JP2001339580A - Image reader and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image with high quality by eliminating a periodic noise in an image signal caused by frequency spread. SOLUTION: A frequency spread unit 33 modulates a system clock clks generated from an oscillator 32 with a low frequency signal to obtain clock signal clks and a timing generating circuit 21 applies circuit division processing or the like to the clocks clks to generate timing signals required for a CCD, an analog signal processing circuit and an analog/digital converter circuit or the like. Furthermore, the timing generating circuit 21 generates a reset signal (reset) to reset the frequency spread unit 33. The timing generating circuit 21 outputs the reset signal (reset) at a time when it is at the outside of a valid image area of the CCD to reset the frequency spread unit 33. The switching timing by an output of the reset signal (reset) is made to be synchronous with a main scanning synchronizing signal.

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 capable of reducing unnecessary radiation intensity of electromagnetic waves by frequency spreading.

[0002]

2. Description of the Related Art With the demand for higher image quality, digital copiers and the like tend to have higher pixel density. Also, the copy speed has been increasing year by year. Image scanners are also required to have a higher pixel density and a higher reading speed.

[0003] In a conventional image reading apparatus, an image is converted to CC.
The signal processing from the reading at D to the conversion to a digital image signal is performed as follows. First, an analog image signal of odd-numbered and even-numbered pixels is output from a CCD that has read an image of a document, and is output to an analog signal processing circuit. The analog signal processing circuit includes a sample hold circuit, a black level correction circuit, an amplifier circuit, a multiplex circuit, and an amplifier circuit. The analog image signal is converted into a continuous analog image signal by being sampled and held by a sample pulse by a sample-and-hold circuit, and thereafter, the black level correction circuit corrects the variation in the dark output level of the CCD. After the outputs of the odd and even pixels of each color signal are adjusted to a certain level in the amplifier circuit, the outputs of the odd and even pixels are multiplexed in the multiplex circuit to form an image signal. This image signal is amplified to a predetermined degree by an amplifier circuit, and is converted into an 8-bit digital image signal by an A / D conversion circuit. In the shading correction circuit, the digital image signal thus obtained is read by a CCD with the reflected light of the white reference plate irradiated by the exposure light source to obtain a predetermined density level, and the CCD is obtained.
And the unevenness of the light distribution of the irradiation system is corrected and output to a predetermined interface. Timing signals necessary for driving the CCD and other circuits are generated by a timing generation circuit and output to each circuit. A microcomputer that centrally controls each part of the image reading device includes a timing generation circuit,
It controls operations of an analog signal processing circuit, an A / D conversion circuit, a shading correction circuit, and the like.

[0004]

In the conventional image reading apparatus, as the pixel density increases and the image reading speed increases, a photoelectric conversion element such as a CCD for reading an image and a photoelectric conversion element at a subsequent stage. The clock frequency when driving an analog signal processing circuit that performs various kinds of signal processing on the image signal output from the device becomes high, which causes a problem that unnecessary radiation of electromagnetic waves increases.

Therefore, in order to prevent such a problem, it is conceivable to provide a component that spreads the frequency after the oscillator used to generate the clock frequency to reduce the unnecessary radiation intensity at the frequency peak. . That is, the clock frequency having the frequency waveform shown in FIG. 11 becomes the frequency waveform shown in FIG. 12 by spreading the frequency of the clock by the frequency spreader, and the unnecessary radiation intensity becomes smaller than that in FIG. .

However, in the circuit configuration of the conventional image reading apparatus, if a frequency spreader is used for the analog timing generation circuit, the timing deviation between the output of the CCD and the sample pulse, the clock of the A / D conversion circuit, The level of the obtained image signal periodically fluctuates in one line due to the deviation of the sampling point from the analog image signal, and the level is changed (see FIG. 13).
And if this is repeated for many lines, the level of the level will appear finely as a streak on the read image as a result,
There is a problem that a human eye looks like a moire (see FIG. 14).

Further, since periodic noise is generated in an image, there is a problem that the S / N ratio becomes worse as compared with a case where no frequency spreader is used.

It is an object of the present invention to obtain a high-quality image by removing periodic noise of an image signal due to frequency spreading.

Another object of the present invention is to remove periodic noise of an image signal by simple means.

Another object of the present invention is to obtain a high-quality image by preventing the fluctuation of the timing signal generated when the frequency spreader is reset from appearing in the image.

