JP3480229B2 - Image reading device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus used in a digital copying machine or an image reader, and more specifically, each light receiving sensor at the time of reading an image with a light receiving sensor such as a plurality of CCD chips of a photoelectric conversion unit. The present invention relates to an image reading apparatus for shading-correcting a reading level difference of the image reading apparatus using a shading plate.

[0002]

2. Description of the Related Art Generally, a CCD (charge coupled device) chip has a different sensitivity for each pixel, and a light source for illuminating a document has uneven light distribution. Therefore, in order to stably perform high-quality image reading in an image reading apparatus using CCD chips, it is necessary to correct the reading level difference between CCD chips.

Conventionally, as an image reading apparatus for correcting the reading level difference between CCD chips, for example, Japanese Patent Laid-Open No. 6-78.
The one described in Japanese Patent No. 147 is known. This image reading device reads a shading plate as a reference reading plate in a plurality of lines by a CCD chip extending in the main scanning direction, calculates an average value of data of a plurality of lines for each pixel, and calculates a maximum value of the calculated average value. The average value and the minimum value are obtained and displayed on the LCD (liquid crystal display device) of the operation panel, and the operator who sees this determines the presence or absence of abnormal pixels or dust on the shading plate. Further, in the case of an image reading apparatus having a light source such as a halogen lamp having a light distribution characteristic having several peaks, it is determined that the light amount is insufficient when the average value of the read data of the shading plate for each pixel is less than or equal to a predetermined value. There is one that causes an error display.

[0004]

The pixel data obtained by reading the shading plate in a plurality of lines by the CCD is shown in FIG. 28 (A) by superimposing the pixel on the horizontal axis and the output on the vertical axis. Pixel data is distributed in a predetermined width W in a convex curve M having a high central portion due to the light distribution characteristic of the fluorescent lamp light source. Here, the image reading apparatus of the above publication calculates the average value of the data of a plurality of lines for each pixel and displays the maximum value, the average value, and the minimum value of the calculated average value. The reference data is the same convex curve M as shown in FIG. 28 (B) when there is no dust or the like on the shading plate or defective pixels.
The displayed maximum value, average value, and minimum value are Max, Ave, and Min in the figure, respectively. On the other hand, when dust or a defective pixel is present on the shading plate, the output of the pixel corresponding to the dust or the like is remarkably reduced, and the average value of the pixel data is also as shown by Min in FIG. 28 (C). It is significantly lower than Ave, and the operator can judge that there is dust or the like at this location. However, since the pixel reading device of the above publication calculates the average value of the read data of a plurality of lines for each pixel, shot noise superimposed on the read data of the shading plate due to the electric circuit system of the device is generated. There is a problem in that the image is erased by averaging and cannot be detected, and the correction based on the shading data on which the shot noise is superimposed causes defects such as shading streaks in a document image to be read later.

Pixel data obtained by reading the shading plate illuminated by a halogen lamp with a plurality of lines by the image reading apparatus disclosed in the above publication is similarly superimposed and shown in FIG. 29 (A). Due to the light distribution characteristics of the halogen lamp, a waveform M having a short period and a small amplitude is formed and distributed with a predetermined width W. Then, the correction reference data after the averaging process is as follows when there is no dust or the like on the shading plate.
The waveform M is similar as shown in FIG. 29 (B), but if there is dust or the like, the average value data of pixels corresponding to the dust or the like is shown in FIG. 29 (C). As indicated by Min, it is significantly lower than Ave, and the operator can judge that there is dust or the like. However, even in this case, since the averaging process is performed, the influence of the light distribution of the light source can be eliminated and dust can be detected, but the read data of the shading plate is caused by the electric circuit system of the device. There is a problem in that the shot noise that has been superimposed cannot be detected, and defects such as shading lines appear in the document image that is read later.

Therefore, an object of the present invention is to provide an image reading apparatus which can detect image noise and a decrease in the light amount of a light source due to an electric circuit system and the like and can obtain a good original read image without shading streaks. To provide.

[0007]

In order to achieve the above-mentioned object, the invention of claim 1 provides a photoelectric conversion unit for receiving reflected light from a document and converting it into an electric signal, and an analog signal from this photoelectric conversion unit. An A / D conversion unit for converting into a digital signal,
A shading plate as a reference reading plate for correcting the reading level difference of each light receiving sensor of the photoelectric conversion unit,
In an image reading device equipped with a shading correction unit that calculates the read data of the shading plate and the read data of the actual document and corrects the reading level difference of the light receiving sensors, the shading plate is read in a plurality of lines to form an image. Averaging data generation means for averaging data for each corresponding pixel on the line to generate correction reference data, and reading the shading plate in a plurality of lines to hold the peak of the image data for each corresponding pixel on the line. Peak hold data generating means for generating the correction reference data, and the difference between the correction reference data obtained by the averaging data generating means and the correction reference data obtained by the peak hold data generating means, and the calculated difference Is superimposed on the image data by determining whether or not And further comprising a judging means for judging the magnitude of the noise are.

In the shading correction prior to reading the original, the reflected light from the shading plate is received by the photoelectric conversion section on a plurality of lines and converted into an analog electric signal, and this electric signal is then converted by the A / D conversion section. After being converted into a digital signal, correction reference data for the shading correction unit is generated. Here, the averaged data generating means averages the image data of a plurality of lines, which is a digital signal from the A / D conversion unit, for each corresponding pixel on the line to generate the correction reference data, and the peak hold. The data generating means holds the peak value of the image data for each corresponding pixel on the plurality of lines to generate the correction reference data. Therefore, when the digital signal from the A / D converter does not include shot noise caused by the electric circuit system of the device, the variation of the correction reference data of both the averaging data generating means and the peak hold data generating means. Is small. On the other hand, when the shot noise is included, the read shot noise does not affect the correction reference data of the averaging data generation unit that obtains the average value with the corresponding pixel data of other lines, and the correction reference Although the variation of the data is small, the variation of the correction reference data is increased by affecting the correction reference data of the peak hold data generating means for which the peak value is obtained with the corresponding pixel data of another line.

Here, the judging means calculates the difference between the correction reference data obtained by the averaged data generating means and the peak hold data generating means. Therefore, if the calculated difference is equal to or more than a predetermined value, the peak hold method is used. The variation of the correction reference data of is large and shot noise is included.
That is, it is determined that the noise is large, and when the calculated difference is less than the predetermined value, it is determined that the variation in the correction reference data of both formulas is small and shot noise is not included, that is, the noise is small. Therefore, if the determination means determines that the noise is large, there is a cause of noise in the electric circuit system, etc. Therefore, by removing this cause, the correction reference data is made noise-free, and a good original without shading lines is obtained. A read image can be obtained.

