JP2016152563A - Image reading device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable accurate distinguishment between a sensor output indicating incident of disturbance light and a sensor output indicating incident of light reflected on a document affected by the disturbance light, so as to detect the disturbance light with high accuracy.SOLUTION: An image reading device 2 comprises: a reading unit 110 that includes a light source 101, optical lens 102, and image sensor 103; an A/D converter 104 that performs A/D conversion of an output from the image sensor 103; and an image processing part 105 that performs image processing of processing a digital signal output from the A/D converter 104 to create image data of a document D, the image processing part performing the image processing by using a value of a digital signal that is smaller than a value during document reading by a predetermined value during data sampling of disturbance light.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image reading apparatus and an image forming apparatus, and more particularly to a technique for detecting disturbance light.

  An image reading apparatus that optically reads a document placed on a contact glass to generate image data is provided in an image forming apparatus such as a multifunction peripheral. Some image reading apparatuses can detect the size of a document placed on a contact glass during image reading. As an example, as disclosed in Patent Document 1 below, a switch that detects opening / closing of a document cover that covers a contact glass is provided, and the document is irradiated by a light source just before the document cover is closed, and the reflected light is received by a light receiving element. A technique has been proposed in which an image is picked up and the document size is detected from the input data. This technology monitors data input to the image reading unit immediately before the document cover is closed, acquires image data including disturbance light incident from outside the document, and is obtained when the document cover is closed. By comparing with the image data to be detected, an image portion that does not include disturbance light components is specified, and the document size is detected.

JP-A-9-135330

  Digital image reading apparatuses are roughly classified into a method using a charge coupled device (CCD) and a method using a contact image sensor (CIS). The former illuminates a document placed on the contact glass from the lower surface of the contact glass, reflects the reflected light by a plurality of mirrors and makes it enter an optical lens, and the optical lens receives an optical image of the document by an image sensor ( In this case, the image is read by performing reduction image formation on the CCD) and is called a reduction optical system. The latter reads an image by forming an optical image of a document on an image sensor (in this case, a CIS) using an equal magnification erecting optical system such as a SELFOC (registered trademark) lens. Called.

  In the reduction optical system, for example, the sensor size corresponding to a pixel size of 42.3 μm when the original surface is divided by 600 dpi is as small as about 4.7 μm to 9.325 μm. It has been reduced to 1110 times. On the other hand, in the 1 × optical system, the pixel size and the sensor size are the same. Therefore, the sensor light-receiving surface of the equal-magnification optical system has an area ratio of 20 to 80 times that of the sensor light-receiving surface of the reduction optical system. Therefore, even if there is a difference depending on the brightness of the lens, when the reading speed is the same, the amount of illumination light with which the sensor output is equivalent is relatively small such as 1/10 or less of the reduction optical system in the 1 × optical system. The amount of light is enough.

  Here, as disclosed in Patent Document 1, when acquiring image data including disturbance light incident from outside the document in a state where the document cover is opened, the amount of light that the disturbance light itself enters the image sensor is The same regardless of the image reading method. However, as described above, the amount of illumination light with the same sensor output is less in the equal magnification optical system than in the reduction optical system, so the sensor output when ambient light is incident is lower than that in the reduction optical system. The same magnification optical system is also larger. Therefore, in the same-magnification optical system, in the case of a document with a small thickness, when ambient light passes through the document from the back and enters the sensor, its spectral amount increases, and although it is reflected light from the document, The reflected light of this part may exceed the threshold value determined as disturbance light. For this reason, there is a risk of erroneous determination that there is no document even in an area where the document is actually present, and there is a possibility that the document size cannot be detected correctly. Also, if the sensor output after A / D conversion is saturated when disturbance light is incident, the disturbance light detection itself does not function.

  The present invention has been made to solve the above problem, and accurately discriminates between a sensor output indicating the incidence of disturbance light and a sensor output indicating the incidence of reflected light on a document affected by the disturbance light. It is an object to enable disturbance light to be detected with high accuracy.

