JP2001257881A - Image scanning apparatus and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress cyclic level variation of an image signal even when an analog type timing signal generation part uses a frequency diffuser. SOLUTION: This image scanning apparatus which reads an original image to a solid-state image pickup element 6 and converts the image data signal outputted from the solid-state image pickup element 6 into a digital signal to perform image processing is equipped with a timing signal generation part 28 which generates a timing signal by diffusing by a frequency diffuser the frequency of the clock signal outputted from an oscillator in the image processing, and a black offset level adjusting means which suppresses level variation of an image signal due to the frequency diffusion of the frequency diffuser. Consequently, even when the analog type timing signal generation part uses the frequency diffuser, the cyclic level variation of the image signal can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image reading apparatus and an image forming apparatus for performing digital image processing by inputting an original image to a solid-state image sensor by a reading optical system.

[0002]

2. Description of the Related Art As described in Japanese Patent Application Laid-Open No. 9-98152, when data processing is performed in synchronization with a clock signal in a microprocessor or the like, the clock signal is susceptible to EMI (electromagnetic interference). It has been proposed to spread the frequency of a clock signal to reduce the oscillation width.

On the other hand, with the demand for higher image quality, image forming apparatuses such as digital copying machines tend to have higher pixel density. Also, the image forming speed has been increasing year by year,
Higher image reading speeds are also required. And, as the pixel density increases and the reading speed increases,
As the frequency of the clock signal increases, unnecessary radiation of electromagnetic waves increases accordingly.

Therefore, it has been considered that the spreading of the frequency of the clock signal as described above is also applied to an image reading apparatus. FIG. 10 shows the waveform of the reference clock signal generated by the oscillator, and FIG. 11 shows the waveform after the frequency of the clock signal has been spread. The unnecessary radiation is reduced.

FIG. 2 is a block diagram showing the electrical connection configuration of the image reading apparatus of the present invention. Since the electrical connection configuration is the same as that of the related art, the image reading apparatus will be described with reference to FIG. An example of the processing will be described. Image processing of each part
This image processing is performed when a timing signal generated by spreading the frequency of a clock signal output from an oscillator is generated.

First, a document image is read line by line and C
Input to CD6. The odd-numbered and even-numbered pixel image signals Vo output from the CCD 6 in synchronization with the timing signal are output.
, Ve are sampled and held by a sample and hold circuit 18 using a sample pulse to convert the image signal into a continuous analog signal.
After correcting the variation in the dark output of the CCD 6 in
The output of the odd-numbered and even-numbered pixels of each color signal is adjusted to a fixed level in the amplifying circuit 20, and the output of the odd-numbered and even-numbered pixels is processed in the multiplex circuit 21 to obtain the image signal V.
Subsequently, the image signal V is amplified to the level of the reference voltage for A / D conversion in the amplifier circuit 22, and is converted into 8-bit digital data by the A / D converter circuit 23. The digital image signal obtained in this manner is converted into a shading correction circuit 24.
The shading correction is performed to correct variations in the sensitivity of the CCD 6 and uneven light distribution of the halogen lamp 9 illuminating the original. The shading correction is performed based on the read density level by illuminating a white reference plate disposed on an extended surface of the original reading surface with a halogen lamp 9 and reading the reflected light with a CCD 6.

[0007]

By the way, in each process from the image signal output by the CCD to the shading correction process, a signal necessary for driving is generated by a timing signal generation section and input to each circuit. However, when a frequency spreader is used in an analog timing signal generator, a timing shift between a CCD output and a sample pulse, a sampling point shift between a clock of an A / D conversion circuit and analog image processing, and the like cause As shown in FIG. 12, the level of the digital image signal periodically fluctuates in one line, and the level is changed. When this process is repeated for a number of lines, the change in the output frequency is not synchronized between the lines as shown in FIG. 13, and the level of the level appears as a streak and looks like a moire. In FIG. 13, streaks are generated on a straight line connecting high-level portions of each line and a straight line connecting low-level portions. Further, since periodic noise is generated in the image, the S / N ratio is deteriorated as compared with the case where the frequency spreader is not used.

An object of the present invention is to suppress a periodic level fluctuation of an image signal even when a frequency spreader is used in an analog timing signal generator.

