JP2014120893A - Image reader, control method of the same, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform image reading processing using a right/left division reading system at faster speed and with high quality.SOLUTION: An image sensor includes a plurality of photoelectric conversion elements which are continuously arranged and output received light as a pixel signal. A first region from one end of arrangement to a prescribed position in the arrangement and a second region from the prescribed position to the other end of the arrangement are divided and the pixel signals are outputted from the plurality of photoelectric conversion elements. When the image sensor receives reflected light from a background plate, an average value of pixel values is calculated from the plurality of pixel signals outputted from at least one of the first region and the second region. Correction is performed on shading correction in accordance with a comparison result obtained by comparing the average value with a reference value. The correction for one shading correction is performed for every one or more document images when the document images are continuously read.

Description

  The present invention relates to an image reading apparatus that reads a document image and outputs it as digital image data, a control method for the image reading apparatus, and an image forming apparatus.

  An image that reflects the light from the light source on the document image, receives the reflected light with an image sensor using a photoelectric conversion element such as a CCD (Charge Coupled Device), obtains a pixel signal, and outputs image data obtained by reading the document image Readers are known. In the image reading apparatus, pixels of photoelectric conversion elements are arranged in the main scanning direction, and an original or an image sensor is moved in the sub scanning direction, thereby reading an image of one original.

  In such an image reading apparatus, shading correction for correcting unevenness when reading a document image is performed. In shading correction, a reference white plate (referred to as a reference white plate) is read in the main scanning direction, black reference is read, and the level for each pixel is read using the read white reference and black reference data. Make corrections.

  In a model capable of continuously reading a plurality of documents, the reference white plate for performing shading correction is read once every time a predetermined number of documents are read or once every predetermined time. It is known to perform intermittent shading correction.

  In the case of intermittent shading correction, when reading a document without reading a reference white plate, shading correction is performed using the previously acquired shading correction data.

  More specifically, in the intermittent shading correction, every time when the reference white plate is not read, the background plate provided on the reading surface of the original is read, and the level change as a result of reading the background plate is shaded for one line. Reflect shading correction data at once and perform shading correction. By performing the intermittent shading correction, the reading operation time is shortened, and the productivity of the original reading operation is ensured.

  By the way, there is known a left-right divided readout method in which signal readout from an image sensor is performed in the main scanning direction. Patent Document 1 discloses an image reading apparatus using a left and right divided readout method. In the image reading apparatus using the left / right divided readout method, a signal processing unit that processes a signal read from the image sensor is provided for each signal read by being divided from the image sensor. According to this left and right division reading method, parallel processing can be performed on signals read in each of the divided areas of the image sensor, so that the document image reading operation by the image reading apparatus can be speeded up.

  However, the conventional intermittent shading correction has a problem that it is not compatible with the left and right divided readout method.

  That is, in the image reading apparatus that employs the left / right divided readout method, as described above, a signal processing unit is provided for each divided area. For this reason, there is a possibility that a difference based on variation in characteristics of each signal processing unit may occur in the correction result obtained by reading the background plate in each divided area every time the reference white plate is not read. The difference between the correction result areas appears as a density difference at the boundary of the division in the image based on the image data obtained by reading the document.

  In the shading correction performed by reading the reference white plate, level correction is performed for each pixel, and thus such a density difference does not occur at the boundary of division.

  In the above-mentioned Patent Document 1, in order to reduce the difference between the divided areas in the shading correction, a technique for creating a lookup table or an arithmetic expression with reference to a predetermined gray scale chart and correcting each shading correction coefficient is disclosed. It is disclosed. However, this Patent Document 1 does not disclose intermittent shading correction, and hence the problems associated with intermittent shading correction as described above cannot be solved.

  The present invention has been made in view of the above, and an object of the present invention is to enable image reading processing using the left and right divided reading method to be performed at higher speed and higher quality.

  In order to solve the above-described problems and achieve the object, the present invention includes a plurality of photoelectric conversion elements that output continuously received and received light as pixel signals, and the plurality of photoelectric conversion elements are connected to one end of the array. A light reading unit that outputs a pixel signal by dividing the first region from the first position to a predetermined position in the array and the second region from the predetermined position to the other end of the array, and receives reflected light from the first reference plate A first correction unit that performs shading correction using the pixel signal output by the light reading unit, and a reflected light from the second reference plate received by the light reading unit, at least in the first region and the second region A calculation unit that calculates an average value of pixel values from a plurality of pixel signals output from one side, a second correction unit that corrects shading correction by the first correction unit according to a comparison result of comparing the average value with a reference value, , Original image In the case of continuous reading, in response to one of the correction by the first correction unit, and having a control unit for executing the correction by the second correction unit for each of one or more original images.

  According to the present invention, there is an effect that the image reading process using the left and right divided reading method can be executed at higher speed and with higher quality.

FIG. 1 is a diagram schematically showing a structure of an example of an image reading apparatus applicable to each embodiment. FIG. 2 is a diagram illustrating a configuration of an example of an image sensor using a CCD applied to each embodiment. FIG. 3 is a block diagram illustrating the configuration of an example of the image reading apparatus according to each embodiment. FIG. 4 is a timing chart showing an example of the operation in the sheet through mode of the image reading apparatus according to each embodiment. FIG. 5 is an example timing chart for explaining correction processing for shading correction according to the existing technology. FIG. 6 is a diagram schematically showing the result of level correction with respect to shading correction according to the existing technology. FIG. 7 is an example timing chart for explaining correction processing for shading correction according to the first embodiment. FIG. 8 is a diagram illustrating an example of a background plate reading range according to the first embodiment. FIG. 9 is a diagram schematically showing the result of level correction for shading correction according to the existing technique according to the first embodiment. FIG. 10 is a block diagram illustrating a configuration of an example of a correction unit according to the first embodiment. FIG. 11 is a block diagram illustrating a configuration example of a level correction coefficient calculation unit according to the first embodiment. FIG. 12 is a block diagram illustrating a configuration of an example of an average calculation unit according to the first embodiment. FIG. 13 is a diagram illustrating an example of the background plate reading range according to the first modification of the first embodiment. FIG. 14 is a diagram illustrating an example of a background plate reading range according to the second embodiment. FIG. 15 is an example timing chart for explaining correction processing for shading correction according to the second embodiment. FIG. 16 is a diagram illustrating a configuration of an example of an image forming apparatus according to the third embodiment.

  Exemplary embodiments of an image reading apparatus, an image reading apparatus control method, and an image forming apparatus will be described below in detail with reference to the accompanying drawings.

(Configuration applicable to each embodiment)
FIG. 1 schematically shows the structure of an example of an image reading apparatus applicable to each embodiment. An image reading apparatus 100 shown in FIG. 1 is a scanner device or a single scanner device mounted on an image forming apparatus such as a digital copying machine, a digital multifunction peripheral, or a facsimile machine, and has a function of performing correction for shading correction according to each embodiment. Includes an image signal processing unit. The image reading apparatus 100 irradiates a document that is a subject with irradiation light from a light source, performs image processing on a pixel signal output from an image sensor that receives reflected light from the document, and reads image data of the document. be able to.

  As shown in FIG. 1, the image reading apparatus 100 includes a contact glass 101 on which a document is placed, a first carriage 106 including a light source 102 for document exposure and a first reflection mirror 103, a second reflection mirror 104, and a first reflection mirror 104. And a second carriage 107 including three reflecting mirrors 105. Further, the image reading apparatus further corrects various distortions caused by an image sensor 109 on which a plurality of photoelectric conversion elements are mounted, a lens unit 108 for forming an image on the image sensor 109, a reading optical system, and the like. A reference white plate 110 used for the above and a sheet-through reading slit 111 are provided.

