JP2016092617A - Image reading device, image forming device, control method of image reading device, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve detection accuracy of foreign matters in a read image.SOLUTION: A read image read with a reading section and a luminance value for detecting foreign matters on a reading glass are compared. The read image and a pixel width for detecting the foreign matters on the reading glass are compared. On the basis of the results, the foreign matters on the reading glass are detected.SELECTED DRAWING: Figure 14

Description

  The present invention relates to an image reading technique for reading a document while conveying the document in a predetermined direction on a reading glass.

  As an image reading apparatus constituting the image forming apparatus, an image reading apparatus equipped with an automatic document feeder (ADF: Automatic Document Feeder) is known. This image reading apparatus conveys an original from the automatic document feeder into the apparatus, and reads an image of the original sliding on the reading glass surface by using a reading sensor arranged below the reading glass surface. For this reason, when a foreign substance (dust (paper dust, glue, etc.)) adheres to the reading glass surface, a streak-like image is mixed in a partial area of the read image in parallel with the sub-scanning direction (document transport direction). May occur. In order to avoid such a problem, a technique has been proposed in which the adhesion of foreign matter is detected, a warning is issued, and the removal of the deposit is promoted (Patent Document 1).

JP 2005-1117090 A

  In Patent Document 1, one threshold for luminance is set, and the continuity of luminance different from the threshold by a predetermined value or more is determined, and an image in the read image is determined as a foreign object. However, even if the foreign matter has a wide pixel width, if the brightness of the foreign matter does not differ from the threshold value by more than a predetermined value, it is determined that the image constituting the pixel width is not a foreign matter. There is a case where the image is output as a streak. In addition, even if the threshold for luminance is set high in order to detect a foreign object when the luminance does not differ from the threshold by a predetermined value or more, the number of objects that are detected as a foreign object increases, and image correction is performed on the detected foreign object. The image quality may be degraded.

  The present invention has been made in view of the above problems, and an object thereof is to provide an image reading technique capable of improving the detection accuracy of foreign matter in a read image.

In order to achieve the above object, an image reading apparatus according to the present invention comprises the following arrangement. That is, a reading unit capable of optically reading image information of a document on a reading glass;
First comparison means for comparing a read image read by the reading unit with a luminance value for detecting foreign matter on the reading glass;
A second comparison means for comparing the read image with a pixel width for detecting foreign matter on the reading glass;
Detecting means for detecting foreign matter on the reading glass based on a comparison result between the first comparing means and the second comparing means.

  According to the present invention, it is possible to improve the detection accuracy of foreign matter in a read image.

1 is a cross-sectional view of an image forming apparatus. 1 is an external perspective view of an image forming apparatus. It is sectional drawing of an image reading apparatus. It is a figure which shows the structure around an image sensor unit. It is a figure which shows the internal structure of an image sensor unit. It is a figure which shows a reflected light path. It is a figure which shows light quantity distribution of a light source. It is a figure which shows the other structural example of an image sensor unit. It is a block diagram which shows the structure of an image signal processing part. It is a figure which shows an example of the stripe-shaped area | region which arises in image data. It is a figure which shows several judgment criteria for a foreign material detection. It is a figure for demonstrating the method to detect a foreign material. It is a flowchart which shows an image reading process. It is a flowchart which shows the detail of a foreign material detection process.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments do not limit the present invention according to the claims, and all combinations of features described in the embodiments are not necessarily essential to the solution means of the present invention. . In addition, the same reference number is attached | subjected to the same component and description is abbreviate | omitted.

  The image forming apparatus according to the present embodiment includes an image reading device that optically reads a document. Further, the image forming apparatus can realize a copy function, a printer function, a facsimile function, and a composite function thereof. Further, the image reading apparatus may be configured as a scanner independently from the image forming apparatus.

  FIG. 1 is a cross-sectional view of the image forming apparatus according to the present embodiment along the sheet conveyance direction. FIG. 2 is an external perspective view of the image forming apparatus of FIG. FIG. 3 is a cross-sectional view of the image reading apparatus provided in the image forming apparatus along the document conveyance direction.

<Image forming apparatus>
The image forming apparatus 100 shown in FIG. 1 is roughly divided into an apparatus main body 101, an image reading apparatus 103 provided on the upper part of the apparatus main body 101, and an automatic document feeder (ADF: auto) provided on the upper part of the image reading apparatus 103. Document feeder) 126.

  The automatic document feeder 126 includes an ADF separation unit 115, a paper discharge conveyance unit 116, a document discharge unit 117, a document pressing plate 118 that presses a book document, and a sheet document conveyance unit 121. The automatic document feeder 126 separates the sheet document D as a recording medium placed on the document placing table 106 one by one by the ADF separation unit 115 and supplies the separated sheet document D to the image reading device 103. The image reading apparatus 103 optically reads the sheet original D, which is fed onto the flow reading glass 109 serving as a reading glass, by the automatic original supply apparatus 126 by the image sensor unit 108 in a stopped state. Here, the image sensor unit 108 serving as a reading unit is configured by, for example, a line sensor.

