Abstract:
According to an embodiment of the present invention, an image reader comprises a plurality of light receiving elements configured to receive light from an object to be read and to convert the light into image signals. The image reader further comprises means for determining a distance between the object and the plurality of light receiving elements at a plurality of different positions of the object. Moreover the image reader comprises means for selecting at least one correction process portion based at least on the distance between the object and the plurality of light receiving elements. The image reader comprises means for applying the at least one selected correction process to the image signal.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Japanese Patent Application No. 2006-060111, filed on Mar. 6, 2006, the disclosure of which is incorporated herein by reference in its entirety. 
     FIELD OF THE INVENTION 
     The present invention relates to image readers. 
     BACKGROUND OF THE INVENTION 
     A known image reader for reading a document is mounted on a facsimile, a copier, a scanner, or a combination thereof. The known image reader includes an auto document feeder (“ADF”) reading mechanism which automatically conveys a document, or an flat bed (“FB”) reading mechanism which reads an image. The ADF reading mechanism automatically conveys the document on a contact glass, radiates light to the document from a side opposite to the contact glass, and reads a reflection light by the image sensor to obtain the image of the document as image signals. 
     The ADF reading mechanism includes a guide plate which is biased toward the contact glass by a spring, and the document is conveyed between the guide plate and the contact glass. When a resilient document such as a glossy paper, is conveyed, the guide plate is raised, which may cause the document to float. Particularly, when a close-contact-type image sensor is used as the image sensor, a focal length of the image sensor is relatively short and consequently, when the document floats, it is difficult to obtain accurate focusing, e.g., it is difficult to obtain a clear image and focused. 
     SUMMARY OF THE INVENTION 
     Therefore a need has arisen for image readers which overcome these and other shortcomings of the related art. A technical advantage of the present invention is that the image reader may maintain a quality image regardless of any floating of the document. 
     According to an embodiment of the present invention, an image reader comprises a plurality of light receiving elements configured to receive light from an object to be read and to convert the light into image signals. The image reader further comprises means for determining a distance between the object and the plurality of light receiving elements at a plurality of different positions of the object. Moreover the image reader comprises means for selecting at least one correction process portion based at least on the distance between the object and the plurality of light receiving elements. The image reader comprises means for applying the selected at least one correction process to the image signal. For example, the various means in this embodiment may comprise a processor which is configured to execute software. 
     According to another embodiment of the present invention, an image reader comprises a first plurality of light receiving elements configured to receive light from an object to be read and to convert the light into image signals. The image reader is configured to move the object in a predetermined direction. The image reader further comprises a guide plate configured to guide the object and a second plurality of light receiving elements configured to read the guide plate. The image reader still further comprises means for determining a distance between the object and the first plurality of light receiving elements at a plurality of different positions of the object. Moreover the image reader comprises means for selecting at least one correction process portion based at least on the distance between the object and the first plurality of light receiving elements. The image reader comprises means for applying the selected at least one correction process to the image signal. For example, the various means in this embodiment may comprise a processor which executed software. 
     Other objects, features, and advantages will be apparent to persons of ordinary skill in the art from the following detailed description of the invention and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention, the needs satisfied thereby, and the features and technical advantages thereof, reference now is made to the following descriptions taken in connection with the accompanying drawings. 
         FIG. 1  is a perspective view of a multi-function machine which comprises an image reader, according to an embodiment of the present invention. 
         FIG. 2A  is an explanatory view of an operation of an ADF reading mechanism. 
         FIG. 2B  is an explanatory view of an operation of an FB reading mechanism. 
         FIG. 3A  is a block diagram of a control portion of the multi-function machine of  FIG. 1 . 
         FIG. 3B  is an explanatory view of a memory region of a ROM of the control portion of  FIG. 3A . 
         FIG. 4  is a perspective view of an image sensor. 
         FIG. 5A  is an explanatory view of an image sensor when a sheet having a relatively small resiliency is conveyed. 
         FIG. 5B  is an explanatory view of the image sensor when a sheet having a relatively large resiliency is conveyed. 
         FIG. 6  is a plan view of an ADF platen and an FB platen. 
         FIG. 7A  is a graph of a relationship between a floating quantity of a document and an output ratio of image signals. 
         FIG. 7B  is an example of an emphasis parameter table. 
         FIG. 8  is an explanatory view of a positional relationship between a block of the image sensor and the document; 
         FIG. 9A-9E  are explanatory views for explaining emphasis processing. 
         FIG. 10A  is a cross-sectional view of a guide plate and a contact glass during a smoothing processing. 
