshold value corresponding to the read image data is the same for all the pixel data constituting the read image data. However, the control unit 30 uses a different threshold value depending on the position to pre-print the image. May be removed. For example, the read image data is divided into a plurality of regions, and the threshold value of a region having a relatively large gradation value of pixel data corresponding to an assumed preprinted image is increased, and the threshold value of a region having a small gradation value is decreased. , And so on. In particular, in the inspection image, in the vicinity of an area where the original image and the preprinted image are superimposed, the preprinted image should be removed more reliably. Therefore, the threshold value of the corresponding area is reduced to reduce the original image data. You may make it approach the gradation value contained.
In this way, the control unit 30 can remove only the preprinted image from the read image with higher accuracy even when the inspection image includes gray of various brightness levels.

  In the embodiment described above, the control unit 30 performs the process of comparing the entire image data in the collation process in step SA4 and step SB5. However, the control unit 30 may perform the collation process of comparing a part of the image data. Good. For example, when characters are included in the preprinted image, a black image may be included in the preprinted image. In this case, an image representing the pre-printed image remains in the binarized read image C, and even if the control unit 30 performs the collation process, mismatched pixels appear accordingly. Therefore, the control unit 30 performs the collation process only on the pixel data corresponding to the vicinity of the image area of the document image. This is because even if a black image is included in the preprinted image, the preprinted image is limited to an area different from the image area of the original image so as not to hinder the visibility of the contents of the original image. This is because they are often used.

In the first embodiment described above, the control unit 30 binarizes the document image data in step SA1, but the control unit 30 only needs to perform the collation processing in step SA4, so the control unit 30 reads in step SA2. It may be performed after generation of image data or after binarization in step SA3. Also in the second embodiment described above, the control unit 30 may binarize the document image data before the collation process in step SB5.
The control unit 30 binarizes the document image data and the read image data. However, the control unit 30 may reduce the number of gradations such as four gradations.

2 is a block diagram illustrating a hardware configuration of the configuration of the image forming apparatus. FIG. 1 is a diagram illustrating an apparatus configuration of an image forming apparatus according to an embodiment of the present invention. It is a figure which shows an example of a preprinted image. It is a figure which shows an example of a document image. It is a figure explaining the structure of an infrared reading part. It is a functional block diagram which shows the function implement | achieved by a control part and a memory | storage part. It is a flowchart which shows the procedure of the operation | movement which the control part which concerns on 1st Embodiment test | inspects an image. It is a figure which shows an example of a test | inspection image. It is a figure which shows an example of the image which read the test | inspection image. It is a flowchart which shows the procedure of the operation | movement which the control part which concerns on the embodiment test | inspects an image. It is a graph which shows the relationship between the gradation value of the pixel data which comprise the original image based on 2nd Embodiment, and a threshold value. FIG. 6 is a diagram showing gradation values of pixel data constituting a region W of a document image according to the same embodiment. It is a figure showing an example of a threshold of pixel data which constitutes field W concerning the embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 10 ... Image forming part, 11 ... Tray, 12 ... Conveyance roll, 13 ... Image forming unit, 14 ... Fixing device, 20 ... Infrared reading part, 21 ... Infrared light source, 22 ... Imaging lens , 23 ... Image sensor, 30 ... Control unit, 31 ... Reduction processing unit, 32 ... Verification unit, 40 ... Storage unit, 50 ... UI unit, 60 ... Communication unit.

Claims (1)

An image that absorbs light in the infrared wavelength region, a first image, the infrared wavelength region in the document image data on a sheet and the second image brightness is low is formed than said first image rather based Irradiating means for irradiating light of
Obtaining means for obtaining the original image data that is a basis of an image formed on the sheet;
Generation means for receiving reflected light in the infrared wavelength region reflected by the sheet from the light irradiated by the irradiation means, and generating read image data having a gradation corresponding to the amount of received light with a predetermined number of gradations When,
In accordance with the gradation value of the pixel data constituting the read image data generated by the generation unit, for each of the pixel data, the brightness between the brightness of the first image and the brightness of the second image is set. A calculating means for calculating a corresponding threshold value;
A reduction means for reducing the number of gradations of the read image data by comparing the gradation value of each pixel data constituting the read image data with a threshold value calculated for each of the pixel data by the calculation means ;
Inspection means for comparing gradation values of pixel data at corresponding positions between the read image data whose number of gradations has been reduced by the reduction means and the document image data, and outputting data representing the comparison result. An image inspection apparatus.

Images