Abstract:
An image reading apparatus includes a reading unit, an extraction unit and a generation unit. The reading unit outputs reference plate reading information. The extraction unit sets a pixel of the reference plate reading information as a notice pixel and repeatedly extracts one of the notice pixel as a target pixel until the number of the target pixels is more than a predetermined value when a ratio of a pixel value of the notice pixel to an initial value is more than a predetermined range. The generation unit generates correction information by substituting a pixel value of the target pixel with a correction value using the initial value when the extraction unit extracts all pixels of the reference plate reading information, and generates correction information by setting the pixel values of all the pixels as the initial value when the extraction unit does not extract all the pixels.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2011-206119 filed Sep. 21, 2011. 
       BACKGROUND 
     Technical Field 
       [0002]    The present invention relates to an image reading apparatus, an image forming apparatus and a computer-readable medium. 
       SUMMARY 
       [0003]    (1) According to an aspect of the invention, an image reading apparatus includes a reading unit, an extraction unit and a generation unit. The reading unit includes a plurality of photoelectric conversion elements and outputs reading information indicating pixel values for each pixel corresponding to each of the photoelectric conversion elements by reading a document and a reference plate. The reading unit outputs reference plate reading information by reading the reference plate. The extraction unit sets a pixel of the reference plate reading information as a notice pixel and that repeatedly extracts one of the notice pixel as a target pixel until the number of the target pixels is more than a predetermined value when a ratio of a pixel value of the notice pixel to an initial value is more than a predetermined range, a value of the initial value being set according to a pixel position in advance. The generation unit generates correction information. When the extraction unit extracts all pixels of the reference plate reading information, the generation unit generates the correction information acquired by substituting a pixel value of the target pixel with a correction value using the initial value in the reference plate reading information. When the extraction unit does not extract all the pixels of the reference plate reading information, the generation unit generates the correction information acquired by substituting the pixel value of the target pixel with the correction value using the initial value and by substituting a pixel value of a pixel which is not set as the notice pixel with the initial value in the reference plate reading information, or the generation unit generates the correction information acquired by setting the pixel values of all the pixels as the initial value in the reference plate reading information. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    Exemplary embodiments of the invention will be described in detail based on the following figures, wherein: 
           [0005]      FIG. 1  is a diagram illustrating an overall configuration of an image reading apparatus according to a first embodiment. 
           [0006]      FIG. 2  is a diagram illustrating a hardware configuration of the image reading apparatus. 
           [0007]      FIG. 3  is a diagram illustrating a rear surface image reading control unit in detail. 
           [0008]      FIG. 4  is a diagram illustrating a curve corresponding to initial data and a curve corresponding to reference plate reading data. 
           [0009]      FIG. 5  is a flowchart illustrating a content of a shading correction information generation processing routine in the image reading apparatus according to the first embodiment. 
           [0010]      FIG. 6  is a diagram illustrating an average value deduction section. 
           [0011]      FIG. 7  is a flowchart illustrating a content of a shading correction information generation processing routine in an image reading apparatus according to a second embodiment. 
           [0012]      FIG. 8  is a flowchart illustrating a content of a shading correction information generation processing routine in an image reading apparatus according to a third embodiment. 
           [0013]      FIG. 9  is an outline view schematically illustrating an image forming apparatus according to a fourth embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. 
         [0015]    First, referring to  FIG. 1 , an overall configuration of an image reading apparatus  10  according to a first embodiment will be described. 
         [0016]    As shown in  FIG. 1 , the image reading apparatus  10  includes a dual auto document feeder (DADF)  12  including a rear surface image reading unit  28 , and a surface image reading unit  14 . 
         [0017]    The DADF  12  is configured to include a platen  20  on which a document  18  recorded with an image is placed, a taking out roll  22  that takes out the documents  18  placed on the platen  20  one by one, a transport path  24  with a plurality of pairs of transport roll  26 , the rear surface image reading unit  28 , a reference plate  46  placed opposite to the rear surface image reading unit  28 , and a paper ejecting unit  30  in which a document of which reading is completed is ejected. 
