Abstract:
An image reading apparatus includes a moving unit, a first detecting unit, and a second detecting unit. The moving unit moves a calibration plate in the main scanning direction relatively to a reading apparatus. The calibration plate is a plate for calibrating the reading apparatus. The reading apparatus has a reading unit and reading glass. The reading unit is arranged in the main scanning direction. The reading glass is disposed on a reading surface side of the reading unit. The first detecting unit detects an abnormality on the calibration plate from reading results. The reading results are obtained in such a manner that, while the moving unit is controlled to move the calibration plate, the reading unit reads the calibration plate. The second detecting unit detects an abnormality on the reading glass from the reading results.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2016-121197 filed Jun. 17, 2016. 
       BACKGROUND 
     Technical Field 
       [0002]    The present invention relates to an image reading apparatus, an image reading method, and a non-transitory computer readable medium. 
       SUMMARY 
       [0003]    According to an aspect of the invention, there is provided an image reading apparatus including a moving unit, a first detecting unit, and a second detecting unit. The moving unit moves a calibration plate in a main scanning direction relatively to a reading apparatus. The calibration plate is a plate for calibrating the reading apparatus. The reading apparatus has a reading unit and reading glass. The reading unit is arranged in the main scanning direction. The reading glass is disposed on a reading surface side of the reading unit. The first detecting unit detects an abnormality on the calibration plate from reading results. The reading results are obtained in such a manner that, while the moving unit is controlled to move the calibration plate, the reading unit reads the calibration plate. The second detecting unit detects an abnormality on the reading glass from the reading results. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    Exemplary embodiment of the present invention will be described in detail based on the following figures, wherein: 
           [0005]      FIG. 1  is a diagram illustrating the schematic configuration of an image forming apparatus according to the present exemplary embodiment; 
           [0006]      FIG. 2  is a diagram illustrating the schematic configuration of an image reading unit of the image forming apparatus according to the present exemplary embodiment; 
           [0007]      FIG. 3  is a perspective view of the appearance of the image reading unit of the image forming apparatus according to the present exemplary embodiment; 
           [0008]      FIG. 4  is a block diagram illustrating the configuration of a control system of the image reading unit of the image forming apparatus according to the present exemplary embodiment; 
           [0009]      FIG. 5A  is a diagram illustrating a trail which indicates how a calibration plate is moved in a lapse of time and which is obtained in the case where reading is performed while the calibration plate is moved; 
           [0010]      FIG. 5B  is a diagram illustrating an exemplary density profile of a calibration plate (white reference board) which is obtained in the case where abnormalities, such as dust and dirt, occur; 
           [0011]      FIG. 6  is a diagram illustrating exemplary reading results from a charge coupled device (CCD) sensor which are obtained when an abnormality on the calibration plate and an abnormality on reading glass are present; 
           [0012]      FIG. 7A  is a diagram illustrating an example in which the number of samples of reading results from the CCD sensor is less than the required number because of abnormality; 
           [0013]      FIG. 7B  is a diagram illustrating an example in which the number of samples is increased by decreasing the moving speed of the calibration plate; 
           [0014]      FIG. 8A  is a diagram illustrating an example in which multiple abnormalities are present on the calibration plate and in which a reading period matches an interval at which an abnormality occurs; 
           [0015]      FIG. 8B  is a diagram illustrating an example in which the moving speed of the calibration plate is decreased in the case of the example in  FIG. 8A ; 
           [0016]      FIG. 8C  is a diagram illustrating an example in which the moving speed of the calibration plate is increased in the case of the example in  FIG. 8A ; 
           [0017]      FIG. 9  is a diagram illustrating an example in which images of the calibration plate which are successively captured do not overlap each other in the X direction; 
           [0018]      FIG. 10  is a flowchart of an exemplary process flow performed by a reading control device of the image forming apparatus according to the present exemplary embodiment; 
           [0019]      FIG. 11  is a diagram illustrating an example in which pieces of data obtained by reading the calibration plate at the maximum resolution are regularly thinned out; and 
           [0020]      FIG. 12  is a diagram illustrating an example in which pieces of data obtained by reading the calibration plate at the maximum resolution are irregularly thinned out. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    An exemplary embodiment will be described by referring to the drawings.  FIG. 1  is a diagram illustrating the schematic configuration of an image forming apparatus according to the present exemplary embodiment. 
