JP2004260541A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus in which the influence of image noise on an output image is suppressed while the radiation noise is suppressed by adjusting the frequency spread width of a timing pulse in accordance with an image quality mode. <P>SOLUTION: This image forming apparatus is provided with an image read part 31a which is driven with the timing pulse to read an image, applies prescribed conversion to the read image and outputs the converted image as an image signal, and an image processing part 34 which is driven with the same timing pulse to process the output corresponding to prescribed image processing and an image mode on the basis of the image signal. In the image forming apparatus, the timing pulse is subjected to frequency spreading in which a reference frequency is continuously modulated at a prescribed period, and the width of the frequency spread is changed in accordance with the image quality mode. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus configured to change a frequency spread width of a clock according to an image quality mode.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as one of digital image forming apparatuses (hereinafter, image forming apparatuses) using an electrophotographic process, there are a digital copying machine, a facsimile, and the like. In recent years, along with technological innovations in the technical fields related to digital technology, image processing technology, image forming technology, etc., image forming that forms a faithful image of a document by increasing the resolution at the time of reading the document and the resolution at the time of forming the image. Equipment is increasing. In addition, output tends to be further accelerated as the resolution of an image increases.
[0003]
In the image forming apparatus as described above, an original is read by an image reading device, decomposed into countless minute pixels, subjected to image processing, exposed by an exposure device according to the read pixels, and placed on a photoconductor. The formed electrostatic latent image is developed and visualized. A clock or timing pulse is supplied to an image processing circuit for reading and processing such an image.
[0004]
On the other hand, increasing the resolution means increasing the number of pixels per unit area, and increasing the output speed leads to an increase in the number of pixels processed per unit time. Therefore, in order to realize high resolution and high speed, it is necessary to further increase the speed of a clock and a timing pulse supplied to the above-described image processing circuit. The adverse effect of clocks and timing pulses that increase in speed is that the level of radiation noise radiated from circuits and devices that generate or use these clocks and timing pulses to other circuits and devices or to the outside increases, Devices become more susceptible to noise, which is a major cause of malfunctions and failures of circuits and devices.
[0005]
Therefore, as a measure to reduce the level of the radiation noise, particularly the peak level, the frequency of a clock or a timing pulse is periodically shifted (spread) to modulate the frequency. Specifically, with the center of the reference frequency of the reference clock as the center, the frequency is regularly changed by a predetermined modulation width toward higher frequencies, and then the frequency is regularly changed by a predetermined modulation width toward lower frequencies. Return to frequency. It is known that the level of radiated noise is reduced by repeating this change periodically.
[0006]
Also, if the modulation width (diffusion width) for modulating from the reference frequency is increased, the waveform of the peak portion of the radiated noise becomes an integrated waveform, and the peak level can be further reduced. However, if the frequency of the clock is changed periodically, the timing pulse for control and driving generated based on the clock will have the same modulation, otherwise the generation of radiated noise will be partially reduced. Can only be reduced.
[0007]
On the other hand, the image reading and processing of the image forming apparatus includes a CCD for reading a document in pixel units, an analog signal processing unit for converting the information of the read pixel converted into a charge level by the CCD into an analog signal, and an analog signal processing unit. Is converted into a digital signal by an A / D converter and an image processing circuit that processes an image composed of the digital signal. These are all driven by timing pulses generated based on the clock. Therefore, if the frequency modulation width of the clock is increased in order to suppress the level of radiation noise from the clock, the timing pulse is similarly modulated, and the timing shifts when transferring and detecting the charge of the CCD pixel unit. The charge level cannot be correctly detected. That is, the density level of each read pixel is disturbed, and image noise is mixed or disturbed, and side effects appear in the form of image quality deterioration.
[0008]
According to Patent Document 1, a timing pulse generated based on a clock whose frequency is spread at ± 0.5% or ± 1.0% as described above is converted into an analog signal processing unit, an A / D conversion unit, and an image processing unit. To reduce the radiation noise of clocks and timing pulses. In this method, noise is mixed into the image as described above. However, a diffusion period SYNC signal is output for each clock diffusion period, and the charge level of the CCD is synchronized with the line period at the time of reading. By correcting the line shift, apparent image noise is reduced.