[0009]

According to a first aspect of the present invention, there is provided an image reading apparatus which inputs a document image to a solid-state imaging device by a reading optical system, and converts an image data signal output from the solid-state imaging device into a digital signal. An image reading apparatus that performs image processing by using a timing signal generation unit that generates a timing signal by spreading the frequency of a clock signal output from an oscillator during the image processing by a frequency spreader; Black offset level adjusting means for suppressing the level fluctuation of the image signal caused by the black offset level adjusting means.

Therefore, the periodic fluctuation of the level of the image signal is suppressed by the black offset level adjusting means.

According to a second aspect of the present invention, there is provided an image reading apparatus which inputs a document image to a solid-state imaging device by a reading optical system, converts an image data signal output from the solid-state imaging device into a digital signal, and performs image processing. In the reading device, a timing signal generating unit for generating a timing signal by spreading a frequency of a clock signal output from an oscillator at the time of the image processing by a frequency spreader, and synchronizing a change in a frequency spread rate by the frequency spreader with a main scanning. Synchronization control means for synchronizing with a signal.

Therefore, the change of the output frequency is synchronized in each line by the synchronization control means.

According to a third aspect of the present invention, there is provided an image reading apparatus for inputting a document image to a solid-state imaging device by a reading optical system, converting an image data signal output from the solid-state imaging device into a digital signal, and performing image processing. In the reading device, a timing signal generating unit for generating a timing signal by spreading a frequency of a clock signal output from an oscillator at the time of the image processing by a frequency spreader, and synchronizing a change in a frequency spread rate by the frequency spreader with a main scanning. A synchronization control unit for synchronizing with a signal; and a black offset level adjusting unit for suppressing a level variation of an image signal caused by frequency spreading by the frequency spreader.

Therefore, the change of the output frequency is synchronized in each line by the synchronization control means, and the periodic fluctuation of the level of the image signal is suppressed by the black offset level adjustment means.

According to a fourth aspect of the present invention, there is provided an image reading apparatus.
Alternatively, in the invention described in the third aspect, the black offset level adjusting means executes the black offset level adjusting value for one line.

Accordingly, the periodic fluctuation of the level of the image signal is more accurately suppressed by the black offset level adjusting means.

According to a fifth aspect of the present invention, there is provided an image reading apparatus according to the first aspect.
Alternatively, in the invention described in the third aspect, the black offset level adjusting means executes the black offset level adjusting value in accordance with phase information of a timing signal generated from the timing signal generator.

Therefore, periodic fluctuations in the level of the image signal are suppressed by the black offset level adjusting means. Since the black offset level adjustment value corresponding to the phase information of the timing signal has a small amount of information, a small-capacity memory can be used as a memory for storing the black offset level adjustment value.

According to a sixth aspect of the present invention, there is provided an image reading apparatus for inputting a document image to a solid-state imaging device by a reading optical system, converting an image data signal output from the solid-state imaging device into a digital signal, and performing image processing. In the reading device, a timing signal generating unit that generates a timing signal by spreading a frequency of a clock signal output from an oscillator at the time of the image processing by a frequency spreader, and a value obtained by dividing black shading data by white shading data to 2 ⁿ Level correction means for performing shading correction with a correction value multiplied by -1 (n = the number of bits of image data) to suppress a level fluctuation of an image signal caused by frequency spreading by the frequency spreader.

Here, the black shading data is a dark output in the entire main scanning direction of the solid-state image pickup device when the illumination system on the original reading surface is turned off, and the white shading data is an illumination system for lighting the illumination system. This is the output in the entire main scanning direction of the solid-state image sensor when reading the white reference plate in the state.

Therefore, periodic level fluctuation of the image signal is suppressed by the level correcting means.

According to a seventh aspect of the present invention, there is provided the image forming apparatus according to the first aspect.
7. An image reading device according to claim 1, further comprising: a printing unit that outputs image data read by the image reading device.

Therefore, when reading the original image, the level fluctuation of the image is suppressed, and thus, it is possible to improve the image quality when printing.

[0024]

FIG. 1 shows a first embodiment of the present invention.
This will be described with reference to FIG. 1 is a longitudinal sectional front view showing a schematic configuration of an image reading apparatus, FIG. 2 is a block diagram showing an electrical connection configuration, FIG. 3 is a block diagram showing an electrical configuration of a timing signal generator, and FIG. 5 is a time chart in the case of synchronizing the change in the main scanning synchronization signal, FIG. 5 is an explanatory diagram schematically showing the concept of the black level offset adjusting means, and FIG. 6 synchronizes the change in the frequency spreading factor with the main scanning synchronization signal. FIG. 7 is an explanatory diagram showing the level of an image signal read in a state where the image signal is read, and FIG. 7 is an explanatory diagram showing the level of the image signal after being adjusted by the black offset level adjusting means.

