Patent Publication Number: US-10326908-B2

Title: Image reading apparatus and image reading method

Description:
TECHNICAL FIELD 
     The present invention relates to an image reading apparatus and an image reading method for optically scanning a document to generate image data. 
     BACKGROUND ART 
     As an image reading apparatus to be applied to a copying machine, a scanner, a facsimile, and so forth, a contact image sensor that scans a document as a reading object with a one-dimensional image pickup device (line sensor) to generate image data corresponding to the document is put into practical use. The contact image sensor includes a plurality of sensor chips arranged linearly in a main-scanning direction, and each of the plurality of sensor chips includes a plurality of image pickup elements arranged linearly in the main-scanning direction at a predetermined arrangement pitch. However, since no image pickup element is disposed between adjacent sensor chips of the plurality of sensor chips, if the arrangement pitch of the image pickup elements is small, there arises a problem in which a loss of data corresponding to a position between the adjacent sensor chips is conspicuous and quality of a read image is degraded. 
     As a countermeasure for this, proposed is an apparatus in which a plurality of sensor chips are linearly arranged so that the arrangement pitch of image pickup elements between the adjacent sensor chips is twice as large as the arrangement pitch of image pickup elements in each of the sensor chips, and a loss of data in a position between the adjacent sensor chips is interpolated by signal processing (e.g., see Patent Document 1). Patent Document 1 describes an apparatus using, as interpolation data, an average value of data of two pixels at both sides of a data loss position corresponding to the position between the adjacent sensor chips, and also describes an apparatus using, as interpolation data, a value obtained from a calculation made by using a quartic approximate curve derived from data of two pixels at each side (i.e., four pixels in total) of the data loss position corresponding to the adjacent sensor chips. 
     PRIOR ART REFERENCE 
     Patent Reference 
     Patent Document 1: Japanese Patent Application Publication No. 2003-101724 (paragraphs 0039 to 0067 and  FIGS. 3 to 5 ) 
     SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
     The apparatus described in Patent Document 1, however, has a problem in which an accurate image at the data loss position cannot be reproduced if image information having high frequency components is present at a position on a document corresponding to the data loss position between the adjacent sensor chips. 
     The present invention has been made to solve the problem in the conventional art described above, and its object is to provide an image reading apparatus and an image reading method capable of preventing a loss of data at a position corresponding to a position between adjacent sensor chips, thereby enhancing quality of a read image. 
     Means of Solving the Problem 
     An image reading apparatus according to the present invention includes: N sensor chips arranged in a first direction, N being an integer of two or more, each of the N sensor chips including a plurality of image pickup elements arranged in the first direction; N optical systems that respectively form, on the N sensor chips, reduced-size images of N reading ranges arranged in the first direction on a document; and an image processing section that uses image data of overlap regions that are regions where adjacent reading ranges of image data of the N reading ranges overlap each other, the image data of the overlap regions being image data generated by the N sensor chips, thereby obtaining positions in the first direction of the overlap regions of the adjacent reading ranges, obtains, from the positions in the first direction, magnifications of read images and synthesis positions that indicate positions where two pieces of the image data are combined, performs image processing of correcting the magnifications in the first direction of the image data of the N reading ranges, and combines the image data of the N reading ranges subjected to the image processing, thereby generating synthesized image data. 
     Effect of the Invention 
     According to the present invention, N optical systems can remove a loss of data at a position corresponding to a position between adjacent sensor chips of N sensor chips that are arranged in a main-scanning direction and can eliminate distortion (a positional difference between the synthesis positions) of N pieces of image data generated due to the N optical systems. As a result, high-quality synthesized image data corresponding to reading ranges on a document can be generated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a functional block diagram illustrating a schematic configuration of an image reading apparatus according to a first embodiment of the present invention. 
         FIG. 2A  is a side view illustrating ranges of light travelling from a document at a reference position toward sensor chips of an image pickup unit, and  FIG. 2B  is a plan view illustrating ranges (ranges on the document) of the light travelling toward the sensor chips and reading ranges to be read by the sensor chips in the case of  FIG. 2A . 
         FIG. 3  is a plan view schematically illustrating a plurality of sensor chips of the image pickup unit illustrated in  FIG. 1 . 
         FIG. 4A  is a diagram illustrating an example of ranges (ranges on the document) of light travelling from the document at the reference position toward the sensor chips and a graphic pattern on the document,  FIG. 4B  is a diagram illustrating an example of images incident on the sensor chips in the case of  FIG. 4A , and  FIG. 4C  is a diagram illustrating image data generated by the sensor chips in the case of  FIG. 4B . 
         FIG. 5A  is a side view illustrating ranges of light travelling toward the sensor chips from a document at a position closer to the image pickup unit than the reference position, and  FIG. 5B  is a plan view illustrating ranges (ranges on the document) of light travelling toward the sensor chips and reading ranges to be read by the sensor chips in the case of  FIG. 5A . 
         FIG. 6A  is a diagram illustrating an example of ranges (ranges on the document) of light travelling toward the sensor chips from a document at a position closer to the image pickup unit than the reference position and a graphic pattern,  FIG. 6B  is a diagram illustrating images incident on the sensor chips in the case of  FIG. 6A , and  FIG. 6C  is a diagram illustrating image data generated by the sensor chips in the case of  FIG. 6B . 
         FIG. 7A  is a side view illustrating ranges of light travelling toward the sensor chips of the image pickup unit from a document at a position farther from the image pickup unit than the reference position, and  FIG. 7B  is a plan view illustrating ranges (ranges on the document) of light travelling toward the sensor chips and reading ranges to be read by the sensor chips in the case of  FIG. 7A . 
         FIG. 8A  is a diagram illustrating an example of ranges (ranges on the document) of light travelling toward the sensor chips from a document at a position farther from the image pickup unit than the reference position and a graphic pattern on the document,  FIG. 8B  is a diagram illustrating images incident on the sensor chips in the case of  FIG. 8A , and  FIG. 8C  is a diagram illustrating image data generated by the sensor chips in the case of  FIG. 8B . 
         FIG. 9  is a diagram for explaining an operation of a similarity degree calculator illustrated in  FIG. 1 . 
         FIGS. 10A to 10F  are diagrams for explaining an operation of a synthesis position estimating unit illustrated in  FIG. 1 . 
         FIGS. 11A to 11C  are diagrams for explaining an operation of a synthesizing unit in the case of  FIGS. 4A to 4C  where a document is at the reference position. 
         FIGS. 12A to 12C  are diagrams for explaining an operation of the synthesizing unit in the case of  FIGS. 6A to 6C  where the document is at a position closer to the image pickup unit than the reference position. 
         FIGS. 13A to 13C  are diagrams for explaining an operation of the synthesizing unit in the case of  FIGS. 8A to 8C  where the document is at a position farther from the image pickup unit than the reference position. 
         FIG. 14  is a hardware configuration diagram illustrating an example of a configuration of an image reading apparatus according to a second embodiment of the present invention. 
         FIG. 15  is a flowchart schematically illustrating an example of processing (an image reading method according to the second embodiment) executed by a computation device of the image reading apparatus according to the second embodiment. 
         FIG. 16  is a block diagram illustrating a configuration example of a synthesizing unit in the image reading apparatus according to the first embodiment. 
         FIG. 17  is a block diagram illustrating a configuration example of a synthesis magnification setting unit in the synthesizing unit of the image reading apparatus according to the first embodiment. 
         FIG. 18  is a block diagram illustrating a configuration example of a synthesis magnification setting unit in a synthesizing unit in an image reading apparatus according to a third embodiment. 
         FIGS. 19A to 19C  are diagrams for explaining an operation of the synthesizing unit in a case where a document is at a position closer to an image pickup unit than a reference position in the synthesizing unit according to the third embodiment. 
         FIGS. 20A to 20C  are diagrams for explaining an operation of the synthesizing unit in a case where the document is at a position farther from the image pickup unit than the reference position in the synthesizing unit according to the third embodiment. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     &lt;1&gt; First Embodiment 
     &lt;1-1&gt; Configuration of First Embodiment 
       FIG. 1  is a functional block diagram illustrating a schematic configuration of an image reading apparatus  1  according a first embodiment of the present invention. As illustrated in  FIG. 1 , the image reading apparatus  1  includes an image pickup unit  2 , an A-D (analog-to-digital) converter  3 , and an image processing section  4 . The image processing section  4  includes an image memory  41 , a similarity degree calculator  42 , a synthesis position estimating unit  43 , and a synthesizing unit  44 . The image reading apparatus  1  may include a conveyance section that conveys a document and a control section that controls the entire apparatus. The conveyance section and a processor serving as the control section will be described in a second embodiment mentioned later. 
