Patent Publication Number: US-2012026199-A1

Title: Image display device and image display method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2010-168499, filed on Jul. 27, 2010, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image display device and an image display method. 
     2. Description of the Related Art 
     It is conventionally known that when an image display device displays an input image with a resolution lower than that of a display unit by simply enlarging the input image, because pixels of the input image are enlarged and displayed, diagonal lines and edges in the enlarged image are displayed in a stepwise manner and thus the image quality is degraded. 
     A bilinear method is a well-known method as one of image interpolation techniques for suppressing such a stepwise display of diagonal lines and edges (see, for example, Japanese Patent Application Laid-open No. 2003-283815). 
     According to the bilinear method, pixels on an enlarged image are inversely mapped at corresponding positions on an input image, and pixel values of the inversely-mapped pixels on the enlarged image are determined by linear interpolation by using pixel values of nearest four pixels on the input image from the inversely-mapped pixels. 
     That is, according to the bilinear method, an enlarged image is generated by estimating pixel values of pixels to be interpolated in the enlarged image based on respective values of pixels of the input image. 
     Therefore, an image display device using the bilinear method can suppress a stepwise display of diagonal lines and edges by blurring the diagonal lines and edges in an enlarged image when an input image with a resolution lower than that of a display unit is to be enlarged and displayed. 
     However, when an input image with a resolution lower than that of the display unit is to be enlarged and displayed, there is a problem that the image display device using the bilinear method cannot display a high-resolution enlarged image while utilizing the resolution of the display unit. 
     That is, when an input image with a resolution lower than that of the display unit is to be enlarged and displayed, the image display device using the bilinear method blurs all diagonal lines and edges in the enlarged image. 
     Consequently, when the image display device using the bilinear method enlarges and displays an input image having regions in which diagonal lines and edges are to be emphasized, the diagonal lines and edges to be emphasized in an enlarged image are blurred, and thus the image quality of the enlarged image is degraded. 
     Accordingly, when the image display device using the bilinear method enlarges and displays of an input image with a resolution lower than that of the display unit, the image display device cannot display a high-resolution enlarged image while utilizing the resolution of the display unit. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to at least partially solve the problems in the conventional technology. 
     According to an aspect of an embodiment of the invention, An image display device includes an enlarged-image generating unit that generates an enlarged image by performing an enlarging process on an input image; a reduced-image generating unit that generates a reduced image by performing a reducing process other than an inverse process of the enlarging process on the enlarged image; a difference detecting unit that detects a difference between a pixel value of a pixel on the reduced image and a pixel value of a corresponding pixel on the input image; and a correcting unit that corrects a pixel value of a pixel on the input image or the enlarged image based on the difference that is detected by the difference detecting unit. 
     According to an aspect of an embodiment of the invention, An image display method includes generating an enlarged image by performing an enlarging process on an input image; generating an reduced image by performing a reducing process other than an inverse process of the enlarging process on the enlarged image; detecting a difference between a pixel value of a pixel on the reduced image and a pixel value of a corresponding pixel on the input image; and correcting a pixel value of a pixel on the input image or the enlarged image based on the difference that is detected. 
     The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts an outline of an image display technique according to an embodiment of the present invention; 
         FIG. 2  is a block diagram of a configuration of an image display device according to the embodiment; 
         FIG. 3  is a block diagram of a configuration of an image enlarging unit according to the embodiment; 
         FIGS. 4A to 4F  depict an operation of an enlarged-image generating unit according to the embodiment; 
         FIG. 5  depicts an operation of a reduced-image generating unit according to the embodiment; 
         FIGS. 6A and 6B  are examples of an operation of the image enlarging unit according to the embodiment; 
         FIGS. 7A and 7B  are examples of an operation of the image enlarging unit according to the embodiment; 
         FIG. 8  is an example of an operation of the image enlarging unit when repeating a feedback of a difference to a latter-stage adding unit according to the embodiment for plural times; 
         FIGS. 9A and 93  are examples of an operation of the image enlarging unit when repeating a feedback of a difference to the latter-stage adding unit according to the embodiment for plural times; and 
         FIG. 10  is a flowchart of a process performed by the image display device according to the embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Exemplary embodiments of an image display device and an image display method according to the present invention will be explained below in detail with reference to the accompanying drawings. 
     Prior to detailed explanations of an embodiment of the present invention, an outline of an image display technique according to the embodiment is explained with reference to  FIG. 1 .  FIG. 1  depicts the outline of the image display technique. 
     The image display technique according to the present embodiment is a technique of displaying a high-precision enlarged image of an input image in a display unit when the input image with a resolution lower than that of the display unit is to be enlarged and displayed while utilizing the resolution of the display unit that displays the image. 
     Specifically, as shown in  FIG. 1A , in the image display technique according to the present embodiment, an enlarged image P 1  is generated by performing a predetermined enlarging process on an input image P 0 . Next, in the image display technique, a reducing process other than an inverse process of the enlarging process performed when generating the enlarged image P 1  is performed on the enlarged image P 1 , thereby generating a reduced image P 2 . 
