JP4194210B2 - Image reading apparatus and method for controlling image reading apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image reading apparatus. And method for controlling image reading apparatus In particular, Shading board Reading apparatus having a shading correction function for obtaining a correction value based on the read data and correcting the reading unevenness using the correction value And method for controlling image reading apparatus About.
[0002]
[Prior art]
FIG. 2 is a diagram showing a schematic configuration of a conventional image reading apparatus.
[0003]
As shown in FIG. 2, the image of the original 204 placed on the original platen glass 203 illuminated by the original illumination lamp 201 is photoelectrically converted via the first mirror 205, the second mirror 206, the third mirror 207, and the lens 208. The image is formed on the element CCD 209 and the line image of the original 204 is read. The CCD 209 is composed of a plurality of elements arranged in the main scanning direction. The document illumination lamp 201 and the first mirror 205 move in the direction of the arrow, and sequentially read the line images. At this time, the second mirror 206 and the third mirror 207 also move in the direction of the arrow, and are driven by a drive system (not shown) so that the distance (optical path length) from the document surface to the CCD 209 is constant.
[0004]
A reading sequence of the image reading apparatus having such a configuration will be described below.
[0005]
When an original 204 is placed on the platen glass 203 by an operator and a reading command is input by a start button or the like, the image reading apparatus first performs a shading correction process.
[0006]
Shading correction processing is image processing that corrects reading unevenness in the reading system, particularly the optical system, and corrects uneven lighting in the illumination system, a decrease in the amount of light at the periphery of the optical lens, and uneven sensitivity in each pixel of the CCD, and outputs from the reading system. The dynamic range of all the pixel data in the image data is made equal.
[0007]
The procedure of the shading correction process will be described below.
[0008]
The shading correction is performed by the member arrangement shown in FIG. In the member arrangement shown in FIG. 2, when a shading correction execution command is input from a CPU (not shown), the image reading device turns on the lamp 201 and illuminates the shading plate 211 attached to the platen glass 203. . The image of the illuminated shading plate 211 is read as a line image by the CCD 209 via the first mirror 205, the second mirror 206, the third mirror 207, and the lens 208.
[0009]
The shading plate 211 is coated with a paint having a predetermined uniform white density, and the whiteness of the shading plate 211 determines the reference white color of the document 204. Processing of the signal output from the CCD 209 will be described with reference to FIG.
[0010]
FIG. 3 is a block diagram showing a signal processing circuit for signals output from the CCD 209.
[0011]
The analog image signal output from the CCD 209 is sent out pixel by pixel sequentially from the top pixel of the CCD 209. The sent image data is input to an analog amplifier (AMP) 301 and is amplified by a predetermined amplification factor. The signal-amplified image data is input to the A / D converter 302 and converted into 8-bit digital image data having an amplitude range of 0 to 255. The output of the A / D converter 302 is input to the shading correction circuit 303, converted into image data in which the nonuniformity of the image data is corrected, converted into a predetermined image format via the I / F circuit 304, and the image Output to the outside of the reader.
[0012]
The line image of the shading plate 211 is sequentially signal-processed by the signal processing circuit, but the signal before being input to the shading correction circuit 303 is as shown in FIG.
[0013]
FIG. 4 is a diagram showing a shading plate reading profile before shading correction. In FIG. 4, the horizontal axis indicates the pixel address of the CCD 209, and the vertical axis indicates the signal level from 0 to 255. The pixel address is 7500 pixels that can read 297 mm in the A3 short side direction when the resolution of the image reading apparatus is 600 dpi, and the signal level is black for data 0 and white for data 255.
[0014]
As shown in FIG. 4, the read image of the shading plate 211 before the shading correction processing is not uniform in data even though the shading plate 211 has uniform whiteness. That is, for example, due to uneven illumination of the lamp 201 and a decrease in the amount of light around the lens 208, the data in the vicinity of the first pixel and the vicinity of the 7500th pixel are low. Data irregularity occurs as in the case of B and B pixels. The pixel A has low sensitivity, and the pixel B has high sensitivity.
[0015]
The shading correction process is an image process for correcting the above-described reading unevenness, and the configuration of the shading correction circuit will be described with reference to FIG.
[0016]
FIG. 5 is a block diagram showing a schematic configuration of the shading correction circuit.