         FIG. 10B  is a cross-sectional view of a guide plate and a contact glass during an emphasis processing. 
         FIG. 10C  is a cross-sectional view of a guide plate and a contact glass during a smoothing processing. 
         FIG. 11A  is an explanatory view of when a relatively thin document is used. 
         FIG. 11B  is an explanatory view of when a relatively thick document is used. 
         FIG. 12  is a flow chart of an operation of the image reader of  FIG. 1 . 
         FIG. 13  is a flow chart for calculating an emphasis parameter. 
         FIG. 14  is a block diagram of a mechanism of the image sensor; 
         FIG. 15  is an explanatory view of the flow of signals from the image sensor. 
         FIG. 16  is an explanatory view of a table which may indicate a correspondence between a type and a thickness of the document. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the present invention and their features and technical advantages may be understood by referring to  FIGS. 1-16 , like numerals being used for like corresponding portions in the various drawings. 
     Referring to  FIGS. 1 and 2 , the multi-function machine  1  may perform a plurality of functions, such as a fax function, a scanning function, and a copying function. The multi-function machine  1  may comprise an ADF reading mechanism comprising auto document feeder (“ADF”) document set tray  3 , an document guide  5 , sheet feed rollers  7   a - 7   d , a contact glass  11 , an image sensor  21 , a guide plate  12 , and a spring member  13  which biases the guide plate  12 . The multi-function machine  1  also may comprise a flat bed (“FB”) reading mechanism in which a FB pushing plate  17 , an FB platen  19  comprising glass, and the image sensor  21 . 
     Referring to  FIG. 2A , when an image is read using the ADF reading mechanism, a document  4  initially may be positioned on the ADF document set tray  3 , and then a reading operation may be instructed. The document  4  may be conveyed by rotating the sheet feeding rollers  7   a - 7   d , and the document  4  may pass between the guide plate  12  and the contact glass  11 . The image sensor  21  which is arranged below and relatively close to the contact glass  11  may be an image of the document  4  via the contact glass  11 . Alternatively, referring to  FIG. 2B , when an image is read using the FB reading mechanism, the document B first may be positioned on the FB platen  19 , and the document B then may be pushed to the FB platen  19  by the FB pushing plate  17 . The image sensor  21  then may read the image of the document B while moving in the sub-scanning direction indicated by an arrow shown in  FIG. 4B . 
     Further, a reference white plate  16  may be positioned on a lower portion of the document guide  5  for adjusting the white reference of the image sensor  21 . 
     Referring to  FIG. 3A , the multi-function machine  1  also may comprise a main board  28 . The main board may comprise a CPU  30 , a RAM  31 , a ROM  32 , a gate array  33 , an Network Control Unit (“NCU”)  34 , a modem  35 , an EEPROM  36 , a CODEC  37 , a Direct Memory Access Controller (“DMAC”)  38  or the like. These parts may be connected to each other through a bus line  26 . The bus line  26  may comprise an address bus, a data bus, and control signal lines. Moreover, the image sensor  21 , a recording unit  22 , a manipulation unit  23 , a display unit  24 , and an external connection unit  25  may be connected to the gate array  33 . A public telephone line  27  may be connected to the NCU  34 . 
     The RAM  31  may be used as a line buffer memory for the read image and as an operation region of the CPU  30 , the modem  35  may perform modulation, demodulation, and the like of facsimile data. The EEPROM  36  may store various types of flags, predetermined information, or the like. Alternatively, the gate array  33  may perform as an input/output interface between the CPU  30  and respective parts, such as image sensor  21 . The CODEC  37  may perform coding and decoding of the facsimile data, the DMAC  38  may read data into the RAM  31  and may read data from the RAM  31 . 
     The recording unit  22  may comprise a laser printer and may record an image to a recording sheet. The manipulation unit  23  may transmit manipulation signals to the CPU  30  in response to a user operating a manipulation button. The manipulation unit  23  also may be used when a thickness or a type of the document  4  is selected. The display unit  24  may comprise a Liquid Crystal Display (“LCD”) and may display an operation state of the multi-function machine  1 . The external connection unit  25  may be used when an external device, such as a personal computer, is connected to the multi-function machine  1 . 
