Abstract:
When an image-reading module moves along and scans a glass plate of an original document bed, a flexible wiring connecting the image-reading module to a fixing point takes various shapes depending on the position of the image-reading module so as to come close to or apart from a second metallic casing of an image-reading apparatus and a first metallic casing accommodating a signal processing unit. Since insulating members are provided on the first metallic casing, a predetermined or more distance between the wiring and the surface of the first metallic casing can be always kept constant, so that an analog signal transmitting through a conductive member within the wiring can be prevented from being largely affected by changes in electrostatic capacitance.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an image-reading apparatus and an image-forming apparatus, each having an image sensor, and in particular relates to an image-reading apparatus and an image-forming apparatus, each having a contact image sensor. 
   2. Description of the Related Art 
   Recently, in response to demand for reduction in cost and electric power consumption of a light source, in addition to an image scanner using a demagnification optical system constituted of a charge coupled device (referred to below as a CCD) and a lens, which are combined therewith, a contact image sensor (referred to below as a CIS) is increasing to be used, which is constituted of a 1× magnification image-forming optical system of a distributed index lens, such as a SELFOC™ lens; and a CCD line sensor or a CMOS (complementary metal-oxide semiconductor) line sensor; which are combined therewith using a light source, such as a light-emitting diode (referred to below as an LED) or a xenon lamp. 
   For example, when an original document is read at a speed of about 25 ipm (images per minute) with a color copying machine, whereas an original document surface illuminance of about 30,000 lux is necessary for the demagnification optical system using the CCD, an examined review has been obtained in that the contact image sensor can read the sheet at the same reading speed and substantially the same S/N with an original document surface illuminance of about 3,000 lux, which is 1/10 of the above. The CIS has such an advantage. 
   The CIS also has a feature that an image scanner can be reduced in thickness, weight, and size by using the CIS. Then, in order to follow this feature, a configuration is proposed, in which signal transmission between an image-signal processing circuit board having an image-signal processing circuit for processing an image signal and the CIS is performed using analog signals. 
   When the signal transmission is performed with analog signals in such a manner, since the CIS need not have a digital circuit mounted thereon for processing an image signal, the reduction in thickness and weight is enabled. In fact, the inventor tried to mount the digital circuit on the CIS, but abandoned it because of the increase in thickness, width, and weight due to the mounting of the circuit board and components. 
   By the configuration in that a digital signal is not transferred between the CIS and an image-signal processing section, radio wave noise can be reduced. Recently, it is essential to conform to various regulations against producing radio wave noise of United State Federal Communications Committee (FCC) and Voluntary Control Council for Interference by Information Technology Equipment (VCCI), so that an examined result has been obtained in that analog transmission, which can reduce the radio wave noise, is advantageous more than digital transmission. 
   In such analog transmission, the CIS and the image-signal processing section are connected therebetween using an inexpensive flexible flat cable (referred to below as an FFC) or flexible print circuit (referred to below as an FPC), so that an image signal from the image sensor can be transmitted in an analog state. 
   On the other hand, in an image scanner section of a copying machine, in consideration of a life enduring the number of scanning times of about one million and pushing a heavy book document on a glass plate of an original document bed, it has been vital to improve the rigidity of a casing of the image-reading apparatus by making it of a metal. If the casing for accommodating the image-signal processing circuit board having the image-signal processing circuit for operating the apparatus with a high-frequency clock is made of a metal, an effect on the radio-wave noise suppression can also be brought out. Therefore, in the copying machine, wiring of the FFC or FPC and the grounded metallic casing exist together. 
   However, if the metallic casing and the wiring exist together, the capacitance between the wiring and the metallic casing varies with the movement or deformation of the wiring due to the scanning operation, so that the waveform of the analog signal changes, producing a problem. If such unnecessary changes in the waveform are generated, noise is incorporated in the image signal, resulting in unevenness and stripes in the finally produced images, which deteriorate image quality. 