[0009]
According to Patent Document 2, a clock that does not spread the frequency is supplied to the CCD, the analog signal processing unit, and the A / D conversion unit in order to avoid the occurrence of image noise. A timing pulse subjected to frequency spreading is supplied to an image processing unit that does not cause noise.
[0010]
Further, according to Patent Document 3, generation of radiation noise is suppressed by supplying timing pulses subjected to frequency spreading to all of the CCD, the analog signal processing unit, the A / D conversion unit, and the image processing unit. Therefore, a black offset level adjusting means for suppressing the level fluctuation of the image signal due to the frequency spread is newly provided, and thereby the periodic level fluctuation (image noise) of the image signal is suppressed.
[0011]
[Patent Document 1]
JP-A-2002-281252
[Patent Document 2]
JP-A-2002-33858
[Patent Document 3]
JP 2001-257881 A
[0012]
[Problems to be solved by the invention]
However, in the method according to Patent Document 1, since a timing pulse with a spread frequency is supplied to all the circuits related to image reading and image processing, a great effect can be expected in suppressing radiation noise. A synchronization circuit that generates a synchronization signal is required.Furthermore, since the timing pulse for frequency spreading and the analog processing system synchronize on a line-by-line basis, even if the image deviation due to the line timing deviation can be corrected, No consideration is given to the timing shift caused by the frequency spread of the plurality of pixels, and the likelihood of image noise appearing due to the shading being disturbed in the line is high.
[0013]
In the method according to Patent Literature 2, a normal clock is supplied to an analog processing system in which the timing of each pixel may be shifted as a side effect of frequency spreading, so that generation of image noise is suppressed. However, the processing system for supplying the frequency-spread timing pulse is limited, and a clock without the frequency spread is also supplied, so that the generation of radiation noise cannot be significantly suppressed.
[0014]
Further, in the method according to Patent Literature 3, as in the method according to Patent Literature 1, a timing pulse whose frequency is spread is supplied to all processing systems related to image reading and processing, and thus is effective in suppressing radiation noise. However, a new black offset level adjusting means for suppressing the occurrence of image noise is required, which complicates the circuit configuration and raises the cost.
[0015]
The present invention has been made in view of such a situation, and adjusts the frequency spread width of a timing pulse in accordance with an image quality mode to suppress the occurrence of radiation noise and reduce the influence of image noise on an output image. It is an object of the present invention to provide an image forming apparatus capable of suppressing the occurrence.
[0016]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, an image reading unit driven by a timing pulse to read a document, performs a predetermined conversion, and outputs an image signal, and an image reading unit driven by the timing pulse and based on the image signal. An image processing unit that performs image processing according to an image quality mode, wherein the timing pulse is a timing pulse subjected to frequency spreading in which a reference frequency is continuously modulated in a predetermined cycle. , The width of the frequency spread is changed according to the image quality mode.
[0017]
The image quality mode is a plurality of modes corresponding to the gradation of image formation, and the timing pulse has a frequency spread width corresponding to each of the plurality of image quality modes.
[0018]
The timing pulse is configured so that the frequency spread width is small when the gradation in the image quality mode is high, and the frequency spread width is large when the gradation in the image quality mode is low.
[0019]
The width of the frequency spread of the timing pulse can be changed for each reading line when the image reading unit reads the document.
[0020]
The image processing unit determines an image quality mode of a determination area including a plurality of continuous reading lines including the newest line read by the image reading unit, and is driven by a timing pulse having a frequency spread width according to the image quality mode. Then, the next line is read.
[0021]
Alternatively, the image quality mode is a mode selected in advance by a user or a mode automatically determined and selected by the image forming apparatus when a document is pre-scanned by the image reading unit.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a front sectional view schematically showing a digital color copying machine (hereinafter, a copying machine) equipped with an image reading unit and an image processing unit as an example of an image forming apparatus according to the present invention. In FIG. 1, a copying machine 1 is schematically composed of a scanner unit 2 for reading and processing an image of a document and an output unit 10 for outputting the processed image on a sheet.