         [0022]    An image forming apparatus  10  includes a display/operation unit  12 , a controller  14 , an image generating unit  16 , an image forming unit  18 , and a discharge unit  20 . 
         [0023]    The display/operation unit  12  includes a display unit such as a liquid crystal display and an operation unit for setting various settings for image formation. In the present exemplary embodiment, for example, the display/operation unit  12  is operated so that various settings, such as various conditions for image formation and a recording medium type with which an image is formed, are set. 
         [0024]    The controller  14  has overall control of the units of the image forming apparatus  10 , and controls the units of the image forming apparatus  10  according to information which is set by using the display/operation unit  12 . The controller  14  is constituted, for example, by a microcomputer including a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and an input/output unit. In the ROM, programs for controlling operations for image formation are stored in advance. The programs loaded on the RAM are executed by the CPU, whereby operations of the units of the image forming apparatus  10  are controlled. 
         [0025]    The image generating unit  16  reads a document image, and thereby generates image information describing the document image. Alternatively, the image generating unit  16  obtains image information transmitted from an external computer, and thereby generates image information of a document image that is to be formed. 
         [0026]    The image forming unit  18  includes a paper feeding unit  22 , a conveying unit  24 , an image processor  26 , an image forming unit  28 , a fixing unit  30 , and an image reading unit  32 . 
         [0027]    The paper feeding unit  22  stores recording paper serving as a recording medium, and supplies the recording paper to the conveying unit  24 . In the present exemplary embodiment, the paper feeding unit  22  stores recording paper wound into a roll. The recording paper is pulled out and supplied to the conveying unit  24 . The paper feeding unit  22  may include multiple accommodating units for storing different sizes and types of paper. In this case, paper of the size and type which are set by using the display/operation unit  12  is supplied from a corresponding one of the accommodating units to the conveying unit  24 . When image information is obtained from the outside, paper of the type specified from the outside is supplied from a corresponding one of the accommodating units to the conveying unit  24 . 
         [0028]    The conveying unit  24  conveys the recording paper supplied by the paper feeding unit  22  to the position at which the image is to be formed on the recording paper, and conveys, to the discharge unit  20 , the recording paper on which the image has been formed. 
         [0029]    The image processor  26  receives the image information which is generated by the image generating unit  16  or which is received by the image generating unit  16  from the outside, performs image processing so that the image is ready to be processed by the image forming unit  28 , and outputs, to the image forming unit  28 , the image information having been subjected to the image processing. 
         [0030]    The image forming unit  28  receives the image information from the image processor  26 , and forms, on the recording paper, an image represented by the image information. For example, the image forming unit  28  may employ an electrophotographic system in which an image is transferred onto the recording paper, or may employ an inkjet system or the like in which an image is formed on the recording paper by ejecting ink onto the recording paper. 
         [0031]    The fixing unit  30  performs processing for fixing the image onto the recording paper. In the processing for fixing, at least one of pressuring and heating of the recording paper on which an image has been formed is performed, whereby the image is fixed onto the recording paper. 
         [0032]    The image reading unit  32  reads the recording paper on which the image has been formed, and obtains image information for performing various types of correction (such as misregistration correction and color correction). 
         [0033]    The discharge unit  20  winds, into a roll, the recording paper on which the image has been formed and stores the wound recording paper. 
         [0034]    The specific configuration of the image reading unit  32  will be described.  FIG. 2  is a diagram illustrating the schematic configuration of the image reading unit  32  of the image forming apparatus  10  according to the present exemplary embodiment. 
         [0035]    In the description below, the X direction indicates the depth direction (the main scanning direction) of the image forming apparatus  10 ; the Y direction indicates the lengthwise direction (the subscanning direction which is the conveying direction of the recording paper) of the image forming apparatus  10 ; and the Z direction indicates the height direction of the image forming apparatus  10 . 
         [0036]    As illustrated in  FIG. 2 , the image reading unit  32  includes a radiating unit  36  and an imaging unit  38 . The radiating unit  36  is disposed above a conveyance path  44  for the recording paper. The radiating unit  36  which includes a pair of LED light sources  36 A and  36 B radiates light toward the recording paper on which an image has been formed. In each of the LED light sources  36 A and  36 B, multiple LEDs are disposed in the X direction. It is assumed that the length of the radiation area is larger than the width of the largest recording paper that is to be conveyed. 