[0017]
In FIG. 5, 501 is a switch, 502 is a line memory, and 503 is a multiplier. When performing shading correction, first, the switch 501 is connected to the Y side by a CPU (not shown), and image data is input to the line memory 502.
[0018]
The line memory 502 has a capacity of 7500 addresses × 16 bits, and can capture all pixel data from the CCD 209. Further, since it has a 16-bit data width, it can store up to 256 additional data per pixel. When the switch 501 is tilted to the Y side, the CPU (not shown) samples the data profile from the CCD 209 shown in FIG. If the CPU (not shown) is controlled so that the addition data for 256 times can be sampled in the line memory, the influence of image data dispersion (S / N ratio) can be reduced. When sampling is completed, a CPU (not shown) calculates a data correction value for the shading target value for each pixel. For example, when the shading target value is 245 and the average read value of the pixel A in FIG. 4 is 160, the data correction value of the pixel A is 245/160 = 1.53, and the average of the pixel B in FIG. If the read value is 210, the data correction value for pixel B is 245/210 = 1.17.
[0019]
When the calculation of the correction values for all pixels is completed, the CPU (not shown) overwrites the line memory 502 with the correction value for each pixel. Thereafter, the switch 501 is moved down to the X side to control the image data to be input to the multiplier 503. The output of the line memory 502 is connected to the other input of the multiplier 503, and correction data of the corresponding pixel is input to the multiplier 503 every time pixel data from the CCD 209 is input. Accordingly, the multiplier 503 outputs image data in which the reading unevenness of the CCD 209 is corrected.
[0020]
FIG. 6 shows the output of the shading correction circuit 303 when the shading plate 211 is read. The relationship between the vertical axis and the horizontal axis is the same as in FIG. 4, and the shading target value is 245. As can be seen from the figure, the read data is 245 for all pixels.
[0021]
FIG. 7A shows a copy image obtained when the image reading apparatus reads a uniform halftone original, performs shading correction processing, and performs copying by the copying apparatus based on the read data.
[0022]
Note that such a shading correction method using a line memory is a very general method. For example, Japanese Patent Application Laid-Open No. 11-187263 also describes the method in the section “Prior Art”.
[0023]
However, since white paint is applied to the shading plate 211, when dust enters the paint and the dust is in the shading position, proper shading correction cannot be performed as described later. In addition, when the shading plate 211 is attached to the platen glass 203, dust may be mixed between the shading plate 211 and the platen glass 203. In this case as well, proper shading correction cannot be performed.
[0024]
FIG. 8 is a diagram showing a data profile before shading when dust is present at the shading position. FIG. 8 shows that dust exists at the position of the pixel C.
[0025]
If the shading correction value is generated by the above-described method while dust is present at the position of the pixel C, and the read value of the pixel C is 120, the correction value of the pixel C is 245/120 = 2.04. Therefore, it is greatly different from the original correction value 245/220 = 1.11. Accordingly, when a uniform halftone original is read, shading correction is performed using such correction values, and copying is performed by the copying apparatus based on the obtained data, white stripes as shown in FIG. 71 occurs.
[0026]
In order to prevent this problem, a technique is known in which dust on the shading plate 211 is detected and shading correction is performed at a position where there is no dust. For example, when the data profile is sampled using the line memory 502 shown in FIG. 5, edge enhancement processing is performed in the pixel direction, and the data difference between the adjacent pixel and the target pixel is determined in advance at the slice level. If it is larger than that, it is determined that there is dust in the pixel of interest, and the shading position is shifted. The slice level is set so that it does not hit the pixel A and the pixel B shown in FIG.
[0027]
[Problems to be solved by the invention]
However, the conventional dust detection method of the shading plate performed by diverting the line memory of the image reading apparatus as described above performs dust determination based on a uniform slice level, so that accuracy corresponding to various types of data profiles is achieved. It is difficult to perform dust determination well, and there is a problem that there is a high possibility of erroneous detection such as detection of dust when there is no dust, or detection of dust even when there is dust.
[0028]
When the shading correction value is determined, the line memory is overwritten with the shading correction value data, and the data profile is lost. Therefore, it is difficult to re-determine the shading correction value even if a false detection is noticed.