An image reading apparatus according to a second aspect of the present invention is an image reading apparatus including the same photoelectric conversion unit, A / D conversion unit, shading plate, and shading correction unit as described above, and the same averaged data generating means and peak hold as described above. A difference between the correction reference data obtained by the data generation means and the averaged data generation means and the correction reference data obtained by the peak hold data generation means is calculated for a plurality of pixels in a predetermined area, and the average value of the calculated differences is calculated. And determining means for determining the magnitude of noise superimposed on the image data by determining whether or not the average value is equal to or more than a predetermined value. Since this image reading apparatus is different from the apparatus according to claim 1 only in the configuration of the judging means, it operates in the same manner as described above, and shot noise caused by an electric circuit system or the like of the apparatus is generated in the digital signal from the A / D converter. If is not included, the variations in the correction reference data according to both formulas are small. On the other hand, if shot noise is included, the read shot noise is
Only the variation of the correction reference data by the peak hold data generating means becomes large.

Here, the determination means calculates the difference between the correction reference data obtained by the averaged data generation means and the peak hold data generation means for a plurality of pixels in a predetermined area,
An average value of the calculated differences is obtained, and it is determined whether or not this average value is equal to or larger than a predetermined value. Then, if the calculated difference is equal to or greater than the predetermined value, it is determined that the variation in the correction reference data of the peak hold method is large and shot noise is included, and if the calculated difference is less than the predetermined value, both It is determined that the variation in the correction reference data of the method is small and shot noise is not included. Therefore, for the same reason as described above, it is possible to obtain a good original read image without shading streaks. It should be noted that, since this apparatus obtains an average value of the difference between the correction reference data by both methods in a predetermined area and judges whether or not this average value is equal to or more than a predetermined value, it is different from the apparatus of claim 1. It is not suitable for detecting local, sudden noise, but is suitable for detecting constant noise.

An image reading apparatus according to a third aspect of the present invention further comprises warning means for issuing a warning when the judgment means judges that the calculated difference or average value is equal to or more than a predetermined value and noise is large. It is characterized by The warning means is
When the determination unit determines that the noise is large, the display unit displays "Noise is large" as a warning, for example.
Therefore, the user of the apparatus can prevent the deterioration of the original read image by stopping the apparatus when reading the shading plate and stopping the reading of the original.

An image reading apparatus according to a fourth aspect of the present invention further comprises a light quantity adjusting means for increasing / decreasing a light quantity of a light source for illuminating the original according to the magnitude of noise, based on the judgment result of the judging means. . When the determination means determines that the noise is large, for example, when the determination means determines that the noise is small, for example, the light amount of the light source is increased to strengthen the illumination and relatively reduce the noise. Even if it is weakened, it does not hinder the reading of originals, so the amount of light from the light source is reduced to save power consumption. Therefore, it is possible to prevent deterioration of the original read image due to noise reduction to some extent, and it is possible to save power.

According to a fifth aspect of the present invention, there is provided an image reading apparatus further comprising a reading mode limiting means for limiting the reading mode when the noise is large based on the determination result of the determining means. When the determination unit determines that the noise is large, the read mode limiting unit limits the use of a mode for reading an object that cannot be properly read unless the noise is small. Therefore, it is possible to prevent such an object from being erroneously read and the read image from being deteriorated.

An image reading apparatus according to a sixth aspect of the present invention is characterized in that the reading mode limiting means enables only the character reading mode and disables the photo reading mode when the noise is large. When the determination means determines that the noise is large, the reading mode limiting means needs to reproduce halftones.Therefore, the use of the photo reading mode for reading a photograph that cannot be read well unless the noise is small is restricted, and the noise is large. Enables only the character reading mode to read readable characters. Therefore, it is possible to prevent a photograph from being mistakenly read and the read image from being deteriorated.

According to another aspect of the image reading apparatus of the present invention, the determination means determines the magnitude of noise even when the light source illuminating the original is turned off, and the determination result of the determination means when the light source is turned on and off is determined. It is characterized by further comprising a noise cause determining means for determining whether the cause of the noise is in the optical system or the electric circuit of the image reading device. The averaged data generation means and the peak hold data generation means first generate correction reference data for the data read from the shading plate in the light source lighting state, and the determination means calculates the difference between both generated correction reference data. When the calculated difference is equal to or larger than the predetermined value, it is determined that the noise is large. Based on this determination, the noise cause determination means determines, for example, whether or not the light amount of the light source is the maximum, and if not, gradually increases the light amount to the maximum value, and if the noise still does not decrease, it is determined that there is no abnormality in the light source and the light source is turned off. To do. Next, the noise cause judging means maximizes the gain of the electric circuit, while the judging means reads the unshaded shading plate, and the corrections generated by the averaging data generating means and the peak hold data generating means, respectively. Similar processing is performed on the reference data to determine the magnitude of noise caused by the electric circuit itself. Therefore, the noise cause determination means is
If it is determined that the noise is large, it is determined that the electric circuit has a cause of noise, and if it is determined that the noise is not large,
Judge that the optical system excluding the light source has a cause of noise. Therefore, the operator or maintenance staff of the device stops reading subsequent documents etc. based on the judgment result of the noise-causing means,
Not only the deterioration of the read image can be prevented, but also the location of the noise can be known and the repair can be performed quickly.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to the embodiments shown in the drawings. FIG. 1 is an overall configuration diagram of a digital copying machine using the image reading apparatus of the present invention. This digital copying machine comprises an image reading device 10 on the upper side and an image recording device 20 on the lower side. The image reading device 10
Is a manual document reader 16 and a document flow reader 1
7, a reduction optical system is used to apply light from a light source 11 to an original, and the reflected light is reflected by a mirror 12 and a lens 13.
An image is formed on the CCD 14 in a line shape through a photoelectric conversion to obtain an analog electric signal which is photoelectrically converted, and the analog electric signal is converted into digital data in the image processing unit 15, and then image processing such as scaling and image quality correction is performed. It is supposed to be given. The CCD 14 is 400 dpi (dot / inch)
It has a resolution of up to A3 and can read documents up to A3 size (about 5000 dots per line). Scanning the original is
If the direction perpendicular to the paper surface of FIG. 1 of the linear CCD 14 is the main scanning direction and the direction orthogonal to this is the sub scanning direction y,
In the case of a manually placed document, the CCD 14 is used in the main scanning direction and the mirror 12 is moved in the sub scanning direction in the horizontal direction. In the case of document follow shot, the CCD 14 is used in the main scanning direction and the document is conveyed in the sub scanning direction. I am doing it.

