Abstract:
With the present invention, by changing the scanning timing of a CCD line sensor in accordance with the amount of scanning misregistration corresponding to a magnification, misregistration of less than one line can be accurately corrected, thereby eliminating degradation of MTF, which has occurred in conventional apparatuses.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to an image scanning apparatus, such as a scanner, which scans an original image, wherein light from a light source is irradiated onto an original document, and the reflected light thereof is guided by an optical system such as a mirror, thereby the original image is formed by three CCD line sensors of R (red), G (green) and B (blue).  
           [0003]    2. Description of the Related Art  
           [0004]    Recently, image scanning apparatuses, such as scanners, which scan an original image, have been put to practical use, wherein light from a light source is irradiated onto an original document, and the reflected light thereof is guided by an optical system such as a mirror, thereby the original image is formed by three CCD line sensors of R (red), G (green) and B (blue).  
           [0005]    At this time, the light from the light source is irradiated onto an original image, and the reflected light thereof is guided to each CCD sensor via a plurality of mirrors.  
           [0006]    A color image forming apparatus having such a scanner has been proposed.  
           [0007]    That is to say, in Jpn. Pat. Appln KOKAI Publication No. 5-75792, there is proposed a color image forming apparatus comprising a light source which irradiates light onto a document, color separation means for optically separating the reflected light or transmitted light from the document into a plurality of colors, image scanning means for converting each color-separated light into an electric signal by a plurality of photoelectric transfer means and outputs the electric signal, and image recording means for storing a color image based on the electric signal from the image scanning means, which is characterized by having storage means for storing beforehand misregistration of the image formed by the separated lights, due to a relative positional error or the like of the plurality of photoelectric transfer means, delay means for delaying the output electric signal from each photoelectric transfer means, and delayed amount control means for setting the delayed amount by the delay means in accordance with the output of the storage means.  
           [0008]    In this manner, as measures against scanning misregistration of the color CCD sensor, heretofore, the signal after the photoelectric transfer is delayed to prevent the scanning misregistration, to thereby prevent the color difference of the output image. Moreover, in the case of performing scaling by a color plain paper copier, in the vertical scanning direction, there are generally a method of performing scaling by changing the scanning rate of the scanner, and a method of performing scaling by means of image processing. With the method of changing the scanning rate of the scanner, since the color CCD sensor has such a construction that a plurality of line sensors are arranged at a certain pitch, scanning misregistration occurs in the vertical scanning direction. In order to correct this misregistration, there is known a method in which correction by a multiple of the line sensor pitch is performed by a line memory in accordance with the scanning rate, and correction of less than one line is presumed from the peripheral pixels.  
           [0009]    With the above-described related art, correction is performed based on a value after scanning. Therefore, correction in a unit of line is possible, but correction of less than one line has to be performed based on a value calculated by taking a weight average from the front and back two pixels, since the actual misregistration image cannot be taken in. With this method, there is a problem in that the MTF (Modulation Transfer Function) deteriorates due to taking the weight average.  
         BRIEF SUMMARY OF THE INVENTION  
         [0010]    It is an object of the present invention to provide an image scanning apparatus which does not require fine registration adjustment by the optical system, and does not cause color difference, in a scanning apparatus which scans a color document image, using a plurality of CCD sensors.  
           [0011]    In order to achieve the above object, the document scanning apparatus of the present invention comprises: a scanning section which reads and scans a document line by line in the horizontal scanning direction thereof, with a relative movement of the document in the vertical scanning direction; a shift mechanism which shifts the scanning section and the document relative to each other in the vertical scanning direction of the document at various speeds based on the scanning magnification; a CCD line sensor for the color red, to which an image for each line is guided from the scanning section, to convert it into pixel signals of a plurality of pixels based on the density of the red color component; a CCD line sensor for the color green provided parallel with the CCD line sensor for the color red with a predetermined distance therebetween, to which an image for each line is guided from the scanning section, to convert it into pixel signals of a plurality of pixels based on the density of the green color component; a CCD line sensor for the color blue provided parallel with the CCD line sensor for the color green with a predetermined distance therebetween, to which an image for each line is guided from the scanning section, to convert it into pixel signals of a plurality of pixels based on the density of the blue color component; a memory section which stores beforehand alienation time comprising a line unit component and a pixel unit component between the respective CCD line sensors, in such a state that the scanning section and the document are relatively shifted by the shift mechanism, at a different speed based on various scanning magnifications; a modification section which, at the time of scanning at a predetermined scanning magnification, reads the alienation time between the respective CCD line sensors based on this magnification, and modifies the output timing of the pixel signal from the each CCD line sensor, based on the pixel unit component of this readout alienation time; and a delay section which delays the pixel signal in a unit of one line, obtained by changing the output timing of the pixel signal from the each CCD line sensor by the modification section, by the line unit component of the alienation time. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0012]    [0012]FIG. 1 is a block diagram showing the schematic construction of a color image forming apparatus comprising a scanner section, as one example of an image scanning apparatus of the present invention;  
         [0013]    [0013]FIGS. 2 and 3 are sectional views showing the schematic construction of the color image forming apparatus, respectively;  
         [0014]    [0014]FIG. 4 is a sectional view showing the schematic construction of the scanner section;  
         [0015]    [0015]FIGS. 5 and 6 are diagrams showing the construction of a CCD line sensor;  
         [0016]    [0016]FIGS. 7A to  7 F are timing charts showing a signal in the main part of the CCD line sensor;  
         [0017]    [0017]FIG. 8 is a diagram showing the relation of pitches between a scaling rate and the CCD line sensors;  
         [0018]    [0018]FIG. 9 is a block diagram showing the internal construction of a control circuit of the color image forming apparatus;  
         [0019]    [0019]FIGS. 10A to  10 J are timing charts showing the timing of the CCD output and pixel data output, when the magnification is 100%;  
         [0020]    [0020]FIGS. 11A to  11 P are timing charts showing the timing of the CCD output and pixel data output, when the magnification is 106%;  
         [0021]    [0021]FIG. 12 is a diagram showing the construction of the CCD line sensor; and  
         [0022]    [0022]FIGS. 13A to  13 L are timing charts showing the timing of the CCD output and pixel data output, when the magnification is 106%. 
