Patent Publication Number: US-9898973-B2

Title: Display device, electronic apparatus and method of driving display device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from Japanese Application No. 2015-081611, filed on Apr. 13, 2015, the contents of which are incorporated by reference herein in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a display device, an electronic apparatus, and a method of driving a display device. 
     2. Description of the Related Art 
     In recent years, the demand for display devices for mobile apparatuses such as mobile phones and electronic paper has been increased. In the display devices, one pixel includes a plurality of sub-pixels that output light of different colors, and various colors are displayed through one pixel by switching ON and OFF of display of the sub-pixels. In the display devices, display characteristics such as resolution and luminance have been improved year after year as well. However, since an aperture ratio decreases as resolution increases, it is necessary to increase luminance of a backlight in order to implement high luminance, which leads to an increase in power consumption of the backlight. 
     In order to solve this problem, a technique that adds a white sub-pixel serving as a fourth sub-pixel to red, green, and blue sub-pixels known in the art has been proposed. According to this technique, a current value of the backlight is reduced as the white sub-pixel enhances the luminance, and thus the power consumption is reduced. 
     To reduce the luminance of the backlight, there is a method of performing image analysis, reducing the luminance of the backlight based on luminance and saturation of an image and reducing power consumption. In this case, when the image is determined to be high in neither luminance nor saturation as an analysis result of input signals of the image, the luminance of the backlight is reduced. However, there are cases in which even in the image determined to be high in neither luminance nor saturation, when the luminance of the backlight is reduced, a deterioration in a display quality is recognized. 
     SUMMARY 
     According to an aspect, a display device includes an image display panel including a plurality of pixels arranged in a matrix form, a light source unit that irradiates the image display panel with light and a signal processing unit that controls the pixels based on an input signal of an image, and controls an irradiation amount of light of the light source unit. The signal processing unit includes a pixel index value calculating unit that calculates a pixel index value serving as an index for obtaining the irradiation amount of the light emitted from the light source unit based on the input signal for each pixel, a chunk determining unit that performs consecutiveness determination which determines whether or not a pixel, having a pixel index value between an upper boundary value larger than a pixel index value of a starting pixel and a lower boundary value smaller than the pixel index value of the starting pixel, is consecutive from the starting pixel, and determines a region of consecutive pixels as a chunk, a chunk index value calculating unit that calculates a chunk index value serving as an index value of the chunk based on the pixel index values of the pixels of the chunk, a region index value calculating unit that calculates a region index value serving as an index value of an entire target region based on the pixel index values of all the pixels of the target region, and a light irradiation amount deciding unit that compares the chunk index value with the region index value, and decides the irradiation amount of the light of the light source unit in the target region based on one of the chunk index value and the region index value by which the irradiation amount of the light is increased. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating an exemplary configuration of a display device according to a first embodiment; 
         FIG. 2  is a conceptual diagram of an image display panel according to the first embodiment; 
         FIG. 3  is an explanatory diagram of a light source unit according to the present embodiment; 
         FIG. 4  is a schematic diagram illustrating a region of an emission surface of a light source unit; 
         FIG. 5  is a block diagram illustrating an overview of a configuration of a signal processing unit according to the first embodiment; 
         FIG. 6  is a conceptual diagram of an extended HSV color space that is extendable by the display device according to the present embodiment; 
         FIG. 7  is a conceptual diagram illustrating a relation between a hue and saturation of an extended HSV color space; 
         FIG. 8  is an explanatory diagram illustrating an example for describing consecutiveness determination; 
         FIG. 9  is a flowchart for describing is a flowchart for describing a chunk index value calculation process; 
         FIG. 10  is a flowchart for describing a horizontal-direction chunk index value calculation process; 
         FIG. 11  is a flowchart for describing a vertical-direction chunk index value calculation process; 
         FIG. 12  is a flowchart illustrating a region light irradiation value calculation process; 
         FIG. 13  is a schematic diagram for describing luminance distribution information; 
         FIG. 14  is a diagram illustrating a light source look-up table; 
         FIG. 15  is an explanatory diagram for describing an example of an irradiation amount of light of a pixel displayed on a display device; 
         FIG. 16  is an explanatory diagram for describing an example of an irradiation amount of light of a pixel displayed on a display device; 
         FIG. 17  is an explanatory diagram for describing when horizontal-direction chunk determination is performed; 
         FIG. 18  is an explanatory diagram for describing when horizontal-direction chunk determination is performed; 
         FIG. 19  is an explanatory diagram for describing an example in which horizontal-direction chunk determination is performed; 
         FIG. 20  is an explanatory diagram for describing an example in which vertical-direction chunk determination is performed; 
         FIG. 21  is an explanatory diagram illustrating an example for describing consecutiveness determination according to the second embodiment; 
         FIG. 22  is a flowchart for describing a consecutiveness determination value calculation method according to the second embodiment; 
         FIG. 23  is a flowchart for describing a consecutiveness determination value calculation method according to the second embodiment; 
         FIG. 24  is a diagram illustrating an example of an electronic apparatus to which the display device according to the first embodiment is applied; and 
         FIG. 25  is a diagram illustrating an example of an electronic apparatus to which the display device according to the first embodiment is applied. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings. The disclosure is given by way of example, and modifications that maintain the gist of the present invention and are easily conceivable by those skilled in the art are included in the present invention. To further clarify the description, the width, thickness, shape, and the like of each component may be schematically illustrated in the drawings as compared to actual aspects, and they are given by way of example and interpretation of the present invention is not limited to them. The same elements as those described in the description with reference to some drawings are denoted by the same reference numerals through the description and the drawings, and detailed descriptions thereof will be omitted in some cases. 
