JP2006229644A - Image reading apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology of reducing a radiation noise level while minimizing production of image noise. <P>SOLUTION: The image reading apparatus is configured to include a timing signal generating section for generating a timing signal to control operations of a CCD sensor and an image data processing section. The timing signal generating section includes: a first frequency spread circuit 161 for applying frequency spread processing to a reference clock generated from a source oscillator 160 at a first spread rate; a second frequency spread circuit 162 for applying frequency spread processing to the reference clock at a second spread rate; a first timing generating circuit 163 for generating a first timing signal to control operations of a color image data processing system by using the first frequency spread clock; and a second timing generating circuit 164 for generating a second timing signal to control operations of a black/white image data processing system by using the second frequency spread clock. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image reading apparatus such as an image scanner.

  In recent years, image reading apparatuses have been required to improve productivity and resolution, and in order to meet these demands, document image reading operations tend to increase in speed. Such a high-speed trend becomes a factor that increases radiation noise such as electromagnetic interference (EMI) from the image reading apparatus. Therefore, it is necessary for the image reading apparatus to take measures against radiation noise in conjunction with the speeding up of the reading operation.

  Frequency spread technology is used as a countermeasure against radiation noise. In the frequency spread technique, by periodically modulating the clock oscillation frequency, the radiation noise is prevented from concentrating on a specific frequency, and the radiation noise level (peak value) is apparently reduced. However, when the frequency spread technology is adopted in an analog processing system circuit including a CCD (Charge Coupled Device), the frequency cycle of the main scanning line and the frequency spread become non-synchronized as shown in FIG. There has been a problem that beat noise (diagonal stripes) corresponding to the period of the image is generated in the image.

  Therefore, Patent Document 1 below describes a technique for reducing apparent noise by changing a diagonal line to a vertical line by synchronizing a main scanning line period and a frequency spreading period. Patent Document 2 below describes a technique for reducing radiation noise by using a reference clock for an analog processing system including a CCD and using a frequency spread clock for a digital processing system.

JP 2003-8845 A JP 2001-94734 A

  However, the technique disclosed in Patent Document 1 requires a means for resetting the frequency spreading cycle for each main scanning line cycle or generating the main scanning line cycle for each frequency spreading cycle. As a result, the apparatus configuration is significantly changed and the cost is increased.

  In addition, the technique described in Patent Document 2 has a drawback that radiation noise cannot be sufficiently reduced because a reference clock is used for an analog processing system. In particular, the radiation noise from the analog processing system around the CCD is conspicuous in the configuration of the image reading apparatus, and in some cases it is also the largest noise radiation source. Therefore, the technology using the frequency spread clock only for the digital processing system is sufficient. Cannot be expected.

  An image reading apparatus according to the present invention includes an image reading sensor for reading an image of a document, image data processing means for processing image data read by the image reading sensor, and operations of the image reading sensor and the image data processing means. The image reading sensor includes a color image reading sensor unit and a monochrome image reading sensor unit, and an image data processing unit. The first image data processing means for processing the color image data read by the color image reading sensor unit and the second image data for processing the black and white image data read by the sensor unit for black and white image reading And a timing signal generating means for generating a reference clock, and a first signal for frequency-spreading the reference clock at a first spreading factor. Using a wave number spreading means, a second frequency spreading means for frequency spreading the reference clock at a second spreading factor, and a first frequency spreading clock frequency spread by the first frequency spreading means, a color image reading A first generation unit that generates a first timing signal for controlling operations of the sensor unit and the first image data processing unit, and a second frequency spread clock that is frequency-spread by the second frequency spread unit are used. And a second generation unit that generates a second timing signal for controlling the operation of the monochrome image reading sensor unit and the second image data processing unit.

  In the image reading apparatus according to the present invention, the operation of the color image reading sensor unit and the first image data processing means for processing the color image data is obtained by frequency spreading the reference clock with the first spreading factor. Control is performed according to a first timing signal generated using the first frequency spread clock. The operation of the monochrome image reading sensor unit and the second image data processing means for processing the monochrome image data uses the second frequency spread clock obtained by frequency spreading the reference clock with the second spreading factor. Control is performed according to the second timing signal generated in this manner.