  The image reading apparatus 103 can also read a sheet original D or a book original placed by a user on an original table glass 107 which is a reading glass. At that time, the image sensor unit 108 optically reads the sheet document D and the book document while moving in the sub-scanning direction. The sub-scanning direction is a left-right direction in FIG. 1, and the main scanning direction is a direction intersecting the sub-scanning direction, that is, a direction indicated by an arrow B in FIG. The document pressing plate 118 is formed by being laminated with a member such as a white sheet or sponge in order to prevent the document placed on the document table glass 107 from floating. The document pressing plate 118 is extended until the left end 118a of the document pressing plate 118 is positioned on the left side of the book reading range start position 107a and the right end 118b is positioned on the right side of the book reading range end position 107b.

  The image reading apparatus 103 sends image reading information to the printing unit 104 of the apparatus main body 101. The apparatus main body 101 prints an image on the sheet P (recording medium) stacked on the cassette paper feeding unit 112 based on the image reading information read by the image reading apparatus 103. The printing unit 104 is, for example, an electrophotographic printing mechanism that uses an LED array. In that case, the apparatus main body 101 includes an LED head unit 110. In addition, the apparatus main body 101 includes a plurality of paper discharge trays 113a to 113c configured to be capable of stacking a plurality of sheets P on top of the image forming unit 111, the cassette paper feeding unit 112, and the printing unit 104. A sheet discharge unit 113 and a cartridge cover unit 114 are included. Further, the apparatus main body 101 includes a joining unit 119 that joins the image reading apparatus 103 and the printing unit 104, a facsimile control unit 120, a double-sided conveyance unit cover 122, a conveyance direction switching unit 123, and a resist conveyance unit 124. The apparatus main body 101 includes an MP (multi-paper) paper feeding unit 125 and a double-sided conveyance unit 150 in the printing unit 104.

  FIG. 2 is an external perspective view of the image forming apparatus 100. As illustrated in FIG. 2, the image forming apparatus 100 includes an operation unit 105. The operation unit 105 includes a display unit such as a display, input keys such as a numeric keypad, and various buttons such as a start button (copy button). The operation unit 105 can receive various instructions from the user, or the user can check the state of the image forming apparatus 100 on the display. The ADF pressure plate 102 is rotatably attached to the image reading apparatus 103 by a hinge portion 102a, and the user can open and close the automatic document feeder 126 in the direction of a double arrow A in FIG. One hinge portion 102 a is provided on each of the left and right sides of the back side of the apparatus main body 101, and the user can open the ADF pressure plate 102 rearward by lifting the front side of the ADF pressure plate 102. The hinge portion 102a can hold the ADF pressure plate 102 in a state of being opened at a predetermined angle, for example, 70 degrees, by a combination of members such as a damper, a cam, and a spring member. The user places a document such as a sheet document or a book document on the platen glass 107 with the ADF pressure plate 102 opened.

  FIG. 3 is a diagram showing an internal configuration of the image reading device 103 and the automatic document feeder 126 of the image forming apparatus 100. The image reading apparatus 103 may be integrated with the image forming apparatus 100 as shown in FIG. 1, or may be configured as a separate body. As shown in FIG. 3, a white sheet 109 c is provided on the lower surface of the jump table 109 b that projects from the upper part of the document table glass 107. The image reading device 103 performs shading correction of the image sensor unit 108 when the reading position of the image sensor unit 108 is below the white sheet 109c. In the image reading apparatus 103, the image sensor unit 108 passes under the jump table 109b for each scanning operation for reading a document. That is, shading correction is performed for each scanning operation, and the influence of the change in the light amount of the light source in the movable image sensor unit 108 with time can be reduced.

[Sheet original scanning operation]
Here, with reference to FIGS. 1 to 3, a flow reading operation when the image forming apparatus 100 executes image reading will be described. As shown in FIGS. 1 and 2, the document placing table 106 is provided on the ADF pressure plate 102. A pair of sliders 106 a are provided on the document placing table 106 so as to be slidable in a direction perpendicular to the sheet document conveying direction (that is, the sheet document width direction indicated by the arrow B). By this pair of sliders 106 a, both sides of the sheet document stacked on the document placing table 106 can be aligned. That is, the width alignment of the sheet original can be performed by the pair of sliders 106a. An original length sensor 106b is provided on the original placing table 106, and the length of the set sheet original can be detected.

  In FIG. 3, the ADF separation unit 115 is provided with a plurality of document width sensors 115d for detecting the presence and width of a sheet document in the width direction of the sheet document. Only one document width sensor 115d is shown in FIG. The image forming apparatus 100 can detect the document size and the document setting direction based on detection signals from the document width sensor 115d and the document length sensor 106b. In FIG. 3, the sheet document conveying unit 121 is provided with a document feeding sensor 121 h and a document edge sensor 121 i. The document feed sensor 121h can detect whether or not a sheet document has been sent from the ADF separation unit 115 and the passage of the rear end of the sheet document. The document edge sensor 121i can detect the passage of the leading edge and the trailing edge of the sheet document. The detection signal is used for image reading timing control. The ADF separation unit 115 includes a pickup roller 115a that moves up and down by an actuator (not shown), a separation roller 115b, a retard roller 115c that presses against the separation roller 115b and rotates in the reverse direction, and the like.