The image recording device 20 converts digital image data input from the image processing unit 15 into an analog electric signal by the laser diode drive unit 21,
The laser light emission source 22 converts this into an optical signal of strong and weak pixel by pixel, and the photosensitive drum 24 is passed through the polygon mirror 23.
The toner imaged on the top and strongly adhered to the paper 2
Transfer to the surface of No. 5, 400dpi by electrophotographic method,
An image with 256 gradations is reproduced.

FIGS. 2 and 3 are flowcharts showing the overall operation of the digital copying machine having the mode switching function and the original mode setting subroutine, respectively. In step S1 of FIG. 2, the document is set on the document table, and in step S2,
A copy mode such as "photograph mode" or "character mode" is set according to the type of document, and in step S3, the number of copies, the automatically set paper size, document density, etc. are manually set. When the setting is completed, if the copy start button is pressed in step S4, copying starts in step S5, the original scanning system starts to move in step S6, and the CCD is scanned while scanning in step S7.
14 reads the image data, the image processing unit 15 processes the read image data in step 8, and the image recording device 20 prints out the processed image data in step S9.

As shown in the subroutine of FIG. 3, the document mode setting in step S2 is performed by the document mode button 34 when the display shown in FIG. 4A is displayed on the operation panel of the copying machine in step S11. When is pressed, the display is changed to that shown in FIG. 4B, and in step S12, if any one of the "photograph" and "text" buttons 36 and 37 is pushed, depending on the type of original to be copied, Accordingly, steps S13, S
14 is switched to the photo mode circuit, and in steps S15 and S16, the mode is switched to the character mode circuit, respectively. On the other hand, when the "initial screen" button 38 is pressed in step S12, step S1
7, the panel is reset in S18, and the display returns to that shown in FIG. FIG. 4 shows the screen of the operation panel for setting the original mode. After the original is set on the original table, the original density, magnification, and paper size are set with the buttons 31, 32, and 33, respectively. , Press the original mode switching button 32. When the panel screen is switched to that shown in FIG. 4 (B), if one of the photo and character buttons 36 and 37 is pressed according to the type of document, and then the "initial screen" button 38 is pressed, the screen shown in FIG. After returning to the initial screen of (1) and setting the number of copies with a ten key (not shown), the copy start button 35 is pressed to start copying.

FIG. 5 is an overall control block diagram of the digital copying machine. The overall control unit 41 controls all other blocks, and the panel control unit 42 displays the operation panel 43 described in FIG. The IR scanning control unit 44 detects the depression of the copy start button 35 (see FIG. 4A) and activates the scan motor 45 to control the interface for key input and the image of the document to be scanned is displayed. Processing control unit 46
Under the control of 1), the image processing circuit 47 reads and performs predetermined image processing. The image-processed data is output to an external device via the I / F (interface) unit 48, or stored in the memory unit 50 under the control of the memory control unit 49, and the image stored in the memory unit 50 is stored. After being sent to the engine unit 52, the data is printed under the control of the printer control unit 51.

FIG. 6 is a diagram showing image processing blocks corresponding to 46 and 47 in FIG. The image processing block includes a CCD 14 as a photoelectric conversion unit that converts reflected light from a document into an electric signal, and an A / D conversion unit that converts an analog signal input from the CCD 14 through an analog processing circuit 62 into a digital signal. 63, and a white shading plate 1 provided at the end of the document table to obtain a reference white output.
8 (see FIG. 1), the first shading circuit 65 as an averaging data generating means for averaging the image data read in a plurality of lines for each corresponding pixel on the line to generate the correction reference data; A second shading circuit 66 as peak hold data generating means for holding the peak of the image data for each corresponding pixel and generating correction reference data, and the first shading circuit 65.
Of the shading circuits 65, 66 according to the state of the correction reference data obtained in step S1 or the result of comparing the two correction reference data obtained by the first and second shading circuits 65, 66 with each other. A comparator 72 and a CPU 73 for selecting and operating any one of them, and a lamp light amount monitor sensor 76 for directly monitoring the light amount of the light source 11 (see FIG. 1) are provided.

The analog processing circuit 62 processes the input analog signal by circuits such as sample / hold, gain amplification, and clamp, and outputs it as a signal having a predetermined dynamic range. The digital signal from the A / D converter 63 is branched into two directions and input to the first and second shading circuits 65 and 66, and a plurality of lines read while the original image reading slider is moving the position of the shading plate. While sequentially writing the data in the respective line RAMs 64 and 67, the former circuit 65 obtains an average value for each pixel (averaging method), and the latter circuit 66 holds the peak value for each pixel (peak hold method). ). CPU73
Is a determination means (FIG. 20), a warning means (FIG. 23), a light amount adjusting means (FIG. 24), a reading mode limiting means (FIG. 25), and a noise cause determining means (FIGS. 26 and 27), which will be described later with reference to the drawings.
Make up. When there is a predetermined level difference or more between the pixel data of a pixel and the pixel data of its neighboring pixels in the linear correction reference data obtained by the first and second shading circuits 65 and 66, the CPU 73 Pixels are extracted as singular points (see FIG. 10), or standard deviations of pixel data of both formulas are calculated for a series of plural pixels, and then the magnitudes of both standard deviations are compared (see FIG. 11). Then, the appearance of the singularity in both equations, or the magnitude of the standard deviation is compared by the comparator 72, and based on the result,
Decide the shading method to be used for reading the original (Fig. 9
), The determined shading circuit 65 or 6
6 is selected by the selector 68, and it functions as the light quantity adjusting means and the noise cause judging means based on the detection signal from the lamp light quantity monitor sensor 76.

Then, only the shading circuit 65 or 66 as the shading correction unit selected by the selector 68 operates in the shading method, and the light source 11 (see FIG. 1) is used for the image data read from the original.
(See (1)) and outputs it to the image processing circuit 69 after correcting the unevenness of the light distribution of the CCD 14 and the pixel sensitivity of the CCD 14, and after performing processing such as reflectance / density conversion, MTF correction, and enlargement / reduction complementation, I The data is output from the / F unit 70 to the image recording device 20 (see FIG. 1) or an externally connected device. Histogram circuit 71
Creates a histogram of image data, performs AE (automatic exposure) processing, calculates the amount of data variation from the histogram during shading operation, and excludes data outside a certain range from the targets of averaging and peak hold processing. To do. The series of processes described above is performed by the CPU 73, the ROM 75,
It is controlled by the timing controller 74.