     The image pickup unit  2  includes N (where N is an integer of two or more) sensor chips arranged linearly on a substrate. Each of the N sensor chips includes a plurality of image pickup elements that are linearly arranged. A direction (first direction) along which the plurality of image pickup elements are arranged will be referred to as a main-scanning direction. The N sensor chips are arranged in the main-scanning direction in such a manner that the image pickup elements of the N sensor chips are linearly arranged. The image pickup unit  2  includes N optical systems (cells) that form, on the N sensor chips, size-reduced images of a plurality of reading ranges on a document. Each of the N optical systems includes, for example, a lens and a diaphragm. The N optical systems prevent a loss of data at a position corresponding to a position between adjacent sensor chips of the N sensor chips that are linearly arranged. That is, the N sensor chips and the N optical systems are arranged in such a manner that two adjacent reading ranges (also referred to as reading regions) to be read by the adjacent sensor chips of the N sensor chips partially overlap each other in the ends of the adjacent reading ranges. These overlapping parts of the reading ranges (the regions that overlap each other) serve as overlapping regions (overlap regions). 
     An image signal SI generated by optically scanning the document with the image pickup unit  2  is converted to digital image data DI in the A-D converter  3 . The image data DI is then input to the image processing section  4 , and stored in the image memory  41  in the image processing section  4 . 
       FIG. 2A  is a side view illustrating ranges  28  of light travelling from a document  26  at a reference position P toward the sensor chips  21  of the image pickup unit  2  through the lenses  24 , the diaphragms  23  having apertures  23   a , and the lenses  22 .  FIG. 2B  is a plan view illustrating ranges (ranges on the document  26 )  29  of the light travelling toward the sensor chips  21  and reading ranges  2 A to be read by the sensor chips  21  in the case of  FIG. 2A . In the drawings, the main-scanning direction is represented by an x axis, and a sub-scanning direction orthogonal to the main-scanning direction is represented by a y axis. 
     Each of the N optical systems of the image pickup unit  2  includes the lens  22 , the diaphragm  23  having the aperture  23   a , and the lens  24 . In the following description, k is an integer of not less than 1 and not more than N. The k-th sensor chip  21  in the N sensor chips will be also represented by  21 ( k ). The k-th lens in the N lenses  22  will be also represented by  22 ( k ). The k-th lens in the N lenses  24  will be also represented by  24 ( k ). Similarly, the (k−1)th and (k+1)th sensor chips and lenses will be represented by the numbers indicating the order of arrangement in brackets. 
     The image reading apparatus  1  may include an illumination  27  that irradiates the document  26  with light. The illumination  27  can include, for example, an LED (light emitting diode) as a light source and a light guide member such as a resin member for converting light emitted from the LED to illumination light on the document  26 . This light guide member is, for example, a cylindrical light guide member which has a length approximately equal to a width of the document  26 . Light reflected on the document  26  is focused by the lenses  24 . Unnecessary part of the light focused by the lenses  24  is blocked by the diaphragms  23 , and necessary part of the light passes through the apertures  23   a  of the diaphragms  23 . Light that has passed through the apertures  23   a  of the diaphragms  23  reaches the plurality of image pickup elements of the sensor chips  21  through the lenses  22 . 
     A range  28 ( k −1) indicated by a broken line in  FIG. 2A  and a range  29 ( k −1) indicated by a broken line in  FIG. 2B  represent ranges of light that has reached the sensor chip  21 ( k −1). A range  28 ( k ) indicated by a broken line in  FIG. 2A  and a range  29 ( k ) indicated by a broken line in  FIG. 2B  represent a range of light that has reached the sensor chip  21 ( k ). A range  28 ( k +1) indicated by a broken line in  FIG. 2A  and a range  29 ( k +1) indicated by a broken line in  FIG. 2B  represent a range of light that has reached the sensor chip  21 ( k +1). 
     The N sensor chips  21  and the N optical systems are arranged in such a manner that two adjacent reading ranges (e.g., a reading range  2 A(k−1) and a reading range  2 A( k ), and a reading range  2 A( k ) and a reading range  2 A(k+1) in  FIG. 2B ) on the document  26  to be read by adjacent sensor chips of the N sensor chips  21  partially overlap each other (e.g., regions having a width L 1  in  FIG. 2B ). The overlapping reading ranges (which are regions overlapping each other) having the width L 1  in the x axis direction serve as overlapping regions (overlap regions). 
     In  FIG. 2A , the document  26  is conveyed in a direction perpendicular to the drawing sheet on which  FIG. 2A  is drawn and in a direction from the back to the front (+y axis direction) or from the front to the back (−y axis direction). The document  26  may be stationary with the image pickup unit  2  being conveyed from the direction from the back to the front (+y axis direction) or from the front to the back (−y axis direction). In other words, at least one of the document  26  and the image pickup unit  2  moves so that the document  26  and the image pickup unit  2  move relative to each other in the sub-scanning direction (second direction). 
       FIG. 3  is a plan view schematically illustrating the plurality of sensor chips  21  of the image pickup unit  2 .  FIG. 3  shows the sensor chips  21 ( k −1) and  21 ( k ) of the N sensor chips  21 . Each of the N sensor chips  21  includes a plurality of red image pickup elements (R image pickup elements)  211  each having a red (R) optical filter disposed on the image pickup element, a plurality of green image pickup elements (G image pickup elements)  212  each having a green (G) optical filter disposed on the image pickup element, a plurality of blue image pickup elements (B image pickup elements)  213  each having a blue (B) optical filter disposed on the image pickup element, and a readout circuit  214 . For the k-th sensor chip  21 ( k ), these components are also represented as an R image pickup element  211 ( k ), a G image pickup element  212 ( k ), a B image pickup element  213 ( k ), and a readout circuit  214 ( k ). Similarly, for the other sensor chips  21 , the numbers indicating the order of arrangement are shown in brackets. 
     Light reflected on the document  26  is focused on the image pickup elements of the individual colors of the sensor chips  21 . The R image pickup elements  211  perform photoelectric conversion on red light of the focused light, the G image pickup elements  212  perform photoelectric conversion on green light of the focused light, and the B image pickup elements  213  perform photoelectric conversion on blue light of the focused light. Electrical signals obtained by the photoelectric conversion are sequentially read out by the readout circuit  214  and output as signals SI. 
     The (k−1)th sensor chip  21 ( k −1) and the k-th sensor chip  21 ( k ) are arranged in such a manner that the R image pickup elements of the (k−1)th sensor chip  21 ( k −1) and the R image pickup elements of the k-th sensor chip  21 ( k ) are arranged on the same line, the G image pickup elements of the (k−1)th sensor chip  21 ( k −1) and the G image pickup elements of the k-th sensor chip  21 ( k ) are arranged on the same line, and the B image pickup elements of the (k−1)th sensor chip  21 ( k −1) and the B image pickup elements of the k-th sensor chip  21 ( k ) are arranged on the same line. Other adjacent sensor chips have similar positional relationships. 
     Although  FIG. 3  shows an example in which the line of the plurality of R image pickup elements, the line of the plurality of G image pickup elements, and the line of the plurality of B image pickup elements are arranged vertically in this order on the sensor chips  21 , the positions of these image pickup elements may be replaced. In the case of not obtaining color images, sensor chips each including a plurality of image pickup elements arranged in a single line and provided with no optical filters may be used. 
       FIGS. 2A and 2B  illustrate a case where the document  26  at the reference position P is conveyed in a +y axis direction or a −y axis direction in the drawings. The reference position P is a predetermined position, and is, for example, a position at a predetermined distance from a glass surface  25 . Here, the reference position P as the predetermined position is a position previously set by a user operation or the like, and is set by, for example, measuring a distance from the glass surface  25  as a reference, before the process is performed (not shown in the drawings). 
     The ranges  29  of light in  FIG. 2B  represent ranges, on the document  26 , of light focused by the lenses  24 . The range  29 ( k −1) of light is a range of light focused by the lens  24 ( k −1). The range  29 ( k ) of light is a range of light focused by the lens  24 ( k ). The range  29 ( k +1) of light is a range of light focused by the lens  24 ( k +1). 
     Since the plurality of image pickup elements are linearly arranged in the sensor chips  21  illustrated in  FIG. 3 , the reading ranges  2 A of light among the ranges  29  of light focused by the lenses  24  are received by the sensor chips  21  and subjected to photoelectric conversion. The reading range  2 A(k−1) is received by the sensor chip  21 ( k −1). The reading range  2 A( k ) is received by the sensor chip  21 ( k ). The reading range  2 A(k+1) is received by the sensor chip  21 ( k +1). The reading range  2 A(k−1) and the reading range  2 A( k ) overlap each other in a part having the width L 1  in the x axis direction. Similarly, the reading range  2 A( k ) and the reading range  2 A(k+1) overlap each other in a part having the width L 1  in the x axis direction. These parts of the reading ranges that overlap each other in parts each having the width L 1  in the x axis direction are overlap regions. 
