Abstract:
An image reading device comprises: a light source; a first optical element that focuses light emitted from the light source, the emitted light being reflected by a medium in a first detection area; a first detector that outputs first detection information in response to arrival of light in the first detection area; a second optical element that guides to a second detection area a portion of the light emitted from the light source, which portion does not arrive at the reflective medium in the first detection area; a second detector that outputs second detection information responsive to detection of light at the second detection area; and a generator that generates image data of the medium by revising the first detection information on the basis of the second detection information.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based on and claims priority under 35 U.S.C. 119 from Japanese Patent Application No. 2009-190326, which was filed on Aug. 19, 2009. 
       BACKGROUND 
     Technical Field 
       [0002]    The present invention relates to an image reading device. 
         [0003]    There is known in the art a technique referred to as shading correction. This technique is employed in a variety of optical systems to compensate for light fluctuation in an optical system, and is employed also in some image reading devices. 
       SUMMARY 
       [0004]    According to an aspect of the present invention, there is provided an image reading device comprising: a light source; a first optical element that focuses light emitted from the light source, the emitted light being reflected by a medium in a first detection area; a first detector that outputs first detection information in response to arrival of light in the first detection area; a second optical element that guides to a second detection area a portion of the light emitted from the light source, which portion does not arrive at the reflective medium in the first detection area; a second detector that outputs second detection information responsive to detection of light at the second detection area; and a generator that generates image data of the medium by revising the first detection information on the basis of the second detection information. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    An exemplary embodiment of the invention will now be described in detail based on the following figures, wherein: 
           [0006]      FIG. 1  shows a functional configuration of image reading device  10 ; 
           [0007]      FIGS. 2 and 3  are schematic diagrams of sensor unit  20 ; 
           [0008]      FIG. 4  shows a spectrum of light emitted from light source  21  and diffracted by diffraction unit  25 ; 
           [0009]      FIGS. 5 and 6  show further examples of sensor unit  20 ; 
           [0010]      FIG. 7  is a schematic diagram of sensor unit  20 ; and 
           [0011]      FIG. 8  shows yet another example of sensor unit  20 . 
       
    
    
     DETAILED DESCRIPTION 
     Exemplary Embodiment 
       [0012]      FIG. 1  is a block diagram showing a configuration of image reading device  10 . An image in a predetermined area (hereinafter, “reading area RA”) of a manuscript MS is read by sensor unit  20  (hereinafter, “main scan”). A detailed description of sensor unit  20  will be provided later in the text. Carriage  30  is equipped with a motor for moving manuscript MS to a next reading position after a main scan has been carried out. Each time a main scan is performed a sub-scan is performed in a direction perpendicular to the direction of the main scan (hereinafter, sub-scan direction). Each time a main scan is performed on manuscript MS, sensor unit  20  obtains and outputs image data of manuscript MS to controller  40 . 
         [0013]    Controller  40  includes a processor such as a central processing unit (CPU) and storing means such as a random access memory (RAM) to control sender unit  20  and carriage  30 . Also, controller  40  performs image processing as will be described later in detail. During image processing RAM is used as a work area for the processor. Memory  50  may be a Read Only Memory (ROM), a hard drive, a semiconductor memory, or any other appropriate memory device, the memory being configured to store image data and other information. Input unit  60  includes a touch panel, a keyboard, or the like by which a user inputs instructions including, for example, a selection instruction, a confirmation instruction, a deletion instruction, and so on to image reading device  10 . Instructions input by the user via input unit  60  are output under control of controller  40 . 
         [0014]    Description will now be directed to a configuration of sensor unit  20 . Light source  21  includes a light source such as a Light Emitting Diode (LED) that emits light toward manuscript MS placed on a holder  22 . Holder  22  on which manuscript MS is placed consists of an optically transparent member made of glass or the like. Emitted light passing though holder  22  is diffused by manuscript MS. Focusing unit  23  that includes a lens such as a gradient index lens (GRN) acts to focus light to obtain an equal-magnification image and thereby guide the diffused light to first sensor  24 . First sensor  24  includes photoelectric conversion elements for detecting an intensity of light diffused by manuscript MS. 
