Patent Publication Number: US-2020303440-A1

Title: Image capturing device, liquid discharge device, and image capturing method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2019-050651, filed on Mar. 19, 2019. The contents of which are incorporated herein by reference in their entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image capturing device, a liquid discharge device, and an image capturing method. 
     2. Description of the Related Art 
     A system configured to acquire a color image of an image capturing target by using a single-plate image sensor including a color filter disposed on a light receiving element has been known. For example, in a known system, obtained image information of each pixel is corrected by using information of pixels nearby to interpolate color information for the pixel, thereby generating color image data. 
     However, with this technology, decrease of sharpness and false color sometimes occur to an edge area in which brightness abruptly changes. To avoid this, a disclosed system (for example, Japanese Unexamined Patent Application Publication No. 2011-61249) includes a plurality of color filters disposed between the image capturing target and the light receiving element, and switches color components of light incident on the light receiving element by switching the color filters at each image capturing. 
     However, the conventional technology needs an actuator for switching the filters, which leads to complication of the device, and thus it has been difficult to obtain highly accurate color image data with a simple configuration. 
     SUMMARY OF THE INVENTION 
     According to an aspect of the present invention, an image capturing device includes an image capturing unit, a movement control unit, an acquisition unit, and a generation unit. The image capturing unit includes a single-plate image sensor including color filters disposed on two-dimensionally arrayed light receiving elements. The image capturing unit is configured to capture an image of an image capturing region on an image capturing target. The movement control unit is configured to move the image capturing region such that images of each of a plurality of pixel areas on the image capturing target are captured by light receiving elements corresponding to respective color filters of colors different from each other. The acquisition unit is configured to acquire image data of the image capturing region each time the image capturing region is moved. The generation unit is configured to generate color image data of the image capturing region from a plurality of pieces of the image data. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view illustrating an exemplary liquid discharge device; 
         FIG. 2  is a top view illustrating an exemplary mechanical configuration of the liquid discharge device; 
         FIG. 3  is a schematic diagram of an exemplary elevation mechanism; 
         FIG. 4  is an explanatory diagram of a specific example of an image capturing device; 
         FIG. 5  is an explanatory diagram of a schematic configuration of a control mechanism of the liquid discharge device; 
         FIG. 6  is a block diagram illustrating an exemplary control mechanism of the image capturing device; 
         FIG. 7  is an enlarged pattern diagram of color filters of an image sensor; 
         FIG. 8  is an enlarged pattern diagram of the color filters of the image sensor; 
         FIG. 9  is a pattern diagram illustrating exemplary demosaicing; 
         FIG. 10  is a pattern diagram illustrating exemplary demosaicing through linear interpolation; 
         FIG. 11A  is a pattern diagram illustrating an exemplary image capturing region of a pattern in which light and dark parts are alternately repeated; 
         FIG. 11B  is a pattern diagram illustrating exemplary color image data obtained through demosaicing by a conventional scheme; 
         FIG. 12A  is an explanatory diagram of image data obtained at each movement of the image capturing region; 
         FIG. 12B  is an explanatory diagram of image data obtained at each movement of the image capturing region; 
         FIG. 12C  is an explanatory diagram of image data obtained at each movement of the image capturing region; 
         FIG. 12D  is an explanatory diagram of image data obtained at each movement of the image capturing region; 
         FIG. 13  is a flowchart illustrating an exemplary process of processing executed by a demosaicing unit; and 
         FIG. 14  is a diagram illustrating an exemplary hardware configuration of an image processing unit. 
     
    
    
     The accompanying drawings are intended to depict exemplary embodiments of the present invention and should not be interpreted to limit the scope thereof. Identical or similar reference numerals designate identical or similar components throughout the various drawings. 
     DESCRIPTION OF THE EMBODIMENTS 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present invention. 
     As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. 
     In describing preferred embodiments illustrated in the drawings, specific terminology may be employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents that have the same function, operate in a similar manner, and achieve a similar result. 
     An embodiment of the present invention will be described in detail below with reference to the drawings. 
     An embodiment has an object to obtain highly accurate color image data with a simple configuration. 
     An image capturing device, a liquid discharge device, and an image capturing method according to the present embodiment will be described below in detail with the accompanying drawings. In the present embodiment, the following description is made with an example in which the image capturing device is applied to the liquid discharge device. However, application of the image capturing device is not limited to the liquid discharge device. 
       FIG. 1  is a perspective view illustrating an exemplary liquid discharge device  100  according to the present embodiment.  FIG. 2  is a top view illustrating an exemplary mechanical configuration of the liquid discharge device  100 . 
     As illustrated in  FIG. 1 , the liquid discharge device  100  according to the present embodiment includes a carriage  5  configured to form an image on a recording medium  16  reciprocated in a main-scanning direction (the direction of arrow X in  FIG. 1 , hereinafter referred to as a main-scanning direction X) and intermittently conveyed in a sub-scanning direction (the direction of arrow Y in  FIG. 1 , hereinafter referred to as a sub-scanning direction Y). The main-scanning direction X is parallel to a two-dimensional plane of the recording medium  16  (in other words, in the plane direction of a platen plate  13 ). The sub-scanning direction Y is parallel to the two-dimensional plane of the recording medium  16  and orthogonal to the main-scanning direction X. 
     The recording medium  16  is an exemplary image capturing target. The image capturing target is a target, an image of which is captured by an image capturing unit to be described later. The following description of the present embodiment is made with an example in which the image capturing target is the recording medium  16 . However, the image capturing target of the image capturing unit is not limited to the recording medium  16 . 
     The carriage  5  is supported by a main guide rod  3  extended in the main-scanning direction X. The carriage  5  is provided with a coupling piece  5   a . The coupling piece  5   a  is engaged with a sub guide  4  provided in parallel to the main guide rod  3 , thereby stabilizing the posture of the carriage  5 . 