         [0018]    The rear surface image reading unit  28  is a fixed and contact type image sensor configured to include a light source  28 B that has a plurality of light emitting elements arranged in a main scanning direction and irradiates illumination light to the document  18  and the reference plate  46 , and a line sensor  28 A that photo-measures the document  18  and the reference plate  46  illuminated by the light source  28 B which are divided into a plurality of pixels and outputs reading data depending on a pixel value photo-measured for each pixel. The rear surface image reading unit  28  includes a rod lens array (not shown) and the light reflected at the document  18  or the reference plate  46  is photo-measured by the line sensor  28 A through the rod lens array. The reference plate  46  as a reference plate which is read by the line sensor  28 A in shading correction information generation processing to be described below may adopt, for example, a white resin plate or a metal plate painted with a white color. 
         [0019]    Meanwhile, the surface image reading unit  14  includes a transparent platen glass  32  where the document  18  may be provided on the top surface thereof and a surface reading position is positioned on the top surface of the platen glass  32 . A light source  34  configured to irradiate the illumination light toward the surface of the document  18 , a first reflection mirror  36  configured to receive the reflection light reflected at the surface of the document  18 , a second reflection mirror  38  configured to bend a progression direction of the reflection light reflected by the first reflection mirror  36  at 90°, and a third reflection mirror  40  configured to further bend a progression direction of the reflection light reflected by the second reflection mirror  38  at 90° are provided below the platen glass  32  at the surface reading position. The surface image reading unit  14  includes a lens  42  and a photoelectric conversion unit  44  including a plurality of pixels. The surface image reading unit  14  reads the surface of the document  18  by imaging the reflection light reflected at the third reflection mirror  40  to the photoelectric conversion unit  44  by the lens  42 . 
         [0020]    According to the image reading apparatus  10  of the first embodiment configured as described above, the document  18  placed on the platen  20  is taken out by the taking out roll  22  one by one to be sent to the transport path  24 . 
         [0021]    The document  18  sent to the transport path  24  is transported up to the surface reading position by the surface image reading unit  14  by the pairs of transport roll  26  and the surface of the document  18  may be read by the surface image reading unit  14 . Thereafter, the document  18  is transported to the rear surface image reading unit  28  installed at the transporting direction downstream side of the surface reading position, and a rear surface of the document  18  is read by the rear surface image reading unit  28  and thereafter, the document  18  is ejected to the paper ejecting unit  30 . 
         [0022]    In the image reading apparatus  10  according to the first embodiment, a fluorescent lamp is adopted as the light source  34 , but the present invention is not limited thereto, and other light sources such as, for example, a plurality of light emitting diodes (LED) arranged in a direction crossing the transporting direction of the document  18  may be adopted. 
         [0023]    In the image reading apparatus  10  according to the first embodiment, as the photoelectric conversion unit  44 , a charge coupled device (CCD) line sensor constituted by a plurality of CCDs is adopted, but the present invention is not limited thereto, and a solid photographing element such as, for example, a complementary metal-oxide semiconductor (CMOS) image sensor may be adopted. 
         [0024]    In the image reading apparatus  10  according to the first embodiment, the light source  34 , the first reflection mirror  36 , the second reflection mirror  38 , and the third reflection mirror  40  are movable in the direction of arrow A of  FIG. 1 . As a result, when the DADF  12  is opened above the surface image reading unit  14  and the document  18  is placed on the top surface of the platen glass  32 , the image recorded in the document  18  may be read by moving the light source  34 , the first reflection mirror  36 , the second reflection mirror  38 , and the third reflection mirror  40  in the direction of arrow A while the illumination light from the light source  34  is irradiated toward the document  18 . 
         [0025]    Next, a hardware configuration of the image reading apparatus  10  will be described with reference to  FIG. 2 . The image reading apparatus  10  is configured to primarily include a controller  50 , an image reading control unit  52 , a DADF control unit  54 , a rear surface image reading control unit  56 , and a user interface (UI)  60 . 
         [0026]    Among them, the controller  50  controls the entirety of the image reading apparatus  10 . The controller  50  receives reading data from each of the image reading control unit  52  and the rear surface image reading control unit  56 . The controller  50  receives a signal indicating a user&#39;s instructions which is inputted from the UI  60 . 