   The degree of the deterioration in image quality is no longer negligible, and it is so remarkable as being visually and easily recognizable when reading a halftone chart with an optical density D of 0.3. Therefore, such deterioration in image quality significantly reduces the commodity value. 
   Such deterioration in image quality is not produced in an image scanner having a resin casing for accommodating the image-signal processing circuit board, and it is specific to an image scanner having a metallic casing. 
   SUMMARY OF THE INVENTION 
   In view of such problems, the present invention has been made, and it is an object thereof to provide an image-reading apparatus capable of improving image quality when the output of a CIS is an analog signal, and a metallic casing is used in an image-signal processing section. 
   In order to achieve the object mentioned above, in accordance with an aspect of the present invention, an image-reading apparatus according to the present invention comprises a contact image sensor for reading an image from an original document; a wiring for transmitting an image signal produced by the contact image sensor as an analog signal; an image-signal processing circuit for processing the image signal received from the wiring; a metallic casing for accommodating the image-signal processing circuit therein; and an insulating member formed on a region on the external surface of the metallic casing where the wiring might come into contact with the metallic casing. 
   In accordance with another aspect of the present invention, an image-reading apparatus according to the present invention comprises a contact image sensor for reading an image from an original document; a wiring for transmitting an image signal produced by the contact image sensor as an analog signal; an image-signal processing circuit for processing the image signal received from the wiring; a first metallic casing for accommodating the contact image sensor, the image-signal processing circuit, and the wiring therein; and a first insulating member formed on a region on the internal surface of the first metallic casing where the wiring might come into contact with the metallic casing. 
   By the structure described above, waveform deformation of an analog signal due to variations in electrostatic capacitance can be prevented with a simplified and inexpensive configuration. Thereby, unevenness and stripes produced on images corresponding to such deformation can be prevented, enabling image quality to be improved. 
   Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic sectional view of a structure of an image-forming apparatus according to an embodiment of the present invention. 
       FIG. 2  is a schematic plan view of an image scanner section  200  in the image-forming apparatus according to the embodiment of the present invention. 
       FIG. 3  is a sectional view of a structure of a CIS module  202 . 
       FIG. 4  is an exploded perspective view showing the CIS module  202 . 
       FIG. 5  is an enlarged schematic view of a color line sensor  2024  accommodated within the CIS module  202  showing its microscopic part. 
       FIG. 6  is a schematic view of the color line sensor  2024  macroscopically showing the configuration thereof. 
       FIG. 7 , which is comprised of  FIGS. 7A and 7B , is a block diagram showing the configuration of the image-signal processing section  207  in the image scanner section  200 . 
       FIGS. 8A to 8D  are schematic views showing the relationship between the movement of the CIS module  202  and the behavior of a wiring  208  when insulating members  210  and  211  are not provided. 
       FIG. 9  is a drawing showing unevenness and stripes on the images obtained when the insulating members  210  and  211  are not provided. 
       FIG. 10  is a schematic view showing a situation prior to scanning starting when the insulating members  210  and  211  are provided. 
       FIG. 11  is a drawing showing unevenness and stripes on the images obtained when the insulating members  210  and  211  are provided. 
       FIG. 12  is a timing chart showing the reading operation of an image signal in the CIS module  202 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   An image-reading apparatus and an image-forming apparatus according to an embodiment of the present invention will be specifically described below with reference to the attached drawings.  FIG. 1  is a schematic sectional view showing a structure of the image-forming apparatus according to the embodiment of the present invention; and  FIG. 2  is a schematic plan view showing an image scanner section  200  in the image-forming apparatus according to the embodiment of the present invention. 
   The image-forming apparatus according to the embodiment, as shown in  FIG. 1 , comprises the image scanner section (image-reading device)  200  for reading an original document to perform digital signal processing and a printing section (printing device)  300  for printing an image on paper in full color corresponding to the original document image read by the image scanner section  200 . 
   In the image scanner section  200 , as shown in  FIGS. 1 and 2 , a CIS module  202  is accommodated in a carriage  201  made of a resin. At both ends of the CIS module  202 , sliding members  220  and  221  are attached, respectively. The CIS module  202  is constructed so that the sliding members  220  and  221  are pushed on a glass (platen) plate  205  of an original document bed with spring members (not shown) built in the carriage  201 . On the glass (platen) plate  205  of the original document bed, an original document  204  is placed, which is pushed on the platen plate  205  by an original document pressure plate  203 . 