In FIG. 1, a contact glass 3 and a pressure plate (not shown) for pressing a document 4 on the contact glass 3 are provided on an upper surface of a housing 2 of the image reading apparatus 1. A white reference plate 5 for shading correction is provided near one end of the contact glass 3.

A reading optical system 7 for inputting a document image to a linear image sensor (hereinafter referred to as a CCD) 6 which is a solid-state image sensor is provided inside the housing 2. The reading optical system 7 includes a halogen lamp 9 and a first mirror 10 mounted on a first traveling body 8, a second mirror 12 and a third mirror 13 mounted on a second traveling body 11, and a CCD 6.
And a convergent lens 14 facing the front surface of the lens. The first traveling body 8 and the second traveling body 11 are provided so as to travel in a one-to-two relationship in traveling speed by a stepping motor (not shown). That is, in the process of moving the first traveling body 8 and the second traveling body 11 in the direction of arrow A, the image of the original 4 on the contact glass 3 is illuminated by the halogen lamp 9, and the reflected image of the original 4 Second and third mirror 1
It is configured to be deflected by 0, 12, and 13 and converged by the converging lens 14 and input to the CCD 6.
The CCD 6 is provided on the sensor substrate 15. The sensor board 15 is connected to a signal processing board 17 by a cable 16.
It is connected to the.

As shown in FIG. 2, a sample hold circuit 18, a black level correction circuit 19, an amplifier circuit 20, a multiplex circuit 21, an amplifier circuit 22, an A / D converter A circuit 23, a shading correction circuit 24, and an interface 25 are sequentially connected. Here, the sample hold circuit 18, the black level correction circuit 19, the amplifier circuit 20, the multiplex circuit 21, and the amplifier circuit 22 constitute an analog signal processing unit 26. The analog signal processing unit 26, the A / D conversion circuit 2
3. The shading correction circuit 24 is connected via a bus 27 to a CPU (not shown) constituting a microcomputer.

Next, the CCD 6, the sample hold circuit 1
8, the configuration of the timing signal generation unit 28 that sends a timing signal to each unit of the black level correction circuit 19, the amplification circuit 20, the multiplex circuit 21, the amplification circuit 22, the A / D conversion circuit 23, and the shading correction circuit 24 will be described.

As shown in FIG. 3, the timing signal generator 28 spreads (spectrum spreads) the frequency of a reference clock signal output from an oscillator (hereinafter referred to as OSC) 29 by a frequency spreader 30 to generate a timing signal. Generate The frequency spreader 30 includes a spreading factor switching circuit 31
Are spread with a frequency spreading factor determined by the signals of Q1 and Q2 input from. As shown in Table 1, the spreading factor of the frequency is determined by the combination of the input Q1 and Q2.

[0030]

[Table 1]

Further, the image reading device 1 converts the frequency of the clock signal output from the OSC 29 into a frequency spreader 30
And a synchronization control means for synchronizing the change in the frequency spreading factor by the frequency spreader 30 with the main scanning synchronization signal when the signal is spread by the following.

That is, in the time chart of FIG. 4, the main scanning synchronization signal LSYNC and the main scanning gate signal LG
When ATE is “L”, the image reading signal is valid. Then, the main scanning synchronization signal LSYNC and the main scanning gate signal L
When GATE is “H” (outside the effective reading area), the frequency is temporarily switched to a value different from the frequency spreading factor in the image reading area. This set value is returned to the original set value while being outside the effective image area. The switching timing is LS
Synchronous with YNC.

In the present embodiment, LSYNC, LGAT
When E is “H” (outside the effective reading area), Q1
= 0, Q2 = 1 (frequency spreading factor is ± 1.8%), and L
When SYNC and LGATE are "L" (in the effective reading area), Q1 = 1, Q2 = 0 (frequency spreading factor is ±
1.8%).

Further, the image reading apparatus 1 according to the present invention
As shown in (2), by giving a desired black offset level adjustment value to the black level correction circuit 19, the frequency spreader 3
A black offset level adjusting means for suppressing a level fluctuation of the image signal caused by the frequency spreading by 0 is provided. This black offset level adjusting means will be described later.

