JP5198485B2 - Image reading apparatus, white reference chart, shading correction method, and image forming apparatus - Google Patents

Description

  The present invention relates to a document reading apparatus in which a reading unit for reading an image of a document being conveyed on a document conveyance path and a reference white plate for shading correction are arranged with the document conveyance path interposed therebetween, and a white reference used for shading correction in this document reading apparatus The present invention relates to a chart, a shading correction method, and an image forming apparatus including the document reading device.

  In an image reading apparatus that reads an image of a document by a reading unit composed of an imaging element such as a CCD, luminance unevenness due to the characteristics of the optical system and the imaging system included in the reading unit is eliminated, and the entire surface of the read image has a uniform brightness. Then, shading correction is performed. The reading means has a reading range with a length comparable to the entire width of the original in a direction orthogonal to the original conveying direction, and the image data read from the white original by the reading means is uniform over the entire area perpendicular to the conveying direction. A correction value for shading correction is determined so as to have brightness.

  When the apparatus is shipped from the factory or maintenance is performed by a service person, a white reference chart for shading correction is arranged in the document conveyance path, and a reading unit determines a correction value for shading correction based on image data read from the chart.

  However, the characteristics of the optical system and the imaging diameter system of the reading means may change over time even during normal use in which image data is read from a document being conveyed on the document conveyance path. The reading means is disposed on the back surface of the transparent guide plate exposed in the document conveyance path, and dust such as paper dust attached to the guide plate when the document passes through the document conveyance path is read by the reading means, Black streaks occur in the document image data along the conveyance direction.

  Therefore, in a conventional image reading apparatus that reads an image from a document that is being transported along a document transport path, there is a device in which a reading unit and a white reference member are arranged in a part of the document transport path so as to face a position where the document is sandwiched (see FIG. For example, see Patent Document 1.)

  At the time of shading correction, a correction value for shading correction is determined based on the image data of the white reference member read by the reading unit in a state where the original is not conveyed in the original conveyance path. A white reference member is always arranged in the image reading apparatus, and shading correction can be performed not only at the time of factory shipment of the apparatus or maintenance by a service person but also at an arbitrary timing at the time of reading a document image. It is also possible to remove the influence of dust attached to the guide plate on the image data of the document.

JP 2001-313794 A

  However, since the reading unit and the white reference member are arranged with the document conveyance path interposed therebetween, the distance from the reading unit to the white reference member does not match the distance from the reading unit to the image surface of the document, and the white reference member The correction value based on the image data may include an error with respect to the correction value of the original image data. In particular, reading means such as a CIS (contact image sensor) used for reading an image of a document being conveyed on the document conveyance path generally has a shallow depth of field, and a white reference is obtained when focusing on the image surface of the document. Do not focus on the member. For this reason, the image data read from the image surface of the document cannot be accurately subjected to shading correction only by the correction value determined using only the image data of the white reference member always arranged in the apparatus.

  An object of the present invention is to adjust a correction value at the time of reading a document image based on image data read from both a white chart arranged in the document conveyance path and a white reference member arranged fixedly in the apparatus, An object of the present invention is to provide an image reading apparatus, a white reference chart for shading correction, a shading correction method, and an image forming apparatus capable of performing accurate shading correction on image data of a document at an arbitrary timing.

  The image reading apparatus of the present invention includes a document tray, a paper discharge tray, a plurality of conveying members, a reading unit, a white reference member, and a control unit. The document tray places a document before image reading. The paper discharge tray accommodates the original after image reading. The plurality of transport members are arranged along a document transport path from the document tray to the paper discharge tray. The reading unit is arranged to face the image surface of the document at a reading position set between two adjacent conveying members among the plurality of conveying members. The white reference member is arranged to face the reading unit so as to sandwich the document at the reading position. The control unit performs shading correction that corrects image data read by the reading unit from the document conveyed from the document tray when the document image is read. The control unit includes a first reference image data read from a white reference document whose reading means is positioned at a reading position during predetermined adjustment, a second reference image data read from a white reference member by the reading means, and a document. A correction value for shading correction is determined based on the third reference image data read by the reading unit from the white reference member before the document conveyed from the document tray at the time of image reading before image reading reaches the reading position.