     
    
       [0023]    Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.  
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0024]    The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0025]    The image forming apparatus according to an embodiment of the present invention will now be described with reference to the drawings.  
         [0026]    [0026]FIG. 1 is a block diagram for explaining a color digital copying machine  1  comprising a scanner section, as one example of an image scanning apparatus of the present invention. As shown in FIG. 1, the color digital copying machine  1  comprises a control section (CPU)  101 , a scanner section  102  having an automatic document feeder (ADF)  17  described below, a color printer section  103 , and an operation panel  104 , and is connected to an external apparatus  106  such as a personal computer, via a line  105  such as a LAN.  
         [0027]    The control section (CPU)  101  is to control the whole color digital copying machine  1 .  
         [0028]    The scanner section  102  is to read the image information of an object to be copied (not shown) placed on a document table by the automatic document feeder (ADF)  17  as contrast of light, to thereby generate an image signal.  
         [0029]    The color printer section  103  is to form an image corresponding to the image signal supplied from the scanner section  102  or the external apparatus  106 .  
         [0030]    The operation panel  104  is to perform various setting.  
         [0031]    [0031]FIGS. 2 and 3 are diagrams showing the inner structure, respectively, for explaining the color digital copying machine  1 .  
         [0032]    On the upper part of the apparatus body  10 , the automatic document feeder (hereinafter referred to as “ADF”)  17  which also serves as a cover, and feeds a document in sheet form one by one, is provided so as to be freely opened or closed. A platen may be attached as the cover instead of this ADF  17 . On the front upper face of the apparatus body  10 , there is provided an operation panel  104  comprising various operation keys for instructing copying conditions and copy start or setting the magnification, and various displays.  
         [0033]    On the right side of the apparatus body  10 , a paper feed cassette  57  which can store paper in a small quantity, and a large capacity paper feed cassette  55  which can store paper in a large quantity are provided respectively detachably. The paper feed cassette  57  comprises a manual feed tray  56  to supply paper manually.  
         [0034]    On the lower part of the apparatus body  10 , there are provided paper feed cassettes  52 ,  53  and  54  detachably. In each paper feed cassette, sheets of paper in the same size are stored in the horizontal direction and in the vertical direction, so as to be selected according to need. On the left side of the apparatus body  10 , there is provided a finisher  80  to receive copied paper.  
         [0035]    In the apparatus body  10 , there are provided the scanner section  102  as obtaining means for obtaining image data, and the color printer section  103  as image forming means, for realizing the copying function and the facsimile function.  
         [0036]    On the upper face of the apparatus body  10 , there are arranged a document table  13  comprising a transparent glass, on which an object to be scanned, that is, a document D is placed, and the ADF  17  for automatically feeding the document D onto this document table  13 . This ADF  17  is arranged freely openably with respect to the document table  13 , and also functions as a cover for bringing the document D placed on the document table  13  into intimate contact with the document table  13 .  
         [0037]    The ADF  17  comprises a document tray  8  where the document D is set, an empty sensor  9  which detects the presence of the document, a pick-up roller  14  to pick up the document D one by one from the document tray  8 , a feed roller  15  for carrying the picked up document D, a registration roller pair  16  for registering the tip of the document D, a registration sensor (not shown) provided on the upstream side of the registration roller pair  16  to detect when the document D arrives, a size sensor (not shown)to detect the size of the document D, and a carrier belt  18  arranged so as to cover substantially the whole document table  13 . Plural sheets of documents set upwards in the document tray  8  are picked up sequentially from the lowest paper, that is, from the last page, registered by the registration roller pair  16 , and then transferred to a predetermined position on the document table  13  by the carrier belt  18 .  
         [0038]    In the ADF  17 , a reversing roller  20 , a non-reversing sensor  21 , a flapper  22 , and a feeder output roller  23  are arranged at the end portion on the side opposite to the registration roller pair  16 , putting the carrier belt  18  therebetween. The document D whose image information has been scanned by the scanner section  102  described later is carried from the document table  13  by the carrier belt  18 , onto a document ejection section  24  on the upper face of the ADF  17 , via the reversing roller  20 , the flapper  22 , and the feeder output roller  23 .  
         [0039]    In the case of scanning the reverse of the document D, by changing over the flapper  22 , the document D carried by the carrier belt  18  is reversed by the reversing roller  20 , and carried again to a predetermined position on the document table  13  by the carrier belt  18 .  
         [0040]    The ADF  17  comprises a paper feed motor to drive the pick-up roller  14 , the feed roller  15  and the registration roller pair  16 , and a carrier motor to drive the carrier belt  18 , the reversing roller  20 , and the feeder output roller  23 .  