     At this time, in the image display technique according to the present embodiment, the reduced image P 2  having the same image size as that of the input image P 0  is generated. Next, as shown in  FIG. 1A , in the image display technique, a difference ( 1 ) between a pixel value of a pixel on the input image P 0  and a pixel value of a corresponding pixel on the input image P 2  is detected. 
     At this detection, when the reproducibility of the input image P 0  due to the enlarged image P 1  is not decreased by the enlarging process, the value of the difference ( 1 ) becomes substantially “0”, and the value of the difference ( 1 ) becomes larger or smaller than “0” when the decreasing level of the reproducibility is larger. 
     Therefore, in the image display technique according to the present embodiment, as shown in  FIG. 1A , an input image P 3  is generated by correcting a pixel value of a pixel on the input image P 0  by adding the difference ( 1 ) to a pixel value of a corresponding pixel on the input image P 0 . An enlarged image P 4  is then generated by performing an enlarging process on the input image P 3  having its pixel value corrected. 
     In this manner, in the image display technique according to the present embodiment, a pixel value of a pixel on the input image P 0  is corrected based on an assumption that the reproducibility of the input image is decreased by the enlarging process. In the image display technique according to the present embodiment, the enlarged image P 4  is regenerated from the input image P 3  having its pixel value corrected. Therefore, according to the image display technique, the enlarged image P 4  with a reproducibility of the input image higher than that of the enlarged image P 1  can be regenerated. 
     In the image display technique according to the present embodiment, a reducing process other than an inverse process of the enlarging process performed when generating the enlarged image P 4  is performed on the regenerated enlarged image P 4 , thereby regenerating a reduced image P 5 . 
     Next, as shown in  FIG. 1A , in the image display technique according to the present embodiment, a difference ( 2 ) between a pixel value of a pixel on the initially input image P 0  of which a pixel value is not corrected and a pixel value of a corresponding pixel on the regenerated reduced image P 5  is redetected. 
     At this redetection, when the reproducibility of the input image due to the enlarged image P 4  is sufficiently improved, the value of the difference ( 2 ) becomes substantially “0”, and when the reproducibility of the input image due to the enlarged image  94  is not sufficiently improved, the value of the difference ( 2 ) becomes larger or smaller than “0”. 
     Therefore, in the image display technique according to the present embodiment, as shown in  FIG. 1A , an enlarged image P 6  of a corrected pixel value is regenerated by adding the difference ( 2 ) to a pixel value of a corresponding pixel on the regenerated enlarged image P 4 . 
     As explained above, in the image display technique according to the present embodiment, the enlarged image P 6  with a reproducibility of the input image P 0  higher than that of the input image P 0  due to the enlarged image P 4  can be generated by reflecting on the enlarged image P 6  a difference between a pixel value of a pixel on the reduced image P 5  of the enlarged image P 4  and a pixel value of a pixel on the input image P 0 . 
     With this arrangement, according to the image display technique of the present embodiment, as shown in  FIG. 1B , the reproducibility of the input image P 0  due to the enlarged image can be improved each time when an enlarged image is regenerated. 
     Further, in the image display technique according to the present embodiment, it is possible to repeatedly perform an addition of a difference to a pixel value of a pixel on an enlarged image, a regeneration of a reduced image from an enlarged image to which a difference is added, and a redetection of a difference between a pixel value of a pixel on the regenerated reduced image and a pixel value of a pixel on the input image P 0 . 
     With this arrangement, in the image display technique according to the present embodiment, the reproducibility of an input image due to an enlarged image can be improved only by repeating an addition of a difference to a pixel value of a pixel on an enlarged image without repeatedly performing an enlarging process. Details of this repeating process are described later with reference to  FIG. 8 . 
     As described above, in the image display technique according to the present embodiment, a pixel value of a pixel on an input image is corrected based on an assumption that the reproducibility of the input image is decreased by an enlarging process. In the image display technique according to the present embodiment, an enlarged image is regenerated from an input image of which a pixel value is corrected. Therefore, according to the image display technique, it is possible to regenerate an enlarged image with a reproducibility of an input image higher than that of an enlarged image generated from an initially input image of which a pixel value is not corrected. 
     Further, in the image display technique according to the present embodiment, an enlarged image is regenerated, which reflects a difference between a pixel value of a pixel on a reduced image of a regenerated enlarged image and a pixel value of a pixel on an initially input image. Therefore, according to the image display technique, it is possible to regenerate an enlarged image with a reproducibility of an input image higher than that of an enlarged image generated from an input image of which a pixel value is corrected. 
     As explained above, in the image display technique according to the present embodiment, because an enlarged image with an improved reproducibility of an input image can be generated, when an input image with a resolution lower than that of the display unit is enlarged and displayed, a high-precision enlarged image utilizing the resolution of the display unit can be displayed. 
     An embodiment of an image display device and an image display method to which the image display technique according to the present embodiment is applied are explained below in detail with reference to  FIGS. 2 to 10 . 
     As an example, an in-vehicle image display device that displays a one-segment broadcasting image and an image input from a car navigation system as well as an image of normal digital television broadcasting that uses 12 segments is explained below. 
       FIG. 2  is a block diagram of a configuration of an image display device  1  according to the present embodiment.  FIG. 2  depicts only constituent elements necessary to explain the characteristics of the image display device  1 , and descriptions of general constituent elements will be omitted. 
