JP2022040985A - Image reading device, image forming apparatus, image processing method, and program - Google Patents

Abstract

To provide an image reading device, an image forming apparatus, an image processing method, and a program with which the accuracy of determination of an abnormal pixel is hardly reduced.SOLUTION: An image reading device 10A comprises: an image reading unit; a color reference member 51A; and a determination unit. The image reading unit reads an image of a sheet conveyed through a conveyance path R1. The color reference member 51A is arranged opposite to the image reading unit with the conveyance path R1 therebetween. The determination unit determines an abnormal pixel based on a result of comparison between the density value of every pixel and a determination threshold for a plurality of images of the color reference member 51A read by the image reading unit at a plurality of timings different in the position of the color reference member 51A opposite to the image reading unit.SELECTED DRAWING: Figure 13

Description

The present invention relates to an image reader, an image forming apparatus, an image processing method and a program.

As a related technique, an image reader capable of removing or reducing streaky images caused by foreign substances is known (see, for example, Patent Document 1). When the sheet-through reading method is performed, foreign matter such as dust, dust, or paper dust on the sheet to be transported may be attached to the contact glass, or scratches or stains may be attached to the contact glass. In this case, a relatively dense streak image extending in the sub-scanning direction may appear in the scanned image, and the image reading device according to the related technique can remove or reduce such a streak image. And.

An image reading device according to a related technique includes an image reading unit capable of reading an image of a conveyed sheet, a density calculation unit, a threshold value determination unit, a determination unit, and an image processing unit. Before reading the sheet, the density calculation unit creates a histogram showing the number of pixels for each density value for the second scanned image read from the color reference member by the image reading unit, and determines the second threshold value based on the histogram. .. The determination unit determines that among the pixels of the second scanned image, the pixel having a density value higher than the second threshold value is the second abnormal pixel indicating an abnormality.

Further, in the related technology, the density calculation unit creates a histogram showing the number of pixels for each density value for the image corresponding to the margin area of the sheet among the first scanned images read from the sheet by the image reading unit. The first threshold value is determined based on. The determination unit is a pixel having a density value higher than the first threshold value among the pixels of the first scanned image, and the pixel whose position in the main scanning direction coincides with the second abnormal pixel is the first abnormality indicating an abnormality. Determined as a pixel. Then, the image processing unit corrects the density value of the pixel whose position in the main scanning direction coincides with the (first) abnormal pixel in the first scanned image.

Japanese Patent No. 6344062

In the configuration of the related technology, foreign matter, scratches, stains, etc. of the color reference member may be erroneously detected as foreign matter, scratches, stains, etc. of the contact glass, and the determination accuracy of the abnormal pixel may be lowered.

An object of the present invention is to provide an image reading device, an image forming device, an image processing method, and a program in which the determination accuracy of abnormal pixels is unlikely to decrease.

The image reading device according to one aspect of the present invention includes an image reading unit, a color reference member, and a determination unit. The image reading unit reads an image of a sheet transported through a transport path. The color reference member is arranged so as to face the image reading unit with the transport path interposed therebetween. The determination unit is a density value and a determination threshold value for each pixel of a plurality of images of the color reference member read by the image reading unit at a plurality of timings at which the portions of the color reference member facing the image reading unit are different. The abnormal pixel is determined based on the comparison result with.

The image forming apparatus according to another aspect of the present invention includes the image reading device and an image forming unit that forms an image of the sheet read by the image reading device on another sheet.

In the image processing method according to another aspect of the present invention, the image of the sheet conveyed through the transport path is read by the image reading unit, and the image reading unit is arranged so as to face the image reading unit across the transport path. Based on the comparison result between the density value for each pixel and the determination threshold for a plurality of images of the color reference member read by the image reading unit at a plurality of timings at which the portions of the color reference member facing the image reading unit are different. To determine an abnormal pixel.

The program according to another aspect of the present invention reads an image of a sheet conveyed through a transport path by an image reading unit, and a color reference arranged so as to face the image reading unit with the transport path interposed therebetween. Abnormality based on the comparison result between the density value for each pixel and the determination threshold for a plurality of images of the color reference member read by the image reading unit at a plurality of timings at which the parts facing the image reading unit of the member are different. It is a program for determining a pixel and causing one or more processors to execute.

According to the present invention, it is possible to provide an image reading device, an image forming device, an image processing method, and a program in which the determination accuracy of abnormal pixels is unlikely to decrease.

FIG. 1 is a schematic diagram showing a configuration of an image forming apparatus according to a basic configuration. FIG. 2 is a schematic diagram showing a configuration of an image reader according to a basic configuration. FIG. 3 shows the configuration of the image reading device according to the basic configuration, and is an enlarged view of the region Z1 of FIG. FIG. 4 is a block diagram showing an example of the configuration of the image forming apparatus according to the basic configuration. FIG. 5 is a diagram showing an example of a histogram of an image in a margin area when the sheet is newspaper. FIG. 6 is a flowchart showing an example of an image processing method according to a basic configuration. FIG. 7 is a conceptual diagram showing an example of a reading operation by the image reading device according to the basic configuration. FIG. 8 is a diagram showing an example of a histogram of each image of the color reference member and the special paper. FIG. 9 is a schematic view showing an example of correction by the image reader according to the basic configuration. FIG. 10 is a schematic view showing an example of correction by the image reader according to the basic configuration. FIG. 11 is a schematic view showing an example of correction by the image reader according to the basic configuration. FIG. 12 is a conceptual diagram showing the effect of the image reading device according to the basic configuration. FIG. 13 shows the configuration of the image reading device according to the embodiment, and is an enlarged view of the area Z1 of FIG. FIG. 14 is a flowchart showing an example of the image processing method according to the embodiment. FIG. 15 is a conceptual diagram showing an example of a reading operation by the image reading device according to the embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The following embodiments are examples that embody the present invention, and are not intended to limit the technical scope of the present invention.

(Basic configuration)
[1] Schematic configuration of the image forming apparatus First, the schematic configuration of the image forming apparatus 1 according to this basic configuration will be described with reference to FIGS. 1 to 4.

As an example in this basic configuration, the image forming apparatus 1 is a multifunction device having a plurality of functions such as a scanning function for reading an image, a printing function for forming an image based on image data, a facsimile function, and a copying function. The image forming apparatus 1 includes an image reading apparatus 10 and an image forming unit 3. That is, the image reading device 10 according to this basic configuration constitutes the image forming device 1 together with the image forming unit 3.

The image reading device 10 has a function of reading an image from the sheet Sh1 (see FIG. 2), and is installed above the image forming unit 3 as an example. The image forming unit 3 has a function of forming an image of the sheet Sh1 read by the image reading device 10 on another sheet Sh2 (see FIG. 1). The image reading device 10 includes an image reading unit 2 (see FIG. 2) that reads an image of the sheet Sh1 conveyed through the transport path R1 (see FIG. 3). As an example in this basic configuration, the image forming unit 3 includes a plurality of paper feed trays 31, a transfer device 32, a fixing device 33, and the like, and is an electrograph based on an image (image data) output from the image reading device 10. An image is formed on another sheet Sh2 by the method. The image forming unit 3 forms not only the image read by the image reading device 10 but also an image (image data) input from an information processing device or the like outside the image forming device 1 on a sheet (separate sheet Sh2). May be good. Further, the image forming unit 3 may be configured to form an image on a sheet (separate sheet Sh2) by an image forming method other than the electrophotographic method such as an inkjet method.

As shown in FIG. 2, the image reading device 10 has a device main body 4 and a document cover 5. The document cover 5 is arranged above the apparatus main body 4 and is provided so as to be openable / closable (rotatable) with respect to the apparatus main body 4. When the document cover 5 is in the "open" state, the upper surface of the apparatus main body 4 is exposed, and when the document cover 5 is in the "closed" state, the upper surface of the apparatus main body 4 is covered with the document cover 5. Therefore, by opening and closing the document cover 5, it is switched whether or not the upper surface of the apparatus main body 4 is exposed. A cover open detection sensor such as a limit switch is provided on a support portion (hinge portion) for opening and closing the document cover 5. Therefore, for example, when the document cover 5 is opened in an attempt to read the image of the document by the user, the cover open detection sensor is activated and the detection signal (cover open detection signal) is output to the processing unit 6 described later. ..

The device main body 4 of the image reading device 10 has a first contact glass 41, a second contact glass 42, an image reading unit 2, a processing unit 6, and the like. The first contact glass 41 and the second contact glass 42 form a part of the upper surface of the apparatus main body 4. Thereby, the light from the upper surface side (upper side) of the apparatus main body 4 can be taken into the apparatus main body 4 through the first contact glass 41 and the second contact glass 42. The original document (sheet Sh1) to be read is placed on the first contact glass 41. The second contact glass 42 will be described later. The image reading unit 2 reads the image of the sheet Sh1 through the first contact glass 41 or the second contact glass 42. The processing unit 6 is electrically connected to the image reading unit 2, and the image data (image data) read by the image reading unit 2 is input from the image reading unit 2. That is, the image reading device 10 includes an image reading unit 2 for reading the image of the sheet Sh1 and a processing unit 6 for receiving the image data in the device main body 4.

The image reading unit 2 includes a reading unit 20, mirrors 21 and 22, an optical lens 23, and an optical sensor 24. As an example in this basic configuration, the image reading unit 2 is a CCD system using a CCD (Charge Coupled Device) as an optical sensor 24. However, the image reading unit 2 is not limited to the CCD system, and may be a CIS (Contact Image Sensor) system.

The reading unit 20 includes a light source 201 and a mirror 202, and can be moved in the sub-scanning direction D2 (see FIG. 2) by a drive mechanism using a drive motor such as a stepping motor, for example. The light source 201 includes a plurality of light emitting elements arranged in the main scanning direction D1 (direction orthogonal to the paper surface of FIG. 2), and, as an example, a plurality of LEDs (Light Emitting Diodes). The light source 201 irradiates linear light (line light) extending in the main scanning direction D1 toward the first contact glass 41 provided on the upper surface of the apparatus main body 4. Therefore, when the reading unit 20 is moved in the sub-scanning direction D2 by the drive motor, the linear light emitted from the light source 201 to the first contact glass 41 is scanned in the sub-scanning direction D2. The main scanning direction D1 and the sub-scanning direction D2 are both directions along the upper surface of the apparatus main body 4 and orthogonal to each other.