[0023]
The scanner unit 2 includes an optical unit 30 including a lens, a mirror, or a prism (not shown), a CCD 31 that receives light from a document via the optical unit 30 to form an image, and a pixel 31 of the formed image. An analog signal processing unit 32 that converts the charge level of each element of the corresponding CCD 31 into an analog signal; an A / D conversion unit 33 that converts the analog signal into a digital signal; and image processing that performs image processing on the digital signal of each pixel And a unit 34.
[0024]
The output unit 10 includes image forming units 3Y, 3M, 3C, and 3K for yellow, magenta, cyan, and black, toner hoppers 4Y, 4M, 4C, and 4K corresponding to these colors, and a sheet P as a recording medium. , A paper feed guide 6, a paper feed timing roller 7, a paper feed timing motor 7a for driving the paper feed timing roller 7, a transport belt 8, and a transport belt for driving the transport belt A roller 11 and a transport belt motor 11a, a transfer roller 12, a fixing unit 13, paper discharge rollers 14 to 16, a discharge roller 18, a discharge unit 19, a control unit 20, and an input unit and a display unit (not shown). It comprises an operation unit 27 provided.
[0025]
Further, the image forming units 3Y, 3M, 3C, and 3K of the respective colors include a developing unit 22, a photoconductor 23, and a photoconductor motor 23a for driving the photoconductor, a charger 24, an exposure device 25, and a cleaning unit 26, respectively. It is configured.
[0026]
Next, a schematic operation of the copying machine 1 having the above configuration will be described. First, after a document is set on the scanner unit 2, when the operation unit 27 is operated to start copying, the optical unit 30 operates to scan the document. Light from the original is input to the image processing unit 34 as a digital signal image via the CCD 31, the analog signal processing unit 32, and the A / D conversion unit 33. The image processing unit 34 performs predetermined image processing such as shading correction and image processing according to the image quality mode, separates the color into yellow, magenta, cyan, and black, respectively, and then displays the image data according to an instruction from the control unit 20. The image data is temporarily stored in a memory not to be used, or is sent to the image forming units 3Y to 3K substantially in parallel with the original scanning.
[0027]
On the other hand, the photoreceptor 23 charged by the charger 24 of each of the image forming units 3Y to 3K is exposed by the exposure device 25 in accordance with the above-described color-separated image signal for each color, and forms an electrostatic latent image on its surface. . The photoreceptor 23 on which the electrostatic latent images of the respective colors are recorded is developed by the developing device 22 with the corresponding color toner, and a visible image is formed on the surface. Such an image forming process is performed for each color.
[0028]
The paper P fed from the paper feed cassette 5 is guided and sent out by the paper feed guide 6, but stops temporarily with the leading end thereof being held by the paper feed timing roller 7. When the paper feed timing motor 7a is driven by a signal from the control unit 20 in synchronization with the image formation on the photoconductor 23, the paper feed timing roller 7 transports the paper P with the transport belt motor 11a. The belt is conveyed to the upper surface of the conveyor belt 8 rotating counterclockwise by the belt roller 11. Then, the sheet P is attracted to the upper surface of the transport belt 8 and passes through the transfer roller 12 to which the transfer voltage is applied so that the image of each color is transferred to the sheet P when passing immediately below the image forming units 3Y, 3M, 3C, and 3K. P is sequentially transferred to P.
[0029]
In this way, the four color toners that form a full-color image by being overlapped on the sheet P are fixed to the sheet P by being heated and pressed when the sheet P passes through the fixing unit 13. Thereafter, the paper P is sequentially conveyed by the paper discharge rollers 14, 15 and 16, and is guided to be discharged to the discharge unit 19 via the discharge roller 18.
[0030]
FIG. 2 is a diagram illustrating the relationship between the frequency and time of a timing pulse whose frequency is modulated (spread). The vertical axis represents frequency and the horizontal axis represents time, and the graph shows frequency-modulated timing pulses. A graph D1 (solid line) shows a timing pulse having the largest frequency spread width, a graph D3 (dotted line) shows a timing pulse having the smallest frequency spread width, and a graph D2 (dashed line) shows an intermediate point between these two. I have. As described above, the timing pulse used in the present invention has a frequency spread as in the conventional example.
