JP2007195009A - Image reading apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce unevenness of an image even if light source of one side is switched off during reading in both-side reading which reads images of both front and rear sides of a draft by one conveyance of the draft. <P>SOLUTION: The first face of the draft is illuminated by an illumination lamp 74, and read by a CCD image sensor 78. On the other hand, a second face of the draft is illuminated by an LED array arranged on a CIS (contact image sensor) 50, and read by a line sensor. A reading position of the line sensor is in a downstream side of a draft conveyance direction from the reading position of the CCD image sensor 78. While the line sensor reads the second face of the draft; reading of the first face finishes, and the illumination lamp 74 shifts from a lighting condition to a lighting off condition. Density correction is performed to data read after the illumination lamp 74 puts off out of image data of the second face read by the line sensor. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image reading apparatus that reads an image on an original, and more particularly, to an image reading apparatus that can read images on both sides of the original by conveying the original once.

  Conventionally, an image reading device (automatic double-sided reading device) that automatically reads image information on both sides of a document without user intervention is used as a reading device such as a copying machine or a facsimile, or a scanner for computer input. . As these automatic double-sided reading devices, a method of reading a document by reversing the front and back with a document reversing unit is most widely adopted. In this type of automatic double-sided reading device, after a front image is read by a specific original reading unit, the original is turned upside down and conveyed again to the specific original reading unit to read an image on the back side. However, in such automatic double-sided reading by front / back reversal, it is necessary to discharge the original once, then reverse it and transport it again to the original reading unit. For this reason, it takes a lot of time for double-sided reading, and productivity of double-sided reading is reduced. In view of this, a technique has been studied in which two document reading sections are provided on both the front and back sides of a document path for transporting a document to automatically read both the front and back surfaces of the document with a single document transport.

  As a conventional technique that employs such a double-sided scanning method, for example, a front surface reading unit that reads one surface (front surface) of a document is arranged opposite to a document path through which the document is conveyed. There is a technique in which a back side reading unit that reads the other side (back side) of a document is arranged on the downstream side in the document transport direction so as to face the document path (see, for example, Patent Document 1). Here, as the front surface reading unit and the back surface reading unit, a light source (front surface light source, back surface light source) extending in a direction orthogonal to the document conveyance direction and an optical sensor arranged in parallel adjacent to the light source A device provided with (front surface light sensor, back surface light sensor) is used. Each reading unit uses each light source to irradiate light on the front surface or back surface of the document, and the reflected light reflected from the irradiated document is received by each light sensor. Reading.

  Further, in such an automatic double-sided reading device, if each light source is always turned on, the heat generation amount and power consumption of the light source will increase. Therefore, in Patent Document 1, the front surface light source and the back surface light source are turned on immediately before starting the capturing of the image data of the corresponding surface, and are turned off immediately after the capturing of the image data of the corresponding surface is stopped.

JP 2002-111977 A (5th page, FIG. 2)

Incidentally, in Patent Document 1, the front surface reading position by the front surface light sensor and the back surface reading position by the rear surface light sensor are shifted with respect to the document transport direction. For this reason, while the back surface light source is turned on and the back surface image is read by the back surface light sensor, the front surface light source is turned off when the front surface image is read by the front surface light sensor. Then, the reading result (especially image density) by the back surface light sensor changes before and after the surface light source is turned off.
For such a problem, Patent Document 1 describes that the amount of light of at least one of the front surface light source and the back surface light source is reduced during a period in which image data is simultaneously captured from the front surface light sensor and the back surface light sensor. .

  However, since various types of originals such as thick paper and thin paper can be used as the manuscript, how much light quantity of the front light source or the back light source should be reduced during the period when the image data of the front surface and the back surface is simultaneously captured. Is unknown. Therefore, when the degree of reduction of the light amount of the front light source or the back light source is wrong, there is a problem that the density change of the back image that occurs before and after the front light source is turned off cannot be suppressed.

  The present invention has been made to solve such a technical problem, and an object of the present invention is to perform one side reading during reading in double-sided scanning for reading images on both front and back sides of a document with a single conveyance of the document. Even when the light source is turned off, the object is to reduce image unevenness.

  For this purpose, an image reading apparatus to which the present invention is applied includes a conveyance path through which a document is conveyed, a first light source that irradiates a first surface of a document from one side of the conveyance path, and a first document. A first sensor that receives reflected light from the surface, a first reading unit that reads image data on the first surface of the document, and a second that irradiates the second surface of the document from the other side of the conveyance path. And a second sensor for receiving reflected light from the second surface of the document, and a second sensor that reads image data on the second surface of the document downstream of the first reading unit in the document transport direction. Of the image data of the second surface of the document read by the reading unit, the lighting control unit that controls the lighting of the first light source, and the second sensor, the image of the first surface of the document by the first sensor It is read after the first light source is turned off by the lighting control unit upon completion of data reading. And a correction unit that performs density correction on the data.

  The image reading apparatus further includes a transmittance determining unit that determines the transmittance of the document based on the pattern matching result between the image data of the first surface of the document and the image data of the second surface of the document, and a correction unit Can be characterized in that a correction coefficient for correcting the density of data is set in accordance with the transmittance of the document determined by the transmittance determining unit. A white reference member disposed opposite to the second sensor; shading data obtained by reading the white reference member with the second sensor when the first light source and the second light source are turned on; It further includes an acquisition unit that acquires a ratio with the sub-shading data obtained by reading the white reference member with the second sensor when only the second light source is turned on, and the correction unit is acquired by the acquisition unit It is possible to set a correction coefficient for correcting the density of the data in accordance with the ratio.

  From another point of view, the image reading apparatus to which the present invention is applied includes a conveyance path through which the document is conveyed, a first light source that irradiates the first surface of the document from one side of the conveyance path, and the document. A first sensor for receiving reflected light from the first surface of the first document, and a first reading unit for reading image data on the first surface of the document, and irradiating the second surface of the document from the other side of the conveyance path A second light source that receives the reflected light from the second surface of the document and a second sensor that reads image data on the second surface of the document, and the second sensor reads the image data. The image data read with the first light source and the second light source turned on, and the first light source turned off and the second light source turned on among the image data of the second surface obtained A correction unit that performs different density correction on the read image data is included.