     As shown in  FIG. 2 , the image display device  1  includes a low-voltage differential signaling (LVDS) receiver  2 , a contour correcting unit  3 , a color control unit  4 , an image-quality adjusting unit  5 , a gamma adjusting unit  6 , a dithering unit  7 , an image enlarging unit  8 , and a timing control unit  9 . 
     The LVDS receiver  2  is an image interface that receives an input of an image signal from a digital-broadcast receiving unit (not shown) or the like, and outputs a received image signal to the contour correcting unit  3 . An image corresponding to an image signal received by the LVDS receiver  2  is hereinafter referred to as “input image”. 
     The image signal in the present embodiment includes respective pixel values of each pixel on an input image. The pixel value represents the strength of R (red), G (green), B (blue) in each pixel and the brightness of each pixel. 
     The contour correcting unit  3  is a processing unit that performs a contour correcting process of emphasizing a contour of a subject, a character, a graph or the like in an input image on an image signal that is input from the LVDS receiver  2 , and outputs the image signal after the contour correcting process to the color control unit  4 . 
     The color control unit  4  is a processing unit that performs a color control process of adjusting a shade of a subject, a graph or the like in an input image and gradation of a color to an image signal that is input from the contour correcting unit  3 , and outputs an image signal after the color control process to the image-quality adjusting unit  5 . 
     The image-quality adjusting unit  5  is a processing unit that performs an image-quality adjusting process of adjusting the contrast and brightness of an input image on an image signal that is input from the color control unit  4 , and outputs an image signal after the image-quality adjusting process to the gamma adjusting unit  6 . 
     The gamma adjusting unit  6  is a processing unit that performs a gamma adjusting process of correcting a gamma value of each pixel according to the display characteristics of a display unit (not shown) that displays an image on an image signal that is input from the image-quality adjusting unit  5 , and outputs an image signal after the gamma adjusting process to the dithering unit  7 . 
     The dithering unit  7  is a processing unit that performs a dithering process of causing a display unit to express an intermediate color to be expressed by an expressible chromatic number on an image signal that is input from the gamma adjusting unit  6 , and outputs an image signal after the dithering process to the image enlarging unit  8 . 
     The image enlarging unit  8  is a processing unit that performs, when enlargement of a input image is used, an enlarging process of matching an image size of the input image with a size of a display region of a display unit on an image signal that is input from the dithering unit  7 , and outputs an image signal after the enlarging process to the timing control unit  9 . 
     The image enlarging unit  8  performs the enlarging process on an image signal of an input image when the resolution of the input image is lower than that of the display unit and also when the input image is displayed in an image size smaller than the display region of the display unit when the image signal is output as it is. 
     The image enlarging unit  8  outputs an image signal that is input from the dithering unit  7  as it is to the timing control unit  9  when enlargement of an input image is not used, that is, when the resolution of the input image is equal to or higher than that of the display unit. 
     Particularly, the image enlarging unit  8  is configured to generate a high-precision enlarged image utilizing the resolution of the display unit by correcting a pixel value of a pixel on an input image or the resolution of an enlarged image generated from the input image, when the input image in enlarged and displayed. Details of the configuration and operations of the image enlarging unit  8  are described later with reference to  FIGS. 3 to 10 . 
     The timing control unit  9  is a processing unit that causes a display unit to display an image by outputting an image signal input from the image enlarging unit  8  to the display unit at a predetermined timing. For example, the timing control unit  9  outputs an image signal at a timing synchronized with a horizontal synchronization signal and a vertical synchronization signal having been determined in advance by the display unit. 
     The configuration of the image enlarging unit  8  according to the present embodiment is explained next.  FIG. 3  is a block diagram of the configuration of the image enlarging unit  8 . As shown in  FIG. 3 , the image enlarging unit  8  includes an enlarged-image generating unit  81 , a reduced-image generating unit  82 , a difference detecting unit  83 , and a correcting unit  84 . The correcting unit  84  includes a former-stage adding unit  841  and a latter-stage adding unit  842 . 
     The enlarged-image generating unit  81  is a processing unit that generates an enlarged image of an input image from the dithering unit  7  by performing an enlarging process using the bilinear method on an image signal of the input image via the former-stage adding unit  841 . 
     The enlarged-image generating unit  81  then outputs an image signal of a generated enlarged image to the timing control unit  9  or the reduced-image generating unit  82  via the latter-stage adding unit  842 . An operation of the enlarged-image generating unit  81  is explained below with reference to  FIGS. 4A to 4F . 
       FIGS. 4A to 4F  depict an operation of the enlarged-image generating unit  81  according to the present embodiment. The operation is explained based on an assumption that the resolution of an input image is 400×234 pixels (EGA) and the resolution of a display unit is 800×480 pixels (VGA). 
     The enlarged-image generating unit  81  inversely maps each of 800×480 pixels that constitute an enlarged image to be generated onto an input image. The enlarged-image generating unit  81  then determines a pixel value of each pixel on an enlarged image by linear interpolation using pixel values of four pixels that are nearest to pixels of the enlarged image that is inversely mapped on the input image. 