Another object of the present invention is to perform shading correction using a black level value and a white level value,
The purpose is to more accurately remove periodic noise in the image signal to obtain a higher quality image.

Another object of the present invention is to detect a black level value and a white level value before image reading, thereby more accurately removing the periodic noise of the image signal and obtaining a higher quality image. Is to get. In the third aspect, an object of the present invention is to correct the level fluctuation of the image signal more accurately by performing the black level detection and the white level detection before reading the image.

[0013]

According to a first aspect of the present invention, there is provided a scanning optical system for exposing and scanning an original, and a photoelectric system for receiving reflected light of the original by the exposure and scanning to obtain an image signal of the original. A conversion element, a signal processing circuit for performing various signal processing on the image signal, a shading correction circuit for performing shading correction of the image signal after the signal processing, an oscillator, and the photoelectric conversion element based on an output of the oscillator. A timing generating circuit for generating a timing signal for timing the operation of the signal processing circuit; a frequency spreader for spreading the frequency of the output of the oscillator; And a synchronizing means for synchronizing with a main scanning synchronizing signal for synchronizing in the main scanning direction when an image is read by the image reading apparatus.

Therefore, by synchronizing the change in the frequency spreading factor with the main scanning synchronization signal, the periodic noise of the image signal can be made uniform in each line, and the periodic noise of the image signal is removed by shading correction. As a result, a high-quality image can be obtained.

According to a second aspect of the present invention, in the image reading apparatus according to the first aspect, the synchronization means synchronizes a change in the frequency spreading factor with respect to the main scanning synchronization signal with the main scanning synchronization signal. And outputting a reset signal for resetting the frequency spreader.

Therefore, by outputting a reset signal for resetting the frequency spreader, it is possible to synchronize the change in the frequency spread rate with the main scanning synchronization signal. Can be removed.

According to a third aspect of the present invention, in the image reading apparatus according to the second aspect, the synchronizing means synchronizes a change in the frequency spreading factor with the main scanning synchronizing signal outside an effective image area. is there.

Therefore, the change of the frequency spreading factor with respect to the main scanning synchronization signal is synchronized outside the effective image area of the photoelectric conversion element, so that the fluctuation of the timing signal generated when the frequency spreader is reset is prevented from appearing in the image. Thus, a high-quality image can be obtained.

According to a fourth aspect of the present invention, in the image reading apparatus according to any one of the first to third aspects, the shading correction circuit is configured to determine a black level value of each pixel in the main scanning direction from the image signal. And a white level detection unit that detects a white level value of each pixel in the main scanning direction from the image signal, and performs the shading correction based on the black level value and the white level value. Is what you do.

Therefore, by performing shading correction based on the detected black level value and white level value, the periodic noise of the image signal can be more accurately removed, and
Higher quality images can be obtained.

According to a fifth aspect of the present invention, in the image reading apparatus of the fourth aspect, there is provided a detection execution unit for executing the detection of the black level value and the white level value prior to the operation of reading the image of the document. ing.

Therefore, by performing the detection of the black level value and the white level value prior to the reading operation of the image of the original, the periodic noise of the image signal can be more accurately removed.
Higher quality images can be obtained.

According to a sixth aspect of the present invention, there is provided the image reading apparatus according to any one of the first to fifth aspects, wherein an image is formed on a sheet based on image data read by the image reading apparatus. Image forming apparatus.

Therefore, the same operation and effect as the invention according to any one of the first to fifth aspects can be obtained.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment of the Invention] One embodiment of the present invention will be described as a first embodiment of the present invention.

FIG. 1 is a longitudinal sectional view of a flatbed type image scanner 1 according to Embodiment 1 of the present invention.
The image scanner 1 implements the image reading device of the present invention. As shown in FIG. 1, an image scanner 1 includes a contact glass 3 on which a document 2 is placed,
A first carriage 6 comprising a halogen lamp 4 for exposure and a first reflection mirror 5, a second carriage 9 comprising a second reflection mirror 7 and a third reflection mirror 8, and a CCD linear image sensor as a photoelectric conversion element 10 (hereinafter simply referred to as a CCD 10), a lens unit 11 for forming an image on the CCD 10, and a white reference plate 12 for shading correction. The CCD 10 is provided on a sensor board substrate 13.
Is connected by a connection cable 15 to a signal processing board 14 on which a signal processing circuit (described later) for performing various signal processing on image signals output by the CCD 10 is formed. The halogen lamp 4, the first, second, and third reflecting mirrors 5, 7, 8 and the lens unit 11 constitute a scanning optical system.