  In this configuration, the first and second reference image data are read from the white reference document and the white reference member at the time of predetermined adjustment such as when the apparatus is shipped from the factory or during maintenance by a service person. In addition, the third reference image data read from the white reference member before the original reaches the reading position before reading the original image from when the apparatus is turned on until the image of the original conveyed from the original tray is read. The image data read from the document is corrected by the correction value determined based on the first and second reference image data. The first reference image data is obtained by reading a white image on the image surface of the document.

  Therefore, the reading result of the white image on the image surface of the document is reflected in the correction value, and the correction that eliminates the error due to the mismatch between the distance from the reading unit to the image surface of the document and the distance from the reading unit to the white reference member The shading correction of the image data read from the original is performed based on the value.

In this configuration, it is preferable that the control unit calculates the correction value by multiplying the third reference image data by the first reference image data and dividing by the second reference image data. The reading result of the white image on the image surface of the original can be easily reflected in the correction value.

  In addition, the control unit includes a storage unit that stores the first reference image data and the second reference image data at a predetermined adjustment, and the first reference image data and the first reference image data are read from the storage unit when the document image is read. It is preferable to read the second reference image data. It is possible to reflect the reading result of the white image on the image surface of the document repeatedly in the correction value during normal image reading.

  It is preferable that the control unit executes a first complementing process in which data below a specified value in a part of the second reference image data is supplemented based on data around the part. Moreover, it is preferable that a control part shall perform the 2nd complementation process which complements the data below the regulation value in a part of 3rd reference | standard image data based on the data around the part. Further, it is preferable that the control unit prompts cleaning of the reading unit and the white reference member based on the first and second reference image data. Exact influence of partial contamination of the white reference member can be eliminated, and accurate shading correction can be performed.

  At the time of predetermined adjustment, the control unit arranges a sheet-like white reference chart in which a white portion and an opening are formed as a white reference document along the document conveyance direction, and is arranged on the document conveyance path with the white portion facing the reading unit. In this case, after reading the first reference image data from the white portion, the white reference chart is conveyed to a position where the opening portion faces the reading means, and the second portion is opened in a state where the opening portion faces the reading means. It is preferable to read the reference image data. The first reference image data and the second reference image data can be continuously read using a white reference chart in which a white portion and an opening are formed.

  The white reference chart according to the present invention is arranged as a white reference original at a reading position at a predetermined adjustment, and a white portion and an opening facing the reading means within the interval between two adjacent conveying members along the original conveying path. Is formed. The white portion is formed at a position where it does not come into contact with the conveying member in a state where the opening portion faces the reading unit.

  At the time of predetermined adjustment, after the first white reference data is read by arranging the white reference chart so that the white part faces the reading unit, the white reference chart is moved so that the opening part faces the reading unit. Second reference data can be read. The white portion does not come into contact with the conveying member during the movement of the white reference chart and is not soiled.

  The shading correction method according to the present invention is a shading correction method executed by an image reading apparatus that reads image data from a document being conveyed along a document conveyance path, and is a first and second process performed during a predetermined adjustment. And third and fourth steps performed at the time of normal image reading. In the first step, the first reference image data is read from the white reference original located at the reading position by the reading means arranged at the reading position. In the second step, the second reference image data is read from a white reference member disposed so as to sandwich the document between the reading unit and the reading unit. In the third step, the reading unit reads the third reference image data from the white reference member before the document reaches the reading position. In the fourth step, the image data read by the reading unit from the document that has reached the reading position is corrected based on the first to third reference image data.

  In this configuration, the first and second reference image data are read from the white reference document and the white reference member at the time of predetermined adjustment such as when the apparatus is shipped from the factory or during maintenance by a service person. In addition, the third reference image data read from the white reference member before the original reaches the reading position before reading the original image from when the apparatus is turned on until the image of the original conveyed from the original tray is read. The image data read from the document is corrected by the correction value determined based on the first and second reference image data. The first reference image data is obtained by reading a white image on the image surface of the document.

  Therefore, the reading result of the white image on the image surface of the document is reflected in the correction value, and the correction that eliminates the error due to the mismatch between the distance from the reading unit to the image surface of the document and the distance from the reading unit to the white reference member The shading correction of the image data read from the original is performed based on the value.

  According to the present invention, the reading result of the white image on the image surface of the document can be reflected in the correction value, and the difference between the distance from the reading unit to the image surface of the document and the distance from the reading unit to the white reference member is not possible. An accurate shading correction can be performed on image data of a document at an arbitrary timing using a correction value that eliminates an error due to alignment.