  The sheet original is first stacked on the original placing table 106 by the user with the reading surface (original surface) facing up. Then, the pickup roller 115a descends, presses the sheet document against the document placing table 106, and feeds it between the separation roller 115b and the retard roller 115c. The retard roller 115c and the separation roller 115b separate and convey the sheet document one by one. Next, the registration roller 121a, the lead roller 121b, and the reading and conveying roller 121c convey the sheet document on the flow reading glass 109 in a predetermined direction (sub-scanning direction) along a U-turn paper path along the document guide 121d. To do.

  A sheet document pressing plate 121e pressed by an urging spring (not shown) presses the conveyed sheet document against the reading glass 109 and closely contacts it. During this time, the sheet document is continuously conveyed. At that time, the image sensor unit 108 has already moved to the sheet original reading position 109 a and stopped, and irradiates the sheet original passing over the sheet original reading position 109 a with light from the lower side of the flow reading glass 109. The image reading is executed by receiving the reflected light by the image sensor unit 108. Next, the jump table 109b scoops up the sheet document continuously conveyed to the ADF pressure plate 102 side. A reading and conveying roller (not shown) pressed by the reading and conveying roller 121c by a pressing spring (not shown) and the reading and conveying roller 121c convey the sheet document. Further, the sheet discharge roller 117a and the sheet discharge roller 117b pressed against the sheet discharge roller 117b by the pressing spring discharge the sheet document to the document sheet discharge tray 117c.

  When reading both sides of a document, the paper discharge roller 117a and the paper discharge roller 117b invert the document and convey it again to a document reading position via a flapper (not shown). The document whose image has been read is discharged to the document discharge tray 117c. A sensor for detecting the presence / absence of a recording medium in the conveyance path is appropriately disposed in the conveyance path. When foreign matter such as dust or dirt adheres to the flow reading glass 109 corresponding to the reading position, black streaks appear in the image data. Therefore, in order to prevent this, the image reading apparatus 103 detects a foreign substance area and corrects image data corresponding to the foreign substance area.

[Image sensor unit configuration]
FIG. 4 is a diagram showing a configuration around the image sensor unit 108. 4A is a cross-sectional view along the document conveyance direction, and FIG. 4B is a cross-sectional view along the vertical direction with respect to the document conveyance direction. The image sensor unit 108 irradiates light on an image surface of a sheet document from a light source including an optical system such as an LED and a light guide, and reflects reflected light reflected on the image surface with a SELFOC lens (registered trademark). The image information on the sheet original is read by forming an image on the one-dimensional sensor element array. The image sensor unit 108 moves in the left-right direction in FIG. 4A along the guide shaft 103c by a timing belt 103a, a driving pulley 103b rotated by a driving motor (not shown), and a driven pulley 103f. The image sensor unit 108 is supported by the guide shaft 103c by the carriage 103d and is urged upward by the spring 103e. The timing belt 103a and the carriage 103d are connected by a connecting member 103g. A spacer 108 a is interposed between the image sensor unit 108 and the document table glass 107. The image sensor unit 108 optically reads an image of a document placed on the platen glass 107 in a range from the book reading range start position 107a to the book reading range end position 107b in FIG. 1 while moving at a constant speed. be able to.

  FIG. 5 is a diagram illustrating an internal configuration of the image sensor unit 108. The image sensor unit 108 irradiates a document with light from a light source including an optical system such as the LED 10 and the light guide 11. The reflected light is imaged on the light receiving sensor 13 which is a one-dimensional sensor element array by the Selfoc lens array 12 which is an imaging optical system, so that the image sensor unit 108 optically reads the image information of the document. Can do. The light source may be an axial lamp arranged in the main scanning direction. In the case of color reading, LEDs having different wavelength distributions of three colors of R (red), G (green), and B (blue), which are a plurality of colors, are used as a light source. For monochrome reading, for example, G (green) is used as a monochromatic light source. FIG. 5 shows only one LED for each light guide 11 to be described later for simplification. Here, the light guide 11 is made of resin, for example.

  In the image sensor unit 108, a pair of light guide light sources including an LED 10 that is a light emitting element of a light source and a light guide 11 that guides light emitted from the LED 10 to a sheet document serves as an imaging optical system. The SELFOC lens array 12 is disposed on both sides. A light receiving sensor 13 is provided directly below the selfoc lens array 12. The image sensor unit 108 is disposed in the frame body 14. The light receiving sensor 13 has a plurality of light receiving elements 13 a arranged along the main scanning direction of the image sensor unit 108. As shown in FIG. 5, the LEDs 10 are respectively provided at one end of one light guide 11 and the other end of the other light guide 11. In the image sensor unit 108, the above-described constituent members are arranged at point-symmetrical positions with respect to the central axis C.

  Light emitted from each LED 10 travels in the sheet width direction (that is, the main scanning direction of the arrow B) while being repeatedly reflected in each light guide 11, and is emitted from the light emitting surface 11 a of the entire length of the light guide 11. To do. The light emitted from the light guide 11 irradiates the original E on the original table glass 107 as shown in FIG. 6, passes through the SELFOC lens array 12 and is received by the light receiving sensor 13. The light receiving sensor 13 as a photoelectric conversion element receives the reflected light of the document E and converts the reflected light into an electrical signal.