An image reading apparatus according to an aspect of the present invention includes a contact glass on which an original is placed on an upper surface,
The optical lens having a light source that illuminates the original from the lower surface side of the contact glass, an optical lens that forms an image of reflected light from the original illuminated by the light source, and a plurality of sensor elements in a main scanning direction A reading unit having an image sensor that converts an optical image formed by the optical signal into an electrical signal;
An A / D converter for A / D converting the electrical signal output from the image sensor into a digital signal;
An image processing unit that performs image processing for processing the digital signal output from the A / D converter to generate image data of the document, and when sampling ambient light data, the value is greater than the value at the time of document reading And an image processing unit that performs the image processing using a value of the digital signal that is a value that is smaller by a predetermined amount.

  According to the present invention, it is possible to accurately discriminate between a sensor output indicating the incidence of disturbance light and a sensor output indicating the incidence of reflected light on a document affected by the disturbance light. Even in the image reading apparatus, disturbance light can be detected correctly. As a result, it is possible to detect the document size with high accuracy by removing the influence of disturbance light.

1 is a perspective view illustrating an appearance of an image forming apparatus including an image reading apparatus according to an embodiment of the present invention. 1 is a schematic diagram illustrating an external configuration of an image reading apparatus according to an embodiment of the present invention. 1 is a schematic diagram illustrating an overall configuration of an image reading apparatus. 3 is a flowchart illustrating a first embodiment of disturbance light detection processing by the image reading apparatus. It is a flowchart which shows 2nd Embodiment of the disturbance light detection process by an image reading apparatus. It is a block diagram which shows the structural example of an image sensor, an A / D converter, and an image process part.

  Hereinafter, an image forming apparatus and an image reading apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view illustrating an appearance of an image forming apparatus including an image reading apparatus according to an embodiment of the present invention. An image forming apparatus 1 shown in FIG. 1 includes a housing 1001 formed of a housing.

  The housing 1001 includes a lower housing 1011, an upper housing 120 provided at an upper portion thereof, and a connecting housing 1031 that connects these two housings. A sheet stack portion 107 is formed in an intermediate portion between the lower housing 1011 and the upper housing 120 so as to enter the inner side in a substantially horizontal direction from the side. An operation unit 50 is provided on the front surface of the upper housing 120. The sheet stack unit 107 is provided with a sheet tray 108 on which sheets discharged from the lower housing 1011 are stacked.

  The upper housing 120 includes an image reading device 2 having a flat bed inside and reading a document on the flat bed by a scanner unit or the like. The lower housing 1011 incorporates an image forming mechanism such as a photosensitive drum for forming a toner image on a sheet, an exposure unit and a developing unit, and a fixing unit for fixing the toner image on the sheet. The lower housing 1011 is further provided with a paper feed cassette (paper feed mechanism) 106 that stores recording paper. In this embodiment, an example in which two paper feed cassettes 106 are provided is shown, but the number of paper feed cassettes is not particularly limited. The connection housing 1031 has a built-in paper conveyance path for conveying the recording paper after fixing in the image forming process and discharging it to the sheet tray 108.

  In the image forming apparatus 1, an original image read by the image reading apparatus 2 is formed on a recording sheet fed from one of the sheet feeding cassettes 106 by the image forming mechanism built in the lower housing 1011. The recording paper after the image formation is discharged from the paper conveyance path in the connection housing 1031 to the sheet tray 108.

  FIG. 2 is a schematic diagram showing an external configuration of the image reading apparatus 2 according to the embodiment of the present invention. The image reading device 2 is an image reading device of an equal magnification optical system that reads an image by forming an optical image of a document on an image sensor (CIS) using an equal magnification erecting optical system such as a SELFOC lens. The image reading apparatus 2 is provided on the image reading apparatus main body 10, a contact glass (original table glass) 11 provided on the upper surface of the image reading apparatus main body 10, and the apparatus rear side (back side) of the upper surface of the contact glass 11. A document size support member 12 and a document cover 20 that presses and supports the document D placed on the contact glass 11 are provided.