[0031]
Next, a first embodiment of the present invention will be described with reference to FIGS. FIG. 3 is a schematic block diagram of the first embodiment showing a main circuit portion of the copying machine 1 including a clock circuit. Light from the document enters the CCD 31, and charges are accumulated in elements corresponding to each pixel of the CCD 31. The analog signal processing unit 32 converts a charge level corresponding to each pixel into an analog signal, and the analog signal is converted into a digital signal by the A / D conversion unit 33. These processing systems constitute the image reading unit 31a. Further, the image processing unit 34 processes the digital signal so that a predetermined image is formed, and outputs the processed digital signal to the image forming units 3Y to 3K or the memory 41 described later.
[0032]
The control unit 20 controls the entire copying machine 1 and includes a main control circuit 40 and a memory 41, and includes an operation unit 27, image forming units 3Y to 3K, an image processing unit 34, and control signals and data. Exchange is taking place. Further, a clock circuit 42 for generating a timing pulse necessary for reading an image by the scanner unit 2 and processing the image is provided. The clock circuit 42 may be provided in the scanner unit 2.
[0033]
The clock circuit 42 includes a reference clock generation circuit 43 that generates a reference clock, a frequency spreading circuit 44 that performs frequency spreading of a predetermined width using the frequency of the reference clock as a reference frequency, and the same based on the frequency-spread clock. A timing pulse generation circuit 45 for generating a timing pulse having a reference frequency and a frequency spread width, and a spread width adjusting circuit 46 for outputting a parameter to the frequency spread circuit 44 for setting the frequency spread width of the clock are provided. The timing pulse output from the timing pulse generation circuit 45 is supplied to the CCD 31, the analog signal processing unit 32, the A / D conversion unit 33, and the image processing unit. Further, the parameters output from the diffusion width adjusting circuit 46 can be changed by an instruction from the main control circuit 40.
[0034]
Next, the image quality mode output by the copying machine 1 will be described. Normally, the digital copier performs image processing in the image processing unit 34 based on the output image quality mode together with predetermined processing such as shading correction. Representative examples of such image quality modes include a “character mode”, a “photo mode”, and a “text / photo mixed mode”.
[0035]
"Character mode" is a mode that is usually applied when a document mainly composed of characters and lines is output. The document is read and processed in binary or low gradation, and output in binary or low gradation. I do. As a result, it is possible to obtain an output image in which the processing time is short, the image is sharp, and the density is clear. The “photo mode” is a mode applied to processing and output when a photograph or a printed matter on which a photograph is posted is a document, and the document is read in multiple gradations such as 256 gradations to perform multi gradation processing. Go and output. Therefore, it is possible to obtain an output image with a fine texture and continuous shades. That is, this is a mode that is inconsistent with the “character mode” in gradation. In the "text / photo mixed mode" mode, which is used when text and a photograph are simultaneously present in a document, the document is output in a "character mode" and a "photo mode" in order to output both the text and the photo image with satisfactory quality. ] Is read and processed at a substantially intermediate gradation, and output at a substantially intermediate gradation.
[0036]
In the copying machine 1, it is possible to switch between such a mode automatically and manually by using the operation unit 27. When the mode is manually changed, the user further operates the operation unit 27. One of “text mode”, “photo mode”, and “text / photo mixed mode” must be selected. In the case of automatic switching, the whole or a part of the original is pre-scanned when the original is read, and the copying machine 1 recognizes and determines which mode image quality is closest to the original.
[0037]
As is clear from the above description of the image quality mode, in the case of the "character mode", a document having a sharp gradation is output as such, so that even if a little image noise is mixed in the processing process in the image reading unit 31a. , It is hard to appear in the output image, and even if it appears, it is hard to recognize and inconspicuous. In the case of the “photo mode”, the image is reproduced by multi-gradation, that is, a delicate change of pixels. Therefore, if image noise is mixed, the image is likely to appear in the output image and be easily recognized. The “text / photo mixed mode” is an intermediate level.
[0038]
In the present invention, by appropriately utilizing such properties of the image, it is possible to reduce the radiation noise due to the clock and the timing pulse without deteriorating the image quality of the output image. That is, as described with reference to FIG. 2, the graph D <b> 1 is a timing pulse in which the generation of radiation noise is the smallest but the image noise is most likely to occur because the spread width of the frequency is the largest. The graph D3 is a timing pulse in which the emission noise is the largest but the image noise is the least likely to occur because the spread width of the frequency is the smallest. Graph D2 is intermediate between these.