  According to the image reading apparatus of the present invention, when applying the frequency spreading technique, a spreading factor suitable for a color image data processing system including a color image reading sensor unit and a first image data processing unit, and a monochrome image reading The color image data and the monochrome image data can be processed in different systems by separately setting diffusion rates suitable for the monochrome image data processing system including the sensor unit and the second image data processing means. Therefore, by selecting optimum diffusion rates for color / monochrome, it is possible to reduce the radiation noise level while minimizing the occurrence of image noise.

  FIG. 1 is a schematic diagram showing the configuration of an image reading apparatus to which the present invention is applied. The illustrated image reading apparatus 1 includes a document pressing unit 3 with an automatic document feeder (ADF) that automatically feeds a document 2 to be processed to a preset document reading position. The document pressing unit 3 is supported on the apparatus main body 4 so as to be opened and closed by a hinge mechanism or the like, and is opened and closed by a user. A platen glass 5 serving as a document table is provided on the upper surface of the apparatus body 4. The document 2 to be processed is set (placed) on the platen glass 5.

  On the other hand, an optical scanning system that optically reads an image of a document is incorporated in the apparatus main body 4. This optical scanning system includes a full rate carriage 6, a half rate carriage 7, an imaging lens 8, and a CCD sensor 9. A lamp 10 and a first mirror 11 are mounted on the full rate carriage 6, and a second mirror 12 and a third mirror 13 are mounted on the half rate carriage 7. As the lamp 10, a halogen lamp or a xenon lamp is used.

  These carriages 6 and 7 are moved in the sub-scanning direction (left-right direction in the figure) using a common carriage moving motor as a drive source. At this time, the half-rate carriage 7 moves with a movement amount that is 1/2 that of the full-rate carriage 6, so that the carriage 6, 7 moves to any position in the sub-scanning direction from the document surface to the CCD sensor 9. The optical path length is always kept constant.

  On the other hand, the lamp 10 emits light toward the surface to be read of the document 2, and the reflected light from the document surface is sequentially reflected by the first mirror 11, the second mirror 12 and the third mirror 13. The imaging lens 8 forms an image of the light reflected by the third mirror 13 on the imaging surface of the CCD sensor 9 at a predetermined reduction magnification. The CCD sensor 9 is an image reading sensor for reading an image of a document. The CCD sensor 9 generates analog image data corresponding to the image of the document by photoelectrically converting the reflected light from the document in units of pixels.

  FIG. 2 is a block diagram showing a control configuration of the image reading apparatus to which the present invention is applied. In FIG. 2, the image data generated by the CCD sensor 9 is taken into the analog processing unit 14. The analog processing unit 14 performs analog processing on the image data input from the CCD sensor 9, and is configured using, for example, a sample and hold circuit, an AGC (automatic gain control) circuit, an AOC (automatic offset control) circuit, and the like. The The image data analog-processed by the analog processing unit 14 is converted from an analog value into digital multi-value information by an A / D conversion circuit.

  The image data thus A / D converted is given to the image processing unit 15. The image processing unit 15 performs various kinds of image processing (for example, shading correction, gap correction between CCD read pixel columns, color conversion, color correction, gradation correction, enlargement / reduction, screen generation, etc.) on given image data. Is to do. The image data processing system from the analog processing unit 14 to the image processing unit 15 corresponds to image data processing means for processing image data read by the CCD sensor (image reading sensor) 9.

  The timing signal generator 16 generates a timing signal (operation clock) for individually controlling the operations of the CCD sensor 9, the analog processor 14, and the image processor 15. More specifically, the timing signal generation unit 16 is a timing signal for driving the CCD sensor 9 (sensor drive clock), a timing signal for analog processing by the analog processing unit 14 (analog processing clock), and image processing. A timing signal (image processing clock) for image processing in the unit 15 is generated.