[0029]
The present invention has been made in view of such problems, and is an image reading apparatus that enables accurate dust detection. And method for controlling image reading apparatus The purpose is to provide.
[0030]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, an image of an original is displayed. In line units along the main scanning direction A reading means for reading, a creating means for creating a shading correction value for obtaining a shading target value based on data read from the shading plate, and the reading means using the shading correction value created by the creating means. Scanned document image data Shading correction means for correcting shading for Storage means for storing a plurality of lines of images subjected to shading correction by the shading correction means; And the creating means creates a shading correction value based on the read data at the first position of the shading plate, and the shading correction means has a first shading plate different from the first position. 2 position For multiple lines including For the read data, perform the shading correction using the created shading correction value, The storage means stores data for a plurality of lines subjected to shading correction, Above For multiple lines stored in the storage means Data indicating a value brighter than the shading target value In the sub-scanning direction Is included, the creation unit creates a shading correction value based on the read data at the second position, and the shading correction unit reads the reading unit based on the created shading correction value. It is characterized in that shading correction is performed on the image of the original document.
[0031]
According to a fifth aspect of the present invention, there is provided a method for controlling an image reading apparatus, comprising: In line units along the main scanning direction A reading means for reading, a creating means for creating a shading correction value for obtaining a shading target value based on data read from the shading plate, and the reading means using the shading correction value created by the creating means. Scanned document image data Shading correction means for performing shading correction on, Storage means for storing a plurality of lines of images subjected to shading correction by the shading correction means; And a second position of the shading plate that is different from the first position, and a step of creating a shading correction value based on read data at the first position of the shading plate. For multiple lines including For the read data, perform the shading correction using the created shading correction value, Data for a plurality of lines subjected to shading correction is stored in the storage means. Step and said For multiple lines stored in the storage means Data indicating a value brighter than the shading target value In the sub-scanning direction Is included, a shading correction value is created based on the read data at the second position, and shading correction is performed on the image of the document read by the reading unit based on the created shading correction value. And performing.
[0033]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0034]
(First embodiment)
FIG. 1 is a block diagram showing the configuration of a shading correction circuit in the first embodiment of the image reading apparatus according to the present invention. The configuration of the image reading apparatus according to the present invention is basically the same as the configuration of the conventional image reading apparatus shown in FIGS. 2, 3, and 5, and therefore the same parts are denoted by the same reference numerals. The description is omitted.
[0035]
In the shading correction circuit according to the first embodiment, the line memory 101 is newly connected to the output terminal of the multiplier 503. The line memory 101 is provided with a storage capacity for one line of 7500 pixels by 8 bits per pixel, for example.
[0036]
Next, the operation will be described.
[0037]
In the image reading apparatus according to the present invention, when a reading command is input by an operator, first, the switch 501 is tilted to the Y side, and the above-described conventional shading correction value is generated. That is, at the first shading position of the shading plate 211, the shading plate 211 is read, and as a result, for example, the profile including dust shown in FIG. Then, a shading correction value is created based on this profile, and is overwritten and saved in the line memory 502.
[0038]
Next, the image reading apparatus moves the shading position of the shading plate 211 from the first shading position to the second shading position by a drive circuit (not shown). For example, in the case of an image reading apparatus having a resolution of 600 dpi, the second shading position is shifted by about two pixels (about 84 um) from the first shading position.
[0039]
Then, the switch 501 is tilted to the X side, the shading plate 211 is read at the second shading position, and the multiplier 503 uses the shading correction value stored in the line memory 502 for this read profile for each pixel. Is multiplied by this to perform shading correction. The read profile obtained as a result is stored in the line memory 101. The reading profile obtained at this time is the same as the reading profile of the shading plate 211 obtained at the first shading position shown in FIG. 8, and when the shading correction is performed using the shading correction value created based on the reading profile shown in FIG. It becomes like 9.
[0040]
That is, the reading profile obtained when the shading plate 211 is read at the first shading position and the shading correction is performed on the reading profile using the shading correction value stored in the line memory 502 is shown in FIG. Thus, the pixel where the dust at the point C exists is also corrected, and is corrected to the shading target value 245 in the same manner as the other pixels.