  The document cover 20 is a substantially flat member that is rotatably installed with the back side of the apparatus as a rotation axis. The document cover 20 is supported by a document cover support portion 13 provided on the back side of the apparatus so as to be opened and closed in the vertical direction. On the back surface of the document cover 20, that is, on the document D side, a white document mat 21 that can come into surface contact with the contact glass 11 and directly presses the document D is provided. In a state where the document cover 20 is closed, the document mat 21 uniformly presses the document D against the contact glass 11 to bring the document D into close contact with the contact glass 11, and disturbance light is read from the contact glass 11 during image reading. It is prevented from entering the inside of the apparatus main body 10.

  The document cover support unit 13 is provided with a sensor 14 for detecting the open / closed state of the document cover 20, and is used to detect document cover opening / closing provided between the image reading apparatus main body 10 and the document cover support unit 13. The auxiliary member 15, the pressing member 17, and the sensor 14 constitute a document cover open / close detection switch 150.

  The pressing member 17 is provided on the inner surface side of the document cover 20 and on the surface facing the contact glass 11 at a position where it can contact the auxiliary member 15. The pressing member 17 can be expanded and contracted in the pressing direction in a state where the pressing member 17 is pressed in a direction toward the auxiliary member 15 positioned below by, for example, a pressing spring provided inside.

  The auxiliary member 15 is biased upward. The biasing force is a force smaller than the pressing force of the pressing member 17 by the pressing spring. When the document cover 20 is separated from the contact glass 11 and the angle of the document cover 20 with respect to the contact glass 11 is, for example, 30 ° (this angle is a constant angle) or more, the upper tip of the auxiliary member 15 contacts the pressing member 17. Do not touch. In this state, the auxiliary member 15 is stationary at the uppermost position by the biasing.

  On the other hand, when the document cover 20 is rotated in the direction approaching the contact glass 11 from the above posture, and the angle of the document cover 20 with respect to the contact glass 11 becomes an angle smaller than 30 °, the auxiliary member 15 contacts the pressing member 17. It is pushed downward by contact. As described above, the auxiliary member 15 is configured to move in the vertical direction in conjunction with the opening and closing of the document cover 20.

  The sensor 14 has a light emitting element and a light receiving element (not shown). When the document cover 20 is opened at a certain angle or more and the auxiliary member 15 is stationary at the uppermost position, the protrusion 16 formed at the lower tip of the auxiliary member 15 receives the light emitting element and the light receiving element of the sensor 14. It is located between the elements and blocks light between these elements. Thereby, the document cover 20 is detected as an open state by the control unit 180 described later. On the other hand, when the document cover 20 is closed more than the predetermined angle, the pushing of the auxiliary member 15 is started, and when the protrusion 16 moves downward, the light shielding state between the light emitting element and the light receiving element of the sensor 14 is released. The At this time, the document cover 20 is detected as “closed state” by the control unit 180.

  Further, when the document cover 20 rotates in the direction approaching the contact glass 11 and approaches the contact glass 11, the pressing member 17 pushes the auxiliary member 15 to the surface height of the contact glass 11 and comes into contact with the contact glass 11. At this time, the pressing member 17 is pushed into the document cover 20 side against the above-described pressing spring by the contact. When the document cover 20 further rotates and its inner surface comes into close contact with the contact glass 11, the pressing member 17 is pushed to the position of the inner surface of the document cover 20 due to the shrinkage caused by the pushing. At this time, the mechanical switch (not shown) provided in the pressing member 17 is changed from the previous open state to the closed state. When the control unit 180 detects the closed state of the switch, it detects that the original cover 20 is in close contact with the contact glass 11 and is completely closed. When the switch is still in the open state, the control unit 180 detects that the document cover 20 is in the “closed state” in which the document cover 20 is not completely in contact with the contact glass 11. In other words, the “closed state” indicates a state immediately before the document cover 20 is completely closed with close contact with the contact glass 11 and the document cover 20 is still open with respect to the contact glass 11.

  Next, the configuration of the image reading apparatus 2 will be described. FIG. 3 is a schematic diagram illustrating the overall configuration of the image reading apparatus 2, and is a view of the image reading apparatus 2 as viewed from the front side of the image reading apparatus 2 as viewed from the operator positioned in front of the image forming apparatus 1.