     First Embodiment 
     Overall Configuration of Display Device 
       FIG. 1  is a block diagram of an exemplary configuration of a display device according to a first embodiment of the present invention.  FIG. 2  is a conceptual diagram of an image display panel according to the first embodiment. As illustrated in  FIG. 1 , a display device  10  according to the first embodiment includes a signal processing unit  20 , an image display panel driving unit  30 , an image display panel  40 , a light source driving unit  50 , and a light source unit  60 . The signal processing unit  20  receives an input signal (RGB data) from an image output unit  12  of a control device  11 , and transfers a signal generated by performing a predetermined data conversion process on the input signal to the respective units of the display device  10 . The image display panel driving unit  30  controls driving of the image display panel  40  based on the signal received from the signal processing unit  20 . The light source driving unit  50  controls driving of the light source unit  60  based on the signal received from the signal processing unit  20 . The light source unit  60  illuminates the back surface of the image display panel  40  with light based on the signal received from the light source driving unit  50 . The image display panel  40  displays an image based on the signal received from the image display panel driving unit  30  and the light emitted from the light source unit  60 . 
     Configuration of Image Display Panel 
     First, a configuration of the image display panel  40  will be described. The image display panel  40  includes P 0 ×Q 0  pixels  48  (P 0  pixels in the row direction and Q 0  pixels in the column direction) arranged in a two-dimensional (2D) matrix form as illustrated in  FIGS. 1 and 2 .  FIG. 1  illustrates an example in which a plurality of pixels  48  are arranged on a 2D XY coordinate system in the matrix form. In this example, an X direction is the horizontal direction (the row direction), and a Y direction is the vertical direction (the column direction), and the present invention is not limited thereto, and the X direction may be the vertical direction, and the Y direction may be the horizontal direction. 
     Each of the pixels  48  includes a first sub-pixel  49 R, a second sub-pixel  49 G, a third sub-pixel  49 B, and a fourth sub-pixel  49 W. The first sub-pixel  49 R displays a first color (for example, red). The second sub-pixel  49 G displays a second color (for example, green). The third sub-pixel  49 B displays a third color (for example, blue). The fourth sub-pixel  49 W displays a fourth color (for example, white). The first, the second, the third, and the fourth colors are not limited to red, green, blue, and white, respectively, and simply need only to be different from one another, such as complementary colors. The fourth sub-pixel  49 W that displays the fourth color preferably has higher luminance than that of the first sub-pixel  49 R that displays the first color, the second sub-pixel  49 G that displays the second color, and the third sub-pixel  49 B that displays the third color when they are irradiated with light with the same light source lighting amount. In the following description, when it is unnecessary to distinguish the first sub-pixel  49 R, the second sub-pixel  49 G, the third sub-pixel  49 B, and the fourth sub-pixel  49 W, they are referred to as a “sub-pixel  49 .” To distinguish and specify a position at which a sub-pixel is arranged, for example, a fourth sub-pixel in a pixel  48 ( p,q ) is referred to as a “fourth sub-pixel  49 W( p,q ).” 
     The image display panel  40  is a color liquid crystal display panel in which a first color filter passing the first color is arranged between the first sub-pixel  49 R and an image observer, a second color filter passing the second color is arranged between the second sub-pixel  49 G and the image observer, and a third color filter passing the third color is arranged between the third sub-pixel  49 B and the image observer. In the image display panel  40 , no color filter is arranged between the fourth sub-pixel  49 W and the image observer. The fourth sub-pixel  49 W may be provided with transparent resin layer instead of the color filter. By arranging the transparent resin layer in this way, the image display panel  40  can suppress a large step difference of the fourth sub-pixel  49 W which occurs when no color filter is arranged on the fourth sub-pixel  49 W. 
     Configuration of Image Display Panel Driving Unit 
     The image display panel driving unit  30  includes a signal output circuit  31  and a scanning circuit  32  as illustrated in  FIGS. 1 and 2 . The image display panel driving unit  30  holds video signals in the signal output circuit  31  and sequentially outputs the video signals to the image display panel  40 . More specifically, the signal output circuit  31  outputs an image output signal having a certain electric potential corresponding to the output signal from the signal processing unit  20  to the image display panel  40 . The signal output circuit  31  is electrically connected to the image display panel  40  through signal lines DTL. The scanning circuit  32  controls an ON/OFF operation of a switching element (for example, a thin-film transistor (TFT)) that controls an operation (light transmittance) of the sub-pixel  49  in the image display panel  40 . The scanning circuit  32  is electrically connected to the image display panel  40  through wirings SCL. 
     Configurations of Light Source Driving Unit and Light Source Unit 
     The light source unit  60  (light source unit) is arranged on the back surface of the image display panel  40 , and emits light toward the image display panel  40  and illuminates the image display panel  40  with light.  FIG. 3  is an explanatory diagram of the light source unit according to the present embodiment. The light source unit  60  includes a light guide plate  61  and a sidelight light source  62  having at least one side surface of the light guide plate  61  as an incidence surface E. The sidelight light source  62  includes a plurality of light sources  62 A,  62 B,  62 C,  62 D,  62 E, and  62 F arranged facing the incidence surface E. The light sources  62 A to  62 F, for example, are light-emitting diodes (LEDs) of the same color (for example, white). The light sources  62 A to  62 F are arranged along one side surface of the light guide plate  61 , and when a light source arrangement direction in which the light sources  62 A to  62 F are arranged is indicated by LY, incident light of the light sources  62 A to  62 F enter the light guide plate  61  through the entrance surface E in a light entrance direction LX orthogonal to the light source arrangement direction LY. Hereinafter, when it is unnecessary to distinguish the light sources  62 A to  62 F, they are referred to as a “light source  62 .” 