1 is a schematic diagram of a document reading apparatus according to an embodiment of the present invention. It is a figure which shows the image data at the time of the reading of the white original of the 2nd image reading apparatus in the same original reading apparatus, and a white reference board. It is a top view of a white reference chart used for shading correction of the document reading apparatus. (A)-(D) are figures which show the use condition of the same white reference | standard chart. 3 is a block diagram of a control unit of the document reading apparatus. FIG. It is a flowchart which shows a part of process procedure of the control part. It is a figure which shows an example of the complementary process of the reference image data in the process sequence of the control part. It is a flowchart which shows the other part of the process sequence of the control part. It is a figure explaining the discrimination method of the adhesion position of dust in the processing procedure of the control part.

  As shown in FIG. 1, a document reading apparatus 100 according to an embodiment of the present invention is disposed on an upper part of an image forming apparatus such as a copying machine. The document reading device 100 includes an automatic document feeder (hereinafter referred to as “ADF”) 1, a first image reading device 10, and a second image reading device 20.

  The ADF 1 includes a control unit 200 and automatically transports the document along the document transport path F. The first image reading unit 10 is a reduction optical system image reading unit including a light source unit 15, a mirror unit 16, a lens 13, and a CCD (image sensor) 14, and reads an image on the surface side of a document.

  The second image reading device 20 corresponds to the reading means of the present invention, and is a reduction optical system including a light source 21, first to fourth mirrors 22A, 22B, 22C, 22D, a lens 23, and a CCD (image sensor) 24. An image reading unit that reads an image on the back side of the document. The second image reading unit 20 is unitized and stored in the ADF 1. The second image reading unit 20 may be an image reading unit of an equal-magnification optical system such as a contact image sensor for miniaturization.

  The ADF 1 and the main scanning unit 2 are connected by a hinge (not shown), and the upper surface of the main scanning unit 2 can be opened and closed by the rotation of the hinge.

  The first image reading apparatus 10 includes a document table 4 made of a transparent glass plate on the upper surface, and includes a light source unit 15 and a mirror unit 16 in a reciprocating manner in the horizontal direction. The light source unit 15 holds the light source 11 and the first mirror 12A. The mirror unit 16 holds the second mirror 12B and the third mirror 12C.

  The first image reading apparatus 10 corresponds to both the image reading by the document fixing method for reading the image of the document placed on the document table 4 by the user and the document moving method for reading the image of the document conveyed by the ADF 1. Yes.

  When reading an original image by the original fixing method, the light source unit 15 and the mirror unit 16 move to home positions corresponding to the original fixing method, respectively. Thereafter, the light source unit 15 scans the image of the document by moving in the sub-scanning direction (left and right direction with respect to the paper surface) at a constant speed while irradiating the document with light. Similarly, it moves in the sub-scanning direction at a movement speed ½ of the movement speed.

  The light emitted from the light source unit 15 and reflected from the document is reflected by the first mirror 12A, and then the optical path is changed by the second and third mirrors 12B and 12C. The light reflected from the third mirror 12C is passed through the lens 13. The image is formed on the CCD 14 and converted into electrical image data.

  On the other hand, when a document image is read by the document movement method, the light source unit 15 and the mirror unit 16 remain stationary at the home position shown in FIG. 1 and the surface of the document conveyed by the ADF 1 so as to pass above the home position. The image is scanned by irradiating light from the light source 11. The light reflected on the surface of the document is reflected by the first mirror 12A, and then the optical path is changed by the second and third mirrors 12B and 12C. Is converted to

  The ADF 1 includes a pickup roller 6, a plurality of transport roller pairs 7 </ b> A to 7 </ b> E, a resist roller pair 8, a platen roller 2, and a paper discharge roller 9 pair in a document transport path F from the document tray 5 to the paper discharge tray 30. ing. The pickup roller 6 feeds the originals placed on the original tray 5 one by one. The conveyance roller pairs 7A to 7E convey the document along the document conveyance path F. The platen roller 2 presses the document being conveyed on the document conveyance path F toward the platen glass 29. The registration roller pair 8 adjusts the document transport timing. The paper discharge roller pair 9 discharges the original after image reading to the paper discharge tray 30. The document transport path F corresponds to the document transport path of the present invention, and is formed in a substantially U shape around the second image reading device 20.