The mirror 202 reflects the reflected light reflected by the back surface (lower surface) of the sheet Sh1 or the document cover 5 toward the mirror 21 when the light is emitted from the light source 201. The light reflected by the mirror 202 is guided to the optical lens 23 by the mirror 21 and the mirror 22. The optical lens 23 collects the incident light and causes it to enter the optical sensor 24.

The optical sensor 24 is a photoelectric conversion element that converts the received light into an electric signal (voltage or current) according to the amount of light (luminance intensity). The light amount data according to the amount of light received by the optical sensor 24 is subjected to appropriate pre-processing by the processing unit 6 or the pre-circuit circuit in the pre-stage of the processing unit 6. The pre-processing includes γ correction processing for light amount data, color correction processing for adjusting RGB color balance, color conversion processing from RGB data to CMYK data, and the like. The light amount data after the pre-processing is stored in the storage unit 25 (see FIG. 4) described later as an image (read image) read by the image reading unit 2. The processing unit 6 performs a muscle reduction process described later on the scanned image stored in the storage unit 25. The storage unit 25 may be included in the processing unit 6.

The document cover 5 has a document transport device 7. Since the document transfer device 7 is an ADF (Auto Document Feeder), it is referred to as "ADF" in FIG. 4 and also referred to as "ADF7" in the following description. The ADF 7 sequentially conveys one or a plurality of sheets Sh1 set in the original document setting unit 71 of the original cover 5 by a plurality of transfer roller pairs 72. Here, the ADF 7 moves the sheet Sh1 so as to pass the later-described reading position P1 (see FIG. 3) defined on the second contact glass 42 to the right in the sub-scanning direction D2. In other words, the ADF7 transports the sheet Sh1 through the transport path R1 including the reading position P1 on the second contact glass 42. As shown in FIG. 2, the image reading unit 2 reads the image of the sheet Sh1 conveyed on the transport path R1 by the ADF 7 at the reading position P1 in a state where the reading unit 20 is located below the reading position P1. Is possible. That is, the image reading device 10 includes an ADF 7 for transporting the sheet Sh1 through the transport path R1 in the document cover 5.

Further, the document cover 5 of the image reading device 10 has a color reference member 51. The color reference member 51 faces the second contact glass 42 when the document cover 5 is in the “closed” state. The reading position P1 is a position corresponding to the center of the facing surface (lower surface) of the color reference member 51 with the second contact glass 42 in the sub-scanning direction D2. As shown in FIG. 3, a gap forming a part of the transport path R1 is secured between the color reference member 51 and the second contact glass 42. Therefore, the sheet Sh1 set in the document setting unit 71 passes through the gap between the color reference member 51 and the second contact glass 42, so that the reading position P1 passes through the reading position P1 to the right in the sub-scanning direction D2. Will be transported at. The color reference member 51 functions as a transport guide that guides the course of the sheet Sh1 when the sheet Sh1 passes through the gap between the color reference member 51 and the second contact glass 42.

That is, the image reading device 10 includes a color reference member 51 arranged so as to face the image reading unit 2 with the transport path R1 interposed therebetween. Here, the arrangement of the color reference member 51 is such that the image reading unit 2 can read the image of the color reference member 51 from the opposite side of the transport path R1, in other words, the color reference through the transport path R1. Any arrangement may be sufficient as long as the image of the member 51 can be read. Therefore, the color reference member 51 is arranged so as to face the portion of the image reading unit 2 where the light corresponding to at least the image to be read is incident, with the transport path R1 interposed therebetween. That is, in this basic configuration, the color reference member 51 is arranged so as to face at least the reading unit 20 of the image reading unit 2 with the transport path R1 interposed therebetween. The color reference member 51 is not limited to the transport guide, and may be, for example, a shading plate, a transport guide roller, a shading roller, or the like.

The ADF 7 has a first transport roller pair 73 arranged at a predetermined position on the upstream side (left side in FIG. 3) of the sheet Sh1 in the transport direction from the color reference member 51. The first transport roller pair 73 includes a first drive roller 731 and a first driven roller 732. The first drive roller 731 and the first driven roller 732 are in contact with each other at a predetermined pressure. The first transfer roller pair 73 sandwiches the sheet Sh1 between the first drive roller 731 and the first driven roller 732, and conveys the sheet Sh1 toward the reading position P1.

Further, the ADF 7 has a second transport roller pair 74 arranged at a predetermined position on the downstream side (right side in FIG. 3) of the sheet Sh1 in the transport direction from the color reference member 51. The second transport roller pair 74 includes a second drive roller 741 and a second driven roller 742. The second drive roller 741 and the second driven roller 742 are in contact with each other at a predetermined pressure. The second transport roller pair 74 sandwiches the sheet Sh1 between the second drive roller 741 and the second driven roller 742, and ejects the sheet Sh1 that has passed through the reading position P1 to the ejection portion 75 on the document cover 5 (see FIG. 2). Transport toward the transport roller pair 72 on the side.

The ADF 7 has a first driven roller 76 and a second driven roller 77. A first driven roller 76 is arranged between the color reference member 51 and the first transfer roller pair 73 along the transfer path R1 of the sheet Sh1, and between the color reference member 51 and the second transfer roller pair 74. The second driven roller 77 is arranged in. Further, a guide member 43 is provided on the upper surface of the apparatus main body 4 on the downstream side of the second contact glass 42 in the transport direction of the sheet Sh1. The guide member 43 guides the sheet Sh1 conveyed to the gap between the color reference member 51 and the second contact glass 42 while scooping up.

The first driven roller 76 faces the second contact glass 42 at a certain interval, and forms the transport path R1 of the sheet Sh1 together with the second contact glass 42. The first driven roller 76 conveys the seat Sh1 while pressing it downward. The second driven roller 77 faces the guide member 43 at a certain interval, and forms the transport path R1 of the seat Sh1 together with the guide member 43. The second driven roller 77 conveys the sheet Sh1 while pressing it downward.

Further, the ADF 7 has a document sensor 78 arranged at a predetermined position on the upstream side of the sheet Sh1 in the transport direction from the first transport roller pair 73. The document sensor 78 includes, for example, a pair of light emitting and receiving devices, and detects the presence or absence of the sheet Sh1 in a non-contact manner. In this basic configuration, the document sensor 78 is a reflective sensor, but it may be a transmissive sensor.

According to the ADF 7 having the above configuration, the sheet Sh1 set in the document setting unit 71 is conveyed by the first transfer roller pair 73. Further, the sheet Sh1 is conveyed while being guided by the first driven roller 76, and passes through the gap (reading position P1) between the color reference member 51 and the second contact glass 42. After that, the sheet Sh1 is conveyed by the second driven roller 77, the second transfer roller pair 74, and the transfer roller pair 72, and is discharged to the discharge portion 75 provided on the upper surface side of the document cover 5.

The processing unit 6 comprehensively controls the image forming apparatus 1. The processing unit 6 mainly comprises a computer system having one or more processors and one or more memories. In the image forming apparatus 1, the function of the processing unit 6 is realized by executing the program by one or more processors. The program may be pre-recorded in a memory (or storage unit 25), may be provided through a telecommunication line such as the Internet, and may be recorded on a non-temporary recording medium such as an optical disk that can be read by a computer system. May be provided. One or more processors are composed of one or more electronic circuits including semiconductor integrated circuits. Further, the computer system referred to here includes a microcontroller having one or more processors and one or more memories. The processing unit 6 includes a memory used as a temporary storage memory (working area) for various processes executed by the processing unit 6. The processing unit 6 may be a control unit provided separately from the main control unit that collectively controls the image forming apparatus 1.

The storage unit 25 includes one or more non-volatile memories, and information such as a control program for causing the processing unit 6 to execute various processes is stored in advance.

Such an image reading device 10 can read an image by two types of reading methods, a first reading method and a second reading method. The first scanning method is also referred to as a document fixed scanning method. The second reading method is also referred to as a sheet-through reading method. Which of the first and second reading methods is used to perform the reading operation can be arbitrarily selected (switched) by, for example, a user's operation.

In the first reading method, the image reading unit 2 reads an image of a document placed on the first contact glass 41 while moving the reading unit 20 below the first contact glass 41 along the sub-scanning direction D2. It is a reading method. Specifically, the document is placed on the first contact glass 41, the upper surface of the apparatus main body 4 is closed by the document cover 5, and then an image reading instruction is input. Then, the image reading device 10 continuously moves the reading unit 20 from the home position on the side of the second contact glass 42 to the side opposite to the second contact glass 42 (on the right side in FIG. 2), and sequentially 1 from the light source 201. Irradiate the light for the line. Then, the reflected light from the document (or the lower surface of the document cover 5) is guided to the optical sensor 24 via the mirrors 202, 21, 22, and the optical lens 23. As described above, in the reading operation of the original fixed reading method, the image reading device 10 can read the image of the original placed on the first contact glass 41 by the image reading unit 2 through the first contact glass 41. Is.

The second reading method is a method in which the sheet Sh1 (original) is conveyed by the ADF7, and the image of the sheet Sh1 passing through the reading position P1 is read by the image reading unit 2 at the reading position P1. Specifically, a document is set in the document setting unit 71 with the upper surface of the apparatus main body 4 closed by the document cover 5, and an image reading instruction is input. Then, the image reading device 10 moves the reading unit 20 to a predetermined position (sheet-through position) below the second contact glass 42 and corresponding to the reading position P1. In this state, the image reading device 10 continuously irradiates one line of light from the light source 201 while moving the sheet Sh1 by the ADF 7 so as to pass through the reading position P1 along the sub-scanning direction D2. .. The reading operation by the image reading unit 2 is started after a predetermined time has elapsed after the sheet Sh1 is detected by the document sensor 78. Then, the reflected light from the sheet Sh1 is guided to the optical sensor 24 via the mirrors 202, 21 and 22, and the optical lens 23. As described above, in the reading operation of the sheet-through reading method, the image reading device 10 displays the image of the sheet Sh1 conveyed on the second contact glass 42 by the ADF 7 through the second contact glass 42 by the image reading unit 2. It is readable.

