JP2001309136A - Image reader and image processor provided with the image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image reader that can suppress stripe noises caused in an image while reducing harmonic components owing to an operating pulse. SOLUTION: Employing a spread clock for a timing circuit 112 that outputs an operating clock to a 3-line CCD 111 and ADCs 119-121 reduces harmonic components of a reference frequency. A spread spectrum clock generator 137 frequency-modulates a reference clock received from a reference clock oscillator 136 with a sine wave modulation profile and using the operating clock generated on the basis of the obtained spread clock can suppress a stripe noise caused in the case of a triangle wave modulation profile.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus which can be applied to an image processing apparatus such as a scanner, a digital copying machine, a digital color copying machine, a facsimile, a color facsimile, etc. The present invention relates to a technique for reducing EMI due to a driving clock used.

[0002]

2. Description of the Related Art An image reading apparatus uses a large number of clocks such as a transfer clock × 2, a reset clock, a clamp clock, and a final stage clock to drive a CCD for photoelectrically converting a read image. A harmonic component of the fundamental frequency of the clock is generated. In addition, since the CCD substrate is mounted parallel to the lens surface due to the configuration of the optical system, it is often a separate substrate from the timing signal generation circuit for generating the drive clock. in this case,
The harness is connected between the boards, and radiation from this portion is inevitable. On the other hand, in order to reduce such harmonic components generated by the operation clock and conform to the EMI standard, it has been attempted to use a spread spectrum generator for frequency-modulating a clock signal in a reader.

[0003]

However, when frequency modulation for performing spread spectrum is applied to a driving clock for CCD or analog processing in an image reading apparatus, a periodic noise is included in an image signal after sampling, and a streak-like output appears. Images may occur. The present invention has been made in view of the above-described problems of the related art in an image reading apparatus having a photoelectric conversion unit and an analog processing unit that operate by a spread spectrum clock. It is an object of the present invention to provide an image reading apparatus capable of suppressing streak noise generated in an image while reducing image quality, and an image processing apparatus including the image reading apparatus.

[0004]

According to a first aspect of the present invention, there is provided an image processing means including at least one of a line image sensor and an AD (analog-digital) converter for converting an image signal output from the line image sensor into digital data. Clock generating means for frequency-modulating a reference clock with a predetermined modulation profile to generate a spread spectrum clock, and means for generating a timing signal for operating the image processing means based on a clock output from the clock generating means. An image reading apparatus comprising: the modulation profile for generating the spread spectrum clock, wherein the modulation profile has a sine wave shape.

According to a second aspect of the present invention, in the image reading apparatus according to the first aspect, the modulation profile includes sine waves having different periods.

According to a third aspect of the present invention, in the image reading apparatus according to the first or second aspect, the modulation profile includes sine waves having different amplitudes.

According to a fourth aspect of the present invention, in the image reading apparatus of the second or third aspect, the sinusoidal modulation profile is determined so that the center frequency of the spread spectrum is not changed. It is.

According to a fifth aspect of the present invention, in the image reading apparatus according to any one of the first to fourth aspects, the sinusoidal modulation profile can be adjusted.

According to a sixth aspect of the present invention, in the image reading apparatus according to the fifth aspect, the adjustment of the sinusoidal modulation profile is performed by rewriting data in a RAM. .

According to a seventh aspect of the present invention, there is provided an image processing apparatus comprising the image reading apparatus according to any one of the first to sixth aspects.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described based on the following embodiments shown in the accompanying drawings. First, an outline of a digital color copier capable of suitably implementing the image reading apparatus of the present invention will be described. FIG. 1 is a diagram showing an outline of the overall configuration of the digital color copying machine of the present embodiment. This digital color copying machine is roughly divided into a color image reading device and a color image recording device. The color image reading device includes an image reading unit (scanner) 2, an image processing unit 3
On the other hand, the color image recording apparatus has an image writing unit 4, a drum unit 8, a developing unit 10, an intermediate transfer unit 9, a paper feeding unit 11, a fixing unit 12, and a copying machine mechanism unit 6. A system control unit 1, a working unit 5, and an image display unit 7 are provided in order to perform control operations common to both reading and recording apparatuses.