       FIGS. 4A to 4C  are diagrams for explaining images read by the sensor chips  21  in a case where the document  26  at the reference position (P in  FIG. 2A ) is conveyed in the y axis direction.  FIG. 4A  is a diagram illustrating an example of ranges (ranges on the document  26 )  29  of light traveling from the document  26  at the reference position P toward the sensor chips  21  of the image pickup unit  2  through the lenses  24 , the diaphragms  23 , and the lenses  22  and an example of a graphic pattern (e.g., a zigzag pattern constituted by a plurality of repetitive “Λ”-shaped graphics) on the document  26 .  FIG. 4B  is a diagram illustrating an example of images incident on the sensor chips  21  in the case of  FIG. 4A .  FIG. 4C  is a diagram illustrating image data generated by the sensor chips  21  in the case of  FIG. 4B . 
     With reference to  FIGS. 4A to 4C , the case where the graphic pattern in which the plurality of “Λ”-shaped graphics are laterally arranged is printed on the document  26  will be described. To make it easier to understand the following description, in a case where the document  26  at the reference position P is conveyed in the y axis direction, the width (lateral width) of one “Λ”-shaped graphic coincides with the width L 1  in the x axis direction of the overlap regions of the reading ranges  2 A read by the adjacent sensor chips  21 . That is, in  FIG. 4A , the width in the x axis direction of one “Λ”-shaped graphic is equal to the width L 1 . 
     In  FIGS. 4A to 4C , the document  26  is conveyed in the y axis direction with a reading surface thereof facing upward. The reference position P is defined relative to the glass surface  25 , for example. In  FIGS. 4A to 4C , the document  26  is conveyed at a position of the reference position P, and the ranges in the x axis direction of overlap regions OV 2  illustrated in  FIG. 4C  are set in such a manner that the width in the x axis direction of each of the overlap regions OV 2  coincides with the width in the x axis direction of one “Λ”-shaped graphic. In a manner similar to that of the reference position P, the width of each of the overlap regions OV 2  at the reference position P is previously set by a user operation or the like (not shown in the drawings). 
     Next, a case where the document  26  is conveyed in the y axis direction at a position of (reference position−d) mm will be described. Here, d is a positive value.  FIG. 5A  is a side view illustrating ranges of light travelling toward the sensor chips  21  of the image pickup unit  2  from the document  26  closer to the image pickup unit  2  than the reference position P by d mm through the lenses  24 , the diaphragms  23 , and the lenses  22 .  FIG. 5B  is a plan view illustrating ranges (ranges on the document  26 )  29  of light travelling toward the sensor chips  21  and reading ranges  2 A to be read by the sensor chips  21  in the case of  FIG. 5A . 
     The ranges  28  of light focused by the lenses  24  become larger as they approach the glass surface  25  and the document  26  from the lens  24 . The document  26  shown in  FIGS. 5A and 5B  is closer to the lenses  24  than that in  FIGS. 2A and 2B , and thus the ranges  29  on the document  26  are smaller than the ranges in the case of  FIGS. 2A and 2B . Thus, the widths in the x axis direction of the reading ranges  2 A(k−1),  2 A( k ), and  2 A(k+1) are smaller, and a width L 2  in the x axis direction of the overlap regions of the reading range  2 A(k−1) and the reading range  2 A( k ) is smaller than the width L 1  in the x axis direction in the case of  FIGS. 2A and 2B  (L 2 &lt;L 1 ). 
       FIGS. 6A to 6C  are diagrams for explaining images read by the sensor chips  21  in a case where the document  26  is conveyed in the y axis direction at a position of (reference position−d) mm.  FIG. 6A  is a diagram illustrating an example of ranges (ranges on the document  26 )  29  of light traveling toward the sensor chips  21  of the image pickup unit  2  from the document  26  at a position closer to the image pickup unit  2  than the reference position P and the graphic pattern (zigzag pattern) on the document  26 .  FIG. 6B  is a diagram illustrating images incident on the sensor chips  21  in the case of  FIG. 6A .  FIG. 6C  is a diagram illustrating image data generated by the sensor chips  21  in the case of  FIG. 6B . 
     With reference to  FIGS. 6A to 6C , a case where the graphic pattern in which a plurality of “Λ”-shaped graphics are laterally arranged is printed on the document  26  will be described. To make it easier to understand the following description, in a case where the document  26  is conveyed at the position of (reference position−d) mm, the lateral width (width in the x axis direction) of one “Λ”-shaped graphic is larger than the width L 2  in the x axis direction of the overlap regions of the reading ranges  2 A read by the adjacent sensor chips  21 . 
     In  FIGS. 6A to 6C , the width L 2  in the x axis direction of the overlap regions of the adjacent reading ranges  2 A is smaller than the width L 1  in the x axis direction of the overlap region illustrated in  FIG. 4A , as described with reference to  FIGS. 5A and 5B . Thus, as illustrated in  FIG. 6B , the width in the x axis direction of one “Λ”-shaped graphic is not within the width in the x axis direction of each of the overlap regions OV 1 , and extends beyond the overlap region OV 1  in the x axis direction. As illustrated in  FIG. 6C , however, since the overlap regions OV 2  set on the sensor chips  21  are independent of the positional relationship between the glass surface  25  and the document  26 , the graphics outside the overlap regions OV 1  in  FIG. 6B  are also contained within the overlap regions OV 2  on the sensor chips  21 . In the case of  FIG. 6C , images obtained by the sensor chips  21  are enlarged as compared to images obtained in the case of  FIG. 4C . 
     Next, a case where the document  26  is conveyed in the y axis direction at a position of (reference position+d) mm will be described.  FIG. 7A  is a side view illustrating ranges of light travelling toward the sensor chips  21  from the document  26  at a position farther from the image pickup unit  2  than the reference position P through the lenses  24 , the diaphragms  23 , and the lenses  22 .  FIG. 7B  is a plan view illustrating ranges (ranges on the document  26 )  29  of light travelling toward the sensor chips  21  in the case of  FIG. 7A  and reading ranges  2 A to be read by the sensor chips  21 . 
     In  FIGS. 7A and 7B , since the document  26  is located away farther from the lenses  24  than in the case of  FIGS. 2A and 2B , the ranges  29  of light on the document  26  are larger than the ranges in the case illustrated in  FIGS. 2A and 2B . Thus, the widths in the x axis direction of the reading ranges  2 A(k−1),  2 A( k ), and  2 A(k+1) are large, and a width L 3  in the x axis direction of the overlapping regions (overlap regions) of the reading range  2 A(k−1) and the reading range  2 A( k ) is larger than the width L 1  in the x axis direction in the case of  FIGS. 2A and 2B  (L 3 &gt;L 1 ). 
       FIGS. 8A and 8C  are diagrams for explaining images read by the sensor chips  21  in a case where the document  26  is conveyed in the y axis direction at a position of (reference position+d) mm.  FIG. 8A  is a diagram illustrating an example of ranges (ranges on the document  26 )  29  of light traveling toward the sensor chips  21  from the document  26  at a position farther from the image pickup unit  2  than the reference position P and the graphic pattern (zigzag pattern) on the document  26 .  FIG. 8B  is a diagram illustrating images incident on the sensor chips  21  in the case of  FIG. 8A .  FIG. 8C  is a diagram illustrating image data generated by the sensor chips  21  in the case of  FIG. 8B . 
     In  FIGS. 8A to 8C , since the width in the x axis direction of the overlap regions of adjacent reading ranges  2 A is L 3  that is larger than L 1  as described with reference to  FIGS. 5A and 5B , one “A”-shaped graphic falls within a corresponding one of the overlap regions OV 1  as illustrated in  FIG. 8B . However, as illustrated in  FIG. 8C , since the overlap regions OV 2  set on the sensor chips  21  are independent of the positional relationship between the glass surface  25  and the document  26 , the entire overlap regions OV 1  illustrated in  FIG. 8B  are not contained within the overlap regions OV 2  on the sensor chips  21 . In the case of  FIG. 8C , images obtained by the sensor chips  21  are reduced in size as compared to those in the case illustrated in  FIG. 4C . 
     Next, in the image reading apparatus  1 , with respect to the digital image data DI supplied from the A-D converter  3 , the image processing section  4  corrects the magnifications of image data of the reading ranges corresponding to the sensor chips, performs image processing for synthesizing the image data of the reading ranges corresponding to the N sensor chips, and thereby generates synthesized image data D 44 . 
     The image processing section  4  compares the image data of the adjacent overlap regions by using the image data of overlap regions in the image data of the reading ranges (reading regions) corresponding to the N sensor chips in the image data DI stored in the image memory  41 , determines positions of the overlap regions having the highest correlation (also referred to as the highest degree of similarity), which are parts of the reading regions read from the document at the same position, obtains magnifications of read images and synthesis positions that indicate positions where two pieces of image data are combined, based on the positions of the overlap regions, corrects the magnifications of the image data of the reading ranges corresponding to the sensor chips, performs image processing of synthesizing the image data of the reading ranges corresponding to the N sensor chips, and thereby generates the synthesized image data D 44 . A configuration of the image processing section  4  will now be described with reference to  FIG. 1 . 