FIG. 7 shows the first shading circuit 6 of FIG.
5 is a detailed block diagram of No. 5 (averaging method). FIG. In this block diagram, when the image reading device 10 (see FIG. 1) enters the shading data generation mode, the reset circuit 82 resets the data in the line memory 81, and the data is read from the shading plate and the A / D converter 63 (see FIG. Image data of a plurality of lines input via the adder 88.
By this, the data stored in the line memory 81 for each pixel is added and overwritten, and the number of lines is counted by the counter 83, and the reciprocal of this count is the reciprocal ROM 8
4, the product of this calculated value and the added value for each pixel from the line memory 81, that is, the average data is obtained by the multiplier 89, and the reciprocal of the average data for each pixel is the reciprocal ROM 85.
Calculated and stored in. In this way, when the shading data generation mode ends and the normal image reading mode is entered, the selector 68 is set to the multiplier 86 side by an instruction from the CPU 73 (see FIG. 6), and the image data of the document is multiplied by each pixel. The device 86 multiplies the reciprocal stored in the reciprocal ROM 85 to perform shading correction, and then sends it to the image processing circuit 69 (see FIG. 6) in the subsequent stage. When the shading correction is not performed or when the histogram of the shading data is generated by the histogram circuit 72 (see FIG. 6), the selector 68 is set by the CPU 73 on the side where the image data is bypassed by the multiplier 86.

FIG. 8 shows the second shading circuit 6 of FIG.
6 is a detailed block diagram of 6 (peak hold method). FIG. In this block diagram, when the shading data generation mode is entered, the reset circuit 94 resets the data in the line memory 93, and the image data for the first one line read and input from the shading plate is the terminal A of the selector 92. The image data of the second and subsequent lines, which are written into the line memory 93 through the following, are compared with the image data already stored in the line memory 93 by the comparator 91 for each pixel, and the terminals A and B are compared according to the comparison result. The terminal on the side with the larger data is opened and overwritten in the line memory 93, and the line memory holds the maximum data (peak data) in a plurality of lines for each pixel. Thus
When the shading generation mode ends and the image reading mode is entered, the selector 68 is instructed by the CPU 73.
Is set in the multiplier 96 side C, and the reciprocal of the shading data read from the line memory 93 is the reciprocal ROM.
The image data of the original document, which is calculated in 95, is multiplied by the reciprocal number by the multiplier 96 for each pixel to perform shading correction, and then sent to the image processing circuit 69 in the subsequent stage. When the shading correction is not performed or when the histogram of the shading data is generated, the selector 68 is set by the CPU 73 on the side D where the image data is bypassed by the multiplier 96.

FIG. 9 is a flowchart showing a subroutine of the image data reading step S7 described in FIG. The reading of the image data is performed as follows.
When the document scanning system is started and the image reading operation is started, the reading slider is moved to the shading plate 18 (see FIG. 1) in step S21 of FIG. 9, and the scanning position of the shading plate is changed in the width direction in step S22. Reading with a plurality of lines, shading data is generated in step S23, and the number of read lines is counted in step S24. If the number of counts reaches a predetermined n, it is determined to be affirmative in step S25, and the process proceeds to step S26. Proceed to finish reading the shading plate. Next, in step S27 described later as a dust detection subroutine (see FIG. 16),
It is detected whether dust (dirt) adheres to the shading plate or the optical system and if there is dust in the optical system including the mirror, a warning is given in step S30 through step S28 and step S29. After that, if there is dust or the like on the shading plate, or if there is no dust or the like, the process directly proceeds to step S31. In step S31, FIG.
In step S32, a subroutine to be described later, that is, the amount of noise superimposed on the image data is detected. Then, in step S32, a subroutine to be described later, that is, a warning process in FIGS. 21, 24 and 25 is performed according to the detected amount of noise. Further, the procedure proceeds to step S33, and switching of the shading method described later in the subroutine of FIGS. 10 and 11, that is, CP of FIG.
The selector 68 selects one of the first and second shading circuits 65 and 66 via U73. Then, in step S34, main scanning is started, and in step S35, an image original of a predetermined size is read and the process returns to the main routine.

FIG. 10 is a flow chart showing a first example of the subroutine of the switching step S33 of the shading method described in FIG. This subroutine is performed as follows. First, the CPU 73 (see FIG. 6) sequentially reads the correction reference data (average value) D _i for each pixel generated and stored in the first shading circuit 65 (averaging method) of FIG. At S42, the differences Δ between the data of the pixel of interest l and the m pixel data before and after the data Δ
Calculate D _{−m to} ΔD _{+ m} . Next, in step S43, the maximum value ΔD _maxl is calculated from the calculated differences ΔD _{−m to} ΔD _{+ m} , and in step 44, it is determined whether the cumulative number l of the _target pixel has reached the predetermined number P or not. If not, the cumulative pixel number l is incremented in step S45, and the same processing is performed for the (l + 1) th pixel in steps S42 and 43. On the other hand, if the result is affirmative, the process proceeds to step S46. The maximum value Q among the calculated maximum values ΔD _maxl is calculated. Then, in step S47, it is determined whether or not the maximum value Q exceeds a predetermined value G, and if it is affirmative, averaging that is easily affected by dust on the shading plate 18 (see FIG. 1). If there is a singular point in the method, proceed to step S49 to select the peak hold method that is less likely to be affected by dust and the like, and if not, proceed to step S48 and hold the peak hold variation of the correction reference data obtained by shading. Choose less averaging method than by method.
Finally, in step S50, the selector 68 (see FIG. 6) is set according to the selected shading method to operate either the first or second shading circuit 65 or 66, and the process returns to the main routine.

FIG. 11 is a flow chart showing a second example of the subroutine of the switching step S33 of the shading method described in FIG. This subroutine is performed as follows. First, the CPU 73 causes the step S51.
Then, the read range of the correction reference data for each pixel generated and stored in the first and second shading circuits 65 and 66 of FIG. 6, that is, the jth to kth pixels are set, and step S5
In step 2, the data in the above range is read from the first shading circuit 65, and in step S53, the standard deviation σ ₁ of the read data is calculated. Then, in step S54,
The data in the above range is read from the second shading circuit 66, and the standard deviation σ ₂ of the read data is calculated in step S55. Then, in step S56, the two standard deviations σ ₁ and σ ₂ are compared, and the standard deviation σ ₁ is σ ₂
, The variation of the data is smaller on the σ ₂ side,
That is, the peak hold method is selected in step S58,
If the standard deviation σ ₁ is less than or equal to σ ₂ , the averaging method with smaller data variation is selected in step S57. Finally, the selector 68 is set according to the above selection in the same manner as described above, and the process returns to the main routine.