  FIG. 7 is a diagram showing the light amount distribution of the light guide light source of the image sensor unit 108. In FIG. 7, the light amount distribution based on the distance from the LED 10 on the one light guide 11 side is indicated by a solid line, and the light amount distribution based on the distance from the LED 10 on the other light guide 11 side is indicated by a dotted line. It is shown in The light amount distribution of the image sensor unit 108 as a whole is obtained by adding the light amounts of the respective LEDs 10 as indicated by a one-dot chain line. As shown in FIG. 7, the light amount of the light guide light source is averaged with respect to the distance and becomes constant. As shown in FIG. 5, by providing each LED 10 between the two light guides 11 on the opposite side, a light amount distribution in which the light amounts complement each other is obtained. Good read data can be obtained. Note that the LEDs 10 may be provided at both ends of one light guide 11. Further, as shown in FIG. 8, the LED 10 and the light guide 11 may be provided only on one side with the selfoc lens array 12 interposed therebetween.

[Image signal processor]
FIG. 9 is a block diagram illustrating a configuration of an image signal processing unit that processes an image signal obtained from the image sensor unit 108. The CIS 21 performs photoelectric conversion on the detection signal detected by the light receiving sensor 13 of the image sensor unit 108 to generate an analog signal. The CIS 21 includes an LED 10, a light receiving sensor 13, and an AMP • A / D (amplifier / analog / digital) converter 23. The analog signal generated by the CIS 21 is amplified by the amplifier circuit of the AMP / A / D converter 23 and converted into a digital signal by the A / D converter circuit. The sub CPU 30 stores the digital data converted into the digital signal in the memory 27 via the communication I / F 51.

  The image processing circuit 41 rearranges the digital data according to the image information for one line of the sheet document, and executes various image processes. Here, the image processing is, for example, shading correction, filter correction, foreign matter detection processing and foreign matter correction processing described later. The digital data subjected to the image processing is output to the image forming unit 111 via an I / F circuit (interface circuit) 42 or transmitted to an external host computer or the like for image reproduction.

  The sub CPU 30 controls, for example, the lighting time of the LED drive circuit 25 by controlling the image sensor unit 108. Further, the sub CPU 30 controls the AMP / A / D converter 23 based on the set value transmitted from the main CPU 24. The reading unit common power supply 26 can turn ON / OFF the power supply of the image sensor unit 108. The operation unit 105 displays a status display of the image reading apparatus 103 and an operation state of the entire image forming apparatus 100, and accepts a reading instruction from a user. The LED driving circuit 25 is supplied with electric power from the reading unit common power supply 26 and drives each LED of the CIS 21 under the control of the sub CPU 30. The AMP / A / D converter 23 is also supplied with power from the reading unit common power supply 26 and operates under the control of the sub CPU 30.

  The sub CPU 30 can adjust the reading level (luminance level) of the image by setting a conversion level for converting the analog signal in the AMP / A / D converter 23 into a digital signal. The main CPU 24 transmits information such as setting values stored in the memory 27 to the image sensor unit 108 via the sub CPU 30 and the communication I / F 51. Here, the setting value is, for example, a conversion level of the AMP / A / D converter 23 or various setting values for controlling the image sensor unit 108. The sub CPU 30 adjusts the reading level of the AMP / A / D converter 23 based on the set value received from the main CPU 24 and controls the reading unit 50.

  The main CPU 24 controls power supply to the image sensor unit 108 by switching the reading unit common power supply 26 to ON / OFF. The main CPU 24 can detect a failure of the LED 10 or an abnormality of the AMP / A / D converter 23 based on digital data representing image information obtained at the time of shading correction or reading level adjustment. When the image reading apparatus 103 is integrated with the image forming apparatus 100, the main CPU 24 controls the entire image forming apparatus 100 according to a program stored in the memory 27.

  In the present embodiment, the image sensor unit 108 of the image reading apparatus 103 is configured to read an image by the CIS method, but may be configured to read an image by a CCD (Charge Coupled Devices) method. The memory 27 can include a RAM and a ROM. The RAM functions as a work area for the main CPU 24 and a temporary storage area for data. The ROM stores a firmware program for controlling the image forming apparatus 100 and a boot program for controlling the firmware program, and is used by the main CPU 24.

  FIG. 10 is a diagram illustrating an example of a streaky region generated in image data obtained by the image reading device 103 of the image forming apparatus 100.

  As shown in FIG. 10, the image data read via the automatic document feeder 126 may include a base image 221, a read image 222, and a stripe area 223. For example, the streak-like region 223 is generated when foreign matter (dust such as paper powder or glue) adheres to the flow reading glass 109 and appears in the read image as a streak-like region 223 parallel to the sub-scanning direction. If this streak-like area 223 occurs when the reading function (copying, scanning) is used, an image is defective.