         [0037]    The imaging unit  38  includes an imaging optical system which converges light emitted from the radiating unit  36  and reflected from the recording paper on the CCD sensor  40  to form an image. For example, the imaging unit  38  which includes multiple mirrors for changing the optical axis in the Y and Z directions converges light emitted from the radiating unit  36  and reflected from the recording paper on the CCD sensor  40  to form an image. In the present exemplary embodiment, the case in which the CCD sensor  40  is a line sensor will be described as an example. Alternatively, an area sensor may be applied. 
         [0038]    A control substrate  46  including a reading control device  50  and a control circuit  54  which are described below is disposed above the imaging unit  38 . 
         [0039]    The above-described configuration of the image reading unit  32  causes the CCD sensor  40  to output (feed back), to the controller  14  (see  FIG. 1 ) of the image forming apparatus  10 , light which has been converged to form an image, that is, a signal according to image density. The controller  14  corrects an image formed by the image forming unit  28 , on the basis of the signal from the CCD sensor  40 . For example, when an electrophotographic system is applied as the image forming unit  28 , the image forming apparatus  10  corrects the intensity of irradiation light emitted by an exposure apparatus, the position at which an image is formed, and the like on the basis of the signal from the CCD sensor  40 . 
         [0040]    The image reading unit  32  is provided with a calibration plate  34  for performing calibration such as shading correction. The calibration plate  34  is, for example, a predetermined white reference board for which the color is white. 
         [0041]    In the present exemplary embodiment, images are formed on continuous recording paper. Therefore, if the calibration plate  34  is provided in such a manner as to face the image reading unit  32 , the recording paper needs to be ejected to read the calibration plate  34 . Accordingly, as illustrated in  FIG. 3 , the calibration plate  34  is provided in such a manner as to be capable of being moved in the X direction (the direction indicated by an arrow x in  FIG. 3 ) relatively to the image reading unit  32  by using a moving mechanism (not illustrated). When the calibration plate  34  is not being used, the calibration plate  34  is moved to a position which is not in a read range of the image reading unit  32 . When the calibration plate  34  is to be used, the calibration plate  34  is moved into the read range of the image reading unit  32 . The moving mechanism is driven by a calibration plate driving unit  56  (see  FIG. 4 ) described below. In the present exemplary embodiment, an example in which the calibration plate  34  is moved will be described. Alternatively, the image reading unit  32  may be moved, or both may be moved. In the case where the image reading unit  32  is moved, other than the case in which the image reading unit  32  is moved, the imaging optical system in which imaging is performed on the CCD sensor  40  may be moved. 
         [0042]    The image reading unit  32  is provided with a cleaning unit  42  for cleaning dirt from reading glass  48 . When the cleaning unit  42  which is provided with a brush or the like cleans the reading glass  48 , similarly to the calibration plate  34 , the cleaning unit  42  is moved in the X direction, thereby cleaning the reading glass  48 . The cleaning unit  42  is driven by a cleaning driving unit  58  (see  FIG. 4 ) described below. 
         [0043]      FIG. 4  is a block diagram illustrating the configuration of a control system of the image reading unit  32  of the image forming apparatus  10  according to the present exemplary embodiment. 
         [0044]    The image reading unit  32  is controlled by the reading control device  50 . The reading control device  50  is provided with a function of controlling calibration of the image reading unit  32  (such as calibration of the CCD sensor  40  described above). 
         [0045]    Specifically, as illustrated in  FIG. 4 , the reading control device  50  includes a CPU  50 A, a ROM  50 B, a RAM  50 C, and an input/output port  50 D which are connected to one another via buses  50 E, such as an address bus, a data bus, and a control bus. 
         [0046]    In the ROM  50 B, various programs, such as programs for correcting an image and programs for performing various types of calibration of the image reading unit  32 , are stored. The CPU  50 A executes, on the RAM  50 C, various programs stored in the ROM  50 B, thereby exerting various types of control. 
         [0047]    The input/output port  50 D is connected to the control circuit  54 . The control circuit  54  is connected to the radiating unit  36 , the CCD sensor  40 , the calibration plate driving unit  56  for moving the calibration plate  34 , and the cleaning driving unit  58  which drives the cleaning unit  42 . That is, the control circuit  54  is used to drive each of the radiating unit  36 , the CCD sensor  40 , the calibration plate driving unit  56 , and the cleaning driving unit  58 . 