  The image reading apparatus main body 10 is provided with a reading unit 110 in which a light source 101, an optical lens 102, and an image sensor 103 are accommodated in the apparatus main body 100.

  The light source 101 illuminates the document D placed on the contact glass 11 from the lower surface of the contact glass 11.

  The optical lens 102 is an equal-magnification erecting optical system composed of, for example, a Selfoc lens, and forms an image of reflected light from the document D illuminated by the light source 101.

  The image sensor 103 has a plurality of sensor elements (for example, CMOS sensors) in the main scanning direction, which is a direction from the back side to the front side of the image reading device 2, and an optical image formed by the optical lens 102. It converts to an electrical signal.

  The light source 101, the optical lens 102, and the image sensor 103 all extend linearly over the main scanning direction, which is a direction from the back side to the front side of the image forming apparatus 1 and the image reading apparatus 2. The reading unit 110 is moved in the sub-scanning direction by a driving force supplied from a motor (not shown), so that the entire area of the document D in the main scanning direction is sub-scanned by the light source 101, the optical lens 102, and the image sensor 103. Reading is performed in the scanning direction (direction orthogonal to the main scanning direction).

  The image reading apparatus 2 further includes an A / D converter 104, an image processing unit 105, a control unit 180, and a document size detection unit 109.

  The A / D converter 104 converts the electrical signal output from the image sensor 103 into a digital signal. The image processing unit 105 is configured by, for example, an ASIC (Application Specific Integrated Circuit) or the like, and processes the digital signal (read data) output from the A / D converter 104 to generate image data of the document D.

  The control unit 180 includes a CPU and a RAM, and performs overall operation control of the image reading apparatus 2 and the image forming apparatus 1. In addition, the control unit 180 performs control to switch the gain amount of the A / D converter 104. The control unit 180 is an example of a gain switching control unit in the claims.

  The image processing unit 105 performs image processing for processing the digital signal output from the A / D converter 105 to generate image data. For example, the image processing unit 105 performs white reference correction using read data obtained by the image reading device 2 reading a white reference plate (not shown) provided on the contact glass 11.

  The document size detection unit 109 is an image in which each pixel shows disturbance light depending on whether or not each pixel constituting the image data generated by the image processing unit 105 has reached a pixel value indicating a predetermined threshold value. The document size is detected by determining whether or not to perform the process.

  The voltage level digitally converted by the A / D converter 104 is determined for each sensor element, and the voltage level of each sensor element is a gain set by the control unit 180 so that a constant digital output is obtained. Gain is amplified by the value.

  Here, the output from the image sensor 103 varies from sensor element to sensor element in the main scanning direction due to differences in individual sensor sensitivity and light distribution of the light source 101. In order to solve this, correction of the gain amount of the A / D converter 104 and white reference correction are effective. Here, the correction of the gain amount of the A / D converter 104 cannot be performed for each pixel indicated by the output from the image sensor 103. Therefore, the image processing unit 105 performs white reference correction for each pixel. For example, when the A / D converter 104 converts 1V voltage into 8-bit digital data, the control unit 180 causes the output of the sensor element having the highest input data in the main scanning direction to be “240”. The gain amount of the A / D converter 104 is adjusted. Further, the image processing unit 105 performs white reference correction for each pixel so that the numerical value becomes “255” in the entire main scanning direction. The target value by this white reference correction is a “white reference correction coefficient”, which is a numerical value that determines the maximum value of brightness. When this numerical value is reduced, data brighter than the white reference plate can be input. Conversely, when the numerical value is increased, data is saturated even when darker data is input than the white reference plate.

  As described above, the image sensor 103, which is an equal magnification optical system, adjusts the gain amount and the white reference correction coefficient. However, since the sensor sensitivity is higher than that of a reduction optical system such as a CCD, the difference due to the brightness of the optical lens 102 If the reading speed is the same, the amount of illumination light with the same sensor output is clearly smaller than that of the reduction optical system. Therefore, when the gain amount and the white reference correction coefficient are determined as described above according to the original reflected light value of the document D that is not affected by the disturbance light, the thickness of the document D is thin and the disturbance light is reflected on the document D. When the light passes through the back and enters the image sensor 103, even the reflected light from the document D is greatly amplified, and based on the sensor output, the reflected light from the document D and the disturbance light are correctly discriminated. There is a possibility that it cannot be done. For this reason, the document size detection unit 109 may not be able to correctly detect the size of the document D.