Next, a method for detecting adhesion of foreign matter will be described. In the present embodiment, the foreign matter to be detected is dust such as paper dust and glue attached to the surface of the flow reading glass 109. These are different in reflectance from the surface of the document. Therefore, it is possible to extract a signal that may be a foreign substance by comparing the measured value (luminance value) of the CIS 21 with a predetermined threshold value. In order to detect adhesion of a foreign substance in the image reading apparatus 103 of the present embodiment. The determination criteria will be described with reference to FIG.

  The determination criteria are performed with reference to the table shown in FIG. This table is a criterion for setting a larger pixel width for determining a foreign object as the luminance increases. This is because a foreign object having a larger luminance value does not result in a noticeable streak image when outputting an image with a smaller pixel width, but appears as a noticeable streak image when the pixel width is increased, resulting in a decrease in image quality. Because. Here, it is assumed that the read data obtained by reading the white color of the reading conveyance roller 121c is as shown in FIG. Here, the read data is expressed by luminance in pixel units, and a line segment corresponding to the L width in FIG. 11B corresponds to one pixel.

  According to the first criterion, in the read data, a pixel (group) that has a luminance of less than 200 and is continuous for one pixel or more is a pixel (group) corresponding to a foreign object (pixel P1 in FIG. 11B). Judge. Further, according to the second criterion, a pixel group in which the luminance is 200 or more and less than 220 and three or more pixels are continuous in the read data is also a pixel group corresponding to a foreign substance (pixel group P2 in FIG. 11B). It is judged that. For this reason, even if the luminance is 200 or more and less than 220, if the number of continuous pixels is less than 3 pixels, it is determined that the continuous pixel is not a pixel corresponding to a foreign object.

  In the table shown in FIG. 11A described above, the first determination criterion and the second determination criterion are provided, but three or more determination criteria may be provided. For example, the second determination criterion is a luminance value of 200 or more and less than 210, the pixel width for determining a foreign object is 2 pixels or more, the third determination criterion is a luminance value of 210 or more and less than 220, and the pixel width for determining a foreign object is 3 pixels or more. It is good. In this way, by providing a plurality of determination criteria, foreign matters can be detected more accurately, and deterioration in image quality during image correction can be reduced.

  However, in the read data, when one pixel having a luminance of less than 200 and two pixels having a luminance of 200 or more and less than 220 are continuous, those three pixels correspond to foreign matters. Judged as a pixel.

  Further, correction processing is executed at the position (part) of the pixel detected as a foreign substance in the read data. The pixel width to be corrected is set to a predetermined correctable width (for example, 15 pixels), and the correction processing is performed on a portion detected as a foreign object having a larger pixel width, which greatly affects the image quality of the read image. there is a possibility. Therefore, when the pixel width to be corrected is larger than the predetermined correctable width, the correction process is prohibited, and a process for urging the user to clean the reading glass (flow reading glass 109) is executed. In this process, for example, information for prompting cleaning of the flow reading glass 109 is output (displayed) to the operation unit 105.

  Note that the determination criteria set in the table shown in FIG. 11A and the processing for the read data detected as a foreign object are merely examples, and the determination criteria are appropriately changed according to the application and purpose. Just do it. Further, this table is stored in, for example, the memory 27, and settings for changing the contents can be performed via the operation unit 105 as necessary.

  Next, an example of detecting a foreign object will be described with reference to FIG. In this embodiment, first, a foreign object is detected based on the luminance of the pixels constituting the read data, and a pixel on which correction processing is performed is selected based on the pixel width of the pixel corresponding to the detected foreign object.

  FIG. 12A shows a case where a pixel determined to be a foreign object on the first determination criterion and a pixel group determined to be a foreign object on the second determination criterion are continuously present. In this case, these pixel groups are determined as one foreign object.

  FIG. 12B also shows a case in which a pixel group determined as a foreign object on the first determination criterion and a pixel group determined as a foreign object on the second determination criterion exist continuously. However, since the pixel width of the continuous pixels is larger than the correctable width (a predetermined pixel width that allows the execution of the correction process (for example, 15 pixel width)), in this case, the execution of the correction process is prohibited. Then, a process for urging the user to clean the flow-reading glass 109 is executed.

  FIG. 12C shows a case where the pixels determined to be a foreign object on the first determination criterion and the pixel groups determined to be a foreign object on the second determination criterion exist discontinuously (discretely). Yes. In this case, based on the degree of discontinuity (discrete state) between the pixels (groups) determined to be the foreign object and the correctable width, it is determined whether or not to process a plurality of foreign objects as one foreign object.

  Here, an interval between pixels (groups) determined to be a plurality of foreign matters is within a predetermined pixel interval (for example, one pixel interval), and pixels (groups) determined to be a plurality of consecutive foreign matters at the predetermined pixel intervals. It is determined whether or not the total width of the pixel width and the pixel width defined by the number having a predetermined pixel interval is a correctable width. When the total width is a correctable width (within a predetermined pixel width), the plurality of foreign matters are detected as one foreign matter (the left pixel group in FIG. 12C). On the other hand, when the total width is not the correctable width, the plurality of foreign objects are detected as individual foreign objects. However, since the total width is not the correctable width, the correction process is prohibited and the user is prevented from performing the scanning. A process for promoting cleaning of the glass 109 is executed.