     For example, when determining a pixel value of a pixel PA on an enlarged image P shown in  FIG. 4A , the enlarged-image generating unit  81  first inversely maps the pixel PA on the enlarged image P at a coordinate position on an input image p corresponding to a coordinate position of the pixel PA on the enlarged image P, as shown in  FIG. 4B . 
     Next, as shown in  FIG. 4C , the enlarged-image generating unit  81  detects coordinate positions in the input image p of four pixels pa, pb, pc, and pd that are nearest to the pixel PA that is inversely mapped on the input image p. 
     The enlarged-image generating unit  81  then calculates a ratio of two distances, which are a distance from a straight line that connects two pixels pa and pd on the input pixel p to the inversely mapped pixel PA, and a distance from a straight line that connects two pixels pb and pc on the input pixel p to the inversely mapped pixel PA. 
     The enlarged-image generating unit  81  calculates a ratio of two distances, which are a distance from a straight line that connects two pixels pa and pb on the input pixel p to the inversely mapped pixel PA, and a distance from a straight line that connects two pixels pc and pd on the input pixel p to the inversely mapped pixel PA. 
     Next, the enlarged-image generating unit  81  determines a pixel value of the inversely mapped pixel PA by performing linear interpolation by using the calculated ratios and pixel values of the four pixels pa, pb, pc, and pd on the input image p. 
     When determining a pixel value of a pixel PB that constitutes an edge of the enlarged image P as shown in  FIG. 4D , the enlarged-image generating unit  81  inversely maps the pixel PB on the enlarged image P at a coordinate position on the input image p corresponding to a coordinate position of the pixel PB on the enlarged image P as shown in  FIG. 4E . 
     Next, as shown in  FIG. 4F , the enlarged-image generating unit  81  determines a pixel value of the inversely mapped pixel PB by performing linear interpolation by using pixel values of two pixels pe and pf that are adjacent to the inversely mapped pixel PB. 
     For example, as shown in  FIG. 4F , when the inversely mapped pixel PB is present at a middle point between the two pixels pe and pf on the input image p, the enlarged-image generating unit  81  determines an intermediate value of the pixel values of the two pixels pe and pf on the input image p as a pixel value of the pixel PB. 
     The enlarged-image generating unit  81  generates the enlarged image P of the input image by performing the determining process of a pixel value on all pixels of the enlarged image to be generated. The enlarging process performed by the enlarged-image generating unit  81  is not limited to the enlarging process using the bilinear method, and can be an enlarging process using a bicubic method, for example. 
     Referring back to  FIG. 3 , the reduced-image generating unit  82  is a processing unit that generates a reduced image by performing a reducing process of reducing an image size of an enlarged image to an image size of the input image p on the image signal of the enlarged image P that is input from the enlarged-image generating unit  81 . The reduced-image generating unit  82  outputs an image signal of the generated reduced image to the difference detecting unit  83 . 
     The reduced-image generating unit  82  generates a reduced image by performing a reducing process other than the inverse process of the enlarging process performed by the enlarged-image generating unit  81 . For example, the reduced-image generating unit  82  can perform a reducing process using a method of generating a reduced image by dividing an enlarged image into plural pixel blocks and by averaging pixel values of the pixels included in each of the pixel blocks (hereinafter, “average thinning method”). 
     An operation of the reduced-image generating unit  82  is explained with reference to  FIG. 5 .  FIG. 5  depicts an operation of the reduced-image generating unit  82  according to the present embodiment. The reduced-image generating unit  82  generates a reduced image p 1  of 400×234 pixels shown in FIG.  5 A 2  from the enlarged image P of 800×480 pixels shown in FIG.  5 A 1 . 
     For example, as shown in FIG.  5 A 1 , the reduced-image generating unit  82  divides the enlarged image P into plural pixel blocks including 2×2 pixels, 3×2 pixels, and 3×3 pixels, and calculates an average value of pixel values within each of the pixel blocks. When the enlarged image P is divided into plural pixel blocks, pixel values of pixels as fractions that cannot be included in each of the pixel blocks are not used as data for calculating the average value. 
     The reduced-image generating unit  82  generates the reduced image p 1  by determining that an average value of pixel values within each of the calculated pixel blocks is a pixel value of each pixel on the reduced image p 1  corresponding to each of the pixel blocks. 
     Specifically, as shown in  FIG. 5B , the reduced-image generating unit  82  determines that an average value of pixel values included in a pixel block Pα constituted by four pixels at an upper left end of the enlarged image P is a pixel value of a pixel pa at an upper left end of the reduced image p 1 . 
     Similarly, the reduced-image generating unit  82  determines that average values of pixel values within pixel blocks Pβ, Pγ, and PΔ, respectively of the enlarged image P are pixel values of corresponding pixels Pβ, Pγ, and PΔ on the reduced image p 1 . 
     The reducing process performed by the reduced-image generating unit  82  is not limited to a reducing process using the average thinning method, and other reducing processes using an arbitrary method such as the bicubic method can be also used as far as the method thereof is other than that of the inverse process of the enlarging process performed by the enlarged-image generating unit  81 . 