   The movement of the carriage  201  is restricted by a linear guide  218  so as to move only in a sub-scanning direction. To a lower part of the carriage  201 , a timing belt  219  is connected, which is looped and stretched between pulleys  216  and  217  via pulleys  214  and  215 . Around the pulley  217 , a timing belt  212  driven by a stepping motor  213  is also looped. Accordingly, the driving force of the stepping motor  213  is transmitted to the timing belt  219  via the timing belt  212  so as to move the carriage  201  in the sub-scanning direction linking it to the movement of the timing belt  219 . The operation of the stepping motor  213  is controlled by a CPU  131  (see  FIG. 7 ). 
   Wiring  208  for transmitting an analog signal produced by the CIS module  202  is connected to a connector  223  of an image-signal processing section  207  (see  FIGS. 8A to 8D ) via a cable holding member  209  made of a resin. The image-signal processing section  207  comprises a metallic casing and an image-signal processing circuit accommodated within the metallic casing. The wiring  208  is made of a conductive material and a sealing member formed on the surface of the conductive material, and the FFC or FPC may be used therefor; however, it is not specifically limited to these. According to the embodiment, insulating members  210  and  211  are arranged at least in a region where the wiring  208  may come in contact with the metallic casing of the image-signal processing section  207 . The insulating members  210  and  211  are provided so as to sandwich the cable holding member  209  therewith in plan view. The shape such as thickness of the insulating members  210  and  211  is not specifically limited; however, it is preferable that the conductive material of the wiring  208  and the metallic casing of the image-signal processing section  207  be insulated with each other while the space therebetween be more than a predetermined distance so that variations in the electrostatic capacitance therebetween consistently do not affect image quality. 
   The image scanner section  200  is provided with a standard white board  206  as a member for shading correction of read data of the three primary color (red (R), green (G), and blue (B)). The CIS module  202 , the image-signal processing section  207 , and the wiring  208  are accommodated within a metallic casing (second metallic casing)  200   a.    
   On the other hand, the printing section  300  comprises a laser driver  312  for receiving an image signal produced from the image scanner section  200 , a semi-conductor laser  313  to be modulated by the laser driver  312 , a polygon mirror  314  to be propagated by a laser beam emitted from the semi-conductor laser  313 , and a photosensitive drum  317  to be irradiated with a laser beam reflected by an f-θ lens  315  and a mirror  316 . Furthermore, there are provided developers constituted of a magenta (M) developer  319 , a cyan (C) developer  320 , a yellow (Y) developer  321 , and a black (BK) developer  322 . These four developers develop M, C, Y, and BK latent images formed on the photosensitive drum  317  with corresponding toner by alternately touching the photosensitive drum  317 . 
   The printing section  300  is further provided with a transfer drum  323  so as to come into contact with the photosensitive drum  317 . Around the transfer drum  323 , a paper sheet is looped, which is fed from one or more paper cassettes, according to the embodiment, any one of two paper cassettes  324  and  325 . The printing section  300  is also provided with a fuser  326  for transferring toner images developed on the photosensitive drum  317  onto a paper sheet. 
   Next, the CIS module  202  accommodated within the image scanner section  200  will be described.  FIGS. 3 and 4  are a sectional view and an exploded perspective view of the structure of the CIS module  202 , respectively. 
   The CIS module  202 , as shown in  FIGS. 3 and 4 , comprises an illumination light source  2022  comprising a cover glass  2021 , an LED, and an optical waveguide; a 1× magnification image-forming lens  2023  comprising a distributed index lens, such as a SELFOC™ lens; a color line sensor  2024 ; and a substrate  2025  having the color line sensor  2024  mounted thereon. These elements are integrated together with a mould  2026 . 
     FIG. 5  is an enlarged schematic view of the color line sensor  2024  accommodated within the CIS module  202  showing its microscopic part. Referring to  FIG. 5 , each rectangular shape expresses a photo-diode, which is a read pixel. The color line sensor  2024  is for reading with 1× magnification with a resolution of 600 dpi, and the size of an opening of one pixel is 42×42 μm. 