     As illustrated in  FIG. 2 , a plurality of record heads of a record head  6   y  configured to discharge yellow (Y) ink, a record head  6   m  configured to discharge magenta (M) ink, a record head  6   c  configured to discharge cyan (C) ink, and a record head  6   k  configured to discharge black (Bk) ink (hereinafter, the record heads  6   y ,  6   m ,  6   c , and  6   k  are also collectively referred to as a record head  6 ) are mounted on the carriage  5 . The record head  6  is mounted on the carriage  5  with its discharge surface (nozzle surface) facing downward (the recording medium  16  side). The record head  6  is a main image output means. 
     The description continues with reference to  FIG. 1 . A cartridge  7  as an ink supply body for supplying ink to the record head  6  is not mounted on the carriage  5  but is disposed at a predetermined position in the liquid discharge device  100 . The cartridge  7  and the record head  6  are coupled to each other through a pipe (not illustrated), and ink is supplied from the cartridge  7  to the record head  6  through the pipe. 
     The carriage  5  is coupled to a timing belt  11  stretched around a drive pulley  9  and a driven pulley  10 . The drive pulley  9  is rotated by drive of a main-scanning motor  34 . The main-scanning motor  34  is a direct-current (DC) motor. The driven pulley  10  includes a mechanism to adjust its distance to the drive pulley  9  and has a function to provide predetermined tension to the timing belt  11 . The carriage  5  is reciprocated in the main-scanning direction X as the timing belt  11  is fed by drive of the main-scanning motor  34 . Movement of the carriage  5  in the main-scanning direction X is controlled based on an encoder value obtained when a main-scanning encoder sensor  41  provided to the carriage  5  senses a mark on an encoder sheet  40  as illustrated in, for example,  FIG. 2 . 
     The liquid discharge device  100  according to the present embodiment also includes a maintenance mechanism  21  for maintaining reliability of the record head  6 . The maintenance mechanism  21  performs, for example, cleaning and capping of the discharge surface of the record head  6 , and ejection of unnecessary ink from the record head  6 . 
     As illustrated in  FIG. 2 , the platen plate  13  is provided at a position facing the discharge surface of the record head  6 . The platen plate  13  supports the recording medium  16  when ink is discharged from the record head  6  onto the recording medium  16 . The liquid discharge device  100  according to the present embodiment is a wide device in which the travel distance of the carriage  5  in the main-scanning direction X is long. Thus, the platen plate  13  is formed by connecting a plurality of plate members in the main-scanning direction X (the moving direction of the carriage  5 ). The recording medium  16  is sandwiched by conveyance rollers driven by a sub-scanning motor (not illustrated) and is intermittently conveyed on the platen plate  13  in the sub-direction scanning Y. The sub-scanning motor is a direct-current (DC) motor. In addition, a sub-scanning encoder sensor (not illustrated) is provided to the liquid discharge device  100  and acquires the amount of movement in the sub-scanning direction Y as a slit plate is rotated along with rotation of the conveyance rollers. 
     The record head  6  includes a plurality of nozzle lines. An image is formed on the recording medium  16  by discharging ink from the nozzle lines onto the recording medium  16  being conveyed on the platen plate  13 . 
     The above-described components included in the liquid discharge device  100  according to the present embodiment are disposed inside an exterior body  1 . The exterior body  1  is provided with a cover member  2  that can be opened and closed. At maintenance of the liquid discharge device  100  or occurrence of paper jam, the cover member  2  is opened to perform work on a component provided inside the exterior body  1 . 
     The liquid discharge device  100  according to the present embodiment intermittently conveys the recording medium  16  in the sub-scanning direction Y and ejects ink onto the recording medium  16  on the platen plate  13  from the nozzle lines of the record head  6  mounted on the carriage  5  while moving the carriage  5  in the main-scanning direction X while conveyance of the recording medium  16  in the sub-scanning direction Y is stopped, thereby forming an image on the recording medium  16 . 
     The liquid discharge device  100  according to the present embodiment also includes an elevation mechanism  30 .  FIG. 3  is a schematic diagram of an exemplary elevation mechanism  30 . When the recording medium  16  is, for example, a highly elastic sheet or a bent sheet, the recording medium  16  is likely to float over the platen plate  13 . In such a case, the record head  6  is potentially damaged and broken by the recording medium  16 . To avoid this, the liquid discharge device  100  according to the present embodiment includes the elevation mechanism  30  configured to move up and down the carriage  5 . The elevation mechanism  30  includes a carriage elevation motor  32  and a carriage elevation cam  33 . The elevation mechanism  30  moves up and down the carriage  5  as the carriage elevation cam  33  is rotated by drive of the carriage elevation motor  32 . The elevation mechanism  30  of the carriage  5  is not limited to the configuration illustrated in  FIG. 3 . 
     The liquid discharge device  100  according to the present embodiment includes an image capturing device  20 . The image capturing device  20  obtains image data by capturing an image of an image capturing region on the recording medium  16  as an exemplary image capturing target. 
     As illustrated in  FIG. 2 , the image capturing device  20  is fixed to the carriage  5  and reciprocated integrally with the carriage  5  in the main-scanning direction X. The image capturing device  20  captures an image of the image capturing region of the recording medium  16  and obtains image data of one frame at each image capturing. 
       FIG. 4  is an explanatory diagram of a specific example of the image capturing device  20 . 
     The image capturing device  20  includes an image processing unit  26  and an image capturing unit  28 . The image processing unit  26  executes various kinds of image processing on image data obtained by the image capturing unit  28  (described later in detail). The image capturing unit  28  obtains image data by capturing an image of an image capturing region P of the recording medium  16 . 
     The image capturing unit  28  includes an image sensor  22  and a lens  24 . The image sensor  22  is a single-plate image sensor including color filters disposed on two-dimensionally arrayed light receiving elements. 
     Each light receiving element is a well-known photoelectric conversion element configured to output a signal in accordance with the intensity of received light. The light receiving element is, for example, a charge-coupled device (CCD) or a complementary metal-oxide-semiconductor (CMOS). 