Further, in the second reading method, when the sheet Sh1 does not exist at the reading position P1, the color reference member 51 is in the readable area that can be read by the reading unit 20 located at the sheet through position below the reading position P1. Is included. The surface of the color reference member 51 uniformly has a single color, and in this basic configuration, as an example, it uniformly has a white color. Therefore, when the image reading unit 2 performs a reading operation at the reading position P1 in a state where the sheet Sh1 does not exist between the color reference member 51 and the second contact glass 42, the white surface of the color reference member 51 Is read. The image reading device 10 can acquire white reference data from the image obtained by this reading operation.

The image read by the image reading device 10 is composed of a plurality of pixels, and each of the plurality of pixels has a density value corresponding to the density. In this basic configuration, as an example, the density of each pixel is expressed by a density value of 256 steps (8 bits) from "0" to "255", and the density is set so that the thinner the density, the larger the density value. The relationship with the concentration value shall be specified. Therefore, in the image of the surface of the color reference member 51 obtained by the above-mentioned reading operation, basically, the density value of each pixel is a relatively large value corresponding to white, specifically, in the vicinity of "255". It becomes a value.

As shown in FIG. 4, the image forming apparatus 1 according to this basic configuration includes an operation display unit 11 and a communication unit 12 in addition to the image reading device 10 and the image forming unit 3.

The operation display unit 11 is a user interface in the image forming apparatus 1. The operation display unit 11 includes a display unit such as a liquid crystal display that displays various information in response to a control instruction from the processing unit 6, and a switch or touch panel that inputs various information to the processing unit 6 in response to a user operation. Has an operation unit. Further, the image forming apparatus 1 may include, for example, a voice output unit, a voice input unit, or the like as a user interface in addition to or in place of the operation display unit 11. The communication unit 12 is an interface for executing data communication between the image forming apparatus 1 and an external device connected via a communication network such as the Internet or a LAN (Local Area Network).

[2] Configuration for Determining Abnormal Pixels By the way, during the reading operation of the sheet-through reading method (second reading method), foreign matter such as dust, dust, or paper dust on the sheet Sh1 is placed on the second contact glass 42. May be attached, scratched or dirty. In such a case, a relatively dense streak-like streak image L1 (see FIG. 11) extending in the sub-scanning direction D2 may appear in the scanned image read by the image reading device 10. This streak image L1 is visually conspicuous and may cause deterioration of image quality.

Therefore, in order to remove or reduce such a streak image L1, a related technique having the following configuration is known. That is, the image reading device according to the related technology includes an image reading unit capable of reading an image of a conveyed sheet, a (first) density calculation unit, a (first) threshold determination unit, and a (first) determination unit. And an image processing unit. The density calculation unit creates a histogram showing the number of pixels for each density value for the image corresponding to the margin area of the sheet among the (first) scanned images read from the sheet by the image reading unit, and pixels based on the histogram. Calculate the first concentration value with the largest number. The threshold value determination unit determines, as the determination threshold value, a density value whose density is higher by a predetermined value than the first density value, that is, the first density value indicating the background density of the scanned image. Based on the comparison result between the density value of each pixel in the margin area and the judgment threshold value, the judgment unit indicates a pixel having a density value higher than the judgment threshold value among the pixels in the margin area as an abnormality (first) abnormal pixel. Is determined. The image processing unit corrects the density value of the scanned image whose position in the main scanning direction D1 coincides with the abnormal pixel.

However, in the above-mentioned related technology, since the density value whose density is higher by the "predetermined value" than the density value having the largest number of pixels (indicating the background density of the scanned image) is the determination threshold value, "predetermined". Depending on the setting of "value", the determination accuracy of abnormal pixels may decrease. Hereinafter, the “predetermined value” which is the shift amount of the density value from the density value having the largest number of pixels to the determination threshold value is also referred to as a “fixed shift value”.

That is, in the related technology, fixed shift values are compared so as to be able to read an image of a sheet having a relatively large variation in the background density (background density of the scanned image) such as stencil paper, recycled paper, or newspaper. It is set to a large size. As an example, in the case of a sheet such as newspaper in which the variation in the background density is relatively small, the histogram corresponding to the margin area has a relatively large variation in the density value as illustrated in the upper part of FIG. Is created. In the histogram shown in the upper part of FIG. 5, the density value (reference density value) C0 having the largest number of pixels is "200", and there are pixels having a density value of "189" due to variations in the background density. In this example, the fixed shift value ΔC0 is set to a relatively large value of “12” so that the normal density (base density) is not erroneously determined as an abnormal pixel, and the density is increased by “12” from “200”. It is necessary to set the dark concentration value "188" to the determination threshold value Th0.

However, for a sheet having a relatively small variation in the base density, such as special paper, at the determination threshold Th0 determined by using a relatively large fixed shift value ΔC0, foreign matter, scratches, stains, etc. on the second contact glass 42, etc. It becomes easy to overlook the original abnormal pixel caused by. In short, when the fixed shift value ΔC0 is relatively large, the determination threshold value Th0 for determining an abnormal pixel becomes a loose (smaller) value, so that the detection omission of the original abnormal pixel occurs and the determination accuracy of the abnormal pixel deteriorates. there's a possibility that. On the other hand, when the fixed shift value ΔC0 is set to be relatively small, the normal density (normal density) is applied to a sheet having a relatively large variation in the background density (background density of the scanned image) such as stencil paper, recycled paper, or newspaper. The background density) is also likely to be erroneously determined as an abnormal pixel. In short, when the fixed shift value ΔC0 is relatively small, the determination threshold value Th0 for determining an abnormal pixel becomes a strict (small) value, so that even a normal pixel may be excessively abnormal pixel depending on the type of sheet. There is a possibility that the determination will be made and the determination accuracy of the abnormal pixel will decrease.

Therefore, in this basic configuration, by adopting the following configuration, the image reading device 10 in which the determination accuracy of abnormal pixels is unlikely to decrease is provided.

That is, as shown in FIG. 4, the image reading device 10 according to the basic configuration has a determination unit 61 and a threshold value determination unit 62 in addition to the image reading unit 2 that reads the image of the sheet Sh1 conveyed through the transfer path R1. And a correction processing unit 63. In this basic configuration, the determination unit 61, the threshold value determination unit 62, and the correction processing unit 63 are embodied in the processing unit 6. Further, in this basic configuration, the processing unit 6 further has the function of the reading control unit 64. That is, the image reading device 10 according to this basic configuration includes a determination unit 61, a threshold value determination unit 62, a correction processing unit 63, and a reading control unit 64 as one function of the processing unit 6.

The reading control unit 64 causes the image reading unit 2 to perform a reading operation for reading an image for determining an abnormal pixel when the reading operation of the sheet-through reading method is performed. In this basic configuration, two types of images, a first image and a second image, are used as images for determining abnormal pixels. The first image is an image of the color reference member 51 read by the image reading unit 2. The second image is an image of the margin area Rm1 (see FIG. 7) of the sheet Sh1 read by the image reading unit 2. Therefore, the reading control unit 64 causes the image reading unit 2 to perform a reading operation for reading the first image and a reading operation for reading the second image. It has a second read control unit 642. That is, the first reading control unit 641 causes the image reading unit 2 to perform the reading operation during the period when the sheet Sh1 does not exist at the reading position P1 at the time of reading by the sheet-through reading method. The second reading control unit 642 causes the image reading unit 2 to perform a reading operation during the period when the margin region Rm1 of the sheet Sh1 passes through the reading position P1 at the time of reading by the sheet-through reading method.

The determination unit 61 determines an abnormal pixel based on the comparison result between the density value for each pixel and the determination threshold value for the image read by the image reading unit 2. In this basic configuration, the determination unit 61 includes a first determination unit 611 that extracts the first abnormal pixel from the first image, and a second determination unit 612 that extracts the second abnormal pixel from the second image. The first determination unit 611 extracts the first abnormal pixel by comparing the density value for each pixel with the first determination threshold value for the first image. The second determination unit 612 extracts the second abnormal pixel by comparing the density value for each pixel with the second determination threshold value for the second image. The determination unit 61 finally determines the abnormal pixel according to the degree of coincidence between the first abnormal pixel and the second abnormal pixel. Specifically, the determination unit 61 determines that among the first abnormal pixels, the pixels whose positions match the positions of the second abnormal pixel and the main scanning direction D1 are determined as abnormal pixels.

The threshold value determination unit 62 determines the determination threshold value based on the frequency distribution of the density value of each pixel in the image read by the image reading unit 2. The "frequency distribution" here means the distribution status of the data belonging to each class when the collected data is divided into several classes (intervals), and includes a histogram in which the frequency distribution is graphed. That is, the threshold value determination unit 62 determines the determination threshold value based on the histogram of the concentration value as an example. In the present basic configuration, the threshold value determination unit 62 includes a first threshold value determination unit 621 that determines the first determination threshold value from the first image, and a second threshold value determination unit 622 that determines the second determination threshold value from the second image. Have. The first threshold value determination unit 621 determines the first determination threshold value based on the frequency distribution (first histogram G1 shown in the upper part of FIG. 8) for the density value of each pixel in the first image. The second threshold value determination unit 622 determines the second determination threshold value based on the frequency distribution (second histogram G2 shown in the lower part of FIG. 8) for the density value of each pixel in the second image.

The correction processing unit 63 corrects the density value of the pixel whose position in the main scanning direction D1 coincides with the abnormal pixel among the images read by the image reading unit 2. As a result, even if foreign matter, scratches, stains, or the like adhere to the second contact glass 42, the image reading device 10 displays the streak image L1 extending in the sub-scanning direction D2 from the image read by the image reading unit 2. It can be removed or reduced. However, the correction of the density value of the image by the correction processing unit 63 is not an essential configuration for the image reading device 10, and the correction processing unit 63 may be omitted as appropriate. For example, when the image reading device 10 has abnormal pixels due to foreign matter, scratches, stains, etc. on the second contact glass 42, the second contact glass is displayed and / or presented to the user by voice to that effect. The user may be urged to clean the 42.