   On each photo-diode of the color line sensor  2024 , color filters (not shown) of three primary color R, G, and B are provided. The photo-diode, having an R filter for transmitting a red wavelength component of visible light, is arranged in one line so as to form a photo-detector column (photo-sensor)  2024 - 1 . Similarly, the photo-diodes, having G and B filters for respectively transmitting green and blue wavelength components, are arranged for each one line so as to form photo-detector columns  2024 - 2  and  2024 - 3 . In such a manner, three read lines of R, G, and B are formed, and a charge is generated corresponding to luminous power incident into the photo-diode within a storage time. 
   The color line sensor  2024  is provided with a CCD analog shift-resister  2024 - 4  as a charge retransmitting section for retransmitting charges stored in the photo sensors  2024 - 1 ,  2024 - 2 , and  2024 - 3 ; and an output amplifier  2024 - 5  for producing a voltage output signal by converting the charge signal produced by the CCD analog shift-resister  2024 - 4  into a voltage. 
   The above-mentioned three-line photo-detector columns  2024 - 1 ,  2024 - 2 , and  2024 - 3 , each having different optical characteristics, are arranged in parallel with each other so that the R, G, and B sensors read the same line of the original document. The CCD analog shift-resister  2024 - 4  is arranged outside the three-line photo-detector columns in parallel therewith and adjacently to the B photo-detector column  2024 - 3 . These photo-detector columns  2024 - 1 ,  2024 - 2 , and  2024 - 3 , and the CCD analog shift-resister  2024 - 4  take a monolithic structure on the same silicon chip. 
   In a main scanning direction, according to the embodiment, each photo-diode is arranged to have a pixel pitch for each line in the main scanning direction of 42 μm so that the pixel pitch equals the opening size of one pixel in the main scanning direction. On the other hand, in a sub-scanning direction, according to the embodiment, each photo-diode is arranged to have a space between lines of 42 μm so that the space equals the opening size of one pixel in the sub-scanning direction. 
     FIG. 6  is a schematic view of the color line sensor  2024  macroscopically showing the configuration thereof. On a substrate  2024 - 6 ,  16  sensor chips  2024 - 7  are mounted in a line. Since each sensor chip  2024 - 7  produces a signal, signals of 16 channels are simultaneously read corresponding to each chip. 
   Then, the image-signal processing section  207  will be described. The image-signal processing section  207  performs various kinds of processing using a resister and a memory by the control means  131  comprising a CPU.  FIG. 7  is a block diagram of the configuration of the image-signal processing section  207  in the image scanner section  200 . 
   The image-signal processing section  207  comprises a clock generator  121  for generating a clock in one-pixel unit, a main scan address counter  122  for producing the pixel address output of one line by counting the clock from the clock generator  121 , and a decoder  123  for producing various signals by decoding a main scan address produced by the main scan address counter  122 . The main scan address counter  122  is cleared by a HSYNC signal produced from the decoder  123  so as to start counting the main scan address of the next line. 
   The image-signal processing section  207  is further provided with an analog signal processing section (analog signal processing circuit)  101  for producing the output of image signals with 16 channels OS 1  to OS 16  produced from the CIS module  202  by converting them into a digital signal with 8 bits after analog multiplexing and gain/offset adjusting the image signals OS 1  to OS 16 ; a permutation section  102  for dividing the digital signal with 8 bits produced from the analog signal processing section  101  into signals of color components R, G, and B; and a shading correction section  103  for performing shading correction on each color signal using a reading signal of a standard white board  211 . 
   The image-signal processing section  207  is further provided with a between-lines correction section  104  for correcting spatial displacement in sub-scanning directions of color components R, G, and B; an input masking section  106  for converting a color space for reading signals R, G, and B read in the CIS module  202  into an NTSC (National Television System Committee) standard color space; a luminous-power/density conversion section (LOG conversion section)  107  for converting a lightness signal produced from the input masking section  106  into a density signal; and a black character determining section  113  for determining a reference region of the imported image is whether it is a character/drawing-line region or a dot image region so as to produce signals (a masking UCR coefficient control signal ucr, a space filter coefficient control signal filter, and a printer resolution control signal sen) based on the determined result. The image-signal processing section  207  also comprises a line delay memory  108  for delaying an image signal on the basis of a VE and a HSYNC; a masking UCR circuit  109  for calculating to correct the color muddiness of a coloring material in a printer  212  by extracting a black signal (BK) from density signals of the three primary colors based on a masking UCR coefficient control signal ucr; a main-scan variable magnification unit  110  for magnification/reduction of an image signal with a bit width of 8 bits and a black character determining signal produced from the masking UCR circuit  109  (masking UCR coefficient control signal ucr) in the main scanning direction; and a space filter processing section (output filter)  111  for switching edge emphasis processing or smoothing processing based on a space filter coefficient control signal filter. The space filter processing section (output filter)  111  is produced in a printer  212 , which in turn performs printing based on a printer resolution control signal sen. 