  In such an image reading apparatus, the first reading unit and the second reading unit are arranged so as to be shifted in the document conveyance direction, and the first end after the document conveyance direction rear end has passed the reading position by the first sensor. It further includes a lighting control unit that turns off the light source. The correction unit may determine a correction coefficient used for density correction based on the transmittance of the document. Furthermore, the correction unit compares the amount of light received by the second sensor when the first light source and the second light source are turned on with the amount of light received by the second sensor when only the second light source is turned on. A correction coefficient used for density correction can be determined.

  According to the present invention, in double-sided scanning that reads images on both front and back sides of a document with a single conveyance of the document, even if one of the light sources is turned off during reading, density correction is performed according to the light source being turned off. Since it did in this way, the nonuniformity of an image can be reduced.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a diagram showing an image reading apparatus to which the present embodiment is applied. This image reading apparatus is roughly divided into a document feeding device 10 that sequentially conveys documents from a stacked document bundle, a scanner device 70 that reads an image by scanning, and a processing device 80 that processes a read image signal.

  The document feeder 10 includes a document tray 11 on which a bundle of documents composed of a plurality of documents is stacked, a tray lifter 12 that raises and lowers the document tray 11, and a nudger roll 13 that conveys a document on the document tray 11 raised by the tray lifter 12. Is provided. Further, on the downstream side of the nudger roll 13 in the sheet conveyance direction, a mechanism for separating sheets one by one is provided. This separating mechanism has a feed roll 14 that conveys documents on the document tray 11 conveyed by the nudger roll 13 further downstream, and a retard roll 15 that separates the documents supplied by the nudger roll 13 one by one. A takeaway roll 16, a pre-registration roll 17, a registration roll 18, a platen roll 19, and an out-roll 20 are provided in order from the upstream side in the paper conveyance direction in a first conveyance path 31 as a conveyance path through which an original is first conveyed. . The takeaway roll 16 conveys the originals that have been rolled up one by one to a downstream roll. The pre-registration roll 17 conveys the document to a further downstream roll and forms a loop of the document. The registration roll 18 resumes rotation at the same timing after being temporarily stopped, and supplies the document while performing registration adjustment on the document reading unit. The platen roll 19 assists in document conveyance during reading. The out roll 20 conveys the read original further downstream. The first transport path 31 is provided with a baffle 41 that rotates about a fulcrum according to the loop state of the document being transported. Further, a CIS (Contact Image Sensor) 50 is provided between the platen roll 19 and the out-roll 20.

  A second transport path 32 and a third transport path 33 are provided on the downstream side of the out-roll 20, and a transport path switching gate 42 for switching the transport path is attached to these branch portions. Further, on the downstream side of the second conveyance path 32 in the sheet conveyance direction, a discharge tray 40 on which the originals that have been read are stacked, and a first discharge roll 21 that discharges the originals to the discharge tray 40 are provided. Further, the inverter roll 22 and the inverter pinch roll 23 for switching back the document are folded on the fourth transport path 34 for switching back the document that has passed through the third transport path 33. Furthermore, a fifth transport path 35 is provided for guiding the document switched back by the fourth transport path 34 to the first transport path 31 again. Then, a sixth transport path 36 for discharging the document switched back by the fourth transport path 34 to the discharge tray 40, and a sixth transport path 36 for transporting the reversely discharged document to the first discharge roll 21. Two discharge rolls 24 are provided. An exit switching gate 43 for switching the transport path is provided at a branch portion of the fifth transport path 35 and the sixth transport path 36.

  The nudger roll 13 is lifted up and held at the retracted position during standby, and descends to the nip position (original transport position) during transport of the document to transport the uppermost document on the document tray 11. The nudger roll 13 and the feed roll 14 convey a document by connecting a feed clutch (not shown). The pre-registration roll 17 forms a loop by abutting the leading end of the document against the stopped registration roll 18. In the registration roll 18, the front end of the document bitten by the registration roll 18 is returned to the nip position when the loop is formed. When this loop is formed, the baffle 41 opens around the fulcrum and functions so as not to interfere with the loop formed on the document. In addition, the takeaway roll 16 and the pre-registration roll 17 hold a loop of the original being read. By this loop formation, the read timing can be adjusted, and the skew associated with the document conveyance at the time of reading can be suppressed, and the alignment adjustment function can be enhanced. In synchronization with the reading start timing, the stopped registration roll 18 starts rotating, the original is pressed against the second platen glass 72B (described later) by the platen roll 19, and the image is viewed from the lower surface direction by the CCD image sensor 78 described later. Data is read.

  The conveyance path switching gate 42 switches so that the document passing through the out-roll 20 is guided to the second conveyance path 32 and discharged to the discharge tray 40 at the end of reading one-sided document and at the same time when reading both-side documents simultaneously. It is done. On the other hand, the transport path switching gate 42 is switched so as to guide the document to the third transport path 33 in order to invert the document when the double-sided document is sequentially read. The inverter pinch roll 23 is retracted in a state where a feed clutch (not shown) is turned off and the nip is opened when sequentially reading double-sided originals, and guides the originals to the fourth conveyance path (inverter path) 34. Thereafter, the inverter pinch roll 23 is nipped, the original to be inverted by the inverter roll 22 is guided to the pre-registration roll 17, and the original to be reversed and discharged is conveyed to the second discharge roll 24 of the sixth conveyance path 36.

  The scanner device 70 is configured to be capable of placing the document feeder 10 described above, supports the document feeder 10 by an apparatus frame 71, and reads an image of a document conveyed by the document feeder 10. Yes. The scanner device 70 includes a device frame 71 forming a casing, a first platen glass 72A for placing a document to be read in a stationary state, and a light beam for reading a document being conveyed by the document feeder 10. A second platen glass 72B having an opening is provided.

  Further, the scanner device 70 is stationary under the second platen glass 72B or scans the entire first platen glass 72A to read an image and the light obtained from the full rate carriage 73 to the image coupling unit. A half-rate carriage 75 for supplying is provided. The full-rate carriage 73 is provided with an illumination lamp 74 as a first light source for irradiating light on the document, and a first mirror 76A for receiving reflected light obtained from the document. Further, the half-rate carriage 75 is provided with a second mirror 76B and a third mirror 76C that provide the light obtained from the first mirror 76A to the imaging unit. Further, the scanner device 70 includes an imaging lens 77, a CCD (Charge Coupled Device) image sensor 78, and a drive substrate 79. Among these, the imaging lens 77 optically reduces the optical image obtained from the third mirror 76C. The CCD image sensor 78 as the first sensor photoelectrically converts the optical image formed by the imaging lens 77. Furthermore, a CCD image sensor 78 is mounted on the drive substrate 79. Then, an image signal obtained by the CCD image sensor 78 is sent to the processing device 80 via the drive substrate 79. That is, the scanner device 70 forms an image on the CCD image sensor 78 using a so-called reduction optical system.