     In the single-plate image sensor, a color filter of any one of three primary colors such as RGB is disposed on each light receiving element. Thus, each light receiving element obtains color information of any one of RGB colors through single image capturing. 
     In the image sensor  22 , a filter made of color filters of a plurality of colors are disposed along a two-dimensional plane on which the light receiving elements are two-dimensionally arrayed. For example, the filter includes a Bayer array of color filters of RGB colors on the above-described two-dimensional plane. Alternatively, for example, the filter includes a complementary color filter array of color filters of CMYG colors on the above-described two-dimensional plane. The Bayer array is also referred to as a primary color filter array. The complementary color filter array is also referred to as a checker color array. 
     The following description of the present embodiment is made with an example in which the image sensor  22  includes a Bayer array of RGB color filters along a two-dimensional plane on which the light receiving elements are two-dimensionally arrayed. 
     The image capturing unit  28  is attached to the carriage  5  so that the image capturing unit  28  can capture an image of the image capturing region P on the recording medium  16 . 
     Specifically, the lens  24  of the image capturing unit  28  is disposed so that the optical axis of the lens  24  is aligned with a line perpendicular to the surface of the recording medium  16  being conveyed on the platen plate  13 . Specifically, the image capturing unit  28  is attached to the carriage  5  to satisfy this relation. In addition, the image sensor  22  of the image capturing unit  28  is disposed so that the optical axis of the lens  24  is aligned with a line orthogonal to the two-dimensional plane of the light receiving elements provided to the image sensor  22 . 
     With this configuration, the image sensor  22  can obtain image data by capturing an image of the image capturing region P on the recording medium  16 . 
     The positional relation between the image capturing device  20  and the recording medium  16  satisfies the following relation. 
     The size of the image capturing region P on the recording medium  16  in the main-scanning direction X is represented by a 1 . The image capturing region P is a region on the recording medium  16  that the image capturing device  20  can capture an image at single image capturing. The size of the two-dimensional plane on which the light receiving elements of the image sensor  22  are arrayed in the main-scanning direction X is represented by a 2 . The distance between the lens  24  and the recording medium  16  is represented by d 1 . The distance between the lens  24  and the two-dimensional plane of the image sensor  22  is represented by d 2 . With this notation, the relation of Expression (1) below holds. 
         a 1= a 2× d 1/ d 2  (1)
 
     The number of pixels of the two-dimensional plane on which the light receiving elements of the image sensor  22  are arrayed in the main-scanning direction X is represented by x 2 . The size corresponding to each pixel in the image capturing region P in the main-scanning direction X is represented by x 1 . With this notation, the relation of Expression (2) below holds. 
         x 1= a 1/ x 2  (2)
 
     The size of the image capturing region P on the recording medium  16  in the sub-scanning direction Y is represented by b 1 . The size of the two-dimensional plane on which the light receiving elements of the recording medium  16  are arrayed in the sub-scanning direction Y is represented by b 2 . The distance between the lens  24  and the recording medium  16  is represented by d 1 . The distance between the lens  24  and the two-dimensional plane of the image sensor  22  is represented by d 2 . With this notation, the relation of Expression (3) below holds. 
         b 1= b 2× d 1/ d 2  (3)
 
     The number of pixels of the two-dimensional plane on which the light receiving elements of the image sensor  22  are arrayed in the sub-scanning direction Y is represented by y 2 . The size corresponding to each pixel in the image capturing region P in the sub-scanning direction Y is represented by y 1 . With this notation, the relation of Expression (4) below holds. 
         y 1= b 1/ y 2  (4)
 
     In the present embodiment, the image processing unit  26  executes image processing to be described later by using these expressions (described later in detail). 
       FIG. 5  is an explanatory diagram of a schematic configuration of a control mechanism of the liquid discharge device  100  according to the present embodiment. 
     The control mechanism of the liquid discharge device  100  according to the present embodiment includes a higher-level CPU  107 , a ROM  118 , a RAM  119 , an elevation driver  110 , a main-scanning driver  109 , a record head driver  111 , a sub-scanning driver  113 , the carriage  5 , the record head  6 , the main-scanning encoder sensor  41 , the image capturing device  20 , and a sub-scanning motor  36 . The record head  6 , the main-scanning encoder sensor  41 , and the image capturing device  20  are mounted on the carriage  5  as described above. 
     The higher-level CPU  107  governs the entire control of the liquid discharge device  100  by supplying data of an image to be formed on the recording medium  16  and a drive control signal (pulse signal) to each driver. Specifically, the higher-level CPU  107  controls elevation of the carriage  5  by driving the carriage elevation motor  32  through the elevation driver  110 . The higher-level CPU  107  also controls drive of the carriage  5  in the main-scanning direction by controlling the main-scanning motor  34  through the main-scanning driver  109 . The higher-level CPU  107  also controls the timing of ink discharge by the record head  6  through the record head driver  111 . The higher-level CPU  107  also controls drive of the sub-scanning motor  36  through the sub-scanning driver  113 . 
     The main-scanning motor  34  and the sub-scanning motor  36  are each an exemplary first drive unit. The first drive unit relatively moves at least one of the recording medium  16  as the image capturing target and the image capturing device  20  in the main-scanning direction X and the sub-scanning direction Y. In the present embodiment, as described above, the main-scanning motor  34  moves the carriage  5  in the main-scanning direction X. Thus, the image capturing device  20  moves in the main-scanning direction X along with movement of the carriage  5  in the main-scanning direction X. In the present embodiment, as described above, the sub-scanning motor  36  moves the recording medium  16  in the sub-scanning direction Y. 
     The carriage elevation motor  32  is an exemplary second drive unit. The second drive unit changes the distance between the recording medium  16  as the image capturing target and the image capturing device  20 . As described above, the carriage elevation motor  32  moves up and down the carriage  5  by drive of the carriage elevation motor  32 . Thus, in the present embodiment, the distance between the carriage  5  and the recording medium  16  is changed by drive of the carriage elevation motor  32 . 