         [0015]    Diffraction unit  25  includes diffracting element  251  and reflector  252 . Diffracting element  251  consists of a holographic material that is capable of recording an interference pattern. Examples of such materials include, for example, a photopolymer, dichromate salts in a gel, a photographic film containing silver halide, and others. Reflector  252  consists of an optically reflective material. Thus, diffraction unit  25  diffracts light emitted from light source  21 , and this diffracted light reaches second sensor  28  along a path (a detailed description of this path will be provided later in the text). Second sensor  26  includes photoelectric conversion elements such as photo diodes to detect an intensity of light diffracted by diffraction unit  25 . Each of first sensor  24  and second sensor  26  generate detection information according to intensity of light detected, respectively. Light detection information is output to controller  40  where it is generation and amendment of image data is carried out. 
         [0016]    There will now be provided a detailed explanation of sensor unit  20 .  FIG. 2  is a schematic diagram of sensor unit  20 . Manuscript MS is held by holder  22  (not shown in  FIG. 2 ). Reading area RA of manuscript MS is scanned and image data of manuscript MS for reading area RA is obtained. Light source  21  is disposed in a position such that emitted light passing through holder  22  irradiates reading area RA. It is to be noted here that a shielding member (also not shown in  FIG. 2 ) is disposed such that emitted light is prevented from arriving directly at sensor  24  or  26 . Emitted light that arrives at reading area RA of manuscript MS is diffused at the surface of manuscript MS and guided by focusing unit  23  to arrive at first sensor  24 . First sensor  24  includes an array of photoelectric conversion elements for detecting light (hereinafter, “detection areas  24   k ”) that arrives at least at one of detection areas  24 K. Note that hereinafter the direction of arranged photoelectric conversion elements is referred to as “main scanning direction”. 
         [0017]    In the array of photoelectric conversion elements a charge is generated corresponding to an intensity of light detected at least at one of the respective detection areas  24   k . First sensor  24  generates a signal according to the charge generated, amplifies the generated signal, and outputs the amplified signal (hereinafter, “first detection information”) to controller  40 . The output signal includes a value that corresponds to the intensity of light detected at the at least one of the respective detection areas  24   k . The light reflected at reading area RA of manuscript MS is then focused under equal-magnification by focusing unit  23  onto at the least one of the respective detection areas  24   k . By use of the alignment procedure described above, an image in reading area RA of manuscript MS is read by detection of light arriving at least at one of the respective detection areas  24   k . Controller  40  obtains first detection information from positions that differ relative to each other in their sub-scanning directions, to thereby obtain complete image data for manuscript MS. 
         [0018]    Second sensor  26  includes an array of photoelectric conversion elements that detect intensities of light arriving at least at one of the photoelectric conversion elements (hereinafter, “detection areas  26   k ”). Second sensor  26  is disposed so that detection areas  26   k  are aligned in the main scanning direction. Positions of each of respective detection areas  26   k  and each of respective detection areas  24   k  correspond to each other in relation to the main scanning direction. In the array of photoelectric conversion elements a charge is generated corresponding to an intensity of light detected at least at one of the respective detection areas  26   k . Second sensor  26  generates a signal according to the charge generated, amplifies the generated signal, and outputs the amplified signal (hereinafter, “second detection information”) to controller  40 . The output signal includes a value that corresponds to the intensity of light detected at the at least one of the respective detection areas  26   k . The optical path of the light diffracted by diffraction unit  25  arrives at second sensor  26 . Hereafter, alignment of diffraction unit  25  will now be described in detail. 