     The similarity degree calculator  42  calculates the degree of correlation (i.e., the degree of similarity, which will be hereinafter referred to as a similarity degree) by comparing image data of matching regions set in the overlap regions and performing matching processing (obtaining a positional difference between the matching regions) among pixels, by using the image data of the overlap regions which are regions where the adjacent reading ranges overlap each other, out of the image data which are image data generated by the N sensor chips and image data of the N reading ranges on the document. The degree of correlation is calculated and output as similarity degree data (signal D 42 ) that is an index indicating the degree of similarity among the image data of the overlap regions. 
     From the similarity degree data D 42  calculated by the similarity degree calculator  42 , the synthesis position estimating unit  43  estimates the synthesis positions (signal D 43 ) that indicate positions of overlap regions having the highest correlation (having the highest degree of similarity) and positions at which two pieces of image data of adjacent reading ranges are combined, and outputs the position data D 43  indicating the synthesis positions, based on the estimated positions. 
     By using the magnifications for the image data of the N reading ranges based on the synthesis positions estimated by the synthesis position estimating unit  43 , the synthesizing unit  44  sets (i.e., equal magnifies or enlarges or reduces by using the magnifications) the widths in a main-scanning direction of the image data of the N reading ranges, synthesizes the image data, and thereby generates the synthesized image data D 44 . Through repetition of the foregoing processing, image data corresponding to an image on the document as a reading object is generated. The image processing section  4  can make distortion of the image data generated due to the N optical systems and a resultant positional difference between of the synthesis positions inconspicuous. 
     The synthesizing unit  44  is configured as illustrated in, for example,  FIG. 16 . The synthesizing unit  44  illustrated in  FIG. 16  sets synthesis magnifications and synthesis positions of the image data of the reading ranges by using a positional difference between the position data D 43  supplied from the synthesis position estimating unit  43  and synthesis reference positions Pr on the overlap regions, converts the magnifications of the image by using the synthesis magnifications, and combines (also referred to as “connects” or “bonds”) the images of the overlap regions in accordance with the synthesis positions, thereby generating and outputting the synthesized image data D 44 . The synthesis reference positions Pr on the overlap regions are set according to the positions of the overlap regions OV 2  at the reference position P, and are predetermined reference positions previously set by a user operation or the like (not shown in the drawings). 
     As illustrated in  FIG. 16 , the synthesizing unit  44  includes a synthesis magnification setting unit  45 , an image converter  442 , and an overlap region connecting unit  443 . 
     The position data D 43  input to the synthesizing unit  44  from the synthesis position estimating unit  43  is input to the synthesis magnification setting unit  45 . From positional differences between the position data D 43  and the synthesis reference positions Pr in the overlap regions in the main-scanning direction (x axis direction), the synthesis magnifications and the synthesis positions of the image data of the reading ranges are set, and synthesis magnification position data D 45  indicating the synthesis magnifications and the synthesis positions is output. The synthesis magnification setting unit  45  is configured as illustrated in, for example,  FIG. 17 , and includes a reading width calculator  451  and a magnification and synthesis position setting unit  452 . 
     The reading width calculator  451  in the synthesis magnification setting unit  45  calculates reading widths Wc in the main-scanning direction (widths in the main-scanning direction of the reading regions) with respect to the image data of the reading ranges (reading regions) read by the cells, from the position data D 43  supplied from the synthesis position estimating unit  43 . The reading widths Wc can be obtained by calculating a difference between two pieces of position data D 43  obtained in overlap regions at both ends of each reading region. The magnification and synthesis position setting unit  452  sets the synthesis magnifications from a difference between the reading width Wc supplied from the reading width calculator  451  and a width Wr between synthesis reference positions Pr at both ends of the reading region read by each of the cells (i.e., positional differences between the synthesis positions of the reading regions and the reference position), obtains the position data D 43  from the synthesis position estimating unit  43  as positions of synthesis (synthesis positions) converted (moved) by using the set synthesis magnifications, and outputs the obtained data as the synthesis magnification position data D 45  indicating the synthesis magnifications and the synthesis positions. The width Wr between the synthesis reference positions Pr at both ends of the reading region can be previously set based on the synthesis reference positions Pr, and is a reference width previously set by a user operation or the like (not shown in the drawings). 
     The image converter  442  of the synthesizing unit  44  converts the magnifications of the image of the reading regions read by the cells in the image data DI stored in the image memory  41 , by using the synthesis magnifications based on the synthesis magnification position data D 45  supplied from the synthesis magnification setting unit  45 , to thereby correct the magnifications of image data of the reading regions corresponding to the sensor chips and output magnification-converted image data D 442 . In accordance with the synthesis positions based on the synthesis magnification position data D 45 , the overlap region connecting unit  443  combines images of overlap regions in the magnification-converted image data D 442  whose magnifications have been corrected by the image converter  442  to, thereby, generate and output the synthesized image data D 44 . Performing the combination by the overlap region connecting unit  443  by performing, for example, weighting addition of image data at the synthesis positions and its surrounding image data makes it possible to obtain a synthesis image in which distortion of image data and a resultant positional difference between the synthesis positions are made inconspicuous. 
     &lt;1-2&gt; Operation in First Embodiment 
     &lt;Operation of Image Pickup Unit  2 &gt; 
     The image pickup unit  2  outputs a signal SI obtained by photoelectric conversion of light reflected on the document  26  to the A-D converter  3 . The A-D converter  3  converts the signal SI from an analog signal to a digital signal and outputs image data DI based on the digital signal to the image processing section  4 . 
     The image data DI output from the A-D converter  3  is input to the image memory  41  of the image processing section  4 . The image memory  41  temporarily stores the image data DI and outputs image data MO and image data ME in the overlap regions to the similarity degree calculator  42 . The image data MO is image data of overlap regions corresponding to sensor chips in odd-numbered cells. The image data ME is image data of overlap regions corresponding to sensor chips in even-numbered cells. 
     &lt;Operation of Similarity Degree Calculator  42 &gt; 
       FIG. 9  is a diagram for explaining an operation of the similarity degree calculator  42  of the image processing section  4  illustrated in  FIG. 1 . In  FIG. 9 , OV 2 ( k −1, R) represents an overlap region (8×4 pixels) at the right in the x axis direction of image data generated by the (k−1)th sensor chip  21 ( k −1). OV 2 ( k , L) represents an overlap region (8×4 pixels) at the left of image data generated by the k-th sensor chip  21 ( k ) adjacent to the (k−1)th sensor chip  21 ( k −1). Each of CD(− 1 ) to CD(− 7 ) represents a matching region of 4×2 pixels extracted from the overlap region OV 2 ( k −1, R). Here, identification numbers from −1 to −7 in brackets indicate the numbers of the matching regions. Each of CD(1) to CD(7) represents a matching region of 4×2 pixels extracted from the overlap region OV 2 ( k , L). Here, identification numbers from 1 to 7 in brackets indicate the numbers of the matching regions. 
     As illustrated in  FIG. 9 , in the first embodiment, the matching regions CD(− 7 ) to CD(− 1 ) are extracted from the overlap region OV 2 ( k −1, R), and the matching regions CD( 1 ) to CD( 7 ) are extracted from the overlap region OV 2 ( k , L) of the adjacent cell. In the adjacent overlap regions, the matching regions CD(− 7 ) to CD(− 1 ) are extracted from one overlap region OV 2 ( k , R), and the matching regions CD( 1 ) to CD( 7 ) are extracted from the other overlap region OV 2 ( k +1, L). 
     The similarity degree calculator  42  calculates the degree of correlation (degree of similarity) by performing matching processing between pixels in regions at the same position (obtaining positional differences between the regions) in the matching regions CD(− 1 ) to CD(− 7 ) and the matching regions CD( 1 ) to CD( 7 ). For example, an absolute value of the difference between pixels at the same position in the matching region CD(− 1 ) and the matching region CD( 1 ) is calculated, the sum of differential absolute values of the entire matching regions CD(− 1 ) and CD( 1 ) is calculated, and the obtained sum is output as data D 42 ( 1 ) indicating the degree of similarity (hereinafter also referred to as “the sum of differential absolute values” or “similarity degree data”). Similarly, with respect to the matching region CD(− 2 ) and the matching region CD( 2 ), the sum of differential absolute values is calculated and output as data D 42 ( 2 ). With respect to the matching region CD(− 3 ) and the matching region CD( 3 ) to the matching region CD(− 7 ) and the matching region CD( 7 ), similar calculation is performed, and the sums D 42 ( 3 ) to D 42 ( 7 ) of differential absolute values are output. 