  An automatic document feeder (hereinafter abbreviated as “ADF”) 200, which is an automatic document feeder, is mounted on the upper part of the image reading apparatus 100. The ADF 200 can be opened and closed with respect to the contact glass 101. These are connected via a hinge (not shown).

  The ADF 200 includes a document tray 201 as a document placing table on which a document bundle composed of a plurality of documents can be placed. In addition, separation / feeding means including a feeding roller 202 that separates documents one by one from a bundle of documents placed on the document tray 201 and automatically feeds them toward the sheet-through reading slit 111 is also provided.

  Hereinafter, the surface of the feeding roller that faces the scanner light source is referred to as a background plate. Further, the positions of the first carriage 106 and the second carriage 107 where the image sensor 109 can read the background plate through the sheet through reading slit 111 are defined as the home positions of the first carriage 106 and the second carriage 107. To do.

  In the image reading apparatus 100 configured as described above, in the scan mode in which the image surface of the document is scanned (scanned) to read the image of the document, the first carriage 106 and the second carriage 107 are indicated by arrows by a stepping motor (not shown). The document is scanned in the A direction (sub-scanning direction). At this time, in order to keep the optical path length from the contact glass 101 to the image sensor 109 constant, the second carriage 107 moves at a half speed of the first carriage 106.

  At the same time, an image surface which is the lower surface of the document set on the contact glass 101 is irradiated (exposed) by the light source 102 of the first carriage 106. Then, the reflected light image from the image plane is sent to the image sensor 109 via the first reflecting mirror 103 of the first carriage 106, the second reflecting mirror 104 and the third reflecting mirror 105 of the second carriage 107, and the lens unit 108. Images are sent sequentially. Then, a pixel signal is output by photoelectric conversion of the image sensor 109 and converted into a digital signal by a signal processing unit at a subsequent stage. Thereby, the image of the original is read and digital image data is obtained.

  Hereinafter, an operation in which the image sensor 109 outputs a pixel signal by photoelectric conversion is referred to as a reading operation by the image sensor 109. In addition, an operation in which the image sensor 109 reads the reflected light of the reading target is simply described as an operation of reading the reading target.

  On the other hand, in the sheet through mode in which the original is automatically fed and the image of the original is read, the first carriage 106 and the second carriage 107 move to the lower side of the sheet through reading slit 111. Thereafter, the document placed on the document tray 201 is automatically fed in the arrow B direction (sub-scanning direction) by the feeding roller 202, and the document is scanned at the position of the sheet through reading slit 111.

  At this time, the lower surface (image surface) of the automatically fed document is irradiated by the light source 102 of the first carriage 106. Therefore, the reflected light image from the image plane is sent to the image sensor 109 via the first reflecting mirror 103 of the first carriage 106, the second reflecting mirror 104 and the third reflecting mirror 105 of the second carriage 107, and the lens unit 108. Images are sent sequentially. Then, a pixel signal is output by photoelectric conversion of the image sensor 109 and converted into a digital signal by a signal processing unit at a subsequent stage. Thereby, the image of the original is read and digital image data is obtained. The document whose image has been read in this way is discharged to a discharge port (not shown).

  The reflected light from the reference white plate 110 is converted into an analog signal by the image sensor 109 due to the irradiation by the light source 102 started before the image reading in the scan mode or the sheet through mode, and the digital signal is output by the signal processing unit in the subsequent stage. Is converted to As a result, the reference white plate 110 is read, and shading correction at the time of image reading of the document is performed based on the reading result (digital signal).

  In each embodiment, in the sheet-through mode, for one shading correction, a correction coefficient is calculated using a pixel signal obtained by reading the background plate by the image sensor 109 every time one or more times of image reading. Then, intermittent shading correction is performed to correct the shading correction with this correction coefficient. Since the correction coefficient calculation processing by this intermittent shading correction does not involve the movement of the first carriage 106 and the second carriage 107, continuous reading in the sheet through mode can be executed at a higher speed.

  FIG. 2 shows an example of the configuration of an image sensor 109 using a CCD (Charge Coupled Device) applied to each embodiment. The image sensor 109 includes a plurality of photodiodes 21 that are photoelectric conversion elements, a shift gate 22, a CCD analog shift register 23, an output buffer 24, and output terminals OS1, OS2, OS3, and OS4. The image sensor 109 includes a terminal CP to which a clamp clock is input, a terminal RS to which a reset voltage is input, a terminal SH to which a shift control signal is input, and terminals φ1 and φ2 to which a transfer clock is input, respectively. And a terminal Φ2B to which a drive clock is input. Note that the terminal φ2B is input only to the output stage with the lock as the drive clock, like the terminal φ2.

  In general, the CCD output timing is determined based on the timing of the drive clock input to the terminal φ2B. For example, the output of each photodiode 21 accumulated as a charge in the CCD analog shift register 23 is sequentially read out from the CCD analog shift register 23 as a pixel signal according to the drive clock.

  In the image sensor 109 shown in FIG. 2, there are provided four analog shift registers 23 (first half 2 systems: even pixels and odd pixels / second half 2 systems: even pixels and odd pixels). As a result, the F-side pixel signal output from the F-side pixel that is the first half (the range indicated by the region 10F) is output from the output buffer 24 on the left side of FIG. 2, and the second half (the range indicated by the region 10L). An L-side pixel signal output from a certain L-side pixel is output from the right output buffer 24 in FIG. The boundary between the first half system and the second half system of the analog shift register 23 is preferably the central portion of the entire pixel, but is not limited to this example, and may be a predetermined position outside the central portion.

  FIG. 3 shows an exemplary configuration of the image reading apparatus 100 according to each embodiment. The image reading apparatus 100 includes an image processing unit having the same configuration for each of the F-side pixel signal and the L-side pixel signal output from the image sensor 109. That is, for the F-side pixel signal output from the image sensor 109, an analog signal buffer 54F, an AC coupling unit 55F, an analog processing unit 56F, a PGA (Programmable-Gain Amplifier) 57F, and an A / D converter 58F. And an image processing unit. Similarly, for the L-side pixel signal output from the image sensor 109, an analog signal buffer 54L, an AC coupling unit 55L, an analog processing unit 56L, a PGA (Programmable-Gain Amplifier) 57L, and an A / D converter And an image processing unit comprising 58L. Since the image processing unit related to the F-side pixel signal and the image processing part related to the L-side pixel signal have the same operation content, the image processing unit related to the F-side pixel signal will be described below. Description of the image processing unit related to the signal is omitted.

  The F-side pixel signal output from the image sensor 109 is input to the AC coupling unit 55F via the analog signal buffer 54F, the DC component is removed, and input to the analog processing unit 56F, and a predetermined analog such as waveform shaping is performed. Signal processing is applied. The F-side pixel signal output from the analog signal processing unit 56F is input to the PGA 57F, amplified with a predetermined gain, converted into a digital signal by the A / D converter 58F, and corrected as F-side pixel data. 59. Similarly, L-side pixel data obtained by processing the L-side pixel signal and converting it to a digital signal is also input to the correction unit 59.