[0041]
However, since dust exists at point C in the first shading position, an excessive value of the shading correction value is calculated. Using this shading correction value, the reading profile in the second shading position where there is no dust. As shown in FIG. 9, the read data of the point C exceeds the shading target value 245 and sticks to the limit value 255, as shown in FIG.
[0042]
Therefore, it is determined whether or not dust is present at the shading position based on the corrected reading profile shown in FIG. 9 stored in the line memory 101. That is, the presence / absence of a pixel attached to the limit value 255 is determined. If there is a pixel attached, it is determined that dust is present at the first shading position. It is not determined whether there is a pixel attached to the limit value 255, but if there is pixel data having a different value based on whether there is pixel data having a different value compared to surrounding pixel data, the first It may be determined that dust is present at the shading position.
[0043]
If the presence of dust cannot be determined at the second shading position, the shading position is further shifted to the third and fourth shading positions, and the same sequence is executed. If the presence of dust can be determined at any of the shading positions, the position information of the determined shading position is stored in a non-volatile backup element (for example, EEPROM).
[0044]
Thereafter, every time a shading correction value is created, the position information of the shading position is read from the backup element, a shading correction value is created at the shading position indicated by this position information, stored in the line memory 502, and this shading is performed. The shading correction process is performed using the correction value.
[0045]
Note that the processing described above is executed by a CPU (not shown).
[0046]
In addition, the reading profile obtained when the shading correction is performed on the reading profile of the shading plate 211 using the shading correction value stored in the line memory 502 is stored in the line memory 101, and then the line memory 101. The profile may be read out from the image and displayed on a display unit such as an operation unit of the host computer or the image reading apparatus.
[0047]
Although the case where the line memory 101 has a storage capacity for one line has been described in the above embodiment, the number of lines that can be stored in the line memory may be increased to increase the determination accuracy.
[0048]
For example, when a line memory corresponding to the line memory 101 has a storage capacity for four lines, the line memory can read a reading profile for four lines with different reading positions (shading positions) at a shading position including dust. It is possible to store a reading profile obtained as a result of performing shading correction using the generated shading correction value. For example, a data map as shown in FIG. 10 is stored in the line memory.
[0049]
FIG. 10 is a diagram obtained by mapping data after shading correction of reading profiles obtained at four different shading positions on the shading plate using a line memory having a storage capacity for four lines.
[0050]
In this data map, the data of pixel C is all 255 in the line crossing direction, and the surrounding pixels are approximately 245. As can be seen from this data map, it is clear that the data of pixel C is clearly different data. If data after shading correction for multiple lines can be stored in this way, Perpendicular to main scanning direction Since it appears as a line-shaped white streak in the sub-scanning direction, if a calculation process for detecting a white streak is performed, detection can be performed with higher accuracy than dust detection using a line memory for one line.
[0051]
When a shading position without dust is determined by such a method, it is desirable that the mechanical position determination accuracy be high. For example, when the driving means for driving the optical system is a general stepping motor, it is better to use a step angle as small as possible. Or it is good to adjust the gear ratio of a drive system and to take the movement distance of the optical system per step small. In this way, by mechanically improving the positional accuracy of the optical system, a shading correction value at a shading position free from dust can be obtained, and accurate shading correction can be realized.
[0052]
(Second Embodiment)
In the first embodiment, the line memory 101 is added inside the shading correction circuit 303 to realize dust detection on the shading plate. However, in the second embodiment, dust is detected without adding the line memory 101. Make the detection happen. In other words, in a copier configured so that the image reading apparatus is directly connected to the printer, the line memory exists on the printer side, so that it is not necessary to add the line memory 101 by diverting it.
[0053]
FIG. 11 is a block diagram showing the configuration of the image processing circuit on the printer side. The configuration on the image reading apparatus side in the second embodiment is the same as that in the first embodiment except for the shading correction circuit 303. Therefore, in the description of the second embodiment, the first embodiment will be described. The configuration of the image reading apparatus in the form is used. The shading correction circuit according to the second embodiment has a configuration in which the line memory 101 does not exist in the shading correction circuit 303 according to the first embodiment.