The halogen lamp 4 irradiates light at a certain angle with respect to the reading surface of the white reference plate 12 and the contact glass 3, and the light reflected by the white reference plate 12 or the document 2 is first,
The light enters the CCD 10 via the second and third reflecting mirrors 5, 7, 8 and the lens unit 11. The CCD 10 outputs a voltage corresponding to the amount of incident light as an analog image signal. The first and second carriages 6 and 9 move the reading surface of the original 2 and the CCD 1 by driving a stepping motor (not shown).
0 in the sub-scanning direction (arrow A
Direction), and the original 2 is exposed and scanned.

FIG. 2 is a block diagram of the signal processing circuit formed on the signal processing board 14. As shown in FIG. 2, analog image signals Ve and Vo of odd and even pixels are output from the CCD 10, and the analog signal processing circuit 30
Is output to The analog signal processing circuit 30 includes a sample and hold circuit 22, a black level correction circuit 23, and an amplification circuit 2.
4. It comprises a multiplex circuit 25 and an amplifier circuit 26. The analog image signals Ve and Vo are each converted into a continuous analog image signal by being sampled and held by a sample pulse by a sample-and-hold circuit 22, and thereafter, the black level correction circuit 23 varies the level of the dark output of the CCD 10. After the outputs of the odd and even pixels of each color signal are adjusted to a certain level in the amplifier circuit 24, the outputs of the odd and even pixels are multiplexed in the multiplex circuit 25 to become the image signal V.
The image signal V is amplified to a predetermined degree by the amplifier circuit 26, and A / A
The data is converted into an 8-bit digital image signal by the D conversion circuit 27.

The digital image signal thus obtained is supplied to the shading correction circuit 28 by the halogen lamp 4.
The CCD 10 reads the reflected light of the white reference plate 12 illuminated by the CCD 10 to obtain a predetermined density level.
And the light distribution unevenness of the irradiation system is corrected and output to the predetermined interface 29. Timing signals necessary for driving the CCD 10 and other circuits are generated by a timing generation circuit 21 and output to each circuit. A microcomputer 31 for centrally controlling each part of the image scanner 1
Are the timing generation circuit 21 and the analog signal processing circuit 3
0, A / D conversion circuit 27, shading correction circuit 28
Control the operation of

FIG. 3 is a block diagram of the timing generation circuit 21. As shown in FIG. 3, a system clock clk generated by an oscillator 32 is modulated at a low frequency by a frequency spreader 33 to generate a clock clks.
By dividing the frequency of the clock clks in
D10, analog signal processing circuit 30, A / D conversion circuit 2
7 and the like are generated. Also,
The timing generation circuit 21 generates a reset signal reset for resetting the frequency spreader 33. Clock clks
Is modulated at a low frequency, so that an output resulting from a clock generated at a specific frequency is spread around (spread spectrum), and the intensity of the peak value portion is reduced (see FIG. 12).

The spreading factor of the spreading performed by the spreading device 33 is determined by a spreading factor switching circuit 34. That is, the frequency spreading factor is determined by the combination of the two signals Q1 and Q2 output from the spreading factor switching circuit 34 to the frequency spreader 33. FIG. 4 shows an example of the combination.

FIG. 5 is a timing chart of each signal. In FIG. 5, the main scanning synchronization signal LSYNC is
Is a signal for synchronizing in the main scanning direction when an image is read. The main scanning gate signal LGATE is a signal that validates an image signal when it is at the L level. That is, the image signal when the main scanning gate signal LGATE is at the L level becomes the effective image area. The timing generation circuit 21 outputs a reset signal reset outside the effective image area of the CCD 10, that is, when the main scanning gate signal LGATE is at the H level, to reset the frequency spreader 33. The microcomputer 31 synchronizes the switching timing by the output of the reset signal reset with the main scanning synchronization signal LSYNC. This implements a synchronization means. By such control of synchronizing the change in the frequency spreading factor with the main scanning synchronization signal LSYNC, the change in the frequency of the clock clks by the frequency spreader 33 is synchronized in each line, and the level of the digital image signal is as shown in FIG. As shown. Further, by resetting the frequency spreader 33 outside the effective image area of the CCD 10, the CCD
Since the control for synchronizing the change of the frequency spreading factor with the main scanning synchronization signal LSYNC outside the effective image area of 10 is performed, the clock clk
The fluctuation of s does not appear in the image.