  The correction unit 59 includes a first correction unit that performs shading correction on the F-side pixel data and the L-side pixel data, and a second correction unit that performs correction on the shading correction at the time of intermittent shading correction. The correction unit 59 includes a white plate data reading gate signal SHgate, a document data reading gate signal Fgate, background plate reading gate signals Kgate # 1 and # 2, and a black data reading gate signal BKgate generated by a timing generator 60 described later. Based on the gray balance coefficient read from the memory 53 (described later), the reference white plate data and the background plate monitor level extracted from the input F side pixel data and L side pixel data. The side pixel data and the L side pixel data are corrected for each pixel and output as one image data.

  The image reading apparatus 100 further includes a CPU (Central Processing Unit) 50, a light source control unit 51, a scanner motor 52, a memory 53, a correction unit 59, a timing generator 60, and a clock generation unit (CLK) 61. And a light source 102.

  The CPU 50 controls the overall operation of the image reading apparatus 100 using a RAM (Random Access Memory) as a work memory according to a program stored in advance in a ROM (Read Only Memory) (not shown). The light source control unit 51 controls lighting of the light source 102 in accordance with a command from the CPU 50. The timing generator 60 generates a predetermined timing signal from the clock generated by the clock generation unit 61 in accordance with an instruction from the CPU 50. For example, the white plate data reading gate signal SHgate, the document data reading gate signal Fgate, the background plate reading gate signals Kgate # 1 and Kgate # 2 and the black data reading gate signal BKgate input to the correction unit 59 are the timing generator. 60 based on the clock.

  The memory 53 stores a gray balance coefficient GB used for shading correction in advance. Also, the image data obtained by reading the reference white plate 110 by the image sensor 109 with respect to the memory 53 (referred to as reference white plate data) and the background plate monitor level that becomes the reference when the image sensor 109 reads the background plate. And may be further stored.

  FIG. 4 is a timing chart illustrating an example of an operation in the sheet through mode of the image reading apparatus 100 according to each embodiment. In the image reading apparatus 100, pixel data in a desired range can be extracted from the F-side pixel data and L-side pixel data output from the image sensor 109 using a desired gate signal.

  The signal LMP is a lamp control signal for turning on the light source 102. In FIG. 4, when the continuous reading operation in the sheet through mode is started, the light source 102 is turned on under the control of the light source control unit 51 according to the signal LMP, and the F side pixel signal and the L side pixel signal are output from the image sensor 109. Is done. In the correction unit 59, first, in accordance with the black data read gate signal BKgate, F side pixel data and L side pixel data during the assertion period of the black data read gate signal BKgate are acquired, and based on the acquired data, the black level area average value BK Is calculated. This black level area average value BK is used as a reference indicating black. The black level area average value BK is stored in a register of the correction unit 59 or the like.

  Hereinafter, acquiring the F-side pixel data and the L-side pixel data during the assertion period of the black data reading gate signal BKgate will be described as acquiring black data according to the black data reading gate signal BKgate. The same applies to the acquisition of F pixel data and L pixel data using other signals, unless otherwise specified.

When the black data BK is acquired, at time t _a , the first carriage 106 and the second carriage 107 are moved under the control of the CPU 50, and the first carriage 106 reaches a position directly below the reference white plate 110. Here, the reflected light of the reference white plate 110 is received by the image sensor 109, and the reference white plate data is acquired according to the white plate data reading gate signal SHgate. The correction unit 59 calculates the line average value as the reference white level line average value SH for each main scan of the acquired reference white plate data. The reference white level line average value SH is stored in a register included in the correction unit 59, for example. The reference white level line average value SH may be stored in the memory 53.

  When the reference white level line average value SH is acquired, the first carriage 106 and the second carriage 107 are moved to the home position, the reflected light of the background plate is received by the image sensor 109, and the background plate reading gate signal Kgate # 1. Accordingly, the initial background plate data Kdata # 1 is acquired. The acquired initial background plate data Kdata # 1 is stored in a register included in the correction unit 59.

Thereafter, reading of the first document is started. That is driven scanner motor 52 is under the control of the CPU 50, while being automatically fed to the sub-scanning direction by the document tray 201 placed on the document feed roller 202, at time t _1, the original data read gate signal Image data Fr based on the document image is acquired according to Fgate. At this time, the correction unit 59 performs shading correction on the image data Fr for each pixel using the calculated reference white level line average value SH, gray balance coefficient GB, and black level area average value BK. Then, image data obtained by shading correction of the image data Fr is output as output data.

When the output data subjected to the shading correction is expressed as output data Img_o, the shading correction is performed for each pixel of the image data Fr using, for example, a correction formula shown in the following formula (1).
Img_o = {(Fr−BK) / (SH−BK)} × GB (1)

  In each embodiment, the image reading apparatus 100 does not operate the first carriage 106 and the second carriage 107 in reading the second and subsequent documents, and sets the positions of the first carriage 106 and the second carriage 107 to the home position. As described above, the acquisition of the reference white plate data is omitted, and intermittent shading correction is performed.

That is, from the time t ₂ when the reading of the first sheet original is finished, in between time t ₃ when the reading of the second sheet original is started (sheet interval), the background plate data in accordance with a gate signal Kgate # 2 read background plate Kdata # 2 is acquired. Correcting unit 59, and the background plate data KDATA # 2, by the correction coefficient calculated by using the background plate data KDATA # 1 obtained between from the time point t _a time t _1, according to the above Expression (1) Correction for the correction formula is performed, and shading correction is performed on the image data Fr acquired from the second original using the corrected correction formula.

  The image reading apparatus 100 acquires the background plate data Kdata # 2 in the same manner in reading the third and subsequent originals. The correction unit 59 performs level correction on the correction equation according to the equation (1) by using the correction coefficient obtained by using the acquired background plate data Kdata # 2 and the background plate data Kdata # 1 stored in the memory 53. Using the corrected correction formula, shading correction is performed on the image data Fr acquired from the third original.

  More specifically, the correction unit 59 obtains a ratio between the initial background plate data Kdata # 1 stored in the memory 53 and the newly acquired background plate data Kdata # 2, and calculates the value of this ratio. This is applied to the image data after shading correction. As a result, level correction is performed with respect to a change in light quantity with time, and image data is output.

  Thereafter, the image reading apparatus 100 is configured so that a predetermined time elapses after the first original is read, for example, a continuous reading time elapses after a predetermined intermittent interval time, or is determined in advance. The acquisition of the background plate data Kdata # 2 and the reading of the document are repeated until a predetermined number of sheets are read. Then, when a predetermined time has elapsed since the first original is read, the first carriage 106 and the second carriage 107 are moved again to acquire the reference white plate data, and the expression ( Each value of 1) is updated, and then shading correction is performed on the image data Fr read from the original.

  When the reading of the final document is completed, the CPU 50 turns off the light source 102 and ends a series of reading operations by the image reading apparatus 100.

(Correction using existing technology)
Next, prior to the description of the level correction process according to each embodiment, the level correction process according to the existing technology will be described. In the existing technology, the level correction for the above-described shading correction is performed independently for each of the F-side pixel signal and the L-side pixel signal.

  FIG. 5 is an example timing chart for explaining correction processing for shading correction according to the existing technology. FIG. 5 shows an example in which pixel data based on reflected light from the background plate is acquired based on the background plate reading gate signal Kgate # 1 or # 2. Here, the correction unit 59 is described as performing correction processing using an existing technology.

  In FIG. 5, a signal CLK is a clock signal for each pixel, and a signal Bsync is a main scanning synchronization reference signal. Reading (pixel signal output) by the image sensor 109 is started according to the signal Bsync, and each pixel is output from the image sensor 109 in synchronization with the signal CLK.