  Therefore, the image processing unit 105 performs the image processing using the value of the digital signal that is smaller than the value at the time of reading the document by a predetermined amount when sampling the disturbance light data. For example, in the state in which the document cover 20 is opened, in the present embodiment, when the control unit 180 detects that the “open state” is changed to the “closed state”, the control unit 180 performs the A / D conversion. By setting the gain amount of the device 104 to a predetermined value smaller than the value at the time of document reading, the digital signal is set to a value smaller than the value at the time of document reading by a predetermined amount. In other words, the control unit 180 causes the reading unit 110, the A / D converter 104, and the image processing unit 105 to perform data sampling of ambient light with the predetermined amount of gain.

  The predetermined value is a value obtained by amplifying the increased amount of light even when the amount of reflected light of the document D increases due to the influence of disturbance light. Is a value that allows the numerical value after amplification of the amount of light when the disturbance light itself is incident to exceed the threshold value while suppressing the value to not exceed the threshold value used for determining the disturbance light.

  Thereby, the amplification factor for the reflected light of the document D affected by the disturbance light in the A / D converter 104 is suppressed, and even when the document D having a small thickness is placed on the contact glass 11, This avoids a situation where the amount of reflected light of the document D is amplified to an amount that cannot be distinguished from the disturbance light itself. In other words, the disturbance light data after A / D conversion is prevented from being saturated, and the disturbance light is accurately detected.

  Further, instead of the control unit 180 setting the gain amount of the A / D converter 104 to the predetermined value as described above, the image processing unit 105 uses the white reference correction coefficient used in the white reference correction. Is set to a predetermined white reference correction coefficient smaller than the value at the time of reading the document, and white reference correction is performed using the set white reference correction coefficient, whereby the digital signal is converted into a value at the time of reading the document. Alternatively, the value may be smaller by a predetermined amount. The adjustment of the gain amount cannot be performed for each pixel indicated by the output from the image sensor 103, whereas the white reference correction coefficient can be adjusted for each pixel by the image processing unit 105. For this reason, the process of suppressing the numerical value of the amount of light indicating the reflected light of the document D affected by the disturbance light is accurately performed for each pixel that needs the process, and the disturbance light and the reflected light of the document D are more accurately obtained. Detectable.

  Next, a first embodiment of ambient light detection by the image reading device 2 will be described. FIG. 4 is a flowchart showing a first embodiment of the disturbance light detection process performed by the image reading apparatus 2.

  When the control unit 180 detects that the document cover 20 is in the “open state” based on the output from the document cover open / close detection switch 150 (YES in S1), the control unit 180 detects the A / D converter 104. Is set to the predetermined value (S2).

  Thereafter, the control unit 180 causes the reading unit 110 to read an image on the contact glass 11 on which the document D is placed for sampling data of disturbance light (S3). The sensor output from the image sensor 103 of the reading unit 110 is subjected to A / D conversion by the A / D converter 104 with the gain amount of the predetermined value set in S2, and converted into a digital signal for image processing. Image data is obtained by image processing including white reference correction by the unit 105.

  The control unit 180 monitors the state of the document cover open / close detection switch, and performs data sampling of disturbance light by the process of S3 while the document cover 20 is open (NO in S4). For example, the control unit 180 causes the image reading unit 5 to read image data for one line or a plurality of lines as image data representing disturbance light.

  Thereby, for example, the image processing unit 105 performs main scanning among the data of each line read by the image reading unit 5 using the image data generated by the image processing by the image processing unit 105 through the process of S3. It is possible to accurately determine which region in the direction is a region of an image showing disturbance light (an image that is not a document).

  On the other hand, when the control unit 180 detects that the document cover 20 is in the “closed state” based on the output from the document cover open / close detection switch 150 (YES in S4), the control unit 180 displays the A / D converter. The gain value 104 is returned to the normal value (S5). Thereby, when the original image is read by the image reading unit 5, a digital signal based on the gain value of the normal value is output from the A / D converter 104.