  Here, first, when reading an image of a document placed on the first platen glass 72A, the full rate carriage 73 and the half rate carriage 75 move in the scanning direction (arrow direction) at a ratio of 2: 1. . At this time, the light of the illumination lamp 74 of the full rate carriage 73 is applied to the surface to be read of the document. Then, the reflected light from the document is reflected in the order of the first mirror 76 A, the second mirror 76 B, and the third mirror 76 C and guided to the imaging lens 77. The light guided to the imaging lens 77 forms an image on the light receiving surface of the CCD image sensor 78. The CCD image sensor 78 is a one-dimensional sensor and processes one line at the same time. The full rate carriage 73 is moved in this line direction (scanning sub-scanning direction) to read the next line of the document. By executing this over the entire original, reading of one page of the original is completed.

  On the other hand, the second platen glass 72B is constituted by a transparent glass plate having a long plate-like structure, for example. A document conveyed by the document feeder 10 passes over the second platen glass 72B. At this time, the full-rate carriage 73 and the half-rate carriage 75 are stopped at the solid line positions shown in FIG. First, the reflected light of the first line of the document that has passed through the platen roll 19 of the document feeder 10 is imaged by the imaging lens 77 via the first mirror 76A, the second mirror 76B, and the third mirror 76C. An image is read by the CCD image sensor 78 which is the first sensor in the present embodiment. That is, after one line in the main scanning direction is simultaneously processed by the CCD image sensor 78 which is a one-dimensional sensor, the next line in the main scanning direction of the document conveyed by the document feeder 10 is read. After the leading edge of the original reaches the reading position of the second platen glass 72B, the original passes through the reading position of the second platen glass 72B, thereby completing one page of original reading in the sub-scanning direction.

  In the present embodiment, the full-rate carriage 73 and the half-rate carriage 75 are stopped, and the first platen glass 72B is used to read the first surface of the document by the CCD image sensor 78. It is possible to read the second side of the document by the CIS 50 (line sensor 54) in the same manner as when the same document is conveyed instead of coincidence. That is, by using the CCD image sensor 78 and the CIS 50, it is possible to read the images on both the front and back sides of the document with a single conveyance of the document to the conveyance path. At this time, the reading position of the second surface of the document by the CIS 50 is set to the downstream side in the document conveying direction by 30 mm with respect to the reading position of the first surface of the document by the CCD image sensor 78.

  FIG. 2 is a diagram for explaining a reading structure using the CIS 50. As shown in FIG. 2, the CIS 50 is provided between the platen roll 19 and the out roll 20. One side (first side) of the original is pressed against the second platen glass 72B, and the image on the first side is read by the CCD image sensor 78. On the other hand, in the CIS 50, an image on one side (second side) is read from the other side facing through a conveyance path for conveying a document. The CIS 50 includes a housing 50a, a glass 51, an LED (Light Emitting Diode) array 52, a rod lens array 53, and a line sensor 54. Among these, the glass 51 is attached to an opening formed on the conveyance path side of the housing 50a. Further, the LED array 52 as the second light source transmits the light to the second surface of the document through the glass 51. The rod lens array 53 condenses the reflected light from the LED array 52. The line sensor 54 reads the light collected by the rod lens array 53. As the line sensor 54, a CCD, a CMOS sensor, a contact sensor, or the like can be used, and an image having an actual width (for example, A4 longitudinal width 297 mm) can be read. In the CIS 50, an image is captured using the rod lens array 53 and the line sensor 54 without using a reduction optical system. Therefore, the structure can be simplified, the housing can be downsized, and power consumption can be reduced. The CIS 50 can read a color image. That is, a white LED light source is used as the LED array 52, and a set of three columns for RGB three colors is used as the line sensor 54.

  Further, the CIS 50 has a protruding portion 50b that protrudes upstream in the document conveying direction relative to the housing 50a of the CIS 50, a control member 55 that extends from the protruding portion 50b toward the downstream side in the document conveying direction, and a document to be conveyed protrudes. The abutting member 60 is provided. Here, the control member 55 is attached to the document feeder 10 (see FIG. 1) via the CIS 50, but the abutting member 60 is attached to the scanner device 70 (see FIG. 1). A guide 61 is provided on the downstream side of the abutting member 60. An opening 63 is formed between the guide 61 and the abutting member 60. Further, a dust storage portion 62 for storing dust and dirt adhering to the surface of the document is provided at a lower portion of the guide 61 and continuing to the opening 63. The control member 55 and the abutting member 60 are positioned in the conveyance path from the front surface to the rear surface of the document feeder 10 in a direction orthogonal to the document conveyance path (that is, from the front surface to the rear surface of the document feeder device 10). Correspondingly provided.

  Here, the control member 55 is supported by a rotating shaft 551 formed of a screw attached to the above-described projecting portion 50b, and is swingably supported by one end being wound around the rotating shaft 551. A free end, which is an end, is wound around a plate-shaped guide member 552 extending toward the abutting member 60 and the rotary shaft 551, and the end of one arm is inserted into a perforation 50c formed in the protruding portion 50b. The end of the other arm has a torsion spring 553 arranged to urge the guide member 552 toward the abutting member 60. Here, two protrusions 50b are provided at both ends in a direction orthogonal to the document conveyance path, and a rotation shaft 55 and a torsion spring 553 are also provided at both ends correspondingly. On the other hand, the guide member 552 is provided from the front surface to the rear surface in the direction orthogonal to the document conveyance path.

  In the present embodiment, the guide member 552 is made of a metal plate (metal plate) such as SUS. Further, the free end side of the guide member 552 extends in the vicinity of the reading position by the CIS 50, specifically, to a position 3 mm upstream from the reading position in the document transport direction. Further, a hemming bent portion 552a is provided on the free end side of the guide member 552, that is, a portion that comes into contact with the document. By providing this folded portion 552a, when contacting with the conveyed document. The generation of paper dust is suppressed. The guide member 552 is made of a metal sheet metal and can be bent by the torsion spring 553, so that the thickness of the conveyed document can be absorbed and even a document with a folding trace can be stabilized. Can be transported.