The outline of the operation when color copying is performed by the digital color copying machine of the present embodiment is as follows. The image reading unit 2 scans a document illuminated by illumination light from a light source while sub-scanning the document. The reflected light is photoelectrically converted by a three-line CCD sensor to read an image, and the image data is sent to the image processing unit 3. The image processing unit 3 sends to the image writing unit 4 image data that has been subjected to image processing such as scanner γ correction, color conversion, main scanning magnification, image separation, processing, area processing, and gradation correction processing. The image writing unit 4 drives an LD (laser diode) by performing modulation according to the image data. In the drum unit 8, an electrostatic latent image is written by a laser beam from the LD onto a uniformly charged rotating photosensitive drum, and the developing unit 10 attaches toner to make the image visible. The image formed on the photosensitive drum is re-transferred onto the transfer belt of the intermediate transfer unit 9. Four colors (Black: Bk, Cya) for full color copy on the intermediate transfer belt
n: C, Mgenta: M, Yellow: Y) toners are sequentially stacked. In the case of a full-color copy, transfer paper is fed from the paper feed unit 11 at the time when the image forming / transfer process of four colors Bk, C, M, and Y is completed, in synchronization with the intermediate transfer belt,
In the paper transfer section, toners are simultaneously transferred from the intermediate transfer belt to transfer paper in four colors. The transfer paper to which the toner has been transferred is sent to the fixing unit 12 via the conveyance unit, and is thermally fixed by the fixing roller and the pressure roller, and is discharged.

When performing the above-described copying operation, setting of a copy mode and the like designated by a user operation is performed by an input operation on the operation unit 5. The set copy mode and the like are notified to the system control unit 1, and the system control unit 1 performs control processing for executing the set copy mode and the like. At this time, the system control unit 1 issues a control instruction to units such as the image reading unit 2, the image processing unit 3, the image writing unit 4, and the image display unit 7. FIG. 2 is a diagram illustrating an example of the operation panel of the operation unit 5. As shown in FIG. 2, the operation panel of the operation section unit 5 includes a numeric keypad 41 and a mode clear / preheat key 4.
2. Interrupt key 43, image quality adjustment key 44, program key 45, print start key 46, clear / stop key 47, area processing key 48, brightness adjustment knob 4
9, a touch panel key (on the LCD panel 26 in FIG. 3 described later) 50 and an initial setting key 51 are provided.

The ten keys 41 are used to input numerical values such as the number of copies. The mode clear / preheat key 42 is used to cancel the set mode and return to the initial setting, or to set the preheating state by pressing continuously for a certain period of time or more. The interrupt key 43 is used to interrupt during copying and to copy another document. The image quality adjustment key 44 is used to adjust the image quality. The program key 45 is used to register or call a frequently used mode. The print start key 46 is a key for starting copying.
The clear / stop key 47 is used when clearing the input numerical value or when interrupting copying during copying. The area processing key 48 is used to execute a mode such as area processing / editing on the image display unit (display editor) 7. Brightness adjustment knob 49 is LCD
The brightness of the screen of the panel (see FIG. 4 described later) is adjusted. Further, the touch panel key 50 sets a key area in the same range as the range of various keys displayed on the LCD panel, and when the touch panel detects a press within the set range, processing of the set key is performed. I do. The initial setting key 51 is pressed when the user selects each initial setting.

To display an image read from the image reading unit 2 on the image display unit 7 (FIG. 1), the image reading unit 2 starts reading a document image in response to a control instruction from the system control unit 1. , For the image signal from the image reading unit 2,
After performing image processing suitable for display on the image display device in the image processing unit 3, the image data of the document is output to an image display device such as an LCD panel. FIG. 3 is a functional block diagram illustrating a circuit configuration of the image display unit 7.
As shown in FIG. 3, the image display unit 7 is connected to the system control unit 1 via a command line and to the image processing unit 3 via a data line.
IFO (line buffer) 21, DRAM (image data memory) 22, CPU 23, VRAM (video memory)
24, LCDC (LCD controller) 25, LCD
(Liquid crystal panel) 26, ROM 27, SRAM 28, serial communication driver 29, image data signal buffer (driver / receiver) 30, and keyboard 31.

The image data output from the image processing unit 3 is transmitted through the FIFO 21 of the image display unit 7 to
The image data is stored in the DRAM 22 for storing image data by a DMA controller built in the CPU 23. Since the image data control signal is sent to the image display unit 7 together with the image data, it is possible to capture only the effective image area. The valid image data stored in the DRAM 22 is DMA-transferred to the VRAM 24 by the CPU 23. At this time, it is also possible for the CPU 23 to transfer an arbitrary portion of the image data in the DRAM 22 and to perform processing such as enlargement, reduction, thinning, and the like. The image data transferred to the VRAM 24 is stored in an LCDC (LCD controller) 2.
5 is displayed on the LCD panel 26. FIG.
Represents one of the LCD panels of the image display unit 7 shown in FIG.
It is a figure showing an example. The image display unit 7 displays the image L
It is displayed on the CD panel 26. Further, a display editor for designating an area for editing / processing / setting a mode on the display screen may be used. Each setting key in FIG. 4 is a keyboard 3 in the functional block diagram in FIG.
It corresponds to part 1.