  Next, a second embodiment of ambient light detection by the image reading device 2 will be described. FIG. 5 is a flowchart showing a second embodiment of the ambient light detection process performed by the image reading apparatus 2. The description of the same processing as that of the first embodiment described with reference to FIG. 4 is omitted.

  In the second embodiment, instead of the process (S2) in which the control unit 180 in the first embodiment sets the gain amount of the A / D converter 104 to the predetermined value (S2), the image processing unit 105 performs an A / D conversion. The white reference correction coefficient used for the white reference correction for the data indicated by the digital signal output from the D converter 104 is set to the above-described predetermined value that is smaller than the value used during document reading (S12).

  Thereafter, the control unit 180 causes the reading unit 110 to read an image on the contact glass 11 for sampling data of disturbance light (S13). The sensor output from the image sensor 103 of the reading unit 110 is subjected to white reference correction by the image processing unit 105 using the white reference correction coefficient having the predetermined value set in S12. The image processing unit 105 performs image processing including the white reference correction to generate image data.

  Thereby, for example, the image processing unit 105 uses the image data generated by the image processing by the image processing unit 105 through the process of S13, and performs main scanning among the data of each line read by the image reading unit 5. It is possible to accurately determine which region in the direction is a region of an image showing disturbance light (an image that is not a document).

  In the second embodiment, when the control unit 180 detects that the document cover 20 is in the “closed state” based on the output from the document cover open / close detection switch 150 (YES in S14), the image processing unit 105. Returns the value of the white reference correction coefficient to the normal value used during document reading (S15). Thus, when the original image is read by the image reading unit 5, the image processing unit 105 performs white reference correction based on the white reference correction coefficient of the normal value.

  FIG. 6 is a block diagram illustrating a configuration example of the image sensor 103, the A / D converter 104, and the image processing unit 105. The image sensor 103 has a plurality of chips 103A to 103H arranged in the main scanning direction. Each chip has a plurality of sensor elements arranged in the main scanning direction. The A / D converters 104A and 104B have four channels. The electrical signals output from the chips 103A to 103D are input to the channels 1 (CH1) to 4 (CH4) of the A / D converter 104A. In addition, each electrical signal output from the chips 103E to 103H is input to channel 1 (CH1) to channel 4 (CH4) of the A / D converter 104B. The A / D converters 104A and 104B are capable of A / D converting electrical signals input to each channel with individual gains. An image processing unit (ASIC) 105 processes digital signals for 8 channels output from the A / D converters 104A and 104B to generate image data of the document D.

  In the configuration shown in FIG. 6, since the A / D converters 104A and 104B can perform A / D conversion with individual gains for each channel as described above, the adjustment of the gain amount by the control unit 180 described above is as follows. This can be done for each chip. Here, for example, when the image reading by the image reading device 2 is set to read the document D placed on the contact glass 11 on the back side, the image reading device 2 is read. Since the incident amount of disturbance light is larger on the front side of the apparatus than on the rear side of the apparatus, the control unit 180 is applied to some chips arranged on the front side of the apparatus for image reading during sampling of the disturbance light. Only the channel of the corresponding A / D converter 104A, for example, CH1 and CH2, the gain amount may be set to the predetermined value.

  Furthermore, the image processing unit 105 reads the white reference only for the data of each pixel output from the channels (for example, CH1 and CH2) corresponding to the part of the chip for image reading at the time of sampling the disturbance light. You may make it perform the adjustment which changes the white reference correction coefficient used for correction | amendment to the white reference correction coefficient of the predetermined value mentioned above.

  As described above, when sampling ambient light, the gain amount used for the channel data corresponding to a part of the chips arranged on the front side of the apparatus is set to the predetermined value and / or the white reference correction coefficient. By performing the adjustment with the above-described predetermined coefficient, it is possible to shorten the return time when the gain amount or the white reference correction coefficient is returned to the value used when reading the document image.