On the other hand, the abutting member 60 is provided on the upstream side of the document conveyance direction, and guides the document to be conveyed. The document conveyance surface 60a guides the document to be conveyed. And a step surface 60b formed by lowering one step. Further, the step surface 60b is formed so as to face the extension line of the light focus point by the rod lens array 53. On the step surface 60b, a white reference tape (white reference tape made of a biaxially stretched polyester film) is formed. Member) 64 is affixed. Therefore, the white reference tape 64 is attached to the scanner device 70 via the abutting member 60. In the present embodiment, the white reference tape 64 is disposed with the upper surface exposed in the conveyance path, and the upper surface of the white reference tape 64 is slightly behind the upper surface of the document conveyance surface 60a (away from the conveyance path). Is located on the side). Further, at both ends of the abutting member 60 on the conveyance path side (upper side) and in the direction orthogonal to the document conveyance direction with respect to the white reference tape 64, as indicated by the broken lines in the figure, the document conveyance direction is indicated. An extending rib 65 is formed. The rib 65 is integrally formed of resin together with the abutting member 60, and the height of the rib 65 is appropriately selected from the range of 0.1 to 1.0 mm in consideration of the thickness of the conveyed document. Is set. The height of the rib 65 is preferably slightly larger than the thickness of a document that is frequently used. Then, the guide member 552 urged by the torsion spring 553 contacts the rib 65, so that the document is not transported between the guide member 552 and the document transport surface 60a of the abutting member 60. In this state, a gap of 0.1 to 1.0 mm corresponding to the height of the rib 65 is formed.
Further, a white reference plate 66 attached to be in close contact with the first platen glass 72A is provided below the butting member 60 and on the upper side of the first platen glass 72A.

  Here, since the CIS 50 employs the rod lens array 53 as the optical imaging lens, the focal point (field of view) seismic intensity is as shallow as about ± 0.3 mm, which is about the same as when the scanner device 70 is used. The depth is 1/13 or less. When reading with the CIS 50, it is required to keep the reading position of the document within a predetermined narrow range. Therefore, in the present embodiment, the control member 55 is provided, and the document is pressed against the abutting member 60 by the control member 55 and conveyed, so that the posture of the document between the platen roll 19 and the out-roll 20 can be stabilized. It was configured to be controllable. 2 indicates the movement of the original when the control member 55 is provided. It is understood that the document to be conveyed is conveyed while being pressed against the abutting member 60. That is, the control member 55 reads the conveyed document while being pressed against the abutting member 60, thereby improving the sweetness of the focus when the CIS 50 having a shallow depth of field is used.

Next, the processing device 80 shown in FIG. 1 will be described.
FIG. 3 is a block diagram for explaining the processing device 80. The processing device 80 to which this embodiment is applied includes a signal processing unit 81 that processes image data input from sensors (CCD image sensor 78 and line sensor 54 (CIS 50)), a document feeder 10 and a scanner device. And a control unit 90 that controls the operation of 70. The signal processing unit 81 has a function of performing predetermined image processing on outputs from the CCD image sensor 78 that reads the front surface (first surface) of the document and the line sensor 54 of the CIS 50 that reads the back surface (second surface). Have.

  The signal processing unit 81 includes two systems of image processing units that perform various processes such as shading correction and offset correction on a digital signal. Specifically, a first image processing unit 100 that performs image processing on image data on the front surface (first surface) and a second image processing unit 200 that performs image processing on image data on the back surface (second surface). It is. The outputs from the first image processing unit 100 and the second image processing unit 200 are output to an IOT (Image Output Terminal) such as a printer or a host system such as a personal computer (PC). The signal processing unit 81 further includes a shading data setting unit (SHD setting unit) 300 and a transmittance determination unit 400. Here, the SHD setting unit 300 as an acquisition unit sets in advance shading data (SHD) used for shading correction of image data on the front surface (first surface) and the back surface (second surface). Further, the transmittance determining unit 400 determines the degree of show-through, that is, the transmittance of the document from the image data on the front surface (first surface) and the image data on the back surface (second surface).

  On the other hand, the control unit 90 includes an image reading controller 91, a CCD / CIS controller 92, a lamp controller 93, a scan controller 94, and a transport mechanism controller 95. Among these, the image reading controller 91 controls the entire document feeder 10 and the scanner device 70, including various double-sided scanning control and single-sided scanning control. The CCD / CIS controller 92 controls the image data capturing operation by the CCD image sensor 78 and the CIS 50. The lamp controller 93 as a lighting control unit controls the lighting / extinguishing of the LED array 52 of the CIS 50 and the lighting lamp 74 of the full rate carriage 73 in accordance with the reading timing. The scan controller 94 controls the scanning operation by the full rate carriage 73 and the half rate carriage 75 by turning on / off the motor in the scanner device 70. The transport mechanism controller 95 controls motor control, various roll operations, feed clutch operations, gate switching operations, and the like in the document feeder 10. From these various controllers, control signals are output to the document feeder 10 and the scanner device 70, and based on these control signals, these operation controls can be performed. The image reading controller 91 sets a reading mode based on a control signal from the host system, a sensor output detected in the automatic selection reading function, a selection from the user, and the like, and the document feeding device 10 and the scanner device 70 are set. I have control. As this reading mode, there are a double-sided simultaneous reading mode by one pass (without reversal), a reverse double-sided reading mode by reversing pass, a single-sided reading mode by one pass, and the like.

FIG. 4 shows a functional block diagram of the first image processing unit 100, the second image processing unit 200, the SHD setting unit 300, and the transmittance determining unit 400 in the present embodiment.
The first image processing unit 100 includes a shading correction unit 101, a GAP correction unit 102, a γ / gray balance correction unit 103, a color space conversion unit 105, and an enlargement / reduction unit 106. The first image processing unit 100 further includes a filter unit 107, a contrast adjustment unit 108, and a background removal unit 109.
Here, the shading correction unit 101 performs shading correction on the raw image data read by the CCD image sensor 78. The GAP correction unit 102 corrects the positional deviation of the RGB three-color image sensor. The γ / gray balance correction unit 103 corrects γ / gray balance. The color space conversion unit 105 converts the color space of the image data from BGR → L *, a *, b *. The enlargement / reduction unit 106 performs enlargement / reduction processing in the main scanning direction and the sub-scanning direction. The filter unit 107 performs MTF correction and smoothing. A contrast adjustment unit 108 adjusts the contrast of the read document. The background removal unit 109 removes the background of the read document. The first image processing unit 100 includes a shading data storage unit (SHD storage unit) 110 that stores shading data (SHD) for one line in the main scanning direction of the CCD image sensor 78. The SHD (first SHD) stored in the SHD storage unit 110 is set and written by the SHD setting unit 300 as described later.

