JP2006072838A - Image reader and shading correction method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image reader capable of performing high-quality image reading by correcting shading data obtained from a white roller such that the shading data become equal to data when reading a white reference document even when using a contact image sensor as an image reading means and using the white roller as a white reference member. <P>SOLUTION: This image reader has: a shading generation circuit 41 for generating first white shading data by use of reading data obtained by reading a white plane face of a second reading roller 12 facing a second image reading unit 4 for reading an image on a document, and generating second white shading data by use of reading data obtained by reading the white reference document; a comparison circuit 44 for comparing the first white shading data and the second white shading data, and detecting a difference between the two white shading data; and a shading data correction circuit 45 for correcting the first white shading data by use of the difference. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image reading apparatus used for a copying machine, a scanner, and the like, and more particularly to a white reference level creation technique for shading correction.

2. Description of the Related Art Conventionally, in an image reading unit moving type image reading apparatus represented by a flat bed type, shading is performed by reading the density of a reference white plate arranged while the reading carriage moves to the end within the effective reading range. White shading data for correction (data indicating a white reference level) is generated. In addition, in an image reading unit with a fixed image reading unit typified by a sheet-through type, shading data is generated by reading the density of a reference white plate or white roller arranged on the opposite surface of the fixed reading unit. ing.
However, with the conventional shading data generation technology, as time passes, dirt adheres to the surface of the reference white plate or white roller, and the density that should be used as a reference changes depending on the reading position of the reference white plate or white roller, generating shading data. The concentration uniformity required to achieve this could not be maintained. In particular, in the case of the sheet-through type, since the document is conveyed on the surface of the reference white plate or the white roller, there is a problem that the reference white plate or the white roller becomes extremely dirty as the number of uses increases.
Therefore, in a sheet-through type image reading apparatus, shading data may be generated based on white data at the margin at the leading edge of the document or data of several pixels at the end in the main scanning direction where the document does not pass. It was conducted. In the prior art disclosed in Patent Document 1, a groove is formed in a part of the peripheral surface of the reading roller, and a reference white portion for generating shading data is provided on the bottom surface of the groove. In order to prevent the reference white part from becoming dirty.
However, there is not always a margin at the leading edge of the document, and in the data of several pixels at the end in the main scanning direction, appropriate shading data cannot be obtained if there is a large variation between pixels in the main scanning direction. In the conventional technique for forming the indicated groove, paper dust, toner scraps, dust, and the like accumulate.
For this reason, in the prior art disclosed in Patent Document 2, when obtaining shading data from a white reference member, a predetermined range of image data is read in the sub-scanning direction, and the read image data for a plurality of lines in the predetermined range is read. Is divided into a plurality of blocks in the sub-scanning direction, the average value of the image data at each pixel position of each block is obtained, the peak value of the average value of each block is obtained for each pixel position, and the peak value sequence is used as shading data Use.
JP-A-5-319613 JP 2002-152510 A

However, in each of the prior arts described above, when a contact image sensor is used as the image reading unit and a white roller is used as the white reference member, the positional relationship between the contact image sensor 50 and the white roller 51 is as shown in FIG. When the corresponding positions in the longitudinal direction of the contact image sensor 50 and the white roller 51 are shifted due to factors such as variation due to attachment, a difference that differs depending on the position in the main scanning direction occurs, and accurate shading data cannot be generated. there were. If the object of shading data acquisition is a curved surface such as a roller and a flat surface such as paper, there will be a difference in reflected light entering the sensor (see FIG. 13). In other words, when the opposite surface is a curved surface like a roller, there is almost no difference in the plane between the position that matches the optical axis of the contact image sensor and the position that is shifted, even if you intend to read in the same way. On the other hand, it becomes darker as the optical axis shifts, and the data is not appropriate as a reference (see FIG. 14).
The object of the present invention is to solve such problems of the prior art. Specifically, even when a contact image sensor is used as an image reading unit and a white roller is used as a white reference member, By reading the data of the reference white document in advance and correcting the shading data obtained from the white roller to be equal to the data when the white reference document is read, always ensure appropriate reference shading data, An object of the present invention is to provide an image reading apparatus capable of reading a stable and high quality image.