[0054]
In FIG. 11, 1001 is an I / F circuit, 1002 is a log conversion circuit, 1003 is an edge enhancement circuit, 1004 is a γ conversion circuit, and 1005 is a binarization processing circuit. An image signal from the I / F circuit 304 on the image reading apparatus side shown in FIG. 3 is input to the I / F circuit 1001. The log conversion circuit 1002 includes a look-up table composed of a memory such as a RAM, and converts input luminance data into density data. The output of the log conversion circuit 1002 is input to the edge enhancement circuit 1003 to enhance the contrast of the edge portion of the image and convert it into a sharp image. The edge emphasis circuit 1003 is constituted by a matrix operation circuit of 5 × 5 pixels, for example, and has a line memory for four lines. The output of the edge enhancement circuit 1003 is input to the γ conversion circuit 1004, and data correction is performed so that the image data is output in accordance with the density characteristics of the printer unit. Similar to the log conversion circuit 1002, the γ conversion circuit 1004 includes a lookup table composed of a memory such as a RAM. The output of the γ conversion circuit 1004 is input to the binarization processing circuit 1005, and 8-bit multi-value data is converted into binary data. In recent years, the error diffusion processing method is often employed, and the difference of multi-value data that is rounded down or rounded up when binarizing is stored, the difference is distributed to adjacent pixel data, and the density is stored is doing. In order to save the data difference, the binarization processing circuit 1005 also has a line memory for several lines.
[0055]
As described above, the image processing circuit on the printer side has many circuits having line memories for several lines. When performing dust detection in the image reading apparatus using the line memory 101 as in the first embodiment. In addition, any line memory can be temporarily used.
[0056]
For example, a case where the line memory of the binarization processing circuit 1005 shown in FIG.
[0057]
First, the processing in the log conversion circuit 1002 and the γ conversion circuit 1004 is set to through, and is set so that the same signal as the input signal is output. Further, the edge enhancement circuit 1003 writes parameters to be input to the matrix so that edge enhancement is not applied. If such processing is performed, the data output from the image reading apparatus is directly input to the binarization processing circuit 1005 without being deformed. Therefore, the line memory provided in the binarization processing circuit 1005 is used by the same method as that used for the line memory 101 of the first embodiment to detect dust in the image reading apparatus.
[0058]
Thereby, compared with the first embodiment, the line memory 101 can be omitted, and the cost can be reduced.
[0059]
When the dust detection is completed, the setting of each circuit shown in FIG. 11 is returned to the normal setting, and a printer operation having a normal image processing function is performed.
[0060]
In addition, dust detection is positioned as an adjustment item that is carried out at the time of adjustment at the production factory or at the time of installation at the user's home. Ru Therefore, it does not affect the specifications such as the first copy time of the image reading apparatus itself.
[0061]
A storage medium storing software program codes for realizing the functions of the above-described embodiments is supplied to the system or apparatus, and the computer (or CPU or MPU) of the system or apparatus is stored in the storage medium. It goes without saying that the present invention can also be achieved by reading and executing the program code.
[0062]
In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the program code constitutes the present invention.
[0063]
As a storage medium for supplying the program code, for example, a floppy disk, hard disk, optical disk, magneto-optical disk, CD-ROM, CD-R, magnetic tape, nonvolatile memory card, ROM, or the like can be used.
[0064]
Further, by executing the program code read out by the computer, not only the functions of the above-described embodiments are realized, but also the OS running on the computer based on the instruction of the program code is actually Needless to say, the present invention also includes a case in which the functions of the above-described embodiments are realized by performing part or all of the processing and the processing.
[0065]
Further, after the program code read from the storage medium is written to a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, the function expansion is performed based on the instruction of the program code. Needless to say, the present invention includes a case where the CPU or the like provided in the board or the function expansion unit performs part or all of the actual processing and the functions of the above-described embodiments are realized by the processing.
[0066]
【The invention's effect】
As detailed above, according to the present invention, A shading correction value is generated based on the read data at the first position of the shading plate, and the generated shading correction value is used for the read data at the second position of the shading plate different from the first position. If the shading correction data includes data that is brighter than the shading target value, a shading correction value is created based on the read data at the second position, and the created shading Based on the correction value, shading correction is performed on the image of the document read by the reading unit, so that even when dust adheres to the shading plate, a shading position that avoids dust can be detected. Good shading correction can be achieved and high It is possible to provide a position reading image .
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a shading correction circuit in a first embodiment of an image reading apparatus according to the present invention.