The shading correction circuit 28 performs shading correction on the digital image signal containing the periodic noise level. FIG. 7 is a block diagram showing a circuit configuration of the shading correction circuit 28. As shown in FIG. 7, the black level detector 35 detects all image data in the main scanning direction within the effective image area when the halogen lamp 4 is turned off. At this time, the detection unit may read image data of a plurality of lines and calculate an average value of each pixel. Further, depending on the amount of change in the noise level of the digital image signal, it is not necessary to detect all image data in the main scanning direction in the effective image area, and a plurality of image data can be collected. The detected value of the black level at this time is defined as a black level value.

The white level detecting section 36 reads the white reference plate 12 when the halogen lamp 4 is lit, and detects all image data in the main scanning direction within the effective image area. As in the case of black level detection, a plurality of lines may be read and the average value of each pixel may be calculated. The detected value of the white level at this time is defined as a white level value.

Using the black level value and the white level value detected in this way, the shading correction operation section 37 performs shading correction of the digital image signal. That is, if the image data is 8 bits (255), the shading correction calculation of each pixel is as follows.

Image data after shading correction = (read image data−black level value) / (white level value−black level value) × 255 With such shading correction, the frequency spreader 3
The image data in which the image noise due to the frequency spreading of No. 3 has been corrected is as shown in FIG.

FIG. 9 is a flowchart of control by the microcomputer 31 when scanning an image with the image scanner 1. As shown in FIG. 8, first, the black level detector 35 detects a black level value at the time of scanning as described above (step S1). Thereafter, the halogen lamp 4 is turned on (step S2), and the first and second carriages 6, 9 are turned on.
Is started (step S3). Then, when the first carriage 6 reaches the position of the white reference plate 12, the white level detector 36 detects the white level value as described above (step S4).

Thereafter, image reading is performed. That is,
The output of the gate signal FGATE indicating the image reading area in the sub-scanning direction is started (step S5). When the image reading end position is reached, the gate signal FGATE is stopped (step S6), the motor forward of the stepping motor is stopped (step S7), and the motor return is started (step S8), and the first carriage 6 is stopped. When comes to the home position, the motor return is stopped (step S9), and the scan is completed.

As is apparent from the processing of FIG. 8 described above, in scanning, detection of a black level value (step S1) and detection of a white level value (step S4) are performed prior to the image reading operation (step S5). By doing so, a detection execution unit can be realized, and the periodic noise of the image signal due to the frequency spread of the frequency spreader 33 can be more accurately corrected.

[Embodiment of the Invention] FIG. 10 is a block diagram showing a schematic configuration of a copying machine 41 according to a second embodiment of the present invention. The copying machine 41 implements the image forming apparatus of the present invention, and forms an image on paper based on image data read by the image scanner 1 according to the first embodiment of the present invention. And a control unit 43 for controlling the image forming apparatus 41. As a printing method of the printer 42, various methods such as an ink-jet method, a sublimation-type thermal transfer method, a silver halide photographic method, a direct thermal recording method, and a fusion-type thermal transfer method can be used in addition to the electrophotographic method.

[0041]

According to the first aspect of the present invention, the periodic noise of the image signal can be made uniform in each line by synchronizing the change in the frequency spreading factor with the main scanning synchronization signal. A high-quality image can be obtained by removing the periodic noise of the image signal.

According to a second aspect of the present invention, in the image reading apparatus of the first aspect, a change in the frequency spreading factor is synchronized with the main scanning synchronization signal by outputting a reset signal for resetting the frequency spreader. Therefore, periodic noise of the image signal can be removed by simple means.

According to a third aspect of the present invention, in the image reading apparatus according to the second aspect, the change of the frequency spreading rate with respect to the main scanning synchronization signal is synchronized outside the effective image area of the photoelectric conversion element. The fluctuation of the timing signal that occurs when the detector is reset does not appear in the image, so that a high-quality image can be obtained.

