JP2013066066A - Image reader and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image reader capable of detecting the attachment of dust, etc. and the show-through of an image by using only a manuscript to be read first, and also effectively preventing deterioration of an image even with respect to the manuscript to be read first.SOLUTION: An image reader includes: a background board; reading means for acquiring image data by reading one surface side and the other surface side of a manuscript carried onto the background board by carrying means while including show-through from the other surface side to the one surface side and show-through from the one surface side to the other surface side; detection means for detecting a dust candidate pixel from the image data of the image read through the reading means; and determination means for determining the presence/absence of dust that requires correction of image data on the basis of the detection result of the detection means.

Description

  The present invention relates to an image reading apparatus and an image forming apparatus that scan an original in a sub-scanning direction with a linear image sensor and read an image.

  2. Description of the Related Art Conventionally, an image reading apparatus that automatically reads image information of a document is used as a reading apparatus such as a copying machine or a facsimile, or a scanner for computer input.

  As an image reading method in the image reading apparatus, there are a carriage reading method in which an original is placed on a contact glass to read an image, and a sheet through reading method in which an original is conveyed by an ADF (auto document feeder) to read an image. There are two types.

  In the case of the sheet-through reading method, if there is dust or dirt on the document, contact glass, background plate, etc., the dust is held at the same position with respect to the reading sensor when the document is transported. There is a problem that vertical stripes appear in the scanning direction) and image quality is degraded.

  Conventionally, in order to detect the dust and the like, as described in Japanese Patent Application Laid-Open No. 2004-228561, reading of a background plate provided at a document reading position of a document conveying device performed before a document is conveyed to a reading position. A method is known in which image data is compared with read image data at the leading edge of a document, which is a normal margin, which is performed after document conveyance. When dust or the like is detected, the image is corrected based on the detection result so as to reduce vertical stripes.

  A specific example of the detection method described above is shown in FIG. In this detection method, two originals are used, the reading of the background plate before transporting the previous original, the reading of the leading edge of the original of the previous original, the reading of the background plate before conveying the original of the next original, and the next The leading edge of the document is read. Based on the image data obtained by each reading, the presence / absence of dust or the like adhering to the glass (contact glass) for the image reading unit or the background plate is determined.

  The determination result 1 in FIG. 11 is a case where, among the four image data obtained by the above four readings, only a portion that may be dust is detected only in the image data at the leading edge of the previous document. Show. In this case, since there is no possibility of detecting dust or the like in any of the image data of the background plate before transporting the previous document and the background plate before transporting the next document, to the contact glass, the background plate, etc. There is no adhesion of dust, and it is determined that the detected image is an image formed at the leading edge of the document.

  The determination result 2 in FIG. 11 shows a case where a part that may be dust or the like is detected in three pieces of image data other than the image data of the background plate before transporting the previous document among the four pieces of image data. . In this case, the image data of the background plate before transporting the previous document did not detect any possible part such as dust, but the leading edge of the previous document, the background plate before transporting the subsequent document, and the next document In the image data at the leading edge of the document, a portion that may be dust is detected. This is because a part such as dust is detected in any image data on the background plate and the leading edge of the document between the start of the conveyance of the previous document and the start of the conveyance of the next document. It is determined that dust or the like is attached on the contact position, that is, on the contact glass.

  The determination result 3 in FIG. 11 shows a case where a part that may be dust or the like is detected in the image data of the leading edge of the previous document and the image data of the background plate of the next document before transporting the document. In this case, a possible portion such as dust is detected in the image data of the leading edge of the previous document and the background plate before the subsequent document conveyance. This is the position at which a possible part such as dust is detected on either the background plate or the front end of the document between the start of transport of the previous document and the start of transport of the next document. That is, it is determined that dust or the like is attached on the contact glass. In this case, since there is no possibility of detecting dust or the like in the image data at the leading edge of the next document, the document is transported until the next document reaches the image reading unit. It is thought that garbage was removed.

  The determination result 4 in FIG. 11 shows a case where a part that may be dust or the like is detected in the image data of the document leading edge of the previous document and the document leading edge of the next document. In this case, since there is no possibility of detecting dust or the like in any of the image data of the background plate before transporting the previous document and the background plate before transporting the next document, to the contact glass, the background plate, etc. There is no adhesion of dust, and it is determined that the detected images are the images formed on the two document front ends.