     The light source driving unit  50  controls the amount of light output from the light source unit  60 , for example. Specifically, the light source driving unit  50  adjusts an electric current supplied to the light source unit  60  or the duty ratio based on a surface light source device control signal SBL output from the signal processing unit  20 , and controls the irradiation amount of light (intensity of light) with which the image display panel  40  is irradiated. The light source driving unit  50  can performs light source divisional drive control of controlling the amount of light (intensity of light) output from the light sources  62 A to  62 F by controlling the electric current or the duty ratio for the light sources  62 A to  62 F illustrated in  FIG. 3  individually and independently. 
     In the light guide plate  61 , since light is reflected at both end surfaces in the light source arrangement direction LY, for example, an intensity distribution of light emitted from the light sources  62 A and  62 F arranged closer to both end surfaces in the light source arrangement direction LY is different from an intensity distribution of light emitted from the light source  62 C arranged between the light sources  62 A and  62 F. For this reason, the light source driving unit  50  according to the present embodiment needs to control the electric current or the duty ratio for the light sources  62 A to  62 F illustrated in  FIG. 3  individually and independently and control a quantity of light (intensity of light) be to emitted according to the light intensity distributions of the light sources  62 A to  62 F. 
     In the light source unit  60 , incident light from the light sources  62 A to  62 F is emitted in the light entrance direction LX orthogonal to the light source arrangement direction LY and enters the light guide plate  61  through the entrance surface E. The light incident on the light guide plate  61  travels in the incidence direction LX while diffusing. The light guide plate  61  irradiates with the light that has been emitted from the light sources  62 A to  62 F and incident thereon in the illumination direction LZ in which the image display panel  40  is illuminated from the back surface. In the present embodiment, the illumination direction LZ is orthogonal to the light source arrangement direction LY and the light entrance direction LX. 
       FIG. 4  is a schematic diagram illustrating regions on an emission surface of the light source unit. In the display device  10  according to the present embodiment, an emission surface  102  serving as a surface from which the light source unit  60  emits light towards an image display surface serving as a surface on which the image display panel  40  displays an image is virtually divided into a plurality of regions  104 . The regions  104  are divided in a matrix form by a plurality of parting lines  106  parallel to the light entrance direction LX and a plurality of parting lines  108  parallel to the light source arrangement direction LY. Each of the parting lines  106  is formed between two adjacent light sources among the light sources  62 A to  62 F. Thus, the five parting lines  106  are formed at equal intervals. The regions  104  are regions corresponding to the light sources  62 A to  62 F. The two parting lines  108  are formed at equal intervals. Thus, the emission surface  102  is divided into the  18  regions  104  in a 3×6 matrix form. The number of divided regions  104  is not particularly limited thereto, but it is desirable to perform the division in the light source arrangement direction LY according to an arrangement of the light sources. This makes it easy to control the outputs of the respective light sources. The display device  10  sets one of the regions  104  as a target region, and calculates a region light irradiation value 1/α (which will be described later) for each target region. The target region includes the region  104  and a region of the image display surface of the image display panel  40  with which light is emitted from the region  104 . The region of the image display surface is a portion region of the entire image display surface of the image display panel  40 , and includes the pixels  48  within the region. Since the number of regions  104  is arbitrary as described above, one region may occupy the entire emission surface  102  as the region  104 , and one region may occupy the entire region of the image display surface as the region of the image display surface corresponding to the region  104 . 
     Configuration of Signal Processing Unit 
     The signal processing unit  20  processes an input signal received from the control device  11 , and generates an output signal. The signal processing unit  20  converts an input value of the input signal displayed by combining red (the first color), green (the second color), and blue (the third color) into an extended value (output signal) in an extended color space (a HSV (Hue-Saturation-Value, Value is also called Brightness) color space in the first embodiment) extended by red (first color), green (second color), blue (third color), and white (fourth color), and generates the output value. The signal processing unit  20  outputs the generated output signal to the image display panel driving unit  30 . The extended color space will be described later. While the extended color space according to the first embodiment is the HSV color space, it is not limited thereto, and any other coordinate system such as an XYZ color space and a YUV color space may be the extended color space. The signal processing unit  20  also generates the light source control signal SBL to be output to the light source driving unit  50 . 
       FIG. 5  is a block diagram illustrating an overview of a configuration of the signal processing unit according to the first embodiment. The signal processing unit  20  includes a tentative expansion coefficient calculating unit  72 , a hue determining unit  73 , a pixel index value calculating unit  74 , a chunk determining unit  76 , a chunk index value calculating unit  78 , a region index value calculating unit  80 , a light irradiation amount deciding unit  82 , an expansion coefficient calculating unit  84 , and an output signal generating unit  86  as illustrated in  FIG. 5 . The respective units of the signal processing unit  20  may be independent units (circuits or the like) or may be a common unit. 
     The tentative expansion coefficient calculating unit  72  acquires the input signal of the image from the control device  11 , and calculates a tentative expansion coefficient α 1  serving as a tentative coefficient for expanding the input signal for each pixel  48 . The tentative expansion coefficient calculating unit  72  calculates the tentative expansion coefficient α 1  for all the pixels  48  of the image display panel  40 . The tentative expansion coefficient calculating unit  72  calculates saturation and value (also called as brightness) of a color to be displayed based on the input signal for each pixel  48 , and calculates the tentative expansion coefficient α 1  based on the calculated saturation and brightness. A method of calculating the tentative expansion coefficient α 1  through the tentative expansion coefficient calculating unit  72  will be described later. 
     The hue determining unit  73  determines a hue of each pixel based on the input signal. 