         [0041]    The scanner section  102  arranged in the apparatus body  10  has, as shown in FIGS. 2 and 4, a light source  25 , such as a fluorescent lamp, to illuminate the document D placed on the document table  13 , and a first mirror  26  to deflect the reflected light from the document D to a predetermined direction. These light source  25  and first mirror  26  are mounted on a first carriage  27  arranged below the document table  13 . On this first carriage  27 , there is mounted the size sensor  28  to detect the size of the document placed on the document table  13 . The first carriage  27  is movably arranged parallel with the document table  13 , and is moved back and forth below the document table  13 , by a drive motor via a toothed belt or the like (not shown).  
         [0042]    Moreover, a second carriage  29  is movably arranged parallel with the document table  13 , below the document table  13 . On the second carriage  29 , there are mounted a second mirror  30  and a third mirror  31  at a right angle with respect to each other, which sequentially deflects the reflected light from the document D, which has been deflected by the first mirror  26 . The second carriage  29  is driven with respect to the first carriage  27  by a toothed belt which drives the first carriage  27 , and is also moved parallel with the first carriage  27  along the document table  13 , at a rate of half the rate of the first carriage  27 .  
         [0043]    Also, below the document table  13 , there are arranged an image formation lens  32  which focuses the reflected light from the third mirror  31  on the second carriage  29 , and a CCD line sensor  34  comprising three CCD line sensors  34   a ,  34   b  and  34   c , which receives the reflected light focused by the image formation lens  32  and performs photoelectric exchange therewith. The image formation lens  32  is arranged movably via a drive mechanism within a plane including the optical axis of the light deflected by the third mirror  31 , and forms an image of the reflected light at a desired magnification (in the horizontal scanning direction). The CCD line sensors  34   a ,  34   b  and  34   c  photoelectrically exchange the incident reflected light, in accordance with a shift gate signal and an image processing clock (transfer clock) provided from a red color signal processing section (SALT)  122 , a green color signal processing section (SALT)  123  and a blue color signal processing section (SALT)  124 , and outputs an electric signal corresponding to the scanned document D. The magnification in the vertical scanning direction can correspond thereto, by changing the transfer speed by means of the ADF  17  or the moving speed of the first carriage  27 .  
         [0044]    The light from the light source  25  respectively corresponds to the CCD line sensors  34   a ,  34   b  and  34   c , and a difference in the scanning timing is corrected by means of the shift gate signal, a timing of the transfer clock and a circuit in the latter step.  
         [0045]    When the document D carried by the ADF  17  is scanned, the irradiation position of the light source  25  is fixed to a position shown in FIG. 1. Moreover, when the document D placed on the document table  13  is scanned, the irradiation position of the light source  25  is shifted from the left to the right along the document table  13 .  
         [0046]    On the other hand, the color printer section  103  comprises a laser exposure apparatus  40  serving as the exposure means. The laser exposure apparatus  40  comprises a semiconductor laser  41  as a light source, a polygon mirror  36  as a scanning member which continuously deflects the laser beam emitted from the semiconductor laser  41 , a polygon motor  37  as a scanning motor which rotates and drives the polygon mirror  36  at a predetermined number of revolution described later, and an optical system  42  which deflects and guides the laser beam from the polygon mirror  36  to photosensitive drums  44   a  to  44   d  described above. The laser exposure apparatus  40  having such a construction is secured and supported by a support frame (not shown) of the apparatus body  10 .  
         [0047]    The semiconductor laser  41  is ON/OFF controlled according to the image information of the document D scanned by the scanner section  102 , and this laser beam is respectively directed to the photosensitive drums  44   a  to  44   d  via the polygon mirror  36  and the optical system  42 , and by scanning the peripheral face of the photosensitive drums  44   a  to  44   d , an electrostatic latent image is formed on the peripheral face of each photosensitive drums  44   a  to  44   d.    
         [0048]    The image forming section  12  has the freely rotatable photosensitive drums  44   a  to  44   d  as an image carrier arranged substantially in the center of the apparatus body  10 , and a desired electrostatic latent image is exposed and formed on the peripheral face of each photosensitive drums  44   a  to  44   d , by the laser beam from the laser exposure apparatus  40 .  
         [0049]    On the periphery of the photosensitive drums  44   a  to  44   d , there are arranged sequentially: electrification chargers  45  which respectively charge the peripheral face of the photosensitive drums  44   a  to  44   d  to a predetermined charge; developers  46  which supply toner as a developer to the electrostatic latent image formed on the peripheral face of the photosensitive drums  44   a  to  44   d  to develop the image at a desired image density; peeling chargers  47  to separate a material to be transferred (recording medium) that is, the copy paper P fed from a paper feed cassette  52 ,  53 ,  54 ,  55  or  57  from the photosensitive drums  44   a  to  44   d ; transfer chargers  48  which make the toner image formed on the photosensitive drums  44   a  to  44   d  to be transferred onto the paper P; a peeling claw (not shown) which peels the copy paper P from the peripheral face of the photosensitive drums  44   a  to  44   d ; cleaning devices  50  which clean the toner remaining on the peripheral face of the photosensitive drums  44   a  to  44   d ; and discharging devices  51  which discharge the peripheral face of the photosensitive drums  44   a  to  44   d.    