  The gate signal SH_hgate_F and the gate signal SH_hgate_L are gate signals that define the width of main scanning for reading the reference white plate 110 for the H-side pixel signal and the L-side pixel signal, respectively. The background plate main scanning F side gate signal K_hgate_F and the background plate main scanning L side gate signal K_hgate_L are gate signals that define the width of the main scanning for reading the background plate for the F side pixel signal and the L side pixel signal, respectively.

  The background plate F-side reading start position adjustment value Kd_F and the background plate L-side reading start position adjustment value Kd_L are values that define the timing for starting reading of the background plate for the F-side pixel signal and the L-side pixel signal, respectively. is there. Further, the background plate F side reading range adjustment value Kw_F and the background plate L side reading range adjustment value Kw_L are values that define the reading range of the background plate for the F side pixel signal and the L side pixel signal, respectively.

Signal Bsync is asserted immediately after the background plate read gate signal Kgate # 1 or background plate read gate signal Kgate # 2 is asserted at time t _10. After a predetermined number of pixels has passed a predetermined number of signal CLK from the signal BSYNC (after 1 pixel in the example of FIG. 5), the reading of the first line at the time t ₁₁ is started, a gate signal SH_hgate is asserted. The background plate main scanning F side gate signal K_hgate_F is included in the assert range of the gate signal SH_hgate.

Background plate F side reading start position adjustment values the number of pixels specified in Kd_F to (signal after CLK number) after the time t _12, the background plate main scanning F-side gate signal K_hgate_F is asserted. In the correction unit 59, from this point t _12, in the range up to the time t ₁₃ specified by the background plate F side reading range adjustment value Kw_F, F side pixel data is selected. The pixel data is selected for each line included in the assert range of the background plate reading gate signal Kgate # 1 or the background plate reading gate signal Kgate # 2.

The correction unit 59 obtains an F-side correction coefficient KG′_F for correcting the shading correction formula according to the following formula (2) using the selected F-side pixel data. Equation (3) shows an example of a correction equation for calculating the output data Img_o_F by correcting the image data Fr by the shading correction level-corrected using the correction coefficient KG′_F calculated by the equation (2). .
KG′_F = (K_ave1_F / K_ave2_F) × GB (2)
Img_o_F = {(Fr−BK) / (SH−BK)} × KG′_F (3)

  In Equation (2), the value K_ave1_F is the average value of the initial F-side pixel data acquired in the range specified by the background plate F-side reading range adjustment value Kw_F according to the background plate reading gate signal Kgate # 1. Indicates. Further, the value K_ave2_F is an average value of the F-side pixel data obtained by reading the second and subsequent images acquired in the range specified by the background plate F-side reading range adjustment value Kw_F according to the background plate reading gate signal Kgate # 2. Show.

The correction unit 59 similarly obtains the L-side correction coefficient. That is, the time point t ₁₂ after the number of pixels specified by the background plate L side reading start position adjustment values Kd_L, background plate main scanning L-side gate signal K_hgate_L is asserted. In the correction unit 59, from this point t _12, in the range up to the time t ₁₃ specified by the background plate L side reading range adjustment value Kw_L, L-side pixel data is selected.

The correction unit 59 obtains an L-side correction coefficient KG′_L for correcting the shading correction formula according to the following formula (4) using the selected L-side pixel data. Equation (5) shows an example of a correction equation for calculating the output data Img_o_L by correcting the image data Fr by the shading correction level-corrected using the correction coefficient KG′_L calculated by the equation (4). .
KG′_L = (K_ave1_L / K_ave2_L) × GB (4)
Img_o_L = {(Fr−BK) / (SH−BK)} × KG′_L (5)

  In Equation (4), the value K_ave1_L is the average value of the initial L-side pixel data acquired in the range specified by the background plate L-side reading range adjustment value Kw_L according to the background plate reading gate signal Kgate # 1. Indicates. The value K_ave2_L is the average value of the L-side pixel data obtained by reading the second and subsequent images acquired in the range specified by the background plate L-side reading range adjustment value Kw_L according to the background plate reading gate signal Kgate # 2. Show.

  According to the existing technology, the F-side correction coefficient KG′_F and the L-side correction coefficient KG′_L are independently calculated. Therefore, when the F-side pixel data for calculating the F-side correction coefficient KG′_F and the L-side pixel data for calculating the L-side correction coefficient KG′_L are different, the F-side correction coefficient KG ′ _F and the correction coefficient KG′_L on the L side are different. Even if the F-side pixel signal and the L-side pixel signal have the same value, if the characteristics of the analog signal processing units 56F and 56L with respect to the F-pixel signal and the L-pixel signal vary, the F-side pixel data and The L-side pixel data is different, resulting in a difference between the F-side correction coefficient KG′_F and the L-side correction coefficient KG′_L.

  FIG. 6 schematically shows the result of level correction with respect to shading correction according to the existing technology. In FIG. 6, the horizontal axis indicates the position of the pixel (photoelectric conversion element) in the main scanning direction of the image sensor 109, with the center dotted line as a boundary, the left region 10 </ b> F is the F side, and the right region 10 </ b> L is the L side. It has become. The vertical axis indicates the level of output data output from the correction unit 59. In the example of FIG. 6, when the uniform surface is read by the image sensor 109, the value of the output data in the initial state is indicated by a curve 601, and shading correction is performed in which the output level has changed due to factors such as changes over time. The value of the power output data is shown by curve 602.

  As an example, it is assumed that the range in which the background plate is read is a region indicated by ranges 600F and 600L in FIG. In this case, as illustrated in the curve 602, if there is a difference in the output level distribution in the ranges 600F and 600L after a change with time, the values K_ave2_F and K_ave2_L used in the expressions (2) and (4) A difference occurs between the values, and a difference also occurs between the correction coefficient KG′_F and the correction coefficient KG′_L for correcting the shading correction.

  As a result, as shown in FIG. 6, with respect to the shading correction (line 603) that does not use the correction coefficients KG′_F and KG′_L, the output is output to the L side (region 10L) where the output level decreases with time. A larger correction coefficient KG′_L is applied according to the level difference. Therefore, in the output data Img_o_F and Img_o_L calculated by the equations (3) and (5), the output levels at the ends are equal on the F side and the L side as illustrated by the line 604 in FIG. ing. However, at the boundary between the F side and the L side, which is the center of the image, a difference occurs in the output level as shown as FL difference in FIG. 6, and the density difference between the F side and the L side of the image becomes conspicuous. become.

(First embodiment)
Next, the level correction process according to the first embodiment will be described in more detail. FIG. 7 is an example timing chart for explaining correction processing for shading correction according to the first embodiment. In FIG. 7, the meaning of each signal is the same as that of each signal used in FIG.

  In the first embodiment, as the correction coefficient for correcting the shading correction formula, the F-side correction coefficient KG′_F and the L-side correction coefficient KG′_L described in the above-described existing technology are used in common. The coefficient KG ′ is used.

7, the gate signal Kgate # 2 read background plate read gate signal Kgate # 1 or background plate at t ₂₀ signals Bsync is asserted immediately asserted. After a predetermined number of pixels has passed a predetermined number of signal CLK from the signal BSYNC (after 1 pixel in the example of FIG. 7), the reading of the first line at the time t ₂₁ is started, a gate signal SH_hgate is asserted. The background plate main scanning F side gate signal K_hgate is included in the gate signal SH_hgate assert range.