     The pixel index value calculating unit  74  acquires information of the tentative expansion coefficient α 1  of each pixel  48  from the tentative expansion coefficient calculating unit  72 . The pixel index value calculating unit  74  calculates a pixel index value 1/α 1  for each pixel  48  based on the tentative expansion coefficient α 1  of each pixel  48 . The pixel index value calculating unit  74  calculates the pixel index value 1/α 1  for all the pixels  48  of the image display panel  40 . The pixel index value 1/α 1  is an index for obtaining an irradiation amount of light emitted from the light source unit  60 . In the first embodiment, as the value of the pixel index value 1/α 1  increases, the light source lighting amount of the light source unit  60  increases (the reduction rate of the irradiation amount of light decreases). And as the value of the pixel index value 1/α 1  decreases, the light source lighting amount of the light source unit  60  decreases (the reduction rate of the irradiation amount of light increases). The value of the pixel index value 1/α 1  is 1/α 1 . In other words, a value of the pixel index value 1/α 1  of a certain pixel  48  is a reciprocal of the tentative expansion coefficient α 1  in the pixel  48 . 
     The chunk determining unit  76  acquires information of the pixel index value 1/α 1  of the pixel  48  from the pixel index value calculating unit  74 , and acquires information of the hue of the pixel  48  from the hue determining unit  73 . The chunk determining unit  76  performs consecutiveness determination which determines whether or not a starting pixel  48   s  selected from among all the pixels  48  is consecutive to another pixel  48  based on the pixel index value 1/α 1  and the hue information. The chunk determining unit  76  determines a region of the consecutive pixels to be a chunk. The starting pixel  48   s  is a pixel serving as a starting point when the consecutiveness determination is performed. The chunk determining unit  76  selects a pixel, of which the pixel index value 1/α 1  is a predetermined value or more, as the starting pixel  48   s  from among all the pixels  48 . The chunk determining unit  76  may arbitrarily select the starting pixel  48   s  from among all the pixels  48  without deciding a predetermined value. The chunk determining unit  76  determines the region of the pixels determined to be consecutive in the consecutiveness determination as a chunk. The chunk can be indicated to be a pixel group comprised of a plurality of pixels  48  determined to be consecutive in the consecutiveness determination. The chunk determining unit  76  may use or may not use the hue information of the hue determining unit  73 . The consecutiveness determination method performed by the chunk determining unit  76  will be described later in detail. 
     The chunk index value calculating unit  78  acquires information of the pixel index value 1/α 1  of each pixel  48  in the chunk determined by the chunk determining unit  76 . The chunk index value calculating unit  78  calculates a chunk index value 1/α 2  serving as an index value of the chunk based on the information of the pixel index value 1/α 1  of each pixel  48  in the chunk. The chunk index value 1/α 2  is an index for obtaining the irradiation amount of light of the light source unit  60  in the pixel  48  configuring the chunk. A process of calculating the chunk index value 1/α 2  through the chunk index value calculating unit  78  will be described later in detail. 
     The region index value calculating unit  80  acquires the information of the pixel index value 1/α 1  in the pixel  48  in the target region from the pixel index value calculating unit  74 , and acquires the hue information of the pixel  48  in the target region from the hue determining unit  73 . The region index value calculating unit  80  calculates a region index value 1/α 3  serving as an index value of the entire region in the target region based on the information of the pixel index value 1/α 1  and the hue information. The region index value 1/α 3  is an index that is used to obtain the irradiation amount of light of the light source unit  60  to the target region and common to all the pixels  48  in the target region. The region index value calculating unit  80  may use or may not use the hue information of the hue determining unit  73 . A process of calculating the region index value 1/α 3  through the region index value calculating unit  80  will be described later in detail. 
     The light irradiation amount deciding unit  82  acquires information of the chunk index value 1/α 2  from the chunk index value calculating unit  78 , and acquires information of the region index value 1/α 3  from the region index value calculating unit  80 . The light irradiation amount deciding unit  82  compares the value of the chunk index value 1/α 2  with the value of the region index value 1/α 3  in the target region, and decides the irradiation amount of light of the light source unit  60  in the target region based on the value by which the irradiation amount of light of the light source unit  60  is increased. Specifically, the light irradiation amount deciding unit  82  uses one of the value of the chunk index value 1/α 2  in the target region and the value of the region index value 1/α 3  in the target region, that is, the value by which the irradiation amount of light of the light source unit  60  is increased, as the region light irradiation value 1/α. The region light irradiation value 1/α is a value indicating the irradiation amount of light of the light source unit  60 . As the value of the region light irradiation value 1/α increases, the light source lighting amount of the light source unit  60  increases (the reduction rate of the irradiation amount of light decreases). As the value of the region light irradiation value 1/α decreases, the light source lighting amount of the light source unit  60  decreases (the reduction rate of the irradiation amount of light increases). 
     An LD storage unit  83  stores information of luminance distribution information LD of each light source  62  of the light source unit  60 . As described above, the light sources  62  differ in the intensity distribution (luminance distribution) of light emitted therefrom. The luminance distribution information LD indicates information of a luminance distribution of each light source  62 . The light irradiation amount deciding unit  82  decides a region lighting amount 1/α′ serving as a lighting amount of each light source of the light source unit  60  based on the region light irradiation value 1/α and the luminance distribution information LD. The light irradiation amount deciding unit  82  outputs information of the region lighting amount 1/α′ to the light source driving unit  50  as the light source control signal SBL. 
     The light irradiation amount deciding unit  82  calculates a pixel light irradiation amount 1/α 0  based on the region lighting amount 1/α′. The pixel light irradiation amount 1/α 0  is an irradiation amount of light with which the light source unit  60  irradiates each pixels  48 . The expansion coefficient calculating unit  84  acquires the information of the pixel light irradiation amount 1/α 0  from the light irradiation amount deciding unit  82 . The expansion coefficient calculating unit  84  calculates an expansion coefficient α 0  for expanding the input signal of the pixel  48  in the target region based on the value of the pixel light irradiation amount 1/α 0 . 
     The output signal generating unit  86  acquires information of the expansion coefficient α 0  from the expansion coefficient calculating unit  84 . The output signal generating unit  86  generates an output signal for causing the pixel  48  in the target region to display a predetermined color based on the value of the expansion coefficient α 0  and the input signal. The output signal generating unit  86  outputs the generated output signal to the image display panel driving unit  30 . A process of generating the output signal through the output signal generating unit  86  will be described later. 