FIG. 5 shows an example of a screen displayed on the LCD panel 26. As shown in FIG. 5, on the LCD screen, a mode selection such as a color mode, an automatic density, a manual density, an image quality mode, an automatic paper selection, a paper tray, an automatic paper magnification, a magnification (actual magnification), a sort, and a stack. There is a display, and a sub-screen selection display such as create, color processing, double-sided, and scaling is also provided. Further, the LCD panel 26 is used as a touch panel, and keys having the same size as the size of each display unit are set. Some keys can be displayed on the screen by depressing the keys. FIG. 6 shows an example of screen development by pressing the scaling key on FIG. When the scaling key is pressed, the scaling setting screen is scrolled up from the bottom of the screen. On the magnification setting screen, keys for fixed magnification (magnification mode in which a magnification is set in advance) are set. For example, when the touch panel key of the 71% portion is pressed, a scaling ratio of 71% is selected. In addition, the zoom key,
A dimension scaling key and an independent scaling / enlarged continuous shooting key are set on the left side of the screen.

The detection circuit of the above touch panel and its operation will be described. FIG. 7 is a diagram illustrating an example of a configuration of the touch panel detection circuit. FIG. 8 shows a setting state of the potentials of the X and Y electrodes of the touch panel in the detection circuit of FIG. As shown in FIG. 7, the touch panel detection circuit includes a touch panel 71, a controller 72, an A / D converter 73, and an operation switching circuit. The controller 72 sets the detection terminal to the high state, and sets the touch panel 71
The potentials X1, X2, Yl, and Y2 of the respective electrodes are set as shown in FIG. The Yl and Y2 circuits are pulled up by resistors, so when the touch panel 71 is OFF, Yl is + 5v and ON
In the case of, it becomes 0v. Therefore, the ON / OFF state is confirmed from the output of the A / D converter 73. Controller 72
Switches to the measurement mode when the ON state of the touch panel 71 is detected. In the X direction, X1 becomes + 5v and X2 becomes 0v, and the potential at the input position is passed through Yl to the A / D converter 7.
3 and the coordinates are calculated. Further, the coordinates in the Y direction are similarly calculated by switching the circuit. With such a detection circuit, the pressed position of the touch panel 71 is detected.

The circuit configuration and operation of the operation unit 5 in which the image display unit and various input keys are integrated on the operation panel (see FIG. 2) will be described below. FIG. 9 is a functional block diagram illustrating an example of a circuit configuration of the operation unit. As shown in FIG. 9, the operation unit 5 includes a CPU 53, an address latch 54, and an LCDC.
(LCD controller) 55, address decoder 56,
System reset 57, ROM 58, LED driver 5
9, keyboard 60, touch panel 61, LCD module 62, ROM 63, RAM 64, optical transceiver 6
5 is provided. An address signal from the CPU 53 is taken into an address latch 54, and an address signal is applied to each memory for controlling access to the memory. A part of the address signal output from the address latch 54 enters an address decoder 56, where a chip select signal for each IC is created and used for creating a memory map. Also,
Address is ROM58 (or RAM) memory or LCDC
55 and used for addressing. On the other hand, CPU5
The data bus from No. 3 is connected to the ROM 58 and the LCDC 55 to perform bidirectional data communication. LCDC55
In addition to the address bus and the data bus from the CPU 53, an LED driver 59, a keyboard 60, an analog touch panel 61, an LCD module 62, a display data ROM 63, a RAM 64, and the like are connected.
The LCDC 55 is provided with a signal from a keyboard and a touch panel 6.
The display data is created from the data in the ROM 63 and the RAM 64 in accordance with the signal from 1 and the screen display of the LCD module 62 is controlled. An optical transceiver 65 as an optical fiber connector is connected to the CPU 53 to communicate with the outside.