According to the above configuration, the threshold value determination unit 62 can determine an appropriate determination threshold value according to, for example, the variation in the background density of the sheet Sh1, and the image reading device 10 reduces the determination accuracy of abnormal pixels. It has the advantage of being difficult.

[3] Image processing method Next, an example of the procedure of the image processing method executed by the image reading device 10 will be described with reference to FIGS. 6 to 12. Here, steps S1, S2 ... In the flowchart shown in FIG. 6 represent the numbers of the processing procedures (steps) executed by the processing unit 6. The process described below is performed when a document is set in the document setting unit 71 and an image reading instruction is input by a user operation. Further, in FIG. 7, the timing (sampling timing) for reading an image by the image reading unit 2 is conceptually shown with the left-right direction as the main scanning direction D1 and the vertical direction as the time axis. Further, in FIG. 8, the histogram G1 representing the frequency distribution for the first image and the histogram G2 representing the frequency distribution for the second image are shown side by side, with the horizontal axis representing the density value and the vertical axis representing the number of pixels.

<Step S1>
In step S1, the processing unit 6 determines whether or not an image reading instruction has been input by a user operation. When the processing unit 6 determines that the image reading instruction has not been input (S1: No), the processing unit 6 waits. When the processing unit 6 determines that the image reading instruction has been input (S1: Yes), the processing unit 6 proceeds to step S2.

<Step S2>
In step S2, the first reading control unit 641 causes the image reading unit 2 to perform a reading operation before the sheet Sh1 reaches the reading position P1. Specifically, the first reading control unit 641 moves the reading unit 20 to the right of FIG. 2 in the sub-scanning direction D2 by a distance of several lines before the sheet Sh1 is detected by the document sensor 78. At the same time, the image reading unit 2 is made to perform reading operations for several lines. At this time, the image reading unit 2 performs a reading operation for reading the image of the color reference member 51 at the timing shown by the sampling timing St1 in FIG. 7.

<Step S3>
By the above reading operation, the image of the surface of the color reference member 51 is read, and the image reading unit 2 acquires the first image (S3). Here, if no foreign matter, scratches, stains, or the like are attached to the second contact glass 42, the density value of the pixels in the first image is substantially the same as the value in the main scanning direction D1. Further, in this case, when the color reference member 51 is not discolored such as fading, the density values of the pixels of the first image are all close to the density values corresponding to the white surface color of the color reference member 51. It becomes a value. On the other hand, when the color reference member 51 is discolored such as fading, the density value of the pixel of the first image is a small (dark) density value as a whole. This is because a part of the light from the light source 201 reflected by the color reference member 51 and incident on the optical sensor 24 is absorbed by the discolored color reference member 51, and the amount of light incident on the optical sensor 24 is reduced. .. Further, when foreign matter, scratches, stains, etc. are attached to the second contact glass 42, the density value of the pixel in a part of the main scanning direction D1 in the first image is higher than the density value of the other pixels. It will be a small (dark) value. This is because a part of the light from the light source 201 reflected by the color reference member 51 and incident on the optical sensor 24 is diffused or absorbed by foreign matter or the like adhering to the second contact glass 42 and incident on the optical sensor 24. This is because the amount of light emitted becomes smaller.

<Step S4>
Next, in step S4, the first threshold value determination unit 621 creates a first histogram G1 showing the number of pixels for each density value for the first image obtained in step S3, as shown in the upper part of FIG. .. The first histogram G1 shows the distribution state of data (pixels) belonging to each gradation when the density value is divided into 256 gradations for all the pixels of the first image which is the image of the color reference member 51. ing. That is, the larger the corresponding density value in the first image, the larger the frequency (number of pixels) in the first histogram G1.

<Step S5>
Next, in step S5, the first threshold value determination unit 621 determines the first reference density value C1, which is the reference density value in the first image. As an example in this basic configuration, the first reference density value C1 is the density value having the largest number of pixels in the first image, that is, the density value having the maximum frequency in the first histogram G1. In the example of FIG. 8, the density value “236” is the first reference density value C1 from the first histogram G1. However, the first reference density value C1 may be a reference density value in the first image, and is not limited to the density value having the largest number of pixels. For example, the average value, the median value, and the density values of the density values in the first image. Alternatively, it may be a predetermined value (fixed value) or the like.

<Step S6>
Next, in step S6, the first threshold value determination unit 621 determines the first determination threshold value Th1 with reference to the first reference concentration value C1. At this time, in the present basic configuration, the first threshold value determination unit 621 determines the first determination threshold value Th1 based on the frequency distribution (first histogram G1) for the density value of each pixel in the first image. Here, as an example, the first threshold value determination unit 621 is a pixel occupying the total number of pixels obtained from the frequency distribution (first histogram G1) for the density value of each pixel in the image (first image) read by the image reading unit 2. The first determination threshold Th1 is determined using the number ratio. Specifically, the first threshold value determination unit 621 obtains a range of density values in which the ratio of the number of pixels to the total number of pixels is 99.8% centering on the first reference density value C1 in the first histogram G1. The lower limit value (minimum value) in the range of this concentration value is set as the first determination threshold value Th1. In other words, the standard deviation σ is used to obtain a value of ± 3σ with respect to the first reference concentration value C1, and the first threshold value determination unit 621 determines the concentration value of “C1-3σ” as the first determination threshold value Th1. And. As described above, the first threshold determination unit 621 uses the standard deviation σ obtained from the frequency distribution (first histogram G1) for the density value of each pixel in the image (first image) read by the image reading unit 2. The first determination threshold Th1 is determined. This makes the calculation for determining the first determination threshold Th1 relatively simple.

In the example of FIG. 8, the first threshold value determination unit 621 determines the fluctuation shift value ΔC1 determined by the number of pixels ratio to “3” from the first histogram G1. Therefore, the first threshold value determination unit 621 determines the concentration value “233” obtained by subtracting “3” from the first reference concentration value C1 (236) as the first determination threshold value Th1. As described above, in this basic configuration, the first determination threshold value Th1 is set to a value corresponding to the fluctuation shift value ΔC1 that fluctuates depending on the frequency distribution (first histogram G1) while using the first reference concentration value C1 as a reference. To. However, the first threshold value determination unit 621 may determine the first determination threshold value Th1 based on the frequency distribution for the density value of each pixel in the first image, and the values given here are only examples. As another example, the first threshold value determination unit 621 has a density centered on the first reference density value C1 and includes pixels in which the pixel number ratio shown in the total number of pixels is an arbitrary value (95.0% as an example). A range of values may be obtained, and the lower limit value (minimum value) of this concentration value range may be set as the first determination threshold value Th1. In the example of FIG. 8, since the standard deviation σ is “1”, the concentration value obtained by subtracting 3σ (= 3) from the first reference concentration value C1 may be set as the first determination threshold value Th1.

<Step S7>
In step S7, the first determination unit 611 determines whether or not each pixel in the first image is a first abnormal pixel. Specifically, the first determination unit 611 compares the density value of the pixels in the first image with the first determination threshold Th1 for each pixel. The first determination unit 611 determines that a (dark) pixel whose density value is equal to or less than the first determination threshold Th1 is a first abnormal pixel. When the first determination unit 611 determines that the first abnormal pixel is a first abnormal pixel, the first determination unit 611 stores the coordinate position of the main scanning direction D1 for each first abnormal pixel, thereby specifying the position of the main scanning direction D1 of the first abnormal pixel. do.

In this basic configuration, the process of step S7 for determining the first abnormal pixel is performed using a first image different from steps S4 to S6 for determining the first determination threshold value Th1. That is, in executing step S7, the processing unit 6 performs the same processing as in steps S2 and S3 again to acquire the first image. Specifically, the image reading unit 2 performs a reading operation for reading the image of the color reference member 51 at the timing shown by the sampling timing St2 in FIG. 7, and newly acquires the first image. With respect to the newly acquired first image, the first determination unit 611 determines whether or not it is the first abnormal pixel. However, the present invention is not limited to this example, and the same first image as in steps S4 to S6 for determining the first determination threshold value Th1 may be used in the process of step S7 for determining the first abnormal pixel. ..

<Step S8>
Then, in step S8, the second reading control unit 642 determines whether or not the sheet Sh1 is detected by the document sensor 78 based on the output signal of the document sensor 78. When the second reading control unit 642 determines that the sheet Sh1 is not detected by the document sensor 78 (S8: No), the second reading control unit 642 stands by. When the second reading control unit 642 determines that the sheet Sh1 has been detected by the document sensor 78 (S8: Yes), the process proceeds to step S9.

<Step S9>
In step S9, the second reading control unit 642 causes the image reading unit 2 to perform a reading operation after a predetermined time has elapsed from the detection of the sheet Sh1 by the document sensor 78. Specifically, the second reading control unit 642 displays, for example, an image of a margin area Rm1 such as a header area on the leading side in the transport direction of the sheet Sh1 passing through the reading position P1 on the image reading unit 2 for several lines. Let me read it. At this time, the image reading unit 2 performs a reading operation for reading the image in the margin region Rm1 of the sheet Sh1 at the timing shown by the sampling timing St3 in FIG. 7.

<Step S10>
By the above reading operation, the image of the margin region Rm1 of the sheet Sh1 is read, and the image reading unit 2 acquires the second image (S10). Here, if no foreign matter, scratches, stains, or the like are attached to the second contact glass 42, the density value of the pixels in the second image is substantially the same as the value in the main scanning direction D1. Further, in this case, the density values of the pixels of the second image are all close to the density value corresponding to the background density of the sheet Sh1. Further, when foreign matter, scratches, stains, etc. are attached to the second contact glass 42, the density value of the pixel in a part of the main scanning direction D1 in the second image is higher than the density value of the other pixels. It will be a small (dark) value. This is because a part of the light from the light source 201 reflected by the sheet Sh1 and incident on the optical sensor 24 is diffused or absorbed by foreign matter or the like adhering to the second contact glass 42, and the amount of light incident on the optical sensor 24. Is smaller.