     Process Operations of Display Device 
     Pixel Index Value Calculation Process 
     Next, a process of calculating the pixel index value 1/α 1  among process operations of the display device  10  will be described. The pixel index value 1/α 1  is calculated based on the tentative expansion coefficient α 1  as described above.  FIG. 6  is a conceptual diagram of an extended HSV color space that is extendable by the display device of the present embodiment.  FIG. 7  is a conceptual diagram a relation between a hue and saturation of the extended HSV color space. 
     In the display device  10 , each of the pixels  48  includes the fourth sub-pixel  49 W that outputs the fourth color (white), and thus the dynamic range of brightness is increased in the extended color space (the HSV color space in the first embodiment) as illustrated in  FIG. 6 . In other words, in the extended color space extended by the display device  10 , as illustrated in  FIG. 6 , a solid in which a shape in a cross section having saturation axis and a brightness axis in which as the saturation increases, a maximum value of the brightness decreases is a substantially trapezoidal in which an oblique side is a curve is placed on a cylindrical color space displayable by the first sub-pixel  49 R, the second sub-pixel  49 G, and the third sub-pixel  49 B. The signal processing unit  20  stores therein a maximum value Vmax(S) of the brightness having saturation S as a variable in the extended color space (the HSV color space in the first embodiment) expanded by adding the fourth color (white) is stored in the signal processing unit  20 . In other words, the signal processing unit  20  stores the value of the maximum value Vmax(S) of the brightness for each coordinates (values) of the saturation and the hue in the three-dimensional shape of the extended color space illustrated in  FIG. 6 . Since the input signal is configured with input signals for the first sub-pixel  49 R, the second sub-pixel  49 G, and the third sub-pixel  49 B, the color space of the input signal has a cylindrical shape, that is, the same shape as the cylindrical part of the extended color space. 
     The tentative expansion coefficient α 1  is a tentative value used to expand the input signal and convert the color space by the output signal into the extended color space. In the signal processing unit  20 , the tentative expansion coefficient calculating unit  72  obtains the saturation S and the brightness V(S) in the pixel  48  based on the input signal value of the sub-pixel  49  in the pixel  48  in the target region, and calculates the tentative expansion coefficient α 1 . This will be specifically described below. 
     The saturation S and the brightness V(S) are indicated by S=(Max−Min)/Max and V(S)=Max. The saturation S can have values of 0 to 1, the brightness V(S) can have values of 0 to (2 n −1), where n is a display gradation bit number. Max is a maximum value among the input signal values of the three sub-pixels in the pixel, that is, the input signal value of the first sub-pixel  49 R, the input signal value of the second sub-pixel  49 G, and the input signal value of the third sub-pixel  49 B. Min is a minimum value among the input signal values of the three sub-pixels in the pixel, that is, of the input signal value of the first sub-pixel  49 R, the input signal value of the second sub-pixel  49 G, and the input signal value of the third sub-pixel  49 B. A hue H is indicated by a range from 0° to 360° as illustrated in  FIG. 7 . As the hue H varies from 0° to 360°, it sequentially indicates red, yellow, green, cyan, blue, magenta, and red. 
     The signal processing unit  20  receives the input signal serving as information of the image to be displayed from the control device  11 . For each pixel, the input signal includes the information of the image (color) to be displayed at a position of the pixel as the input signal. Specifically, for a (p,q)-th pixel (here, 1≦p≦I and 1≦q≦Q 0 ), a signal including an input signal of the first sub-pixel having the signal value of x 1-(p,q) , an input signal of the second sub-pixel having the signal value of x 2-(p,q) , and an input signal of the third sub-pixel having the signal value of x 3-(p,q)  is input to the signal processing unit  20 . 
     Generally, in the (p,q)-th pixel, saturation S (p,q)  and the brightness (value) V(S) (p,q)  of an input color in the cylindrical HSV color space are calculated by the following Equations (1) and (2) based on the input signal (the signal value of x 1-(p,q) ) of the first sub-pixel, the input signal (the signal value of x 2-(p,q) ) of the second sub-pixel, and the input signal (the signal value of x 3-(p,q) ) of the third sub-pixel.
 
 S   (p,q) =(Max (p,q) −Min (p,q) )/Max (p,q)   (1)
 
 V ( S ) (p,q) =Max (p,q)   (2)
 
     Max (p,q)  is the maximum value among the input signal values of the three sub-pixels  49 , that is, x 1-(p,q) , x 2-(p,q) , and x 3-(p,q) , and Min (p,q)  is the minimum value among the input signal values of the three sub-pixels  49 , that is, x 1-(p,q) , x 2-(p,q) , and x 3-(p,q) . In the first embodiment, n is assumed to be 8. That is, the display gradation bit number is 8 bits (the display gradation has 256 gradation values, that is, 0 to 255). 
     In the signal processing unit  20 , the tentative expansion coefficient calculating unit  72  calculates the tentative expansion coefficient α 1  using Equation (3) based on the brightness V(S) (p,q)  of each pixel  48  in the target region and Vmax(S) of the extended color space. The tentative expansion coefficient α 1  may have a different value according to each pixel  48 .
 
α 1(p,q)   =V max( S )/ V ( S ) (p,q)   (3)
 
     In the signal processing unit  20 , the pixel index value calculating unit  74  calculates a reciprocal of α 1(p,q) , and uses the calculated reciprocal of α (p,q)  as the pixel index value 1/α 1(p,q)  of the (p,q)-th pixel  48 . Accordingly, the signal processing unit  20  calculates the pixel index value 1/α 1  of each pixel  48 . 