  Although not shown in FIG. 11, when no possible part such as dust is detected in any of the above four image data, neither dust is attached nor the image formed on the leading edge of the document. It will not exist.

  Further, as an image reading apparatus adopting a sheet-through reading method, there is an image reading apparatus that reads both sides of a document on which images are formed on both sides with one conveyance without inverting the front and back of the document. In such an image reading apparatus, when an image on one side is read, the image on the other side may show through and image quality may deteriorate. In order to cope with this problem, as described in Japanese Patent Application Laid-Open No. H10-228707, the read double-sided images are compared and the influence of show-through is corrected.

  In the method of comparing the image data of the background plate before document conveyance and the image data of the leading edge of the document described in Patent Document 1 described above, if these two image data are different, the next document is used. Unless further image data is obtained, it cannot be determined whether the cause of the difference is dust or an image on the original. For this reason, there is a possibility that dust or the like cannot be properly detected when the previous document is read.

  Further, in the image reading apparatus described in Patent Document 2 described above, vertical streaks due to dust or the like may occur. Therefore, dust or the like is detected using the method described in Patent Document 1. The image can be corrected. However, even in this image forming apparatus, when the image data of the background plate before the document conveyance is different from the image data of the document leading edge, it is necessary to determine whether the difference is caused by show-through or dust. However, this determination also requires a detection result using the next document. For this reason, there is a possibility that dust or the like cannot be properly detected when the previous document is read.

  The present invention has been made in view of the above problems, and in an image reading apparatus that reads both sides of a document, it is possible to detect adhesion of dust and the like and show-through of an image using only the document that is read first. Another object of the present invention is to provide an image reading apparatus and an image forming apparatus using the same that can effectively prevent image deterioration even with respect to a document that is read first.

  In order to solve the above-described problems and achieve the object, the present invention provides a background plate, a conveyance unit that conveys an original on the background plate, a background plate, and a document conveyed on the background plate by the conveyance unit. A reading unit that obtains read image data including a show-through from the other side to the one side and a show-through from the other side to the other side, and an image read by the reading unit. An image reading apparatus comprising: a detection unit that detects dust candidate pixels from image data; and a determination unit that determines the presence or absence of dust that requires image data correction based on a detection result of the detection unit. To do.

  The present invention also provides an image forming apparatus in which image data obtained by an image reading apparatus is corrected and image formation is performed based on the corrected image data. A reading device is provided.

  According to the present invention, it is possible to detect adhesion of dust or the like and show-through of an image using only the first read original, and effectively prevent image deterioration even for the first read original. There is an effect that can be.

FIG. 1 is a schematic configuration diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a sectional view showing the automatic document feeder of the image forming apparatus. FIG. 3 is a block diagram showing each configuration for performing image data processing in the image forming apparatus. FIG. 4 is a model diagram showing dust attached to the image reading unit of the image forming apparatus. FIG. 5 is a model diagram illustrating the influence of dust attached to the image reading unit on the read image data. FIG. 6 is a block diagram showing an image processing editing unit that performs dust detection processing and dust correction processing, and the surrounding configuration. FIG. 7 is a block diagram showing the configuration of the dust detection unit of the image processing editing unit. FIG. 8 is a model diagram illustrating the show-through of the image on the document. FIG. 9 is a model diagram illustrating a method for determining an image on one side of a document and dust by the dust determination unit of the image processing editing unit. FIG. 10 is a model diagram illustrating a method of determining an image and dust on the other side of the document by the dust determination unit. FIG. 11 is a model diagram for explaining a conventional dust determination method.

  Embodiments of an image reading apparatus and an image forming apparatus according to the present invention will be described below.

  FIG. 1 is a schematic configuration diagram showing a copying machine 1 as an embodiment of an image forming apparatus according to the present invention. The copying machine 1 includes an automatic document feeder (hereinafter simply referred to as ADF) 2, a paper feeding unit 3, an image reading unit 4, and an image forming unit 5.