In order to solve the above-described problems, in the invention described in claim 1, in the image reading apparatus capable of performing shading correction, a reference white plate is disposed opposite to the image reading means for reading the image on the document, First shading data generating means for generating first white shading data using read data obtained by reading a reference white plate surface, and second white shading data using read data obtained by reading a reference white reference document. A second shading data generating means for generating, a difference detecting means for comparing the first white shading data and the second white shading data to detect a difference between the two white shading data, and the difference detecting means A shady that corrects the first white shading data using the detected difference. And a Gudeta correction means.
According to a second aspect of the present invention, in the image reading apparatus according to the first aspect, the second shading data obtained by reading the white reference original is stored, and the difference detection is performed when the original image is read. The first shading data generated by the means is compared with the stored second shading data.
According to a third aspect of the present invention, in the second aspect of the present invention, there is provided instruction means for instructing reading of the white reference original.
According to a fourth aspect of the invention, in the first or second aspect of the invention, when the first and second shading data is generated, a predetermined range of image data is read and read in the sub-scanning direction. An averaging unit that divides the image data for a plurality of lines in the predetermined range into a plurality of blocks in the sub-scanning direction to obtain an average value of the image data for each same pixel position of each block; Peak value extracting means for extracting a peak value from the average value of the block, and a configuration in which a peak value sequence composed of peak values at each pixel position is used as shading data.

According to a fifth aspect of the invention, in the first, second, or fourth aspect of the invention, the second shading data reads a position where a predetermined number of lines have passed in the sub-scanning direction from the leading edge of the document. A start position is set, and a predetermined number of lines are read and generated from the position in the sub-scanning direction.
According to a sixth aspect of the present invention, in the shading correction method for correcting image data read from an original using white shading data, the second white is used by using read data obtained by reading a reference white reference original. Shading data is generated and stored, and when reading a document image, first white shading data is generated using read data obtained by reading a reference white plate surface provided on the image reading surface side that reads an image on the document. The first shading data and the stored second shading data are compared to detect a difference between the two shading data, and the first shading data is corrected using the difference. .
According to a seventh aspect of the invention, in the sixth aspect of the invention, when generating the first and second shading data, a predetermined range of image data is read in the sub-scanning direction, and the read predetermined range of image data is read. Divide the image data for multiple lines into multiple blocks in the sub-scanning direction to obtain the average value of the image data for each pixel position in each block, and obtain the peak value from the average value of each block for each pixel position And a peak value sequence composed of peak values at each pixel position is used as shading data.
In the invention according to claim 8, in the invention according to claim 6 or claim 7, the second shading data has a reading start position at a position where a predetermined number of lines have passed in the sub-scanning direction from the leading edge of the document. A predetermined number of lines are read and generated from the position in the sub-scanning direction.

According to the present invention, in correcting the image data read from the document using the white shading data, the second data is read using the read data obtained by reading the reference white reference document. First, white shading data is generated, and when reading a document image, first white shading data is generated using read data obtained by reading a reference white plate surface disposed on an image reading surface side that reads an image on the document. Since the first shading data and the second shading data are compared to detect the difference between the two shading data, and the first shading data can be corrected using the difference, a contact image sensor is used as the image reading means. When a white roller is used as the white reference member, the contact image sensor and the white roller Even deviate the respective longitudinal direction of the corresponding position, can generate accurate shading data, therefore, it is possible to perform stable image reading of high quality.
Further, in the second aspect of the invention, in the first aspect of the invention, and in the sixth aspect of the invention, the second shading data obtained by reading the white reference original is stored, and the original image is read. Sometimes the first shading data can be compared with the stored second shading data, so that the second shading data need only be generated once at the time of product shipment, for example. Saves time and effort to generate data.
Further, in the invention described in claim 3, in the invention described in claim 2, since it is possible to instruct that the white reference document is read, it is possible to read the white reference document only once, for example, at the time of product shipment. Become.