On the other hand, the second image processing unit 200 includes a shading correction unit 201, a GAP correction unit 202, a γ / gray balance correction unit 203, a density correction unit 204, a color space conversion unit 205, and an enlargement / reduction unit 206. The second image processing unit 200 further includes a filter unit 207, a contrast adjustment unit 208, and a background removal unit 209. That is, the second image processing unit 200 has a configuration different from the first image processing unit 100 in that it includes a density correction unit (correction unit) 204.
Here, the shading correction unit 201 performs shading correction on the raw image data read by the CIS 50. The GAP correction unit 202 corrects the positional deviation of the RGB three-color image sensor. The γ / gray balance correction unit 203 corrects γ / gray balance. The density correction unit 204 performs different density corrections on the front end side and the rear end side of the document according to the lighting / extinguishing state of the illumination lamp 74 and the paper type of the document. The color space conversion unit 205 converts the color space of the image data from BGR → L ^* , a ^* , b ^* . The enlargement / reduction unit 206 performs enlargement / reduction processing in the main scanning direction and the sub-scanning direction. The filter unit 207 performs MTF correction and smoothing. A contrast adjustment unit 208 adjusts the contrast of the read document. The background removing unit 209 removes the background of the read original. The second image processing unit 200 also includes a shading data storage unit (SHD storage unit) 210 that stores shading data (SHD) for one line in the main scanning direction of the line sensor 54. The SHD (second SHD) stored in the SHD storage unit 210 is set and written by the SHD setting unit 300 as described later.

In addition, the SHD setting unit 300 as an acquisition unit includes an SHD acquisition unit 301 and a light amount ratio determination unit 302. The SHD acquisition unit 301 acquires the first SHD from the result obtained by reading the white reference plate 66 in the main scanning direction by the CCD image sensor 78. The acquired first SHD is stored in the SHD storage unit 110. The SHD acquisition unit 301 acquires a second SHD from the result obtained by reading the white reference tape 64 in the main scanning direction by the line sensor 54. Then, the acquired second SHD is stored in the SHD storage unit 210. The second SHD is also output to the light amount ratio determining unit 302. The first SHD and the second SHD are acquired in a state where both the illumination lamp 74 and the LED array 52 are turned on. Further, the SHD acquisition unit 301 performs the second sub-shading based on the result obtained by reading the white reference tape 64 in the main scanning direction by the line sensor 54 with only the LED array 52 turned on and the illumination lamp 74 turned off. Data (second sub SHD) is acquired. The second SHD is output to the light amount ratio determination unit 302.
The light quantity ratio determination unit 302 obtains the ratio (light quantity ratio) between the second SHD and the second sub SHD input from the SHD acquisition unit 301. That is, the light quantity ratio means the ratio of the amount of light received by the line sensor 54 when both the illumination lamp 74 and the LED array 52 are turned on simultaneously and when only the LED array 52 is turned on. The light amount ratio thus obtained is stored in a memory (not shown) provided in the density correction unit 204 of the second image processing unit 200.

  Further, the transmittance determining unit 400 includes an N line memory 401, a pattern matching unit 402, and a transmittance determining unit 403. The N line memory 401 stores 30 mm of data from the front end of the original document among the read data of the first surface input from the CCD image sensor 78. For example, when the reading resolution of the CCD image sensor 78 is 600 dpi, N = 709. The pattern matching unit 402 reads from the leading edge of the first surface reading data for 30 mm from the leading edge of the document read from the N line memory 401 and the reading data for the second surface input from the line sensor 54 of the CIS 50. Pattern matching is performed by sequentially collating the data for 30 mm. A transmittance determining unit 403 determines the transmittance of the document based on the pattern matching result in the pattern matching unit 402. Then, the transmittance determination result by the transmittance determining unit 403 is stored in a memory (not shown) provided in the density correcting unit 204 of the second image processing unit 200.

Next, a document transport method in each document reading mode will be described with reference to FIGS.
FIGS. 5A and 5B are diagrams showing document paths in the single-sided reading mode by one pass and the double-sided simultaneous reading mode by one pass. As shown in FIG. 5A, the documents placed on the document tray 11 are sequentially supplied to the first conveyance path 31 by the nudger roll 13, the feed roll 14, the retard roll 15, and the takeaway roll 16. The As shown in FIG. 5B, the supplied document is moved to the second conveyance path 32 by the conveyance path switching gate 42 via the reading section of the platen roll 19 and the reading section of the CIS 50, and the discharge tray 40. Are sequentially discharged. In the case of single-sided reading, reading is performed using the CCD image sensor 78 of the scanner device 70 shown in FIG. However, single-sided reading using the CIS 50 is also possible. In the case of simultaneous reading on both sides by one pass, the first surface is read using the CCD image sensor 78 of the scanner device 70, and the second surface is read using the CIS 50 during the same conveyance. As a result, it is possible to read both sides of the document by one document pass.

  6A to 6D are diagrams for explaining the double-sided reading mode based on the reverse path. As shown in FIG. 6A, the originals placed on the original tray 11 are sequentially supplied to the first transport path 31, and the platen roll is used by using the CCD image sensor 78 of the scanner device 70 shown in FIG. Reading is performed from below at 19 locations. Then, the transfer path switching gate 42 moves to the fourth transfer path 34 via the third transfer path 33. As shown in FIG. 6B, the document that has completely passed through the third conveyance path 33 is switched back by the inverter roll 22 and the inverter pinch roll 23, and is supplied to the fifth conveyance path 35 by the exit switching gate 43. .