[0039]
The object of the present invention can be solved by controlling the combination of the image quality mode and the nature of the frequency spread width of the timing pulse as described above. FIG. 4 is a flowchart according to the first embodiment for switching the frequency spread width of the timing pulse according to the image quality mode. For convenience of description, as shown in FIG. 2, D1, D2, and D3 are referred to in descending order of the frequency spread width.
[0040]
When copying is started, it is determined in S1 (step 1) whether the selection of the image quality mode is set to manual or automatic. In the case of manual operation, in S2, which image quality mode is set is read, and the process proceeds to S5. If the setting is automatic in S1, the process branches to S3, where a part or all of the document is prescanned, and in S4, the copying machine 1 automatically determines which image quality mode is optimal, and After determining the image quality mode to be performed, the process proceeds to S5. In S5, the process branches to processing according to the set or determined image quality mode. If the image quality mode is the "character mode", the flow branches to S10, if the "text / photo mixed mode", the flow branches to S20, and if the "photograph mode", the flow branches to S30.
[0041]
In S10, the main control circuit 40 outputs an instruction to set the frequency spread width of the clock to D1 (maximum) from the main control circuit 40 to the spread width adjustment circuit 46 according to the image quality mode. In response to this, in S11, the spread width adjustment circuit 46 outputs a parameter corresponding to D1 to the frequency spread circuit 44. In S12, the frequency spreading circuit 44 modulates the reference clock so that the frequency spreading width becomes D1, outputs the clock to the timing pulse generating circuit 45 as a clock whose frequency is spread as D1, and outputs the frequency spreading width. The adjustment processing ends. S20 to S22 are the same as S10 to S12, and are controlled so that the frequency spread width is set to D2. Also, S30 to S32 are the same as S10 to S12, and are controlled so that the frequency spread width is set to D3. Thus, the timing pulse generated by the timing pulse generation circuit 45 based on the frequency-spread clock is supplied to the CCD 31, the analog signal processing unit 32, the A / D conversion unit 33, and the image processing unit 34. The image reading and image processing are performed.
[0042]
As described above, in the first embodiment of the present invention, the image quality mode is manually or automatically determined for each document, and the image reading unit 31a and the image reading unit 31a use the timing pulse having the frequency spread width according to the image quality mode. The processing unit 34 is driven. Therefore, the circuit and the control are simplified, and at the same time, the radiation noise is reduced, and the image noise is hardly visually recognized on the output image. Although the example in which the image quality mode of the entire document is automatically recognized and determined when pre-scanning is performed in S3 of FIG. 4 has been described, a plurality of read lines are sequentially read from the beginning of the document. The image quality mode is automatically determined for each area composed of, and the image quality mode corresponding to the area is stored. When reading for image formation after the pre-scan is completed, the image quality mode is stored for each stored area. It is also possible to change the frequency spread width according to the following. For more detailed control, there is a method of determining an image quality mode for each line described below.
[0043]
Next, a second embodiment of the present invention will be described with reference to FIGS. 1, 2, and 5 to 7. FIG. In the second embodiment, when the image quality mode is set to automatic, when determining the image quality mode of the document, the image quality mode is not determined by pre-scanning the document in advance as in the first embodiment. In this method, the image quality is determined for each predetermined area and the image quality mode is determined almost in parallel with the document reading for image formation, and the result is reflected when the next line is read. Therefore, the image quality mode is determined for each area, that is, substantially for each read line almost in real time, the timing pulse is finely adjusted, and time is not wasted in the prescan.
[0044]
FIG. 5 is a schematic block diagram of a second embodiment showing a main circuit portion of the copying machine 1 including a clock circuit. In the figure, components given the same reference numerals as those in FIG. 3 represent the same components, and redundant description will be omitted. 3 is different from FIG. 3 in that the image processing unit 34 includes an area discriminating circuit 50 for enabling the above-described real-time processing. Is transmitted to the main control circuit 40, and the main control circuit 40 sends a signal designating the frequency spread width to the spread width adjusting circuit according to the information.