  FIG. 12 (d) also shows a case where the pixels determined to be a foreign object on the first determination criterion and the pixel groups determined to be a foreign object on the second determination criterion exist discontinuously (discretely). Yes. In this case, since the interval between the pixels (groups) determined to be a plurality of foreign matters is larger than the predetermined pixel interval (three pixel intervals), the pixel width of each pixel (group) determined to be a plurality of foreign matters is corrected. In the case of the possible width, each foreign substance is detected as a correction target foreign substance (two pixel groups on the left side in FIG. 12D). On the other hand, when the pixel width is not the correctable width, the foreign substance having the pixel width prohibits execution of the correction process, and executes a process for prompting the user to clean the flow reading glass 109. The predetermined pixel interval is stored in, for example, the memory 27 and is stored in the main CPU 24. Further, settings for changing the predetermined pixel interval can be performed via the operation unit 105 as necessary.

  Next, an example of image reading using the automatic document feeder 126 will be described with reference to FIG. The process shown in FIG. 13 is realized, for example, when the main CPU 24 reads a program stored in the ROM of the memory 27 into the RAM and executes it.

  First, when the operation unit 105 detects that the start button (copy button) is pressed, the main CPU 24 moves the image sensor unit 108 to a reading position (flow reading position) immediately below the flow reading glass 109 (S101). Next, the main CPU 24 uses the image sensor unit 108 to read the white color of the opposite reading conveyance roller 121c, detect foreign matter, and perform a foreign matter correction process based on the detection result (pixels in the main scanning direction). Position) is set (S102). Note that there are a predetermined number of reading positions in the sub-scanning direction, and a position where no foreign matter is present is set as a reading position. If there are foreign objects at all the reading positions, a predetermined first priority position is set as the reading position among the predetermined number of reading positions.

  Then, the main CPU 24 executes reading of the original conveyed on the flow reading glass 109 by the image sensor unit 108, and corrects the image obtained by the reading (foreign matter correction) based on the set correction position. Correction processing is executed (S103). After reading, the main CPU 24 determines whether or not there is a next original (S104). If there is a next original (YES in S104), the process returns to S102, foreign object detection is performed again, and a series of operations is repeated. On the other hand, if there is no next original (NO in S104), the process is terminated.

  Next, details of processing for detecting foreign matter (dust) at the image reading position in S104 will be described with reference to FIG. This process is executed when the image forming apparatus 100 executes image reading.

  When detecting a foreign object, first, the main CPU 24 moves the image sensor unit 108 to the sheet document reading position 109a before reading the sheet document, and reads the white color of the opposed reading and conveying roller 121c at that position. The main CPU 24 stores the read white data in the memory 27 (S201).

  Next, the main CPU 24 uses the first determination criterion to determine the foreign object, and among the pixels constituting the white data stored in the memory 27 in S201, the luminance of the target pixel to be processed is the first threshold value. It is determined whether it is less than (S202). Since the first threshold value is stored in the table of the memory 27, the main CPU 24 refers to this table, acquires the first threshold value, and compares it with the luminance of the target pixel. Here, the first threshold is set to 200, and it is compared whether or not the luminance value of the target pixel is less than 200. As a result of the comparison, when the luminance of the pixel of interest is less than the first threshold (YES in S202), the main CPU 24 counts the number of pixels in which pixels having luminance less than the first threshold continue from the pixel of interest (S203).

  On the other hand, if the luminance of the pixel of interest is equal to or higher than the first threshold (NO in S202), the main CPU 24 configures the white data stored in the memory 27 in S201 in order to make a foreign object determination using the second determination criterion. It is determined whether the luminance of the target pixel to be processed is equal to or higher than the first threshold value and lower than the second threshold value among the pixels to be processed (S204). Since the second threshold value is stored in the table of the memory 27, the main CPU 24 obtains the first threshold value and the second threshold value with reference to this table and compares them with the luminance of the target pixel. Here, the first threshold value is 200, the second threshold value is 220, and whether or not the luminance value of the target pixel is 200 or more and less than 220 is compared. If the luminance value of the target pixel is not greater than or equal to the first threshold value and less than the second threshold value (NO in S204), the process proceeds to S209. As a result of the comparison, when the luminance value of the target pixel is 200 or more and less than 220 (YES in S204), the main CPU 24 counts the number of pixels in which a pixel having a luminance less than the first threshold continues from the target pixel (S205).

  Next, it is determined whether or not the pixel width corresponding to the number of consecutive pixels counted in S205 is equal to or greater than a predetermined number of pixels (S206). If the pixel width is not equal to or greater than the predetermined number of pixels (NO in S206), the process proceeds to S209. Here, the table of the memory 27 is referred to, and since the predetermined pixel width is 3 pixels or more, it is determined whether or not the pixel width corresponding to the number of pixels of the pixel of interest and the continuous pixels is 3 pixels or more.

  This is because, as described above, a foreign object with a large luminance value does not become a noticeable streak image when outputting an image with a small pixel width, but it appears as a noticeable streak image when the pixel width becomes large, and the image quality deteriorates. Because it becomes. Therefore, even if the luminance is 200 or more and less than 220, if the number of continuous pixels is less than 3 pixels, it is determined that the pixel does not correspond to a foreign object.