Next, the processing of the image data signal output from the CCD 6 will be described with reference to FIG. The image signals Vo and Ve of the odd-numbered and even-numbered pixels output from the CCD 6 in synchronization with the timing signal generated by the timing signal generation unit 28 are sampled and held by the sample-and-hold circuit 18 using a sample pulse, and the image signal is held. After making the analog signal continuous and correcting the variation of the dark output of the CCD 6 in the black level correction circuit 19, the output of the odd-numbered and even-numbered pixels of each color signal is adjusted to a certain level in the amplification circuit 20, and the odd and even numbers are output in the multiplexing circuit 21. An image signal V is obtained by processing the output of the pixel. Subsequently, the image signal V is subjected to A / D
A / D converter circuit 23 amplifies the voltage to the level of the reference voltage for conversion.
To 8 bits of digital data. The digital image signal thus obtained is subjected to shading correction by the shading correction circuit 24, thereby correcting variations in the sensitivity of the CCD 6 and uneven light distribution of the halogen lamp 9 illuminating the original. The shading correction is performed by setting the white reference plate 5 disposed on the extension surface of the original reading surface to the halogen lamp 9.
Then, the reflected light is read by a CCD, and the reading is performed based on the read density level.

As described above, when performing image processing, as shown in FIG. 4, by synchronizing the change in the frequency spreading factor by the frequency spreader 30 with the main scanning synchronization signal LSYNC, as shown in FIG. , The change in output frequency is synchronized in each line. That is, as shown in FIG. 13, the change of the output frequency is not synchronized between the lines, and the level of the level appears as a streak, and a state in which the line looks moire is avoided. Thereby, the image quality can be improved.

When the frequency spreader 30 has a reset function, the frequency spreader 30 is reset outside the effective reading area to reset the frequency spread cycle, thereby mainly controlling the change in the frequency spread rate. Scan synchronization signal LSY
It can be synchronized with the NC (corresponding to another synchronization control means). With this, as shown in FIG. 6, the change of the output frequency is synchronized in each line.

In the state shown in FIG. 6, the change of the output frequency is synchronized between the lines, but the level of the image signal periodically changes every line. However, as shown in FIG. 5, by giving a black offset level adjustment value to the black level correction circuit and adjusting the black offset level (black offset level correction means), as shown in FIG. Level fluctuation can be suppressed.

In this case, when the black offset level adjustment value obtained by adding the noise level for one line is stored in the memory, and the black offset level adjustment is performed based on the adjustment value, the periodic fluctuation in the level of the image signal is more accurately suppressed. can do.

The black offset level adjustment value corresponding to the phase information of the timing signal generated from the timing signal generation unit 28, in other words, the black offset level adjustment value obtained by adding the noise level for one cycle is stored in the memory. Even if the black offset level is adjusted by the adjustment value, periodic fluctuations in the level of the image signal can be suppressed. In this case, since the stored black offset level adjustment value is as small as one cycle, a small-capacity memory can be used as a memory for storing the noise level.

Next, a second embodiment of the present invention will be described with reference to FIG. The same parts as those in the above embodiment are denoted by the same reference numerals, and description thereof is omitted. This embodiment is an embodiment in which the periodic level fluctuation as shown in FIG. 6 is suppressed as shown in FIG. 7 by the level correcting means instead of the black offset level adjusting means in the above embodiment. It is.
FIG. 8 is an explanatory diagram schematically showing the concept of the level correcting means.

This level correction means divides the black shading data by the white shading data when the image signal to be read is 8 bits, and adds the value to 2 ⁿ -1 (n
(The number of bits of the image data) and the shading correction circuit 24 corrects the correction value. In this example, since the number of bits of the image data is 8, 2 ⁿ −1 is 255.

In this case, the black shading data given to the shading correction circuit 24 is the halogen lamp 9
Is data of the entire area of the CCD 6 in the main scanning direction, which is read in a state where is erased. The white shading data is data in the entire main scanning direction of the CCD 6 read with the halogen lamp 9 turned on. In addition, data for one cycle can be stored as black shading data and used for the above calculation.

Next, an example of an image forming apparatus provided with the above-described image reading apparatus 1 will be described with reference to FIG. Although the image forming apparatus according to the present embodiment is a digital copying machine C, the image forming apparatus including the image reading device 1 includes a facsimile and the like in addition to the copying machine.