FIG. 2 is a diagram illustrating a schematic configuration of a conventional image reading apparatus.
FIG. 3 is a block diagram showing a signal processing circuit for signals output from a CCD.
FIG. 4 is a diagram showing a shading plate reading profile before shading correction.
FIG. 5 is a block diagram showing a schematic configuration of a shading correction circuit.
FIG. 6 is a diagram illustrating an output of a shading correction circuit when a shading plate is read.
FIG. 7 is a diagram showing a copy image obtained when the image reading apparatus reads a uniform halftone original, performs shading correction processing, and then performs copying by the copying apparatus based on the read data.
FIG. 8 is a diagram showing a data profile before shading when dust is present at the shading position.
FIG. 9 is a diagram illustrating a reading profile obtained when shading correction is performed on a reading profile obtained at a shading position without dust using a shading correction value obtained at a shading position with dust;
FIG. 10 is a diagram obtained by mapping data after shading correction of reading profiles obtained at four different shading positions on a shading plate using a line memory having a storage capacity for four lines.
FIG. 11 is a block diagram illustrating a configuration of an image processing circuit on a printer side according to a second embodiment.
[Explanation of symbols]
71 white stripes
101 line memory
201 Document illumination lamp
203 Original glass stand
204 Manuscript
205 First mirror
206 Second mirror
207 Third mirror
208 lenses
209 CCD
211 Shading plate (lightness reference plate)
301 Analog amplifier
302 A / D converter
303 Shading correction circuit
304 I / F circuit
501 Switch
502 line memory
503 Multiplier (Shading correction means)
1001 I / F circuit
1002 log conversion circuit
1003 Edge enhancement circuit
1004 γ conversion circuit
1005 Binarization processing circuit

Claims (5)

Reading means for reading an image of a document line by line along the main scanning direction ;
Creating means for creating a shading correction value for obtaining a shading target value based on data read from the shading plate;
Using the shading correction value created by the creation means, a shading correction means for performing shading correction on the image data of the document read by the reading means ;
Storage means for storing a plurality of lines of images subjected to shading correction by the shading correction means ,
The creating means creates a shading correction value based on the read data at the first position of the shading plate,
The shading correction means performs shading correction on the read data for a plurality of lines including the second position of the shading plate different from the first position, using the generated shading correction value, and performs shading. Storing the corrected data for a plurality of lines in the storage means;
When the data for a plurality of lines stored in the storage means includes a streak in the sub-scanning direction due to data indicating a value brighter than the shading target value, the creating means includes the read data at the second position An image reading unit that generates a shading correction value based on the image, and wherein the shading correction unit performs shading correction on the image of the document read by the reading unit based on the generated shading correction value. apparatus. It said reading means includes an image reading apparatus according to claim 1, wherein a plurality of photoelectric conversion elements arranged in the main scanning direction. The second position, the image reading apparatus according to claim 2, characterized in that the deviation between the first position in the sub-scanning direction forming the main scanning direction perpendicular.   A shading correction value is created based on the read data at the first position of the shading plate, and shading correction is performed on the read data at the second position of the shading plate using the created shading correction value. And when the shading corrected data is a predetermined value, the creating means creates a shading correction value based on the read data at the second position, and the shading correcting means The image reading apparatus according to claim 1, wherein shading correction is performed on an image of a document read by the reading unit on the basis of the shading correction value thus obtained. A reading unit that reads an image of a document line by line in the main scanning direction, a creating unit that creates a shading correction value for obtaining a shading target value based on data read from the shading plate, and the creation unit Using the shading correction value, a shading correction unit for performing shading correction on the image data of the document read by the reading unit, and a plurality of lines of images subjected to the shading correction by the shading correction unit are stored. And a control method of the image reading apparatus having storage means ,
Creating a shading correction value based on the read data at the first position of the shading plate;
For a plurality of lines of the read data including the second position of said different shading plate from the first position, performs a shading correction using the created shading correction value, a plurality of lines which are shading correction Storing the data in the storage means ;
When the data for a plurality of lines stored in the storage means includes a streak in the sub-scanning direction due to data indicating a value brighter than the shading target value, a shading correction value based on the read data at the second position And a step of performing shading correction on the image of the document read by the reading means based on the generated shading correction value.

Images