  If the pixel width is equal to or greater than the predetermined number of pixels (YES in S206), based on the count result counted in S203 or S205, the main CPU 24 determines that the pixel width corresponding to the number of pixels of the pixel of interest and the subsequent pixels is the same. It is determined whether or not the width is a correctable width (a predetermined pixel width (for example, a 15-pixel width) that allows the execution of the correction process) (S207).

  If it is not the correctable width (NO in S207), the main CPU 24 displays a cleaning display on the operation unit 105 indicating that the flow reading glass 109 needs to be cleaned (S214). If it is the correctable width (YES in S207), the main CPU 24 stores, in the memory 27, information indicating the correctable width, the pixel width and the position for the continuous pixels, as the foreign object information to be corrected (S208). ).

  Next, it is determined whether or not the foreign object detection is determined for the pixels constituting the white data stored in the memory 27 in S201 (S209). If foreign matter detection has not been performed for all pixels (NO in S209), the process returns to S202 to determine whether there is a foreign matter to be corrected. If foreign matter detection has been performed for all pixels (YES in S209), it is determined whether there are a plurality of correction target foreign matter information stored in the memory 27 in S208 (S210).

  If there are not a plurality of foreign objects to be corrected (NO in S210), the processing for detecting the foreign substances is terminated. When there are a plurality of foreign objects to be corrected (YES in S210), as shown in FIG. 12, it is determined whether or not the interval between the plurality of foreign substances is within a predetermined pixel interval (S211). Here, it is determined whether or not the interval between the plurality of foreign matters is within one pixel. By this determination, as described above, it is determined whether a plurality of foreign matters are handled as one foreign matter or are handled as individual foreign matters.

  If the interval between the plurality of foreign matters is not within the predetermined pixel interval (NO in S211), the foreign matter information is stored in the memory 27 in S208, and thus the processing for detecting the foreign matter is finished as it is. When the interval between the plurality of foreign matters is within the predetermined pixel interval (YES in S211), the plurality of foreign matters are determined as one foreign matter, and the number of pixels obtained by adding the interval between the plurality of foreign matters and the predetermined pixel interval can be corrected. It is determined whether or not (S212). If the width is correctable (YES in S212), the foreign matter information stored in the memory 27 is updated with a plurality of foreign matters as one foreign matter (S213), and the processing for detecting the foreign matter is terminated. If it is not the correctable width (NO in S212), the main CPU 24 executes a cleaning display indicating that the flow reading glass 109 needs to be cleaned on the operation unit 105 (S214), and ends the foreign object detection processing.

  When the processing in FIG. 14 is completed, the process proceeds to S103 in FIG. 13, and based on the processing result in FIG. 14, the detected image data for one line is detected based on the information stored in the memory 27. The image data corresponding to the position of the foreign object is corrected. Here, as a correction method, for example, a pixel (group) corresponding to a position where a foreign object is detected is deleted and replaced with a normal pixel (group) corresponding to a position where no adjacent / peripheral foreign object is detected. There is a way to do it. Alternatively, there is a method of calculating the luminance of the correction target pixel by linear interpolation using the luminance of the normal pixels on both sides adjacent to the pixel (group) corresponding to the position where the foreign object is detected.

  As described above, according to the present embodiment, foreign object detection is performed using not only the threshold value with respect to the luminance of the read data but also the number of continuous pixels (pixel width). Can be executed. Thereby, the precision of image correction accompanying the detection of a foreign object can be improved. In addition, since foreign matter is detected based on the discrete state of foreign matter, foreign matter detection with higher accuracy can be performed, and the accuracy of image correction can be improved. In addition, since it is possible to accurately notify the user of cleaning of the reading glass, it is possible to provide an image reading apparatus with high image quality.

  In the above embodiment, the first threshold value and the second threshold value are stored in the table of the memory 27. However, the first threshold value and the second threshold value are compared with the scanned image without being stored in the table. The comparison result may be stored in the memory 27.

<Embodiment 2>
In the first embodiment, foreign object detection and image correction are performed every time an image for one main scanning line is read, but the present invention is not limited to this. For example, the foreign matter detection and image correction may be executed for each predetermined line that is two or more main scanning lines to improve the processing speed.

  Further, the determination criteria managed in the table shown in FIG. 11A may be set by further adding characteristic information about the original such as the type of original and the background color of the original. In this case, feature information (for example, background color density or average density) is extracted from the read image, and foreign object detection is performed based on the extracted feature information. Alternatively, the type of the read image is determined, and the foreign object detection is executed based on the determined type.

  In addition, the function of the above embodiment is realizable also with the following structures. That is, it is also achieved by supplying a program code for performing the processing of the present embodiment to a system or apparatus, and a computer (or CPU or MPU) of the system or apparatus executing the program code. In this case, the program code itself read from the storage medium realizes the function of the above-described embodiment, and the storage medium storing the program code also realizes the function of the present embodiment.

  Further, the program code for realizing the function of the present embodiment may be executed by one computer (CPU, MPU), or may be executed by a plurality of computers cooperating. Also good. Further, the program code may be executed by a computer, or hardware such as a circuit for realizing the function of the program code may be provided. Alternatively, a part of the program code may be realized by hardware and the remaining part may be executed by a computer. Further, the CPU is not limited to the one that performs all the processing by one CPU, and a plurality of CPUs may perform the processing while appropriately cooperating.