  The ADF 2 includes a document tray 11 and a transport unit 13 including various rollers. The ADF 2 transports the document placed on the document tray 11 onto the slit glass 7 by the transport unit 13, and the document that has been read by the image reading unit 4 through the slit glass 7 on the slit glass 7. After that, the paper is discharged to the paper discharge tray 12. The ADF 2 is attached to the image reading unit 4 so as to be freely opened and closed via an opening / closing mechanism (not shown).

  The paper feeding unit 3 includes paper feeding cassettes 21 and 22 that store recording papers having different paper sizes, and various rollers that transport the recording papers stored in the paper feeding cassettes 21 and 22 to the image forming position of the image forming unit 5. The sheet feeding means 23 is provided.

  The image reading unit 4 includes a first carriage 25 on which a light source and a mirror member are mounted, a second carriage 26 on which a mirror member is mounted, an imaging lens 27, and an imaging unit 28. The image reading unit 4 irradiates light on a document passing over the slit glass 7 by a light source mounted on the first carriage 25. Then, the reflected light from the original is folded back by each mirror member mounted on the first carriage 25 and the second carriage 26, and the reflected light is imaged by the imaging lens 27 and read by the imaging unit 28.

  The image forming unit 5 includes an exposure device 31, a photosensitive drum 32, a developing device 33, a transfer belt 34, and a fixing device 35. The image forming unit 5 exposes the photosensitive drum 32 by the exposure device 31 based on the read image read by the imaging unit 28 to form a latent image on the photosensitive drum 32, and the photosensitive drum 32 by the developing device 33. The toner is supplied with different colors and developed. The image developed on the photosensitive drum 32 by the transfer belt 34 is transferred to the recording paper supplied from the paper supply unit 3, and the toner of the toner image transferred to the recording paper by the fixing device 35 is melted, so that the recording paper A color image is fixed on the screen.

  As shown in FIG. 2, the document tray 11 includes a movable document table 41 and a pair of side guide plates 42. The movable document table 41 constitutes a substantially first half portion of the document tray 11 in the sheet feeding direction, and rotates in the vertical direction with the base end portion as a fulcrum. In this manner, the document tray 11 can adjust the front end of the document placed on the document tray 11 to an appropriate height by rotating the movable document table 41.

  A table raising sensor 87 is provided above the front end of the movable document table 41. The table raising sensor 87 detects whether or not the front end portion of the document placed on the document placement surface is held at an appropriate height (appropriate sheet feeding position). Note that the proper paper feed position according to the embodiment of the present invention refers to a position where the uppermost document in the bundle of documents and a pickup roller 61 described later come into contact.

  A home position sensor 88 is provided below the front end of the movable document table 41. Home position sensor 88 detects that movable document table 41 is at the home position.

  Document length detection sensors 89 and 90 for detecting whether the orientation of the document is vertical or horizontal are provided in a substantially latter half of the paper feed direction of the document tray 11 so as to be separated in the feeding direction. Yes. As the document length detection sensors 89 and 90, a reflection type sensor that detects without contact by optical means or a contact type actuator type sensor can be used.

  The pair of side guide plates 42 are erected so as to position in the left-right direction with respect to the feeding direction of the document placed on the document tray 11. Since one of the pair of side guide plates 42 can slide in the left-right direction with respect to the paper feeding direction, documents of different sizes can be placed on the document tray 11. A pair of rotating ribs 45 as movable members to be described later are provided on opposing surfaces of the pair of side guide plates 42.

  The other of the pair of side guide plates 42 is fixed, and a set filler 46 that rotates when the document is placed is provided. A document set sensor 82 that detects that a document has been placed on the document tray 11 is provided at the bottom of the movement locus of the tip of the set filler 46. The document set sensor 82 issues a signal for rotating the set filler 46 when a document is placed on the document tray 11. Then, it is detected that the front end of the set filler 46 is detached from the document set sensor 82 and the document is placed.

  The transport unit 13 of the ADF 2 includes a separation feeding unit 51, a pull-out unit 52, a turn unit 53, a first reading transport unit 54, a second reading transport unit 55, and a paper discharge unit 56. .

  The separation feeding unit 51 includes a pickup roller 61 disposed in the vicinity of the sheet feeding port, and a sheet feeding belt 62 and a reverse roller 63 that are disposed so as to face each other across the conveyance path and are in contact with each other.