The main control unit 17 is configured by, for example, a CPU (Central Processing Unit) and the like, and reads out a control program stored in a ROM (Read-Only Memory) 18 to a RAM (Random Access Memory) 19 and executes the image, thereby executing an image. It controls overall processing operations of the reader. Detection signals from various sensors 20 are input to the main control unit 17 as state information in the apparatus itself. The various sensors 20 include, for example, a sensor that detects the open / close state of the document pressing unit 3 and a sensor that detects a document transport position by an automatic document feeder. The ADF control unit 21, the illumination control unit 22, and the scanning control unit 23 control the operation of the control target unit in accordance with instructions and commands from the main control unit 17, respectively. That is, the ADF control unit 2
1 controls the operation of the automatic document feeder installed in the document holding unit 3 described above, and the illumination control unit 22 controls the on / off (lighting and extinguishing) of the lamp 10 mounted on the full-rate carriage 6 described above. The scanning control unit 23 controls the rotation operation of a carriage moving motor (stepping motor or the like) 24.

  In the image reading apparatus configured as described above, for example, when the user sets (places) the document 2 on the platen glass 5 and closes the document pressing unit 3, the user presses a start button provided on an operation panel (not shown). In response to this, the main control unit 17 instructs the scanning control unit 23 to start scanning and drives the motor 24 to move the carriages 6 and 7 in the direction of the arrow in FIG. The unit 22 is instructed to turn on the lamp to turn on the lamp 10. As a result, the image of the document is optically read and scanned by the mirrors 11, 12, 13, the imaging lens 8 and the CCD sensor 9 by moving the carriages 6 and 7 while irradiating the light of the lamp 10 on the document surface. .

  When the user places a document on the document tray of the automatic document feeder and presses the start button, the main control unit 17 receives the instruction and instructs the ADF control unit 22 to start document feeding. By driving the feeding device, the documents are fed one by one from the document tray, and the documents are conveyed to a second document table (not shown) provided separately from the platen glass 5. At this time, the first mirror 6 is arranged in advance by the movement of the carriages 6 and 7 below (substantially directly below) the second document table, and the document fed by the automatic document feeder in this state is placed on the second document table. The image of the original is read and scanned by the optical scanning system while being moved by. Such a document image reading method is also called a continuous reading (CVT) method.

  FIG. 3 is a block diagram showing the internal configuration of the timing signal generator 16. As illustrated, the timing signal generator 16 includes a source oscillator 160, a first frequency spread circuit 161, a second frequency spread circuit 162, a first timing generation circuit 163, a second timing generation circuit 164, a third The timing generation circuit 165 and the selector 166 are provided.

  The source oscillator 160 generates a reference clock having a constant frequency, and is configured using, for example, a crystal oscillator or a crystal oscillator. The first frequency spreading circuit 161 generates a first frequency spreading clock by frequency spreading the reference clock generated by the source oscillator 160 with a first spreading factor. The second frequency spreading circuit 162 generates a second frequency spreading clock by frequency spreading the reference clock generated by the source oscillator 160 with the second spreading factor.

  As shown in FIG. 4, the frequency spreading means that the frequency of the reference clock input from the source oscillator 160 is used as a reference frequency, and the clock frequency is changed continuously (stepwise) with a constant spreading period. A process of spreading a specific frequency band of a clock around a reference frequency. The spreading factor defines the degree of frequency spreading (strength) applied when the reference clock is spread, and as shown in FIG. 5, the spreading rate when the reference clock is spread is large. When the case is small and the case is small, the effect of reducing the EMI noise level is greater when the spreading factor is large than when the diffusion rate is small. Therefore, in the present embodiment, the first spreading factor is the second spreading factor as a magnitude relationship of spreading factors applied when the first frequency spreading circuit 161 and the second frequency spreading circuit 162 spread the reference clock. Or less.