FIG. 12 shows data read by the linear pixels of the CCD 14 when dust is present on the shading plate. As shown in FIG. 12 (A), a CCD in which pixels are arranged in a straight line in the main scanning direction x changes its position in the width W range in the sub scanning direction y, and has n lines with a dust 19 in the center. When the shading 18 is read, the read data of each line is as shown in FIGS. That is, the output of the CCD becomes a convex curve whose central portion becomes high due to the influence of the light distribution of the light source, but only the position where the CCD passes the dust 19 in FIG. 12D corresponds to the dust position. The output of the corresponding pixel sharply drops under the influence of the absorption of dust.

FIGS. 13 and 14 show the data shown in FIGS. 12B to 12E read from the shading plate shown in FIG. 12A after being processed by the averaging method and the peak hold method, respectively. 3 shows shading correction reference data. In the correction reference data by the averaging method shown in FIG. 13 (A), since this method averages the read data of each line for each pixel, the concave portion 26 is seen at a position corresponding to the position of the dust 19. Since the data variations due to shot noise and the like are averaged at other locations,
As shown in the partially enlarged view of FIG. 13B (corresponding to part b of FIG. 13A), the variation between the adjacent correction reference data is small. It should be noted that the original image read later is used as the concave portion 26.
If the shading correction is performed with the incomplete correction reference data having, a so-called shading streak appears at a portion corresponding to the concave portion. On the other hand, in the correction reference data by the peak hold method shown in FIG. 14A, since this method holds the peak values of a plurality of lines for each pixel, the data of the pixel corresponding to the position of the dust 19 is the dust. Since the large value data of the preceding and following lines are held in place of the small value data of FIG. 14, the dents such as the concave portion 26 of FIG. 13 (A) do not appear in the dust reference correction reference data, while FIG. Partial enlarged view of B) (corresponding to part b of FIG. 14A)
As indicated by the peak 27, the variation between adjacent correction reference data is large due to the influence of shot noise and the like. If the original image read later is shading-corrected with the incomplete correction reference data having the noise peak 27, so-called shading streaks appear at the position corresponding to the peak.

FIG. 15 schematically shows the correction reference data obtained by averaging the output of each pixel of the CCD when the shading plate is read by the CCD by the first shading circuit 65 (see FIG. 6). ing. FIG. 15A shows
C when there is no dust on the shading plate corresponding to m pixels before and after the 1st pixel of interest (black circle in the figure)
The CD output is shown, and the maximum value −ΔD _max ; + ΔD _max of the difference ΔD between the data of the target pixel and the data of the peripheral pixels is within a predetermined value because there is no dust. On the other hand, FIG.
(B) shows the CCD output when there is dust on the shading plate corresponding to the target pixel 1 (black circle in the figure),
The maximum value ΔD _max of the data difference ΔD with the peripheral pixels exceeds a predetermined value because the data of the pixel of interest is greatly reduced due to dust.

Therefore, the maximum value ± ΔD shown in FIG.
_{Since max} corresponds to Q described in FIG. 10 and is within the predetermined value G, it is determined that it is a mere variation in data, and it is determined no in step S47 in the figure, and the averaging shading method, That is, while the first shading circuit 65 is selected, the maximum value ΔD shown in FIG.
_{Since max} = Q exceeds the predetermined value G, it is determined that there is dust on the shading plate, and affirmative in step S47, and the peak hold shading method, that is, the second shading circuit 66 is To be selected. In other words, the shading method with the smaller variation in the generated correction reference data is used during document reading (main scan) regardless of whether or not there is dust on the shading plate. It is possible to obtain a good original read image.

The same applies to the switching of the shading method described with reference to FIG. 11, that is, switching between the standard deviations σ ₁ and σ ₂ of the correction reference data obtained by both shading methods. That is, when the dust or the like on the shading plate is read, the correction reference data obtained is as shown in FIG.
As is clear from the comparison between (B) and FIG. 14 (B), the peak hold method has more variation, that is, the standard deviation is smaller,
On the contrary, when the shading plate without dust is read, the obtained correction reference data is as shown in FIG.
As is clear from the comparison of (B), the averaging method has a smaller variation, that is, a smaller standard deviation. Therefore, in steps S56 to S58 in FIG. 11, the shading method with the smaller variation in the generated correction reference data is adopted at the time of reading the original (main scan) regardless of whether or not there is dust on the shading plate. Therefore, it is possible to obtain a good original read image without defects such as shading streaks.

FIG. 16 is a flow chart showing a subroutine of the dust detection step S27 described in FIG.
This subroutine is performed as follows. First, C
In step S61, the PU 73 (see FIG. 6) performs the first
The correction raw data generated and stored in the shading circuit 65 by the averaging method are sequentially read out, and in step S62 described later in the subroutine of FIG. 17, the difference between the data of each pixel of interest and the pixels before and after it is calculated, The maximum value Q of the calculated data differences is obtained. Next, in step S63,
It is determined whether or not the maximum value Q exceeds a predetermined value G, and if the result is affirmative, it is determined in step S64 that there is peculiar pixel data due to dust or the like, and the averaging method flag a is set to a = 1 On the other hand, if not, step S65
Then, the flag a is set to a = 0 because there is no peculiar pixel data. Next, in step S66, the correction raw data generated and stored in the second shading circuit 66 of FIG.
At 67, the difference between the data of each pixel of interest and the pixels before and after it is calculated, and the maximum value Q of the calculated data differences is obtained.
Then, in step S68, it is determined whether or not the maximum value Q exceeds a predetermined value G. If the result is affirmative, it is determined in step S69 that there is peculiar pixel data due to dust or the like, and the peak hold method side On the other hand, while setting the flag b to b = 1, in the case of no, the flag b is set to b = 0 because there is no unique pixel data in step S70.

Subsequently, the CPU 73 causes the step S71.
Then, it is determined whether the logical product a × b of both flags a and b is 1. Here, since dust and the like on the shading plate is read by, for example, one of the reading lines, the peculiar data caused by the dust and the like appears only in the averaging method in which the influence of the peculiar data remains in the correction raw data. Since dusts of optical systems other than the shading plate are read in all the reading lines, the peculiar data caused by the dusts will appear not only in the averaging method but also in the correction raw data of the peak hold method. . Therefore, in the judgment step S71, if there is singular, that is, peculiar data in both formulas, the process proceeds to step S72 and the mirror 12 (see FIG. 1).
On the other hand, if it is determined that there is dust or the like in the optical system including, the process proceeds to step S73 to determine whether the flag a is 1, and if a = 1, the correction raw data of the averaging method is used. Since there is peculiar data in step S74, it is determined in step S74 that there is dust on the shading plate, and if a = 0, step S74.
At 75, it is determined that there is no garbage. When the above steps are completed in this way, the process returns to the main routine.