         [0019]      FIG. 3  shows a schematic diagram of sensor unit  20 . As shown in the figure, diffraction unit  25  is disposed in the side of holder  22  facing light source  21 , where the light emitted from light source  21  arriving at reading area RA is not completely cut off by diffraction unit  25 . The light diffracted by diffracting element  251  and then propagates in diffracting element  251  is reflected by reflector  252 . The reflected light again propagates in diffracting element  251  and exits diffraction unit  25  toward the upper surface S 1  (i.e., the surface facing manuscript MS) of a lens included in focusing unit  23 . In this way, the light exiting diffracting element  251  is diffracted. A case is now supposed such that: a distance between each of a center of surface S 1  and of a diffraction unit  25  in relation to the sub-scanning direction is d 1 ; and a distance between surface S 1  and the surface at which the incident light from diffracting element  251  is diffracted is d 2 ; then an angle θ of the incident light toward surface S 1  satisfies the relation below. 
         [0000]      tan θ= d 1 /d 2
 
         [0020]    Diffraction unit  25  is disposed in a position such that total inertial reflection occurs at surface S 1  for incident light having an incident angle θ, which position is dependent on a refractive index of the lens. As a result, a large proportion of the incident light travelling toward surface S 1  undergoes regular reflection at surface S 1 . Light that does not undergo regular reflection at surface S 1 , and therefore enters focusing unit  23 , necessarily passes through the lens. As a result, arrival of unwanted or extraneous light at first sensor  24  is obviated due to the action of equal-magnification of the lens for focusing light. Second sensor  26  is disposed in a position such that the light that has undergone regular reflection at surface S 1  arrives at least at one of detection areas  26   k . Second sensor  26  detects an intensity of light arriving at the at least one of the detection areas  26   k  and outputs corresponding detection information to controller  40 . 
         [0021]    Controller  40  measures fluctuations in intensity of light emitted from Light source  21  based on the second detection information. In principle, the greater an amount of light arriving at detection areas  26   k , the larger an output signal of detection information becomes. In this regard, it is preferable that diffraction unit  25  is formed so as to diffract light emitted from light source  21 , to as great an extent as possible, in accordance with a spectrum or other characteristics of the emitted light, so that any fluctuation can be measured highly accurately. 
         [0022]      FIG. 4  shows an example of a spectrum of light that is emitted from light source  21  and then diffracted by diffraction unit  25 . In the figure the horizontal axis shows a wavelength λ and the vertical axis shows an intensity P for an incident and diffracted light. As shown in the figure, when the incident light having a spectrum as indicated by SP 1  is emitted from light source  21 , diffracted light has a spectrum having peaks SP 2 , SP 3  and SP 4 . To realize the diffraction characteristic shown in  FIG. 2 , diffracting element  251  is formed by irradiating laser beams having wavelengths λ 2 , λ 3  and λ 4  and interfereable with the light emitted from light source  21  to a base material. 
       &lt;Operation&gt; 
       [0023]    Operation of device  10  will now be described. First, description will be given with reference to  FIG. 3  to an operation of reading an image. As described above, first detection information generated by first sensor  24  based on light emitted from light sensor  21  and then diffused by manuscript MS, is output to controller  40  and then stored in Memory  50 . The first detection information represents a reading area RA of a scanned image of manuscript MS. Sensor unit  20  successively reads images of different reading areas RAs of manuscript MS after each movement of carriage  30  in the sub-scanning direction and outputs each read image to controller  40  upon completion of each main scanning. Controller  40  uses the detection information stored in memory  50  to generate image data of manuscript MS. This first detection information is used also in adjusting the generated image data of manuscript MS as described below. 
         [0024]    Upon occurrence of a change in intensity of light emitted from light source  21 , pixel values of the generated image data of manuscript MS inevitably change since such image data is generated based on emitted light diffused by manuscript MS. To evaluate a change in light emitted, there is provided a path for the emitted light, which path is different from a path of the light for obtaining image data of manuscript MS, so that second sensor  26  detects light that is not affected by the scanning process. Detection of an intensity of light unaffected by the scanning process will now be described in detail. 