     In the description with reference to  FIG. 9 , the overlap regions have a width constituted by eight pixels (in the x axis direction) and a height constituted by four pixels (in the y axis direction), and the matching regions as parts of the overlap regions have a width constituted by two pixels (in the x axis direction) and a height of four pixels (in the y axis direction). However, the present invention is not limited to this example. The degree of similarity may be obtained by using, as the matching regions, the entire overlap region having a predetermined height (width in the y axis direction) and moving the center position sequentially with reference to the center position of the width of the overlap region (the x axis direction), or by fixing a matching region in one overlap region OV 2 ( k −1, R) of the adjacent overlap regions and moving another matching region in the other overlap region OV 2 ( k , L). 
     As the value of each of the similarity degree data D 42 ( 1 ) to D 42 ( 7 ) as the sum of differential absolute values calculated by the similarity degree calculator  42  decreases, the difference between pixels in two matching regions used for the differential calculation decreases, and the degree of correlation (the degree of similarity) increases, that is, the degree of similarity as an index indicating the degree of similarity between the two matching regions increases (more similar to each other). Thus, quality of an image at a joint can be enhanced in such a manner that adjacent two pieces of image data are synthesized by using, as overlap regions that are synthesis positions (joint positions) and are actually read, positions having the smallest sum of differential absolute values (i.e., positions having the highest degree of similarity, that is, positions having the highest correlation) among the sums D 42 ( 1 ) to D 42 ( 7 ) of differential absolute values, and then by setting the magnifications of the image based on the positions. The similarity degree calculator  42  outputs the similarity degree data D 42  including the sums D 42 ( 1 ) to D 42 ( 7 ) of differential absolute values to the synthesis position estimating unit  43 . 
     &lt;Operation of Synthesis Position Estimating Unit  43 &gt; 
       FIGS. 10A to 10F  are diagrams for explaining an operation of the synthesis position estimating unit  43 .  FIGS. 10A and 10B  are diagrams for explaining an operation in a case where the document  26  is at the reference position P (the case of  FIGS. 4A to 4C ).  FIGS. 10C and 10D  are diagrams for explaining an operation in a case where the document  26  is at the position closer to the sensor chips  21  than the reference position P (the case of  FIGS. 6A to 6C ).  FIGS. 10E and 10F  are diagrams for explaining an operation in a case where the document  26  is at the position farther from the sensor chips  21  than the reference position P (the case of  FIGS. 8A to 8C ).  FIGS. 10A, 10C, and 10E  illustrate positional relationships between the matching regions CD(− 7 ) to CD(− 1 ) in the right overlap region OV 2 ( k −1, L) of image data generated by the (k−1)th sensor chip  21 ( k −1) and the matching regions CD( 1 ) to CD( 7 ) in the left overlap region OV 2 ( k , L) of image data generated by the k-th sensor chip  21 ( k ).  FIGS. 10B, 10D, and 10F  are diagrams showing similarity degree data (the sum of differential absolute values) D 42  corresponding to image data of the matching regions illustrated in  FIGS. 10A, 10C, and 10E . 
     In  FIG. 10B , the sum of differential absolute values when x=4, that is, between CD(− 4 ) and CD( 4 ) is the smallest (i.e., the degree of similarity is the highest). In this case, the synthesis position estimating unit  43  outputs the position data D 43  by using x=4 as synthesis positions. 
     In  FIG. 10D , the sum of differential absolute values when x=2, that is, between CD(− 2 ) and CD(2) is the smallest (i.e., the degree of similarity is the highest). In this case, the synthesis position estimating unit  43  outputs the position data D 43  by using x=2 as synthesis positions. 
     In  FIG. 10F , the sum of differential absolute values when x=5, that is, between CD(− 5 ) and CD( 5 ) is the smallest (i.e., the degree of similarity is the highest). In this case, the synthesis position estimating unit  43  outputs the position data D 43  by using x=5 as synthesis positions. 
     At every line, that is, every time when the document  26  is conveyed by a distance corresponding to one pixel in the y axis direction, the similarity degree calculator  42  sets the matching regions CD with respect to the overlap regions which are at both ends of the reading ranges of the sensor chips and have a symmetrical arrangement about a target line, and outputs similarity degree data (sum of differential absolute values) D 42 . Similarly, the synthesis position estimating unit  43  outputs the position data D 43  as the synthesis positions, based on the similarity degree data D 42  that is the sum of differential absolute values calculated by the similarity degree calculator  42  for each line. In the description with reference to  FIGS. 10A to 10F , the position of y=8 is the target line. 
     In the description with reference to  FIGS. 10A to 10F , the position data D 43  as a synthesis position is represented by an integer. However, the synthesis positions may be obtained by obtaining an approximate curve connecting points of the sums of differential absolute values on an orthogonal coordinate system having an x axis and a D 42  axis, and obtaining an x coordinate at a point where the value of D 42  is the minimum value on the approximate curve with accuracy of decimal fractions (also referred to as an accuracy in units of sub-pixels). 
     In the foregoing description, the similarity degree data D 42  is calculated from the sum of differential absolute values in the matching regions set in the overlap regions for each pixel. However, instead of the sum of differential absolute values, the sum of squares of the differences may be used to calculate the similarity degree data D 42 . 
     &lt;Operation of Synthesizing Unit  44 &gt; 
     An operation of the synthesizing unit  44  will now be described. 
       FIGS. 11A to 11C  are diagrams for explaining an operation of the synthesizing unit  44  in a case where the document  26  is at the reference position P (the case of  FIGS. 2A and 2B  and  FIGS. 4A to 4C ).  FIG. 11A  illustrates image data D 41  read out from the image memory  41 .  FIG. 11B  illustrates image data obtained by performing magnification conversion (equal magnification in  FIGS. 11A to 11C ) on the image data D 41  in the x axis direction (the direction of arrangement of the image pickup elements, the direction of arrangement of the plurality of sensor chips) by using the synthesis magnifications indicated by the synthesis magnification position data D 45  supplied from the synthesis magnification setting unit  45  in the synthesizing unit  44 .  FIG. 11C  illustrates the synthesized image data D 44  obtained by synthesizing the image data illustrated in  FIG. 11B  (combining the image data at synthesis positions indicated by the synthesis magnification position data D 45  based on the synthesis positions Pc). 
       FIGS. 4A to 4C  illustrate the case where the document  26  is at the reference position P. Thus, the synthesis positions Pc indicated by the position data D 43  calculated by the synthesis position estimating unit  43  coincide with the synthesis reference positions Pr on the overlap regions. Here, the synthesis reference positions Pr are predetermined positions that are independent of the position of the document  26 . As illustrated in  FIG. 11A , since the calculated synthesis positions Pc coincide with the synthesis reference positions Pr, the width Wc in the x axis direction between two calculated synthesis positions Pc coincides with the width Wr in the x axis direction between two synthesis reference positions Pr (Wc=Wr). Thus, the reading width calculator  451  of the synthesis magnification setting unit  45  in the synthesizing unit  44  calculates the width Wc in the x axis direction between the synthesis positions Pc, and the magnification and synthesis position setting unit  452  sets the synthesis magnifications at, for example, Wr/Wc=1 from the reading width Wc supplied from the reading width calculator  451  and the reference width Wr in the x axis direction between the synthesis reference positions Pr, and the synthesis positions Pc remain at the same synthesis positions. The image converter  442  performs magnification conversion on the image data DI at the synthesis magnifications of 1 (equal magnification) to correct the magnifications of the image data, combines images of the overlap regions, and thereby generates and outputs the synthesized image data D 44 . Thus, in the case of  FIGS. 11A to 11C , the synthesizing unit  44  performs neither enlargement nor reduction on the image data illustrated in  FIG. 11A , and using the image data of the same size illustrated in  FIG. 11B , and synthesizes the image data as illustrated in  FIG. 11C . In this synthesis, the synthesizing unit  44  outputs the synthesized image data D 44  obtained by performing weighting addition on images of the adjacent overlap regions. 
       FIGS. 12A to 12C  are diagrams for explaining an operation of the synthesizing unit  44  in a case where the document  26  is at a position of (reference position−d) mm (the case of  FIGS. 5A and 5B  and  FIGS. 6A to 6C ).  FIG. 12A  illustrates image data D 41  read out from the image memory  41 .  FIG. 12B  illustrates image data obtained by performing magnification conversion (reduction in  FIGS. 12R to 12C ) on the image data D 41  in the x axis direction (the direction of arrangement of the image pickup elements, the direction of arrangement of the plurality of sensor chips  21 ) by using the synthesis magnifications in the synthesis magnification position data D 45  supplied from the synthesis magnification setting unit  45  in the synthesizing unit  44 .  FIG. 12C  illustrates the synthesized image data D 44  obtained by synthesizing the image data illustrated in  FIG. 12B  (combining the image data at the synthesis positions by the synthesis magnification position data D 45  based on the synthesis positions Pc). 