  The second image reading device 20 reads an image on the back side of the document conveyed on the document conveyance path F when a double-sided scanning request is made by the user. That is, the original on which the image on the front surface is read by the first image reading device 10 passes under the light source 21 while being conveyed toward the discharge tray 30 along the original conveyance path F. At this time, the light source 21 emits light toward the back side of the document, and the light reflected from the back side of the document passes through the reading window 32 formed of a transparent member such as glass and sequentially passes through the mirrors 22A to 22D. After the conversion, the image is formed on the CCD 24 through the lens 23 and converted into electrical image data.

  The lower surface of the ADF 1 is a pressing plate 28 that presses the document placed on the document table 4 from above. The ADF 1 can be vertically divided at the position of the document transport path F between the platen roller 2 and the discharge roller pair 9. When the ADF 1 is divided into upper and lower parts, the space between the platen roller 2 and the paper discharge roller pair 9 in the document transport path F is opened to the outside. In the document transport path F, a document sensor 34 is disposed upstream of the transport roller 7D, and a document sensor 35 is disposed downstream of the transport roller 7E. Document sensors 34 and 35 detect the presence or absence of a document in document transport path F. Document sensors 34 and 35 are turned off when a document is detected, and are turned on when no document is detected.

  In the document transport path F, the reading window 32 faces the white reference plate 33 so as to sandwich the document. The white reference plate 33 is a white reference member of the present invention used for shading correction, may constitute a part of the lower surface guide of the document transport path F, and may have a transparent plate material on the upper surface.

  The second image reading device 20 has an imaging range with a length comparable to the width of the maximum size document that can be conveyed in the direction orthogonal to the document conveyance direction in the document conveyance path F. Due to the characteristics of the light source 21, mirrors 22A to 22D and lens 23 constituting the second image reading device 20, and the image pickup system of the CCD 24, the image data of the white document read by the second image reading device 20 is conveyed. It is not uniform in the direction perpendicular to the direction.

  The image data output from the CCD 24 at the time of reading a white document is curved so that the central portion is higher than both ends as shown by the solid line in FIG. Further, the image data output from the CCD 24 at the time of reading the white reference plate 33 is curved in a state where both ends are lower than the image data of the white original, as indicated by a one-dot chain line in FIG. This is because the distance from the CCD 24 to the white reference plate 33 is longer than the distance from the CCD 24 to the back surface (image surface) of the document.

  The white reference chart 300 of the present invention is an example in which openings 301 to 303 and a white reference portion 304 are formed on an A4 size sheet. When the white reference chart 300 is made of a white sheet, the white reference portion 304 need not be formed.

  As shown in FIG. 4, the opening 302 and the white reference portion 304 are formed so as to be positioned between two adjacent conveyance roller pairs 7 </ b> D and 7 </ b> E in the document conveyance direction indicated by the arrow X. The opening 301 is formed at a position facing the document sensor 34 when the opening 302 faces the reading window 32. The opening 303 is formed at a position facing the document sensor 35 when the white reference portion 304 faces the reading window 32.

  As shown in FIG. 5, the control unit 200 is configured by connecting an image memory 204, a panel controller 205, a motor driver 206, a light source driver 207, and an A / D converter 208 to a CPU 201 having a ROM 202 and a RAM 203. Yes.

  The CPU 201 receives detection signals from the document sensors 34 and 35. The CPU 201 controls each input / output device according to a program stored in the ROM 202 in advance.

  Operation data of operation switches in the operation panel 210 is input from the panel controller 205 to the CPU 201. The CPU 201 outputs display data to be displayed on the display in the operation panel 210 via the panel controller 205.

  The CPU 201 outputs a drive signal corresponding to the detection signals of the document sensors 34 and 35 to the motor driver 206 and the light source driver 207. The motor driver 206 drives the carry motor 220 based on the drive signal output from the CPU 201. The light source driver 207 drives the light source 21 based on the drive signal output from the CPU 201. The A / D converter 208 converts the output signal of the CCD 24 into digital data and inputs it to the CPU 201. The CPU 201 stores the digital data input from the A / D converter 208 in the image memory 204 as image data. The RAM 203 is battery-backed up and temporarily stores data input / output to / from the CPU 201. Memory areas MA1 and MA2 of the RAM 203 are storage areas for first reference image data and second reference image data, which will be described later. The memory area MA3 of the RAM 203 is set to a flag F described later.