         [0050]    Image forming units  45   a  to  45   d  are constituted of each above described photosensitive drum  44   a  ( 44   b  to  44   d ) and each peripheral equipment, respectively.  
         [0051]    In this example of the invention, in order to overlap four colors of the Y image, M image, C image and B image, from the upstream side in the direction that an optional point of the carrier belt  67  is moved, that is, in the direction that the copy paper P is carried, each image forming unit  45   a  to  45   d  is arranged in the order of Y, M C and B.  
         [0052]    In the lower part of the apparatus body  10 , the paper feed cassettes  52 ,  53  and  54  capable of being pulled out from the apparatus body  10 , respectively, are arranged in the laminated state, and copy paper having a different size is loaded in each cassette  52 ,  53  and  54 . The large-capacity paper feed cassette  55  is provided by the side of these cassettes  52 ,  53  and  54 , and in this large-capacity paper feed cassette  55 , copy paper having a size which is most frequently used, for example, A4 size copy paper is stored in an amount of about 3000 sheets. Moreover, above the large-capacity paper feed cassette  55 , the paper feed cassette  57  also serving as the manual tray  56  is detachably mounted.  
         [0053]    In the apparatus body  10 , there is formed a carrier passage  58  extending from each cassette through a transfer section located between photosensitive drums  44   a  to  44   d  and the transfer chargers  48 , and at the end of the carrier passage  58 , there is provided a fixation apparatus  60 . On the sidewall of the apparatus body  10  facing the fixation apparatus  60 , an ejection port  61  is formed, and the finisher  80  is mounted in the ejection port  61 .  
         [0054]    In the vicinity of the paper feed cassettes  52 ,  53 ,  54 ,  55  and  57 , a pick-up roller  63  which picks up the paper from the cassette one by one is provided, respectively. In the carrier passage  58 , there are provided a plurality of feed roller pairs  64  which carry the copy paper P picked up by the pick-up roller  63  through the carrier passage  58 .  
         [0055]    On the upstream side of the photosensitive drums  44   a  to  44   d  in the carrier passage  58 , a resist roller pair  65  is provided. The resist roller pair  65  corrects the inclination of the picked up copy paper P, registers the end of the toner image on the photosensitive drums  44   a  to  44   d  with the end of the copy paper P, and feeds the copy paper P to the transfer section at the same speed as the moving speed of the peripheral face of the photosensitive drums  44   a  to  44   d . This side of the resist roller pair  65 , that is, on the feed roller  64  side, an aligning sensor  66  which detects the arrival of the copy paper P is provided.  
         [0056]    The copy paper P picked up one by one from each cassette by the pick-up roller  63  is carried to the resist roller pair  65  by the feed roller pair  64 . Then, after the end of the copy paper P is registered by the resist roller pair  65 , the copy paper P is carried to the transfer section by the carrier belt (transfer belt)  67 .  
         [0057]    In the transfer section, the developer image formed on the photosensitive drums  44   a  to  44   d , that is, the toner image is transferred to the paper P by the transfer charger  48 . The copy paper P on which the toner image has been transferred is peeled off from the periphery of the photosensitive drums  44   a  to  44   d  by the action of the peeling charger  47  and the peeling claw (not shown), and carried to the fixation apparatus  60  via the carrier belt  67  which constitutes a part of the carrier passage  58 . Then, after the developer image has been fused and fixed on the copy paper P by the fixation apparatus  60 , the copy paper P is ejected to a feeder output tray  81  of the finisher  80  via the ejection port  61  by the feed roller pair  68  and the ejection roller pair  69 .  
         [0058]    Below the carrier passage  58 , there is provided an automatic reversing apparatus (ADD)  70  which reverses the copy paper P having passed the fixation apparatus  60  and sends it again to the resist roller pair  65 . The automatic reversing apparatus  70  comprises a temporary accumulation section  71  which accumulates the copy paper P temporarily, a reversing passage  72  separated from the carrier passage  58 , which reverses the copy paper P having passed the fixation apparatus  60  and guides to the temporary accumulation section  71 , a pick-up roller  73  which picks up the copy paper P accumulated in the temporary accumulation section one by one, and a feed roller  75  which feeds the picked up paper to the resist roller pair  65  via a carrier passage  74 . Moreover, at the branching section of the carrier passage  58  and the reversing passage  72 , there is provided a distribution gate  76  which selectively distributes the copy paper P to the ejection port  61  or to the reversing passage  72 .  
         [0059]    In the case where two-sided copy is to be performed, the copy paper P having passed the fixation apparatus  60  is guided to the reversing passage  72  by the distribution gate  76 , and temporarily accumulated in the temporary accumulation section  71  in the reversed state, and then carried to the resist roller pair  65  via the carrier passage  74 , by the pick-up roller  73  and the feed roller pair  75 . After having been registered by the resist roller pair  65 , the copy paper P is carried again to the transfer section, so that the toner image is transferred to the back face of the copy paper P. Thereafter, the copy paper P is ejected to the feeder output tray  81  in the finisher  80 , via the carrier passage  58 , the fixation apparatus  60  and the ejection roller  69 .  
         [0060]    By using this automatic reversing apparatus  70 , it is also possible to eject the paper with the printed face of the paper facing downwards. That is to say, at first, the image is transferred and fixed on the surface of the paper in the manner that the two-sided copy is performed, the paper is accumulated temporarily in the temporary accumulation section  71 , passed through the carrier passage  74  by the pick-up roller  73  and the feed roller pair  75  and registered by the resist roller pair  77 , and then, ejected to the feeder output tray  81  in the finisher  80 , via the carrier passage  58 , the fixation apparatus  60  and the ejection roller  69 .  