   The black character determining section  113  has a known configuration as disclosed in Japanese Patent Laid-Open No. 7-203198, for example. That is, there are provided a character thickness determining section  114  for receiving a signal produced from the input masking section  106 ; an edge detector  115  and a color saturation determining section  116 ; and a look-up table (LUT)  117  for producing the masking UCR coefficient control signal ucr, the space filter coefficient control signal filter, and the printer resolution control signal sen, based on the output signals mentioned above. 
   Then, operation of the image-forming apparatus according to the embodiment will be described. 
   The color line sensor  2024  separates light information from an original document into color components R, G, and B and reads full color images (2 24  colors) so as to produce analog color signals R, G, and B to the image-signal processing section  207  via the wiring  208 . 
   Reading sensor columns for each color of the color line sensor  2024 , each having 7500 pixels, can read the original document on the glass plate  205  of the original document bed, with a resolution of 600 dpi along a length of 297 mm, which is the shorter direction length of the A-3 size, the maximum size placeable on the original document bed. The CIS module  202  moves mechanically by the driving force of the stepping motor  213  so as to scan the entire surface of an original document  204  in a direction (sub-scanning direction) perpendicular to the electrical scanning direction of the reading sensor column (main scanning direction). 
   The image-signal processing section  207  electrically separates the imported signal into components of magenta (M), cyan (C), yellow (Y), and black (BK), and sends them to the printing section  300 . This processing method of the image signal is known, and the detail will be described later. One of the components M, C, Y, and BK is fed to the printer section  300  after single scanning of the original document in the image scanner section  200 , so as to produce image data for one sheet by the original document scanning four-times in total, and images based on the image data are printed out from the printer section  300 . 
   Specifically, in the printer section  300 , an image signal with components of M, C, Y, and BK is fed to the laser driver  312  from the image scanner section  200 . The laser driver  312  modulates the semi-conductor laser  313  corresponding to the image signal. The photosensitive drum  317  is scanned with a laser beam emitted from the semi-conductor laser  313  via the polygon mirror  314 , the f-θ lens  315 , and the mirror  316 , so as to form an electrostatic latent image thereon. 
   The magenta developer  319 , the cyan developer  320 , the yellow developer  321 , and the black developer  322  develop the electrostatic latent image with components of M, C, Y, and BK formed on the photosensitive drum  317  with corresponding toner by alternately touching the photosensitive drum  317 . Then, a paper sheet fed from any one of the paper cassettes  324  and  325  is looped around the transfer drum  323 , so as to transfer the toner image developed on the photosensitive drum  317  onto the paper sheet. In such a manner, the four-color toner images of M, C, Y, and BK are sequentially transferred onto the paper sheet, which in turn is discharged outside through the fuser  326 . 
   The effect of providing the insulating members  210  and  211  will be described by comparing the behavior of the wiring  208  and the resultant unevenness and stripes of images when the insulating members  210  and  211  are provided, with those when the insulating members  210  and  211  are not provided. 
   First, a situation where the insulating members  210  and  211  are not provided will be described.  FIGS. 8A to 8D  are schematic views showing the relationship between the movement of the CIS module  202  and the behavior of the wiring  208  when the insulating members  210  and  211  are not provided. 
   Before the scanning starts, as shown in  FIG. 8B , the wiring  208 , one end being connected to the CIS module  202  via the connector  222 , droops so as to be curved and expanded in a direction separating from the image-signal processing section  207 ; the wiring  208  partly comes in contact with a corner of the metallic casing of the image-signal processing section  207 ; between this contact point and the cable holding member  209 , the wiring  208  is curved so as to belly upward, and connected to an image-signal processing substrate  224  having an image-signal processing circuit (not shown) mounted thereon via the connector  223 . The wiring  208  is also pushed on the surface of the metallic casing of the image-signal processing section  207  with the cable holding member  209 . 