  The control unit 200 may be provided in the image forming apparatus in which the document reading apparatus 100 is disposed or in the control unit of the image forming apparatus.

  The CPU 201 uses the white reference chart 300 shown in FIG. 3 to perform shading correction for predetermined adjustment such as when the document reading apparatus 100 is shipped from the factory or during maintenance by a service person, using the white reference chart 300 shown in FIG. First and second reference image data are created.

  This process is executed when the adjustment mode is selected by the operation of a 210 operation panel (not shown) of a factory worker or service person. When the factory worker or the service person selects the adjustment mode, the CPU 201 notifies the display of the operation panel 210 that the white reference chart 300 is arranged in the original half-lie path F in the state shown in FIG. . In the state shown in FIG. 4A, the document sensors 34 and 35 detect the white reference chart 300, and the opening 302 and the white reference portion 304 are located between the conveyance roller pair 7D and the conveyance roller pair 7E. A factory worker or a service person arranges the white reference chart 300 in a state where the ADF 1 is divided into upper and lower parts and the document conveying path F is opened to the outside, and the ADF 1 is integrated.

  When the original sensor 34, 35 detects the white reference chart 300 (S1), the CPU 201 turns on the light source 21 (S2), and after the light amount of the light source 21 is stabilized, performs a predetermined light amount adjustment (S3), and the transport motor. 220 is driven to start the conveyance of the white reference chart 300 in the arrow X direction by the conveyance roller pair 7D and 7E (S4). In the light amount adjustment, for example, the light amount and the input gain of the light source 21 are adjusted so that the average of data in the range of the central portion 100 mm is 840 (10 bits). The light amount adjustment may be performed after step S5.

  When the white reference chart 300 is conveyed and the opening 303 faces the document sensor 35 as shown in FIG. 4B, the document sensor 35 does not detect the white reference chart 300. When the document sensor 35 is turned on, the CPU 201 determines that the white reference unit 304 faces the reading window 32, reads the first reference image data (S5), and reads the first reference read from the white reference unit 304. The image data is stored in the memory area MA1 of the RAM 203 (S6). The average of the image data read a plurality of times while conveying the white reference chart 300 is used as the first reference image data, so that the influence of dust attached to the white reference portion 304 can be removed.

  Here, the CPU 201 determines whether or not there is data equal to or less than a specified value (for example, 100 for 840) in the first reference image data (S7). When dust such as paper dust is attached to the reading window 32, the pixel data of the CCD 24 corresponding to the position where the dust is attached is significantly lowered. If the first reference image data includes data that is equal to or less than the specified value, the CPU 201 stops conveying the white reference chart 300, notifies the display of the operation panel 210 to clean the reading window 32, and stops the processing. (S8).

  If there is no data equal to or less than the specified value in the first reference image data, the CPU 301 waits for the white reference chart 300 to be conveyed to a position where the opening 302 faces the reading window 32 (S9).

  When the white reference chart 300 is conveyed, as shown in FIG. 4C, when the opening 303 does not face the document sensor 35 and the opening 301 faces the document sensor 34, the document sensor 34 moves the white reference chart 300. It will not be detected. When the document sensor 34 is turned on, the CPU 201 determines that the white reference plate 33 faces the reading window 32 via the opening 302, and reads the second reference image data from the white reference plate 33 (S10). The read second reference image data is stored in the memory area MA2 of the RAM 203 (S11). Note that the light amount adjustment described above may be performed again before step S10.

  Here, the CPU 201 determines whether or not there is data equal to or less than a specified value (for example, 100 for 840) in the second reference image data (S12). When dust such as paper dust adheres to the upper surface of the white reference plate 33, the pixel data of the CCD 24 corresponding to the position where the dust adheres is significantly reduced. If the second reference image data includes data equal to or less than the specified value, the CPU 201 stops the conveyance of the white reference chart 300, notifies the display of the operation panel 210 to clean the white reference plate 33, and stops the processing. (S13).

  When the second reference image data does not include data below the specified value, the CPU 301 transports the white reference chart 300 to a position where the opening 301 faces the document sensor 34 as shown in FIG. The driving of the transport motor 220 is stopped, and the process is completed (S14).

  In the processing of Steps S1 to S14, the white reference portion 304 in the white reference chart 300 does not contact the conveyance roller pair 7D and 7E, so that the white reference portion 304 can be prevented from being stained.