  The pick-up roller 61 is supported by a support arm member 64 attached to the paper feed belt 62, and is between a contact position that contacts the document bundle via a cam mechanism (not shown) and a separation position that is separated from the document bundle. It is designed to move up and down. The paper feeding belt 62 rotates in the feeding direction. The reverse roller 63 rotates in the same direction as that of the paper feed belt 62 when the original is double fed. As a result, the multi-fed originals are separated, and only the original that contacts the paper feeding belt 62 is sent in the feeding direction. Further, when the reverse roller 63 is in contact with the paper feed belt 62 or when only one document is conveyed, the reverse roller 63 is driven by the paper feed belt 62 by the action of a torque limiter (not shown), that is, the paper feed belt 62. The paper belt 62 rotates in the opposite direction.

  The separation feeding unit 51 feeds the document into the sheet feeding port by the rolling contact of the pickup roller 61 with the uppermost document in the document bundle placed on the document tray 11, and the sheet feeding belt when the document is fed in multiple times. 62 and the reverse roller 63 are separated and sent out.

  The pull-out unit 52 has a pull-out roller 65 composed of a pair of rollers arranged so as to sandwich the conveyance path. The pull-out unit 52 adjusts the driving timings of the pull-out roller 65 and the pickup roller 61, thereby aligning the delivered document with primary abutment and pulling out and transporting the aligned document. The pull-out roller 65 is provided with a paper thickness measurement sensor 91 for measuring the paper thickness.

  The turn portion 53 includes an intermediate roller 66 and a reading entrance roller 67 that are a pair of rollers disposed so as to sandwich a curved portion that curves from the top to the bottom of the conveyance path. The turn part 53 turns the original drawn and conveyed by the intermediate roller 66 by conveying the curved part, and conveys the original surface downward by the reading entrance roller 67 to the vicinity of the slit glass 7. ing.

  The first reading / conveying unit 54 includes a roller-shaped first background plate 68 disposed at a position facing the slit glass 7 across the conveyance path, and a pair of rollers disposed so as to sandwich the conveyance path after completion of reading. And a first reading exit roller 69. The first reading / conveying unit 54 conveys the surface of the original conveyed to the vicinity of the slit glass 7 while being in contact with the slit glass 7, and further conveys the original after reading by the first reading exit roller 69. ing.

  The second reading conveyance unit 55 includes a second reading roller 70 as a second background plate disposed at a position facing the second reading unit 101 that reads the back side of the document with the conveyance path interposed therebetween, and the reading of the back side of the document is completed. And a pair of second reading exit rollers 71 disposed so as to sandwich the subsequent conveyance path. The second reading and conveying unit 55 passes the document whose surface has been read by the second reading roller 70 in front of the reading surface of the second reading unit 101 and conveys the document toward the paper discharge port by the second reading exit roller 71. It is like that. In the case where double-sided scanning is not performed, the document passes through the second reading unit 101.

  The paper discharge unit 56 is provided with a pair of paper discharge rollers 72 in the vicinity of the paper discharge port, and discharges the original conveyed by the second reading exit roller 71 to the paper discharge tray 12.

  In addition, the ADF 2 is provided with an abutment sensor 84, a reading entrance sensor 86, a registration sensor 81, and a paper discharge sensor 83 along the conveyance path, and is used for conveyance control such as a conveyance distance and a conveyance speed of the document. It is like that. Further, a document width sensor 85 is provided between the pull-out roller 65 and the intermediate roller 66. The document width sensor 85 is composed of a plurality of light receiving elements arranged in the width direction of the document, and detects the document width based on the light reception result from the irradiation light provided at the opposite position across the conveyance path.

  FIG. 3 is a block diagram illustrating an outline of a control mechanism that processes image data of the multifunction machine 1 according to the present embodiment. The multifunction device 1 has, as a control mechanism for processing image data, an image reading unit 4 as a first reading unit, a second reading unit 101 as a second reading unit, an image data receiving unit 102, and a memory control unit 103. A memory 104, an image processing editing unit 105, a writing image processing unit 106, a VDC 107, a VDB 108, a CPU 109, a ROM 110, a RAM 111, an image memory control unit 114, and an ADF control unit 115. .