<Step S11>
Next, in step S11, the second threshold value determination unit 622 creates a second histogram G2 showing the number of pixels for each density value for the second image obtained in step S10, as shown in the lower part of FIG. .. The second histogram G2 shows the distribution status of the data (pixels) belonging to each gradation when the density value is divided into 256 gradations for all the pixels of the second image which is the image of the margin region Rm1 of the sheet Sh1. Is shown. That is, the larger the corresponding density value in the second image, the larger the frequency (number of pixels) in the second histogram G2. Here, it is assumed that the sheet Sh1 is a special paper having a relatively small variation in the base density.

<Step S12>
Next, in step S12, the second threshold value determination unit 622 determines the second reference density value C2, which is the reference density value in the second image. As an example in this basic configuration, the second reference density value C2 is the density value having the largest number of pixels in the second image, that is, the density value having the maximum frequency in the second histogram G2. In the example of FIG. 8, the density value “241” is the second reference density value C2 from the second histogram G2. However, the second reference density value C2 may be a reference density value in the second image, and is not limited to the density value having the largest number of pixels. For example, the average value, the median value, and the density values of the density values in the second image. Alternatively, it may be a predetermined value (fixed value) or the like.

<Step S13>
Next, in step S13, the second threshold value determination unit 622 determines the second determination threshold value Th2 with reference to the second reference concentration value C2. At this time, in the present basic configuration, the second threshold value determination unit 622 determines the second determination threshold value Th2 based on the frequency distribution (second histogram G2) for the density value of each pixel in the second image. Here, as an example, the second threshold value determination unit 622 is a pixel occupying the total number of pixels obtained from the frequency distribution (second histogram G2) for the density value of each pixel in the image (second image) read by the image reading unit 2. The second determination threshold Th2 is determined using the number ratio. Specifically, the second threshold value determination unit 622 obtains a range of the density value in which the ratio of the number of pixels to the total number of pixels is 99.8% centering on the second reference density value C2 in the second histogram G2. The lower limit value (minimum value) in the range of this concentration value is set as the second determination threshold value Th2. In other words, the standard deviation σ is used to obtain a value of ± 3σ with respect to the second reference concentration value C2, and the second threshold value determination unit 622 determines the concentration value of “C2-3σ” as the second determination threshold value Th2. And. As described above, the second threshold value determination unit 622 uses the standard deviation σ obtained from the frequency distribution (second histogram G2) for the density value of each pixel in the image (second image) read by the image reading unit 2. The second determination threshold Th2 is determined. This makes the calculation for determining the second determination threshold Th2 relatively simple.

In the example of FIG. 8, the second threshold value determination unit 622 determines the fluctuation shift value ΔC2 determined by the number of pixels ratio to “4” from the second histogram G2. Therefore, the second threshold value determination unit 622 determines the concentration value “237” obtained by subtracting “4” from the second reference concentration value C2 (241) as the second determination threshold value Th2. As described above, in this basic configuration, the second determination threshold value Th2 is set to a value corresponding to the fluctuation shift value ΔC2 that fluctuates depending on the frequency distribution (second histogram G2) while using the second reference concentration value C2 as a reference. To. However, the second threshold value determination unit 622 may determine the second determination threshold value Th2 based on the frequency distribution for the density value of each pixel in the second image, and the values given here are only examples. As another example, the second threshold value determination unit 622 has a density centered on the second reference density value C2 and includes pixels in which the pixel number ratio shown in the total number of pixels is an arbitrary value (95.0% as an example). A range of values may be obtained, and the lower limit value (minimum value) of this range of concentration values may be set as the second determination threshold value Th2.

<Step S14>
In step S14, the second determination unit 612 determines whether or not each pixel in the second image is a second abnormal pixel. Specifically, the second determination unit 612 compares the density value of the pixels in the second image with the second determination threshold value Th2 for each pixel. The second determination unit 612 determines that the (dark) pixel whose density value is equal to or less than the second determination threshold Th2 is a second abnormal pixel. When the second determination unit 612 determines that the second abnormal pixel is a second abnormal pixel, the second determination unit 612 identifies the position of the main scanning direction D1 of the second abnormal pixel by storing the coordinate position of the main scanning direction D1 for each second abnormal pixel. do.

In this basic configuration, the process of step S14 for determining the second abnormal pixel is performed using a first image different from steps S11 to S13 for determining the second determination threshold value Th2. That is, in executing step S14, the processing unit 6 performs the same processing as in steps S9 and S10 again to acquire the second image. Specifically, the image reading unit 2 performs a reading operation of reading an image of the margin region Rm1 of the sheet Sh1 at the timing shown by the sampling timing St4 in FIG. 7, and newly acquires a second image. With respect to the newly acquired second image, the second determination unit 612 determines whether or not it is a second abnormal pixel. However, the present invention is not limited to this example, and the same second image as in steps S11 to S13 for determining the second determination threshold value Th2 may be used in the process of step S14 for determining the second abnormal pixel. ..

<Steps S15, S16>
In step S15, the determination unit 61 determines the abnormal pixel according to the degree of coincidence between the first abnormal pixel and the second abnormal pixel. Specifically, the determination unit 61 determines that, among the second abnormal pixels, the pixel whose position (coordinates) in the main scanning direction D1 coincides with the first abnormal pixel is an abnormal pixel. In other words, the pixels at the same position in the main scanning direction D1 are determined to be the first abnormal pixels from the image (first image) of the color reference member 51, and are second from the image (second image) of the margin region Rm1 of the sheet Sh1. 2 When it is determined to be an abnormal pixel, the pixel is determined to be an abnormal pixel. Therefore, when the pixel at a certain position in the main scanning direction D1 is determined to be the first abnormal pixel but not determined to be the second abnormal pixel, or is determined to be the second abnormal pixel but determined to be the first abnormal pixel. If not, it is determined that the pixel is not an abnormal pixel. That is, in both the image of the color reference member 51 (first image) and the image of the margin region Rm1 of the sheet Sh1 (second image), only the pixels determined to be abnormal are the foreign matter of the second contact glass 42. It is determined that the pixel is abnormal due to scratches or stains.

More specifically, when the determination unit 61 scans the pixel position in one direction of the main scanning direction D1 (for example, the right direction in FIG. 7), the determination unit 61 starts a position (start point) at the second abnormal pixel and the first abnormal pixel. ) Are substantially the same (S15: Yes), it is determined that the second abnormal pixel is an abnormal pixel (S16). Here, it is assumed that the "substantial match" of the start position is within a predetermined number of pixels (for example, 3 pixels) as an example. On the other hand, when the determination unit 61 scans the pixel position in one direction of the main scanning direction D1, if the start positions (start points) of the second abnormal pixel and the first abnormal pixel do not substantially match (S15: No), skip step S16 and proceed to step S17. That is, if the start position of the first abnormal pixel is within a predetermined number of pixels from the start position of the second abnormal pixel, the start position of the second abnormal pixel and the first abnormal pixel are substantially the same. In this way, the determination unit 61 may determine the abnormal pixel according to the degree of coincidence between the first abnormal pixel and the second abnormal pixel, and the first abnormal pixel and the second abnormal pixel do not completely match. It may also be determined that the pixel is abnormal. As another example, in the determination unit 61, is the end position (end point) substantially the same between the second abnormal pixel and the first abnormal pixel, or is there an overlapping region between the start position and the end position? May determine the abnormal pixel.

<Step S17>
In step S17, the correction processing unit 63 corrects the density value of the pixel whose position in the main scanning direction D1 coincides with the abnormal pixel among the images read by the image reading unit 2. That is, a pixel whose position is the same as that of the pixel determined to be an abnormal pixel in step S16 in the main scanning direction D1 can cause the streak image L1 in the image of the sheet Sh1 read at this time. The density value of the pixels constituting the above is corrected. At this time, the correction processing unit 63 interpolates the density value for the entire image of one sheet Sh1 for the pixels (pixels constituting the streak image L1) in which the positions of the abnormal pixels and the main scanning direction D1 coincide with each other. By doing so, the density value is corrected.

Specifically, as shown in FIG. 9, the correction processing unit 63 sets the density value of the (dark) pixel whose density value is equal to or less than the second determination threshold Th2 at the position closest to the pixel in the main scanning direction D1. Replace with the density value of normal pixels. That is, when foreign matter, scratches, stains, etc. are attached to the second contact glass 42, the image read by the image reading unit 2 thereafter also has a pixel determined to be an abnormal pixel and a main scanning direction D1. The density value of the pixels whose positions match is equal to or less than the second determination threshold value Th2. As an example, as shown in the upper part of FIG. 10, when the pixels of the pixel array extending in the main scanning direction D1 in the image are assigned pixel numbers "1" to "15" continuous with the main scanning direction D1. In addition, it is assumed that the pixels of the pixel numbers "5" to "11" are abnormal pixels. In this case, the correction processing unit 63 sets the pixel whose position in the main scanning direction D1 coincides with the abnormal pixel, that is, the pixel whose pixel number is "5" to "11" as the pixel constituting the streak image L1. .. Therefore, as shown in the lower part of FIG. 10, the correction processing unit 63 sets the density values of the pixels of the pixel numbers “5” to “11” to the pixels closest to these pixels in the main scanning direction D1, that is, the pixels. The number is replaced with the density value of the normal pixel of "4" or "12".

As a result, as shown in the lower part of FIG. 9, in the main scanning direction D1, the difference between the density value of the pixel in the same range Ra1 as the abnormal pixel and the density value of the peripheral pixel becomes small. In other words, the difference between the density value of the pixels in the range Ra1 and the second reference density value C2 becomes small, and the local decrease in the density value due to foreign matter, scratches, stains, etc. of the second contact glass 42 is suppressed. Will be done. As a result, as shown in FIG. 11, even if the streak image L1 is included in the image Im101 of the entire sheet Sh1 read by the image reading unit 2, the corrected image Im102 has a density value with the surrounding pixels. The difference between is small. Therefore, in the image Im102 of the entire sheet Sh1 after correction, the streak image L1 is removed or reduced. However, the method for correcting the density value by the correction processing unit 63 is not limited to this.