Next, an image reading apparatus to which the present invention is applied, which is provided in the above-described digital color copying machine, will be described in more detail. FIGS. 10 and 11 are overall block diagrams showing a read image signal processing system and a scanner control system (hereinafter, referred to as a scanner IPU (image processing unit) control unit) of the color image reading apparatus of the present embodiment. The function of each element constituting the scanner IPU control unit will be described with reference to FIGS. The CPU 101 on the scanner IPU control unit controls the entire scanner IPU control unit by executing a program stored in the ROM 102 and reading and writing data and the like in the RAM 103. Further, the CPU 101 is the system control unit 1
04 is connected by serial communication, and performs operations instructed by transmission and reception of commands and data. Further, the system control unit 104 is connected to the operation display unit 105 by serial communication, and can set an instruction such as an operation mode in response to a key input instruction from a user. 1 above). On the other hand, the CPU 101 includes a document detection sensor, an HP sensor, a pressure plate open / close sensor,
It is connected to a cooling fan or the like, and controls operations such as detection at 1 / O106 and ON / OFF.
Scanner motor driver 107 receives P from CPU 101
It is driven by the WM output to generate an excitation pulse sequence, and drives the pulse motor 108 for scanning the original.

The original image is illuminated by a halogen lamp 110 driven below a lamp regulator 109, and reflected light from the original surface passes through a plurality of mirrors and lenses to form an image on a light receiving surface of a three-line CCD 111, thereby forming an image on the original surface. The image is read. The three-line CCD 111 is supplied with a driving clock for each line by a timing circuit 112 on the scanner IPU control unit, and receives red, green,
The emitter followers 113 to 115 convert analog image signals of blue (hereinafter, referred to as “R”, “G”, and “B”) odd-numbered fields (hereinafter, referred to as “odd”) and even-numbered fields (hereinafter, referred to as “even”). Output to The analog outputs from the emitter followers 113 to 115 are input to analog processing circuits 116 to 118, respectively, where the subtraction method CDS is executed in the analog processing circuits, and the line clamp is performed by detecting the optical black portion of the CCD.
Each amplifier gain is adjusted to correct so that the output difference of ven disappears. After the gain adjustment, the signals are synthesized by the multiplexer, and finally, after the DC level offset adjustment (detailed in the operation of the phase adjustment mode described later), R,
The G and B signals are input to respective A / D converters (hereinafter referred to as [ADC]) 119 to 121 for RGB.

R input to ADCs 119 to 121,
The G and B analog signals are digitized and input to the shading correction circuit 122. The shading correction circuit 122 has a function of correcting non-uniform light amounts of the illumination system and variations in the pixel output of the CCD. For this purpose, as shown in detail in FIG. 12, a shading operation circuit 122a and a white memory 12 for storing data used for the operation are provided.
2b and a black memory 122c. The data stored in the white memory 122b is obtained by reading the reference white plate, and the data stored in the black memory 122c is obtained by reading when there is no illumination. The shading correction circuit 122 has a bus I / F 122d and a register setting unit control circuit 122e for operating data in the circuit. The image data subjected to the shading correction is input to the inter-line correction memories 123 and 124, and the image data of the B, G, and B and R lines of the three-line CCD 111 is delayed by the memory to read the B, G, and R read image signals. Dot correction circuit 1 that aligns one or more lines
25. The dot correction circuit 125 corrects the dot deviation of the image data output from the inter-line correction memories 123 and 124 within one line of R, G, and B data. Next, the scanner linear correction 126 corrects the linear reflectance data for each color using a look-up table method.

The corrected image data is input to an RGB filter / color conversion process / magnification process / create process circuit 130 via an automatic document color judgment circuit 128, an automatic image separation circuit 129 and a delay memory 127. Routes and image data memories 133 for R, G, and B
The route is divided into the second routes input to 134 and 135. The image data memories 133, 134, and 135 store image data of the maximum reading area of the scanner for each of R, G, and B.
It is composed of a RAM, and it is also possible to take in each image data of R, G, B in one scan, and output from here at the time of full color superimposed image output or at the time of repeat copying.
Return to the root so that you can handle this mode. The automatic document color determination circuit 128 uses ACS (chromatic /
Achromatic determination) processing, that is, determination of black and gray is performed. In the automatic image separation circuit 129, edge determination (determined by the continuity of white pixels and black pixels), halftone dot determination (determined by a repeated pattern of peak / valley peak pixels in an image), and photo determination (character / halftone dot) (When there is image data outside), the area of the character and print (halftone) portion and the photo portion is determined and transmitted to the CPU 101, and the RGB filter, color conversion,
Used for switching parameters and coefficients in printer γ correction, YMCK filter, and gradation processing.