FIG. 17 is a step S for calculating the difference between the data of each pixel of interest described in FIG. 16 and the data before and after it.
62 is a flowchart showing a subroutine of S67. In this subroutine, in step 76, with respect to the correction raw data sequentially read by the averaging method or the peak hold method, the difference ΔD _{−m to} ΔD _{+ m} between the data of the target pixel 1 and the data of m pixels before and after the target pixel 1. _Is calculated, and the maximum value ΔD _maxl of the calculated data difference is obtained in step S77. Next, in step S78, it is determined whether or not the cumulative number l of the target pixels has reached the predetermined value P. If not, the cumulative pixel number l is incremented in step S79 to obtain the (l + 1) th pixel. While the same processing is performed for the pixel of step S76, 77, if the result is affirmative, the process proceeds to step S90 to calculate the maximum Q among the calculated maximum values ΔD _maxl , and then return to the main routine. .

FIG. 18 shows an optical reading system, a shading plate 18, a mirror 12a having dust 19, and a CCD 14.
Shows the output when the shading plate is read by a plurality of lines. The optical reading system is shown in FIG.
As shown in FIG. 1, the shading plate 18, the light source 11, the three mirrors 12a, 12b, and 12c, the lens 13, and the CCD 14 described above with reference to FIG. On the shading plate 18,
There is no dust or the like as shown in FIG. 18 (B), and dust 1 as shown in FIG. 18 (C) is placed on the read line L at substantially the center of the mirror 12a.
There is 9. 18D to 18F show the output when the CCD 14 is moved in the sub-scanning direction y of the shading plate 18 and read at the 1st, 2nd, and nth lines. Due to No. 19, a concave portion 28 appears in the center of each output curve. This is because even if the reading position is moved on the shading plate, the optical path of the reflected light always passes through substantially the center of the mirrors 12a to 12c as can be seen from FIG. 18 (A). Here, if the dust is not on the mirror but on the shading plate 18, the concave portion will not appear as shown in FIGS. 12B, 12C, and 12E due to the movement of the reading position.

19A and 19B, the CCD output of FIGS. 18D to 18F is processed by the averaging method and stored in the first shading circuit 65 (see FIG. 6), or peak hold. The correction raw data processed by the method and stored in the second shading circuit 66 are shown. In this case, FIG. 18 (D)
Since the CCD output of any line of (F) to (F) has a concave portion 28 caused by dust on the mirror, not only the concave portion 29 appears in the averaging method of FIG. 19 (A) but also the peak hold of FIG. 19 (B). The concave portion 30 also appears in the method. Therefore,
Based on the difference in how the concave portions appear in both the averaging and peak hold systems, it is possible to determine whether dust or the like is on the shading plate or in the optical system including the mirror.

FIG. 20 is a flow chart showing the subroutine of step S31 for noise amount detection described in FIG. CPU 73 as the determination means of claim 2 (see FIG. 6)
Is the difference between the correction reference data obtained by the averaging method (correction raw data) and the correction reference data obtained by the peak hold method is calculated for a plurality of pixels in a predetermined area, and the average value of the calculated differences is calculated. The magnitude of noise superimposed on the image data is determined by determining whether or not this average value is equal to or greater than a predetermined value. That is, the CPU 73 reads the correction reference data by the averaging method at step S91 and the correction reference data by the peak hold method at step S92, obtains the difference between the read correction reference data for each pixel at step S93, and then, Step S94
Then, an average value M of the calculated difference in a predetermined central portion range (see FIG. 21B) is calculated, and the process returns to the main routine.

21 and 22 schematically show the noise amount detection method described in FIG. 20 when the noise amount is small and large, respectively. First, the amount of noise is small in FIG.
2, the data of the shading plate 18 read in a plurality of lines by the CCD 14 (see FIG. 1) is shown by superimposing the pixel on the horizontal axis and the output on the vertical axis.
1 (A), the pixel data is distributed with a predetermined width W in a convex curve having a high central portion due to the light distribution characteristics of the fluorescent light source. Then, the correction reference data obtained from these pixel data by the averaging method averages the data of a plurality of lines for each pixel, so that it becomes a curve S1 passing through the center of the predetermined width W, while peaking from the pixel data. The correction reference data obtained by the hold method peak-holds the data of a plurality of lines for each pixel,
The curve S2 passes through the upper edge of the predetermined width W. 21. Here, when the difference (difference) between the correction reference data by both equations, that is, the difference between the curve S2 and the curve S1 is obtained, this difference M is
As shown in (B), since the noise amount is small, it becomes smaller than the predetermined value m. Note that, in step S94 of FIG. 20, the average value of the difference between the curves S1 and S2 in the central predetermined range R is M, but the CPU 73 uses the difference M between S1 and S2 as the determination means defined in claim 1. Can be compared with a predetermined value m for each pixel to determine the magnitude of the noise amount.

When the amount of noise is large, the read data by a plurality of lines on the shading plate are distributed in the form of a convex curve having a wider predetermined width W ', as shown in FIG. The correction reference data obtained by the averaging and peak hold methods from the data are respectively the curve S
1 ', S2'. Here, when the average value of the difference in the center predetermined range R of both correction reference data is calculated, this average value M ′ is larger than the predetermined value m because the noise amount is large as shown in FIG. 22 (B). growing. Also in this case, the CPU
Reference numeral 73 denotes S1 ′, S as the determination means defined in claim 1.
It is possible to determine the magnitude of the noise amount by comparing the difference M ′ of 2 ′ with the predetermined value m for each pixel.

FIG. 23 is a flow chart showing the subroutine of step S32 of the warning processing described in FIG.
The CPU 73 as the warning means of claim 3 issues a warning when it is determined that the amount of noise is large by the above method. That is, the CPU 73 determines in step S95 whether the difference (or average value of the differences) M between the two correction reference data exceeds a predetermined value m. Only when the difference is affirmative, it is determined that the noise is large. After proceeding to S96 to display a "noisy" warning on the display unit of the image reading apparatus, the process returns to the main routine.

24. The light quantity of the light source for illuminating the original is increased or decreased according to the magnitude of the noise judged by the judging means.
7 shows the processing flow of the CPU 73 (see FIG. 6) as the light amount adjusting means of FIG. 6, and this processing is included in the warning processing subroutine of step S32 described in FIG. CPU7
3. First, in step S101, the noise amount detection flow (see FIG.
0)), it is determined whether the average value M of the difference between the correction reference data obtained by both the averaging and peak hold equations in the central predetermined range is larger than the predetermined value m. As much noise is superimposed on
The process proceeds to step S102 in order to reduce noise by increasing the light amount of the lamp (light source). Then, in this step, it is determined whether or not the dimming level of the lamp is the maximum, and if it is not the maximum, the process proceeds to step S103 to increase the lamp light amount by a predetermined amount, while if the lamp light amount is the maximum, the light amount cannot be increased. Therefore, the process proceeds to step S104 to warn by display that the image noise is large, and then returns to the main routine in any case. If it is determined in step S101 that the average value M is less than or equal to the predetermined value m, the process proceeds to step S105 to reduce the power consumption by reducing the lamp light amount, and it is determined whether or not the lamp dimming level is minimum.
Then, if it is determined that the lamp dimming level is not the minimum,
After proceeding to step S106, the lamp is reduced by a predetermined amount, and then the process returns to the main routine. On the other hand, if it is minimum, the light amount cannot be reduced, and therefore the process directly returns to the main routine.