  In step S8 or S13, the reading window 32 or the white reference plate 33 is prompted to be cleaned, and the first reference image data complementing process (first complementing process) or the second in-order image data complementing process (second complementing). Processing) may be selectable. In this case, a flag is set in the memory area MA3 of the RAM 203 for each pixel in the reading range according to the selection status of the complement processing. For example, a flag “1” is set when the complement process is selected only in step S8, a flag “2” is set when the complement process is selected only in step S13, and the complement is performed in both steps S8 and S13. When processing is selected, a flag “3” is set. After step S14, the first reference image data or the second reference image data is complemented according to the flag. Note that the contamination of the white reference plate 33 does not significantly affect the reading of an image from a document passing through the upper surface of the white reference plate 33, and therefore the process of S13 can be omitted.

  For example, as illustrated in FIG. 7, when the flag “1” is set from the Mth pixel to the M + Dth pixel, the complement processing is performed on the first reference image data with respect to the Mth pixel and the M + Dth pixel. Average values A1 and A2 of a predetermined number E of pixels in the vicinity of the pixel are taken. Then, the first reference image data stored in the memory area MA1 is complemented with the values on the straight line connecting the average values A1 and A2 with the data from the Mth pixel to the M + Dth pixel as indicated by the broken line in FIG. To do. Complementary processing can be similarly performed for the second reference image data.

  The CPU 201 executes the process shown in FIG. 9 at an arbitrary timing from when the power is turned on to when the document image starts to be read after the document reader 100 is installed at the user's place of use. This timing includes, for example, when a document is placed on the document tray 5 or when a document image has been read a predetermined number of times. Note that the processing shown in FIG. 9 is preferably executed at a timing other than immediately before reading the document image, such as when the document reader 100 is turned on or when the image forming apparatus is reheated.

  The CPU 201 turns on the light source 21 (S22) and the light quantity of the light source 21 is stabilized when the document sensors 34 and 35 are on and there is no document at the reading position where the reading window 32 is arranged (S21). Thereafter, the same light amount adjustment as described above is performed (S23). Thereafter, the CPU 201 reads the output signal of the CCD 24 as third reference image data (S24). With no document at the reading position, the reading window 32 faces the white reference plate 33, and the CCD 24 receives the reflected light of the light from the light source 21 on the white reference plate 33.

  Here, the CPU 201 determines whether or not there is data equal to or less than a specified value (for example, 100 for 840) in the third reference image data (S25). When dust such as paper dust is attached to the reading window 32 or the white reference plate 33, the pixel data of the CCD 24 corresponding to the position where the dust is attached is significantly lowered. When the CPU 201 has data less than or equal to the specified value in the third reference image data, the CPU 201 determines whether the dust is attached to the reading window 32 or the white reference plate 33 based on the inclination of the third reference image data. Make a decision.

  When the dust adheres to the reading window 32 as shown in FIGS. 9A and 9B due to the difference between the distance from the CCD 24 to the lower surface of the reading window 32 and the distance to the upper surface of the white reference plate 33. There is a difference in the inclination of the third reference image data between the case where it is attached to the white reference plate 33 and the case where it is attached to the white reference plate 33. Therefore, the CPU 201 determines whether dust is attached to the reading window 32 or the white reference plate 33 from the inclination of the range where the data in the third reference image data is reduced.

  When the white reference plate 33 is soiled, the CPU 201 performs the third reference image data complementing process because it does not significantly affect the reading of the document image (S27). This complementing process can be performed in the same manner as the complementing process shown in FIG. When the reading window 32 is soiled, the CPU 201 gives a notice for prompting cleaning of the reading window 32 to the display of the operation panel 210 in order to affect the reading of the document image (S28).

  If there is no data equal to or less than the specified value in the third reference image data, the CPU 201 calculates a correction value for shading correction (S29) and stores it in a predetermined memory area in the RAM 203 (S30).

  For example, the correction value is calculated in step S29 by multiplying the third reference image data by the first reference image data and dividing by the second reference image data for each pixel. By using only the image data of the white reference plate 33, shading correction considering the difference between the distance from the CCD 24 to the image surface of the document and the distance to the white reference plate 33 can be performed without using the white reference chart 300. As a result, after the document reading apparatus 100 is installed at the user's place of use, accurate shading correction can be performed at any timing other than during maintenance by the service person.

  The CPU 201 may store in advance a value obtained by dividing the first reference image data of each pixel by the second reference image data, and multiply the third reference image data by this value in step S29.