As shown in FIG. 9, the above-described image reading apparatus 1 is provided above the main body 100 of the digital copying machine C. Further, a printing unit 101 is provided inside the main body 100. The printing unit 101 uniformly charges the surface of the photoconductor 103 by the charger 102, develops the electrostatic latent image written on the charged portion by the optical writing device 104 by the developing device 105, and develops the developed image. Transfer belt 1
06, and the transferred image is transferred to the fixing device 107.
To form the next image.
Is a known configuration in which the cleaning unit 108 cleans the surface. The optical writing device 104 is of a deflection scanning type that forms an electrostatic latent image by irradiating the photoconductor 103 with laser light modulated based on the image data read by the image reading device 1 described above. However, a line-type optical writing unit that has a large number of light emitting elements along the axial direction of the photoconductor 103 and selectively emits the light emitting elements to form an electrostatic latent image on the surface of the photoconductor 103 is used. It does not matter.

The digital copying machine C according to the present embodiment includes well-known paper feeding units 109, 110, and 111.
A sheet conveying member 114, 115, 116, 1 that conveys the sheet S is provided in a sheet conveying path 113 that extends from these sheet feeding units 109, 110, 111 to a sheet discharging unit (sheet discharging tray) 112.
17 are arranged. Therefore, the sheet S fed from any of the selected sheet feeding units 109, 110, 111
The image is printed by the printing unit 101 in the process of being guided to the paper conveyance path 113 and being discharged to the paper discharge unit 112.

[0047]

According to the image reading apparatus of the first aspect,
A timing signal generator that generates a timing signal by spreading the frequency of a clock signal output from an oscillator with a frequency spreader during image processing, and a black offset that suppresses a level fluctuation of an image signal caused by frequency spreading by the frequency spreader And a level adjustment unit, so that the black offset level adjustment unit can suppress the periodic level fluctuation of the image signal, thereby suppressing the occurrence of streaks due to the image level fluctuation of each line. In addition, the deterioration of the S / N ratio can be prevented.

According to the image reading apparatus of the second aspect, a timing signal generator for generating a timing signal by spreading the frequency of the clock signal output from the oscillator during image processing by the frequency spreader and the frequency spreader A synchronization control unit for synchronizing the change in the frequency spreading factor with the main scanning synchronization signal, so that the change in the output frequency can be synchronized in each line by the synchronization control unit.

According to the third aspect of the present invention, a timing signal generator for generating a timing signal by spreading the frequency of the clock signal output from the oscillator during image processing by the frequency spreader, Synchronization control means for synchronizing the change in the frequency spreading factor with the main scanning synchronization signal, and black offset level adjustment means for suppressing the level variation of the image signal caused by frequency spreading by the frequency spreader, the synchronization control means The change of the output frequency can be synchronized for each line, and in addition, the periodic fluctuation of the level of the image signal can be suppressed by the black offset level adjusting means. The generation of streaks can be suppressed, and the deterioration of the S / N ratio can be prevented.

According to the image reading apparatus of the fourth aspect, in the invention of the first or third aspect, the black offset level adjusting means is executed based on the black offset level adjustment value for one line. The periodic fluctuation of the level of the image signal can be more accurately suppressed by the adjusting means.

According to a fifth aspect of the present invention, in the image reading apparatus of the first or third aspect, the black offset level adjusting means adjusts the black offset level according to phase information of a timing signal generated from the timing signal generating section. Since the adjustment is performed based on the offset level adjustment value, periodic fluctuations in the level of the image signal can be suppressed by the black offset level adjustment unit. Since the black offset level adjustment value corresponding to the phase information of the timing signal has a small amount of information, a small-capacity memory can be used as a memory for storing the black offset level adjustment value.

According to the image reading apparatus of the sixth aspect, a timing signal generator for generating a timing signal by spreading the frequency of the clock signal output from the oscillator by the frequency spreader at the time of image processing, and generating the black shading data. By performing shading correction with a correction value obtained by multiplying the value obtained by dividing by the white shading data by 2 ⁿ -1 (n = the number of bits of the image data), the level fluctuation of the image signal caused by the frequency spread by the frequency spreader is suppressed. And a level correction unit that performs the above-described operation, so that the level correction unit can suppress the periodic fluctuation of the level of the image signal, thereby suppressing the occurrence of streaks due to the image level fluctuation of each line. Further, deterioration of the S / N ratio can be prevented.

According to the image forming apparatus of claim 7, since the image reading apparatus of any one of claims 1 to 6 is provided, it is possible to suppress the level fluctuation of the image when reading the original image. As a result, image quality can be improved during printing.