  The image data read by the image reading unit 4 is input to the image data receiving unit 102. The image data receiving unit 102 performs shading correction on the image data read by the image reading unit 4, and is a photoelectric conversion device used in the level difference due to the region of the image data by the light amount distribution of the light source and the image reading unit 4. The level difference between each pixel generated when reading is corrected.

  The memory control unit 103 stores the transmitted image data in the memory 104 in units of frames, takes out the stored image data for each frame in accordance with an instruction from the CPU 109, and sends it to the image processing editing unit 105 in the next stage.

  The image processing editing unit 105 performs image processing on various types of image data. Note that dust detection processing and dust correction processing, which will be described later, performed in the multifunction machine 1 are performed by the image processing editing unit 105.

  The image data processed by the image processing editing unit 105 is sent to the image memory control unit 114. The image memory control unit 114 adjusts the processing speed between the reading process and the writing process and performs various processes in units of pages. For this reason, although not shown here, an image memory and storage for storing a large amount of image data are provided so as to be compatible with various processes.

  When image data processing is performed by the image memory control unit 114, processing for copying and outputting the image data is performed thereafter. Specifically, the image data is sent again to the image processing editing unit 105, and the image data received by the image processing editing unit 105 is sent to the writing image processing unit 106. The written image processing unit 106 performs image processing for copy output.

  The image data that has been subjected to the image processing by the writing image processing unit 106 is sent to the VDC 107, where the processing for adjusting the shape of the image data for transferring the image data is performed in the VDC 107 and then in the exposure device 31. Sent to the VDB 108.

  The VDB 108 emits a laser diode to perform exposure processing on the photosensitive drum 32, and forms a latent image corresponding to the image data on the photosensitive drum 32.

  On the other hand, the image data read by the second reading unit 101 has the same flow. That is, the image data read by the second reading unit 101 is input to the image data receiving unit 102 and subjected to processing such as shading correction, and then sent to the memory control unit 103.

  The image data read by the image reading unit 4 and the image data read by the second reading unit 101 are processed in parallel up to the memory 104. After the image data is stored in the memory 104, the image data is extracted from the memory 104 and processed in units of frames.

  The CPU 109 performs overall control of image processing in the multifunction machine 1, and a program for that purpose is stored in the ROM 110. A RAM 111 is used as a work area necessary for the CPU 109 to operate.

  The ADF control unit 115 that controls the operation of the ADF 2 performs information communication with the CPU 109 to adjust the document conveyance timing.

  The document reading by the ADF 2 described above is performed by reading the document passing between the slit glass 7 and the background plate 68 while the reading position by the image reading unit 4 is fixed. A case where dust adheres to the reading position of the image reading unit 4 will be described.

  FIG. 4A shows a case where dust is not attached to the reading position. In this case, the image reading unit 4 can read the document without being affected by dust.

  FIG. 4B shows a case where dust D adheres to the slit glass 7 at the reading position. In this case, since dust D exists between the image reading unit 4 and the original, the influence of the dust D occurs on the read image data of the original. Since the image reading unit 4 always reads the dust D, an abnormal image in the sub-scanning direction, so-called vertical streak, is generated on the read image data of the document.

  FIG. 4C shows a case where dust D adheres to the background plate 68 at the reading position. In this case, dust D exists behind the document as viewed from the image reading unit 4. For this reason, the dust D is hidden behind the original during reading of the original, and no abnormal image is generated on the read image data of the original. The dust D is read by the image reading unit 4 except when reading the original.

  FIG. 4D shows a case where dust does not adhere to the reading position and information (for example, vertical lines) I is written on the document. In this case, the image reading unit 4 reads the document as it is without being affected by dust.

  By the way, dust adhering to the reading position is classified into dust that adheres and does not easily move (hereinafter referred to as “fixed dust”) and dust that does not adhere and easily moves (hereinafter referred to as “floating dust”). However, in the dust determination method described later, it is determined whether the image is a dust image or an original image without distinguishing between fixed dust and floating dust.