     The main-scanning encoder sensor  41  outputs, to the higher-level CPU  107 , an encoder value obtained by sensing a mark on the encoder sheet  40 . The higher-level CPU  107  controls drive of the carriage  5  in the main-scanning direction X through the main-scanning driver  109  based on the encoder value from the main-scanning encoder sensor  41 . In addition, a sub-scanning encoder sensor  43  outputs an acquired movement amount in the sub-scanning direction Y to the higher-level CPU  107 . The higher-level CPU  107  controls drive in the sub-scanning direction Y based on the movement amount from the sub-scanning encoder sensor  43 . The liquid discharge device  100  may control drive (scanning) in the main-scanning direction X and the sub-scanning direction Y by using a stepping motor. In this case, the liquid discharge device  100  may include no encoder sensors (the main-scanning encoder sensor  41  nor the sub-scanning encoder sensor  43 ). 
     The image capturing device  20  captures an image of the image capturing region P of the recording medium  16  and obtains image data of one frame at each image capturing. Then, the image processing unit  26  executes various kinds of image processing on a plurality of pieces of the obtained image data and outputs color image data. 
     The ROM  118  stores, for example, computer programs and various kinds of control data of the procedure of processing executed by the higher-level CPU  107 . The RAM  119  is used as a working memory of the higher-level CPU  107 . 
     The following describes the image capturing device  20  in detail. 
       FIG. 6  is a block diagram illustrating an exemplary control mechanism of the image capturing device  20 . 
     The image capturing device  20  includes the image capturing unit  28  and the image processing unit  26 . The image capturing unit  28  and the image processing unit  26  are connected with each other to perform communication of data or signals therebetween. 
     The image capturing unit  28  is provided with the image sensor  22 . The image capturing unit  28  captures an image of the image capturing region P on the recording medium  16 . The image capturing unit  28  may further have at least part of the function of the image processing unit  26 . 
     The image processing unit  26  executes various kinds of image processing on image data received from the image sensor  22 . In the present embodiment, the image processing unit  26  includes an analog-digital (A/D) conversion unit  26 A, a shading correction unit  26 B, a white balance correction unit  26 C, a demosaicing unit  26 D, a color correction unit  26 E, a gamma correction unit  26 F, and an image format conversion unit  26 G. 
     The A/D conversion unit  26 A converts an analog signal received by the image sensor  22  into image data as digital data. The shading correction unit  26 B corrects illumination unevenness of the image data due to variation in the sensitivity of the light receiving elements and difference in the angle of incident light on the light receiving elements. The white balance correction unit  26 C corrects white balance of the image data. The demosaicing unit  26 D generates color image data by using the image data (described later in detail). The color correction unit  26 E provides the color image data with color correction to make spectral characteristics of the color filters closer to ideal characteristics. The gamma correction unit  26 F performs γ correction of the color image data provided with the color correction by the color correction unit  26 E. The image format conversion unit  26 G converts the color image data provided with the γ correction into an optional format. Then, the image format conversion unit  26 G outputs the color image data provided with the format conversion to the higher-level CPU  107 . 
     The following describes the processing at the demosaicing unit  26 D. 
     The description is first made on overview of processing at a conventional demosaicing unit.  FIGS. 7 and 8  are enlarged pattern diagrams of the color filters of the image sensor  22 . For example, the image sensor  22  includes a Bayer array of RGB color filters along the two-dimensional plane on which the light receiving elements are two-dimensionally arrayed. As described above, the image sensor  22  is a single-plate image sensor in which a color filter of any one of three primary colors such as RGB is disposed on each light receiving element. In other words, one color filter of R, G, or B color is disposed on each light receiving element. 
     Thus, each pixel included in image data of one frame obtained from the image sensor  22  only has color information of one color and lacks color information of the remaining two colors. 
       FIG. 9  is a pattern diagram illustrating exemplary demosaicing. As illustrated in  FIG. 9 , the demosaicing unit executes, for each pixel included in image data, interpolation processing that interpolates the lacking color information by using color information of other pixels nearby. The interpolation processing is also referred to as demosaicing. 
       FIG. 10  is a pattern diagram illustrating exemplary demosaicing through linear interpolation. For example, the demosaicing unit linearly interpolates the pixel value of a pixel having no R (red) color information by using the pixel value of a pixel having R color information in the image data. Similarly, the demosaicing unit linearly interpolates the pixel value of a pixel having no G (green) color information by using the pixel value of a pixel having G color information in the image data. Similarly, the demosaicing unit linearly interpolates the pixel value of a pixel having no B (blue) color information by using the pixel value of a pixel having B color information in the image data. The interpolation method is not limited to linear interpolation. 
     Through these pieces of interpolation processing, the demosaicing unit generates, for each pixel, color image data having color information of all RGB colors. 
     Highly accurate color image data can be obtained by the above-described demosaicing when color and luminance are uniform in the image capturing region P. However, color image data largely deviated from actual color information is obtained when at least one of color and luminance is non-uniform in the image capturing region P. The case in which at least one of color and luminance is non-uniform in the image capturing region P is, for example, a case in which the image capturing region P is an image including fine patterns and edges. 
       FIG. 11A  is a pattern diagram illustrating an exemplary image capturing region of a pattern in which light and dark parts are alternately repeated.  FIG. 11B  is a pattern diagram illustrating exemplary color image data obtained through demosaicing in the above-described conventional scheme. When image capturing is performed on the image capturing region illustrated in  FIG. 11A  and demosaicing is performed by the above-described conventional method, color shift (false color) and blur, which do not exist in the image capturing region, potentially occur as illustrated in  FIG. 11B . 