         [0027]    The image reading control unit  52  controls the entire reading process of the image in the image reading apparatus  10 , and specifically, controls for example, the DADF control unit  54 , the rear surface image reading control unit  56 , the surface image reading unit  14 , a scanning control unit  72 , and an illumination control unit  76 . The image reading control unit  52  is configured to be accessible to a surface read only memory (ROM)  68  and a surface non volatile memory (NVM)  70 . Various programs for reading the surface of the document or various information used at that time are stored in the surface ROM  68  or the surface NVM  70 . 
         [0028]    The scanning control unit  72  controls the scanning when reading the document and also controls a motor  74 . The motor  74  integrally moves the light source  34  and various mirrors described in  FIG. 1 . The illumination control unit  76  controls the light source  34 . 
         [0029]    The DADF control unit  54  controls the DADF and receives information from each roller control unit  64  that controls each motor  66  for rotating the taking out roll  22  or the pairs of transport roll  26  described above and from each sensor  62 . As an example of each sensor  62 , a sensor that detects whether the DADF  12  is opened above the surface image reading unit  14  may be adopted. 
         [0030]    The rear surface image reading control unit  56  controls the rear surface image reading unit  28 . The rear surface image reading control unit  56  is configured to be accessible to a rear surface ROM  82 , a rear surface random access memory (RAM)  84 , a rear surface NVM  86 , and a rear surface electrically erasable and programmable read only memory (EEPROM)  88 . 
         [0031]    A program for operating the rear surface image reading control unit  56  or various information used at that time is stored in the rear surface ROM  82  and the rear surface NVM  86 . The rear surface RAM  84  is used when the rear surface image reading control unit  56  operates. Initial data displayed as a pixel value (initial value) for each pixel acquired by photo-measuring a reference plate (an exclusive clean white reference plate different from the reference plate  46 ) without stain by the line sensor  28 A without stain is stored in the rear surface EEPROM  88 . Herein, the stain includes all stains that can be assumed to be attached to the line sensor  28 A or the reference plate  46 , such as paper powder and toner powder. Herein, the case of using the initial data acquired from the clean white reference plate is described, but the initial data may be data to judge a stain pixel by comparing with reference plate reading data outputted by reading the reference plate  46  in a processing to be described below. 
         [0032]    Next, referring to  FIG. 3 , the rear surface image reading control unit  56  will be described in detail. The rear surface image reading control unit  56  has an averaging unit  90  including a line memory  92 , an average value deducing unit  96 , and a register  94 , as shown in  FIG. 3 . Among them, the line memory  92  stores pixel information (pixel value) from reading data outputted by reading in the rear surface image reading unit  28 . The average value deducing unit  96  deduces a pixel value average value that represents an average value of the pixel value represented by the pixel information. The average value is stored in the register  94 . 
         [0033]    The pixel value outputted from the averaging unit  90  is, for example, 3FF (10 bits: hexadecimal) times as an integer. Shading correction information which is represented by each correction value (shading correction pixel value) for shading-correcting each pixel value is stored in a shading memory area  98 , and the 3FF times pixel value is divided by a shading correction pixel value multiplied by a corresponding multiplication coefficient K and the divided value is stored in a subsequent stage memory  100 . The corrected pixel value stored in the subsequent stage memory  100  is subjected to various image processing. 
         [0034]    Herein, shading correction information stored in the shading memory area  98  will be described. 
         [0035]      FIG. 4  shows a graph of a curve Q indicating initial data and a curve R indicating reference plate reading data acquired by reading the reference plate  46 . In  FIG. 4 , a horizontal axis represents the position of the pixel in the main scanning direction and a vertical axis represents a pixel value. Approximately two pixel values influenced by the stain are displayed in the reference plate reading data. In this state, a pixel value (initial value) of the pixel of the initial data and a pixel value (reference plate pixel value) of the pixel of the reference plate reading data, having the same position, are set to α and β, respectively, and value of a ratio thereof (β/α) is examined. 
         [0036]    In a case where a reference plate pixel value is not influenced by the stain, since the curve Q and the curve R are substantially similar to each other, the β/α becomes a value within a predetermined range. Meanwhile, in a case where a reference plate pixel value is influenced by the stain, there is a high possibility that the β/α value will become a value outside the predetermined range. Specifically, when the reference plate pixel value is not influenced by the stain, the β/α value is distributed around a predetermined value (for example, 1.0), but when the reference plate pixel value is influenced by the stain, there is a high possibility that the β/α value will be largely different from 1.0. The pixel which is influenced by the stain is extracted as the stain pixel, and a shading correction pixel value for removing the influence by the stain from a pixel value represented by reading data obtained by reading the document is deduced. 