  The first timing generation circuit 163 uses the first frequency spread clock frequency-spread by the first frequency spread circuit 161 to use the first sensor drive clock φS1, the first analog processing clock φA1, and the first write. The clock φM1 is generated. The clocks φS1, φA1, and φM1 generated by the first timing generation circuit 163 correspond to the first timing signal. The second timing generation circuit 164 uses the second frequency spread clock frequency-spread by the second frequency spread circuit 162 to use the second sensor drive clock φS2, the second analog processing clock φA2, and the second write. The clock φM2 is generated. Clocks φS2, φA2, and φM2 generated by the second timing generation circuit 164 correspond to the second timing signal.

  The third timing generation circuit 165 generates a third write clock φM3 without frequency spread using the reference clock generated by the source oscillator 160. The “third write clock without frequency spread” refers to a write clock generated using the reference clock as it is without performing frequency spread. Therefore, the third write clock φM3 is a clock having a constant frequency, like the reference clock. However, the frequency of the reference clock and the frequency of the third write clock are not necessarily the same frequency.

  The selector 166 includes a first write clock φM1 generated by the first timing generation circuit 161, a second write clock φM2 generated by the second timing generation circuit 162, and a third timing generated by the third timing generation circuit 165. Are used as input clocks, and one of these input clocks is selected and output as an image processing clock.

  FIG. 6 is a block diagram showing the internal configuration of the CCD sensor 9, the analog processing unit 14, and the image processing unit 15. In the figure, a CCD sensor 9 is configured using a CCD sensor having a four-line configuration having four read pixel rows in which light receiving cells such as photodiodes are arranged in a straight line. More specifically, the CCD sensor 9 includes a color image reading sensor unit 91 composed of three read pixel rows each having R, G, and B spectral sensitivity characteristics, and a single monochrome spectral sensitivity characteristic. And a sensor unit 92 for reading black-and-white images composed of a read pixel row. The color image reading sensor unit 91 is driven in accordance with the sensor drive clock φS1 generated by the first timing generation circuit 163, and the monochrome image reading sensor unit 92 is generated by the second timing generation circuit 164. It is driven in accordance with the sensor drive clock φS2.

  The color image reading sensor unit 91 is a main sensor part in a color mode applied when a document to be read is read as a color document (in other words, an image of the document is read as a color image). The monochrome image reading sensor unit 92 is a main sensor portion in a monochrome mode applied when a document to be read is read as a monochrome document (in other words, an image of a document is read as a monochrome image). Therefore, when reading an image of a document in the color mode, the color image data read by the sensor unit 91 for reading a color image is adopted as a reading result of the document image, and when reading an image of the document in the monochrome mode, The monochrome image data read by the image reading sensor unit 92 is adopted as a document image reading result. However, the original image is read by both the color image reading sensor unit 91 and the monochrome image reading sensor unit 92 regardless of whether the color mode or the monochrome mode is applied.

  Among the image data read by the CCD sensor 9, color image data (R, G, B) read by the color image reading sensor unit 91 and a monochrome image read by the monochrome image reading sensor unit 92. The data (BW) is input to the analog processing unit 14, respectively. The analog processing unit 14 includes a first analog processing circuit 141 and a second analog processing circuit 142. The first analog processing circuit 141 performs analog processing in accordance with the first analog processing clock φA1 generated by the first timing generation circuit 163, and the second analog processing circuit 142 includes the second timing generation circuit 164. The analog processing is performed in accordance with the second analog processing clock φA2 generated in step S2. Further, the first analog processing circuit 141 performs color processing on the color image data read by the color image reading sensor unit 91 to generate color image data corresponding to each color component of RGB, and the second The analog processing circuit 142 generates monochrome image data by performing analog processing on the monochrome image data read by the sensor unit 92 for reading monochrome images.

  The color image data generated by the first analog processing circuit 141 is written in the first line memory 25. In addition, the monochrome image data generated by the second analog processing circuit 142 is written in the second line memory 26. Color image data is written in the first line memory 25 in accordance with the first write clock φM1 generated by the first timing generation circuit 163, and the second timing generation is performed in the second line memory 26. Monochrome image data is written in accordance with the second write clock φM2 generated by the circuit 164. Further, the color image data written in the first line memory 15 and the monochrome image data written in the second line memory 16 are read according to the image processing clock output from the selector 166.