Further, in the invention of claim 4, in the invention of claim 1 or 2, and in the invention of claim 7 in the invention of claim 6, when generating the first and second shading data, Read the image data of a predetermined range in the scanning direction, divide the read image data for a plurality of lines of the predetermined range into a plurality of blocks in the sub-scanning direction, find the average value of the image data for each same pixel position of each block, A peak value is extracted from the average value of each block at each pixel position, and a peak value sequence composed of the peak values at each pixel position can be used as shading data, so that white shading data that is not affected by dirt is obtained. Can be compared because the two white shading data are generated in the same way, so the second shading data First shading data correction is possible using data.
Further, in the invention according to claim 5, in the invention according to claim 1, 2, or 4, the invention according to claim 8 is the second shading in the invention according to claim 6 or 7. Since the data can be generated by reading a predetermined number of lines in the sub-scanning direction from the position where a predetermined number of lines have passed from the leading edge of the document as the reading start position, the data is arranged before and after the image reading position. An image can be read when the document is biting both of the two transport rollers for document transport, and therefore, the image can be read without sagging of the document.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the components, types, combinations, shapes, relative positions, and the like described in this embodiment are not merely intended to limit the scope of this description unless otherwise specified, but are merely illustrative examples. .
FIG. 1 is an explanatory diagram of a copying machine showing an embodiment of the present invention. As shown in the figure, the copying machine includes an image scanner 1 constituting an image reading device, an image forming unit 2 for forming an image by an electrophotographic method, and the like. Among them, the image scanner 1 includes a first image reading unit 3, a second image reading unit 4, a document setting unit 5, a document discharge unit 6, a document transport path 7, a plurality of transport rollers 8, as shown in the figure. 1 contact glass 9, 2nd contact glass 10, 1st reading roller 11, 2nd reading roller 12, etc. are comprised.
A document to be read is set in the document setting unit 5, and a document whose image has been read is discharged to the document discharge unit 6. The document transport path 7 is a path through which a document is provided between the document setting unit 5 and the document discharge unit 6, and the document on which image reading is performed is transported one by one through the document transport path 7. The
When reading a document, the mode is switched so that the image is read only by the first image reading unit 3 in the case of a single-sided document, and the first image reading unit 3 and the second image reading unit 4 in the case of a double-sided document. And read the image.

The first image reading unit 3 can read an image of a document placed on the first contact glass 9 at a fixed position, and the document conveyed between the second contact glass 10 and the first reading roller 11. It is also possible to read the image. When reading on the first contact glass 9, the light source and the reflecting mirror move. When reading at the position of the contact glass 10, the first reading roller 11 is rotationally driven at the same speed as the transport roller 8 by a stepping motor (not shown), and presses the transported document against the second contact glass 10.
In the second image reading unit 4 that reads the back image, a contact image sensor is used as a photoelectric conversion element, and a CCD can be used for this. The second reading roller 12 is disposed opposite to the second image reading unit 4 with the document conveying path 7 interposed therebetween. When reading is performed by the second image reading unit 4, the second reading roller 12 is connected to the conveying roller 8 by a stepping motor (not shown). It is rotated at the same speed, and the distance between the image surface of the document and the second image reading unit 4 is kept constant.
On the other hand, the image forming unit 2 includes a photoconductor 14, a laser unit 15, a developing device 16, a transfer device 17, a fixing unit 18, and the like, and the surface of the photoconductor 14 is uniformly formed by a charger (not shown). On the surface of the photoreceptor 14, writing by the laser unit 15 is performed based on the image data read by the first image reading unit 3 or the second image reading unit 4, and an electrostatic latent image is formed. The The electrostatic latent image is visualized as a toner image by the toner supplied from the developing device 16, and the visualized toner image is transferred to a sheet by the transfer device 17. Then, the transferred toner image is fixed on a sheet by the fixing unit 18, and the sheet is discharged to a discharge tray 19.

FIG. 2 is a detailed view of a portion including the second image reading unit 4 and the second reading roller 12 described above, and FIG. 3 is an enlarged sectional view of the second reading roller 12. As shown in FIGS. 2 and 3, the second reading roller 12 is disposed to face the second image reading unit 4, has a substantially circular cross-sectional shape, and is formed in white using rubber or resin as a material. . A reference white reading surface 13 is formed on a part of the outer peripheral portion of the second reading roller 12 along the axis A of the second reading roller 12. In the example shown in FIG. 3, the document D is conveyed as shown by the arrow above the reference white reading surface 13 as shown.
In the above description, the reference white reading surface 13 has the center of curvature B on the straight line a orthogonal to the axis A of the second reading roller 12, and the maximum outer peripheral surface trajectory (reference white reading surface 13 of the second reading roller 12). The second reading roller 12 is provided with a convex curved surface located on the inner side of a substantially circular outer peripheral surface of the second reading roller 12 that is not provided (part indicated by a broken line in FIG. 3).
FIG. 4 is a block diagram mainly showing the configuration of the second image reading unit 4. In FIG. 4, the main body control unit 22 includes a CPU and controls the entire copying machine. The controller 23 also controls a motor and various actuators that drive the transport roller 8 via the controller 23. The operation unit 32 is provided with various keys for performing various operations of the copying machine, a liquid crystal display device, and the like. Although not shown, the first image reading unit 3 has the same configuration as that of the second image reading unit 4 shown in FIG.
With this configuration, in this copying machine, when the double-sided copy mode is selected, the originals set in the original setting unit 5 are conveyed one by one through the original conveying path 7 with the front side facing up, and the first image reading unit The front side image is read by 3 and the back side image is read by the second image reading unit 4. Then, the read front and back images are copied to the front and back surfaces of the same sheet, respectively.