         [0048]    The reading control device  50  having such a configuration is provided with a function of correcting an image formed on the recording paper in such a manner that the CCD sensor  40  is used to read an image recorded on the recording paper and that the reading results are fed back to the controller  14 . Examples of correction of an image include gradation correction, surface density correction, and sheet registration correction. Further, specifically, a predetermined correction pattern is formed for each type of correction on the recording paper, and the correction pattern is measured by using the image reading unit  32  so that various types of correction are performed. 
         [0049]    In addition, the reading control device  50  performs various types of calibration of the image reading unit  32  (for example, calibration such as adjustment of the upper/lower limit value of output from the CCD sensor  40 , shading correction, and correction of a readout value from the CCD sensor  40 ). 
         [0050]    Calibration performed by the image reading unit  32  having such a configuration will be described. In the description below, a case in which shading correction is performed as an example of calibration will be described. 
         [0051]    When shading correction is to be performed, while the calibration plate  34  is being moved in the X direction, the CCD sensor  40  is used to read the calibration plate  34 . In the present exemplary embodiment, an acceleration period, a constant-speed period, and a deceleration period are set in movement of the calibration plate  34 .  FIG. 5A  illustrates a trail which indicates how the calibration plate  34  is moved in a lapse of time. 
         [0052]    When shading correction is to be performed, while the calibration plate  34  is being moved, the calibration plate  34  is read by emitting light from the radiating unit  36  and by using the CCD sensor  40  which receives light reflected from the calibration plate  34 . Based on the reading results, inconsistencies in brightness due to the characteristics of the optical system and the imaging system are corrected so that uniform brightness is obtained. Specifically, when reading is performed by using the CCD sensor  40  while the calibration plate  34  is being moved, as illustrated in  FIG. 5A , multiple reading results (the number of samples A) are obtained at the same position (the same pixel) of the CCD sensor  40 . Therefore, the average, the moving average, or the like is calculated, and a correction value for the reading results is calculated so that uniform brightness is obtained by using the calculation result. 
         [0053]    When the calibration plate  34  is to be read, if abnormalities, such as dust or dirt, occur on the calibration plate  34  or the reading glass  48 , as illustrated in  FIG. 5B , density is reduced due to dust or dirt. Therefore, when calibration such as shading correction is to be performed, erroneous correction is performed on positions at which density is reduced, resulting in reduction in accuracy of calibration. 
         [0054]    Therefore, in the present exemplary embodiment, an abnormality on the calibration plate  34  and an abnormality on the reading glass  48  are distinguished from each other and detected, and measures against each type of abnormality are taken. 
         [0055]    For example, when an abnormality occurs on the calibration plate  34  due to dust, dirt, or the like, comparison of multiple read images of the calibration plate  34  with one another reveals that, as illustrated in  FIG. 6 , density is reduced at the same position of the calibration plate  34  in each of the reading results from the CCD sensor  40 . Therefore, in the present exemplary embodiment, when a density reduction which is equal to or larger than a predetermined value occurs at the same position of the calibration plate  34 , it is determined that an abnormality occurs on the calibration plate  34 , and the abnormal data is excluded from reference data for correction. 
         [0056]    In contrast, when an abnormality occurs on the reading glass  48  due to dust, dirt, or the like, density abnormalities are present at the same position in the read range of the CCD sensor  40 , and, as illustrated in  FIG. 6 , density abnormalities occur in all of the pixels in the Y direction (subscanning direction) in a calibration plate  34  portion in reading results. Therefore, in the present exemplary embodiment, when reductions in density occur at the same position in the read range of the CCD sensor  40 , it is determined that an abnormality occurs on the reading glass  48 . 
         [0057]    When an abnormality is detected on the calibration plate  34 , in the present exemplary embodiment, the moving speed of the calibration plate  34  is changed in accordance with the size of the abnormality on the calibration plate  34 , whereby samples, the number of which is necessary to perform correction and which are other than abnormal samples in which density abnormalities occur due to the abnormality, are obtained. For example, as illustrated in  FIG. 7A , when the number of samples is less than the required number due to the abnormality, the moving speed of the calibration plate  34  is decreased so that the number of samples is increased. In the case in  FIG. 7A , when reading is performed while the calibration plate  34  is being moved, the numbers of samples other than abnormal samples are 1, 2, 2, 1, 1, . . . . At some positions, the number of samples is 1 because of the abnormality. Therefore, the moving speed of the calibration plate  34  is decreased, and reading is performed. By decreasing the moving speed of the calibration plate  34 , as illustrated in  FIG. 7B , the number of samples other than abnormal samples is 3 at all of the positions. Therefore, as an abnormality is larger, the moving speed of the calibration plate  34  is decreased, whereby the number of samples other than abnormal samples is increased. In the case where the abnormality on the calibration plate  34  is large and where it is necessary to substantially decrease the moving speed of the calibration plate  34 , cleaning or change of the calibration plate  34  may be urged. 