  24: main CPU, 27: memory, 25: LED drive circuit, 41: image processing circuit, 105: operation unit, 42: communication I / F, 43: image data generation unit, 108: image sensor unit, 10: LED, 23: AMP A / D converter, 30: sub CPU, 42: I / F circuit, 51: communication I / F, 105: operation unit, 26: reading unit common power source

Claims (15)

A reading unit capable of optically reading the image information of the document on the reading glass;
First comparison means for comparing a read image read by the reading unit with a luminance value for detecting foreign matter on the reading glass;
A second comparison means for comparing the read image with a pixel width for detecting foreign matter on the reading glass;
An image reading apparatus comprising: detection means for detecting foreign matter on the reading glass based on a comparison result between the first comparison means and the second comparison means. 2. The storage device according to claim 1, further comprising a storage unit that stores the luminance value compared by the first comparison unit and the pixel width compared by the second comparison unit. Image reading apparatus. The image reading apparatus according to claim 1, further comprising a correcting unit that corrects a pixel corresponding to the foreign matter detected by the detecting unit. The first comparison unit compares the read image read by the reading unit with a first predetermined luminance value for detecting a foreign object and a second predetermined luminance value higher than the first predetermined luminance value. And
The second comparison unit can determine that correction is necessary when the read image read by the reading unit and the read image are equal to or higher than the first predetermined luminance value and lower than the second predetermined luminance value. A first predetermined pixel width and a second predetermined pixel width that is a pixel width that can be corrected by the correcting unit,
The detection unit is configured such that the read image is equal to or greater than the first predetermined luminance value and less than the second predetermined luminance value, and is equal to or greater than the first predetermined pixel width and within the second predetermined pixel width. The image reading apparatus according to claim 3, further comprising: detecting a foreign matter on the reading glass. The image reading apparatus according to claim 4, further comprising an output unit configured to output information that prompts cleaning of the reading glass based on a detection result of the detection unit. The output means outputs information prompting cleaning of the reading glass when the pixel width of the pixel corresponding to the foreign matter detected by the detection means is larger than the first predetermined pixel width. The image reading apparatus described in 1. A determination means for determining whether or not an interval between pixels corresponding to the plurality of foreign matters is within a predetermined pixel interval when a plurality of foreign matters are detected by the detection means;
The total width of the pixel width corresponding to the plurality of foreign objects and the pixel interval when the determination unit determines that the interval between the pixels corresponding to the plurality of foreign objects is within a predetermined pixel interval. 7. The image reading apparatus according to claim 5, wherein the output unit outputs information that prompts cleaning of the reading glass when is larger than the second predetermined pixel width. A determination means for determining whether or not an interval between pixels corresponding to the plurality of foreign matters is within a predetermined pixel interval when a plurality of foreign matters are detected by the detection means;
The detection means is a case where the determination means determines that the interval between pixels corresponding to the plurality of foreign matters is within a predetermined pixel interval, and the interval between pixels corresponding to the plurality of foreign matters is within a predetermined pixel interval. And when the total width of the pixel widths of the pixels corresponding to the plurality of foreign matters and the interval between the pixels is within the second predetermined pixel width, the plurality of foreign matters are detected as one foreign matter. An image reading apparatus according to any one of claims 4 to 6. A determination means for determining whether or not an interval between pixels corresponding to the plurality of foreign matters is within a predetermined pixel interval when a plurality of foreign matters are detected by the detection means;
The detection unit detects each of the plurality of foreign matters as individual foreign matters when the determination unit determines that an interval between pixels corresponding to the plurality of foreign matters is larger than a predetermined pixel interval. The image reading apparatus according to any one of 1 to 6. The image reading apparatus according to claim 1, wherein the detection unit detects a foreign matter on the reading glass for each predetermined line of a read image read by the reading unit. The predetermined luminance value in the first comparison unit is further set based on feature information including at least one of a background color density of the image and an average density of the image. The image reading apparatus according to any one of 10. The image reading apparatus according to claim 1, wherein the predetermined luminance value in the first comparison unit is further set based on a type of the image. An image reading apparatus according to any one of claims 1 to 12,
An image forming apparatus comprising: a forming unit configured to form, on a recording medium, the read image corrected based on the foreign matter detected by the image reading apparatus. A method for controlling an image reading apparatus that reads an image of a document by a reading unit while conveying the document in a predetermined direction on a reading glass,
A first comparison step of comparing a read image read by the reading unit with a luminance value for detecting foreign matter on the reading glass;
A second comparison step of comparing the read image with a pixel width for detecting foreign matter on the reading glass;
An image reading apparatus control method comprising: a detection step of detecting a foreign matter on the reading glass based on a comparison result between the first comparison step and the second comparison step.   A computer is caused to function as each unit of the image reading apparatus according to any one of claims 1 to 12, or a computer is caused to function as each unit of the image forming apparatus according to claim 13. 14. A program for causing a computer to execute the control method according to 14.

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