FIG. 25 shows a processing flow of the CPU 73 (see FIG. 6) as the reading restricting means of claim 6 which enables only the character reading mode when the judging means judges that the noise is large. The process is included in the warning process subroutine of step S32 described in FIG. C
First, in step S111, the PU 73 determines that the average value M in the central predetermined range of the difference between the correction reference data calculated by the noise amount detection flow (see FIG. 20) by both the averaging method and the peak hold method is larger. determining whether greater than the value m _1, if affirmative, a lot of noise in the image data is superimposed, after a warning by a display that image noise is large jumps to step S114, the main While returning to the routine, if not, step S
In step 112, it is further determined whether or not the average value M is larger than the smaller predetermined value m ₂ . Then, in this step, if it is determined to be no, the process returns to the main routine as it is because the image noise is small, and if it is determined to be affirmative, the process proceeds to step S113 to determine whether the set mode is character or photograph. to decide. If it is determined in the step S113 that the mode is the photo mode, it is necessary to reproduce the halftone, so noise is a problem even at this level. Therefore, the process proceeds to step S114 to warn that the image noise is large, while the mode is determined to be the character mode. Then, since it is binary data of black and white, noise of this degree does not affect, and the process directly returns to the main routine without warning. That is, when the noise is moderately high, only the character mode is enabled for reading and the photo mode is disabled.

In FIG. 26, the determination means determines the magnitude of noise even when the light source is off, and the cause of the noise is either the optical system or the electric circuit based on the determination result of the determination means when the light source is on or off. The CPU 7 as an example of claim 7, further comprising noise cause determining means for determining whether there is any noise.
3 (see FIG. 6) is shown. CPU73
When the serviceman mode button (not shown) is pressed by the inspector, the display on the operation panel is changed to the serviceman display in step S121, and the noise cause analysis mode button (not shown) on this operation panel is pressed in step S122. Then, the noise cause analysis mode is started. Then, in step S123, the lamp (light source) 11 is turned on, and in step S124
Then, the reading slider is moved to the shading plate 18, and if it is determined in step S125 that the slider has reached the shading position, the process proceeds to step S126 to adjust the gain of the electric circuit. Then, in step S127
Then, it is determined whether or not the circuit gain is the minimum. If it is not the minimum, the circuit system is not saturated, so that the processing proceeds to step S137 in order to read the shading data and detect the noise amount. Assuming that the light quantity of the lamp is sufficient, the above process is omitted and the process jumps to step S128.

In step S137, the data is read from the shading plate, in step S138 the noise amount is detected by the difference between the two shading methods described in the subroutine of FIG. 20, and in step S139, the average value M of the differences is a predetermined value m. Is greater than or equal to. And
If it is determined to be no in step S139, the noise amount is small, and therefore the process ends after step S146 without any problem. On the other hand, if affirmative is determined in step S139, the process proceeds to step S140 and it is determined that the amount of noise is large. Then, in step S141, it is determined whether or not the lamp dimming level is maximum. If not, the process proceeds to step S142. While increasing the lamp light intensity by a predetermined amount in step S1, if it is the maximum, the process proceeds to step S143 in order to check whether the lamp has a defect,
It is determined whether or not the light quantity monitor value L represented by the detection signal from the lamp light quantity monitor sensor 76 (see FIG. 6) is larger than the predetermined value P. Then, in the case of no, since the light amount is insufficient, it is determined that the lamp is defective in step S144, and in step S145,
The display 1 to that effect is displayed on the operation panel, and the process is terminated.

If the answer is YES in step S143, the lamp is normal. If the answer is YES in step S127, it is determined that the gain is minimum and the light intensity is sufficient. Step S12 to check
Go to 8 and turn off the lamp. Then, step S129.
Then, set the gain of the circuit to the maximum, and in step S130,
Read the shading data, and in step S131,
The amount of noise is detected by the difference between the two shading methods described in the subroutine of FIG. And step S
In 132, it is determined whether or not the average value M of the differences is larger than the predetermined value m, and if it is determined as affirmative, it is determined in step S133 that noise is superimposed on the circuit side, and in step S134 the operation panel. Then, display 2 to that effect is displayed, and the process is terminated. If it is determined to be no in step S132, there is no abnormality in the circuit system. Therefore, it is determined that there is an abnormality in the optical system other than the lamp in step S135, and the process proceeds to step S136 to display 3 to that effect and the processing is performed. finish.

FIG. 28 shows a processing flow of an example of the noise cause judging means corresponding to FIG. 26 when the lamp light amount monitor sensor 76 described in FIG. 6 is not provided. Compared with the processing flow of FIG. 26, this processing flow is different from that of FIG. 26 in that steps S143 to S145 of FIG. 26 are not provided, and the step proceeds to step S128 immediately when a positive determination is made in step S141. The numbers are attached and the description is omitted. In this processing flow, the lamp light amount monitor sensor 76
Since it is not possible to detect and display the lamp failure, it is possible to detect and display whether the cause is the circuit side or the optical system other than the lamp when there is a large amount of noise, as described in FIG. can do.

In the above embodiment, the example in which the present invention is applied to the copying machine has been described, but the present invention is not limited to the copying machine, and is also applied to, for example, an image input device for inputting image information to a computer. can do. Further, the warning means of the present invention is not limited to the display on the operation panel, but may be an alarm notification by sound or a warning light. further,
The reading mode limiting means of the present invention may be any one that makes it impossible to use the reading mode susceptible to noise when the noise is large, and is not limited to the one that prohibits the photo reading mode of the above embodiment. I can't.

[0051]

As is apparent from the above description, according to the present invention, two different shading methods of averaging and peak hold are read by the shading plate, and the difference between the correction reference data obtained by both methods is used. Based on this, it is possible to detect the image noise and the decrease in the light amount of the light source due to the optical system including the lamp and the electric circuit, prevent the read image from being deteriorated, and obtain a good original read image without shading streaks. be able to.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of a digital copying machine using an image reading apparatus of the present invention.