   If the sub-scanning of the image is started, the CIS module  202  moves toward the image-signal processing section  207 . According to this movement, the curved portion (loop) of the wiring  208  existing on the image-signal processing section  207  is gradually reduced, and at one time finally, as shown in  FIG. 8B , the curved portion is lost, and part of the wiring  208  is perfectly stuck on the metallic casing  207   a  of the image-signal processing section  207 . 
   Then, as the CIS module  202  further moves, as shown in  FIG. 8C , the wiring  208  comes in contact with the glass plate  205  at a position nearer to the scanning start position than the CIS module  202 , and starts to be curved so as to belly downward by the gravity in between this contact point and the connector  222 . 
   As the CIS module  202  moves furthermore, the region of the wiring  208  contacting with the metallic casing  207   a  of the image-signal processing section  207  is gradually reduced, so that the wiring  208  becomes contact with the image-signal processing section  207  only at a potion pushed by the cable holding member  209 . The curved portion (loop) between the contact point of the wiring  208  to the glass plate  205  and the connector  222  is gradually increased, and at one time finally, as shown in  FIG. 8D , the curved portion drops on and rebounds against the metallic casing of the image-signal processing section  207 . 
     FIG. 9  is a drawing showing unevenness and stripes on the images obtained from the operation described above. Symbols (a) to (d) in the drawing correspond to the states shown in  FIGS. 8A to 8D , respectively. The drawing is obtained when reading an A-3 size halftone chart with an optical density D of 0.3. 
   The range (a) has rather dense reading; in the range (b), stripes are generated at an instant that the wiring  208  tightly comes into contact with the metallic casing; the range (c) has lighter (paler) reading than in the range (a); and in the range (d), a plurality of stripes are generated when the wiring  208  drops on and rebounds against the metallic casing. 
   That is, in between the wiring  208  transmitting an analog signal such as the FFC and the grounded metallic casing, when the wiring  208  is moved and deformed following the scanning, the electrostatic capacitance between both the members is changed. The waveform of the analog signal is thereby changed so as to produce deterioration in image quality such as unevenness and stripes. 
   The degree of the deterioration in image quality is no longer negligible, and as shown in  FIG. 9 , it is so remarkable as being visually and easily recognizable when reading a halftone chart with an optical density D of 0.3, significantly reducing the commodity value. 
   As mentioned above, the resin casing of the image-signal processing section has not such a problem, so that the problem is inherent to the case using the metallic casing. 
   Next, a situation where the insulating members  210  and  211  are provided will be described.  FIG. 10  is a schematic view showing a situation prior to the scanning when the insulating members  210  and  211  are provided. In the example shown in  FIG. 10 , the insulating member  210  was arranged at a position nearer to the scanning start position than to the cable holding member  209 , while the insulating member  211  was arranged at a position nearer to the scanning completion position. As the insulating members  210  and  211 , polyethylene terephthalate (Mylar™ sheet) with a thickness of 0.1 mm was used. 
   The relationship between the movement of the CIS module  202  and the behavior of the wiring  208  was the same as those shown in  FIGS. 8A to 8D .  FIG. 11  is a drawing showing unevenness and stripes of the images obtained when the insulating members  210  and  211  are provided. Symbols (a) to (d) in the drawing correspond to the states shown in  FIGS. 8A to 8D , respectively. The drawing is also obtained when reading an A-3 size halftone chart with an optical density D of 0.3. 
   As shown in  FIG. 11 , the unevenness and stripes existing in  FIG. 9  are not absolutely generated, obtaining extremely excellent images. 
   Then, a processing method of an image signal in the image-signal processing section  207  will be described.  FIG. 12  is a timing chart showing the reading operation of an image signal in the CIS module  202 . 
   For the one-line period of time (350 μs, for example), a charge for one-line with color components R, G, and B, which are accumulated in the respective photo-detector columns (photo-sensors)  2024 - 1 ,  2024 - 2 , and  2024 - 3 , is generally transferred to the CCD analog shift-resister  2024 - 4 , which is a charge transferring section, at the head timing of the next line corresponding to a shift pulse φSH. 
   Then, a signal φRS rises corresponding to a charge transferring clock φM so that the charge received in the charge transferring section  2024 - 4  is sequentially transferred to the output amplifier  2024 - 5 , in which the charge is converted into a voltage and produced as a voltage output signal. At this time, dummy signals d 1  to d 6  for 6 pulses are read out every 16 channels in the output amplifier  2024 - 5 . Next, effective signals are read out by 468 pixels for each color by the repetition of colors R, G, and B, as a manner of G 1 , B 1 , and R 1 ; G 2 , B 2 , and R 2 ; . . . ; and G 468 , B 468 , and R 468 . According to the embodiment, since the one-line CCD analog shift-resister, provided commonly to the three-line photo-detector columns, transmits the charge with three-color components, such reading timing is taken. 