  On the other hand, the reading of the image data from the respective line memories 25 and 26 is performed according to the image processing clock output from the selector 166. Further, the image data read from each of the line memories 25 and 26 is taken into the image processing unit 15. The image processing unit 15 performs image processing according to the image processing clock output from the selector 166. The image processing unit 15 includes a first shading correction circuit 151, a second shading correction circuit 152, a first gap correction circuit 153, a second gap correction circuit 154, and a black as a part of various image processing circuits. A streak correction circuit 155 is provided.

  The first shading correction circuit 151 performs shading correction of the color image data read from the first line memory 25, and the second shading correction circuit 152 reads from the second line memory 26. The shading correction of the monochrome image data that has been performed is performed. The first gap correction circuit 153 performs gap correction on the color image data subjected to the shading correction by the first shading correction circuit 151. The second gap correction circuit 154 includes the second shading correction circuit. The gap correction of the black and white image data subjected to the shading correction in 152 is performed.

  The black stripe correction circuit 155 uses the color image data that has been gap-corrected by the first gap correction circuit 153 and the black and white image data that has been gap-corrected by the second gap correction circuit 154 to correct black stripes. The processing is performed. A black streak is a foreign object (dust, scratch, etc.) at the reading position (position where the original image is read) set on the second original platen when the original image is read by the flow reading method. This is streak-like image noise that occurs when the foreign matter is continuously read by the optical scanning system. Foreign matter (foreign matter causing black streaks) present at the reading position is not read by both the color image reading sensor unit 91 and the monochrome image reading sensor unit 92.

  Therefore, in the black stripe correction circuit 155, the image data read by one of the sensor unit 91 for color image reading and the sensor unit 92 for black and white image reading has a stripe-like shape having a density level higher than a predetermined level. When a line image (line image along the sub-scanning direction) is detected and the same line image is not detected in the image data read by the other sensor unit at the same position as the line image, this line image is By extracting the black stripe as a black stripe and replacing the pixel value corresponding to the black stripe portion with the pixel value corresponding to the background density of the original or the pixel value corresponding to the original image density of the original, Remove as image noise. The image data corrected by the black streak correction unit 155 is given to the image processing circuit subsequent to the black streak correction circuit 155.

  In the image reading apparatus described above, the color image data read by the color image reading sensor unit 91 is analog processed by the first analog processing circuit 141 and then written in the first line memory 25. The monochrome image data read by the sensor unit 92 for reading monochrome images is analog-processed by the second analog processing circuit 142 and then written to the second line memory 26. At this time, the color image reading sensor unit 91 is driven in accordance with the first sensor driving clock φS1 generated from the first timing generation circuit 163, and the monochrome image reading sensor unit 92 is driven at the second timing. Driving is performed according to the second sensor drive clock φS2 generated from the generation circuit 164. Also, the color image data writing operation to the first line memory 25 is performed according to the first writing clock φM1 generated from the first timing generation circuit 163, and the monochrome image to the second line memory 26 is obtained. The data write operation is performed in accordance with the second write clock φM2 generated from the second timing generation circuit 164.

  Thus, the color image data written in the first line memory 25 and the monochrome image data written in the second line memory 26 are read out to the image processing unit 15 according to the common image processing clock output from the selector 166, respectively. It is. Therefore, the read timing of color image data from the first line memory 25 to the image processing unit 15 and the read timing of monochrome image data from the second line memory 26 to the image processing unit 16 are synchronized with each other. . The color image data read from the first line memory 25 is subjected to shading correction by the first shading correction circuit 151 and then subjected to gap correction by the first gap correction circuit 153. The black and white image data read from the second line memory 26 is subjected to shading correction by the second shading correction circuit 152 and then subjected to gap correction by the second gap correction circuit 154. The color and black and white image data subjected to the gap correction in this way are taken into the black stripe correction circuit 155, where black stripes are corrected. Such an image processing operation in the image processing unit 15 is performed according to an image processing clock output from the selector 166.