         [0037]    As the shading correction pixel value, a case can be considered where the reference plate pixel value of the stain pixel is substituted with a correction value using an initial value or a case can be considered where the reference plate pixel value of the stain pixel is substituted with the initial value. However, when the initial value is used as the shading correction pixel value, a vertical strip is generated according to the positional deviation of a lens stain as disclosed in JP 2010-011297 A which is problematic. Meanwhile, when the reference plate pixel value of the stain pixel is substituted with the correction value using the initial value as the shading correction value, a problem occurs as the processing amount becomes excessive depending on the number of the stain pixels. Therefore, in the present embodiment, shading correction information is selectively generated either using the initial value or substituting with the correction value depending on the number of extracted stain pixels. 
         [0038]    Next, referring to  FIG. 5 , the shading correction information generation processing routine will be described, which is executed in the image reading apparatus of the first embodiment. The routine is executed just before the reading of the document. 
         [0039]    At step  100 , the reference plate reading data are acquired by reading the reference plate  46  by the rear surface image reading unit  28 . 
         [0040]    Next, at step  102 , a notice pixel position counter i which is a variable representing a pixel position of a notice pixel set in the reference plate reading data and a stain pixel number counter k for counting the number of extracted stain pixels are initialized (set to 0, respectively). For example, a pixel position of the right end of the reference plate reading data may be set to 1, a pixel position of a subsequent left pixel may be set to 2, and so on, and a pixel position of the left end may be set to n. 
         [0041]    Next, at step  104 , by determining whether the pixel position counter i is larger than n, it is determined whether all pixels of the reference plate reading data are set as the notice pixel. When the notice pixel position counter i is equal to or less than n, the process proceeds to step  106  to increase the notice pixel position counter i by 1, and the process proceeds to step  108 . 
         [0042]    At step  108 , the initial data stored in the rear surface EEPROM  88  is read. The pixel of the pixel position i of the reference plate reading data acquired at step  100  is set as the notice pixel i, and compared with the pixel value (initial value) i of the pixel position i of the read initial data. For example, a ratio of the pixel value of the notice pixel i to the initial value i is calculated and is compared with a predetermined range. 
         [0043]    Next, at step  110 , it is determined whether the notice pixel i is the stain pixel based on the comparison result at step  108 . For example, when the ratio is more than the predetermined range, it may be determined that the notice pixel i is the stain pixel. When the notice pixel i is the stain pixel, the process proceeds to step  112  to increase the stain pixel number counter k by 1, and the pixel position i is stored in a predetermined storage area, and the process proceeds to step  114 . Meanwhile, when the notice pixel i is not the stain pixel, the process proceeds to step  114  directly. 
         [0044]    At step  114 , it is determined whether the stain pixel number counter k becomes a predetermined upperlimit value k max . The upperlimit value k max  is predetermined according to a processing capability of the apparatus or precision required for shading correction. If k≠k max , the process returns to step  104 , and the processing at steps  104  to  114  are repeated. When not positively determined at step  104  but positively determined at step  114 , that is, when the stain pixel number k is more than the upperlimit value k max  before processing is terminated with respect to all the pixels of the reference plate reading data, the process proceeds to step  116 . At step  116 , the initial data are set as the shading correction information and stored in the shading memory area  98 , and the processing is terminated. In this case, the vertical strip by the lens stain still occurs, but is smaller as compared to the influence caused by the remaining stain pixel. 
         [0045]    Meanwhile, when not positively determined at step  114  but positively determined at step  104 , that is, when the processing of all the pixels of the reference plate reading data is terminated while the stain pixel number k is not more than the upperlimit value k max , the process proceeds to step  118 . At step  118 , the pixel position of the stain pixel stored in the predetermined area at step  112  is read, and the shading correction information acquired by substituting the pixel value of the stain pixel in the reference plate reading data with the correction value using the initial value of the same pixel position of the initial data is generated, and stored in the shading memory area  98 . Thereafter, the processing is terminated. 