       FIGS. 6A to 6C  illustrate the case where the document  26  is at a position of (reference position −d) mm. Thus, the synthesis positions Pc in the drawing indicated by the position data D 43  calculated by the synthesis position estimating unit  43  do not coincide with the synthesis reference positions Pr in the overlap regions, and the synthesis positions Pc are outside the synthesis reference positions Pr. As illustrated in  FIG. 12A , since the synthesis positions Pc indicated by the calculated position data D 43  are outside the synthesis reference positions Pr, the width Wc in the x axis direction between two calculated synthesis positions Pc is larger than the width Wr in the x axis direction between two synthesis reference positions Pr (Wc &gt;Wr). Accordingly, the reading width calculator  451  of the synthesis magnification setting unit  45  in the synthesizing unit  44  calculates the width Wc in the x axis direction between the synthesis positions Pc, and the magnification and synthesis position setting unit  452  sets the synthesis magnifications as, for example, a Wr/Wc magnification (a value indicating a reduction magnification less than 1) from the reading width Wc supplied from the reading width calculator  451  and the reference width Wr in the x axis direction between the synthesis reference positions Pr, and converts the synthesis positions Pc to positions obtained by the Wr/Wc magnification conversion. The image converter  442  performs magnification conversion on the image data DI at the synthesis magnifications of Wr/Wc to correct the magnifications of the image data, combines images of the overlap regions, and generates and outputs the synthesized image data D 44 . Thus, in the case of  FIGS. 12A to 12C , the synthesizing unit  44  reduces the image data illustrated in  FIG. 12A , and makes the synthesis positions Pc coincide with the synthesis reference positions Pr as illustrated in  FIG. 12B . As a reduction magnification, a Wr/Wc magnification can be used, for example. Thereafter, as illustrated in  FIG. 12C , the synthesizing unit  44  synthesizes image data by using image data illustrated in  FIG. 12B . In this synthesis, the synthesizing unit  44  performs weighting addition on images of the adjacent overlap regions to thereby output bonded synthesized image data D 44 . 
       FIGS. 13A to 13C  are diagrams for explaining an operation of the synthesizing unit  44  in a case where the document  26  is at a position of (reference position+d) mm (the case of  FIGS. 7A and 7B  and  FIGS. 8A to 8C ).  FIG. 13A  illustrates image data D 41  read out from the image memory  41 .  FIG. 13B  illustrates image data obtained by performing magnification conversion (enlargement in  FIGS. 13A to 13C ) on the image data D 41  in the x axis direction (the direction of arrangement of the image pickup elements, the direction of arrangement of the plurality of sensor chips) by using the synthesis magnifications in the synthesis magnification position data D 45  supplied from the synthesis magnification setting unit  45  in the synthesizing unit  44 .  FIG. 13C  illustrates the synthesized image data D 44  obtained by synthesizing the image data illustrated in  FIG. 13B  (combining the image data at synthesis positions by the synthesis magnification position data D 45  based on the synthesis positions Pc). 
       FIGS. 8A and 8C  illustrate the case where the document  26  is at a position of (reference position+d) mm. Thus, the synthesis positions Pc indicated in the drawings by the position data D 43  calculated by the synthesis position estimating unit  43  do not coincide with the synthesis reference positions Pr on the overlap regions, and the synthesis positions Pc are inside the synthesis reference positions Pr. As illustrated in  FIG. 13A , since the synthesis positions Pc indicated by the calculated position data D 43  are inside the synthesis reference positions Pr, the width Wc in the x axis direction between two calculated synthesis positions Pc is smaller than the width Wr in the x axis direction between two synthesis reference positions Pr (Wc&lt;Wr). Accordingly, the reading width calculator  451  of the synthesis magnification setting unit  45  in the synthesizing unit  44  calculates the width Wc in the x axis direction between the synthesis positions Pc, and the magnification and synthesis position setting unit  452  sets the synthesis magnifications as, for example, a Wr/Wc magnification (a value indicating an enlargement magnification greater than 1) from the reading width Wc supplied from the reading width calculator  451  and the reference width Wr in the x axis direction between the synthesis reference positions Pr, and converts the synthesis positions Pc to positions obtained by the Wr/Wc magnification conversion. The image converter  442  performs magnification conversion on the image data DI at the synthesis magnifications of Wr/Wc to correct the magnifications of the image data, combines images of the overlap regions, and generates and outputs the synthesized image data D 44 . Thus, in the case of  FIGS. 13A to 13C , the synthesizing unit  44  enlarges the image data illustrated in  FIG. 13A , and makes the synthesis positions Pc coincide with the synthesis reference positions Pr as illustrated in  FIG. 13B . As an enlargement magnification, a Wr/Wc magnification can be used, for example. Thereafter, as illustrated in  FIG. 13C , the synthesizing unit  44  synthesizes image data by using image data illustrated in  FIG. 13B . In this synthesis, the synthesizing unit  44  outputs the synthesized image data D 44  combined by performing weighting addition on images of the adjacent overlap regions. 
     &lt;1-3&gt; Effect of First Embodiment 
     As described above, the image reading apparatus  1  according to the first embodiment has a configuration in which the plurality of sensor chips  21  are linearly arranged while the adjacent reading ranges on the document  26 , such as adjacent reading ranges  2 A(k−1) and  2 A( k ) and adjacent reading ranges  2 A( k ) and  2 A(k+1), overlap each other, by using optical systems such as the lenses  24  and the plurality of sensor chips  21  are linearly arranged, and can obtain image data without a loss of data between adjacent sensor chips  21 . 
     In addition, the image processing section  4  estimates the synthesis positions Pc serving as the position of the overlap regions, and based on the synthesis positions Pc as the positions of the overlap regions, obtains magnifications of read images to perform magnification conversion (equal magnification, enlargement, or reduction) on the image data in the x axis direction, and synthesizes the image data obtained by the magnification conversion. Thus, even when the distance from the reference position P to the document  26  changes, a joint between adjacent images (a synthesis position) can be made inconspicuous. 
     &lt;2&gt; Second Embodiment 
     Part of the functions of the image reading apparatuses  1  according to the first embodiment and a third embodiment described later may be implemented by a hardware configuration, or a computer program executed by a microprocessor including a CPU (central processing unit). In a case where part of the functions of the image reading apparatus  1  is implemented by a computer program, the microprocessor can load a computer program from a computer-readable storage medium and execute the computer program, thereby implementing the part of the functions of the image reading apparatus  1 . 
       FIG. 14  is a block diagram illustrating a hardware configuration in which part of the functions of the image reading apparatus can be implemented by a computer program. As illustrated in  FIG. 14 , an image reading apparatus  1   a  includes an image pickup unit  2 , an A-D converter  3 , a computation device  5 , a conveyance section  6  that conveys a document in a y axis direction (illustrated in  FIGS. 2A and 2B ). The computation device  5  includes a processor  51  including a CPU, a RAM (random access memory)  52 , a nonvolatile memory  53 , a mass-storage unit  54 , and a bus  55 . As the nonvolatile memory  53 , a flash memory can be used, for example. As the mass-storage unit  54 , a hard disk (magnetic disk) device, an optical disk storage device, and a semiconductor storage device can be used, for example. The conveyance section  6  can be configured as a mechanism that moves the image pickup unit  2 . 
     The A-D converter  3  has the same function as the A-D converter  3  of  FIG. 1 , converts an electrical signal SI output from the image pickup unit  2  to digital image data DI, and stores the image data DI in the RAM  52  (functioning as the image memory  41 ) through the processor  51 . 
     The processor  51  can load a computer program from the nonvolatile memory  53  or the mass-storage unit  54  and execute the loaded computer program, thereby implementing the function of the image processing section  4  in the first embodiment. 
       FIG. 15  is a flowchart schematically illustrating an example of processing executed by the computation device  5  of the image reading apparatus  1   a  according to the second embodiment. As illustrated in  FIG. 15 , first, the processor  51  executes similarity degree calculation process (step S 11 ). This process is a process similar to the process of the similarity degree calculator  42  in  FIG. 1 . Next, the processor  51  executes a synthesis position estimation process (step S 12 ). This process has the same details as those of the process of the synthesis position estimating unit  43  in  FIG. 1 . Lastly, the processor  51  performs magnification conversion (i.e., performs a process for enlargement, reduction, or equal magnification) on the image data stored in the RAM  52  by using a magnification based on the synthesis positions obtained at step S 12 , synthesizes the image data subjected to the magnification conversion, and outputs synthesized image data (step S 13 ). 
     The image reading apparatus  1   a  according to the second embodiment can enhance quality of a read image by eliminating a loss of data at a position corresponding to a position between the adjacent sensor chips. In the second embodiment, aspects except those described above are the same as those described in the first embodiment. 
     &lt;3&gt; Third Embodiment 
     In the image reading apparatus  1  described in the first embodiment, the synthesis magnification setting unit  45  of the synthesizing unit  44  in the image processing section  4  is configured as illustrated in  FIG. 17 , the reading width Wc in the main-scanning direction of each reading region (the width in the main-scanning direction between positions at both ends) is calculated from position data D 43  at both ends of each cell, and the synthesis magnifications and the synthesis positions are set based on the reading width Wc and the width Wr between the synthesis reference positions Pr. However, a synthesis magnification setting unit  45   b  as illustrated in  FIG. 18  may be used to calculate an overlap amount in reading from the position data D 43  so that the synthesis magnifications and the synthesis positions are set according to the difference between the overlap amount in reading and an overlap amount corresponding to the synthesis reference positions Pr (referred to as a reference overlap amount). 