<Step S18>
In step S18, the processing unit 6 determines whether or not the scanned image to be processed exists in the storage unit 25. That is, the correction process by the correction process unit 63 in step S17 is performed for each sheet Sh1 with respect to the image of the entire sheet Sh1. Therefore, when the image reading unit 2 reads the images of the plurality of sheets Sh1, the storage unit 25 has another scanned image to be processed even after the correction processing for the image of one sheet Sh1 is completed. There is an image of Sheet Sh1. When the processing unit 6 determines that the image to be processed exists in the storage unit 25 (S18: Yes), the processing unit 6 returns to step S9. When the processing unit 6 determines that the image to be processed does not exist in the storage unit 25 (S18: No), the processing unit 6 proceeds to step S19.

<Step S19>
In step S19, the processing unit 6 determines whether or not the document setting unit 71 has a sheet Sh1 for which the image has not been read yet, based on the output signal of the document sensor provided at the predetermined position of the document setting unit 71. Is determined. When the processing unit 6 determines that the sheet Sh1 exists in the document setting unit 71 (S19: No), the processing unit 6 returns to step S9. When the processing unit 6 determines that the sheet Sh1 does not exist in the document setting unit 71 (S19: Yes), the processing unit 6 ends a series of processing. The procedure of the image processing method described above is only an example, and the order of processing shown in the flowchart of FIG. 6 may be changed as appropriate.

As described above, in the present basic configuration, the determination threshold value used for determining the abnormal pixel is based on the frequency distribution of the density value of each pixel in the image read by the image reading unit 2 in the threshold value determining unit 62. ,It is determined. That is, as compared with the case where the density value having a density higher by "a predetermined value" than the reference density value having the largest number of pixels becomes the determination threshold value Th0 as in the above-mentioned related technology, the image reading according to this basic configuration is performed. In the device 10, it becomes easy to appropriately determine the determination threshold value. That is, the determination threshold value is not fixedly determined using a "predetermined value" such as the fixed shift value ΔC0, but is a frequency for the density value of each pixel in the image read by the image reading unit 2. It is dynamically determined based on the distribution. Therefore, for example, the threshold value determination unit 62 can determine an appropriate determination threshold value according to the variation in the background density of the sheet Sh1, and the image reading device 10 has an advantage that the determination accuracy of abnormal pixels is unlikely to decrease. There is.

For example, assuming that the fixed shift value ΔC0 is set to a relatively large value of “12” as in the above-mentioned related technology, the sheet Sh1 having a relatively small variation in the base density, such as special paper, is used. The second determination threshold Th2 is a loose (small) value. That is, when the second histogram G2 as illustrated in the lower part of FIG. 8 is obtained, the second determination threshold value Th2 is the concentration obtained by subtracting the fixed shift value ΔC0 “12” from the second reference concentration value C2 (241). The value is "229". Therefore, the second determination threshold Th2 becomes a small value, and as shown on the left side of FIG. 12, the range Ra1 of the pixels determined to be abnormal pixels is relatively narrow, and the density value of the pixels in the range Ra1 and the second. The difference from the reference concentration value C2 is also relatively large. As a result, it is difficult to suppress the local decrease in the density value due to foreign matter, scratches, stains, etc. of the second contact glass 42, and the streak image L1 is likely to remain in the corrected image.

On the other hand, in this basic configuration, since the second determination threshold value Th2 is determined using the fluctuation shift value ΔC2 that fluctuates based on the frequency distribution, a sheet having a relatively small variation in the base density like a special paper. For Sh1, the second determination threshold value Th2 is also an appropriate value. That is, when the second histogram G2 as illustrated in the lower part of FIG. 8 is obtained, the second determination threshold value Th2 is the concentration obtained by subtracting the fluctuation shift value ΔC2 “4” from the second reference concentration value C2 (241). The value is "237". Therefore, the second determination threshold Th2 becomes an appropriate value, and as shown on the right side of FIG. 12, the range Ra1 of the pixel determined to be an abnormal pixel is also appropriate, and the density value and the second reference density of the pixels in the range Ra1 are also appropriate. The difference from the value C2 is also relatively small. As a result, the local decrease in the density value due to foreign matter, scratches, stains, etc. of the second contact glass 42 is easily suppressed, and the streak image L1 is less likely to remain in the corrected image.

On the other hand, in this basic configuration, since the second determination threshold value Th2 is determined using the fluctuation shift value ΔC2 that fluctuates based on the frequency distribution, the variation in the base density of the stencil paper, recycled paper, newspaper, etc. is relatively large. Even for a large sheet Sh1, the second determination threshold value Th2 is an appropriate value. That is, when the second histogram G2 as illustrated in the lower part of FIG. 5 is obtained, the second threshold value determination unit 622 determines the fluctuation shift value ΔC2 determined by the number of pixels ratio to be “12”. Therefore, the second threshold value determination unit 622 determines the concentration value “188” obtained by subtracting “12” from the second reference concentration value C2 (200) as the second determination threshold value Th2. Therefore, even if the type of the sheet Sh1 is changed, the second determination threshold value Th2 becomes an appropriate value, and it is easy to suppress a local decrease in the concentration value due to foreign matter, scratches, stains, etc. of the second contact glass 42. , The streak image L1 is less likely to remain in the corrected image.

Further, in the present basic configuration, the threshold value determination unit 62 determines the first determination threshold value Th1 based on the frequency distribution of the first image and the second determination threshold value Th2 based on the frequency distribution of the second image. Do at least one of the processing. Then, the determination unit 61 determines the abnormal pixel according to the degree of coincidence between the first abnormal pixel determined using the first determination threshold Th1 and the second abnormal pixel determined using the second determination threshold Th2. do. Therefore, the determination unit 61 distinguishes between abnormal pixels caused by foreign matter, scratches, stains, etc. adhering to the second contact glass 42 and streaky images such as ruled lines formed on the sheet Sh1 and abnormal pixels. Can be determined. Moreover, if the first determination threshold Th1 is determined based on the frequency distribution of the first image which is the image of the color reference member 51, for example, even if the color reference member 51 is discolored such as fading, the first determination threshold Th1 Can be set to an appropriate value according to the frequency distribution of the first image.

Further, in the present basic configuration, the threshold value determination unit 62 determines both the first determination threshold value Th1 and the second determination threshold value Th2. Therefore, it is possible to set an appropriate second determination threshold value Th2 according to the variation in the base density of the sheet Sh1 while setting an appropriate first determination threshold value Th1 according to discoloration such as fading of the color reference member 51, and the first abnormality. The determination accuracy of both the pixel and the second abnormal pixel is unlikely to decrease.

[4] Modification Example The plurality of components included in the image forming apparatus 1 may be dispersedly provided in a plurality of housings. For example, at least one of the determination unit 61, the threshold value determination unit 62, the correction processing unit 63, and the reading control unit 64 is not limited to the configuration realized as one function of the processing unit 6, but is a housing separate from the processing unit 6. It may be provided in.

Further, the image reading device 10 may have a function of reading an image (image data), and it is not essential to configure the image forming device 1 together with the image forming unit 3. That is, the image reading device 10 is not limited to the aspect as a part of the image forming apparatus 1 having a function of forming an image, but is embodied in various embodiments. For example, the image reading device 10 may be a scanner or a facsimile machine that does not have a function of forming an image (image forming unit 3) and outputs the read image (image data) to the outside.

Further, it is not essential that the image reading device 10 can read an image by two kinds of reading methods, a first reading method (fixed document reading method) and a second reading method (sheet-through reading method). do not have. That is, the image reading device 10 may not have the function of reading an image by the original fixed reading method, as long as the image can be read by the sheet-through reading method.

Further, in the basic configuration, the determination unit 61 determines the abnormal pixel according to the degree of coincidence between the first abnormal pixel and the second abnormal pixel, but this configuration is not essential, and the determination unit 61 is, for example, the first. Only one of the abnormal pixel and the second abnormal pixel may be determined. In this case, the processing unit 6 uses the determined first abnormal pixel or the second abnormal pixel as an abnormal pixel, and the correction processing unit 63 corrects the density value and the like.

Further, in the basic configuration, the threshold value determination unit 62 determines both the first determination threshold value Th1 and the second determination threshold value Th2 based on the frequency distribution of the first image and the second image, respectively, but this configuration is indispensable. is not it. That is, the threshold value determination unit 62 determines one of a process of determining the first determination threshold value Th1 based on the frequency distribution of the first image and a process of determining the second determination threshold value Th2 based on the frequency distribution of the second image. You may only do. In this case, the determination threshold value of the first determination threshold value Th1 and the second determination threshold value Th2, whichever is not determined by the threshold value determination unit 62, may be preset as a fixed value.

Further, in the basic configuration, the image of the header region on the leading side of the sheet Sh1 is read as the first image, but the present invention is not limited to this, and for example, the image of the footer region of the sheet Sh1 may be read as the first image.

Further, in the basic configuration, the relationship between the concentration and the concentration value is specified so that the thinner the concentration is, the larger the concentration value is, but the relationship is not limited to this. For example, the higher the concentration is, the larger the concentration is. The relationship between and the concentration value may be specified.

(Embodiment)
In the image reading device 10A (see FIG. 13) according to the present embodiment, the determination unit 61 distinguishes between foreign matter, scratches, stains, etc. of the color reference member 51A and foreign matter, scratches, stains, etc. of the second contact glass 42. It is different from the image reading device 10 according to the basic configuration in that it determines an abnormal pixel. Hereinafter, the same configurations as the basic configurations will be designated by common reference numerals and description thereof will be omitted as appropriate.

In the present embodiment, the determination unit 61 distinguishes between the foreign matter, scratches, stains, etc. of the color reference member 51A and the foreign matter, scratches, stains, etc. of the second contact glass 42, and therefore, basically, the first determination unit The functions of 611 and the first threshold value determination unit 621 are different from the basic configuration. Therefore, the functions of the second determination unit 612 and the second threshold value determination unit 622 are basically the same as the basic configuration.