In the above, when reading an image, the light from the light source 24 lit by the lighting control signal from the controller 23 irradiates the document surface, the reflected light is condensed by the lens, and the document is read by the gate signal from the controller 23. The contact image sensor (sensor chip) 25 reads an image on the document surface at the timing when the first reading roller 11 and the second reading roller 12 are reached. The read image data is temporarily stored in the frame memory 29 via the AMP circuit 26, the A / D conversion circuit 27, and the image processing circuit 28 provided on each of the front and back sides, and then the output control circuit 30 and the interface (I / F) Transfer to the main body control unit 22 via the circuit 31.
In this copying machine, the image processing circuit 33 performs image processing such as white shading correction, black shading correction, and γ correction on the image data of the document. In this white shading correction, the white shading data used for the white shading correction of the back surface image data is generated by reading the reference white reading surface 13 of the second reading roller 12 disposed opposite to the second image reading unit 4. .
In the above description, the timing for reading the reference white reading surface 13 is just before the original reaches the installation position of the second image reading unit 4 in this embodiment. FIG. 5 shows the timing chart. In FIG. 5, XSHGATE indicates this. XSFGATE is the timing for reading the document data on the back side.
Hereinafter, generation of white shading data according to each embodiment of the present invention will be described.

FIG. 6 is a block diagram of the white shading processing unit 40 of this embodiment that performs white shading correction. As shown in the figure, a shading data generation circuit 41 that generates white shading data based on a signal input from the second image reading unit 4 having a built-in contact image sensor, and a white generated by reading from the reference white reading surface 13. A first memory 42 for storing shading data, a second memory 43 for storing white shading data generated by reading a white reference document, and white shading data stored in the memories 42 and 43 for each main scanning. Comparing circuit 44 that detects the difference by comparing each pixel in the direction, shading data that corrects white shading data generated by reading from the reference white reading surface 13 using the difference and generates final white shading data Using the correction circuit 45 and its final white shading data Comprising a like document correction circuit 46 for correcting the draft data.
In this embodiment, the image reading means described in the claims is realized by the second image reading unit 4, and the first white shading data generation means and the second white shading data generation means are realized by the shading generation circuit 41. The difference detection means is realized by the comparison circuit 44, and the shading data correction means is realized by the shading data correction circuit 45.
With this configuration, in this embodiment, the second white shading data is generated using the read data obtained by reading the reference white reference document, and the reference white plate surface is read when reading the document image. First white shading data is generated using the data, the first shading data and the second shading data are compared to detect a difference between the two shading data, and the first shading data is determined based on the difference. Then, the image data of the original is corrected using the corrected first shading data.

The reason why the original image data is corrected by the first white shading data generated from the data obtained by reading the reference white plate surface at the time of reading the original is that the light source and the like are deteriorated with time. If this correction is not performed, the image data at the time of reading the document will be read as dark as the light source becomes dark. Therefore, for example, if the value of the first white shading data at a certain pixel position is 250 at the start of use and becomes 200 due to deterioration of the light source, the image data at that pixel position is (250 / 200) correction is performed.
However, as shown in FIGS. 12 to 14, the level of the reference white plate decreases with respect to the image data on the document at both ends in the main scanning direction. In this embodiment, the second data obtained from the white reference document is used. The correction coefficient is obtained from the white shading data of the image and the first white shading data obtained from the reference white reading surface 13 as the reference white plate, and the original document data is corrected with the first white shading data corrected with the correction coefficient. To do.
In this method, white shading data is generated from the read data. For example, image data at each pixel position is read for a predetermined number of lines, an average value is obtained for each pixel position, and an average value corresponding to the number of pixel positions on one line is obtained. The average value sequence consisting of the white shading data.