         [0058]    When an abnormality occurs on the calibration plate  34  at multiple positions, as illustrated in  FIG. 8A , the reading period matches an interval at which an abnormality occurs, and the number of samples other than abnormal samples is 0. In this case, similarly to the case of an abnormality on the reading glass  48 , a density abnormality occurs at all of the pixels in the Y direction in a calibration plate  34  portion in the reading results. Since such a state occurs at multiple positions in the main scanning direction, it is determined that abnormalities occur on the calibration plate  34 , and the moving speed of the calibration plate  34  is changed.  FIG. 8B  illustrates a case in which the moving speed of the calibration plate  34  is decreased, and the number of samples other than abnormal samples is increased. In this case, as illustrated in  FIG. 8C , if the moving speed of the calibration plate  34  is increased, the number of samples other than abnormal samples is also increased. Therefore, the moving speed of the calibration plate  34  may be increased. 
         [0059]    When reading is performed while the calibration plate  34  is being moved, in the case where images of the calibration plate  34  which are successively captured do not overlap each other in the X direction as illustrated in  FIG. 9 , it is impossible to perform these processes. Therefore, in the present exemplary embodiment, the relationship among the moving speed of the calibration plate  34 , the size of the calibration plate  34  (the width in the X direction), and an interval at which the CCD sensor  40  performs reading is such that captured images of the calibration plate  34  overlap each other in the X direction. 
         [0060]    In contrast, when an abnormality is detected on the reading glass  48 , the cleaning unit  42  is driven to clean the reading glass  48 , and the calibration plate  34  is then read again. 
         [0061]    A specific process performed by the reading control device  50  when the image reading unit  32  having the above-described configuration is calibrated will be described.  FIG. 10  is a flowchart of an exemplary process flow performed by the reading control device  50  of the image forming apparatus  10  according to the present exemplary embodiment. The process illustrated in  FIG. 10  will be described as a process performed when shading correction is performed on the image reading unit  32 . 
         [0062]    In step  100 , the CPU  50 A controls driving of each of the calibration plate driving unit  56  and the CCD sensor  40  via the control circuit  54  so that the calibration plate  34  is moved and read. Then, the process proceeds to step  102 . 
         [0063]    In step  102 , the CPU  50 A determines whether or not an abnormality occurs on the reading glass  48  on the basis of reading results obtained by reading the calibration plate  34 . In the determination, it is determined whether or not the following conditions are satisfied: a density abnormality occurs at the same position in the read range of the CCD sensor  40 ; and, as illustrated in  FIG. 6 , a density abnormality occurs at all of the pixels in the Y direction (subscanning direction) in a calibration plate  34  portion in the reading results. If the determination result is positive, the process proceeds to step  104 . If the determination result is negative, the process proceeds to step  112 . 
         [0064]    In step  104 , the CPU  50 A drives the cleaning driving unit  58  via the control circuit  54  to operate the cleaning unit  42 , and the process proceeds to step  106 . Thus, the cleaning unit  42  removes the abnormality, such as dust or dirt, on the reading glass  48 . 
         [0065]    In step  106 , the CPU  50 A controls driving of the calibration plate driving unit  56  and the CCD sensor  40  via the control circuit  54  so that the calibration plate  34  is moved and read again. Then, the process proceeds to step  108 . 
         [0066]    In step  108 , for example, the CPU  50 A determines whether or not the area of the abnormal portion on the reading glass  48  is still equal to or greater than a predetermined reference value even after cleaning, thereby determining whether or not it is impossible to perform correction. If the determination result is positive, the process proceeds to step  110 . If the determination result is negative, the process proceeds to step  112 . 
         [0067]    In step  110 , the CPU  50 A performs a warning process and ends the series of processes. For example, the CPU  50 A notifies the controller  14  that the reading glass  48  is to be changed, whereby the controller  14  outputs a warning by displaying a message or the like describing that the reading glass  48  is to be changed, on the display/operation unit  12 . 