  The document supplied to the fifth conveyance path 35 is again supplied to the first conveyance path 31. Then, as shown in FIG. 6C, the document is read from below by the CCD image sensor 78 of the scanner device 70. At this time, the document is in an inverted state from the case shown in FIG. 6A, and the second surface that is different from the first surface is read. The original on which the second side has been read is in an inverted state, and if it is discharged as it is to the discharge tray 40, the page order of the loaded original after reading will be out of order. Therefore, as shown in FIG. 6C, the document whose second surface has been read is moved to the fourth transport path 34 via the third transport path 33 using the transport path switching gate 42. The document supplied to the fourth conveyance path 34 and completely passing through the exit switching gate 43 is discharged to the discharge tray 40 by the outlet switching gate 43 via the sixth conveyance path 36 as shown in FIG. Is done. This makes it possible to align the page order of the original after reading in the first double-sided reading mode in which images on both sides of the original are sequentially read.

  As described above, in the present embodiment, after reading one side (first side) of the document using the CCD image sensor 78, the document is reversed and the other side (second side) is read by the first sensor. Using the CIS 50, which is a second sensor provided on the other side of the first sensor and the first sensor together with the first sensor together with the double-sided reading mode by the reversing path for sequentially reading. A double-sided simultaneous reading mode with one pass for reading both the front and back surfaces (first surface and second surface) with one transport was prepared. These modes are configured to be selectable automatically or based on a user designation or the like as necessary. This makes it possible to select the duplex scanning mode appropriately according to the application, such as whether monochrome output, color output, speed (productivity), or image quality is important. Can be used.

  Next, the first SHD, second SHD, and light quantity ratio acquisition processing executed before starting the image reading operation in each reading mode described above will be described with reference to the flowchart shown in FIG. This process is performed, for example, when the image reading apparatus is turned on.

  As the process starts, the scan controller 94 moves the full rate carriage 73 directly below the white reference plate 66 (step 101). Next, the lamp controller 93 turns on the illumination lamp 74 and the LED array 52 (step 102). Then, the CCD / CIS controller 92 causes the CCD image sensor 78 to read the white reference plate 66 (step 103), and outputs the read image data to the SHD setting unit 300 of the signal processing unit 81. Next, in the SHD setting unit 300, the SHD acquisition unit 301 generates shading data (first SHD) for one line in the main scanning direction based on the image data of the white reference plate 66, and the obtained first SHD is subjected to the first image processing. The data is stored in the SHD storage unit 110 provided in the unit 100 (step 104).

  After the acquisition of the first SHD is completed in this way, the CCD / CIS controller 92 causes the CIS 50 (line sensor 54) to read the white reference tape 64 (step 105), and the obtained image data is used as a signal processing unit. 81 to the SHD setting unit 300. Next, in the SHD setting unit 300, the SHD acquisition unit 301 creates shading data (second SHD) for one line in the main scanning direction based on the image data of the white reference tape 64, and uses the obtained second SHD as the second image. The data is stored in the SHD storage unit 210 provided in the processing unit 200 (step 106). The obtained second SHD is also output to the light amount ratio determining unit 302.

When the acquisition of the second SHD is completed, the lamp controller 93 turns off the illumination lamp 74 (step 107). At this time, the LED array 52 remains lit. In this state, the CCD / CIS controller 92 causes the CIS 50 (line sensor 54) to read the white reference tape 64 again (step 108), and outputs the obtained image data to the SHD setting unit 300 of the signal processing unit 81. To do. Next, in the SHD setting unit 300, the SHD acquisition unit 301 generates shading data (second sub SHD) for one line in the main scanning direction based on the image data of the white reference tape 64 (step 109). The two sub SHDs are output to the light amount ratio determining unit 302.
Then, the light amount ratio determining unit 302 calculates a light amount ratio (second SHD / second sub SHD) which is a ratio between the input second SHD and the second sub SHD, and the result is calculated by the second image processing unit 200. The data is stored in a memory (not shown) provided in the density correction unit 204 (step 110).

Next, the operation control by the processing device 80 in the double-sided simultaneous reading mode by one pass will be described in detail with reference to the timing chart shown in FIG.
After the leading edge of the document reaches the registration roll 18, the transport mechanism controller 95 drives the registration roll 18 at time t0. Thereby, the conveyance of the document toward the reading position is started. Next, the lamp controller 93 turns on the illumination lamp 74 and the LED array 52 slightly before the time t1 when the leading end of the document in the conveyance direction reaches the reading position by the CCD image sensor 78. At time t1, the CCD / CIS controller 92 starts capturing image data (surface image data) by the CCD image sensor 78. Next, the CCD / CIS controller 92 starts capturing image data (back surface image data) by the line sensor 54 at time t2 when the leading end of the document in the conveyance direction reaches the reading position by the CIS 50 (line sensor 54). Thereafter, the transport mechanism controller 95 stops the driving of the registration roll 18 at time t <b> 3 immediately after the trailing end of the original in the transport direction passes through the registration roll 18. Next, the lamp controller 93 turns off the illumination lamp 74 at time t4 immediately after the rear end in the document transport direction passes the reading position by the CCD image sensor 78. At the same time t4, the CCD / CIS controller 92 finishes the capturing of the surface image data by the CCD image sensor 78. Then, the lamp controller 93 turns off the LED array 52 at time t5 immediately after the rear end in the document transport direction passes the reading position by the CIS 50 (line sensor 54). At the same time t5, the CCD / CIS controller 92 ends the back image data capture by the line sensor 54.

Here, a period during which surface image data is read by the CCD image sensor 78 (hereinafter referred to as a surface reading period A) is from time t1 to time t4. The surface reading period A is divided into a first surface reading period A1 from time t1 to time t2 when only surface reading is performed and a second surface reading period A2 from time t2 to time t4 when double-sided reading is performed. . Here, the first surface reading period A1 corresponds to a time during which the document is conveyed by 30 mm.
On the other hand, the period during which the back image data is read by the CIS 50 (line sensor 54) (hereinafter referred to as the back surface reading period B) is from time t2 to time t5. The back surface reading period B is divided into a first back surface reading period B1 from time t2 to time t4 when double-sided reading is performed, and a second back surface reading period B2 from time t4 to time t5 when only back surface reading is performed. . Here, the second back surface reading period B2 corresponds to a time during which the document is conveyed by 30 mm as in the first front surface reading period A1.

  In the surface reading period A, since both the illumination lamp 74 and the LED array 52 are continuously lit, a large amount of light does not change during the capturing of the surface image data. On the other hand, in the back surface reading period B, the illumination lamp 74 is turned off and only the LED array 52 is turned on in the second back surface reading period B2. For this reason, the amount of light that passes through the original and is received by the line sensor 54 may vary during capture of the back side image data. Therefore, there is a possibility that the density of the back side image data on the rear end side of the original may be changed depending on the transparency of the sheets constituting the original.