[Brief description of the drawings]

FIG. 1 is a vertical sectional front view showing a schematic configuration of an image reading apparatus according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing an electrical connection configuration.

FIG. 3 is a block diagram illustrating an electrical configuration of a timing signal generation unit.

FIG. 4 is a time chart when synchronizing a change in the frequency spreading factor with a main scanning synchronization signal.

FIG. 5 is an explanatory diagram schematically showing the concept of a black level offset adjusting unit.

FIG. 6 is an explanatory diagram showing a level of an image signal read in a state where a change in a frequency spreading factor is synchronized with a main scanning synchronization signal.

FIG. 7 is an explanatory diagram showing a level of an image signal after being adjusted by a black offset level adjusting unit.

FIG. 8 is an explanatory diagram schematically showing a concept of a level correcting unit according to the second embodiment of the present invention.

FIG. 9 is a longitudinal sectional front view showing an example of an image forming apparatus equipped with an image reading device.

FIG. 10 is a graph showing a waveform of a clock signal oscillated from an oscillator.

FIG. 11 is a graph showing a waveform obtained by spreading the frequency of a clock signal oscillated from an oscillator.

FIG. 12 is an explanatory diagram showing a level variation of one line of an image signal when a frequency is spread in an analog timing signal generation unit.

FIG. 13 is an explanatory diagram showing level fluctuations of a plurality of lines of an image signal when a frequency is spread in an analog timing signal generation unit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image reading apparatus 4 Original 6 Solid-state image sensor 7 Reading optical system 28 Clock signal generation part 29 Oscillator 30 Frequency spreader 101 Printing part S Paper

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 2H108 AA01 CA03 CB01 FA00 5B047 AA01 BA02 BB02 CA06 CB17 5C072 AA05 BA08 BA11 BA17 EA05 FB12 LA02 MA01 MB01 RA15 UA02 UA09 UA11 UA14 5C077 LL19 MM03 PQ13 PP06

Claims (7)

[Claims] An image reading device that inputs a document image to a solid-state imaging device by a reading optical system, converts an image data signal output from the solid-state imaging device into a digital signal, and performs image processing; A timing signal generation unit that generates a timing signal by spreading a frequency of a clock signal output from an oscillator with a frequency spreader; and a black offset level adjustment that suppresses a level change of an image signal caused by frequency spreading by the frequency spreader. Means for reading an image. 2. An image reading apparatus which inputs a document image to a solid-state imaging device by a reading optical system, converts an image data signal output from the solid-state imaging device into a digital signal, and performs image processing. A timing signal generating unit that generates a timing signal by spreading the frequency of a clock signal output from an oscillator with a frequency spreader; and a synchronization control unit that synchronizes a change in the frequency spreading rate by the frequency spreader with a main scanning synchronization signal. An image reading apparatus comprising: 3. An image reading apparatus which inputs a document image to a solid-state imaging device by a reading optical system, converts an image data signal output from the solid-state imaging device into a digital signal, and performs image processing. A timing signal generating unit that generates a timing signal by spreading the frequency of a clock signal output from an oscillator with a frequency spreader; and a synchronization control unit that synchronizes a change in the frequency spreading rate by the frequency spreader with a main scanning synchronization signal. An image reading apparatus comprising: a black offset level adjusting unit that suppresses a level change of an image signal caused by frequency spreading by the frequency spreader. 4. The black offset level adjusting means according to claim 1, wherein
The image reading apparatus according to claim 1, wherein the image reading is performed based on a black offset level adjustment value for a line. 5. The image according to claim 1, wherein the black offset level adjusting means executes the black offset level adjusting means based on a black offset level adjusting value corresponding to phase information of a timing signal generated from the timing signal generating section. Reader. 6. An image reading apparatus which inputs a document image to a solid-state imaging device by a reading optical system, converts an image data signal output from the solid-state imaging device into a digital signal, and performs image processing. A timing signal generator for generating a timing signal by spreading a frequency of a clock signal output from the oscillator by a frequency spreader; and a value obtained by dividing black shading data by white shading data to 2 ⁿ -1 (n = image data An image reading apparatus comprising: a level correction unit configured to execute shading correction using a correction value multiplied by (number of bits), thereby suppressing a level change of an image signal due to frequency spreading by the frequency spreader. 7. An image forming apparatus comprising: the image reading device according to claim 1; and a printing unit that outputs image data read by the image reading device.