         [0068]    In step  112 , the CPU  50 A determines whether or not an abnormality occurs on the calibration plate  34  on the basis of the reading results obtained by reading the calibration plate  34 . In the determination, multiple read images of the calibration plate  34  are compared with one another, and, for example, as illustrated in  FIG. 6 , it is determined whether or not density reduction occurs at the same position of the calibration plate  34  in each of the read images. If the determination result is positive, the process proceeds to step  114 . If the determination result is negative, the process proceeds to step  120 . 
         [0069]    In step  114 , the CPU  50 A determines whether or not the moving speed of the calibration plate  34  needs to be changed. In the determination, for example, it is determined whether or not the number of samples which are other than abnormal samples and which are arranged in the Y direction is equal to or less than a predetermined number due to an abnormality on the calibration plate  34 . If the determination result is positive, the process proceeds to step  116 . If the determination result is negative, the process proceeds to step  120 . 
         [0070]    In step  116 , the CPU  50 A determines the moving speed of the calibration plate  34 , and the process proceeds to step  118 . The moving speed of the calibration plate  34  is determined on the basis of the reading results obtained in step  100  so that a speed that causes the number of samples which are other than abnormal samples and which are arranged in the Y direction to be increased is determined. If a large-sized abnormality on the calibration plate  34  makes it impossible to determine a speed that causes the number of samples which are other than abnormal samples and which are arranged in the Y direction to be increased, the process may proceed to step  110  to perform a warning process. 
         [0071]    In step  120 , the CPU  50 A uses the reading results from the CCD sensor  40  to perform shading correction, and ends the series of processes. 
         [0072]    In the above-described exemplary embodiment, when an abnormality is detected on the calibration plate  34 , the moving speed of the calibration plate  34  is changed, and the calibration plate  34  is read. However, the method for addressing an abnormality on the calibration plate  34  is not limited to this. 
         [0073]    For example, instead of change of the moving speed of the calibration plate  34 , the sampling period used when the CCD sensor  40  reads the calibration plate  34  may be changed. Specifically, compare the case in which reading is performed at the maximum resolution (left diagram in  FIG. 11 ) with the case in which thinning is regularly performed (at certain intervals) on data obtained at the maximum resolution (right diagram in  FIG. 11 ). It shows that reading results similar to those obtained when the moving speed of the calibration plate  34  is changed are obtained. That is, by changing the number of samples obtained by thinning out data obtained at the maximum resolution, reading results similar to those obtained when the moving speed of the calibration plate  34  is changed are obtained. When the sampling period for the CCD sensor  40  is changed, as illustrated in  FIG. 12 , thinning may be irregularly performed (not at certain intervals) on data obtained at the maximum resolution. Irregular thinning is performed so that a large number of samples in a portion in which an abnormality occurs on the calibration plate  34  are obtained and so that a larger number of pieces of data in a portion in which an abnormality does not occur are removed, achieving use of less memory capacity. Alternatively, regular thinning and irregular thinning may be used for different cases. For example, irregular thinning may be applied when the memory capacity is equal to or less than a predetermined capacity, and regular thinning may be applied when the memory capacity is larger than the predetermined capacity. 
         [0074]    Another example of a method for addressing an abnormality on the calibration plate  34  may be a method in which both of the moving speed of the calibration plate  34  and the sampling period are changed. 
         [0075]    In the above-described exemplary embodiment, the case in which the calibration plate  34  is capable of being moved in the X direction (main scanning direction) is described. Alternatively, the calibration plate  34  may be moved in the Y direction (subscanning direction). In this case, when an abnormality occurs on the calibration plate  34 , the calibration plate  34  may be shifted in the subscanning direction to read a surface on which a smaller-sized abnormality occurs. 
         [0076]    In the above-described exemplary embodiment, shading correction is described as an example of calibration of the image reading unit  32 . However, this is not limiting. For example, other calibration, such as adjustment of the amount of light from the radiating unit  36 , and gain adjustment for the CCD sensor  40 , may be applied. 
         [0077]    Programs describing the process performed by the reading control device  50  of the image forming apparatus  10  according to the above-described exemplary embodiment may be stored in a storage medium and may be distributed. 
         [0078]    The present invention is not limited to the description above. Needless to say, other than the description above, various changes may be made without departing from the gist of the present invention.