     Chunk Index Value Calculation Process 
     Next, the consecutiveness determination performed by the chunk determining unit  76  and the chunk index value calculation process will be described. In the consecutiveness determination, the chunk determining unit  76  selects the starting pixel  48   s  serving as the starting point at which the consecutiveness determination starts among all the pixels  48  of the image display panel  40 . The chunk determining unit  76  performs the consecutiveness determination on the pixel  48  at a sampling point extracted from among all the pixels  48  of the image display panel  40 . The chunk determining unit  76  performs the consecutiveness determination on the pixels  48  at the sampling point in a determination direction Z from the starting pixel  48   s , sequentially along the determination direction Z. The determination direction Z is the horizontal direction (the X direction) and the vertical direction (the Y direction). The chunk determining unit  76  performs the consecutiveness determination in both the horizontal direction and the vertical direction. The chunk determining unit  76  may perform the consecutiveness determination in either of the horizontal direction and the vertical direction or may perform the consecutiveness determination using a direction oblique from the horizontal direction or the vertical direction as the determination direction Z. The horizontal direction is a direction in which a writing position moves when an image is written on the image display panel  40 . In other words, a moving direction of a pixel whose signal is processed at the time of data processing is the horizontal direction. The vertical direction is a direction orthogonal to the horizontal direction as described above. The chunk determining unit  76  analyzes the pixel at the sampling point and thus can reduce an operation process to be smaller than when all the pixels  48  are analyzed without using the sampling point. Preferably, the sampling points are set at predetermined pixel intervals. The sampling points may deviate in either of the horizontal direction and the vertical direction or may overlap. The chunk determining unit  76  may perform the consecutiveness determination on all the pixels  48  without using the sampling point. 
     Specifically, when the starting pixel  48   s  is selected, the chunk determining unit  76  calculates a consecutiveness determination value for the consecutiveness determination based on the pixel index value 1/α 1  of the starting pixel  48   s . In the first embodiment, the consecutiveness determination value includes an upper boundary value Up and a lower boundary value Bo. The upper boundary value Up is a value larger than the pixel index value 1/α 1  of the starting pixel  48   s , and a lower boundary value Bo is a value smaller than the pixel index value 1/α 1  of the starting pixel  48   s . The chunk determining unit  76  sets a value that is larger than the pixel index value 1/α 1  of the starting pixel  48   s  by a predetermined value A 1  as the upper boundary value Up. The chunk determining unit  76  sets a value that is smaller than the pixel index value 1/α 1  of the starting pixel  48   s  by a predetermined value A 2  as the lower boundary value Bo. The predetermined values A 1  and A 2  are values that are set in advance and have the same value. The predetermined values A 1  and A 2  may be different values or may be changed according to a setting performed by an operator, for example. 
     After the upper boundary value Up and the lower boundary value Bo are calculated, the chunk determining unit  76  performs the consecutiveness determination on the pixel  48  at the sampling point in the determination direction Z from the selected starting pixel  48   s . A pixel on which the consecutiveness determination is performed is indicated by a determination pixel  48   u . The chunk determining unit  76  determines the determination pixel  48   u  to be a pixel consecutive to the starting pixel  48   s , when the pixel index value 1/α 1  of the determination pixel  48   u  is a value between the lower boundary value Bo and the upper boundary value Up (a value that is equal to or larger than the lower boundary value Bo and equal to or less than the upper boundary value Up). The chunk determining unit  76  determines the determination pixel  48   u  to be a pixel inconsecutive to the starting pixel  48   s , when the pixel index value 1/α 1  of the determination pixel  48   u  is a value out of the range of the value between the lower boundary value Bo and the upper boundary value Up. When the determination pixel  48   u  is determined to be consecutive, the chunk determining unit  76  sets the pixel  48  at the next sampling point as the determination pixel  48   u , and performs the same consecutiveness determination. The chunk determining unit  76  determines the pixels  48  between the starting pixel  48   s  and the pixel  48  determined to be consecutive immediately before the pixel  48  determined to be inconsecutive, as the consecutive pixels. 
     When the determination pixel  48   u  is determined to be inconsecutive, the chunk determining unit  76  suspends the consecutiveness determination. The chunk determining unit  76  selects the determination pixel  48   u  determined to be inconsecutive as a new starting pixel  48   s . The chunk determining unit  76  resumes the consecutiveness determination using the new starting pixel  48   s  as the starting point. The pixels  48  determined to be consecutive in one consecutiveness determination are consecutive to each other, but the pixels  48  in different consecutiveness determinations are inconsecutive to each other. 
     In further detail, an immediately previous pixel  48   t  is a pixel that has undergone the consecutiveness determination immediately before the determination pixel  48   u . The chunk determining unit  76  determines the starting pixel  48   s  to the determination pixel  48   u  to be consecutive, when the pixel index value 1/α 1  of the immediately previous pixel  48   t  is the value between the lower boundary value Bo and the upper boundary value Up, and the pixel index value 1/α 1  of the determination pixel  48   u  is the value between the lower boundary value Bo and the upper boundary value Up. In other words, when the immediately previous pixel  48   t  is not the value between the lower boundary value Bo and the upper boundary value Up, the immediately previous pixel  48   t  is determined to be inconsecutive. Thus even when the determination pixel  48   u  to be determined next is the value between the lower boundary value Bo and the upper boundary value Up, the determination pixel  48   u  is determined to be inconsecutive to the starting pixel  48   s.    
       FIG. 8  is an explanatory diagram of an example for describing the consecutiveness determination. An example of the above-described consecutiveness determination will be described with reference to  FIG. 8 . In  FIG. 8 , a horizontal axis indicates each pixel  48  at the sampling point, and a vertical axis indicates the pixel index value 1/α 1  of each pixel  48  at the sampling point. In other words,  FIG. 8  illustrates the pixel index value 1/α 1  of each pixel  48  at the sampling point. 