     The description continues with reference to  FIG. 6 . To solve the above-described problem, the demosaicing unit  26 D according to the present embodiment includes a movement control unit  26 H, an acquisition unit  26 K, a frame memory  26 L, and a generation unit  26 M. 
     The movement control unit  26 H moves the image capturing region P so that an image of each of a plurality of pixel areas on the recording medium  16  is captured by a light receiving element corresponding to one of the color filters of a plurality of colors different from each other. The movement control unit  26 H does not necessarily need to be provided to the demosaicing unit  26 D. The movement control unit  26 H may be provided to, for example, the higher-level CPU  107 . 
     Each pixel area on the recording medium  16  corresponds to one of the light receiving elements of the image sensor  22 . In other words, each pixel area on the recording medium  16  is an area on the recording medium  16 , an image of which is captured by one light receiving element. In the configuration illustrated in  FIG. 4 , each pixel area is an area of x 1 ×y 1  on the recording medium  16 , which has a size of x 1  in the main-scanning direction X and a size of y 1  in the sub-scanning direction Y (refer to area E in  FIG. 4 ). 
     As described above, the image sensor  22  is a single-plate image sensor in which a color filter of any one of three primary colors such as RGB is disposed on each light receiving element. In other words, one color filter of R, G, or B color is disposed on each light receiving element. 
     In the present embodiment, the movement control unit  26 H moves the image capturing region P at each image capturing (of one frame) so that an image of each pixel area on the recording medium  16  is captured by one of the light receiving elements corresponding to the respective color filters of the three colors of RGB (in other words, light receiving elements different from each other). 
     Specifically, the movement control unit  26 H includes a calculation unit  26 I and a movement unit  26 J. The calculation unit  26 I calculates the amount of each movement of the image capturing region P in at least one of the main-scanning direction X and the sub-scanning direction Y based on the array interval of the light receiving elements of the image sensor  22  and the distance between the image capturing unit  28  and the recording medium  16 . 
     Specifically, as described above, the calculation unit  26 I calculates the size x 1  corresponding to one pixel in the image capturing region P in the main-scanning direction X as the amount of movement in the main-scanning direction X by using Expressions (1) and (2) described above. In addition, as described above, the calculation unit  26 I calculates the size y 1  corresponding to one pixel in the image capturing region P in the sub-scanning direction Y as the amount of movement in the sub-scanning direction Y by using Expressions (3) and (4) described above. 
     The amount of movement in each of the main-scanning direction X and the sub-scanning direction Y may be any movement amount with which image capturing is performed by light receiving elements corresponding to color filters of colors different from each other, and is not limited to a size corresponding to one pixel in the image capturing region P. 
     The calculation unit  26 I may calculate the amount of movement in each of the main-scanning direction X and the sub-scanning direction Y in advance and store the calculated amount of movement in a storage unit. 
     Then, the movement unit  26 J moves the image capturing region P by the calculated amount of movement. Specifically, the movement unit  26 J controls a first drive unit  17  (the main-scanning motor  34  and the sub-scanning motor  36 ) to move the image capturing region P by the calculated amount of movement. 
     The acquisition unit  26 K acquires the image data of the image capturing region P each time the image capturing region P is moved. Specifically, each time the image capturing region P is moved, the acquisition unit  26 K acquires the image data input from the image sensor  22  and corrected by the A/D conversion unit  26 A, the shading correction unit  26 B, and the white balance correction unit  26 C. 
     For example, the movement control unit  26 H moves, for each image capturing area P′ on the recording medium  16 , the image capturing region P in a first main-scanning direction XA as one of directions along the main-scanning direction X, in a first sub-scanning direction YA as one of directions along the sub-scanning direction Y, and then in a second main-scanning direction XB as the other direction along the main-scanning direction X (refer to  FIG. 4 ). 
     The movement in the first main-scanning direction XA and the second main-scanning direction XB is achieved by movement of the carriage  5  in the main-scanning direction X. The movement in the sub-scanning direction Y is achieved by movement of the recording medium  16  in the sub-scanning direction Y. For example, the recording medium  16  is conveyed in a second sub-scanning direction YB as one of directions along the sub-scanning direction Y (refer to  FIGS. 1 and 4 ). In this case, the image capturing region P is moved in the first sub-scanning direction YA as the other direction along the sub-scanning direction Y by conveying the recording medium  16  in the second sub-scanning direction YB. 
     The image capturing area P′ is a area on the recording medium  16  as the unit of movement of the image capturing region P. The movement control unit  26 H sets a plurality of image capturing areas P′ at least partially overlapping with each other on the recording medium  16 . Then, the movement control unit  26 H moves, for each image capturing area P′, the image capturing region P so that an image of each of a plurality of pixel areas included in the image capturing area P′ is captured by a light receiving element corresponding to one of the color filters of a plurality of colors different from each other. Then, the acquisition unit  26 K acquires the image data of the image capturing region P each time the image capturing region P is moved. 
     Accordingly, the acquisition unit  26 K acquires, for each image capturing area P′, the image data indicating R color information, the image data indicating G color information, and the image data indicating B color information. 
     Specific description is made with reference to  FIGS. 12A to 12D .  FIGS. 12A to 12D  are each an explanatory diagram of image data  60  obtained at each movement of the image capturing region P. 
     For example, the acquisition unit  26 K acquires image data  60 A illustrated in  FIG. 12A  as the image data  60  of the image capturing region P. The movement control unit  26 H moves the image capturing region P, for example, by the movement amount “x 1 ” in the first main-scanning direction XA. Then, the acquisition unit  26 K acquires the image data of the image capturing region P at a position to which the movement is made. Accordingly, image data  60 B illustrated in  FIG. 12B  is obtained. In the image data  60 B, the positions of the color filters (light receiving elements) of the image sensor  22  relative to the recording medium  16  are moved from those in the image data  60 A by one pixel (one light receiving element) in the first main-scanning direction XA. 