         [0061]    The three CCD line sensors  34   a ,  34   b  and  34   c  described above are for RED, for GREEN and for BLUE in the order of from the bottom, as shown in FIG. 5. For example, the CCD line sensors  34   a ,  34   b  and  34   c  are configured to have 8000 pixels, respectively, and arranged on one printed board, parallel therewith.  
         [0062]    The size per one pixel of the CCD line sensors  34   a ,  34   b  and  34   c  is 8×8 μm, and the number of pixels in one line is 8000. The 8000 pixels are constituted of an effective pixel area formed by 7500 pixels, and a dummy pixel area formed by 250 pixels on the both sides thereof. The interval between the CCD line sensors  34   a ,  34   b  and  34   c  for each color is 64 μm, and it corresponds to an 8-line interval, calculated as the number of pixels of the CCD line sensors  34   a ,  34   b  and  34   c.    
         [0063]    At this time, the 8 lines in the document D on the document table  13  correspond to 8 lines per 42.3 μm, as shown in FIG. 4. At the time of scanning by the ADF  17  at the equal magnification, movement of the document D by 42.3 μm corresponds to one line.  
         [0064]    Therefore, in the case where the original image is scanned at the equal magnification, there is a difference of 8 lines in the vertical scanning direction, at the document scanning position between the CCD line sensors  34   a ,  34   b  and  34   c  for each color. Hence, in order to obtain the image information for the same line in the original image, this line difference has to be corrected in the data. Therefore, in the case where the original image is scanned at the equal magnification, the CCD line sensors  34   a ,  34   b  and  34   c  for each color scan the image of the original image away from each other by 8 lines. Hence, it is necessary to correct the line difference in the data, in order to obtain the image information for the same line on the original image.  
         [0065]    If it is assumed that the scanning order of the same line in the original image is in the order of from RED to GREEN to BLUE (in the order of from the CCD line sensor  34   a ,  34   b  and  34   c ), in order to obtain the image data for the same line with the image that is now being scanned with the BLUE CCD line sensor, the GREEN image needs only to be delayed by 8 lines, and the RED image needs only to be delayed by 16 lines. Moreover, when an enlarged image at 400% is to be obtained by changing the shift speed of the scanning position to ¼, it is necessary to delay the GREEN image by 32 lines, and the RED image by 64 lines. Conversely, when a reduced image at 50% is to be obtained by making the shift speed double, the GREEN image needs only to be delayed by 4 lines, and the RED image by 8 lines.  
         [0066]    The CCD line sensors  34   a ,  34   b  and  34   c  are configured by photodiodes  110 R,  110 G and  110 B, shift gates  111 R,  111 G and  111 B, CCD analog shift registers  112 R,  112 G and  112 B, and output buffers  113 R,  113 G and  113 B, as shown in FIG. 6.  
         [0067]    The photodiodes  110 R,  110 G and  110 B are to perform photoelectric exchange of the original image, and the photoelectrically exchanged electric charge for each pixel is respectively output to the shift gates  111 R,  111 G and  111 B.  
         [0068]    The shift gates  111 R,  111 G and  111 B are to transfer the photoelectrically exchanged electric charge to the CCD analog shift registers  112 R,  112 G and  112 B, respectively, based on the shift gate signals SH-R, SH-G and SH-B, shown in FIG. 7A. The shift gate signals SH-R, SH-G and SH-B are output by the red color signal processing section (SALT)  122 , the green color signal processing section (SALT)  123  and the blue color signal processing section (SALT)  124 , for each light accumulation time (tINT) for one line. The shift gate signals SH-R, SH-G and SH-B can be supplied independently for each shift gate  111 R,  111 G and  111 B, to thereby independently control the transfer timing.  
         [0069]    The CCD analog shift registers  112 R,  112 G and  112 B output the electric charge for one line sequentially pixel by pixel to the output buffers  113 R,  113 G and  113 B, based on the transfer clock (charge transfer clock) φ 1 R, φ 2 R, φ 1 G, φ 2 G, φ 1 B and φ 2 B shown respectively in FIGS. 7B to  7 E. The transfer clock φ 2 R (φ 2 G, φ 2 B) are the reversed phase (opposite phase) of the transfer clock φ 1 R, (φ 1 G, φ 1 B).  
         [0070]    The transfer clock φ 1 R, φ 2 R, φ 1 G, φ 2 G, φ 1 B and φ 2 B are supplied from a clock generation section (not shown), so as to be supplied independently for each CCD analog shift register  112 R,  112 G,  112 B, so that the transfer timing can be controlled separately.  
         [0071]    The output buffers  113 R,  113 G and  113 B are to output the electric charge transferred, respectively, from the CCD analog shift registers  112 R,  112 G and  112 B as a voltage signal (CCD output signal), as shown in FIG. 7F.  
         [0072]    For example, the CCD output signal is in the order of from an idle portion, an optical shield portion, a dummy pixel portion, an effective pixel portion, a dummy pixel portion and an idle portion, between the shift gate signals.  
         [0073]    These CCD line sensors  34   a ,  34   b  and  34   c  perform scanning processing, taking into consideration a difference in the scanning timing in the horizontal scanning direction and in the vertical scanning direction.  