  As described with reference to FIG. 4, due to dust adhering to the reading position, an abnormal image in the sub-scanning direction is generated in the read image data. The influence of dust on the read image data will be described below.

  FIG. 5 shows image data read by the image reading unit 4. The horizontal direction indicates the main scanning direction, and the vertical direction indicates the sub-scanning direction (time axis). Dust (b), dust (c), and document information (d) correspond to the dust described in FIG. 4, and are described in the dust on the slit glass 7, the dust on the background plate 68, and the document, respectively. Shows the information.

  In the case of dust (b), the image reading unit 4 always reads this dust regardless of whether there is a document. For this reason, abnormal images occur both inside and outside the document area.

  In the case of dust (c), the image reading unit 4 does not read the dust while reading the document, and reads the dust when the document is not being read.

  In the case of document information (d), the image reading unit 4 reads this information while reading the document, and does not read this information when the document is not being read.

  As described above, only the dust (b), that is, dust on the slit glass 7 appears as an abnormal image in the read image data of the document, and the dust (c), that is, dust on the background plate 68 does not appear as an abnormal image. . Information (d) is information on the document itself. Therefore, it is necessary to judge only dust (b) as dust.

  As described above, the dust detection process and the dust correction process are performed by the image processing editing unit 105. Hereinafter, the configuration of the image processing editing unit 105 will be described.

  As illustrated in FIG. 6, the image processing editing unit includes a dust detection unit 201, a dust determination unit 202, a line memory 203, and a dust correction unit 204.

  The dust detection unit 201 performs dust pixel position detection processing based on the image data input from the memory control unit 103. Note that the following two types of image data are used for detection. One is read image data of the background board 68 acquired before reading the document. The dust detection operation for this image data is referred to as first dust detection. The other is read image data at the leading edge of the document acquired during document reading. The dust detection operation for this image data is called second dust detection. The first dust detection result and the second dust detection result are stored in the line memory 203 via the dust determination unit 202, respectively.

  The dust determination unit 202 determines whether dust is to be detected from the first dust detection result and the second dust detection result stored in the line memory 203. Specifically, the result of the first dust detection and the result of the second dust detection are compared, and the pixel in which the dust common to both is detected is determined as the above-described dust (b), that is, the dust on the slit glass 7. To do. This dust determination result is stored in the line memory 203.

  In addition, the dust determination unit 202 determines whether the detection results match from the first dust detection result and the second dust detection result, and the determination result is transferred to the CPU 109.

  The dust correction unit 204 performs correction processing on the image data input from the memory control unit 103 in accordance with the dust determination result stored in the line memory 203. Specifically, the dust correction unit 204 replaces pixels determined to have dust with interpolation data calculated from image data of surrounding pixels. The image data corrected by the dust correction unit 204 is output to the subsequent image processing of the image processing editing unit 105, and various other image processing is performed.

  The CPU 109 executes the ADF 2 document conveyance controlled by the ADF control unit 115, the document reading by the image reading unit 4, and the dust detection operation by the dust detection 201 in accordance with the match determination result by the dust determination unit 202. Select an action. Specifically, when the coincidence determination result is Yes (match), the ADF control unit 115, the image reading unit 4, and the dust detection unit 201 are controlled not to execute the first dust detection before the next document reading. To do.

  As shown in FIG. 7, the dust detection unit 201 includes a first detection unit 301, a second detection unit 302, a show-through information detection unit 303, and a DDR-SDRAM (hereinafter referred to as “DDR”) 304.

  The first detection unit 301 reads the read image data of the background plate 68 acquired before the original is conveyed to the image reading unit 4 and the read image data on the front side of the front end of the original conveyed to the image reading unit 4. Perform dust detection.

  The second detection unit 302 reads the image data of the second reading roller 70 acquired before the document is conveyed to the second reading unit 101, and the back side of the leading end of the document conveyed to the second reading unit 101. Dust detection is performed on the read image data.

  The show-through information detection unit 303 detects show-through of a document image, which will be described later.

  The DDR 304 adjusts the transmission timing of the image data to the show-through information detection unit 303 according to the status of the system used.

  The detection of the show-through of the document image by the show-through information detection unit 303 described above will be described.