     Subsequently, the movement control unit  26 H moves the image capturing region P by the movement amount “y 1 ” in the first sub-scanning direction YA. The movement control unit  26 H conveys the recording medium  16  by the movement amount “y 1 ” in the second sub-scanning direction YB. Through this conveyance, the image capturing region P is moved in the first sub-scanning direction YA as the opposite direction along the sub-scanning direction Y. 
     Then, the acquisition unit  26 K acquires the image data of the image capturing region P at a position to which the movement is made. Accordingly, image data  60 C illustrated in  FIG. 12C  is obtained. In the image data  60 C, the positions of the color filters (light receiving elements) of the image sensor  22  relative to the recording medium  16  are moved from those in the image data  60 B by one pixel (one light receiving element) in the first sub-scanning direction YA. 
     Subsequently, the movement control unit  26 H moves the image capturing region P by the movement amount “x 1 ” in the second main-scanning direction XB. Then, the acquisition unit  26 K acquires the image data of the image capturing region P at a position to which the movement is made. Accordingly, image data  60 D illustrated in  FIG. 12D  is obtained. In the image data  60 D, the positions of the color filters (light receiving elements) of the image sensor  22  relative to the recording medium  16  are moved from those in the image data  60 C by one pixel (one light receiving element) in the second main-scanning direction XB. 
     In this manner, the image data  60  in which the positions of the color filters relative to the recording medium  16  are shifted by one pixel (one light receiving element) is obtained for each image capturing area P′ under control of the movement control unit  26 H. As described above, the amount of movement may be any amount with which images of the pixel areas (areas E) on the recording medium  16  are captured by the light receiving elements corresponding to the respective color filters different from each other at each movement, and is not limited to one pixel. 
     The description continues with reference to  FIG. 6 . Each time the image capturing region P is moved, the acquisition unit  26 K acquires the image data of the image capturing region P and stores the acquired image data in the frame memory  26 L. 
     The generation unit  26 M generates the color image data of the image capturing region P from a plurality of pieces of the image data. 
     In the present embodiment, the generation unit  26 M generates, for each image capturing area P′, the color image data from a plurality of pieces of the image data. 
     As described above, the pieces of the image data each include color information of any one of R, G, and B colors for a pixel area included in the image capturing area P′. Thus, the generation unit  26 M obtains color information of a plurality of colors by reading, for each pixel, color information of the corresponding pixel position in the pieces of the image data. Then, the generation unit  26 M generates, for each pixel, color image data in which color information of a plurality of colors (in other words, RGB colors) is defined. 
     In this manner, the generation unit  26 M generates color image data in which actually obtained color information of RGB colors is defined for each pixel. Accordingly, the demosaicing unit  26 D can generate highly accurate color image data with reduced generation of calculation error due to the interpolation processing, color shift (false color), and blur. 
     When the filter includes a Bayer array of color filters of RGB colors on the two-dimensional plane of the light receiving elements of the image sensor  22 , two pieces of G color information corresponding to each pixel area are obtained in some cases. In this case, one of the pieces of G color information may be used. 
     In the present embodiment, the image capturing device  20  includes no focusing mechanism, and thus is a fixed-focal-point device with fixed focusing. For example, in the image capturing device  20 , the focal position of the lens  24  provided to the image capturing device  20  is at the position of the platen plate  13 . Thus, non-focused and blurred image data is obtained when the recording medium  16  having a large thickness is placed on the platen plate  13 . 
     To avoid this, the acquisition unit  26 K controls the carriage elevation motor  32  as the second drive unit to acquire image data in which the focal point of the image capturing device  20  coincides with the recording medium  16 . As described above, the carriage  5  is moved up and down by drive of the carriage elevation motor  32 , and the distance between the carriage  5  and the recording medium  16  is changed. 
     Then, the acquisition unit  26 K may acquire image data in which the focal position of the image capturing device  20  is on the recording medium  16 . 
     For example, the position of the image capturing device  20  is fixed in the main-scanning direction X and the sub-scanning direction Y. Then, in this state, the acquisition unit  26 K controls the carriage elevation motor  32  to change the distance between the image capturing device  20  and the recording medium  16 , thereby acquiring a plurality of pieces of image data. Then, among the acquired pieces of image data, a piece of image data in which the focal point is matched (focusing is achieved) most may be used to generate color image data. In addition, the acquisition unit  26 K may fix the distance between the image capturing device  20  and the recording medium  16  to the distance at which the image data with the matched focal point is obtained, and may execute the subsequent processing. 
     The following describes exemplary processing executed by the demosaicing unit  26 D of the image processing unit  26  according to the present embodiment.  FIG. 13  is a flowchart illustrating an exemplary process of processing executed by the demosaicing unit  26 D. 
     The following description assumes that the calculation unit  26 I calculates and stores the amount of movement in each of the main-scanning direction X and the sub-scanning direction Y in advance. The demosaicing unit  26 D executes processing at steps S 200  to S 214  for each image capturing area P′ of the recording medium  16 . 
     First, the acquisition unit  26 K acquires the image data  60 A of the image capturing region P (step S 200 ). Through the processing at step S 200 , the acquisition unit  26 K acquires, for example, the image data  60 A illustrated in  FIG. 12A . The acquisition unit  26 K stores the acquired image data  60 A in the frame memory  26 L. 
     The movement control unit  26 H moves the image capturing region P by the movement amount “x 1 ” in the first main-scanning direction XA (step S 202 ). Specifically, the movement control unit  26 H moves the image capturing region P of the image capturing device  20  by moving the carriage  5  by the movement amount “x 1 ” in the first main-scanning direction XA. 
     The acquisition unit  26 K acquires the image data of the image capturing region P at a position to which the movement is made at step S 202  (step S 204 ). For example, the acquisition unit  26 K acquires the image data  60 B illustrated in  FIG. 12B . The acquisition unit  26 K stores the image data  60 B in the frame memory  26 L. 