  The above description of the embodiment is to be considered in all respects as illustrative and not restrictive. The scope of the present invention is shown not by the above embodiments but by the claims. Furthermore, the scope of the present invention is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.

1-ADF
5-Document tray 30-Paper discharge tray 7D, 7E-Conveying roller pair (conveying member)
20-second image reading device (reading means)
32-reading window 33-white reference plate (white reference member)
DESCRIPTION OF SYMBOLS 100- Document reading apparatus 200- Control part 300- White reference chart F- Document conveyance path

Claims (10)

A document tray for placing a document before image reading;
A paper discharge tray for storing originals after image reading;
A plurality of conveying members arranged along a document conveying path from the document tray to the paper discharge tray;
A reading unit disposed so as to face the image surface of the document at a reading position set between two adjacent conveying members among the plurality of conveying members;
A white reference member disposed opposite to the reading unit so as to sandwich a document between the reading unit and the reading unit;
A controller that performs shading correction for correcting image data read from the document conveyed from the document tray by the reading unit when reading a document image;
The control unit includes: a first reference image data read from the white reference original positioned at the reading position by the reading unit at a predetermined adjustment; and a second reference image read from the white reference member by the reading unit. The shading correction for the shading correction based on the data and the third reference image data read from the white reference member by the reading unit before the document conveyed from the document tray before reading the document image reaches the reading position. Determine the correction value,
At the time of the predetermined adjustment, a sheet-like white reference chart in which a white portion and an opening are formed along the document conveyance direction as the white reference document is arranged on the document conveyance path with the white portion facing the reading unit. When the first reference image data is read from the white portion, the white reference chart is transported to a position where the opening faces the reading means, and the opening faces the reading means. An image reading apparatus that reads the second reference image data in a state in which the second reference image data is being read .   2. The image reading apparatus according to claim 1, wherein the control unit calculates the correction value by multiplying the third reference image data by the first reference image data and dividing the third reference image data by the second reference image data. .   The control unit has storage means for storing the first reference image data and the second reference image data at the time of the predetermined adjustment, and the first reference image is read from the storage means before reading the document image. The image reading apparatus according to claim 1, wherein the image data and the second reference image data are read out.   4. The control unit according to claim 1, wherein the control unit executes a first complementing process for complementing data equal to or less than a specified value in a part of the second reference image data based on data around the part. The image reading apparatus described in 1.   5. The control unit according to claim 1, wherein the control unit executes a second complementing process for complementing data equal to or less than a predetermined value in a part of the third reference image data based on data around the part. The image reading apparatus described in 1.   The image reading apparatus according to claim 1, wherein the control unit performs a process for prompting cleaning of the reading unit when a part of the first reference image data includes data equal to or less than a predetermined value. .   The image reading according to any one of claims 1 to 6, wherein the control unit performs a process of prompting cleaning of the reference white member when data of a predetermined value or less is included in a part of the second reference image data. apparatus. An image reading apparatus according to any one of claims 1 to 7, with a an image forming unit for forming an image on a sheet based on image data read by the image reading device when reading the original picture Forming equipment. When said predetermined adjustment in the image reading apparatus according to any one of claims 1 to 7, is arranged as the white reference document to the reading position, facing the reading means within said distance between two adjacent conveying members A white reference chart in the form of a sheet in which a white portion and an opening are formed along the document conveyance direction,
The white reference chart which formed the white part in the position which does not contact the conveyance member in the state where the opening is facing the reading means. A shading correction method executed by an image reading apparatus that reads image data from a document being conveyed along a document conveyance path,
The first reference image data is read from the white reference original located at the reading position by the reading means arranged at the reading position at a predetermined adjustment, and the original is sandwiched at the reading position. Reading the second reference image data from the white reference member;
Before reading the document image, the reading unit reads the third reference image data from the white reference member before the document reaches the reading position, and based on the first to third reference image data, Correcting the image data read by the reading means from the document that has reached the reading position;
At the time of the predetermined adjustment, a sheet-like white reference chart in which a white portion and an opening are formed along the document conveyance direction as the white reference document is opposed to a reading unit in which the white portion is arranged at a reading position. Including the step of positioning before the step of reading the first reference image data,
A shading correction method including a step of conveying the white reference chart so that the opening is positioned at the reading position after the step of reading the first reference image data .

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