  First, a state in which an image on the front surface or the back surface of a document shows through on the back surface or front surface of the document will be described with reference to FIG. FIG. 8A shows a state in which when the front side of the document is read by the image reading device, the image on the back side is seen through (through) and read by the image reading device. FIG. 8B shows a state in which when the back side of the document is read by the image reading device, the image on the front side is seen through the back side (shown back) and read by the image reading device. Such show-through may not occur due to the influence of the background level of the document, the thickness of the paper, and the like. In that case, show-through to the front surface of the image on the back surface can be caused by applying light from the surface (back surface) opposite to the surface on which the document is read (front surface).

  A dust determination method by the dust determination unit 202 of the image processing editing unit 105 will be described with reference to FIGS. 9 and 10. Note that the dust is quite small and the digital value captured by the image reading apparatus is low, so that it does not face behind. It is assumed that the timing for reading both sides of the document and the timing for reading the show-through are the same.

  FIG. 9 shows a method of determining the image and dust on the document surface by the dust determination unit 202 using determination results 1 to 4 as an example. In any of the determination results 1 to 4, there is no possibility of dust in the image data obtained by reading the background plate 68 before the document is conveyed to the image reading unit 4. When a portion that may be dust appears on the front end surface of the document conveyed to the document reading unit 4 (second stage state), it cannot be determined whether it is dust or an image of the document.

[Judgment result 1]
No image is detected in the read image data of the back surface of the leading edge of the document by the second reading unit 101 (third stage state). Therefore, it can be seen that show-through to the front surface of the back image does not occur. Further, from the read image data on the back surface, show-through to the back surface of the front image is not detected (fourth stage state). Therefore, it can be seen that there is no image on the surface. That is, since there is no image on the front surface of the original document and no image on the back surface, it is determined that dust appears in the image data on the front surface of the original document.

[Judgment result 2]
An image is detected in the read image data of the back surface of the leading edge of the document by the second reading unit 101 (third stage state). In addition, show-through on the back of the front image is also detected (fourth stage state). For this reason, it is determined that an image exists on the front surface of the original document and that the image on the back surface shows through on the front surface.

[Judgment result 3]
An image is detected in the read image data of the back surface of the leading edge of the document by the second reading unit 101 (third stage state). Further, from the read image data on the back surface, show-through to the back surface of the front image is not detected (fourth stage state). For this reason, it is determined that there is no image on the front surface and the image on the back surface shows through on the front surface.

[Judgment result 4]
No image is detected in the read image data of the back surface of the leading edge of the document by the second reading unit 101 (third stage state). Therefore, it can be seen that show-through to the front surface of the back image does not occur. Also, show-through on the back of the front image is detected (fourth stage state). For this reason, it is determined that an image exists on the surface of the leading edge of the document.

  FIG. 10 shows a determination result 5 to 8 as an example of a method for determining the image and dust on the back side of the document by the dust determination unit 202. In any of the determination results 5 to 8, there is no possibility of dust in the image data read by the second reading roller 70 before the document is conveyed to the second reading unit 101. When a portion that may be dust appears on the back surface of the front end of the document conveyed to the second reading unit 101 (second stage state), it cannot be determined whether it is dust or an image of the document.

[Judgment result 5]
No image is detected in the read image data on the surface of the leading edge of the document by the image reading unit 4 (third stage state). Therefore, it can be seen that show-through on the back surface of the front image does not occur. Further, no show-through to the front side of the back side image is detected from the read image data of the front side (fourth stage state). Therefore, it can be seen that there is no image on the back surface. That is, since there is no image on the back surface of the front end portion of the document and there is no image on the front surface, it is determined that dust appears in the image data on the back surface of the front end portion of the document.

[Judgment result 6]
An image is detected in the read image data on the surface of the leading edge of the document by the image reading unit 4 (third stage state). In addition, show-through to the front surface of the back image is also detected (fourth stage state). For this reason, it is determined that an image exists on the back surface of the front end portion of the document and that the image on the front surface shows through on the back surface.

[Judgment result 7]
An image is detected in the read image data on the surface of the leading edge of the document by the image reading unit 4 (third stage state). Further, no show-through to the front side of the back side image is detected from the read image data of the front side (fourth stage state). For this reason, it is determined that there is no image on the back surface and the image on the front surface is show-through on the back surface.