The R, G, B image data that has passed through the delay memory 127 is input to an RGB filter of an RGB filter, a color conversion process, a scaling process, and a create processing circuit 130. The RGB filter performs processing such as MTF correction of R, G, and B, smoothing, edge enhancement, and through by switching and setting the filter coefficient according to the determination result of the previous area. In the subsequent color conversion processing circuit, the R, G, B data is converted to YM
CK conversion, UCR and UCA processing are executed. Further, the image data input to the scaling processing circuit is enlarged /
Execute the reduction process. After this processing, the image data is branched, and a part of the branched image data is input to the image display unit 132 via the I / F. By doing so, the read image is displayed on the image display unit 13 of the digital color copying machine.
2 can be displayed on the LCD panel (see FIG. 3) and the reading result can be monitored. The create processing circuit performs create editing and color processing. In the create edit, italic, mirror, shadowing, hollowing out processing and the like are executed. In color processing, processing such as color conversion, designated color erasure, and under color is performed.

The write processing circuit 131 for printer γ correction, YMCK filter, etc. sets coefficients to be used for printer γ conversion and YMCK filter based on the determination of the previous area. In the gradation process included in the writing process, a dither process is executed, and in the video control, a writing timing setting, an image region, a white region setting, a test pattern generation such as a gray scale and a color patch can be performed,
It is processed so that it can be output to an LD (laser diode) in the writing processing of the final image data, and is output to the LD. The execution of each of the above-described functional processes is performed by performing the setting and operation of each process according to an instruction of the system control unit 104 using a program stored in the ROM 102 connected to the CPU 101.

Here, the processing system of the photoelectric conversion processing of the read image by the three-line CCD and the analog processing of the image signal, which are the parts which are deeply related to the present invention, in the scanner IPU control unit in the color image reading of the above-described embodiment are described in detail. Will be described. FIG. 12 is a block diagram of such a processing system for the read image signal, and shows a part of the processing system shown in FIGS. The same components as those shown in FIGS. 10 and 11 are denoted by the same reference numerals. Referring to FIG. 12, the operation of the processing system will be described focusing on the control operation using the spread spectrum clock as the operation clock signal according to this embodiment. The spread spectrum clock is generated by inserting a spread spectrum clock generator (hereinafter, referred to as “SSG”) 137 between the reference clock oscillator 136 and the timing circuit 112. Timing generation circuit 11
In step 2, a timing pulse signal including all operation clocks used in the image signal processing system is generated in synchronization with the clock generated by the SSG 137 and input to each circuit. The SSG 137 used here is the reference clock oscillator 1
The frequency modulation is carried out on the clock inputted from 36 within a predetermined spectrum range.

Here, as an example of frequency modulation, a conventional spread spectrum clock generation IC S
SFTG (Spread Spectrum Frequency Timing Generat)
ion) W180. The W180 modulates the frequency (period) of the reference clock within the range of ± 1% (Fis in manual P.4 of SSFTG W180).
gure4). The modulation frequency fm is obtained by the following equation. Assuming that the reference clock frequency is 17.5 MHz, fm = 31 × (reference clock frequency / 16) = 33.9.
06 kHz Tm = 1 / fm = 29.493 μS With this modulation method, the output of the PLL inside the spread spectrum clock generator 137 is modulated, and the peak value is attenuated by spreading the band of the tuned clock signal. The decay rate of the peak value is obtained by the following equation depending on the order of harmonics and the degree of modulation. dB = 6.5 + 9.1 log10 (P) +9.1 log
10 (F) P = percentage of diffusion (%), F = frequency at which attenuation was measured (M
Hz) As described above, the higher the frequency is, the larger the diffusion ratio is, the larger the attenuation effect becomes.

SSG 137 by SSFTG W180
When the is used in a reading system, the following phenomenon occurs. Each clock of the CCD system (φ1, φ2, φ1L, φCLB, φRB, φTG) from the timing circuit 112,
Analog processing system clocks (SHP, SHD, SDE
2, MPX, CLP, etc.), an ADC clock, and an IPU clock (ICLK, LSYNC, etc.) are supplied to each block. In a digital circuit with a synchronization circuit, a clock modulated by the SSG 137 with respect to a reference clock is input to the timing circuit 112, so that all synchronization is achieved, and the setup time and the hold time for the clock signal may be impaired. There is no operational problem. On the other hand, in the analog circuit, in the analog output section, there is no problem if the signal output portion can maintain a sufficient flatness. This generally becomes more difficult as the operating frequency increases. The reason is that although the analog signal and the sampling clock are synchronized, if the sampling point has an inclination, the sample value slightly changes. In particular, the output of the 3-line CCD 111 and the internal signals of the analog processing circuits 116 to 118 are affected by clock noise and the like, and periodic noise depending on the modulation frequency of the spread clock is generated.