  The timing signals (φS1, φA1, φM1) generated from the first timing generation circuit 163 are obtained by frequency-spreading the reference clock generated by the source oscillator 160 by the first frequency spread circuit 161. The timing signal (φS2, φA2, φM2) generated from the second timing generation circuit 164 is generated using the frequency spread clock, and the reference clock generated by the source oscillator 160 is used as the second frequency spread circuit. This is generated using a second frequency spread clock obtained by frequency spreading at 162. The first frequency spread clock is obtained by frequency spreading a reference clock with a first spreading factor, and the second frequency spread clock is obtained by frequency spreading the reference clock with a second spreading factor. It is obtained.

  Therefore, the color image data processing system including the color image reading sensor 91, the first analog processing circuit 141, and the first line memory 25 is obtained by frequency-spreading the reference clock with the first spreading factor. It operates according to the timing signals (φS1, φA1, φM1) generated using the first frequency spread clock, and the monochrome image reading sensor unit 92, the second analog processing circuit 142, and the second line memory 26 are provided. The black-and-white image data processing system including this operates in accordance with the timing signals (φS2, φA2, φM2) generated using the second frequency spread clock obtained by frequency spreading the reference clock with the second spreading factor. become.

  Here, comparing the effect of image noise due to frequency spread between color image data and monochrome image data, color image data is subtle even if the image noise density due to frequency spread is low. Noise tends to be noticeable due to differences in color, etc., but in the case of black and white image data, if the density of image noise due to frequency diffusion does not exceed a certain level, it will be erased from the image data by binarization processing etc. Therefore, it does not remain as noise. That is, the black and white image data is less noticeable in noise than the color image data. Because of the difference in the influence of image noise due to such frequency spreading, the spreading factor (first spreading factor) of the first frequency spreading clock that is the source of the timing signal applied to the monochrome image data processing system is the color image data processing. It is desirable to set it higher than the spreading factor (second spreading factor) of the second frequency spread clock that is the source of the timing signal applied to the system.

  Thereby, in the color image data processing system, the influence of the image noise can be suppressed small by operating according to the timing signal generated using the second frequency spread clock whose frequency spreading rate is relatively low. it can. In the monochrome image data processing system, radiation noise can be greatly reduced by operating according to the timing signal generated using the first frequency spread clock having a relatively high frequency spreading factor. As a result, the color image data and the monochrome image data can be processed in different systems by separately setting the diffusion rate suitable for the color image data processing system and the diffusion rate suitable for the monochrome image data processing system. Therefore, by selecting optimum diffusion rates for color / monochrome, it is possible to reduce the radiation noise level while minimizing the occurrence of image noise. The color image data processing system can also be operated using a clock that has passed through the second frequency spreading circuit 162 or a clock that has a second spreading factor of substantially zero.

  In addition, as the configuration of the timing signal 16, the first write clock φM1 generated by the generation unit first timing generation circuit 163, the second write clock φM2 generated by the second timing generation circuit 164, and the third timing generation are generated. The selector 166 is provided with the third write clock φM3 generated by the circuit 165 as an input clock, and the selector 166 selects and outputs one of the write clocks as an image processing clock. The image processing can be performed according to the image processing clock output from. As a result, the image processing clock to be applied to the image processing unit 15 can be appropriately selected from three write clocks φM1, φM2, and φM3 having different frequency spread specifications, thereby further reducing the radiation noise level. It becomes.

  In the above embodiment, color image data is input to the first line memory 25 and monochrome image data is input to the second line memory in order to input the color and monochrome image data to the image processing unit 15 in synchronization. 26, each image data is read out to the image processing unit 15 by a common image processing clock. However, in order to realize synchronization of image data input, two line memories 25 and 26 are necessarily provided. There is no need. For example, when only the first line memory 25 is provided, the φM2 image processing clock from the first line memory 25 is synchronized with the output timing of the image data from the second analog processing circuit 142 on the side not having the line memory. By reading the image data according to the above, both image data can be synchronized and input to the image processing unit 15. Further, the line shift that occurs at that time can be corrected (absorbed) by a gap memory or the like at the subsequent stage.