[0045]
FIG. 6 is a diagram in which numbers are assigned to lines on which a document is sub-scanned. Hereinafter, a schematic method in which the area determination circuit 50 determines the image quality mode for each area of the document will be described. The line from which the original is first read by the sub-scanning of the CCD 31 is denoted by L1, and sequentially denoted by L2, L3,..., Ln.
[0046]
FIG. 7 shows a flowchart according to the second embodiment in which the frequency spread width of the timing pulse is switched according to the image quality mode. For convenience of description below, as shown in FIG. 2, the timing pulses are referred to as D1, D2, and D3 in descending order of the frequency pulse width. When copying is started, it is determined in S40 whether the selection of the image quality mode is set to manual or automatic. In the case of manual, in S41, which image quality mode is set is read, and the process proceeds to S42. Since the flow after S42 is the same as S5 to S32 in FIG. 4, the description is omitted.
[0047]
In S40, if the selection of the image quality mode is set to automatic, the process branches to S50. In S50, a control signal is sent from the main control circuit 40 to the spread width adjusting circuit 46, and the frequency spread width of the timing pulse is initialized to D3 which minimizes the possibility of image noise. Thereafter, in step S51, the lines L1, L2, and L3 are sequentially read by the CCD 31, and in step S52, the line L1 + L2 + L3 is treated as a determination area by the area determination circuit 50. In S53, the image quality mode of the determination area is determined by the area determination circuit 50. If it is determined that the mode is the "character mode", control signals are sent from the area determination circuit 50 to the main control circuit 40 and the spread width adjustment circuit 46 in S54, and the frequency spread width of the timing pulse is set to D1. If it is determined in step S53 that the mode is the "photograph mode", the process branches to step S55, where control signals are sent from the area determination circuit 50 to the main control circuit 40 and the diffusion width adjustment circuit 46, respectively. Is set to
[0048]
Then, in S56, it is determined whether or not the last line read is the last line of the document. If the last line is the last line, this flow ends and the flow returns to the normal operation. If it is not the last line, the next line Ln is read in S57. At this time, the frequency spread width of the timing pulse at the time of reading the line Ln follows the determination of the image quality mode in the determination area in S53. In other words, the frequency spread width at the time of reading the line Ln is based on the determination result of the image quality mode of the determination area including L (n−3), L (n−2), and L (n−1). Has become something.
[0049]
When the reading of the line Ln is completed, the line L (n-3) is removed, and the lines L (n-2), L (n-1), and Ln form the next determination area. Thereafter, the flow returns to S53, the image quality mode of the new determination area is determined, and this repetition continues until reading of the document is completed. Therefore, at the same time as reading the original for each line for forming an image, the image quality mode is substantially determined for each line.
[0050]
As described above, in the second embodiment, when the selection of the image quality mode is set to be automatic, the image quality mode is substantially determined for each line, and the timing is set to an appropriate frequency spread width for each line. A pulse is set. Therefore, compared with the method according to the first embodiment in which the frequency spread width is set for each document according to the image quality, finer control of the frequency spread can be performed, and the suppression of the radiation noise generated by the timing pulse can be reduced. The effect on image quality due to image noise, which is a side effect, is controlled for each line, so that efficient and highly effective results can be obtained.
[0051]
In the above description of the second embodiment, an example has been described in which the determination area is formed by three read lines, but the number of read lines that form the determination area is not limited to this example. Further, the example in which the determination in S52 and S53 in FIG. 7 is one of the “character mode” and the “photo mode” has been described. However, a mode other than these two modes, for example, an intermediate mode, may be further provided. It is.
[0052]
In the first and second embodiments described above, two or three image quality modes have been described as examples, but the actual image quality mode is not limited to these examples. For example, various image quality modes may be provided in a color image forming apparatus, such as a "line drawing / illustration mode" close to a "character mode" and a "printed material mode" close to a photo mode. In that case, without being limited to the three frequency spread widths, it is also possible to control with a spread width other than three by obtaining the correlation between the frequency spread width and the effect of the image noise on the image quality. The size of the diffusion width may be set within a range in which the side effect does not affect.
[0053]
【The invention's effect】
According to the present invention, it is possible to uniformly supply a frequency-spread timing pulse to the image reading unit and the image processing unit, so that it is possible to greatly suppress the generation of radiation noise due to the timing pulse. Further, since the frequency spread width is changed according to the image quality mode, there is an excellent effect that image noise caused by the frequency-spread timing pulse is less likely to appear in the image and is less noticeable.