         [0046]    The correction value used for substitution at step  118  may be deduced as described below. In the following description, a variable put with a parenthesis like A[ ] represents an array. A[ ]←B[ ] represents that array B is substituted into array A. That is, the ones having the same subscription have the same value by the substitution. As described above, the initial data InitDT[ ] is stored in the rear surface EEPROM  88 . A correction average value InitAve of an average value of all pixels of the initial data InitDT[ ] is stored in the rear surface NVM  86 . 
         [0047]    First, the reference plate pixel value of the reference plate reading data acquired at step  100  is substituted into SampAveDT[ ]. An average value of all or some of SampAveDT[ ] is deduced and substituted into a pixel value average value SampAve. Herein, the average value of a portion of SampAveDT[ ] represents average pixel values of pixels which exist in an average value deduction section when a center portion in the main scanning direction is set as the average value deduction section, as shown in  FIG. 6 . SampAveDT[ ] and SampAve are once held on the line memory  92  and the register  94 , respectively. 
         [0048]    A ratio of the average pixel value SampAve to the correction average value InitAve (SampAve/InitAve) is substituted into the multiplication coefficient K. A value acquired by multiplying initial data InitDT[i] by the multiplication coefficient K is set as a correction value CorInitDT[i] of the pixel position i. The multiplication by the multiplication coefficient K is used to set each value of InitDT[ ] to be substantially the same as each value of SampAveDT[ ]. That is, the multiplication is used to set a ratio of each value of CorInitDT[ ] and each value of SampAveDT[ ] to approximately 1.0. 
         [0049]    That is, the reference plate pixel value SampAveDT[i] for the pixel position i of the stain pixel to be substituted is substituted with a value CorInitDT[i] acquired by multiplying the initial data InitDT[i] by K, the ratio of the average pixel value SampAve and the correction average value InitAve. 
         [0050]    Shading correction is performed with respect to the reading data obtained by reading the document by using the shading correction information generated as described above. 
         [0051]    Next, a second embodiment will be described. Since a configuration of an image reading apparatus of the second embodiment is the same as that of the image reading apparatus  10  of the first embodiment, a description thereof will be omitted. 
         [0052]    In the image reading apparatus of the second embodiment, since shading correction information generation processing is different from that of the first embodiment, a shading correction information generation processing routine of the second embodiment will be described with reference to  FIG. 7 . In the shading correction information generation processing of the second embodiment, processing step  200  is executed instead of the processing step  116  of the shading correction information generation processing of the first embodiment. 
         [0053]    When not positively determined at step  104  but positively determined at step  114 , that is, when the stain pixel number k is more than the upperlimit value k max  before the processing is terminated with respect to all the pixels of the reference plate reading data, the process proceeds to step  200 . At step  200 , the pixel position of the stain pixel stored in the predetermined area at step  112  is read, and the pixel value of the stain pixel in the reference plate reading data is substituted with the correction value using the initial value of the same pixel position of the initial data. As the correction value, the same correction value as the correction value used at step  118  of the shading correction information generation processing of the first embodiment may be used. Pixel values of pixels of which the pixel positions are subsequent to i+1, that is, pixels which are not subjected to the processing of steps  108  to  112  are substituted with the initial values of the same pixel positions of the initial data. By conducting the process as described above, the shading correction information is generated and stored in the shading memory area  98  and the processing is terminated. 
         [0054]    Next, a third embodiment will be described. Since the configuration of an image reading apparatus of the third embodiment is the same as that of the image reading apparatus  10  of the first embodiment, description thereof will be omitted. 
         [0055]    In the image reading apparatus of the third embodiment, shading correction information generation processing is different from that of the first embodiment, and a shading correction information generation processing routine of the third embodiment will be described with reference to  FIG. 8 . The same reference numerals are given to the same processings as the first embodiment and a detailed description thereof will be omitted. 
         [0056]    First, at step  300 , the width of a document to be read is detected in reading the document executed after the routine. Herein, for ease of description, it is assumed that a document  18  is set so that a right end of the document and a right end (a reading start position of the line sensor  28 A) of the line sensor  28 A coincide with each other. That is, the document width is detected as an area corresponding to a pixel position of the line sensor  28 A. 