FIG. 7 is a flowchart of a white reference original reading operation. In this operation flow, first, the main body control unit 22 determines whether or not the white reference document is read, and in the case of the white reference document reading, it is determined whether or not the reading is performed at the time of shipment from the factory (S1). The reference document reading is a special reading mode that is not used by a general user. A key for setting this mode (this is an instruction means according to claim 3) is provided in a hidden place or the like, and the main body control unit 22 detects that the white reference document is read by detecting that this key is pressed. In addition, the determination of whether or not to read at the time of factory shipment is defined as the reference document reading that performs the reading at the time of shipment from the factory first, for example, when the first white reference document reading is executed Information indicating this is stored in a non-volatile memory (not shown) in the control unit 22, and the information is referred to.
In the case of factory shipment (YES in S1), the main body control unit 22 conveys the set white reference original (S2), causes the second image reading unit 4 to read the white reference original, and from the read image data Second white shading data is generated (S3), and the white shading data is stored in the second memory 43 (S4). The second memory 43 is a nonvolatile memory.
On the other hand, when it is determined that it is not at the time of factory shipment (NO in S1), the reading operation is not performed and the process is terminated.
In the above, when it is necessary to read the white reference original again, such as when the second image reading unit 4 or the second reading roller 12 is replaced after shipment, the white shading data generated again from the white reference original is obtained. May be stored in a third memory different from the white reference original shading data at the time of shipment from the factory, and thereafter the white shading data may be corrected using the data in the third memory. The white shading data may be updated.

FIG. 8 is an operation flow at the time of reading a document in double-sided copying or the like. The main body control unit 22 starts the reading operation, and then the reference white reading surface 13 of the second reading roller 12 by the second image reading unit 4. Is read (S11), and first white shading data is generated (S12). Then, the white shading data is stored in the first memory 42 (S13).
Subsequently, the main body control unit 22 compares the first white shading data stored in the first memory 42 with the second white shading data stored in the second memory 43 at the time of shipment from the factory for each corresponding pixel. Is calculated (S14), and the first white shading data in the first memory 42 is corrected based on the correction coefficient (S15). Further, when the original is read, the original data is corrected using the corrected shading data (S16), and the shading correction operation is terminated.
The first white shading data correction does not necessarily need to be performed every time an original image is read. In that case, for example, a non-volatile memory is required to store the corrected first white shading data. .
Thus, according to this embodiment, even when the contact image sensor is used as the image reading unit and the white roller is used as the white reference member, the white shading data generated using the white reference document as a reference is stored in advance. When reading a document, the data obtained from the white roller used as the white shading data can be corrected using the stored white shading data. Therefore, for example, the longitudinal directions of the contact image sensor and the white roller are shifted from each other. Even in such a case, appropriate shading correction can be performed, and stable and high-quality image reading can be realized.

In this embodiment, when generating the first and second shading data, a predetermined range of image data is read in the sub-scanning direction, and the read image data for a plurality of lines is divided into a plurality of blocks in the sub-scanning direction. By calculating the average value of the image data for each block for each pixel, the peak value (whitest value) is extracted from the average value for each pixel of each block, and the peak value is used as the shading data for each pixel. To do.
FIG. 9 shows an example of a reading place on the white reference original. As shown in the drawing, a signal XSHGATE for generating shading data is asserted after m lines from the leading edge of the document (set to a level with a signal) and read from the reference white reading surface 13 of the second reading roller 12 which is a white reference roller. After reading the same number of lines as the case, the XSHGATE is closed. The position after the m-th line from the leading edge of the document is set as the reading start position, as shown in FIG. 10, when transporting the document, two transports for transporting the document disposed before and after the second image reading unit 4 This is because it is desired to read the document when both the rollers 8a and 8b are biting. If the original is not sandwiched between the front and rear transport rollers 8a and 8b and is slack, the distance from the contact image sensor to the original cannot be kept constant, so the original data may not be read constantly. .

FIG. 11 shows an operation flow at the time of reading the white reference document of this embodiment. The operation flow will be described below with reference to FIG. Although the description is omitted, the same operation flow is performed when reading from the reference white reading surface 13 of the second reading roller 12 which is a white reference roller. In this embodiment, the averaging means and the peak value extracting means described in claim 4 are realized by the main body control unit 22.
First, the white reference document is read by the same number of lines as the main body control unit 22 reads from the white reference roller (S21). The read image data is divided into n blocks by L lines (S22), and an average value (simple average) of the image data at each pixel position is obtained for the L lines of each block (S23). Further, a peak value (maximum value) is extracted for each pixel from the average value of each block (S24), and the peak value sequence for one line is used as shading data (S25).
Thus, according to this embodiment, the white shading data of each pixel is averaged for each block, and the peak value of the average value of each block is adopted as the white shading data. Data can be obtained, and this method is used when generating the first shading data as well as when generating the second shading data, so it is possible to compare two white shading data Accordingly, it is possible to correct the first shading data using the second shading data.