         [0074]    [0074]FIG. 8 shows the relation of the pitch (line) between the respective CCD line sensors  34   a ,  34   b  and  34   c , based on the scaling magnification described above.  
         [0075]    The interval between the CCD line sensor  34   a  and the CCD line sensor  34   b , and the interval between the CCD line sensor  34   b  and the CCD line sensor  34   c  respectively change as follows according to the magnification.  
         [0076]    For example, when the magnification is 95%, the interval therebetween is 7.6 lines; when 96%, 7.68 lines; when 97%, 7.76 lines; when 98%, 7.84 lines; when 99%, 7.92 lines; when 100%, 8 lines; when 101%, 8.08 lines; when 102%, 8.16 lines; when 103%, 8.24 lines; when 104%, 8.32 lines; when 105%, 8.4 lines; and when 106%, 8.48 lines. Also, the pitch (interval between sensors) gradually changes by 1% in the range of from 25% to 400%, other than the ones described above.  
         [0077]    The above change occurs because the optical system such as the light source  25  moves in the vertical scanning direction at a different shift speed based on the magnification.  
         [0078]    The relation of the pitch (line) between the respective CCD line sensors  34   a ,  34   b  and  34   c , based on the scaling magnification described above is registered beforehand in the internal memory  101   a  in the control section  101  described later, or in the internal memory  120   a  in the scan CPU  120 .  
         [0079]    Next, the circuit construction of the above scanner section  4  will be described with reference to FIG. 9.  
         [0080]    That is to say, an SCN-CPU  120  is provided as a control section which controls the whole scanner section  4 . This SCN-CPU  120  is connected to the control section  101 .  
         [0081]    To this SCN-CPU  120  are connected the red color signal processing section (SALT)  122 , the green color signal processing section (SALT)  123 , the blue color signal processing section (SALT)  124  and an arithmetic unit (LAKE)  125 , via a CPU bus  121 . These respective processing sections are constructed by ASIC.  
         [0082]    An output from the above-described CCD line sensor  34   a  (CCD output signal) is amplified by an amplifier  126   a , and the signal converted to a digital signal by an analog-to-digital converter  127   a  is supplied to the red color signal processing section  122 . The red color signal processing section  122  is to output a red color signal (R) in a unit of a pixel, which has been subjected to processing such as signal detection in the digital signal of the red color component supplied from the analog-to-digital converter  127   a , level adjustment and mixing ratio adjustment, and this red color signal (R) is output to the arithmetic processing section  125 . The red color signal processing section  122  is to output the shift gate signal SH-R to the CCD line sensor  34   a  at a different timing in accordance with the magnification supplied from the SCN-CPU  120 .  
         [0083]    An output from the above-described CCD line sensor  34   b  (CCD output signal) is amplified by an amplifier  126   b , and the signal converted to a digital signal by an A/D converter  127   b  is supplied to the green color signal processing section  123 . The green color signal processing section  123  is to output a green color signal (G) in a unit of a pixel, which has been subjected to processing such as signal detection in the digital signal of the green color component supplied from the analog-to-digital converter  127   b , level adjustment and mixing ratio adjustment, and this green color signal (G) is output to the arithmetic processing section  125 . The green color signal processing section  123  is to output the shift gate signal SH-G to the CCD line sensor  34   b  at a different timing in accordance with the magnification supplied from the SCN-CPU  120 .  
         [0084]    An output from the above-described CCD line sensor  34   c  (CCD output signal) is amplified by an amplifier  126   c , and the signal converted to a digital signal by an analog-to-digital converter  127   c  is supplied to the blue color signal processing section  124 . The blue color signal processing section  124  is to output a blue color signal (B) in a unit of a pixel, which has been subjected to processing such as signal detection in the digital signal of the blue color component supplied from the analog-to-digital converter  127   c , level adjustment and mixing ratio adjustment, and this blue color signal (B) is output to the arithmetic processing section  125 . The blue color signal processing section  125  is to output the shift gate signal SH-B to the CCD line sensor  34   c  at a different timing in accordance with the magnification supplied from the SCN-CPU  120 .  
         [0085]    The arithmetic processing section  125  is to perform the arithmetic processing such as white balance and gamma control with respect to each color signal (R, G, B) in a unit of a pixel from the red color signal processing section  122 , the green color signal processing section  123  and the blue color signal processing section  124 , and each color signal (R, G, B) is output to an image processing section  92  as a result of the processing.  
         [0086]    Moreover, two line memories  125   a  and  125   b  are connected to the arithmetic processing section  125 . The arithmetic processing section  125  stores a pixel signal delayed in a unit of a line by a delay circuit, in the line memories  125   a  and  125   b , at a delay timing corresponding to the magnification supplied from the SCN-CPU  120 , thereby the pixel signal can be used for correction of misregistration in a unit of a line of the respective CCD line sensors  34   a ,  34   b  and  34   c.    
         [0087]    For example, when a pixel signal for one line is supplied from the blue color signal processing section  124 , the image data of the line supplied from the signal processing section  123 , which is 8 lines ahead, is stored in the line memory  125   a , and the image data of the line supplied from the signal processing section  123 , which is 16 lines ahead with respect to the line supplied from the signal processing section  124 , is stored in the line memory  125   b . As a result, the image data for each color on the same line in the document D is output to the image processing section  140 .  
         [0088]    When the magnification is 100%, since the shift gate signals SH-R, SH-G, SH-B are synchronous, each color image data becomes complete by the shift gate signal for 16 times.  