Background plate main scanning gate signal K_hgate is asserted at time t ₂₂ after the number of pixels specified by background plate reading start position adjustment value Kd. In the correction unit 59, from this point t _22, in the range up to the time t ₂₃ specified by the range adjustment value Kw reading background plate, F-side pixel data and the L-side pixel data is selected.

  FIG. 8 shows an example of the background plate reading range according to the first embodiment. As illustrated in FIG. 8, in the first embodiment, in the area 700 of the background plate, reading is performed by the F-side pixel 700 </ b> F that is read by the F-side pixel of the image sensor 109, and L is read by the L-side pixel. A background plate monitor region 701 as a background plate reading range is set so as to straddle the side region 700L. The first position corresponding to the background plate reading start position adjustment value Kd with respect to the reference position 710 (for example, the pixel position on the F side of the image sensor 109) is, for example, the F pixel side end of the background plate monitor area 701. The width of the background plate monitor area 710 is from the end on the F pixel side to the second position corresponding to the background plate reading range adjustment value Kw. The first position is included in the F-side region 700F, and the second position is included in the L-side region 700L.

The correction unit 59 calculates an average value for each of the background plate reading gate signals Kgate # 1 and Kgate # 2 using both the F side pixel data and the L side pixel data acquired from the background plate monitor region 701. . Then, using the average value K_ave # 1 of the assertion range of the background plate reading gate signal Kgate # 1 and the average value K_ave # 2 of the assertion range of the background plate reading gate signal Kgate # 2, the following equation (6) is used. Then, a correction coefficient KG ′ for the shading correction formula is calculated. Equation (7) shows an example of a correction equation for calculating the output data Img_o by correcting the image data Fr by the shading correction corrected using the correction coefficient KG ′ calculated by the equation (6).
KG ′ = (K_ave # 1 / K_ave # 2) × GB (6)
Img_o = {(Fr−BK) / (SH−BK)} × KG ′ (7)

  FIG. 9 schematically shows the result of level correction for shading correction according to the existing technology according to the first embodiment. In FIG. 9, the meaning of each part is the same as in FIG. In the example of FIG. 9, when the uniform surface is read by the image sensor 109, the value of the output data in the initial state is indicated by a curve 610, and the shading correction is performed in which the output level has changed due to factors such as changes over time. The value of the power output data is indicated by a curve 611.

  As shown in FIG. 9, in the first embodiment, the background plate is read in a region 600C that is a range including both the regions 10F and 10L. Therefore, the correction coefficient KG ′ for the shading correction formula is shared between the F side and the L side as illustrated in FIG. 9. Therefore, in the correction of fluctuation after shading correction, there is no difference in the output level at the boundary between the F-side region 10F and the L-side region 10L as shown in FIG. And density difference between the L side and the L side are suppressed.

  In FIG. 9, an example of the correction result of the shading correction when the correction coefficient KG ′ is not used is indicated by a line 612, and an example of the correction result when the correction coefficient KG ′ is used is indicated by a line 613. A region 10F in which the correction result indicated by the line 612 is uniformly corrected as a whole by the correction coefficient FL common to the F side and the L side, and is indicated by a “no FL difference” portion on the line 613. And a correction result with no difference in the output level at the boundary between the region 10L.

  On the other hand, in the first embodiment, since the correction coefficient for the shading correction formula is shared between the F side and the L side, when there is a large difference in output level between the F side and the L side, correction is performed on one side. There is a risk of malfunction. However, in recent years, a light source using a light-emitting element such as an LED (Light Emitting Diode) that has a stable fluctuation in main scanning distribution over time has become widespread. This problem can be solved by using the light source 102 using such a light emitting element.

  The background plate reading start position adjustment value Kd and the background plate reading range adjustment value Kw described above can be changed. For example, the background plate reading start position adjustment value Kd and the background plate reading range adjustment value Kw are stored in a register included in the correction unit 59, and the stored contents of the register are rewritten. The background plate reading gate signal Kgate # 1 and the background plate reading gate signal Kgate # 2 can be changed in the same manner, and the number of lines used for calculating the correction coefficient can be changed.

  As a result, when the main scanning level fluctuates greatly due to changes over time, or when fluctuations vary, the main scanning position of the background plate monitor area 701 by the main scanning and the number of pixels to be read are varied to change the level correction coefficient. The accuracy of can be adjusted. Further, when acquiring the background plate at the timing between the sheets, the number of sub-scanning lines determined by the background plate reading gate signal Kgate # 1 and the background plate reading gate signal Kgate # 2 is matched with the specifications of the model. Thus, the range of the background plate monitor area 701 can be optimized and the accuracy of level correction can be adjusted.

  FIG. 10 shows an exemplary configuration of the correction unit 59 according to the first embodiment. The correction unit 59 includes a level correction coefficient calculation unit 400, a document data generation unit 401, a black data calculation unit 402, an SH data calculation unit 403, and an SH correction calculation unit 404.

  The correction unit 59 uses the F-side pixel data output from the A / D converter 58F and the L-side pixel data output from the A / D converter 58L, for example, in the order of main scanning in the image sensor 109 for each pixel. Are input as a series of pixel data Img_i.

  The level correction coefficient calculation unit 400 receives the input pixel data Img_i and is supplied with the background plate reading gate signals Kgate # 1 and Kgate # 2 and the background plate main scanning gate signal K_hgate from the timing generator 60. Further, the level correction coefficient calculation unit 400 reads the gray balance coefficient GB from the memory 53. The level correction coefficient calculation unit 400 calculates a correction coefficient KG ′ based on these input signals and data. The calculated correction coefficient KG 'is stored in a register (not shown). A detailed description of the level correction coefficient calculation unit 400 will be described later.

  The document data generation unit 401 receives the pixel data Img_i and is supplied with the document data reading gate signal Fgate from the timing generator 60. The document data generation unit 401 extracts the document data Fr for each pixel from the input pixel data Img_i in accordance with the document data reading gate signal Fgate and outputs it.

  The black data calculation unit 402 receives the pixel data Img_i and is supplied with the black data reading gate signal BKgate from the timing generator 60. The black data generation unit 402 extracts pixel data in a black level reading region that reads a black level from input pixel data Img_i according to the document data reading gate signal Fgate, and calculates an average value. The calculated average value is stored in a register (not shown) or the like as the black level area average value BK.

  The SH data calculation unit 403 receives pixel data Img_i and is supplied with a white plate data reading gate signal SHgate from the timing generator 60. The SH data calculation unit 403 extracts the reference white plate data of the line for each pixel from the input pixel data Img_i according to the white plate data reading gate signal SHgate, and calculates the average value of the extracted reference white plate data for each line. The calculated average value is stored in a register (not shown) or the like as a reference white level line average value SH.

  The SH correction calculation unit 404 reads the correction coefficient KG ′, the black level area average value BK, and the reference white level line average value SH from the level correction coefficient calculation unit 400, the black data calculation unit 402, and the SH data calculation unit 403, respectively. Then, using these read values, the original data Fr input for each pixel is subjected to the shading correction and the correction by the correction coefficient KG ′ for the shading correction in accordance with the above-described equations (6) and (7). The output pixel data Img_o is generated and output.

  FIG. 11 shows an exemplary configuration of the level correction coefficient calculation unit 400. The level correction coefficient calculation unit 400 includes an average calculation unit 500, a divider 501, a register 502, a comparator 503, a multiplier 504 and a subtractor 505, and a switch SW506.