         [0025]    The second detection information generated by second sensor  26  based on the light emitted from light source  21  and diffracted by diffraction unit  25  is output to controller  40 . Controller  40  stores the generated second detection information in memory  50 . Controller  40  generates information representative of the intensity of the light diffracted by diffraction unit  25 . Since the generated information does not depend on the light diffused by the light at reading area RA, the generated information can be taken as a reference for determining any fluctuation in light emitted from light source  21 . Hereinafter, the second detection information is referred to as “luminosity reference information”. 
         [0026]    As described above, a portion of light emitted from light source  21  reaches at least one of detection areas  24   k  and  26   k  via different paths; namely, image data based on light diffracted by diffraction unit  25  and generated by reading manuscript MS at the same time as the luminosity reference information is generated based on light that is diffracted by diffraction unit  25  arrives at least at one of detection areas  26   k . For example, a standard luminosity can be set at a pre-determined level for light emitted from light source  21 , which level is of an optimum intensity; and a difference between an intensity represented by the generated luminosity reference information and the standard luminosity can then be calculated so as to compensate for any fluctuation in the emitted light. 
         [0027]    Based on the process described above, controller  40  revises detection information detected at least at one of detection areas  24   k  based on an amount of fluctuation determined an intensity of light detected at least at one of detection areas  26   k . Accordingly, pixel values included in the image data of manuscript MS, which is generated based on the detection information, are revised. For example, if the standard luminosity is 255 and the intensity of the light detected at least at one of detection areas  26   k  is 230, it can be deduced that light passing through focusing unit  23  and arriving at first sensor  24  has decreased in intensity by 230/255 due to instability in output from light source  21 . In this case, pixel values included in the image data obtained by at least one of detection areas  24   k  in corresponding relation to at least one of detection areas  26   k  can be revised appropriately by increasing the light intensity by 255/230. 
         [0028]    As detection areas  26   k  of second sensor  26  are disposed in corresponding positions of detection areas  24   k  of first sensor  24 , the revision of pixel values described above is performed for each set of detection areas  24   k  and  26   k . In other words, fluctuations in luminosity resulting from instability in output from light source  21  is adjusted for each of pixel values corresponding to a set of areas. This adjustment process is performed after completion of a main scanning process. The adjustment process can be performed after completion of all sub-scanning processes i.e., after complete image data for manuscript MS had been obtained. Alternatively, the adjustment process can be performed after detection at each of detection areas  24   k  and at a respective one of the detection areas  26   k  has been completed. 
         [0029]    As will be apparent from the foregoing description, controller  40  revises pixel values included in image data on the basis of luminosity reference information, generates revised image data based on the revised pixel values, and stores the revised image data in memory  50 . The revised image data and the luminosity reference information are generated based on light emitted from light source  21  and detected at least at one of detection areas  24   k  and  26   k , respectively. Thus, fluctuations in light intensity resulting from instability in output from light source  21  is measured at a time of obtaining image data of manuscript MS. Thus, if an intensity of emitted light fluctuates during scanning manuscript MS, the obtained image data is adjusted in real time based on luminosity reference information that is representative of a current fluctuation. In this way, compensation of fluctuations can be readily incorporated in providing finalized image data. 
         [0030]    It is to be noted here that the exemplary embodiment described above can be modified in various aspects as outlined below. 
       Modified Example 1 
       [0031]    In the exemplary embodiment, a transparent hologram that includes diffracting element  251  and reflector  252  is provided. It is possible to provide an optical element for diffracting emitted light, which element functions as a reflective hologram. In this case, emitted light from light source  21  is diffracted at the surface of the reflective hologram, then undergoes regular reflection at surface S 1 , and finally arrives at second sensor  26 . Also, it is possible to absorb light passing through the reflective hologram without undergoing reflection using a light absorber that is provided in place of reflector  252 . As a result, arrival of light at second sensor  26  that has not undergone diffraction in the reflective hologram is obviated and thereby noise luminosity standard information is avoided. 