     Subsequently, the movement control unit  26 H moves the image capturing region P by the movement amount “y 1 ” in the first sub-scanning direction YA (step S 206 ). Specifically, the movement control unit  26 H conveys the recording medium  16  by the movement amount “y 1   l ” in the second sub-scanning direction YB. Through this conveyance, the image capturing region P is moved in the first sub-scanning direction YA as the opposite direction along the sub-scanning direction Y. 
     The acquisition unit  26 K acquires the image data  60 C of the image capturing region P at a position to which the movement is made at step S 206  (step S 208 ). For example, the acquisition unit  26 K acquires the image data  60 C illustrated in  FIG. 12C . The acquisition unit  26 K stores the acquired image data  60 C in the frame memory  26 L. 
     The movement control unit  26 H moves the image capturing region P by the movement amount “x 1 ” in the second main-scanning direction XB (step S 210 ). Specifically, the movement control unit  26 H moves the image capturing region P of the image capturing device  20  by moving the carriage  5  by the movement amount “x 1 ” in the second main-scanning direction XB. 
     The acquisition unit  26 K acquires the image data of the image capturing region P at a position to which the movement is made at step S 210  (step S 212 ). For example, the acquisition unit  26 K acquires the image data  60 C illustrated in  FIG. 12C . The acquisition unit  26 K stores the image data  60 C in the frame memory  26 L. 
     Subsequently, the generation unit  26 M generates the color image data of the image capturing region P from the pieces of the image data  60  (the image data  60 A, the image data  60 B, the image data  60 C, and the image data  60 D) obtained through the above-described processing (step S 214 ). Then, the present routine is ended. 
     As described above, the liquid discharge device  100  according to the present embodiment includes the image capturing unit  28 , the movement control unit  26 H, the acquisition unit  26 K, and the generation unit  26 M. The image capturing unit  28  includes the single-plate image sensor  22  including color filters disposed on two-dimensionally arrayed light receiving elements, and captures an image of the image capturing region P on the image capturing target (recording medium  16 ). The movement control unit  26 H moves the image capturing region P such that images of each of a plurality of pixel areas (areas E) on the image capturing target (recording medium  16 ) are captured by the light receiving elements corresponding to the respective color filters of a plurality of colors different from each other. The acquisition unit  26 K acquires the image data of the image capturing region P each time the image capturing region P is moved. The generation unit  26 M generates the color image data of the image capturing region P from a plurality of pieces of the image data  60 . 
     The pieces of the image data  60  used to generate the color image data each include color information of any one of R, G, and B colors for each pixel area included in the image capturing area P′. Thus, the generation unit  26 M obtains color information of a plurality of colors by reading, for each pixel, color information of the corresponding pixel position in the pieces of the image data. Then, the generation unit  26 M generates, for each pixel, color image data in which color information of a plurality of colors (in other words, RGB colors) is defined. 
     Specifically, in the present embodiment, the generation unit  26 M generates color image data in which actually obtained color information of RGB colors is defined for each pixel. Accordingly, the acquisition unit  26 K can generate highly accurate color image data with reduced generation of calculation error due to the interpolation processing, color shift (false color), and blur. 
     The liquid discharge device  100  according to the present embodiment does not need, for example, a mechanism for switching a plurality of filters at each image capturing. 
     Thus, the liquid discharge device  100  according to the present embodiment can obtain highly accurate color image data with a simple configuration. 
     The liquid discharge device  100  according to the present embodiment also includes the first drive unit  17  (the main-scanning motor  34 , the sub-scanning motor  36 ) configured to relatively move at least one of the image capturing target (recording medium  16 ) and the image capturing unit  28  in the main-scanning direction X and the sub-scanning direction Y orthogonal to the main-scanning direction X. The movement control unit  26 H controls the first drive unit  17  to move the image capturing region P. 
     The movement control unit  26 H includes the calculation unit  26 I configured to calculate the amount of each movement of the image capturing region P in at least one of the main-scanning direction X and the sub-scanning direction Y based on the array interval of the light receiving elements of the image sensor  22  and the distance between the image capturing unit  28  and the image capturing target (recording medium  16 ), and the movement unit  26 J configured to move the image capturing region P by the amount of movement. 
     The movement control unit  26 H moves, for each image capturing area P′ on the image capturing target (recording medium  16 ), the image capturing region P in the first main-scanning direction XA as one of directions along the main-scanning direction X, in the first sub-scanning direction YA as one of directions along the sub-scanning direction Y, and then in the second main-scanning direction XB as the other direction along the main-scanning direction X. The acquisition unit  26 K acquires, for each image capturing area P′, the image data for each movement of the image capturing region P. The generation unit  26 M generates, for each image capturing area P′, color image data from the pieces of the image data. 
     The liquid discharge device  100  according to the present embodiment also includes the second drive unit (carriage elevation motor  32 ) configured to change the distance between the image capturing target (recording medium  16 ) and the image capturing unit  28 . The acquisition unit  26 K controls the second drive unit (carriage elevation motor  32 ) to acquire the image data in which the focal point of the image capturing unit  28  coincides with the image capturing target (recording medium  16 ). 
     The image sensor  22  includes a Bayer array of the color filters of RGB colors. 
     Alternatively, the image sensor  22  includes a complementary color filter arrayed of color filters of CMYG colors. 
     The liquid discharge device  100  includes the image capturing device  20 , and the record head  6  configured to discharge liquid onto the recording medium  16  as the image capturing target. 
     The image capturing method according to the present embodiment is performed by a computer, the image capturing method including: moving, by the image capturing unit  28  that includes the single-plate image sensor  22  including color filters disposed on two-dimensionally arrayed light receiving elements and is configured to capture an image of the image capturing region P on the image capturing target (recording medium  16 ), the image capturing region P such that images of each of a plurality of pixel areas on the image capturing target (recording medium  16 ) are captured by the light receiving elements corresponding to the respective color filters of a plurality of colors different from each other; acquiring the image data of the image capturing region P each time the image capturing region P is moved; and generating color image data of the image capturing region P from a plurality of pieces of the image data. 