[0054]
In addition, if the image quality is determined in parallel with the original reading, it is possible to control the appropriate image quality mode and the frequency spread width of the timing pulse for each original reading line, thereby effectively suppressing radiation noise and reducing image noise. The effect of reduction is also increased.
[0055]
Furthermore, in order to achieve both the suppression of radiation noise and the reduction of the effect of image noise on the output image, there is no need for a complicated synchronization circuit or image noise suppression circuit as in the prior art, and the cost is reduced and the cost is reduced. It can be realized with a simple configuration.
[Brief description of the drawings]
FIG. 1 is a front cross-sectional view schematically illustrating an image processing unit as an example of an image forming apparatus according to the present invention and a digital color copier equipped with the image processing unit.
FIG. 2 is a diagram showing the relationship between the frequency and time of a clock whose frequency is modulated (spread) and the timing pulse.
FIG. 3 is a schematic block diagram of a first embodiment showing a main circuit portion of the copying machine 1 including a clock circuit.
FIG. 4 shows a flowchart according to a first embodiment for switching a frequency spread width of a timing pulse according to an image quality mode.
FIG. 5 is a schematic block diagram of a second embodiment showing a main circuit portion of the copying machine 1 including a clock circuit.
FIG. 6 is a diagram in which lines for sub-scanning a document are numbered;
FIG. 7 shows a flowchart according to a second embodiment for switching the frequency spread width of the timing pulse according to the image quality mode.
[Explanation of symbols]
1 Copier
2 Scanner section
3Y-3K image forming unit
4Y-4K toner hopper
5 Paper cassette
6 Paper feed guide
7a Feeding timing motor
7 Paper feed timing roller
8 Conveyor belt
10 Output section
11 Conveyor belt roller
11a Transport belt motor
12 Transfer roller
13 Fixing unit
14-16 paper ejection roller
18 Discharge roller
19 Discharge section
20 control unit
22 Developing device
23 Photoconductor
23a Photoconductor motor
24 Charger
25 Exposure equipment
26 Cleaning unit
27 Operation section
30 Optical part
31 CCD
31a Image reading unit
32 Analog signal processing unit
33 A / D converter
34 Image processing unit
40 Main control circuit
41 memory
42 Clock Circuit
43 Reference Clock Generation Circuit
44 Frequency Spreading Circuit
45 Timing pulse generation circuit
46 Diffusion width adjustment circuit
50 area discrimination circuit

Claims (7)

An image reading unit driven by a timing pulse to read an original, perform predetermined conversion and output as an image signal, and an image process driven by the timing pulse to perform image processing according to an image quality mode based on the image signal And an image forming apparatus comprising:
The timing pulse is a timing pulse subjected to frequency spreading in which a reference frequency is continuously modulated at a predetermined cycle, and is configured such that a width of the frequency spreading is changed according to the image quality mode. An image forming apparatus. 2. The image quality mode according to claim 1, wherein the plurality of modes correspond to tone levels of image formation, and the timing pulse has a frequency spread width corresponding to each of the plurality of image quality modes. 3. Image forming apparatus. The timing pulse is changed such that the frequency spread width is small when the gradation in the image quality mode is high, and the frequency spread width is large when the gradation in the image quality mode is low. The image forming apparatus according to claim 1 or 2. 4. The image forming apparatus according to claim 1, wherein a width of the frequency spread of the timing pulse is changeable for each reading line when the image reading unit reads the document. 5. . The image processing unit determines an image quality mode of a determination area including a plurality of continuous reading lines including the newest line read by the image reading unit, and a timing pulse having a frequency spread width according to the image quality mode. The image forming apparatus according to claim 1, wherein the next line is read by being driven by the image forming apparatus. 4. The image forming apparatus according to claim 1, wherein the image quality mode is a mode that is previously selected for each document by a user. 4. The image quality mode according to claim 1, wherein the document is pre-scanned by the image reading unit, and is automatically determined and selected by the image forming apparatus. 5. 5. The image forming apparatus according to claim 1.

Images