  The average calculator 500 calculates the average values K_ave # 1 and K_ave from the input pixel data Img_i according to the background plate reading gate signals Kgate # 1 and Kgate # 2 and the background plate main scanning gate signal K_hgate supplied from the timing generator 60. # 2 is calculated.

  FIG. 12 shows an exemplary configuration of the average calculation unit 500. The average calculation unit 500 includes switches 5001, 5005, 5007, and 5008, an adder 5002 and a divider 5006, a counter CNT 5004, and registers 5003 and 5009.

  The switches 5001 and 5005 are closed during the assertion period of the background plate main scanning gate signal K_hgate. The input pixel data Img_i is selected by the switch 5001 as pixel data within the assertion period of the background plate main scanning gate signal K_hgate, and is input to one input terminal of the adder 5002. The output of the register 5003 is input to the other input terminal of the adder 5002. The output of the adder 5002 is stored in the register 5003. The register 5003 stores the input pixel data Img_i accumulated within the assertion period of the background plate main scanning gate signal K_hgate.

  The output of the adder 5002 is also input to a counter CNT 5004 that counts the number of input data. The output of the counter CNT 5004 is input to the divisor input terminal of the divider 5006.

  The output of the register 5003 is input to the dividend input terminal of the divider 5006 via the switch 5005. The divider 5006 divides the output of the register 5003 by the count value of the counter CNT5004, whereby the average value of the input pixel data Img_i within the assertion period of the background plate main scanning gate signal K_hgate is calculated.

  The output of the divider 5006 is input to switches 5007 and 5008 which are closed during the assertion period of the background plate reading gate signals Kgate # 1 and Kgate # 2. The output of the switch 5007 is stored in the register 5009 as the average value K_ave # 1 of the initial background plate data Kdata # 1. The value stored in the register 5009 is updated every time the switch 5008 is closed. The output of the switch 5008 is output as the average value K_ave # 2 of the second and subsequent background plate data Kdata # 2.

  Returning to FIG. 11, the average values K_ave # 1 and K_ave # 2 output from the average calculator 500 are input to the divider 501. Divider 501 divides average value K_ave # 1 by average value K_ave # 2 to obtain a ratio between average value K_ave # 1 and average value K_ave # 2. The value of this ratio indicates the degree of change of the average value K_ave # 2 with respect to the average value K_ave # 1.

  The output of the divider 501 is input to one input terminal of the multiplier 504. One output of the register 502 is input to the other input terminal of the multiplier 504. The register 502 stores a gray balance coefficient GB read from the memory 53 and a correction coefficient KG ′ output from a switch 506 described later. From one output of the register 502, the gray balance coefficient GB is output.

Multiplier 504 multiplies the output of divider 501 by the gray balance coefficient GB and outputs a value KG according to the following equation (8). The value KG is input to the subtraction input terminal of the subtractor 505 and also input to one selection input terminal of the switch 506. The correction coefficient KG ′ read from the register 502 is input to the other selection input terminal of the switch 506.
KG = (K_ave # 1 / K_ave # 2) × GB (8)

  The correction coefficient KG ′ read from the register 502 is input to the subtracted input terminal of the subtractor 505. The subtractor 505 calculates a difference ΔKG between the value KG and the correction coefficient KG ′ and inputs the difference ΔKG to one input terminal of the comparator 503. A threshold KG_lim stored in advance in the register 502 is input to the other input terminal of the comparator 503. The threshold value KG_lim may be stored in advance in the memory 53 and input from the memory 53 to the comparator 504 via the register 502.

The comparator 504 compares the difference ΔKG input to one input terminal with the threshold value KG_lim input to the other input terminal, and the difference ΔKG is a value within the range of the threshold value KG_lim according to the following equation (9), for example. Is determined (threshold KG_lim ≧ 0).
| ΔKG | ≦ KG_lim (9)

  If the comparator 503 determines that the difference ΔKG satisfies the equation (9) and is a value within the range of the threshold KG_lim, the switch 506 selects one selection input terminal. In this case, the value KG is output from the level correction coefficient calculation unit 400 as the correction coefficient KG ′. At the same time, the value KG is supplied to the register 502, and the previous correction coefficient KG 'already stored is updated with the value KG.

  On the other hand, when the comparator 503 determines that the difference ΔKG does not satisfy Expression (9) and exceeds the threshold KG_lim, the comparator 503 selects the other selection input terminal at the switch 506. In this case, the previous correction coefficient KG ′ stored in the register 502 is output from the level correction coefficient calculation unit 400.

  Thus, in the first embodiment, the value KG obtained by dividing the average value K_ave # 1 by the average value K_ave # 2 is compared with the previous correction coefficient KG ′, and the value KG and the previous correction coefficient KG ′ are compared. When the difference ΔKG is equal to or larger than a predetermined value, the previous correction coefficient KG ′ is used without using the value KG obtained this time. As a result, the correction coefficient KG ′ can be calculated without being affected by sudden level fluctuations due to noise or dust. The threshold value KG_lim can be changed according to reading accuracy, specifications, and the like.

  In the above description, the divider 501 calculates the ratio between the initial average value F_ave # 1 and the second and subsequent average values F_ave # 2, but this is not limited to this example. For example, the average value F_ave # 2 for the second and subsequent sheets may be compared with a predetermined fixed value. The initial average value K_ave # 1 and the fixed value can be considered as reference values for the average value K_ave # 2 to be compared.

(First modification of the first embodiment)
In the first embodiment described above, the background board monitor region 701 is set to include both the F-side region 700F and the L-side region 700L, but this is not limited to this example. That is, as illustrated in FIG. 13, the background board monitor region 701 ′ is included in one of the F-side region 700F and the L-side region 700L without straddling the F-side region 700F and the L-side region 700L. You may do it. As a method for calculating the correction coefficient KG ′, the same method as that described in the first embodiment can be applied.

  The correction coefficient KG ′ is calculated based on an average value of a plurality of pixel data read from the background board monitor region 701 and is used as a coefficient common to the F side and the L side. Therefore, even in this case, similarly to the description in FIG. 9, when the fluctuation after shading correction is corrected, a difference occurs in the output level at the boundary between the F-side region 10F and the L-side region 10L. In other words, the occurrence of a density difference between the F side and the L side of the image is suppressed.

(Second modification of the first embodiment)
In the first embodiment described above, the average value K_ave # 1 and K_ave # 2 are calculated using the pixel signals continuously output in the line in the background plate monitor region 701. Is not limited to this example. That is, each average value K_ave # 1 and K_ave # 2 may be calculated using pixel signals at discrete positions in the background board monitor region 701.

(Second Embodiment)
Next, a second embodiment will be described. FIG. 14 shows an example of the background plate reading range according to the second embodiment. In the first embodiment and the modifications of the first embodiment described above, one background plate monitor region 701 or 701 ′ is provided in the background plate region 700. On the other hand, in the second embodiment, background board monitor areas 702F and 702L are provided in the F side area 700F and the L side area 700L of the background board monitor area 700, respectively.

  In this case, two reading start position adjustment values and two reading range adjustment values are set to determine the positions of the background plate monitor areas 702F and 702L. That is, as illustrated in FIG. 14, the background plate reading start position adjustment value Kd # 1 and the background plate reading range adjustment value Kw # 1 are set for the background plate monitor region 702F (region # 1). Similarly, a background plate reading start position adjustment value Kd # 2 and a background plate reading range adjustment value Kw # 2 are set for the background plate monitor region 702L (region # 2).