     When a pixel  48   a1  is selected as the starting pixel  48   s , and the consecutiveness determination is performed as illustrated in  FIG. 8 , the chunk determining unit  76  calculates an upper boundary value Up a1  of the pixel  48   a1  and a lower boundary value Bo a1  of the pixel  48   a1  based on the pixel index value 1/α 1  of the pixel  48   a1 . 
     After the upper boundary value Up a1  and the lower boundary value Bo a1  are calculated, the chunk determining unit  76  sets a pixel  48   a2  serving as the determination pixel  48   u  at the sampling point next to the pixel  48   a1  in the determination direction Z. The chunk determining unit  76  determines whether or not the pixel  48   a2  is consecutive to the pixel  48   a1 . As illustrated in  FIG. 8 , the pixel index value 1/α 1  of the pixel  48   a2  is a value between the upper boundary value Up a1  and the lower boundary value Bo a1 . Thus, the chunk determining unit  76  determines the pixel  48   a2  to be consecutive to the pixel  48   a1 . 
     After the pixel  48   a2  is determined to be consecutive, the chunk determining unit  76  sets a pixel  48   a3  serving as the pixel at the sampling point next to the pixel  48   a2  as the determination pixel  48   u . The chunk determining unit  76  determines whether or not the pixel  48   a3  is consecutive to the pixel  48   a1 . As illustrated in  FIG. 8 , the pixel index value 1/α 1  of the pixel  48   a3  is a value between the upper boundary value Up a1  and the lower boundary value Bo a1 . Thus, the chunk determining unit  76  determines the pixel  48   a3  to be consecutive to the pixel  48   a1 . 
     After the pixel  48   a3  is determined to be consecutive, the chunk determining unit  76  similarly performs the consecutiveness determination on a pixel  48   a4  serving as the pixel at the sampling point next to the pixel  48   a3 . As illustrated in  FIG. 8 , the pixel index value 1/α 1  of the pixel  48   a4  is a value out of the range between the upper boundary value Up a1  and the lower boundary value Bo a1 . Thus, the chunk determining unit  76  determines the pixel  48   a4  to be inconsecutive to the pixel  48   a1 . The chunk determining unit  76  determines the pixel  48   a1  to the pixel  48   a3  to be consecutive, and determines a plurality of pixels  48  of the pixel  48   a1  to the pixel  48   a3  as a chunk. 
     Since the pixel  48   a4  is determined to be inconsecutive to the pixel  48   a1 , the chunk determining unit  76  suspends the consecutiveness determination using the pixel  48   a1  as the starting pixel  48   s . Then, the chunk determining unit  76  newly resumes the consecutiveness determination using the pixel  48   a4  as the starting pixel  48   s . The chunk determining unit  76  similarly calculates an upper boundary value Up a4  and a lower boundary value Bo a4  of the pixel  48   a4 . The chunk determining unit  76  performs the consecutiveness determination on a pixel  48   a5  serving as the pixel at the sampling point next to the pixel  48   a4 . As illustrated in  FIG. 8 , the pixel index value 1/α 1  of the pixel  48   a5  is a value between the upper boundary value Up a4  and the lower boundary value Bo a4 . Thus, the chunk determining unit  76  determines the pixel  48   a5  to be consecutive to the pixel  48   a4 . The chunk determining unit  76  repeatedly performs the same consecutiveness determination process as described above. 
     As described above, the chunk determining unit  76  performs the consecutiveness determination, and determines the pixels  48  determined to be consecutive as a chunk. The chunk index value calculating unit  78  acquires information (position information) of the pixels configuring the chunk and information of the pixel index value 1/α 1  of the pixels  48  included in the chunk from the chunk determining unit  76 . The chunk index value calculating unit  78  sets the maximum value among the pixel index values 1/α 1  of all the pixels  48  included in the chunk as the chunk index value 1/α 2  of the chunk. The chunk index value 1/α 2  is a value common to the pixels  48  included in the chunk. Among all the pixels  48  included in the chunk, the starting pixel  48   s  is also included. 
     A process flow of a process of calculating the chunk index value 1/α 2  will be described with reference to a flowchart.  FIG. 9  is a flowchart for describing the chunk index value calculation process. As illustrated in  FIG. 9 , based on the consecutiveness determination result of the chunk determining unit  76 , the chunk index value calculating unit  78  calculates the chunk index value 1/α 2  in the horizontal direction (step S 10 ) and calculates the chunk index value 1/α 2  in the vertical direction (step S 12 ). The process of steps S 10  and S 12  will be described later. The process of step S 10  and the process of step S 12  may be performed in parallel or sequentially. 
     When the horizontal direction and the chunk index value 1/α 2  in the vertical direction are calculated, the chunk index value calculating unit  78  determines whether or not the chunk index value 1/α 2  in the horizontal direction is larger than the chunk index value 1/α 2  in the vertical direction (step S 14 ). When the chunk index value 1/α 2  in the horizontal direction is determined to be larger than the chunk index value 1/α 2  in the vertical direction (Yes in step S 14 ), the chunk index value calculating unit  78  decides the chunk index value 1/α 2  in the horizontal direction as the chunk index value 1/α 2  (step S 16 ), and then ends the current process. When the chunk index value 1/α 2  in the horizontal direction is not larger than the chunk index value 1/α 2  in the vertical direction (No in step S 14 ), that is, when the chunk index value 1/α 2  in the horizontal direction is determined to be equal to or less than the chunk index value 1/α 2  in the vertical direction, the chunk index value calculating unit  78  determines whether or not the chunk index value 1/α 2  in the horizontal direction is smaller than the chunk index value 1/α 2  in the vertical direction (step S 17 ). 