  Therefore, in the present embodiment, the occurrence of such density fluctuations is suppressed by performing predetermined processing on the back surface image data thus captured. Specifically, the correction coefficient is determined based on the light amount ratio acquired by the processing shown in FIG. 7 and the transmittance of the original acquired when reading the double-sided original, and read in the second back side reading period B2. Density correction processing is performed on the back image data.

FIG. 9 is a flowchart for explaining the flow of density correction processing for back surface image data.
When double-sided reading is started in the double-sided simultaneous reading mode (step 201), surface image data for 30 mm from the leading edge of the original is sequentially stored in the N-line memory 401 of the transmittance determining unit 400 from the CCD image sensor 78 (step 202). ). Further, with a slight delay, back side image data of 30 mm from the front end of the document is sequentially input from the CIS 50 (line sensor 54) to the pattern matching unit 402 of the transmittance determining unit 400 (step 203). Then, the pattern matching unit 402 performs pattern matching while matching the front and back sides of the front side image data for 30 mm from the front end of the original read from the N line memory 401 and the back side image data for 30 mm from the front end of the input document. Step 204). Then, the pattern matching unit 402 outputs the pattern matching execution result to the transmittance determining unit 403. Next, the transmittance determination unit 403 determines the transmittance of the document that is currently being captured based on the input pattern matching execution result, and the determination result, that is, the document transmittance is determined as the second image. The data is stored in a memory (not shown) provided in the density correction unit 204 of the processing unit 200 (step 205). Then, the density correction unit 204 determines a correction coefficient to be used from the relationship between the document transmittance and the light amount ratio stored in a memory (not shown) (step 206).

Next, the density correction unit 204 determines whether the back side image data to be processed is within 30 mm from the trailing edge of the document, in other words, the back side image data read in the second back side reading period B2. It is judged whether or not (step 207). Here, if the back surface image data to be processed is not within 30 mm from the trailing edge of the document, in other words, if it is the back surface image data read in the first reading period B1, the density correction unit 204 performs correction. Density correction is performed with the coefficient set to 1.00 (data does not change before and after processing), and the back side image data subjected to density correction is output (step 208). On the other hand, if the back side image data to be processed is within 30 mm from the trailing edge of the document, the density correction unit 204 performs density correction using the correction coefficient determined in step 206, and the density correction is performed. The back image data is output (step 209). Then, it is determined whether or not the next line, that is, the back image data exists (step 210). If the next line exists, the process returns to step 207 to continue the processing. On the other hand, if there is no next line, the series of processing is terminated.
In this example, in step 208, the correction coefficient is set to 1.00 and the density correction is performed. However, the output may be performed without performing the density correction as it is.

  Now, the above-described processing flow will be described with specific examples. Here, FIG. 10A and FIG. 10B show a front image and a back image of one original. On the other hand, FIG. 10C shows surface image data (raw data) captured by the CCD image sensor 78 when this original is read in the double-sided simultaneous reading mode. When the transmittance of the sheet constituting the document is high, the back side image is slightly exposed in the front surface image data. On the other hand, FIG. 10D shows the back surface image data (raw data) captured by the CIS 50 (line sensor 54) when this original is read in the double-sided simultaneous reading mode. In the present embodiment, as described above, the illumination lamp 74 is turned off during the reading of the back image by the CIS 50, and therefore, an area 30 mm from the rear end of the document in the back image data (corresponding to the second back reading period B2). In the area), the density of the back image is reduced.

  Therefore, in the present embodiment, in step 204 described above, pattern matching is performed to determine the document transmittance. Specifically, the front surface image data captured in the first front surface reading period A1 and the back surface image data captured in the period B1a corresponding to the first front surface reading period A1 in the first back surface reading period B1 are used. Pattern matching is performed. That is, pattern matching is performed using front and back image data having a front / back relationship on the front side of the document. In the example shown in FIG. 10C and FIG. 10D, since the “F” symbol of the back image is transparent to some extent, it is determined from the pattern matching execution result that there is a predetermined amount of transmittance. It will be.

FIG. 11 shows an example of a correction coefficient acquisition table stored in the density correction unit 204. This correction coefficient acquisition table associates the original transmittance and the light amount ratio with the correction coefficient.
When the original transmittance is high, the light emitted from the illumination lamp 74 passes through the original and is easily received by the line sensor 54. In such a case, if the illumination lamp 74 is turned off in the middle of taking back image data, the amount of decrease in the amount of received light after turning off increases, so that the density of the back image in this region is apparently lowered. For this reason, in this embodiment, the correction coefficient is increased as the document transmittance increases. When the original transmittance is 0% (for example, the sheet constituting the original is thick paper), the amount of light received by the line sensor 54 is not affected by turning on / off of the illumination lamp 74 (light is applied to the original). Therefore, the correction coefficient is set to 1.00 (constant before and after density correction).
Further, as the light amount ratio is lower, that is, as the second SHD is smaller than the first SHD, the light emitted from the illumination lamp 74 is more easily transmitted through the document and received by the line sensor 54. In such a case, if the illumination lamp 74 is turned off in the middle of taking back image data, the amount of decrease in the amount of received light after turning off increases, so that the density of the back image in this region is apparently lowered. For this reason, in the present embodiment, the correction coefficient is increased as the light quantity ratio increases.

  In step 207, it is determined whether or not the back side image data to be processed is captured within 30 mm from the trailing edge of the document. That is, it is determined whether the data is captured during the first back surface reading period B1 or the second back surface reading period B2. When the back side image data to be processed is captured within 30 mm from the trailing edge of the document, the density is corrected with the correction coefficient acquired from the correction coefficient acquisition table shown in FIG. 11 based on the document transmittance and the light amount ratio. Correction is performed. By performing such density correction processing, the back image data output from the density correction unit 204 approaches the back image shown in FIG. That is, an image in which the density change is suppressed is also provided on the rear end side of the document.

  As described above, in the present embodiment, the line sensor is used when both the illumination lamp 74 and the LED array 52 are turned on, and when the illumination lamp 74 is turned off and only the LED array 52 is turned on. The density correction applied to the back side image data fetched at 54 is made different. For this reason, the illumination lamp 74 is turned off even when the illumination lamp 74 is turned off at the end of reading the front image of the document while reading the back image of the document using the CIS 50 (line sensor 54), for example. Before and after, the density change of the back surface image data can be suppressed, and the image unevenness in the back surface image data can be reduced.