     Referring to  FIG. 3B , various programs, such as a distance measuring program  32   a , an image correction program  32   b , a document detection program  32   c , a copying control program  32   d , a facsimile control program  32   e  or a scanner control program  32   f  are stored in the ROM  32 . The distance measuring program  32   a  may be a program for measuring distances between the object to be read and the light receiving elements. The object to be read may be a document. Further, the image correction program  32   b  may be a program for applying a predetermined correction process to the image signals in response to the distances measured by the distance measuring program  32   a . The document detection program  32   c  may be a program for detecting the thickness or the type of the document  4 . For example, the user may input the thickness or the type of the document  4  via the manipulation unit  23 . Further, the image reader also may comprise a sensor, and the thickness or the type of the document  4  may be detected based on the information from the sensor. In this embodiment, the copying control program  32   d , the FAX control program  32   e , and the scanner control program  32   f  are programs for controlling the copying function, the fax function, and the scanning function, respectively. 
     Referring to  FIG. 4 , the image sensor  21  may comprise a plurality of sensor IC chips  2   a ,  2   b ,  2   c ,  2   d ,  2   e ,  2   f ,  2   g ,  2   h ,  2   i ,  2   j , and  2   k  arranged on a substrate. Each of the IC chips  2  may comprise a plurality of light receiving elements  20  formed thereon. The plurality of light receiving elements  20  may be arranged in a line at a predetermined interval in the main scanning direction orthogonal to the sub-scanning direction. Moreover, the sensor IC chips  2   a - 2   k  may be divided into a plurality of blocks, e.g., blocks B 1 -B 5 . 
     Referring to  FIG. 5 , the sensor IC chips  2  and the substrate  14  may be positioned within a frame  49  with a light source  15 , a light guide portion  46 , and a lens array  47 . The light source  15  may comprise light emitting elements  15 R,  15 G, and  15 B which emit light of red, green, and blue respectively, and hence, white light may be outputted from the light source. The light emitted from the light source  15  passes through the light guide unit  46  and the contact glass  11  and is radiated to the document  4 . The light reflected from the document  4  passes through the contact glass  11  and the lens array  47  and reaches the plurality of light receiving elements  20 . The plurality of light receiving elements  20  which receive the reflected light output image signals, and the image signals are transmitted to the main board  28  via a connector  18  and a flexible flat cable  39 . 
     As shown in  FIG. 14 , the image sensor IC chip  2  may comprise known photo transistors PT 1 -PTn which may comprise, for example, several thousands light receiving elements  20 . The photo transistors PT 1 -PTn, upon reception of light, store charges corresponding to received light quantities. The circuit of the image sensor IC chip  2  may be substantially similar to the circuit of a known image sensor IC chip. 
     Referring to  FIG. 15 , the gate array  33  may comprise a CIS control block  43  which supplies a start pulse SP, a clock signal CLK, and the like to the image sensor  21  under a systematic control of the CPU  30 . The gate array  33  also may comprise an analog front end (“AFE”) circuit which may comprise a sample holding circuit (“S/H”)  40 , a multiplexer  41 , and an analog/digital converter (“A/D”)  42 , an AFE control block  44  which transmits various control signals to the AFE circuit, a memory writing control block  45  which samples and sequentially writes digital signals outputted from the analog/digital converter  42  into a predetermined region of an image memory contained in the RAM  31 , and the like. 
     The start pulse SP may be inputted to the image sensor IC chips  2   a  and  2   k  with respect to the blocks B 1 -B 5 , and may be inputted to the respective left image sensor IC chips  2   b ,  2   e , and  2   h  with respect to the blocks B 2 -B 4 . Referring to  FIG. 14 , for example, to the image sensor IC chip  2   c  at the center of the block B 2 , a serial out signal SO may be outputted from a terminal P 4  of the left image sensor IC chip  2   b , and the driving of the left image sensor IC chip  2   b  may begin upon inputting of the serial out signal SO as the start pulse SP. Image sensor IC chips  2  of other block B 3 -B 4  may operate substantially the same way. The driving of the center image sensor IC chips  2   e ,  2   f , and  2   i  may begin after the driving of the left image sensor IC chips  2   b ,  2   e , and  2   h  is finished in each of the blocks B 2 -B 4 . When the driving of the center image sensor IC chips  2   c ,  2   f  and  2   i  is finished, the driving of the right image sensor IC chips  2   d ,  2   g , and  2   j  may begin. Here, the clock signal CLK which is transmitted from the gate array  33  may be inputted to eleven image sensor IC chips  2   a - 2   k ) respectively in division. 