With respect to the generation of periodic noise depending on the modulation frequency of the spread clock, an analog signal is input from the three-line CCD 111 to the analog processing circuits 116 to 118 via the emitter followers 113 to 115, and the SHD
(Sampling and holding) The phenomenon will be described below, taking as an example the case of sampling with a clock signal. FIG.
3A is a diagram for explaining sampling of a pixel signal at the black output of the three-line CCD 111, and FIG.
The relationship between the CCD output and the SHD clock is shown in FIG.
Is an enlarged view of the sampling point and the reference frequency ± 1.
5 shows a fluctuation range of a sampling point when modulating with a% width. In the drawing, the clock cycle becomes longer.
In other words, the direction in which the frequency decreases becomes +. In order to simplify the description, a case will be described in which the output portion monotonically decreases within the range of the sampling point as shown in FIG. In this case, the image data takes the MIN value when it fluctuates by + 1% with respect to the sampling point of the reference frequency, and takes the MAX value when it fluctuates by -1%. The data has a noise component that fluctuates periodically.

The above described periodically fluctuating noise will be described. FIG. 14 is a diagram illustrating image noise for each line in order to explain a situation in which streak-like noise occurs in an image due to a periodically varying noise component. FIG. 14 shows how noise due to the modulation frequency moves line by line. A peak indicates a bright part where image data is high, and a valley indicates a dark part where image data is low, and fluctuates between the MAX value and the MIN value in FIG. A horizontal broken line on each line indicates a DC level set for each line by a CLP clock (line clamp signal). The magnitude of the image data output of each line is determined by the difference from the horizontal broken line. In FIG. 14, the image data becomes higher as the arrow of the mountain portion is longer, resulting in image noise. In this case, the phase of the modulation frequency is not synchronized with CLP, LSYNC (main scanning line synchronization signal), and φTG (CCD transfer gate clock) (not shown). When the phase shifts from line to line, the image noise becomes periodic and appears as streak-like noise.
When no modulation (no diffusion) is performed, the black output is processed, so that the image data does not have a periodic fluctuation as shown in FIG. 14 and the phase shifts for each line. Since there is no noise, no streak noise occurs.

The above-mentioned image noise is generated when the sampling point of the analog output shifts due to the frequency modulation of the SSG 137.
It is believed to depend on 37 modulation profiles. The modulation profile of SSG 137 currently used in copiers is described in the manual P.S. 4 has a shape substantially similar to a triangular wave, as shown in FIG. In the case of a triangular wave, since the waveform changes rapidly, the generated noise also changes abruptly, giving a stimulus to vision, and the noise is clearly recognized. According to the present invention, the modulation profile for spread spectrum of the reference clock is not changed so that the image noise is reduced by reducing the stimulus to the visual sense. Image noise is reduced by using the SSG 137 that performs frequency modulation.

To confirm this, simulations were performed for the case where the modulation profile of the SSG was a triangular wave and the case where the modulation profile was a sine wave. The simulation was performed for one line on the assumption that noise fluctuation due to SSG occurs between gradations 100 to 150 when the modulation profile of SSG is triangular and sinusoidal. The results are shown in FIG. 21 (for a triangular waveform) and FIG. 22 (for a sine waveform). Since the triangular modulation profile shown in FIG. 21 changes sharply, the streak is clearly visible, and the sinusoidal modulation profile shown in FIG. 22 is less clear and has been improved. You can see that.