  In the present embodiment, when the density correction is performed on the back surface image data captured by the line sensor 54 after the illumination lamp 74 is turned off, the correction coefficient is determined based on the transmittance of the document. The transmittance of the document is an index indicating the amount of light that is irradiated from the back side and transmitted through the document, and is a major factor for density fluctuation. Therefore, more accurate density correction can be performed by determining the correction coefficient according to the transmittance of the document. Here, in the present embodiment, when determining the transmittance of the document, pattern matching is performed on the front surface image data and the back surface image data obtained by actually reading the front surface and the back surface of the document. For this reason, it is possible to obtain the transmittance of the target document itself, and to improve the density correction accuracy.

  Further, in the present embodiment, when density correction is performed on the back surface image data captured by the line sensor 54 after the illumination lamp 74 is turned off, the line sensor 54 is turned on with both the illumination lamp 74 and the LED array 52 turned on. The correction coefficient is determined based on the ratio (light quantity ratio) of the second sub SHD acquired by the line sensor 54 in a state where only the second SHD and the LED array 52 acquired in step S3 are turned on. The light amount ratio is an index indicating the wraparound of light from the illumination lamp 74 to the line sensor 54, and is a major factor with respect to density fluctuations like the transmittance of the original. Therefore, more accurate density correction can be performed by determining the correction coefficient according to the light amount ratio. In this embodiment, since the correction coefficient is determined from both the transmittance and the light amount ratio of the original, the density correction accuracy can be further improved.

  In the present embodiment, an image on the first surface (front surface) of the document is read on the upstream side in the document conveyance direction, and an image on the second surface (back surface) of the document is read on the downstream side in the document conveyance direction. However, the reverse order may be used. In this embodiment, the first surface of the document is read using the reduction optical system and the second surface of the document is read using the contact optical system. However, the present invention is not limited to this. That is, they may be reversed, or both may be constituted by a reduction optical system or a contact optical system.

It is the figure which showed the image reading apparatus with which this Embodiment is applied. It is a figure for demonstrating the structure of CIS. It is a block diagram of a processing apparatus. It is a block diagram of a signal processing part. (a), (b) is a figure for demonstrating the original pass of the single-sided reading mode by 1 pass, and the double-sided simultaneous reading mode by 1 pass. (a)-(d) is a figure for demonstrating the document path | pass of the double-sided reading mode by a reverse path | pass. It is a flowchart which shows the flow of acquisition processing of 1st SHD, 2nd SHD, and light quantity ratio. It is a timing chart for demonstrating the operation control in the double-sided simultaneous reading mode by 1 pass. It is a flowchart for demonstrating the flow of the density correction process with respect to back surface image data. (a) is a diagram showing a front image formed on a document, (b) is a diagram showing a back image formed on the same document, and (c) is captured by a CCD image sensor in a double-sided simultaneous reading mode by one pass. Front image data (raw data) and (d) are diagrams showing back image data (raw data) captured by a line sensor. It is a figure which shows an example of the correction coefficient acquisition table stored in a density correction part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Document feeder, 50 ... CIS, 52 ... LED array, 54 ... Line sensor, 64 ... White reference tape, 66 ... White reference plate, 70 ... Scanner device, 74 ... Illumination lamp, 78 ... CCD image sensor, 80 ... Processing unit 81 ... Signal processing unit 90 ... Control unit 100 ... First image processing unit 200 ... Second image processing unit 204 ... Density correction unit 300 ... Shading data (SHD) setting unit 301 ... SHD acquisition , 302... Light quantity ratio determining unit, 400... Transmittance determining unit, 401... N line memory, 402... Pattern matching unit, 403.

Claims (7)

A transport path through which the document is transported;
A first light source that irradiates the first surface of the document from one side of the conveyance path and a first sensor that receives reflected light from the first surface of the document; A first reading unit for reading image data;
A second light source that irradiates the second surface of the document from the other side of the transport path and a second sensor that receives reflected light from the second surface of the document; A second reading unit that reads image data of the second surface of the document on the downstream side in the conveyance direction of the document;
A lighting control unit for controlling lighting of the first light source;
Of the image data of the second surface of the document read by the second sensor, the lighting control unit performs the reading by the first sensor when the image data of the first surface of the document is read by the first sensor. An image reading apparatus including a correction unit that performs density correction on data read after the first light source is turned off. A transmittance determining unit that determines the transmittance of the document based on a pattern matching result between the image data of the first surface of the document and the image data of the second surface of the document;
The image reading apparatus according to claim 1, wherein the correction unit sets a correction coefficient for correcting the density of the data according to the transmittance of the original determined by the transmittance determination unit. A white reference member disposed opposite to the second sensor;
When only the second light source is turned on, and the shading data obtained by reading the white reference member with the second sensor when the first light source and the second light source are turned on. An acquisition unit for acquiring a ratio with the sub-shading data obtained by reading the white reference member with the second sensor;
The image reading apparatus according to claim 1, wherein the correction unit sets a correction coefficient for correcting the density of the data according to the ratio acquired by the acquisition unit. A transport path through which the document is transported;
A first light source that irradiates the first surface of the document from one side of the conveyance path and a first sensor that receives reflected light from the first surface of the document; A first reading unit for reading image data;
A second light source that irradiates the second surface of the document from the other side of the conveyance path and a second sensor that receives reflected light from the second surface of the document; A second reading unit for reading image data;
Of the image data of the second surface read by the second sensor, the image data read in a state where the first light source and the second light source are turned on, and the first light source is turned off. And a correction unit that performs different density correction on the image data read with the second light source turned on. The first reading unit and the second reading unit are arranged to be shifted in the transport direction of the document;
The image reading apparatus according to claim 4, further comprising a lighting control unit that turns off the first light source after a trailing end of the document in the transport direction has passed a reading position by the first sensor.   The image reading apparatus according to claim 4, wherein the correction unit determines a correction coefficient used for density correction based on the transmittance of the document.   The correction unit receives the amount of light received by the second sensor when the first light source and the second light source are turned on, and light received by the second sensor when only the second light source is turned on. 5. The image reading apparatus according to claim 4, wherein a correction coefficient used for density correction is determined from a ratio to the amount.

Images