     Referring back to  FIG. 3 , the difference detecting unit  83  is a processing unit that detects, based on an image signal of an input image that is input from the dithering unit  7  and an image signal of a reduced image that is input from the reduced-image generating unit  82 , a difference between a pixel value of a pixel on an input image and a pixel value of a corresponding pixel on a reduced image, and outputs the difference to the correcting unit  84 . 
     The difference detecting unit  83  detects a difference between a pixel value of a pixel on an input image and a pixel value of a corresponding pixel on a reduced image by subtracting a pixel value of a pixel on the reduced image from a pixel value of each pixel on the input image. 
     Next, when an image signal of a reduced image is input from the reduced-image generating unit  82  at a first time after an image signal of a new input image is input to the image enlarging unit  8 , the difference detecting unit  83  outputs a detected difference to the former-stage adding unit  841  of the correcting unit  84 . 
     Thereafter, when an image signal of a reduced image is input from the reduced-image generating unit  82  at a second time or after the second time after an image signal of a new input image is input to the image enlarging unit  8 , the difference detecting unit  83  outputs a detected difference to the latter-stage adding unit  842  of the correcting unit  84 . 
     The correcting unit  84  is a processing unit that improves the reproducibility of an input image of an enlarged image by correcting a pixel value of a pixel on an input image or the enlarged image based on a difference that is input from the difference detecting unit  83 . An example of an operation of the image enlarging unit  8  is explained based on an operation of the correcting unit  84  with reference to  FIGS. 6A and 6B  and  FIGS. 7A and 7B . 
       FIG. 6  and  FIG. 7  are examples of the operation of the image enlarging unit  8  according to the present embodiment. An example of the operation of the image enlarging unit  8  performed on a certain pixel (hereinafter, “target pixel”) of an input image is explained here. Numerical values within parenthesis in  FIGS. 6 and 7  denote pixel values and numerical values within parenthesis with a sign “+” (plus) denote differences to be added to pixel values. 
     In the following explanations, an image signal of an input image is referred to as “input image”, an image signal of an enlarged image is referred to as “enlarged image”, and an image signal of a reduced image is referred to as “reduced image”, to facilitate explanations. 
     As shown in  FIG. 6A , in the image enlarging unit  8 , an input image that is input from the dithering unit  7  is input to the enlarged-image generating unit  81  and to the difference detecting unit  83  via the former-stage adding unit  841 . 
     When an input image is input, the enlarged-image generating unit  81  generates an enlarged image from the input image by an enlarging process using the bilinear method described above, and outputs the generated enlarged image to the reduced-image generating unit  82 . 
     Next, when the enlarged image is input from the enlarged-image generating unit  81 , the reduced-image generating unit  82  generates a reduced image having the same image size as that of the input image from the enlarged image by a reducing process using the average thinning method described above, and outputs the generated reduced image to the difference detecting unit  83 . 
     It is assumed that a pixel value of a target pixel on the input image is (50) and that a pixel value of the target pixel on the reduced image is (30), as shown in  FIG. 6A . That is, it is assumed that a pixel value of the target image that is (50) at the beginning is decreased to (30) after undergoing the enlarging process and the reducing process. 
     The difference detecting unit  83  then detects a difference between pixel values of corresponding pixels by subtracting a pixel value of a pixel on the reduced image from a pixel value of a corresponding pixel on the input image. In this case, the difference detecting unit  83  detects (20) as a difference between pixel values of the target pixel. 
     Performing the enlarging process and the reducing process on the input image can be assumed as the cause of a decrease of the pixel value of the target pixel from (50) to (30). Therefore, the pixel value of the target pixel on the reduced image can be set closer to the initial value of (50) by increasing the pixel value of the target pixel on the input image by 20 and by further performing the enlarging process and the reducing process again. 
     That is, the reproducibility of an input image due to the enlarged image can be improved by adding a difference detected at the first time to a pixel value of the corresponding pixel and by performing the enlarging process and the reducing process at the second time. Therefore, the difference detecting unit  83  outputs a difference of each pixel detected at a first detection of the difference to the former-stage adding unit  841 , as shown in  FIG. 6B . 
     As shown in  FIG. 7A , the former-stage adding unit  841  adds a difference that is input from the difference detecting unit  83  to respective pixel values of a corresponding pixel on the input image, and outputs the input image having added with the difference to the enlarged-image generating unit  81 . 
     Next, the enlarged-image generating unit  81  regenerates an enlarged image from the input image having added with a difference for each corresponding pixel, and outputs a regenerated enlarged image to the reduced-image generating unit  82 . The reduced-image generating unit  82  then regenerates a reduced image from the regenerated enlarged image, and outputs the regenerated reduced image to the difference detecting unit  83 . 
     The difference detecting unit  83  then redetects a difference between pixel values of each pixel by subtracting a pixel value of a pixel on the regenerated reduced image from a pixel value of a corresponding pixel on the input image. As shown in  FIG. 7A , the difference detecting unit  83  detects ( 10 ) as a difference between pixel values of a target pixel when a pixel value of the target pixel on the regenerated reduced image is ( 40 ). 
     In this manner, a difference between a pixel value of a pixel on the input image and a pixel value of a corresponding pixel on a reduced image can be decreased by feeding back a result of the first detection of the difference to a pixel value of a corresponding pixel on the input image, where the first detection is performed by the difference detecting unit  83 . That is, the reproducibility of the input image due to the enlarged image can be improved by the feedback. 