     When a reading operation of the document  4  begins in response to an operation of the manipulation unit  23  by a user, the start pulse SP outputted from the gate array  33  may be inputted to a terminal P 1 , and a shift register  29  sequentially brings a plurality of transistors FET 1 -FETn into an ON state in the predetermined direction in response to the clock signal CLK inputted to a terminal P 2 . Then, charges which are stored in the plurality of phototransistors PT 1 -PTn may be discharged in a predetermined order, may be amplified by an amplifier Op, and thereafter, may be outputted in series from a terminal P 3  as image signals AO. The image signals AO may be analog signals. The image sensor IC chip  2  also may comprise a terminal P 4  which outputs a serial out signal SO at a point of time that the image signal is outputted from the final phototransistor PTn. Further, the image sensor IC chip  2  also may comprise a voltage VDD applying terminal P 5  for supplying drive electricity necessary for operating the respective parts in the inside of the image sensor IC chip  2 , and a terminal P 6  which is connected to a ground GND. 
     For example, in the block B 2 , when the start pulse SP is inputted to the terminal P 1  of the image sensor IC chip  2   b , the image signal AO may be outputted from the terminal P 3  in response to the clock signal CLK. After the FETn assumes an ON state in response to the clock signal CLK, e.g., after the image sensor IC chip  2   b  finishes outputting the image signal AO, the serial out signal SO may be outputted from the terminal P 4  and may be inputted to the image sensor IC chip  2   c  as the start pulse SP of the image sensor IC chip  2   c . Thereafter, the serial out signal SO of the image sensor IC chip  2   c  may be outputted in the same manner and may be inputted to the image sensor IC chip  2   d  as the start pulse SP of the image sensor IC chip  2   d . Then, the image signal of the image sensor IC chip  2   d  may be outputted from the output terminal Ch 2 . 
     Referring to  FIG. 15 , respective analog read signals outputted from respective output terminals Ch 1 -Ch 5  of blocks B 1 -B 5  of the image sensor  21  may be transmitted to the gate array  33  via the flexible flat cable  39 , and may be temporarily stored until the respective image signals become stable at predetermined output levels in the sample holding circuit  40 . Thereafter, the analog read signals may be sequentially subjected to analog/digital conversion based on instructions from the AFE control block  44 . 
     Referring to  FIG. 5A  and  FIG. 5B , as described above, the guide plate  12  may be biased by the spring member  13 . In conveying a sheet having relatively little resiliency, such as a plain paper, the document  4  may pass a position where accurate focusing is obtained, as shown in  FIG. 5A , and hence, it is possible to obtain an image of relatively high resolution. Nevertheless, when a document having a substantial amount of resiliency, such as an ink jet special paper, is conveyed, the resiliency of the spring member  13  is affected by the resiliency of the document, and hence, the document  4  may float together with the guide plate  12 , as shown in  FIG. 5B . In  FIG. 5B , due to the floating of the document  4 , a distance L from the plurality of light receiving element  20  to the document  4  is greater than the corresponding distance L, in the state shown in  FIG. 5A . In such a state, the plurality of light receiving element  20  may not be able to obtain accurate focusing, and hence, the resolution of the image may be decreased. 
     This drawback particularly arises when the size of the image reader is reduced. When the size of the image reader is reduced, a curvature of a conveying path is decreased, and hence, the guide plate  12  may be particularly susceptible to floating when the document  4  having substantial resiliency is conveyed. 
     A floating quantity of the document  4  may be measured by using a plurality of light receiving elements  20   a  which are portions of the plurality of light receiving elements  20 . Referring to  FIG. 6 , the contact glass  11  may be formed with a length greater than a width of the document. Areas  11 A and  11 B of the contact glass  11  may be regions outside the document  4 . Accordingly, when the document  4  passes the contact glass  11 , the plurality of light receiving elements  20   a  corresponding to the area  11 A and  11 B of the contact glass  11  are not used for reading the document  4 . The plurality of light receiving elements  20   a  may be one of or both of portions at both ends of the plurality of light receiving elements  20 . The guide plate  12  may be read by using the plurality of light receiving elements  20   a  which are not used for reading the document  4 . 
     Referring to  FIG. 7A , the distance from the guide plate  12  to a surface of the contact glass  11  is taken on an axis of an abscissas, and a value which is obtained by dividing the output of the image signal from the plurality of light receiving element  20  with a corresponding output when the distance is 0.0 mm is taken on an axis of ordinates. As may be understood from the graph, the output ratio when the distance is 0.0 mm, i.e., a state in which the guide plate  12  contacts the contact glass  11 , is 1.0, and when the guide plate  12  floats, the output ratio increases. Further, it may be understood from the graph that the output ratio is a maximum value in the vicinity of the distance being 0.2 mm, and the output ratio decreases when the guide plate  12  floats further. 