         [0089]    When the magnification is 106%, since the shift gate signals SH-R, SH-G, SH-B are asynchronous, and deviated by ½ line, each color image data becomes complete by the shift gate signal for 17 times.  
         [0090]    To the above-descriged SCN-CPU  120  are connected a scanner motor driver (SDV)  126  which drives the scanner motor  16 , a regulator (LRG)  127  which controls lighting of the light source  25 , a cooling fan (FAN)  128 , a platen sensor  129  which detects the existence of a document on the document table  8 , a home position sensor  130  which detects the top position of the document on the document table  8 , and an automatic paper size (APS) sensor  131  which detects the size of the document on the document table  8 .  
         [0091]    In the above-described construction, the scanning processing based on the magnification will now be described.  
         [0092]    At first, the scanning processing when a copy at magnification setting of 100% is instructed will be described.  
         [0093]    That is to say, based on turning on of the copy key, the control section  101  reads 8 lines as a pitch between sensors based on the magnification setting of 100% from the internal memory  101   a,  and outputs it to the scan CPU  120 .  
         [0094]    As a result, the scan CPU  120  outputs a timing signal of the shift gate signals SH-R, SH-G, SH-B, synchronized with respect to the respective signal processing sections  122 ,  123  and  124 . As a result, the signal processing sections  122 ,  123  and  124  output the synchronized shift gate signals SH-R, SH-G, SH-B, as shown in FIG. 10A.  
         [0095]    Moreover, the scan CPU  120  does not set a delay with respect to the output from the signal processing section  122  by means of the arithmetic processing section (LAKE)  125 , and sets a delay for 8 signals of the shift gate signal SH-R with respect to the output from the signal processing section  123 , and sets a delay for 16 signals of the shift gate signal SH-R with respect to the output from the signal processing section  124 .  
         [0096]    By the above setting, the signal processing sections  122 ,  123  and  124  output the shift gate signals SH-R, SH-G, SH-B at the synchronized same timing, respectively. Moreover, the transfer clocks φ 1 R, φ 2 R, φ 1 G, φ 2 G, φ 1 B and φ 2 B are supplied at the same timing, as shown in FIGS. 10B and 10C.  
         [0097]    As a result, the CCD output signal for each color of the CCD line sensors  34   a ,  34   b  and  34   c  becomes image data shifted by 8 lines, as shown in FIGS. 10D, 10E and  10 F, and guided to the signal processing sections  122 ,  123  and  124 . Thereby, the signal processing sections  122 ,  123  and  124  output the image data in a unit of a line to the arithmetic processing section  125 , synchronous to the respective shift gate signal.  
         [0098]    Moreover, the arithmetic processing section  125  receives the image data for each line of each color of the signal processing sections  122 ,  123  and  124 , synchronous to the shift gate signal SH-R, and the image data from the signal processing section  122  is subjected to the delay processing for 16 lines based on the shift gate signal SH-R, and the image data from the signal processing section  123  is subjected to the delay processing for 8 lines based on the shift gate signal SH-R. These delayed image data are stored in the line memories  125   b  and  125   a , respectively.  
         [0099]    That is to say, at present, the image data of the line supplied from the signal processing section  123  which is 8 lines ahead with respect to the line supplied from the signal processing section  124  is stored in the line memory  125   a , and the image data of the line supplied from the signal processing section  123  which is 16 lines ahead with respect to the line supplied from the signal processing section  124  is stored in the line memory  125   b.    
         [0100]    Therefore, when the image data for the blue color of the 17th line is supplied from the signal processing section  124 , based on the shift gate signal SH-R, as shown in FIG. 10G, the arithmetic processing section  125  outputs the image data for the green color of the 17th line stored in the line memory  125   a , and the image data for the red color of the 17th line stored in the line memory  125   b , together with the image data for the blue color, at the same time to the image processing section  140 , as shown in FIGS. 10H, 10I and  10 J.  
         [0101]    Next, the scanning processing when a copy at a magnification setting of 106% is instructed will be described.  
         [0102]    That is to say, based on turning on of the copy key, the control section  101  reads 8.48 lines as a pitch between sensors based on the magnification setting of 106% from the internal memory  101   a , and outputs it to the scan CPU  120 .  
         [0103]    As a result, the scan CPU  120  outputs a timing signal of the shift gate signals SH-R, SH-G, SH-B, corresponding to the shift amount based on the above-described pitch between sensors, with respect to the respective signal processing sections  122 ,  123  and  124 . As a result, the signal processing sections  122 ,  123  and  124  output the shift gate signals SH-R, SH-G, SH-B corresponding to the shift amount, as shown in FIGS. 11A, 11B and  11 C. At this time, the shift gate signals SH-R and SH-B are shifted substantially by one line, and hence, a synchronized signal is used.  
         [0104]    Moreover, the scan CPU  120  sets a delay for one signal of the shift gate signal SH-R, with respect to the output from the signal processing section  122  by means of the arithmetic processing section (LAKE)  125 , sets a delay for 9 signals of the shift gate signal SH-R with respect to the output from the signal processing section  123 , and sets a delay for 17 signals of the shift gate signal SH-R with respect to the output from the signal processing section  124 .  