     The following describes an exemplary hardware configuration of the image processing unit  26 . 
       FIG. 14  is a diagram illustrating an exemplary hardware configuration of the image processing unit  26 . 
     The image processing unit  26  has a hardware configuration of a normal computer, in which a central processing unit (CPU)  11 A, a read only memory (ROM)  11 B, a random access memory (RAM)  11 C, an I/F  11 D, and the like are connected with each other through a bus  11 E. 
     The CPU  11 A is an arithmetic device configured to control the image processing unit  26  according to the present embodiment. The ROM  11 B stores, for example, a computer program that achieves various kinds of processing performed by the CPU  11 A. The RAM  11 C stores data necessary for various kinds of processing performed by the CPU  11 A. The I/F  11 D is an interface for transmitting and receiving data. 
     A computer program for executing processing executed by the image processing unit  26  according to the present embodiment is incorporated in the ROM  11 B or the like in advance and provided. The computer program executed by the image processing unit  26  according to the present embodiment may be recorded and provided as a file of a format installable or executable on the image processing unit  26  on a computer-readable recording medium such as a CD-ROM, a flexible disk (FD), a CD-R, or a digital versatile disc (DVD). 
     The embodiment is described above, but the above-described embodiment is presented as an example and not intended to limit the scope of the invention. The above-described novel embodiment may be achieved in other various forms and may be omitted, replaced, and changed in various manners without departing from the spirit of the invention. The above-described embodiment is included in the scope and spirit of the invention and also included in the invention recited in the claims and equivalents thereof. 
     For example, the liquid discharge device  100  is not limited to an aspect in which an image is formed by adhering liquid onto the recording medium  16 . For example, the liquid discharge device  100  may be a stereoscopic shaping device of an inkjet scheme. In this case, for example, the liquid discharge device can be used as a stereoscopic shaping device (three-dimensional shaping device) configured to discharge shaping liquid onto a powder layer in which powder is layered to shape a stereoscopic shaped object (three-dimensional shaped object). Alternatively, the liquid discharge device may be a stereoscopic shaping device configured to discharge shaping liquid for shaping a stereoscopic shaped object and form the shaped object by discharging the shaping liquid into a stack. 
     The liquid discharge device  100  according to the present embodiment is not limited to visualization of a meaningful image such as a character or a figure by discharged liquid. For example, formation of a meaningless pattern or the like and shaping of a three-dimensional image are also included. 
     The recording medium  16  means a medium to which liquid can at least temporarily adhere, such as a medium to which liquid can adhere and be fixed or a medium that liquid can adhere to and permeate. Specific examples thereof include recording media such as a sheet, record paper, a record sheet, a film, and cloth, electronic components such as an electronic substrate and a piezoelectric element, and media such as a powder layer, an organ model, and an examination cell, and include all media to which liquid can adhere when not particularly limited otherwise. 
     The material of the recording medium  16  may be a material to which liquid can at least temporarily adhere, such as paper, thread, fiber, cloth, leather, metal, plastic, glass, wood, or ceramic. 
     For example, control operation of each component included in the liquid discharge device  100  according to the above-described embodiment may be executed by using hardware, software, or a composite configuration thereof. 
     When processing is executed by using software, a computer program in which a sequence of processing is recorded may be installed and executed on a memory in a computer incorporated in dedicated hardware. Alternatively, the computer program may be installed and executed on a memory in a general-purpose computer capable of executing various kinds of processing. 
     For example, the computer program may be recorded on a recording medium such as a hard disk or a read only memory (ROM) in advance. Alternatively, the computer program may be temporarily or permanently stored (recorded) on a removable recording medium. Such a removable recording medium may be provided as what is called packaged software. Examples of the removable recording medium include various recording media such as a magnetic disk and a semiconductor memory. 
     The computer program is installed onto a computer from a removable recording medium as described above. Alternatively, the computer program is wirelessly forwarded onto the computer from a download site. Alternatively, the computer program is forwarded onto a computer through a network in a wired manner. 
     According to an embodiment, it is possible to obtain highly accurate color image data with a simple configuration. 
     The above-described embodiments are illustrative and do not limit the present invention. Thus, numerous additional modifications and variations are possible in light of the above teachings. For example, at least one element of different illustrative and exemplary embodiments herein may be combined with each other or substituted for each other within the scope of this disclosure and appended claims. Further, features of components of the embodiments, such as the number, the position, and the shape are not limited the embodiments and thus may be preferably set. It is therefore to be understood that within the scope of the appended claims, the disclosure of the present invention may be practiced otherwise than as specifically described herein. 
     The method steps, processes, or operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance or clearly identified through the context. It is also to be understood that additional or alternative steps may be employed. 
     Further, any of the above-described apparatus, devices or units can be implemented as a hardware apparatus, such as a special-purpose circuit or device, or as a hardware/software combination, such as a processor executing a software program. 
     Further, as described above, any one of the above-described and other methods of the present invention may be embodied in the form of a computer program stored in any kind of storage medium. Examples of storage mediums include, but are not limited to, flexible disk, hard disk, optical discs, magneto-optical discs, magnetic tapes, nonvolatile memory, semiconductor memory, read-only-memory (ROM), etc. 
     Alternatively, any one of the above-described and other methods of the present invention may be implemented by an application specific integrated circuit (ASIC), a digital signal processor (DSP) or a field programmable gate array (FPGA), prepared by interconnecting an appropriate network of conventional component circuits or by a combination thereof with one or more conventional general purpose microprocessors or signal processors programmed accordingly. 
     Each of the functions of the described embodiments may be implemented by one or more processing circuits or circuitry. Processing circuitry includes a programmed processor, as a processor includes circuitry. A processing circuit also includes devices such as an application specific integrated circuit (ASIC), digital signal processor (DSP), field programmable gate array (FPGA) and conventional circuit components arranged to perform the recited functions.