[Judgment result 8]
No image is detected in the read image data on the surface of the leading edge of the document by the image reading unit 4 (third stage state). Therefore, it can be seen that show-through on the back surface of the front image does not occur. In addition, show-through to the front surface of the back image is detected (fourth stage state). Therefore, it is determined that an image exists on the back surface of the leading edge of the document.

  In the conventional method described above (see FIG. 11), it is necessary to read the image on the background plate 68 before the next original is conveyed and to make a determination using the image of the leading edge of the next original conveyed. It was. However, in the determination method executed in the image reading apparatus and the image forming apparatus according to the present embodiment, it is not necessary to use the next document, and image correction including the influence of the show-through image is performed on the first document. It can be carried out.

  When dust or the like is detected by the above-described determination method, the image data is corrected so as to reduce vertical stripes.

  Note that if no possible part of dust is detected in any of the above-described image data, there is no attachment of dust or an image formed on the leading edge of the document. In addition, when a portion that may be dust or the like is detected in any image, it can be seen that dust or the like exists on the slit glass 7 or the slit glass (not shown) of the second reading unit 101. In this case, it is preferable that image data correction for reducing vertical stripes is performed without performing the above-described determination method.

  In the above-described embodiment, the determination of reading both sides of the document is performed using the two reading mechanisms of the image reading unit 4 and the second reading unit 101. However, the present invention is not limited to this, and determination can be made if both sides of the document can be read. Therefore, only one reading mechanism may be used and both sides of the document may be read by inverting the document.

1 Copier 2 Automatic document feeder (ADF)
DESCRIPTION OF SYMBOLS 3 Paper feed part 4 Image reading part 5 Image formation part 7 Slit glass 13 Conveyance part 21, 22 Paper feed cassette 23 Paper feed means 25 1st carriage 26 2nd carriage 27 Imaging lens 28 Imaging part 31 Exposure apparatus 32 Photosensitive drum 33 Developing Device 34 Transfer Belt 35 Fixing Device 41 Movable Document Table 42 Side Guide Plate 46 Set Filler 51 Separation Feeder 52 Pull-Out Portion 53 Turn Portion 54 First Reading Transport Portion 55 Second Reading Transport Portion 56 Paper Discharge Portion 61 Pickup Roller 62 Feed belt 63 Reverse roller 64 Support arm member 65 Pull-out roller 66 Intermediate roller 67 Reading entrance roller 68 First background plate 69 First reading exit roller 70 Second reading roller 87 Table lift sensor 88 Home position sensor 89, 90 Document length Sensor 91 Paper Thickness Measurement Sensor 101 Second Reading Unit 201 Dust Detection Unit 202 Dust Determination Unit 203 Line Memory 204 Dust Correction Unit 301 First Detection Unit 302 Second Detection Unit 303 Back-through Information Detection Unit 304 DDR-SDRAM

JP 2009-033291 A JP 2005-142669 A

Claims (4)

A background board,
Conveying means for conveying the document onto the background plate;
The background plate and the one side and the other side of the document conveyed on the background plate by the conveying means are shown from the other side to the one side and from the one side to the other side. Reading means for obtaining read image data including a show-through of
Detection means for detecting dust candidate pixels from image data of an image read by the reading means;
Determination means for determining the presence or absence of dust that requires correction of image data based on a detection result by the detection means;
An image reading apparatus comprising: The background plate has a first background plate and a second background plate,
The reading means has first reading means for reading an image located on the first background plate, and second reading means for reading an image located on the second background plate,
2. The image reading apparatus according to claim 1, wherein the first reading unit reads the first background plate and the one surface side of the document, and the second reading unit reads the second background plate and the other surface side of the document. .   3. A storage unit that stores the image data, the detection result, and the determination result, and the image data, the detection result, and the determination result stored in the storage unit are retrieved as necessary. The image reading apparatus described.   An image forming apparatus in which image data obtained by an image reading apparatus is corrected and image formation is performed based on the corrected image data, wherein the image reading apparatus is any one of claims 1 to 3. An image forming apparatus comprising the image reading apparatus described above.

Images