     By reading the guide plate  12  using the plurality of light receiving elements  20   a  when the document  4  is conveyed, and by measuring the output of the image signal, the floating quantity of the guide plate  12  may be obtained based on the relationship shown in  FIG. 7A . Then, predetermined correction processing may be applied to the read image of the document  4  corresponding to the floating quantity of the guide plate  12 . 
     Referring to  FIG. 8 , in reading the document  4  of A4 size, the blocks B 2 -B 4  may be used for reading the image, and the image signals may be outputted from the output terminals Ch 2 -Ch 4 . In contrast, in reading the document  4  of A3 size, the plurality of light receiving elements  20  of the blocks B 1 -B 5  may be used for reading the image, and the image signals may be outputted from the output terminals Ch 1 -Ch 5 . Then, the plurality of light receiving elements  20   a  in the blocks B 1  and B 5  may be used for measuring the floating quantity of the guide plate  12 . Further, the plurality of light receiving elements  20  in some of the B 2  and B 4  blocks and the blocks B 1  and B 5  may be used for measuring the floating quantity of the guide plate  12  in case of A4 size document  4 . 
     To perform the emphasis processing or the smoothing processing, a filter shown in  FIG. 9A , for example, may be prepared, and an arithmetic operation shown in  FIG. 9C  may be performed using the pixel data values, e.g., image signals outputted from the plurality of light receiving elements  20 ) shown in  FIG. 9B . Moreover, the degrees of emphasis and smoothness may be altered by altering the numerical values of the filters. Here, although a 3×3 filter is used in the example shown in  FIG. 9A , a 5×5 filter, a 7×7 filter, or the like may be used. 
     Referring to  FIG. 10A , when the document  4  is conveyed, a distal end of the document  4  passes between the contact glass  11  and the guide plate  12 . At this point of time, the guide plate  12  and the document  4  may be pushed due to a biasing force of the spring member  13 , and hence, an image of high resolution may be obtained. Thereafter, when a center portion of the document  4  passes between the contact glass  11  and the guide plate  12 , as shown in  FIG. 10B , the guide plate  12  floats due to the resiliency of the document  4 , and the accurate focusing may not obtained. Then, when a rear end of the document  4  passes between the contact glass  11  and the guide plate  12  as shown in  FIG. 10C , the document  4  again may be pushed, and hence, an image of high resolution may be obtained. 
     A correction quantity of the image may be changed corresponding to the floating quantity of the document  4 . For example, as shown in  FIG. 10B , the emphasis processing may be applied when the floating quantity of the document  4 , i.e., the distance from the plurality of light receiving element  20  to the document  4 , is greater than a predetermined range, and as shown in  FIG. 10A  and  FIG. 10C , when the floating quantity of the document  4  is less than the predetermined range, the smoothing processing may be applied. When the floating quantity of the document  4  falls within a predetermined range, neither the emphasis processing nor the smoothing processing may be performed. Because of such processing, which has uniform resolution may be obtained. It may be applicable if a maximum value of the predetermined range and a minimum value of the predetermined range are same. 
     On the other hand, when the thickness of the document  4  is relatively thin, as shown in  FIG. 11A , the surface of the guide plate  12  and the surface of the document  4  may be substantially at the same height, and hence, the correction quantity of the image may be determined by taking only the floating quantity of the guide plate  12  into consideration. Nevertheless, when the thickness of the document  4  is relatively thick, as shown in  FIG. 11B , if the correction quantity of the image is determined by taking only the floating quantity of the guide plate  12  into consideration, accurate focusing may not be obtained. Accordingly, by allowing the setting of the thickness of the document  4 , the correction quantity of the image may be determined based on the floating quantity of the guide plate  12  and the thickness of the document  4 . For example, the correction quantity of the image may be determined by subtracting the thickness of the document  4  from the floating quantity of the guide plate  12 . Further, when the thickness of the document  4  is relatively thick, the document may approach the image sensor  21  further closer due to the rigidity of the document. The correction quantity of the image may be determined also by estimating such a case. 
     The user may set the thickness of the document  4  using the manipulation unit  23 , or alternatively, a sensor which detects the thickness of the document  4  may be provided so as to automatically detect the thickness of the document  4 . 
     Further, types of the document  4  may be set and the correction processing of the image may be performed on a condition that the document  4  having relatively large resiliency, such as ink jet special paper or glossy paper, is set. 