         [0105]    By the above setting, the signal processing sections  122  and  124  output the shift gate signals SH-R and SH-B at the synchronized same timing, respectively, and the signal processing section  123  outputs the shift gate signal SH-G at a timing delayed by ½ line. Moreover, the transfer clocks φ 1 R, φ 2 R, φ 1 B and φ 2 B are supplied at the same timing, as shown in FIGS. 11D, 11E,  11 H and  11 I. The transfer clocks φ 1 G and φ 2 G are supplied at a timing delayed by ½ line, as shown in FIGS. 11F and 11G.  
         [0106]    As a result, the CCD output signal for each color of the CCD line sensors  34   a ,  34   b  and  34   c  becomes image data shifted by 8 lines, as shown in FIGS. 11J, 11K and  11 L, and the CCD output signal of the CCD line sensor  34   b  is guided to the signal processing section  123  at a timing delayed by ½ line. Thereby, the signal processing sections  122 ,  123  and  124  output the image data in a unit of line to the arithmetic processing section  125 , synchronous to the respective shift gate signal.  
         [0107]    Moreover, the arithmetic processing section  125  receives the image data for each line of each color of the signal processing sections  122 ,  123  and  124 , synchronous to the shift gate signal SH-R. The image data from the signal processing section  122  is subjected to the delay processing for 17 lines based on the shift gate signal SH-R, the image data from the signal processing section  123  is subjected to the delay processing for 8 lines based on the shift gate signal SH-R, and the image data from the signal processing section  124  is subjected to the delay processing for one line based on the shift gate signal SH-R. The delayed image data from the signal processing section  123  is stored in the line memory  125   b , and the delayed image data from the signal processing section  122  is stored in the line memory  125   a.    
         [0108]    That is to say, at present, the image data of the line supplied from the signal processing section  123  which is 8 lines ahead with respect to the line supplied from the signal processing section  124  is stored in the line memory  125   a , and the image data of the line supplied from the signal processing section  123  which is 16 lines ahead with respect to the line supplied from the signal processing section  124  is stored in the line memory  125   b.    
         [0109]    Therefore, when the image data for the blue color of the 17th line is supplied from the signal processing section  124 , based on the shift gate signal SH-R, shown in FIG. 11M, the arithmetic processing section  125  outputs the image data for the green color of the 17th line stored in the line memory  125   a , and the image data for the red color of the 17th line stored in the line memory  125   b , together with the image data for the blue color, at the same time to the image processing section  140 , as shown in FIGS. 11N, 110 and  11 P. As a result, the registered image data is supplied.  
         [0110]    This registered image data is subjected to the image processing in the image processing section  140 , and thereafter, is printed out in a color printer section  103 .  
         [0111]    The above example is a case where the magnification is 106%, and in the case of other magnifications, the processing is performed similarly.  
         [0112]    As described above, the scanning timing of the CCD line sensor is changed, in accordance with the scanning misregistration amount, thereby enabling accurate correction with respect to the misregistration of less than one line. With the scanner using the color CCD sensor, misregistration of less than one line which occurs at the time of enlargement and reduction can be corrected.  
         [0113]    Moreover, when the magnification is 106%, since the scanning timing is delayed by ½ line, the MTF is not degraded, and hence image reproduction with fidelity becomes possible.  
         [0114]    Furthermore, by adjusting the timing of the shift gate signal and the transfer clock for each color of the CCD line sensor, that is, by controlling the shift gate signal and the transfer clock, the transfer clock can be output continuously for one line, and hence adaptation for high-speed driving is possible.  
         [0115]    With respect to the image scanning misregistration of less than one line, the input timing of the shift gate signal to each CCD line sensor of RED, GREEN and BLUE can be controlled corresponding to the scanning misregistration, independently for each CCD line sensor of RED, GREEN and BLUE.  
         [0116]    Furthermore, the input timing of the shift gate signal and the transfer clock to the CCD line sensor can be controlled corresponding to the scanning misregistration, independently for each CCD line sensor of RED, GREEN and BLUE.  
         [0117]    By designating the shift amount of the shift gate signal as a multiple of the transfer clock, the correction can be performed at accuracy for the number xx of pixels of the CCD line sensor.  
         [0118]    In the above embodiment, the description has been made of a case where the transfer clock is supplied separately to each CCD line sensor. However, the present invention is not limited thereto, and as shown in FIG. 12, the operation is similarly performed even in the case where the transfer clocks φ 1  and φ 2  are supplied commonly to each CCD line sensor.  
         [0119]    In this case, however, as shown in FIGS. 13A, 13B and  13 C, while the shift gate signals SH-R, SH-G, SH-B are output, the transfer clocks φ 1  and φ 2  halt, as shown in FIGS. 13D and 13E. By the halt of these transfer clocks φ 1  and φ 2 , the output of the CCD output signal for each color of the CCD line sensors  34   a ,  34   b  and  34   c  is interrupted, as shown in FIGS. 13F, 13G and  13 H.  
         [0120]    Therefore, when the image data for the blue color of the 17th line is supplied from the signal processing section  124 , based on the shift gate signal SH-R, as shown in FIG. 13I, the arithmetic processing section  125  outputs the image data for the green color of the 17th line stored in the line memory  125   a , and the image data for the red color of the 17th line stored in the line memory  125   b , together with the image data for the blue color, at the same time to the image processing section  140 , as shown in FIGS. 13J, 13K and  13 L.  
         [0121]    The above embodiment is for the case where the magnification is 106%, but is similarly performed for the case where other magnifications are used.  
         [0122]    Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.