     &lt;3-1&gt; Configuration of Third Embodiment 
       FIG. 18  is a block diagram illustrating a configuration of the synthesis magnification setting unit  45   b  that is used instead of the synthesis magnification setting unit  45  in the synthesizing unit  44  ( FIG. 16 ), in the image processing section  4  in the image reading apparatus  3  according to the third embodiment. In  FIG. 18 , constitutional elements that are the same as or correspond to those described in the first embodiment with reference to  FIGS. 1, 16, and 17  are designated by the same reference characters as those in the first embodiment. 
     In  FIG. 18 , the synthesis magnification setting unit  45   b  of the synthesizing unit  44  in the image processing section  4  according to the third embodiment includes an overlap amount calculator  453  and a magnification and synthesis position setting unit  452   b . The other part of the configuration and operation in the image processing section  4  and the synthesizing unit  44  are the same as the configuration and operation described in the first embodiment, and detailed description thereof will be omitted. 
     The synthesizing unit  44  ( FIG. 16 ) sets the synthesis magnifications and the synthesis positions in the main-scanning direction of image data of reading ranges from a positional difference between position data D 43  supplied from the synthesis position estimating unit  43  and the synthesis reference positions Pr in the overlap regions, performs magnification conversion on images by using the synthesis magnifications, and combines images of the overlap regions based on the synthesis positions, thereby generating and outputting the synthesized image data D 44 . Here, the synthesis reference positions Pr in the overlap regions are set according to the positions of the overlap regions OV 2  at the reference position P, and a width (also referred to as a reference overlap amount) OVWr in the main-scanning direction of the overlap regions OV 2  is also a predetermined value that is previously set by a user operation or the like (not shown in the drawings). 
     The synthesis magnification setting unit  45   b  in the synthesizing unit  44  calculates the width OVWc (a synthesis overlap amount) in the main-scanning direction of the overlap region from the position data D 43  supplied from the synthesis positions estimating unit  43 , sets the synthesis magnifications and the synthesis positions in the main-scanning direction of the image data of the reading ranges based on a difference between the width OVWc and the reference overlap amount OVWr at the reference position P based on the synthesis reference positions Pr (i.e., a positional difference between the synthesis positions in the reading regions from the reference positions), and outputs the synthesis magnification position data D 45  indicating the synthesis magnifications and the synthesis positions. 
     In  FIG. 18 , the overlap amount calculator  453  in the synthesis magnification setting unit  45   b  calculates the width (the synthesis overlap amount) OVWc in the main-scanning direction of the overlap region at both ends of the reading region read by each of the cells that actually overlap, from the position data D 43  supplied from the synthesis position estimating unit  43 . At this time, two synthesis overlap amounts OVWc 1  and OVWc 2  at both ends in each reading region are calculated, and the synthesis overlap amounts OVWc include the overlap amounts OVWc 1  and OVWc 2 . The synthesis overlap amounts OVWc (OVWc 1 , OVWc 2 ) can be calculated from positions on the reading regions of the position data D 43  obtained in the overlap regions at both ends of the image data of the reading region. For example, in the case of obtaining the position data D 43  as a center position of the overlap regions, the position indicated by the position data D 43  is converted to a distance (position) in the main-scanning direction from an end of the reading region read by each of the cells so that the distance is calculated as a synthesis overlap amount. 
     The magnification and synthesis position setting unit  452   b  in the synthesis magnification setting unit  45   b  sets the synthesis magnifications from a difference between the synthesis overlap amount OVWc supplied from the overlap amount calculator  453  and the reference overlap amount OVWr at the reference position P based on the synthesis reference positions Pr (i.e., a positional difference between the synthesis positions of the reading regions and the reference position), obtains the position data D 43  from the synthesis position estimating unit  43  as positions of synthesis (synthesis positions) converted (moved) by using the set synthesis magnifications, and outputs the obtained positions as the synthesis magnification position data D 45  indicating the synthesis magnifications and the synthesis positions. For the synthesis overlap amounts OVWc, since the two overlap amounts OVWc 1  and OVWc 2  at both ends of the reading region are calculated, two conversion magnifications are obtained from ratios between the overlap amounts and the reference overlap amount OVWr, and from an average value of the two conversion magnifications at the both ends, the synthesis magnifications of the reading region in the cell is obtained. 
     In the foregoing description, the synthesis magnifications of the reading regions of the cells are obtained from the average values of the two conversion magnifications at both ends. However, a magnification may be obtained at each position in the main-scanning direction in each reading range so that the magnification linearly changes between the two conversion magnifications at both ends, or the minimum value or the maximum value of the two conversion magnifications at both ends may be set as a magnification in the cell. In this manner, if the magnifications can be set according to the two overlap amounts OVWc 1  and OVWc 2  and the reference overlap amount OVWr, similar effects can be obtained. 
     From the synthesis magnification position data D 45  output from the magnification and synthesis position setting unit  452   b  in the synthesis magnification setting unit  45   b , the image converter  442  of the synthesizing unit  44  performs magnification conversion on images of reading region read by each of the cells of image data DI stored in the image memory  41 , and corrects magnifications of the image data of the reading ranges corresponding to the sensor chips. The overlap region connecting unit  443  combines images of the overlap regions of the magnification-converted image data D 442  whose magnifications have been corrected, and thereby generates and outputs the synthesized image data D 44 . 
     &lt;3-2&gt; Operation of Third Embodiment 
     &lt;Operations of Synthesizing Unit  44  and Synthesis Magnification Setting Unit  45   b&gt;   
     Operations of the synthesizing unit  44  and the synthesis magnification setting unit  45   b , mainly an operation of the synthesis magnification setting unit  45   b , will be described. In operations of the synthesizing unit  44  and the synthesis magnification setting unit  45   b  in a case where the document  26  is at the reference position P, as illustrated in  FIGS. 11A to 11C , the synthesis positions Pc indicated by the position data D 43  coincide with the synthesis reference positions Pr on the overlap regions, and thus, the two synthesis overlap amounts OVWc 1  and OVWc 2  coincide with the reference overlap amount OVWr (i.e., OVWc 1 , OVWc 2 =OVWr). Thus, the overlap amount calculator  453  of the synthesis magnification setting unit  45   b  in the synthesizing unit  44  calculates the synthesis overlap amounts OVWc, and the magnification and synthesis position setting unit  452   b  sets the synthesis magnifications at, for example, OVWc/OVWr=1 from the synthesis overlap amounts OVWc supplied from the overlap amount calculator  453  and the reference overlap amount OVWr, and the synthesis positions Pc remain at the same synthesis positions. The image converter  442  performs magnification conversion on the image data DI at the synthesis magnifications of 1 (equal magnification) to correct the magnifications of the image data, combines the images of the overlap regions, and thereby generates and outputs the synthesized image data D 44 . 
     Thus, in the case of  FIGS. 11A to 11C , the synthesizing unit  44  performs neither enlargement nor reduction on the image data illustrated in  FIG. 11A , and using image data of the equal magnification illustrated in  FIG. 11B , and synthesizes the image data as illustrated in  FIG. 11C . In the synthesis, the synthesizing unit  44  performs weighting addition on the images of the adjacent overlap regions to thereby output bonded synthesized image data D 44 . 
       FIGS. 19A to 19C  are diagrams for explaining operations of the synthesizing unit  44  and the synthesis magnification setting unit  45   b  in a case where the document  26  is at a position of (reference position−d) mm (the case of  FIGS. 5A and 5B  and  FIGS. 6A to 6C ).  FIGS. 19A to 19C  show operations that are similar to those in the case of  FIGS. 12A to 12C , but are different in obtaining the synthesis magnifications and the synthesis positions from not the reading width Wc but the synthesis overlap amounts OVWc (OVWc 1 , OVWc 2 ) at both ends of the reading region read by each of the cells.  FIG. 19A  illustrates the image data D 41  read out from the image memory  41 .  FIG. 19B  illustrates the image data obtained by performing magnification conversion (reduction in  FIGS. 19A to 19C ) on the image data D 41  in the x axis direction (the direction of arrangement of the image pickup elements, the direction of arrangement of the plurality of sensor chips  21 ) by using the synthesis magnifications in the synthesis magnification position data D 45  supplied from the synthesis magnification setting unit  45   b  in the synthesizing unit  44 .  FIG. 19C  illustrates the synthesized image data D 44  obtained by synthesizing the image data illustrated in  FIG. 19B  (combining the image data at synthesis positions by the synthesis magnification position data D 45  based on the synthesis positions Pc). 