In correction unit 59, average calculation unit 500 calculates average values K_ave # 1 and K_ave # 2 for background plate monitor regions 702F and 702L, respectively. Considering the case where the average value K_ave # 1 is calculated, for example, the correction unit 59 includes two average calculation units 500, and the first average calculation unit 500 sets the average value K_ave # 1 for the background board monitor region 702F. Calculate (average of region # 1). Similarly, the second average calculator 500 calculates an average value K_ave # 1 for the background board monitor region 702L (the region # 2 is averaged). And according to following Formula (10), the average of area | region # 1 average and area | region # 2 average is calculated, and it is set as the initial average value K_ave # 1.
K_ave # 1 = (average of area # 1 + average of area # 2) / 2 (10)

  The average value K_ave # 2 for the second and subsequent sheets is also obtained by calculating the average of the area # 1 average and the area # 2 average in the same manner as this average value K_ave # 1. Thus, the average values K_ave # 1 and K_ave # 2 calculated based on the pixel signals read from the background plate monitor areas 702F and 702L provided in the F-side area 700F and the L-side area 700L, respectively, are stored in the divider 501. The signals are input to one and the other input terminals, respectively. Since the subsequent operation of the correction unit 59 is not different from that of the first embodiment, description thereof is omitted here.

  FIG. 15 is an example timing chart for explaining correction processing for shading correction according to the second embodiment. In FIG. 15, the meaning of each signal is the same as that of each signal used in FIG.

15, gate signal Kgate # 2 read background plate read gate signal Kgate # 1 or background plate at t ₃₀ signals Bsync is asserted immediately asserted. After a predetermined number of pixels has passed a predetermined number of signal CLK from the signal BSYNC (after 1 pixel in the example of FIG. 15), with the reading of the first line at t ₃₁ is started, a gate signal SH_hgate is asserted.

  In the second embodiment, since two background plate monitor regions 702F and 702L are provided for the background plate monitor region 700, the background plate main scanning F side gate signal K_hgate is 2 within the gate signal SH_hgate assert range. There are provided assertion periods.

That is, first, in the F-side region 700F, from the time t ₃₂ after the number of pixels specified by the background plate reading start position adjustment values Kd # 1, until the time t ₃₃ specified by the range adjustment value Kw # 1 reading background plate Is the first assertion period of the background plate main scanning gate signal K_hgate. Based on the pixel signal read from the background plate during the first assertion period, the area # 1 average is calculated.

Moreover, the scope of in the L-side region 700L, from the time t ₃₄ after the number of pixels specified by the background plate reading start position adjustment values Kd # 2, to the point t ₃₅ specified by the range adjustment value Kw # 2 read background plate Is the second assertion period of the background plate main scanning gate signal K_hgate. Based on the pixel signal read from the background plate during the second assertion period, the area # 2 average is calculated.

  As described above, in the second embodiment, the background plate monitor regions 702F and 702L are provided in the F-side region 700F and the L-side region 700L of the background plate monitor region 700, respectively, so that the correction coefficient KG ′ is calculated. The end of the image sensor 109 can be included in the monitor area. Furthermore, the amount of calculation of processing can be reduced by locally monitoring an optimal place without taking the background board monitor area | region 702F and 702L widely in that case.

  In the second embodiment, since the correction coefficient KG ′ is calculated using the average value of the area # 1 average and the area # 2 average calculated from the F-side area 700F and the L-side area 700L, respectively. The correction coefficient KG ′ is shared by the F-side region 700F and the L-side region 700L, and the difference between the output levels at the boundary between the F-side region 10F and the L-side region 10L when correcting the variation after shading correction. The occurrence of a density difference between the F side and the L side of the image is suppressed.

  In addition, it is possible to take in the 2nd modification of the 1st form mentioned above to this 2nd Embodiment.

(Third embodiment)
Next, a third embodiment will be described. In the third embodiment, the image reading apparatus 100 according to the first embodiment and the modifications of the first embodiment described above and the second embodiment is incorporated into an image forming apparatus having a printing and copying function. This is an example. FIG. 16 shows an exemplary configuration of an image forming apparatus 300 according to the third embodiment.

  As shown in FIG. 16, the image forming apparatus 300 is provided with an ADF 800 on an upper part of a contact glass 101 on which an original is placed, and a hinge or the like (not shown) is provided so that the ADF 800 can be opened and closed with respect to the contact glass 101. Are connected through.

  The ADF 800 includes a document tray 801 as a document placing table on which a document bundle composed of a plurality of documents can be placed. Further, when a print key on an operation unit (not shown) is pressed, the originals are separated one by one from the original bundle placed on the original tray 801 with the image surface facing upward, and automatically fed to the sheet through reading slit 111. Alternatively, a separating / feeding unit including a feeding roller 802 and a conveying belt 803 for conveying toward the contact glass 101 is also provided.

  The document fed by the feeding roller 802 or the conveyance belt 803 is read out on the upper surface of the ADF 800 by the conveyance belt 803 and the discharge roller 804 after image reading is performed as described with reference to FIG.

  Here, the operation of the controller (not shown) and the ADF 800 when the document is conveyed to the reading position of the contact glass 101 by the ADF 800 will be described.

  The feeding motor of the ADF 800 is driven by an output signal from the controller. When the feeding start signal generated by pressing the print key on the operation unit is input, the controller turns on the feeding motor. It is designed to drive forward / reverse. When the feeding motor is driven to rotate forward, the feeding roller 802 rotates clockwise to automatically feed the document located at the uppermost position from the bundle of documents toward the sheet through reading slit 111 or the contact glass 101. Be transported. When the leading edge of the document is detected by the document set detection sensor 805, the controller drives the feed motor in the reverse direction based on the output signal from the document set detection sensor 805. This prevents subsequent documents from entering and prevents separation.

  When the document set detection sensor 805 detects the trailing edge of the document, the controller also counts a rotation pulse of a conveyance belt motor (not shown) from this detection point, and when the rotation pulse reaches a predetermined value, the conveyance belt By stopping the driving of 803 and stopping the conveying belt 803, the document is stopped at the reading position on the contact glass 101. Further, when the trailing edge of the document is detected by the document set detection sensor 805, the feeding motor is driven again, and the subsequent document is separated and automatically fed as described above. Then, the sheet is conveyed toward the contact glass 101, and when the pulse of the feeding motor from the time when the document is detected by the document set detection sensor 805 reaches a predetermined pulse, the feeding motor is stopped and the next document is detected. To wait first.

  When the document stops at the reading position on the contact glass 101, the image of the document is read. When this image reading is completed, a signal indicating that is input to the controller, so that the controller drives the conveyor belt motor in the normal direction by this signal, and the document is discharged from the contact glass 101 by the conveyor belt 803. Unload to 804.

  In this way, a document bundle placed on the document tray 801 in the ADF 800 with the image surface of the document facing up is automatically fed from the top document by pressing the print key, for example, a reading position on the contact glass 101. It is conveyed to.

  The document which has been conveyed to the reading position and stopped is discharged from the discharge port by the conveying belt 803 or the like after reading the image. Further, when it is detected that there is a next document on the document tray 801, the next document is automatically fed and conveyed onto the contact glass 101 as with the previous document.