       Modification Example 2 
       [0032]    In the exemplary embodiment, light diffracted by diffraction unit  25  is regularly reflected at surface S 1  to be guided to second sensor  26 . It is possible to employ a planar mirror for guiding the light to second sensor  26 .  FIG. 5  shows a schematic diagram of sensor unit  29  according to the modified example 2. As shown in the figure, a planar mirror  27  is disposed for example in a surface S 2  of focusing unit  23  facing diffraction unit  25 . In this case, second sensor  26  is disposed in a position where the light is diffracted by diffraction unit  25  and reflected regularly by planar mirror  27 . An interference pattern is recorded on the diffracting element  251  upon exposure to light such that emitted light from light source  21  is diffracted toward planar mirror  27 . 
         [0033]    In modified example 2, a planar mirror is provided to reflect light diffracted by diffraction unit  25 . However, it is also possible to guide the diffracted light to second sensor  26  using a focusing mirror.  FIG. 6  shows a schematic diagram of sensor unit  20  according to modified example 3. As shown in the figure, a focusing mirror  28  is disposed on a side surface (Surface S 2 ) of focusing unit  23  facing diffraction unit  25 . Second sensor  26  is disposed at a position at which the light diffracted by diffraction unit  25  and reflected by focusing mirror  28  arrives. With regard to focusing mirror  28 , a condition of the surface, light axis, and position in the surface S 2  can be each determined so that parallel incident light beam from diffraction unit  25  after being reflected by focusing mirror  28  is focused on detection areas  26   k . Preferably, diffraction unit  25  according to this modified example has a larger size than that of second sensor  26 . In this case, the intensity of light per unit area arriving at detection areas  26   k  become larger than that diffracted by diffraction unit  25 . In other words, an accuracy of detected information output by second sensor  26  becomes higher than in a case where planar mirror  27  is employed. As a result, less fluctuation in light intensity occurs and therefore is detected. 
       Modified Example 4 
       [0034]    In the exemplary embodiment, diffraction unit  25  which includes a transparent hologram is employed to guide the emitted light to second sensor  26 . It is possible to employ other optical devices that diffract the emitted light, which includes a diffractive lens, a combination of a reflective hologram, a lens, a mirror and the like. In the exemplary embodiment, holder  22  is fixed to sensor unit  20 , as a result of which a relative position between holder  22  and remaining members of sensor unit  20  is maintained constant. Moreover, it is possible to dispose a holder independent of sensor unit  20 .  FIG. 7  shows a schematic diagram of sensor unit  20   a  according to modified example 5. Manuscript MS is held by holder  22   a , which holder is fixed directly to a cabinet of image reading device  10 . Sensor unit  20   a  includes light source  21 , focusing unit  23 , first sensor  24  and second sensor  26 . Sensor unit  20   a  is moved by a movement mechanism such as a motor (not shown in the figure) to a position for a next scanning in the sub-scanning direction each time a main scanning process has been completed, and before a next main scanning process is initiated. In this way, sensor unit  20   a  repeats the main scanning process and the sub-scanning process while moving to appropriate positions so as to obtain complete image data for manuscript MS. 
       Modified Example 6 
       [0035]    In the exemplary embodiment, controller  40  revises image data by comparing first and the second detection information detected at least at one of respective detection areas  24   k  and  26   k . It is possible to perform the adjustment process based on first and second detection information detected at positions that do not co-correspond. Alternatively, the adjustment process can be performed on the basis only of the second detection information obtained from at least one of detection areas  26   k . It is to be noted here that image reading device  10  performs adjustment of luminosity of image data by obtaining luminosity reference information while scanning manuscript MS, in a manner similar to that employed in the exemplary embodiment. 