     In a manner similar to those of  FIGS. 6A to 6C  and  FIGS. 12A to 12C ,  FIGS. 19A to 19C  illustrate the case where the document  26  is at a position of (reference position −d) mm, and thus, the illustrated synthesis positions Pc indicated by the position data D 43  calculated by the synthesis position estimating unit  43  do not coincide with the synthesis reference positions Pr on the overlap regions, and the synthesis positions Pc are outside the synthesis reference positions Pr. Since the synthesis positions Pc indicated by the calculated position data D 43  are outside the synthesis reference positions Pr, the two overlap amounts OVWc 1  and OVWc 2  are smaller than the reference overlap amount OVWr (i.e., OVWc 1 &lt;OVWr, OVWc 2 &lt;OVWr). Thus, the overlap amount calculator  453  of the synthesis magnification setting unit  45   b  in the synthesizing unit  44  calculates the synthesis overlap amounts OVWc (OVWc 1 , OVWc 2 ). Based on the synthesis overlap amounts OVWc supplied from the overlap amount calculator  453  and the reference overlap amount OVWr, the magnification and synthesis position setting unit  452   b  sets two conversion magnifications at both ends at an OVWc 1 /OVWr magnification and an OVWc 1 /OVWr magnification (values indicating a reduction magnification less than 1), sets the synthesis magnifications OVWc/OVWr in the reading region read by each of the cells from an average value of the two conversion magnifications at both ends, and converts the synthesis positions Pc to positions obtained by the magnification conversion. Then, the image converter  442  performs magnification conversion on the image data DI at the synthesis magnifications of OVWc/OVWr, corrects the magnifications of the image data, combines the images of the overlap regions, and thereby generates and outputs the synthesized image data D 44 . 
     From the above description, in the case of  FIGS. 19A to 19C , the synthesizing unit  44  reduces in size the image data illustrated in  FIG. 19A , and makes the synthesis positions Pc coincide with the synthesis reference positions Pr as illustrated in  FIG. 19B . As a reduction magnification, an OVWc/OVWr magnification can be used, for example. Thereafter, as illustrated in  FIG. 19C , the synthesizing unit  44  synthesizes the image data by using the image data illustrated in  FIG. 19B . In the synthesis, the synthesizing unit  44  performs weighting addition on images of the adjacent overlap regions to thereby output bonded synthesized image data D 44 . 
       FIGS. 20A to 20C  are diagrams for explaining operations of the synthesizing unit  44  and the synthesis magnification setting unit  45   b  in a case where the document  26  is at a position of (reference position+d) mm (the case of  FIGS. 7A and 7B  and  FIGS. 8A to 8C ).  FIGS. 20A to 20C  show operations that are similar to those in the case of  FIGS. 13A to 13C , but are different in obtaining the synthesis magnifications and the synthesis positions from not the reading width Wc but the synthesis overlap amounts OVWc (OVWc 1 , OVWc 2 ) at both ends.  FIG. 20A  illustrates the image data D 41  read out from the image memory  41 .  FIG. 20B  illustrates the image data obtained by performing magnification conversion (enlargement in  FIGS. 20A to 20C ) on the image data D 41  in the x axis direction (the direction of arrangement of the image pickup elements, the direction of arrangement of the plurality of sensor chips  21 ) by using the synthesis magnifications in the synthesis magnification position data D 45  supplied from the synthesis magnification setting unit  45   b  in the synthesizing unit  44 .  FIG. 20C  illustrates the synthesized image data D 44  obtained by synthesizing the image data illustrated in  FIG. 20B  (combining the image data at synthesis positions by the synthesis magnification position data D 45  based on the synthesis positions Pc). 
     In a manner similar to those of  FIGS. 8A to 8C  and  FIGS. 13A to 13C ,  FIGS. 20A to 20C  illustrate the case where the document  26  is at a position of (reference position+d) mm, and thus, the illustrated synthesis positions Pc indicated by the position data D 43  calculated by the synthesis position estimating unit  43  do not coincide with the synthesis reference positions Pr on the overlap regions, and the synthesis positions Pc are inside the synthesis reference positions Pr. Since the synthesis positions Pc indicated by the calculated position data D 43  are inside the synthesis reference positions Pr, the two overlap amounts OVWc 1  and OVWc 2  are larger than the reference overlap amount OVWr (i.e., OVWc 1 &gt;OVWr, OVWc 2 &gt;OVWr). Thus, the overlap amount calculator  453  of the synthesis magnification setting unit  45   b  in the synthesizing unit  44  calculates the synthesis overlap amounts OVWc (OVWc 1 , OVWc 2 ). Based on the synthesis overlap amounts OVWc supplied from the overlap amount calculator  453  and the reference overlap amount OVWr, the magnification and synthesis position setting unit  452   b  sets two conversion magnifications at both ends at an OVWc 1 /OVWr magnification and an OVWc 2 /OVWr magnification (value indicating an enlargement magnification greater than 1), sets the synthesis magnification OVWc/OVWr in the reading region read by each of the cells from an average value of the two conversion magnifications at both ends, and converts the synthesis positions Pc to positions obtained by the magnification conversion. Then, the image converter  442  performs magnification conversion on the image data DI at the synthesis magnifications of OVWc/OVWr, corrects the magnifications of the image data, combines images of the overlap regions, and generates and outputs the synthesized image data D 44 . 
     From the above description, in the case of  FIGS. 20A to 20C , the synthesizing unit  44  enlarges the image data illustrated in  FIG. 20A , and makes the synthesis positions Pc coincide with the synthesis reference positions Pr as illustrated in  FIG. 20B . As an enlargement magnification, an OVWc/OVWr magnification can be used, for example. Thereafter, as illustrated in  FIG. 20C , the synthesizing unit  44  synthesizes the image data by using the image data illustrated in  FIG. 20B . In the synthesis, the synthesizing unit  44  performs weighting addition on the images of the adjacent overlap regions to thereby output bonded synthesized image data D 44 . 
     With respect to the synthesis overlap amounts OVWc 1  and OVWc 2  at both ends of the reading region illustrated in  FIGS. 19A to 19C  and  FIGS. 20A to 20C , even in such a case that one of the synthesis overlap amounts OVWc 1  and OVWc 2  is reduced or enlarged and the other is calculated at a different magnification, since the magnification and synthesis position setting unit  452   b  sets the synthesis magnifications OVWc/OVWr in the reading region read by each of the cells from the average value of two conversion magnifications, magnifications that do not cause a large distortion can be set. 
     &lt;3-3&gt; Effect of Third Embodiment 
     As described above, in the image reading apparatus  1  according to the third embodiment, the synthesis magnification setting unit  45   b  calculates the synthesis overlap amounts in reading from the position data D 43 , and sets the synthesis magnifications and the synthesis positions from the difference between the synthesis overlap amounts and the reference overlap amount. Thus, by performing magnification conversion (equal magnification, enlargement, or reduction) in the x axis direction on the image data and synthesizing the image data obtained by the magnification conversion, even when the distance from the reference position P to the document  26  changes, a joint between adjacent images (a synthesis position) can be made inconspicuous. Consequently, quality of a read image can be enhanced without a loss of data at a position corresponding to a position between adjacent sensor chips. 
     The image reading apparatus  1  according to the third embodiment may be implemented by a computer program that is executed by the microprocessor in the computation device  5  of the image reading apparatus  1   a  according to the second embodiment. In this case, effects similar to those described above can be obtained. 
     INDUSTRIAL APPLICABILITY 
     The present invention is applicable to a copying machine, a facsimile, a scanner, and so forth that have the function of scanning a reading object such as a document to obtain image information. 
     DESCRIPTION OF REFERENCE CHARACTERS 
       1 ,  1   a  image reading apparatus;  2  image pickup unit;  3  A-D converter;  4  image processing section;  5  computation device;  6  conveyance section;  21 ,  21 ( k ) sensor chip;  22 ,  22 ( k ) lens;  23  diaphragm;  23   a  aperture;  24 ,  24 ( k ) lens; glass surface;  26  document (reading object);  27  illumination;  28 ,  28 ( k ) range of light travelling from document to image pickup unit;  29 ,  29 ( k ) range of light travelling from document toward image pickup unit;  2 A,  2 A( k ) reading range;  41  image memory;  42  similarity degree calculator;  43  synthesis position estimating unit;  44  synthesizing unit;  51  processor;  52  RAM;  53  nonvolatile memory;  54  mass-storage unit;  211 ,  212 ,  213  image pickup element; L 1 , L 2 , L 3  width of overlap region; OV 1 ( k −1, R) overlap region at the right of (k−1)th image data; OV 1 ( k , L) overlap region at the left of k-th image data; P reference position; Pc synthesis position; Pr synthesis reference position; x main-scanning direction; y sub-scanning direction (document conveyance direction);  45 ,  45   b  synthesis magnification setting unit;  442  image converter;  443  overlap region connecting unit;  451  reading width calculator;  452 ,  452   b  magnification and synthesis position setting unit;  453  overlap amount calculator.