         [0057]    Next, steps  100  to  114  are executed similarly as the first embodiment. 
         [0058]    When not positively determined at step  104  but positively determined at step  114 , that is, when the stain pixel number k is more than the upperlimit value k max  before processing is terminated with respect to all the pixels of the reference plate reading data, the process proceeds to step  302 . 
         [0059]    At step  302 , it is determined whether the pixel position i is smaller than the document width. For example, when the document width detected at step  300  is for m pixels, it is determined whether i&lt;m. If i&lt;m, the stain pixel number k is more than the upperlimit value k max  before the processing of pixels in the area corresponding to the document width of the reference plate reading data is terminated, and as a result, the process proceeds to step  116 . Meanwhile, if i≧m, the stain pixel number k is not more than the upperlimit value k max  at least in the area corresponding to the document width of the reference plate reading data, and as a result, the process proceeds to step  118 . In this case, even though the stain pixel remains at the pixel position after i+1, there is no influence on the reading data of the document. 
         [0060]    The third embodiment described the case in which the right end of the document and the right end of the line sensor  28 A coincide with each other, but, may be applied even in the case, for example, in which the document is set to the center of a readable area of the line sensor  28 A. In this case, a range from a pixel position corresponding to the right end of the document to a pixel position corresponding to a left end is detected as the document width, and the processing steps  108  through  112  may be executed from the pixel position corresponding to the right end of the document. 
         [0061]    Even in the third embodiment, step  200  may be executed instead of step  116  as in the second embodiment. 
         [0062]    In a processing flow of each of the flowcharts described in the first to third embodiments as an example, a processing sequence may be replaced, a new step may be added, or an unnecessary step may be deleted within the scope without departing from the spirit of the present invention. 
         [0063]    Next, a fourth embodiment will be described. The fourth embodiment is an image forming apparatus  11  with the image reading apparatus  10  of any one of the first to third embodiments. 
         [0064]    As shown in  FIG. 9 , the image forming apparatus  11  of the fourth embodiment is configured to include the image reading apparatus  10 , an image forming unit  80 , a paper feeding unit  82 , and a print ejection unit  84 . The configuration of the image reading apparatus  10  is the same as that of the image reading apparatus  10  of the first embodiment. 
         [0065]    The image forming unit  80  which prints a document image on a paper by an electrophotographic method includes an endless intermediate transfer belt, an image forming unit transferring a toner image of each color (Y: yellow, M: magenta, C: cyan, and K: black) to the intermediate transfer belt, and an optical part forming an electrostatic latent image on a photoreceptor drum by exposing the photoreceptor drum (to be described below) of the image forming unit with laser light modulated based on the image information. 
         [0066]    The image forming unit includes the photoreceptor drum, a charger that charges the surface of the photoreceptor drum uniformly, a development part that forms a toner image generated by developing the electrostatic latent image formed on the surface of the photoreceptor drum by the optical part with the toner of each color, and a transfer roller that presses the intermediate transfer belt onto the photoreceptor drum. The intermediate transfer belt is driven by a driving roller connected to a motor. 
         [0067]    The image forming unit  80  includes a transfer part that transfers the toner image formed on the intermediate transfer belt on the paper fed from the paper feeding unit  82 , a fixing part that fixes the toner image transferred to the paper on the paper, and an ejection roller that ejects the paper passing through the fixing part to the print ejecting unit  84 . 
         [0068]    The paper feeding unit  82  includes a plurality of paper cassettes receiving papers having different directions, sizes, and paper qualities and a plurality of rollers for taking out the paper from each paper cassette to transport the paper to the transfer part of the image forming unit  80 . 
         [0069]    According to the image forming apparatus  11  of the fourth embodiment configured as above, the document is read by the image reading apparatus  10 , and an image is formed on the paper fed from the paper feeding unit  82  in the image forming unit  80  based on the reading data acquired by correcting the read data using the generated shading correction information. 
         [0070]    In the fourth embodiment, the image forming apparatus that adopts the electrophotographic image forming unit has been described, but the present invention may be applied even to an inkjet type image forming apparatus. 
         [0071]    In each embodiment, the present invention has been applied to the rear surface image reading unit, but the present invention may be applied even to the generation of the shading correction information of the surface image reading unit. 
         [0072]    The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.