     However, when the feedback is repeated for plural times, the enlarging process needs to be performed each time. Therefore, as shown in  FIG. 7B , the difference detecting unit  83  outputs a difference between pixel values of each pixel detected at a second detection of the difference to the latter-stage adding unit  842 . 
     Next, the latter-stage adding unit  842  adds a redetected difference ( 10 ) to the pixel value of the target pixel. That is, the latter-stage adding unit  842  feeds back and adds the difference that is input from the difference detecting unit  83  to a pixel value of a corresponding pixel on the enlarged image that is input from the enlarged-image generating unit  81 . 
     The latter-stage adding unit  842  then outputs an enlarged image that is generated by adding the difference to the timing control unit  9 . In this manner, the reproducibility of the input image due to the enlarged image can be also improved by adding a difference detected by the difference detecting unit  83  to the enlarged image. 
     When a difference detected by the difference detecting unit  83  is added to the enlarged image in this way, the reproducibility of the input image due to the enlarged image improved by feeding back (rough adjusting) the difference to the former-stage adding unit  841  can be further improved (finely adjusted) while omitting the enlarging process. 
     While an enlarged image is output to the timing control unit  9  after a difference is fed back once to the latter-stage adding unit  842 , the difference can be fed back to the latter-stage adding unit  842  repeatedly. 
     That is, operations such that the latter-stage adding unit  842  adding a difference to a pixel value of an enlarged image, the reduced-image generating unit  82  generating a reduced image, and the difference detecting unit  83  detecting a difference between pixel values are repeatedly performed, and when a predetermined ending condition is satisfied after repeating these operations, an enlarged image can be output to the timing control unit  9 . 
     An example of an operation of the image enlarging unit  8  when repeating a feedback of a difference to the latter-stage adding unit  842  for plural times is explained with reference to  FIG. 8  and  FIGS. 9A and 9B .  FIG. 8  and  FIGS. 9A and 9B  are examples of the operation of the image enlarging unit  8  when repeating a feedback of a difference to the latter-stage adding unit  842  according to the present embodiment for plural times. 
     As shown in  FIG. 8 , in the image enlarging unit  8 , when a difference between pixel values of a target pixel detected at an N-th time by the difference detecting unit  83  is (Y) ((N-TH)DIFFERENCE=Y), the difference detecting unit  83  outputs the detected difference (Y) to the latter-stage adding unit  842 . At this time, the difference detecting unit  83  outputs differences between pixel values of all pixels on the input image to the latter-stage adding unit  842 . 
     Next, the latter-stage adding unit  842  adds the difference (Y) to a corresponding pixel value of the target pixel on the enlarged image that is input from the enlarged-image generating unit  81  (see (A- 2 ) in  FIG. 8 ). The latter-stage adding unit  842  then outputs to the reduced-image generating unit  82  an enlarged image that is generated by adding differences between pixel values of all pixels on the enlarged image. 
     The reduced-image generating unit  82  then generates a reduced image from the enlarged image that is input from the latter-stage adding unit  842 , and outputs the generated reduced image to the difference detecting unit  83 . At this time, it is assumed that a pixel value of a target pixel is (Z) (see (A- 3 ) in  FIG. 8 ). 
     In this case, the difference detecting unit  83  detects (X−Z) as a result of an (N+1)-th detection of a difference between pixel values of the target pixel (((N+1)-TH) DIFFERENCE=Y−Z). In this case, the difference detecting unit  83  detects differences between pixel values of all pixels on the input image and pixel values of all pixels on the reduced image, and outputs each of the detected differences of each pixel to the latter-stage adding unit  842 . 
     Thereafter, in the image enlarging unit  8 , operations such that the latter-stage adding unit  842  adding a difference between pixel values of a target pixel to a pixel value on an enlarged image, the reduced-image generating unit  82  generating a reduced image, and the difference detecting unit  83  detecting a difference between pixel values are repeatedly performed. 
     In the image enlarging unit  8 , when an absolute value of a difference detected by the difference detecting unit  83  becomes equal to or smaller than a predetermined threshold value (|DIFFWEWNCE|≦THREDHOLD VALUE) the feedback of a difference to the latter-stage adding unit  842  ends (END FEEDBACK). 
     At this time, the feedback can be ended when absolute values of differences for all pixels become equal to or smaller than a predetermined threshold value or when an average of absolute values of differences for all pixels becomes equal to or smaller than a predetermined threshold value. Alternatively, the feedback can be ended when the number of pixels of which differences between pixel values become equal to or smaller than a predetermined threshold value exceeds a predetermined number. 
     The image enlarging unit  8  outputs an enlarged image that is output by the latter-stage adding unit  842  to the timing control unit  9  when the feedback is ended(OUTPUT ENLARGED IMAGE). 
     As described above, as shown in  FIG. 9A , by repeating a feedback of a difference to the latter-stage adding unit  842  for plural times, the image display device  1  can set a difference between a pixel value of a target pixel on the input image and a pixel value of the target pixel on the reduced image close to 0, each time when the feedback is repeated. 