An SSG provided with a means for setting a sinusoidal modulation profile can be implemented as follows. FIG. 15 is a block diagram illustrating a basic configuration of the SSG according to the present embodiment. A method is adopted in which a fluctuation value for providing a sinusoidal modulation profile for reducing EMI is stored in advance in the ROM 85 shown in FIG. 15, and the value is read out according to the modulation cycle. As the operation of the circuit, as shown in FIG. 15, the sum of the signal representing the frequency value of the reference clock obtained via the PLL 80 and the analog signal of the DAC 84 which outputs the signal corresponding to the fluctuation value read from the ROM 85 is obtained. VC obtained through means 81
The frequency of the output is changed as an input to the O 82, that is, the frequency of the reference clock is modulated by the fluctuation value stored in the ROM 85, and is output to the SSG through the buffer 83. As described above, the modulation profile can be set by storing the predetermined fluctuation value in the ROM 85. Further, the modulation profile can be adjusted by setting the modulation profile variably.
If the adjustment is performed using G137 so that the streak is most inconspicuous, the generated streak-like noise can be reduced under optimal conditions. FIG. 16 is a block diagram showing an example of the configuration of an SSG in which a modulation profile can be variably set. As shown in FIG. 16, in order to enable the modulation profile to be changed, a RAM 86 is used as a storage device instead of the ROM 85 in the configuration of FIG. The SSG of FIG. 16 is not different from FIG. 15 except this point. By using a RAM, a plurality of profile data giving different profiles can be prepared without fixing the data stored in the RAM 86, and an image with less noticeable image noise can be obtained from among them.
Profile that gives optimal conditions that can also be reduced. This operation is performed by the CPU 1 of the image reading apparatus rewriting the data in the RAM 86 with the value selected as the modulation profile that gives the optimum condition.

At this time, different modulation profiles are prepared for the sinusoidal modulation profile provided for reducing image noise by changing the period, changing the amplitude, or changing both the period and the amplitude. I do.
In the case of a method in which the period is changed, a profile in which several different periods are combined with one unit of the modulation profile is used, and by using this profile, the period varies and the periodic image noise can be made inconspicuous. In the case of a method of changing the amplitude, a profile in which several different amplitudes are combined with a modulation profile of one unit is used. By using this profile, the level of the image noise varies, so that the image noise is made inconspicuous. Becomes possible. 17 to 20 exemplify the modulation profiles when the period and the amplitude as the variable elements are changed. FIG. 17 shows a case where one profile has two different periods of the modulation profile. In this example, the amplitudes are made equal. FIG. 18 shows a case where two different amplitude modulation profiles are provided in one profile, and the paired upper and lower amplitudes in one cycle are equalized. In this example, the periods are made equal. FIG. 19 shows a configuration in which two different amplitude modulation profiles are provided in one profile, and the upper and lower amplitudes forming a pair in one cycle are different. In this example, the periods are made equal. FIG. 20 shows a modulation profile in which two patterns having different periods and amplitudes coexist in one profile. In addition, FIG.
Other than those shown in 7 to 20, the amplitude or period of the modulation profile may be randomly varied.

As described above, the image noise can be reduced by setting the modulation profile. However, at this time, if the center of the modulation frequency changes, 1
It is also conceivable that a change in the line reading time has an effect such as occurrence of an abnormality. Here, if the center frequency is not changed, occurrence of an abnormality can be prevented. When the amplitude of the modulation profile is changed, the center frequency does not change if the upper and lower areas of the center frequency are equal within one profile.
Two cases can be considered: a case where the upper and lower amplitudes forming a pair in the cycle are equal, and a case where they are not equal as shown in FIG. SSFTG W180 for modulation profile
Manual P. 4 is the shape that can reduce the EMI at present, and the effect of reducing the EMI decreases when the shape is changed. However, the image reading apparatus has room when using the current SSG with respect to the EMI standard. In some cases, taking advantage of this margin, the above profile is changed to reduce image noise, and
The adjustment can be performed so as to satisfy the I standard.

[0036]

According to the present invention, there is provided an image reading apparatus comprising: means for generating a timing pulse for operating an image processing means based on a spread spectrum clock output from the clock generating means. By making the modulation profile for generating the spread spectrum clock into a sinusoidal waveform, it is possible to make the streak noise generated in the image inconspicuous while reducing the harmonic component due to the operation pulse. (2) Effects corresponding to the inventions of claims 2 and 3 In addition to the effects of the above (1), by changing the period, amplitude, or both the period and the amplitude of the sinusoidal modulation profile, and changing the profile, It is possible to provide a means capable of easily and effectively implementing the invention of claim 1. (3) Effects corresponding to the fourth aspect of the invention In addition to the effect of the above (2), an image with less noise can be obtained by determining the modulation profile so that the center frequency of the spread spectrum does not change. it can. (4) Effects corresponding to the fifth aspect of the invention In addition to the effects of the above (2) and (3), the modulation profile can be adjusted so that the sinusoidal modulation profile can be adjusted so that image noise is most inconspicuous. The adjustment can be performed, and an image with less noise can be obtained under the optimum conditions for the apparatus. (5) Effect corresponding to the invention of claim 6 In addition to the effect of the above (4), the adjustment of the sinusoidal modulation profile is performed by rewriting the data in the RAM, thereby facilitating the invention of claim 5. In addition, a means that can be effectively implemented can be provided. (6) Effects corresponding to the invention of claim 7 By using the image reading apparatus according to any one of claims 1 to 6 as a component of an image processing apparatus, the effects of the above (1) to (5) can be obtained. Realized in an image processing device,
The performance of the device can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing an outline of an overall configuration of a digital color copying machine capable of suitably implementing an image reading apparatus of the present invention.