In the present embodiment, the image reading device 10A reads the image of the color reference member 51A by the image reading unit 2 at a plurality of timings at which the portions facing the image reading unit 2 of the color reference member 51A are different from each other. Acquire a plurality of images of 51A. Then, the determination unit 61 determines the abnormal pixel based on the comparison result between the density value for each pixel and the determination threshold value for these plurality of images. Here, the plurality of images of the color reference member 51A are a plurality of first images, and for these plurality of images (first images), the first determination unit 611 determines the density value for each pixel and the first determination threshold value. The first abnormal pixel is extracted based on the comparison result with Th1.

The "portion facing the image reading unit 2 of the color reference member 51A" referred to in the present disclosure is a portion of the color reference member 51A in which the image can be read by the image reading unit 2. Therefore, on the surface of the color reference member 51A, the portion of the image reading unit 2 facing at least the portion of the image reading unit 2 where the light corresponding to the image to be read is incident via the second contact glass 42 is the image of the color reference member 51A. It is a portion facing the reading unit 2. That is, in the present embodiment, on the surface of the color reference member 51A, the portion of the image reading unit 2 facing at least the reading unit 20, in other words, the portion facing the second contact glass 42 is the “color reference member 51A”. It becomes a portion facing the image reading unit 2 of the above. The image reading device 10A reads the image of the color reference member 51A by the image reading unit 2 at a plurality of timings at which the portions facing the image reading unit 2 of the color reference member 51A are different from each other, whereby a plurality of first images are obtained. To get.

Further, in the present embodiment, the color reference member 51A is a rotatable roller, and the portion of the color reference member 51A facing the image reading unit 2 changes as the roller rotates. As an example in the present embodiment, as shown in FIG. 13, the color reference member 51A guides the course of the sheet Sh1 when the sheet Sh1 passes through the gap between the color reference member 51A and the second contact glass 42. It is a guide roller. The color reference member 51A as the transport guide roller is driven by a power source such as a motor and rotates in the direction (counterclockwise) indicated by the arrow A1 in FIG. As a result, the transport guide roller, which is the color reference member 51A, transports the sheet Sh1 while pressing it downward (on the side of the second contact glass 42). In such a color reference member 51A, the portion facing the image reading unit 2, that is, the portion facing the second contact glass 42 changes due to its rotation (rotation).

Further, in the present embodiment, the plurality of images of the color reference member 51A acquired at a plurality of timings in which the portions facing the image reading unit 2 of the color reference member 51A are different are M images (M is an integer of 2 or more). Is. Then, the determination unit 61 determines that N pixels out of the M images are abnormal pixels at the same position in the main scanning direction D1 from the comparison result between the density value and the determination threshold value. do. Here, "N" is an integer less than or equal to "M". In this embodiment, as an example, N is assumed to have the same value as M. In other words, in all of the M images of the color reference member 51A, the determination unit 61 refers to pixels that are determined to be abnormal from the comparison result between the density value and the determination threshold value at the same position in the main scanning direction D1 as abnormal pixels. judge.

More specifically, when the first determination unit 611 scans the pixel positions in one direction of the main scanning direction D1, the start positions (start points) of the pixels determined to be abnormal in the N first images are determined. If they are substantially the same, it is determined that the pixel is the first abnormal pixel. Here, it is assumed that the "substantial match" of the start position is within a predetermined number of pixels (for example, 3 pixels) as an example. As described above, if the pixels determined to be abnormal are determined to be abnormal at substantially the same position in the N (first) images, the determination unit 61 may not completely match the positions of the pixels. , (1st) It may be determined as an abnormal pixel. As another example, in the N (first) images, the determination unit 61 substantially matches the end positions (end points) of the pixels determined to be abnormal, or is between the start position and the end position. The (first) abnormal pixel may be determined depending on whether or not there is an overlapping region.

Further, in the present embodiment, the threshold value determination unit 62 displays two or more images of the color reference member 51A read by the image reading unit 2 at two or more timings at which the portions facing the image reading unit 2 of the color reference member 51A are different. Is used to determine the determination threshold. That is, the first threshold value determination unit 621 determines the first determination threshold value Th1 by using two or more first images out of the plurality of first images as described above. The threshold value determination unit 62 determines the determination threshold value based on the frequency distribution for the density value of each pixel in two or more images. That is, the first threshold value determination unit 621 determines the first determination threshold value Th1 based on the frequency distribution (histogram) for the density value of each pixel in the two or more first images.

By the way, as a related technique, as described in the basic configuration, a technique for extracting a first abnormal pixel from one first image is known. That is, the image reading device according to the related technology includes an image reading unit capable of reading an image of a conveyed sheet, a density calculation unit, a threshold value determination unit, a determination unit, and an image processing unit. Before reading the sheet, the density calculation unit creates a histogram showing the number of pixels for each density value for the first image (second scanned image) read from the color reference member by the image reading unit, and the first image is based on the histogram. 1 Determine the determination threshold (second threshold). The determination unit determines that among the pixels of the first image, the pixel having a density value higher than the first determination threshold value is the first abnormal pixel (second abnormal pixel) indicating an abnormality.

Further, in the related technology, the density calculation unit is a histogram showing the number of pixels for each density value for the image corresponding to the margin area of the sheet among the second images (first scanned images) read from the sheet by the image reading unit. Is created, and the second determination threshold (first threshold) is determined based on the histogram. The determination unit is a pixel having a density value higher than that of the second determination threshold among the pixels of the second image, and a pixel whose position in the main scanning direction coincides with the first abnormal pixel is referred to as an abnormal pixel indicating an abnormality. judge. Then, the image processing unit corrects the density value of the second image in which the position in the main scanning direction D1 coincides with the abnormal pixel.

However, in the above-mentioned related technique, foreign matter, scratches, stains, etc. of the color reference member may be erroneously detected as foreign matter, scratches, stains, etc. of the contact glass, and the determination accuracy of the abnormal pixel may be lowered. That is, in the related technology, foreign matter, scratches, stains, etc. of the color reference member cannot be distinguished from foreign matter, scratches, stains, etc. of the contact glass. It may be judged that. In the first place, if the color reference member is foreign matter, scratched, or dirty, the sheet is located in front of the color reference member when the image of the sheet is read, so that the read image is not affected. In this case, for example, if there is a ruled line or the like at the same position as the first abnormal pixel in the margin area of the sheet in the main scanning direction D1, the pixel at that position is determined to be an abnormal pixel and the density value is corrected. May be said. As a result, an inaccurate image (original information) may be read as an image on the sheet.

On the other hand, in the present embodiment, by adopting the following configuration, the image reading device 10A is provided in which the determination accuracy of abnormal pixels is less likely to decrease. Hereinafter, an example of the procedure of the image processing method executed by the image reading device 10A will be described with reference to FIGS. 14 and 15. Here, steps S101, S102 ... In the flowchart shown in FIG. 14 represent the numbers of the processing procedures (steps) executed by the processing unit 6. The processes described below (steps S101 to S109) are processes from the input of the image reading instruction to the determination of the first abnormal pixel, and are adopted in place of steps S2 to S7 in the flowchart of FIG. Will be done. Further, in FIG. 15, the timing (sampling timing) for reading an image by the image reading unit 2 is conceptually shown with the left-right direction as the main scanning direction D1 and the vertical direction as the time axis.

<Step S101>
In step S101, the processing unit 6 sets the variable M to "1". In the present embodiment, as an example, the image (first image) of the color reference member 51A is read in each state in which the color reference member 51A is rotated by one-third. Therefore, the upper limit of the variable M is assumed to be "3" in this embodiment.

<Steps S102, S103>
Next, in step S102, the first reading control unit 641 causes the image reading unit 2 to perform a reading operation before the sheet Sh1 reaches the reading position P1. Specifically, the first reading control unit 641 moves the reading unit 20 to the right of FIG. 2 in the sub-scanning direction D2 by a distance of several lines before the sheet Sh1 is detected by the document sensor 78. At the same time, the image reading unit 2 is made to perform reading operations for several lines. At this time, the image reading unit 2 performs a reading operation for reading the image of the color reference member 51A at the timing shown by the sampling timing St11 in FIG. By the above reading operation, the image of the surface of the color reference member 51A is read, and the image reading unit 2 acquires the first image (S103).

<Step S104>
Next, in step S104, the first threshold value determination unit 621 creates a first histogram G1 showing the number of pixels for each density value for the first image obtained in step S103. Further, the first threshold value determination unit 621 determines the first reference density value C1 which is the reference density value in the first image, and is based on the first histogram G1 while using the first reference density value C1 as a reference. The first determination threshold Th1 is determined. As an example, as in the basic configuration, the first threshold value determination unit 621 determines the concentration value “233” obtained by subtracting “3” from the first reference concentration value C1 (236) as the first determination threshold value Th1.

<Step S105>
In step S105, the first determination unit 611 determines whether or not each pixel in the first image is an abnormality candidate pixel as a candidate for the first abnormality pixel. Specifically, the first determination unit 611 compares the density value of the pixels in the first image with the first determination threshold Th1 for each pixel. The first determination unit 611 determines that the (dark) pixel whose density value is equal to or less than the first determination threshold Th1 is an abnormality candidate pixel. When the first determination unit 611 determines that it is an abnormality candidate pixel, it stores the coordinate position of the main scanning direction D1 for each abnormality candidate pixel, thereby specifying the position of the abnormality candidate pixel in the main scanning direction D1.

In the present embodiment, the process of step S105 for determining the abnormality candidate pixel is performed using a first image different from step S104 for determining the first determination threshold value Th1. That is, in executing step S105, the processing unit 6 performs the same processing as in steps S102 and S103 again to acquire the first image. Specifically, the image reading unit 2 performs a reading operation for reading the image of the color reference member 51A at the timing shown by the sampling timing St12 in FIG. 15, and newly acquires the first image. With respect to the newly acquired first image, the first determination unit 611 determines whether or not the first image is an abnormality candidate pixel. However, the present invention is not limited to this example, and the same first image as in step S104 for determining the first determination threshold value Th1 may be used for the process of step S105 for determining the abnormality candidate pixel.

<Step S106>
Next, in step S106, the processing unit 6 determines whether or not the variable M is “3” or more. When the processing unit 6 determines that the variable M is not 3 or more (S106: No), the process proceeds to step S107. When the processing unit 6 determines that the variable M is 3 or more (S106: Yes), the process proceeds to step S109.