     By performing processes described above, as shown in  FIG. 9B , the image display device  1  can set the reproducibility of the input image due to the enlarged image close to the level of the input image each time when the feedback is repeated. 
     Therefore, for example, even when an input image having a region in which diagonal lines or edges may be emphasized is enlarged and displayed, the image display device  1  can display a high-definition enlarged image while utilizing the resolution of the display unit because the diagonal lines and edges can be correctly reproduced. 
     Although an ending condition in this example is that an absolute value of a difference becomes equal to or smaller than a predetermined threshold value, the ending condition can be that the number of times of feedbacks to a difference of the latter-stage adding unit  842  reaches a predetermined number of times set in advance. With this arrangement, a processing amount used for a feedback of a difference can be restricted. 
     A process performed by the image display device  1  is explained next with reference to  FIG. 10 .  FIG. 10  is a flowchart of a process performed by the image display device  1  according to the present embodiment.  FIG. 10  depicts only a process necessary to explain the characteristics of the image display device  1 , and descriptions of general processing will be omitted. 
     Among the processes performed by the image display device  1 , a process performed by the image enlarging unit  8  is explained here. As shown in  FIG. 10 , in the image enlarging unit  8 , when an input image is input from the dithering unit  7 , the enlarged-image generating unit  81  performs an enlarging process on the input image, thereby generating an enlarged image of the input image (Step S 101 ). 
     The enlarged-image generating unit  81  generates an enlarged image of 800×480 pixels (VGA) from an input image of 400×234 pixels (EGA) by performing image interpolation by the bilinear method, and outputs the generated enlarged image to the reduced-image generating unit  82 . 
     The reduced-image generating unit  82  generates a reduced image having the same image size (400×234 pixels) as that of the input image from the enlarged image that is input from the enlarged-image generating unit  81  (Step S 102 ), and outputs the generated reduced image to the difference detecting unit  83 . At this time, the reduced-image generating unit  82  generates the reduced image by the average thinning method mentioned above, instead of the bilinear method. 
     Next, the difference detecting unit  83  detects a difference between a pixel value of a pixel on the reduced image input from the reduced-image generating unit  82  and a pixel value of a corresponding pixel on the input image input from the dithering unit  7  (Step S 103 ), and outputs a detected difference between pixel values of each pixel to the former-stage adding unit  841 . 
     At this time, the difference detecting unit  83  detects a difference between a pixel value of a pixel on the input image that is used by the enlarged-image generating unit  81  to generate the enlarged image at Step S 101  and a pixel value of a corresponding pixel on the reduced image that is generated by the reduced-image generating unit  82  at Step S 102 . 
     Next, the former-stage adding unit  841  adds the difference input from the difference detecting unit  83  to the pixel value of the pixel on the input image input from the dithering unit  7  (Step S 104 ), and outputs the input image having added with the difference to the enlarged-image generating unit  81 . At this time, the former-stage adding unit  841  adds a difference between pixel values of a corresponding pixel on the input image that is used by the enlarged-image generating unit  81  to generate the enlarged image at Step S 101 . 
     The enlarged-image generating unit  81  then regenerates an enlarged image from the input image to which a difference is added for each pixel that is input from the former-stage adding unit  841  (Step S 105 ), and outputs the regenerated enlarged image to the reduced-image generating unit  82 . 
     The reduced-image generating unit  82  then regenerates a reduced image from the regenerated enlarged image that is input from the enlarged-image generating unit  81  (Step S 106 ), and outputs the regenerated reduced image to the difference detecting unit  83 . 
     Next, the difference detecting unit  83  redetects a difference between a pixel value of a pixel on the regenerated reduced image that is input from the reduced-image generating unit  82  and a pixel value of a corresponding pixel on the input image from the dithering unit  7  (Step S 107 ), and outputs a redetected difference between pixel values of each pixel to the latter-stage adding unit  842 . 
     At this time, the difference detecting unit  83  detects a difference between a pixel value of a pixel on the input image that is used by the enlarged-image generating unit  81  to generate the enlarged image at Step S 101  and a pixel value of a corresponding pixel on the reduced image that is regenerated by the reduced-image generating unit  82  at Step S 106 . 
     Next, the latter-stage adding unit  842  adds the redetected difference that is input from the difference detecting unit  83  to the enlarged image that is input from the enlarged-image generating unit  81  (Step S 108 ). 
     At this time, the latter-stage adding unit  842  adds a redetected difference between pixel values of each pixel that is input from the difference detecting unit  83  to a pixel value of a corresponding pixel on the enlarged image, and holds the enlarged image to which the difference is added until a determination result at Step S 109  (explained below) is determined. 
     Next, the difference detecting unit  83  determines whether an absolute value of the difference that is redetected at Step S 107  is equal to or smaller than a predetermined threshold value (Step S 109 ). This threshold value can be arbitrarily set. 
     This threshold value is set as follows, for example. First, the reproducibility of the input image due to the enlarged image is monitored while sequentially changing plural threshold values. As a result of the monitoring, a largest absolute value among threshold values having been determined to have no visual problem in the reproducibility of the input image can be set as the threshold value. 