  As described above, according to the present embodiment, in the image reading apparatus 2 of the equal magnification optical system, the sensor output (pixel value) indicating the incidence of disturbance light and the reflection on the document D affected by the disturbance light. The sensor output (pixel value) indicating the incidence of light can be accurately discriminated, and the document size can be detected with high accuracy.

  The present invention is not limited to the configuration of the above embodiment, and various modifications can be made. For example, in the first embodiment, the control unit 180 performs a process (S2) of setting the gain amount of the A / D converter 104 to the predetermined value. In the second embodiment, the image processing unit 105 Is a process of setting the white reference correction coefficient used for the white reference correction for the data indicated by the digital signal output from the A / D converter 104 to the above-described predetermined value smaller than the value used at the time of document reading (S12). That is, at the time of detecting ambient light, a process (S2) for setting the gain amount of the A / D converter 104 to the predetermined value or the white reference correction coefficient described above is determined in advance. One of the processes (S12) for setting a value is selectively performed, but both of these processes may be performed in an overlapping manner.

  In the above embodiment, the image reading apparatus 2 is an equal magnification optical system. However, the above-described gain amount and / or white reference correction coefficient can be applied to a reduction optical system image reading apparatus having a low reading speed. It is possible to apply document size detection processing by changing the above.

  The configuration and processing shown in the above embodiment using FIGS. 1 to 6 are only one embodiment of the present invention, and are not intended to limit the present invention to the configuration and processing.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Image reading apparatus 11 Contact glass 20 Document cover 50 Operation part 100 Main part 101 Light source 102 Optical lens 103 Image sensor 103A-103H Chip 104, 104A, 104B A / D converter 105 Image processing part 180 Control part 110 Reading unit D Document

Claims (6)

A contact glass on which an original is placed;
The optical lens having a light source that illuminates the original from the lower surface side of the contact glass, an optical lens that forms an image of reflected light from the original illuminated by the light source, and a plurality of sensor elements in a main scanning direction A reading unit having an image sensor that converts an optical image formed by the optical signal into an electrical signal;
An A / D converter for A / D converting the electrical signal output from the image sensor into a digital signal;
An image processing unit that performs image processing for processing the digital signal output from the A / D converter to generate image data of the document, and when sampling ambient light data, the value is greater than the value at the time of document reading An image reading apparatus comprising: an image processing unit that performs the image processing using a value of the digital signal that is a value that is smaller by a predetermined amount. A document cover that is rotatably installed so that surface contact with the contact glass is possible,
A gain amount of the A / D converter when the ambient light data sampling is performed in a state where the document cover is not in surface contact with the contact glass is determined in advance to be smaller than a gain amount value at the time of document reading. And a gain switching control unit for setting the value to
The A / D converter is configured such that the digital signal is set to a value smaller than a value at the time of reading a document by a predetermined amount based on a gain amount of the predetermined value set by the gain switching control unit. The image reading apparatus according to claim 1, wherein The document cover is provided with the rotation shaft of the rotation on the back side of the image reading device,
The image sensor has a plurality of elements arranged in a main scanning direction that is a direction from the back side to the front side of the image reading device,
The reading unit reads the document placed on the contact glass on the back side,
The gain switching control unit can set a different gain amount for each of the plurality of elements of the A / D converter, and the gain amount is determined in advance when the disturbance light data sampling is performed. 3. The image reading apparatus according to claim 2, wherein the setting to the predetermined value is performed only for a predetermined part of the plurality of sensor elements on the front side in the main scanning direction.   The image processing unit starts from a predetermined value smaller than a value of a white reference correction coefficient used for white reference correction at the time of reading a document with respect to data indicated by the digital signal output from the A / D converter. The image reading apparatus according to claim 1, wherein white digital correction is performed using a white reference correction coefficient to reduce the digital signal by a predetermined amount from a value at the time of original reading.   The image processing unit can set a white reference correction coefficient for each pixel constituting the digital signal output from the A / D converter, and when performing the image processing at the time of data sampling of the disturbance light, the predetermined value is determined in advance. The image reading apparatus according to claim 4, wherein the white reference correction coefficient is set to the predetermined value for only a part of the elements.   An image forming apparatus comprising the image reading apparatus according to claim 1.

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