<Steps S107, S108>
In step S107, the processing unit 6 increments the variable M. Next, in step S108, the first reading control unit 641 rotates the color reference member 51A by one-third. As a result, on the surface of the color reference member 51A, a portion displaced by one-third of the circumference in the circumferential direction faces the second contact glass 42, and the image reading unit 2 of the color reference member 51A and the like. The opposite part of is changed.

Then, the processing unit 6 returns to step S102 and repeatedly executes steps S102 to S105. In the second step S102, the image reading unit 2 performs a reading operation for reading the image of the color reference member 51A at the timing shown by the sampling timing St13 in FIG. Then, in the second step S105, the image reading unit 2 performs a reading operation of reading the image of the color reference member 51A at the timing shown by the sampling timing St14 in FIG. Then, even in the second step S105, when the first determination unit 611 determines that the abnormality candidate pixel is an abnormality candidate pixel, the first determination unit 611 stores the coordinate position of the main scanning direction D1 for each abnormality candidate pixel, so that the main scan of the abnormality candidate pixel is performed. The position of the direction D1 is specified.

After that, the processing unit 6 increments the variable M in step S107, and in step S108, the first reading control unit 641 further rotates the color reference member 51A by one-third. As a result, on the surface of the color reference member 51A, a portion displaced by one-third of the circumference in the circumferential direction faces the second contact glass 42, and the image reading unit 2 of the color reference member 51A and the like. The opposite part of is further changed. Then, the processing unit 6 returns to step S102 and repeats steps S102 to S105 again. In the third step S102, the image reading unit 2 performs a reading operation for reading the image of the color reference member 51A at the timing shown by the sampling timing St15 in FIG. Then, in the third step S105, the image reading unit 2 performs a reading operation for reading the image of the color reference member 51A at the timing shown by the sampling timing St16 in FIG. Then, even in the third step S105, when the first determination unit 611 determines that the abnormality candidate pixel is an abnormality candidate pixel, the first determination unit 611 stores the coordinate position of the main scanning direction D1 for each abnormality candidate pixel, so that the main scan of the abnormality candidate pixel is performed. The position of the direction D1 is specified.

<Step S109>
In step S109, the first determination unit 611 sets the density value and the determination threshold at the same position in the main scanning direction D1 in N of the M images of the color reference member 51A (N = M in this embodiment). A pixel determined to be abnormal from the comparison result of is determined to be an abnormal pixel. That is, since the upper limit of the variable M is "3" here, the first determination unit 611 is a pixel (abnormality candidate pixel) that is determined to be abnormal at the same position in the main scanning direction D1 in the three first images. ), It is determined that the abnormality candidate pixel is the first abnormality pixel. When the first determination unit 611 determines that the first abnormal pixel is a first abnormal pixel, the first determination unit 611 stores the coordinate position of the main scanning direction D1 for each first abnormal pixel, thereby specifying the position of the main scanning direction D1 of the first abnormal pixel. do.

The procedure of the image processing method described above is only an example, and the order of processing shown in the flowchart of FIG. 14 may be changed as appropriate.

As described above, in the present embodiment, from the images of the color reference member 51A acquired at a plurality of timings (sampling timings St12, St14, St16) in which the portions of the color reference member 51A facing the image reading unit 2 are different from each other. Determine abnormal pixels. That is, in the present embodiment, the abnormal pixel (first abnormal pixel) is determined from the images of a plurality of locations of the color reference member 51A. Therefore, in the case of foreign matter, scratches, stains, etc. of the color reference member 51A, if the abnormality does not appear in the plurality of first images in the same manner, foreign matter, scratches, stains, etc. of the color reference member 51A can be used. It is possible to distinguish foreign matter, scratches, dirt, etc. from the second contact glass 42. Therefore, the determination unit 61 excludes foreign matter, scratches, stains, etc. from the color reference member 51A from the abnormal pixels (first abnormal pixels), so that the determination unit 61 originally causes foreign matter, scratches, stains, etc. on the second contact glass 42. It becomes easy to determine the abnormal pixel of the above as an abnormal pixel. As a result, the image reading device 10A has an advantage that the determination accuracy of abnormal pixels is unlikely to decrease.

Further, in the present embodiment, since the portion of the color reference member 51A facing the image reading unit 2 is changed as the roller rotates as the color reference member 51A, images of a plurality of locations of the color reference member 51A can be easily acquired. can.

Further, in the present embodiment, the determination unit 61 determines that N of the M images are abnormal (abnormal candidate pixels) from the comparison result between the density value and the determination threshold value at the same position in the main scanning direction D1. The determined pixel is determined to be an abnormal pixel (first abnormal pixel). Therefore, if the value of "N" with respect to "M" is adjusted, the determination accuracy of the abnormal pixel can be easily adjusted. Here, N is not limited to the same value as M, and for example, M may be "3" and N may be "2".

Further, in the present embodiment, not only the determination of the abnormal pixel (first abnormal pixel) but also the determination of the determination threshold value (first determination threshold Th1) used for the determination of the abnormal pixel is performed at a plurality of locations (2) of the color reference member 51A. (More than one place) images are used. Therefore, the first determination threshold value Th1 can be set in consideration of the local discoloration of the color reference member 51A, which leads to improvement in the determination accuracy of the abnormal pixel (first abnormal pixel). In particular, in the present embodiment, since the frequency distribution of the first image is used to determine the determination threshold value (first determination threshold value Th1), even if there is local discoloration of the color reference member 51A, the determination threshold value (first determination threshold value) is used. It is easy to set the determination threshold Th1) to an appropriate value.

As a modification of the embodiment, the color reference member 51A may be a member other than the rotatable roller, for example, a transport guide as described in the basic configuration. In this case, it is preferable that the color reference member 51A is movable, and the portion of the color reference member 51A facing the image reading unit 2 changes with the movement of the color reference member 51A. That is, if the color reference member 51A moves, for example, in the main scanning direction D1 or the sub-scanning direction D2, the portion of the color reference member 51A facing the image reading unit 2 changes. By such movement, it becomes easier to distinguish between the foreign matter, scratches, stains, etc. of the color reference member 51A and the foreign matter, scratches, stains, etc. of the second contact glass 42. Further, even if the color reference member 51A is a roller, if movement other than rotation, for example, movement in the thrust direction is possible, the portion of the color reference member 51A facing the image reading unit 2 may be affected by the movement. Change.

Alternatively, the color reference member 51A may be fixed and the image reading unit 2 (reading unit 20) may move. Even in this case, the relative positional relationship between the color reference member 51A and the reading unit 20 changes, so that the portion of the color reference member 51A facing the image reading unit 2 changes as the roller rotates. Of course, both the color reference member 51A and the image reading unit 2 (reading unit 20) may be movable.

Further, as a modification of the embodiment, the threshold value determination unit 62 does not have to determine at least one of the first determination threshold value Th1 and the second determination threshold value Th2 based on the frequency distribution (histogram). In this case, the determination threshold value of the first determination threshold value Th1 and the second determination threshold value Th2, whichever is not determined by the threshold value determination unit 62, may be preset as a fixed value.

1 Image forming device 2 Image reading unit 3 Image forming unit 10, 10A Image reading device 51, 51A Color reference member 61 Judgment unit 62 Threshold determination unit 63 Correction processing unit R1 Transport path Rm1 Margin area Sh1 Sheet Th1 First determination threshold Th2 First 2 Judgment threshold

Claims (11)

An image reader that reads the image of the sheet transported through the transport path,
The image reading unit is a color reference member arranged so as to face each other across the transport path.
The comparison result between the density value for each pixel and the determination threshold value for a plurality of images of the color reference member read by the image reading unit at a plurality of timings at which the portions of the color reference member facing the image reading unit are different. A determination unit for determining an abnormal pixel based on the
Image reader. The determination unit
For the plurality of first images, which are the plurality of images, the first abnormal pixel is extracted by comparing the density value for each pixel with the first determination threshold value as the determination threshold value.
For the second image, which is an image of the margin area of the sheet read by the image reading unit, the second abnormal pixel is extracted by comparing the density value for each pixel with the second determination threshold value.
The abnormal pixel is determined according to the degree of coincidence between the first abnormal pixel and the second abnormal pixel.
The image reading device according to claim 1. A threshold value determining unit that determines the determination threshold value using two or more images of the color reference member read by the image reading unit at two or more timings at which the portions of the color reference member facing the image reading unit are different. Further prepare
The image reading device according to claim 1 or 2. The threshold value determination unit determines the determination threshold value based on the frequency distribution for the density value of each pixel in the two or more images.
The image reading device according to claim 3. The color reference member is movable, and the portion of the color reference member facing the image reading portion changes with the movement of the color reference member.
The image reading device according to any one of claims 1 to 4. The color reference member is a rotatable roller, and the portion of the color reference member facing the image reading portion changes with the rotation of the roller.
The image reading device according to any one of claims 1 to 4. The plurality of images are M images, and are
The determination unit determines that N pixels out of the M images are abnormal pixels at the same position in the main scanning direction from the comparison result between the density value and the determination threshold value. ,
The image reading device according to any one of claims 1 to 6. A correction processing unit for correcting the density value of a pixel whose position in the main scanning direction coincides with the abnormal pixel among the images read by the image reading unit is further provided.
The image reading device according to any one of claims 1 to 7. The image reading device according to any one of claims 1 to 8.
An image forming unit for forming an image of the sheet read by the image reading device on another sheet is provided.
Image forming device. Reading the image of the sheet transported through the transport path with the image reader and
A plurality of the color reference members read by the image reading unit at a plurality of timings in which the image reading unit and the color reference member arranged so as to face each other across the transport path have different portions facing the image reading unit. It has the determination of abnormal pixels based on the comparison result between the density value for each pixel and the determination threshold value for the image of.
Image processing method. Reading the image of the sheet transported through the transport path with the image reader and
A plurality of the color reference members read by the image reading unit at a plurality of timings in which the image reading unit and the color reference member arranged so as to face each other across the transport path have different portions facing the image reading unit. Judgment of abnormal pixels based on the comparison result between the density value for each pixel and the judgment threshold value for the image of
A program to run one or more processors.

Images