     Next, when the difference detecting unit  83  determines that an absolute value of the difference that is redetected at Step S 107  is larger than the predetermined threshold value (NO at Step S 109 ), the process shifts to Step S 106 . In this case, the latter-stage adding unit  842  outputs the held enlarged image to the reduced-image generating unit  82 . 
     On the other hand, when the difference detecting unit  83  determines that an absolute value of the difference that is redetected at Step S 107  is equal to or smaller than the predetermined threshold value (YES at Step S 109 ), the latter-stage adding unit  842  outputs the held enlarged image to the timing control unit  9  (Step S 110 ), and ends the process. 
     As described above, the image display device according to the present embodiment corrects a pixel value of a pixel on the input image while assuming a decrease of the reproducibility of the input image by the enlarging process. The image display device then regenerates an enlarged image from the input image of which a pixel value of a pixel is corrected. 
     Therefore, the image display device according to the present embodiment can regenerate an enlarged image with a reproducibility of the input image higher than that of the enlarged image generated from an initially input image of which a pixel value of a pixel is not corrected. 
     Further, the image display device according to the present embodiment regenerates the enlarged image by adding a difference between a pixel value of a pixel on the reduced image of the regenerated enlarged image and a pixel value of a pixel on the initially input image to a pixel value of a corresponding pixel on the regenerated enlarged image. Therefore, the image display device can generate an enlarged image with a reproducibility of the input image higher than that of an enlarged image regenerated from the input image of which a pixel value of a pixel is corrected. 
     The image display device according to the present embodiment can repeat an addition of a difference to an enlarged image, a regeneration of a reduced image from an enlarged image to which a difference is added, and a detection of a difference between a pixel value of a pixel on the regenerated reduced image and a pixel value of a pixel on the input image, until a predetermined ending condition is satisfied. 
     With the above arrangement, the image display device according to the present embodiment can improve the reproducibility of the input image due to the enlarged image without performing the enlarging process of the input image, only by repeatedly adding a difference between a pixel value of a pixel on a reduced image and a pixel value of a pixel on the input image to a pixel value of a corresponding pixel on the enlarged image after generating the enlarged image once. 
     As described above, the image display device according to the present embodiment can generate an enlarged image of an improved reproducibility of the input image. Therefore, the image display device can display a high-precision enlarged image while utilizing the resolution of a display unit when an input image with a resolution lower than that of the display unit is enlarged and displayed. 
     Therefore, the image display device according to the present embodiment can display an enlarged image by correctly reproducing edges of a subject of an image in one-segment broadcasting and characters and diagonal lines of an image of a car navigation system, for example, while utilizing the resolution of the display unit. 
     In the embodiment described above, although there have been explained an addition of a difference to a pixel value of a pixel on the input image and an addition of a difference to a pixel value of a pixel on the enlarged image, it also suffices to perform only one of these additions. 
     For example, when a difference between a pixel value of a pixel on a reduced image of a regenerated enlarged image and a pixel value of a corresponding pixel on the input image is equal to or smaller than a predetermined threshold value as a result of an addition of a difference to a pixel value of a pixel on an input image, an addition of a difference to a pixel value of a pixel on the enlarged image can be omitted. 
     As explained above, when the reproducibility of the input image due to the enlarged image is improved only by adding a difference to a pixel value of the input image, a processing amount of the image display device can be reduced by omitting the addition of a difference to a pixel value of the input image. 
     Further, it can be arranged such that an addition of a difference to a pixel value of the input image is not performed and that a difference between a pixel value of a pixel on a reduced image of an enlarged image that is generated from the input image and a pixel value of a pixel on the input image is added to a pixel value of the pixel on the enlarged image, and when a difference between a pixel value of a pixel on a reduced image of the enlarged image to which the pixel value is added and a pixel value of the pixel on the input image is equal to or smaller than a predetermined threshold value, the enlarged image to which the pixel value is added can be displayed. Also with this arrangement, the processing amount of the image display device can be reduced. 
     In the embodiment described above, although a difference is added to a pixel value of a pixel on the input image for once, the addition can be performed for plural times. That is, it is possible to repeat an addition of a difference to a pixel value of a pixel on the input image, a regeneration of an enlarged image from the input image to which a difference is added, a regeneration of a reduced image from the regenerated enlarged image, and a detection of a difference between a pixel value of a pixel on the regenerated reduced image and a pixel value of a pixel on the input image. 
     In the embodiment described above, an addition of a difference to a pixel value of a pixel on the input image and an addition of a difference to a pixel value of a pixel on the enlarged image are performed in this order. Alternatively, these additions can be performed in the order of an addition of a difference to a pixel value of a pixel on the enlarged image and an addition of a difference to a pixel value of a pixel on the input image. 
     When the number of repeating processes is increased or when an order of processes is changed in this way, the reproducibility of the input image due to the enlarged image can be also improved in a similar manner to that of the embodiment described above. 
     Respective constituent elements of respective units shown in the drawings do not necessarily have to be physically configured in the way as shown in these drawings. That is, the specific mode of distribution and integration of respective units is not limited to the shown ones and all or a part of these units can be functionally or physically distributed or integrated in an arbitrary unit, according to various kinds of load, the status of use or the like. 
     Although the invention has been described with respect to specific embodiments for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.