       Modified Example 7 
       [0036]    In the exemplary embodiment, image reading device  10  obtains luminosity reference information while reading an image of manuscript MS and adjusts a luminosity of read image data based on the luminosity reference image. It is possible also to generate luminosity reference information prior to scanning manuscript MS. In this case, adjustment of image data of manuscript MS is performed after complete image data of manuscript MS is obtained using a method determined on a basis of the luminosity reference information. 
       Modified Example 8 
       [0037]    In the exemplary embodiment, image data is revised as a result of measurement of fluctuations in the emitted light due to instability in output of light source  21 . It is possible to revise image data by measuring a change of signals occurring regardless of light arriving at least at one of detection areas  24   k . The signals may be attributed to noise due to a dark current occurring in a line sensor or to leaked light, i.e., light which arrives at least at one of detection areas  24   k  without passing through focusing unit  23 . Hereinafter, such a noise level is referred to as a “dark reference value”. 
         [0038]      FIG. 8  shows a schematic diagram of sensor unit  20  according to the modified example 8. A third sensor  29  includes an array of photoelectronic conversion elements each of which detects an intensity of light at a respective at least one of detection areas  29   k  to thereby generate detection information and output the information to controller  40 . Third sensor  29  is disposed along the sub-scanning direction at a position in the arrangement of detection areas  29   k  at a predetermined distance from first sensor  24 , at which light passing through focusing unit  23  does not arrive. Each at least one of detection areas  24   k  corresponds to a respective at least one of detection area  29   k  in positions in relation to the sub scanning direction. In the alignment of the optical elements according to modified example 8, light detected by the photoelectronic elements at detection areas  29   k  does not include light diffused by manuscript MS. Generation of detection information (third detection information) by third sensor  29  and obtaining image data of manuscript MS are performed at the same time. Thus, the output third detection information is provided to controller  40  together with the obtained image data. 
         [0039]    The third detection information is used as a reference signal (hereinafter referred to as noise reference information) representative of fluctuation in signals caused by factors that are not relevant to arrival of light at least at one of detection areas  24   k . For example, a background noise level is determined at each of detection areas  24   k  when is no substantial noise is present. True noise is determined by measuring a difference between noise reference information detected at each of detection areas  29   k  and a background noise level. Controller  40  revises detection information detected at least at one of detection areas  24   k  based on the true noise present at least at one of respective detection areas  29   k.    
         [0040]    For example, when noise reference information “5” is detected at least at one of detection areas  29   k  at which a background noise level is “0,” a luminosity detected at least at one of detection areas  24   k  corresponding to the at least one of the detection areas  29   k  is reduced by “5.” Similar adjustment is performed in each set of detection areas  24   k  and  29   k , to remove a noise for each set of the detection areas  24   k  and  29   k . The adjustments can be performed each a single main scanning has been completed. Alternatively, noise reference information is obtained in advance, and adjustment of image data is performed after complete image data for manuscript MS has been obtained using a method employing noise reference information. In a case where detection of leaked light is unnecessary, it is possible to dispose a cover over third sensor  29  to thereby shut out light moving toward third sensor  29 . 
         [0041]    In modified example 8, controller  40  revises luminosity of image data based on noise detected at least at one of detection areas  29   k , generates the revised data based on the revised luminosity and stores the revised image data in memory  50 . Evaluation of noise levels and scanning of manuscript MS are thus performed at a same time, and accordingly if a noise level changes during scanning of manuscript MS, a transient change in the noise level is detected and taken into account in revising image data appropriately. As a result, finalized image data does not contain any fluctuation in pixel vales that may otherwise be present due to fluctuations in noise level. 
         [0042]    The foregoing description of the embodiments of the present invention is 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, a large number of possible 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 in various embodiments, and with the various modifications as suited to a particular use that may be contemplated. It is thus intended that the scope of the invention be defined by the following claims and their equivalents.