FIG. 2 is a diagram showing an example of an operation panel of an operation unit of the digital color copying machine shown in FIG.

FIG. 3 is a functional block diagram showing a circuit configuration of an image display unit of the digital color copying machine shown in FIG.

FIG. 4 is a view showing one embodiment of an LCD panel of the image display unit shown in FIG. 3;

FIG. 5 is a diagram showing an example of a screen displayed on the LCD panel shown in FIG.

FIG. 6 shows an example of screen expansion by pressing a scaling key on the screen shown in FIG.

FIG. 7 is a diagram illustrating an example of a configuration of a touch panel detection circuit.

FIG. 8 shows X and Y of the touch panel in the detection circuit of FIG. 7;
This shows the setting state of the potential of each electrode.

9 is a functional block diagram showing an example of a circuit configuration of an operation unit of the digital color copying machine shown in FIG.

FIG. 10 is an overall block diagram (part 1) mainly showing a read image signal processing system and a scanner control system of the color image reading apparatus to which the present invention is applied.

FIG. 11 is an overall block diagram (part 2) mainly showing a read image signal processing system and a scanner control system of the color image reading apparatus to which the present invention is applied.

FIG. 12 is a block diagram of a processing system of a read image signal in the image reading apparatus to which the present invention is applied.

13A and 13B are diagrams for explaining sample and hold of a pixel signal at a black output of a CCD. FIG.
(B) shows the variation range of the sampling point during frequency modulation.

FIG. 14 is a diagram illustrating an image signal for each line and illustrating a situation in which periodic streak noise occurs in an image.

FIG. 15 is a block diagram illustrating a basic configuration of an SSG.

FIG. 16 is a block diagram showing a configuration of an SSG capable of changing a modulation profile.

FIG. 17 shows an example of an SSG modulation profile having two different period profiles.

FIG. 18 shows an example of an SSG modulation profile having two different amplitude profiles.

FIG. 19 shows another example of an SSG modulation profile with two different amplitude profiles.

FIG. 20 shows an example of an SSG modulation profile having two patterns with different periods and amplitudes.

FIG. 21: SSG with a modulation profile of a triangular waveform
3 shows a simulation image in the case of.

FIG. 22: SSG with modulation profile of sinusoidal shape
3 shows a simulation image in the case of.

[Explanation of symbols]

101: CPU, 104: System control unit, 105: Operation display unit, 111: 3 lines C
CD, 112: timing circuit, 116 to 118: analog processing circuit (for R, G, B), 119 to 121: ADC (A / D converter) (R,
G, B), 136: Reference clock oscillator, 137: Spread spectrum clock generator.

Claims (7)

[Claims] An image processing means including at least one of a line image sensor, an AD converter for converting an image signal output from the line image sensor into digital data, and a spectrum spread by frequency-modulating a reference clock with a predetermined modulation profile. An image reading apparatus comprising: clock generating means for generating a clock; and means for generating a timing signal for operating the image processing means based on a clock output from the clock generating means, wherein the image reading apparatus generates the spread spectrum clock. An image reading device, wherein the modulation profile for causing the image to be read is sinusoidal. 2. The image reading apparatus according to claim 1, wherein the modulation profile includes sine waves of different periods. 3. The image reading apparatus according to claim 1, wherein the modulation profile includes sine waves having different amplitudes. 4. The image reading apparatus according to claim 2, wherein the sinusoidal modulation profile is determined so that the center frequency of the spread spectrum does not change. 5. The image reading apparatus according to claim 1, wherein the sinusoidal modulation profile is adjustable. 6. The image reading apparatus according to claim 5, wherein the adjustment of the sinusoidal modulation profile is performed by a RAM.
An image reading apparatus characterized by rewriting data into the image reading apparatus. 7. An image processing apparatus comprising the image reading device according to claim 1.