FIG. 2 is a flowchart showing the overall operation of the digital copying machine having a mode switching function.

FIG. 3 is a flowchart showing a document mode setting subroutine in FIG.

FIG. 4 is a diagram showing a screen of an operation panel for setting a document mode of the digital copying machine.

FIG. 5 is an overall control block diagram of the digital copying machine.

FIG. 6 is a block diagram showing the image processing block of FIG. 5;

FIG. 7 is a detailed block diagram of the first shading circuit of FIG.

FIG. 8 is a detailed block diagram of a second shading circuit of FIG.

9 is a flowchart showing a subroutine of an image data reading step of FIG.

10 is a flowchart showing a first example of a subroutine of a switching step of the shading method of FIG.

FIG. 11 is a flowchart showing a second example of a subroutine of the switching step of the shading method of FIG.

FIG. 12 C when there is dust on the shading board
It is a figure which shows the data read by CD.

13 is a diagram showing correction reference data after the read data of FIG. 12 is processed by the averaging method.

FIG. 14 is a diagram showing correction reference data after the read data of FIG. 12 is processed by the peak hold method.

FIG. 15 is a diagram showing correction reference data after the output of the CCD reading the shading plate with and without dust is processed by an averaging method.

16 is a flowchart showing a subroutine of a step of dust detection in FIG.

17 is a diagram showing a subroutine of a step of calculating a data difference before and after the pixel of interest in FIG.

FIG. 18 is a diagram showing the output of the CCD reading the shading plate when dust is present on the mirror of the optical system.

FIG. 19 is a diagram showing correction raw data after the read data of FIG. 18 is processed by the averaging method and the peak hold method.

FIG. 20 is a flowchart showing a subroutine of steps of noise amount detection of FIGS. 9 and 26.

FIG. 21 is a diagram illustrating the noise amount detection method of FIG. 20 when the noise amount is small.

FIG. 22 is a diagram illustrating the noise amount detection method of FIG. 20 in the case where the noise amount is large.

23 is a flowchart showing a subroutine of a step of the warning process of FIG.

FIG. 24 is a flowchart showing a subroutine process of a CPU as a light amount adjusting means.

FIG. 25 is a flowchart showing a subroutine process of a CPU as a read limiting unit.

FIG. 26 is a flowchart showing a subroutine process of a CPU that also serves as noise cause determination means.

FIG. 27 is a flowchart showing a modified example of FIG. 26.

FIG. 28 is a diagram showing pixel data read from a shading plate by an image reading apparatus having a conventional fluorescent light source.

FIG. 29 is a diagram showing pixel data read from a shading plate by a conventional image reading device having a halogen lamp.

[Explanation of symbols]

10 ... Image reading device, 11 ... Light source, 12 ... Mirror, 1
4 ... CCD, 15 ... Image processing unit, 62 ... Analog processing circuit, 63 ... A / D converter, 65 ... First shading circuit, 66 ... Second shading circuit, 68 ... Selector, 69 ... Image processing circuit, 72 ... Comparator, 73 ... CP
U, 74 ... Timing control unit, 76 ... Lamp light amount monitor sensor.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-6-292001 (JP, A) JP-A-1-177278 (JP, A) JP-A-6-6589 (JP, A) JP-A-59- 223062 (JP, A) JP-A-3-289872 (JP, A) JP-A-62-172861 (JP, A) JP-A-9-200515 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H04N 1/40-1/409 H04N 1/46 H04N 1/60

Claims (7)

(57) [Claims] 1. A photoelectric conversion unit that receives reflected light from a document and converts it into an electric signal, an A / D conversion unit that converts an analog signal from this photoelectric conversion unit into a digital signal, and each of the photoelectric conversion units. A shading plate as a reference reading plate for correcting the reading level difference of the light receiving sensor, and shading for calculating the reading data of the shading plate and the reading data of the actual document to correct the reading level difference of each of the light receiving sensors. In an image reading apparatus including a correction unit, an averaging data generation unit that reads the shading plate in a plurality of lines and averages image data for each corresponding pixel on the line to generate correction reference data, and the shading plate. It reads in multiple lines and holds the peak of the image data for each corresponding pixel on the line to generate the correction reference data. The peak hold data generating means, the difference between the correction reference data obtained by the averaged data generating means and the correction reference data obtained by the peak hold data generating means is calculated, and the calculated difference is equal to or more than a predetermined value. An image reading apparatus, comprising: a determination unit that determines the magnitude of noise superimposed on image data by determining whether or not it is. 2. A photoelectric conversion unit that receives reflected light from a document and converts it into an electric signal, an A / D conversion unit that converts an analog signal from this photoelectric conversion unit into a digital signal, and each of the photoelectric conversion units. A shading plate as a reference reading plate for correcting the reading level difference of the light receiving sensor, and shading for calculating the reading data of the shading plate and the reading data of the actual document to correct the reading level difference of each of the light receiving sensors. In an image reading apparatus including a correction unit, an averaging data generation unit that reads the shading plate in a plurality of lines and averages image data for each corresponding pixel on the line to generate correction reference data, and the shading plate. It reads in multiple lines and holds the peak of the image data for each corresponding pixel on the line to generate the correction reference data. The peak hold data generating means, the difference between the correction reference data obtained by the averaging data generating means and the correction reference data obtained by the peak hold data generating means is calculated for a plurality of pixels in a predetermined area, and the calculated difference is calculated. The image reading is characterized by including a determination means for determining the average value of the noises and determining whether or not the average value is equal to or more than a predetermined value to determine the magnitude of noise superimposed on the image data. apparatus. 3. The image reading apparatus according to claim 1, wherein the determining means determines that the calculated difference or the average value of the calculated differences is equal to or more than a predetermined value and that the noise is large. An image reading device further comprising warning means for issuing a warning. 4. The image reading apparatus according to claim 1, wherein the light amount of a light source that illuminates the document is increased or decreased according to the magnitude of noise based on the determination result of the determination means. An image reading apparatus further comprising adjusting means. 5. The image reading apparatus according to claim 1, further comprising a reading mode limiting unit that limits the reading mode when noise is large based on the determination result of the determination unit. An image reading device further provided. 6. The image reading apparatus according to claim 5, wherein the reading mode limiting means enables only the character reading mode and disables the photograph reading mode when noise is large. Image reader. 7. The image reading apparatus according to claim 1, wherein the determination unit determines the noise level even when the light source illuminating the document is turned off, and when the light source is turned on. Further, the image reading further comprises noise cause judging means for judging whether the cause of the noise is in the optical system or the electric circuit of the image reading device based on the judgment result of the judging means when the light is off. apparatus.