  The transfer sheets (paper sheets) stacked on the first tray 301, the second tray 302, and the third tray 303, which are the paper feed trays, are the first paper feed unit 311, the second paper feed unit 312 and the third paper feed unit, respectively. The sheet is fed by 313 and conveyed by the vertical conveyance unit 314 to a position where it abuts on a drum-shaped photosensitive member (photosensitive drum) 315 as an image carrier. Actually, any one of the first tray 301, the second tray 302, and the third tray 303 is selected, and the transfer paper is fed therefrom. Also, a recording medium other than transfer paper can be used.

  On the other hand, the image data read by the image reading apparatus 100 is written on the surface of the photoreceptor 315 charged in advance by a charging unit (not shown) by a laser beam from a writing unit 350 in the printer as an image forming unit (there is When the surface is exposed), the portion passes through the developing unit 327, and a toner image is formed there.

  The transfer sheet fed from the selected paper feed tray is transferred by the transfer belt 316 at the same speed as the rotation of the photoconductor 315, and the toner image on the photoconductor 315 is transferred. Further, the toner image is fixed by the fixing unit 317, and is discharged by a paper discharge unit 318 to a paper discharge tray 319 outside the apparatus.

  At this time, if, for example, face-down paper discharge, i.e. paper discharge with the image surface facing down to align the transfer paper in page order, is to reverse the transfer paper with the toner image formed on one side, The transfer paper is conveyed by the paper discharge unit 318 to the double-sided input conveyance path 320, is switched back by the reversing unit 321, and then is discharged to the paper discharge tray 319 through the reverse paper discharge conveyance path 322.

  When images are formed on both sides of the transfer paper, the transfer paper on which the image is formed on one side is conveyed to the double-sided input conveyance path 320 by the paper discharge unit 318 and is switched back by the reverse unit 321. After that, it is sent to the duplex conveying unit 323.

  The transfer paper sent to the double-sided conveyance unit 323 is fed again from the double-sided conveyance unit 323 to transfer the toner image formed on the photoconductor 315 again, and is again applied to the photoconductor 315 by the vertical conveyance unit 314. It is transported to the contact position. Then, after the toner image is transferred to the other surface, the toner image is fixed by the fixing unit 317 and discharged to the paper discharge tray 319 by the paper discharge unit 318.

  The photoconductor 315, the conveyance belt 316, the fixing unit 317, the paper discharge unit 318, and the development unit 327 are driven by a main motor (not shown), and each of the first paper supply unit 311, the second paper supply unit 312 and the third paper supply unit 313 are driven. Are driven by the driving force of the main motor being transmitted by the respective feed clutches. The vertical conveyance unit 314 is driven by the driving force of its main motor being transmitted via an intermediate clutch.

  The writing unit 350 includes a laser output unit 351, an imaging lens 352, and a mirror 353. Inside the laser output unit 351, a laser diode that is a laser light source and a rotating polygon mirror (polygon mirror) that scans the laser light. Or it has a vibrating mirror. The laser light emitted from the laser output unit 351 is deflected by a polygon mirror or a vibration mirror, passes through an imaging lens 352, is folded by a mirror 353, and is focused on the surface of the photoreceptor 315.

  According to the image forming apparatus 300 of the third embodiment shown in FIG. 16, the image reading apparatus 100 according to any one of the first embodiment, each modification of the first embodiment, and the second embodiment. In the level correction for the shading correction when the intermittent shading correction is performed when performing a plurality of continuous copying operations, the level correction is performed in common for the F-side region and the L-side region. For this reason, in the center of the image after level correction, the occurrence of a boundary due to a density difference caused by reading the image sensor 109 separately on the F side and the L side is suppressed, and a high-quality image is formed. Is possible.

  Each of the above-described embodiments is a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the gist of the present invention.

50 CPU
53 Memory 54F, 54L Analog signal buffer 56F, 56L Analog processing unit 59 Correction unit 60 Timing generator 100 Image reading device 101 Contact glass 102 Light source 106 First carriage 107 Second carriage 109 Image sensor 110 Reference white plate 111 Sheet through reading slit 200 ADF
400 Level correction coefficient calculation unit 401 Document data generation unit 402 Black data calculation unit 403 SH data calculation unit 404 SH correction calculation unit 500 Average calculation unit 501 Divider 502 Register 503 Comparator 504 Multiplier 505 Subtractor 506 Switch 700 Area 700F F Side area 700L L side area 701, 701 ', 702F, 702L Background board monitor area

JP 2007-096773 A

Claims (10)

A plurality of photoelectric conversion elements configured to output continuously received and received light as pixel signals; a first region from one end of the array to a predetermined position in the array; An optical reading unit that outputs a pixel signal by dividing the second region from the position to the other end of the array;
A first correction unit that performs shading correction using the pixel signal output by the light reading unit that has received the reflected light from the first reference plate;
Calculation for calculating an average value of pixel values from a plurality of pixel signals output from at least one of the first region and the second region when the light reading unit receives reflected light from the second reference plate. And
A second correction unit that corrects the shading correction by the first correction unit according to a comparison result of comparing the average value with a reference value;
And a control unit that executes correction by the second correction unit for each one or more of the original images with respect to one correction by the first correction unit in the case of continuous reading of the document image. An image reading apparatus. The calculation unit includes:
The image reading apparatus according to claim 1, wherein the average value is calculated from a plurality of pixel signals output from each of the first area and the second area. The calculation unit includes:
3. The average value is calculated from a plurality of pixel signals output from the photoelectric conversion elements arranged continuously across the first region and the second region. 3. The image reading apparatus described. The calculation unit calculates the average value from a plurality of pixel signals output from the photoelectric conversion elements arranged continuously in the first area and the second area, respectively. Alternatively, the image reading apparatus according to claim 2. The second correction unit includes
The image reading apparatus according to claim 1, wherein the average value calculated by the calculation unit at a predetermined timing is used as the reference value. The second correction unit includes
When the light reading unit receives the reflected light from the second reference plate immediately after receiving the reflected light from the first reference plate in order to perform the shading correction, the reflected light causes the reflected light from the light reading unit. The image reading apparatus according to claim 1, wherein the average value calculated by the calculation unit using the output pixel signal is used as the reference value. The calculation unit includes:
The image reading apparatus according to claim 1, wherein a range for selecting the plurality of pixel signals used for calculating the average value is variable. The second correction unit includes
The correction is performed by multiplying the correction coefficient obtained according to the comparison result obtained by comparing the average value with the reference value by the correction value obtained by the shading correction, and when the correction coefficient exceeds the threshold, the correction coefficient obtained last time is used. The image reading apparatus according to claim 1, wherein the correction is performed. A plurality of photoelectric conversion elements configured to output continuously received and received light as pixel signals; a first region from one end of the array to a predetermined position in the array; A light reading step of outputting a pixel signal by dividing the second region from the position to the other end of the array;
A first correction step of performing shading correction using the pixel signal output by the light reading unit that has received the reflected light from the first reference plate;
Calculation for calculating an average value of pixel values from a plurality of pixel signals output from at least one of the first region and the second region when the light reading unit receives reflected light from the second reference plate. Steps,
A second correction step for correcting the shading correction by the first correction step according to a comparison result obtained by comparing the average value with a reference value;
And a control step of executing correction by the second correction step for each one or more of the original images for one correction by the first correction step in the case of continuous reading of the document image. For controlling the image reading apparatus. An image reading apparatus according to any one of claims 1 to 8,
An image forming apparatus comprising: an image forming unit that forms an image based on the pixel signal output from the image reading apparatus.

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