  Furthermore, it is not necessary to add a new circuit by sharing (sharing) each of the line memories 25 and 26 with a mirror image inversion memory. Incidentally, the mirror image reversal memory is a memory used when reading an image of a document moving at a constant speed using an automatic document feeder (a so-called CVT method). When reading an image of a document by the flow reading method and when reading a document set on the platen glass 5, the reading position relationship of the document is reversed in the main scanning direction. Will be reversed. Therefore, when reading an image of a document by the flow reading method, the image data read by the CCD sensor is once written in the mirror image reversal memory, and then the image data is read out in the reverse order from the writing time. Prevents the original image from being reversed.

1 is a schematic diagram illustrating a configuration of an image reading apparatus to which the present invention is applied. It is a block diagram which shows the control structure of the image reading apparatus with which this invention is applied. It is a block diagram which shows the internal structure of a timing signal generation part. It is a figure explaining the principle of frequency spreading. It is a figure explaining the relationship between the spreading factor applied by frequency spreading, and the reduction level of radiation noise. It is a block diagram which shows the internal structure of a CCD sensor, an analog process part, and an image process part. It is a figure which shows the image noise produced by frequency spreading.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image reading apparatus, 2 ... Original, 9 ... CCD sensor, 14 ... Analog processing part, 15 ... Image processing part, 25 ... 1st line memory, 26 ... 2nd line memory, 91 ... For color image reading Sensor unit 92... Sensor unit for reading black and white image, 141... First analog processing circuit, 142... Second analog processing circuit, 151... First shading correction circuit, 152. ... first gap correction circuit, 154 ... second gap correction circuit, 160 ... source oscillator, 161 ... first frequency spread circuit, 162 ... second frequency spread circuit, 163 ... first timing generation circuit, 164 ... Second timing generation circuit, 165 ... Third timing generation circuit, 166 ... Selector

Claims (5)

An image reading sensor for reading an image of a document, an image data processing means for processing image data read by the image reading sensor, and a timing signal for controlling operations of the image reading sensor and the image data processing means An image reading apparatus comprising timing signal generating means for generating
The image reading sensor has a color image reading sensor unit and a monochrome image reading sensor unit,
The image data processing means includes: first image data processing means for processing color image data read by the color image reading sensor unit; and monochrome image data read by the monochrome image reading sensor unit. Second image data processing means for processing,
The timing signal generating means includes means for generating a reference clock, first frequency spreading means for frequency spreading the reference clock with a first spreading factor, and first frequency spreading the reference clock with a second spreading factor. 2 and the first frequency spread clock frequency-spread by the first frequency spread means to control the operation of the color image reading sensor unit and the first image data processing means. And a second frequency spread clock that is frequency-spread by the second frequency spread means, and the black and white image reading sensor unit and the second frequency spread clock. An image reading apparatus comprising: a second generation unit that generates a second timing signal for controlling the operation of the image data processing unit. The image reading apparatus according to claim 1, wherein the first diffusion rate is equal to or less than the second diffusion rate. A line memory for writing image data read by the image reading sensor;
The image reading apparatus according to claim 1, wherein the timing signal generating unit generates a write clock applied when writing the image data to the line memory as one of the timing signals. The line memory has a first line memory for writing the color image data and a second line memory for writing the monochrome image data,
The first generation means generates a first write clock applied when writing the color image data to the first line memory as one of the first timing signals,
The second generation means generates a second write clock applied when writing the monochrome image data to the second line memory as one of the second timing signals,
The timing signal generation means includes third generation means for generating a third write clock without frequency spread using the reference clock, the first write clock, the second write clock, and the third write clock. The image reading apparatus according to claim 3, further comprising: a selector that selects and outputs any one of the write clocks as an image processing clock including a read clock of the line memory. The image reading apparatus according to claim 3, wherein the line memory also serves as a mirror image inversion memory for inverting the positional relationship of image data in the main scanning direction.

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