   Thereafter, the image signals with 16 channels are transferred to the image-signal processing section  207  via the wiring  208 . 
   In the image-signal processing section  207 , as shown in  FIG. 7 , a clock generator  121  generates a clock CLK in one-pixel unit, and a main-scan address counter  122  keeps counting of the number of clocks from the clock generator  121  so as to produce the one-line pixel address output. A decoder  123  decodes the main-scan address from the main-scan address counter  122  so as to produce a sensor drive signal in one-line unit such as a shift pulse and a reset pulse, and an effective region signal VE, representing an effective region in the one-line reading signal from a color image sensor, and a line synchronizing signal HSYNC. The main-scan address counter  122  is cleared by the line synchronizing signal HSYNC so as to start counting the main-scan address of the next line. 
   Image signals with 16 channels OS 1  to OS 16  produced from the CIS module  202  are entered into an analog signal process section  101 . The analog signal process section  101  analog-multiplexes the image signals so as to allocate the image signals OS 1  to OS 6  to ch 1 , the image signals OS 7  to OS 12  to ch 2 , and the image signals OS 13  to OS 16  to ch 3 . After gain and offset adjustments, the analog image signals are converted into digital image signals with 8 bits by a built-in A/D converter so as to produce them. According to the embodiment, since the output from each sensor chip  2024 - 7  of the CIS module  202  is 1 channel, as described above, the number of channels of the reading output can be reduced even when a plurality of sensor chips are arranged, as compared with conventional configurations. Therefore, wiring for processing produced image signals and a circuit scale of an analog processor can be simplified. 
   The digital image signals ch 1  to ch 3  with 8 bits produced from the analog signal processing section  101  are separated into signals R 1 , G 1 , and B 1  with color components R, G, and B in a permutation section  102 . Then, on each color signal, a known shading correction using reading signals of a standard white board  206  is performed in a shading correction section  103 . The standard white board  206  is a white board having substantially uniform reflection characteristics in visible light. On the basis of data read out from the standard white board  206 , shading correction is performed on original-document reading data produced from the respective photo-detector columns (photo-sensors)  2024 - 1  to  2024 - 3  for color components R, G, and B. 
   The spatial displacements of R, G, and B in the sub-scanning direction of the shading-corrected color signals of R, G, and B are corrected in a between-lines correction section  104 . In the CIS module  202  according to the embodiment, as shown in  FIG. 5 , the three-line photo-detector columns (photo-sensors)  2024 - 1 ,  2024 - 2 , and  2024 - 3  are arranged in parallel with each other leaving a predetermined space in between (42 μm being equal to the opening size of one pixel in the sub-scanning direction). As the lines of R, G, and B are displaced by one-pixel in the sub-scanning direction in such a manner, different positions in the sub-scanning direction are simultaneously read, so that it is necessary to be corrected for taking the same position as image data. Therefore, the correction is performed thereon using the known so-called 3-line correction technique. 
   This 3-line correction is used as an essential technique when an existing color 3-line CCD is used. Generally, a technique is taken in that the image signal of the previously read out line (B signal according to the embodiment) is stored in a memory so as to align it with the image signals of the other two lines, which are read in retard, (R signal and G signal according to the embodiment). In such a manner, by aligning the R and G signals, which are delayed relative to the B signal in the sub-scanning direction, with the B signal, the spatial displacement is corrected. 
   In the CIS module  202  used according to the embodiment, since spaces between the three reading lines of R, G, and B are the one-pixel pitch, which is an integer multiple of the pixel size in the sub-scanning direction, the correction process can be simplified. As long as the space is an integer multiple of the one pixel size in the sub-scanning direction, the lines may be arranged at intervals of double or triple (two or three pixels). 
   Output signals R 3 , G 3 , and B 3  of the between-lines correction section  104  are entered into the input masking section  106 . In the input masking section  106 , in order to convert the color space of the reading signals of R, G, and B, which are read out in the CIS module  202 , into a standard color space of NTSC, the matrix arithmetic operation is performed according to the following equation 1. 
   