     Referring to  FIG. 16 , a table  50  in which types and thicknesses of the document  4  are made to correspond to each other may be preliminarily stored. Further, the user may set the types of the document  4 . The thickness corresponding to the kind of the set document  4  may be read from the table  50 , and the correction quantity of the image may be determined based on the floating quantity of the guide plate and the thickness of the document  4 . Due to such processing, even when the user does not know the thickness of the document, the user may accurately perform the correction of the image. Here, the table  50  may be stored in the ROM  32 , for example. 
     Referring to  FIGS. 12 and 13 , the image sensor  21  may be moved to a position of the reference white plate  16  (S 1 ) and the light quantity adjustment is performed (S 2 ). Thereafter, the reading of respective color white-black level data may be performed (S 3 ), and respective color shading data may be calculated (S 4 ), thus adjusting the white reference. Then, the processing returns to step S 5  in which the image sensor  21  is moved to the ADF reading position, e.g., below the contact glass  11 , and the reading of the guide plate  12  may be performed in step S 6 . Due to the processing in step S 6 , the output value of the image signal when the guide plate  12  is read in a state that the document  4  is not conveyed may be obtained. 
     Thereafter, the processing advances to step S 7  in which the conveying of the document  4  begins. Then, in step S 8 , the detection of the floating quantity of the document  4  and the determination of the correction processing corresponding to the floating quantity (calculation of emphasis parameter) may be performed. 
     Step S 8  is explained in detail in  FIG. 13 . First of all, in step S 11 , various set values, such as information on which the plurality of light receiving elements  20   a  are used for reading the guide plate  12  may be inputted. When, in step S 12 , the guide plate  12  is read in a state that the document  4  is conveyed, and the output value of the image signal is obtained. Further, the reading of the image of the document  4  may be also simultaneously performed. Here, for example, among the light receiving elements  20  which are arranged in a line, the reading of the image of the document  4  may be performed by the plurality of light receiving elements  20  ( 20   b  shown in  FIG. 4 ) arranged at the center, and the reading of the guide plate  12  may be performed by the plurality of light receiving elements  20   a  positioned at both ends. 
     Thereafter, the processing advances to step S 13  in which the floating quantity of the document is detected. Here, the output ratio may be obtained by using the output value (obtained in step S 6 ) when the guide plate  12  is read in a state that the document  4  is not conveyed and the output value (obtained in step S 12 ) when the guide plate  12  is read in a state that the document  4  is conveyed. Here, for example, it is determined that the floating of the document  4  is present when the output ratio is greater than 1, and the floating of the document  4  is not present when the output ratio is less than 1. 
     Thereafter, the processing advances to step S 14  in which the emphasis parameter is calculated. Here, for example, the emphasis parameter table shown in  FIG. 7B  is preliminarily prepared and the emphasis parameter is changed depending on whether the floating of the document  4  is present or not present. For example, the filter for emphasis processing (see  FIG. 9E ) may be selected or the filter for smoothing processing (see  FIG. 9D ) may be selected. 
     Here, in step S 13 , the graph shown in  FIG. 7A  may be preliminarily stored and how many mm the document  4  is floated may be calculated using the graph and the obtained output ratio. Further, a plurality of filters may be prepared for applying the emphasis processing or the smoothing processing. In step S 14 , the filter may be selected corresponding to the floating quantity of the document  4 . 
     Referring to  FIG. 12 , after calculating the emphasis parameter, the processing advances to step S 9  and the correction processing may be applied to the image signal of the document  4 . Thereafter, in step S 10 , it is determined whether or not a next page exists. Here, if the next page exits, the processing returns to S 7  in which the reading of the next document  4  is performed. 
     The calculation of the emphasis parameter in step S 8  and the correction processing in step S 9  may be collectively performed for every 1 page of the document, or may be performed in parallel with the document reading operation. By performing the calculation of the emphasis parameter in step S 8  and the correction processing in step S 9  a plurality of times in the sub scanning direction within 1 page of the document, the image of favorable quality may be even when the distance L from the light receiving element  20  to the document  4  fluctuates during reading of the document. 
     While the invention has been described in connection with exemplary embodiments, it will be understood by those skilled in the art that other variations and modifications of the exemplary embodiments described above may be made without departing from the scope of the invention. Other embodiments will be apparent to those skilled in the art from a consideration of the specification or practice of the invention disclosed herein. It is intended that the specification and the described examples are considered merely as exemplary of the invention, with the true scope of the invention being indicated by the flowing claims.