1 is an explanatory diagram of a copying machine showing an embodiment of the present invention. FIG. 1 is a detailed view of a main part of a copying machine showing an embodiment of the present invention. FIG. 3 is an enlarged cross-sectional view of a main part of the copier showing an embodiment of the present invention. 1 is a configuration block diagram of a main part of a copying machine showing an embodiment of the present invention. 2 is a timing chart of the main part of the copying machine showing an embodiment of the present invention. 1 is a configuration block diagram of a main part of a copying machine showing a first embodiment of the present invention. FIG. 3 is an operation flowchart of the main part of the copier showing the first embodiment of the present invention. FIG. 6 is another operation flowchart of the main part of the copier showing the first embodiment of the present invention. FIG. 9 is a diagram for explaining the operation of a main part of a copying machine showing a second embodiment of the present invention. Explanatory drawing of the principal part of a copying machine showing a second embodiment of the present invention. FIG. 6 is an operation flowchart of the main part of a copying machine showing a second embodiment of the present invention. Explanatory drawing for demonstrating the problem which invention is going to solve. Another explanatory view for explaining a problem to be solved by the invention. Another explanatory view for explaining a problem to be solved by the invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image scanner 2 Image formation part 3 1st image reading unit 4 2nd image reading unit 8 Conveyance roller 11 1st reading roller 12 2nd reading roller 13 Reference | standard white reading surface 22 Main body control part 23 Controller 33 Image processing circuit 40 White shading Processing unit 41 Shading data generation circuit 42 First memory 43 Second memory 44 Comparison circuit 45 Shading data correction circuit 46 Document correction circuit

Claims (8)

  In the image reading apparatus capable of performing shading correction, a first white shading data is provided using read data obtained by reading a reference white plate surface by disposing a reference white plate facing an image reading means for reading an image on a document. A first shading data generation unit that generates second white shading data using read data obtained by reading a reference white reference document, and the first white shading A difference detection unit that detects the difference between the two white shading data by comparing the data and the second white shading data, and corrects the first white shading data using the difference detected by the difference detection unit. Image reading characterized by comprising shading data correction means Apparatus.   2. The image reading apparatus according to claim 1, wherein the second shading data obtained by reading the white reference document is stored, and the first shading data generated by the difference detecting unit at the time of reading the document image is stored. An image reading apparatus having a configuration for comparing with stored second shading data.   3. The image reading apparatus according to claim 2, further comprising instruction means for instructing reading of a white reference document.   3. The image reading apparatus according to claim 1, wherein when generating the first and second shading data, a predetermined range of image data is read in the sub-scanning direction, and read for a plurality of lines of the predetermined range. An averaging means for dividing the image data into a plurality of blocks in the sub-scanning direction to obtain an average value of the image data at each pixel position in each block, and a peak from the average value of each block at the same pixel position An image reading apparatus comprising: a peak value extracting means for extracting a value; and a peak value sequence including peak values at each pixel position is used as shading data.   5. The image reading apparatus according to claim 1, wherein the second shading data has a reading start position at a position where a predetermined number of lines have passed from the leading edge of the document in the sub-scanning direction. An image reading apparatus characterized in that a predetermined number of lines are read and generated in a scanning direction.   In a shading correction method for correcting image data read from a document using white shading data, second white shading data is generated and stored using read data obtained by reading a reference white reference document. When reading a document image, first white shading data is generated using read data obtained by reading a reference white plate surface arranged on the image reading surface side for reading an image on the document, and the first shading data is stored. A shading correction method comprising: comparing the second shading data, detecting a difference between the two shading data, and correcting the first shading data using the difference.   7. The shading correction method according to claim 6, wherein when generating the first and second shading data, a predetermined range of image data is read in the sub-scanning direction, and the read image data for a plurality of lines in the predetermined range is sub-scanned. The image data is divided into a plurality of blocks in the scanning direction, the average value of the image data for each pixel position of each block is obtained, the peak value is extracted from the average value of each block for each pixel position, and each pixel position A shading correction method characterized in that a peak value sequence composed of peak values is used as shading data. 8. The shading correction method according to claim 6, wherein the second shading data has a reading start position at a position where a predetermined number of lines have passed from the leading edge of the document in the sub-scanning direction, and a predetermined value in the sub-scanning direction from that position. A shading correction method characterized by reading and generating the number of lines.

Images