According to a fourth aspect of the present invention, in the image reading apparatus according to any one of the first to third aspects, shading correction is performed on the basis of the detected black level value and white level value, thereby obtaining an image. Periodic noise of the signal can be more accurately removed, and a higher quality image can be obtained.

According to a fifth aspect of the present invention, in the image reading apparatus according to the fourth aspect, the detection of the black level value and the white level value is performed prior to the operation of reading the image of the original, so that the image signal of the image signal is detected. More accurately remove periodic noise,
Higher quality images can be obtained.

The invention according to claim 6 has the same operation and effect as the invention according to any one of claims 1 to 5.

[Brief description of the drawings]

FIG. 1 is a vertical sectional view of an image scanner according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a signal processing circuit of the image scanner.

FIG. 3 is a block diagram of a timing generation circuit of the image scanner.

FIG. 4 is a diagram illustrating an example of a combination of two signals Q1 and Q2 for determining a frequency spreading factor by a spreading factor switching circuit of the image scanner.

FIG. 5 is a timing chart of each signal of the image scanner.

FIG. 6 is a diagram showing levels of image signals before shading correction processed by the image scanner.

FIG. 7 is a block diagram of a shading correction circuit of the image scanner.

FIG. 8 is a diagram showing levels of image signals after shading correction processed by the image scanner.

FIG. 9 is a flowchart of control by a microcomputer when an image is scanned by the image scanner.

FIG. 10 is a block diagram illustrating a schematic configuration of a copying machine according to a second embodiment of the present invention;

FIG. 11 is a graph showing an example of a frequency waveform of a clock frequency generated by an oscillator.

FIG. 12 is a graph showing an example of a frequency waveform when the clock frequency is spread.

FIG. 13 is a diagram illustrating a level of an image signal when a clock frequency is spread.

FIG. 14 is a diagram showing the level of an image signal when a clock frequency is spread.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 image reading device 4 scanning optical system 5 scanning optical system 7 scanning optical system 8 scanning optical system 10 photoelectric conversion element 11 scanning optical system 21 timing generation circuit 30 signal processing circuit 27 signal processing circuit 28 signal processing circuit, shading correction circuit 32 oscillator 33 Frequency Spreader 35 Black Level Detector 36 White Level Detector 41 Image Forming Device

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04N 1/407 H04N 1/40 101B F-term (Reference) 2H108 AA01 CB01 DA06 5B047 AA01 BB02 CA06 CB17 DA04 DC01 5C072 AA01 BA11 BA18 EA05 FB08 FB23 UA02 WA04 5C077 LL03 LL04 LL19 MM03 MM20 NP07 PP06 PP07 PP44 PP45 PQ05 PQ08 SS01 SS03

Claims (6)

[Claims] 1. A scanning optical system for exposing and scanning a document, a photoelectric conversion element for receiving reflected light of the document by the exposure scanning to obtain an image signal of the document, and various kinds of signal processing for the image signal A shading correction circuit that performs shading correction of the image signal after the signal processing; an oscillator; and a timing signal that determines the operation timing of the photoelectric conversion element and the signal processing circuit from the output of the oscillator. A frequency generator for generating a signal obtained by frequency-spreading the output of the oscillator; and a change in the frequency spread rate by the frequency spreader, which is mainly used when reading an image with the photoelectric conversion element. A synchronization unit for synchronizing with a main scanning synchronization signal for synchronizing in a scanning direction. 2. The synchronizing means synchronizes the change of the frequency spreading factor with the main scanning synchronization signal by outputting a reset signal for resetting the frequency spreader in synchronization with the main scanning synchronization signal. The image reading device according to claim 1, wherein 3. The image reading apparatus according to claim 2, wherein the synchronization unit synchronizes a change in the frequency spreading factor with the main scanning synchronization signal outside an effective image area. 4. A shading correction circuit for detecting a black level value of each pixel in the main scanning direction from the image signal, and detecting a white level value of each pixel in the main scanning direction from the image signal. The image reading device according to any one of claims 1 to 3, further comprising: a white level detection unit configured to perform the shading correction based on the black level value and the white level value. 5. The image reading apparatus according to claim 4, further comprising a detection execution unit that executes the detection of the black level value and the white level value prior to an operation of reading an image of a document. 6. An image forming apparatus comprising: the image reading device according to claim 1; and forming an image on a sheet based on image data read by the image reading device.