     
       
         
           
             
               
                 
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                           R 
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                           4 
                         
                       
                     
                     
                       
                         
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                           4 
                         
                       
                     
                     
                       
                         
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                 = 
                 
                   
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                             a 
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                             11 
                           
                         
                         
                           
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                             12 
                           
                         
                         
                           
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                             13 
                           
                         
                       
                       
                         
                           
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                             21 
                           
                         
                         
                           
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                             22 
                           
                         
                         
                           
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                             23 
                           
                         
                       
                       
                         
                           
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                             31 
                           
                         
                         
                           
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                             32 
                           
                         
                         
                           
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                             33 
                           
                         
                       
                     
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                 [ 
                 
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   Wherein values of a 11 , a 12 , a 13 , a 21 , a 22 , a 23 , a 31 , a 32 , and a 33  are determined so that the color reproducibility in the NTSC color space is optimized. 
   Lightness signals R 4 , G 4 , and B 4  produced from the input masking section  106  are converted into density signals C 0 , M 0 , and Y 0  by the luminous-power/density conversion section (LOG conversion section)  107  configured by the look-up table ROM, and are received in the black character determining section  113 . 
   The black character determining section  113  determines a reference region of the imported image is whether it is a character/drawing-line region or a dot image region. If it is determined to be the character/drawing-line region, the black character determining section  113  produces a command to increase the black color to the masking UCR circuit  109  as a masking UCR coefficient control signal ucr (3 bits); produces a command to emphasize the contour to the output filter  111  as a space filter coefficient control signal filter (2 bits); and produces a command to switch the produced print screen ruling into a fine screen ruling to the printer  212  as a printer resolution control signal sen (1 bit). As a result, a black character/drawing-line is conspicuously printed beautifully. On the other hand, if the reference region is determined to be the dot image region, the black character determining section  113  produces a command to make the dot opaque to the output filter  111  as the space filter coefficient control signal filter; and produces a command to switch the produced print screen ruling into an excellent gradation-reproducibility ruling to the printer  212  as the printer resolution control signal sen. The details thereof are disclosed in Japanese Patent Laid-Open No. 7-203198. 
   The line delay memory  108  delays image signals C 0 , M 0 , and Y 0  by the line delay until a black character determining signal produced in the black character determining section  113 , such as a masking UCR coefficient control signal ucr, a space filter coefficient control signal filter, and a printer resolution control signal sen. As a result, the image signals C 0 , M 0 , and Y 0  and the black character determining signal (masking UCR coefficient control signal ucr), which are for the common pixel, are simultaneously entered into the masking UCR circuit  109 . 
   The masking UCR circuit  109  extracts a black signal (BK) from imported three primary color signals Y 1 , M 1 , and C 1 , and further performs arithmetic operation for correcting color muddiness of a color material in the printer  212  based on the masking UCR coefficient control signal ucr. Then, image signals Y 2 , M 2 , C 2 , and BK 2  are sequentially produced every reading operation with a predetermined bit width (8 bits). 
   The main-scan variable magnification unit  110  performs magnification/reduction of the image signals Y 2 , M 2 , C 2 , and BK 2  and the black character determining signal (masking UCR coefficient control signal ucr) in the main scanning direction by a known interpolation calculation, so as to produce image signals Y 3 , M 3 , C 3 , and BK 3 . 
   The space filter processing section (output filter)  111  performs switching of edge emphasis processing or smoothing processing on the image signals Y 3 , M 3 , C 3 , and BK 3 , based on the space filter coefficient control signal filter produced from the LUT  117 , so as to produce processed image signals Y 4 , M 4 , C 4 , and BK 4  to the printer  212 . 
   According to the embodiment, the casing  207   a  of the image-signal processing section  207  and the casing  200  of the printer section  200  are metallic; however, the scope of the present invention is not limited to this and we obviously have a concept of variation in electrostatic capacitance due to relative positional displacement between the wiring such as the FFC and the metallic casing. Therefore, in the case where the wiring  208  can come into contact with the internal surface of the metallic casing  200   a , an insulating member may be used on the region. 
   The thickness of the insulating member is not limited to the value described above; however, more than about 0.1 mm may be preferable, and the larger in thickness, the more advantages can be obtained. The shape of the insulating member is not limited to a sheet to be bonded on the metallic casing, and it may be molded integrally with the metallic casing as an insulating molded member. 
   While the present invention has been described with reference to what are presently considered to be the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.