     When the chunk index value 1/α 2  in the horizontal direction is determined to be smaller than the chunk index value 1/α 2  in the vertical direction (Yes in step S 17 ), the chunk index value calculating unit  78  decides the chunk index value 1/α 2  in the vertical direction as the chunk index value 1/α 2  (step S 18 ), and then ends the current process. In other words, the chunk index value calculating unit  78  sets a larger one of the chunk index value 1/α 2  in the horizontal direction and the chunk index value 1/α 2  in the vertical direction as the chunk index value 1/α 2 . When the chunk index value 1/α 2  of the chunk in the horizontal direction is determined to be not smaller than the chunk index value 1/α 2  in the vertical direction (No in step S 17 ), that is, when the chunk index value 1/α 2  in the horizontal direction is equal to the chunk index value 1/α 2  in the vertical direction, the chunk index value calculating unit  78  decides the chunk index value 1/α 2  according to a hue priority (step S 19 ). Specifically, of the chunk index value 1/α 2  in the horizontal direction and the chunk index value 1/α 2  in the vertical direction, the chunk index value 1/α 2  that is higher in the hue priority is decided as the chunk index value 1/α 2 . For example, yellow, yellowish green, cyan, green, magenta, violet, red, and blue is the descending order of high priorities. 
     Next, a method of calculating (deciding) the chunk index value 1/α 2  in the horizontal direction will be described.  FIG. 10  is a flowchart for describing a horizontal-direction chunk index value calculation process. In the signal processing unit  20 , the chunk determining unit  76  performs the consecutiveness determination using the horizontal direction as the determination direction Z, and calculates the chunk index value 1/α 2  in the horizontal direction based on the determination result of the consecutiveness determination. 
     As illustrated in  FIG. 10 , in the signal processing unit  20 , the chunk determining unit  76  extracts the pixel index value 1/α 1  of the starting pixel  48   s  (step S 22 ), and determines whether or not the pixel index value 1/α 1  of the starting pixel  48   s  is equal to or larger than a threshold value (step S 24 ). Here, the threshold value is a predetermined value and used as a reference for determining the pixel index value 1/α 1  to be in a range in which chunk detection need not be considered (an adjustment of the present embodiment is unnecessary). 8′h20 is used as an example of the threshold value, but the threshold value is not limited thereto. When the pixel index value 1/α 1  of the starting pixel  48   s  is determined to be neither equal to nor larger than the threshold value (No in step S 24 ), that is, when the pixel index value 1/α 1  is determined to be smaller than the threshold value, the chunk determining unit  76  proceeds to step S 34 . 
     When the pixel index value 1/α 1  of the starting pixel  48   s  is determined to be equal to or larger than the threshold value (Yes in step S 24 ), the chunk determining unit  76  decides a consecutiveness determination value for the consecutiveness determination (step S 25 ). In the first embodiment, the consecutiveness determination value is the upper boundary value Up and the lower boundary value Bo calculated based on the pixel index value 1/α 1  of the starting pixel  48   s.    
     After the consecutiveness determination value is decided, the chunk determining unit  76  extracts the pixel index value 1/α 1  of the sampling point adjacent to the starting pixel  48   s  in the horizontal direction (step S 26 ), and determines whether or not the pixel at the sampling point is consecutive to the starting pixel  48   s  (step S 28 ). The chunk determining unit  76  determines that the pixel at the sampling point is consecutive to the starting pixel  48   s , when the pixel index value 1/α 1  of the pixel at the sampling point is a value within the range of the consecutiveness determination value (the value between the upper boundary value Up and the lower boundary value Bo). For example, the chunk determining unit  76  may determine that the pixels of the sampling points are consecutive, when the pixels of the sampling points corresponding to a set number of 2 or more are consecutive to the starting pixel  48   s . In other words, in this case, when the starting pixel  48   s  is consecutive to a pixel  48   k  serving as the pixel  48  at the next sampling point, and the starting pixel  48   s  is inconsecutive to a pixel  48   l  at the next sampling point of the pixel  48   k , the chunk determining unit  76  determines that the starting pixel  48   s  is inconsecutive to the pixel  48   k.    
     When the pixel is determined to be inconsecutive (No in step S 28 ), the chunk determining unit  76  holds a sampling flag, resets a consecutiveness detection signal (step S 30 ), and proceeds to step S 34 . The consecutiveness detection signal is a signal indicating ON while the sampling point is consecutive. When the pixel is determined to be consecutive (Yes in step S 28 ), the chunk determining unit  76  holds the pixel index values 1/α 1  of the starting pixel  48   s  and the pixel  48  at the sampling point and the flags thereof (step S 32 ), and then proceeds to step S 34 . 
     When determination of the sampling point is performed, the chunk determining unit  76  determines whether or not it has reached the boundary of the region in the horizontal direction (step S 34 ). When it is determined to have not reached the boundary of the region in the horizontal direction (No in step S 34 ), the chunk determining unit  76  returns to step S 22 , and the same process as described above on the next sampling point. The chunk determining unit  76  repeats the process until it reaches the boundary of the region in the horizontal direction as described above. When it is determined to have reached the boundary of the region in the horizontal direction (Yes in step S 34 ), the chunk determining unit  76  determines whether or not it has reached the boundary of the image, that is, the end of the pixel of the image display panel (step S 36 ). 
     When it is determined to have not reached the boundary of the image (No in step S 36 ), the chunk determining unit  76  holds the pixel index value 1/α 1  and the flag (step S 38 ), and then returns to step S 22 . When it is determined to have reached the boundary of the image (Yes in step S 36 ), the chunk determining unit  76  determines whether or not the horizontal-direction consecutiveness determination process ends, that is, determines whether or not the consecutiveness determination has been performed on all the sampling points of the image (step S 40 ). 
     When the horizontal-direction consecutiveness determination is determined not to end (No in step S 40 ), the chunk determining unit  76  shifts to a next line, resets the consecutiveness detection signal and the flag (step S 42 ), and returns to step S 22 . When the horizontal-direction consecutiveness determination is determined to end (Yes in step S 40 ), the chunk determining unit  76  decides the chunk index value 1/α 2  in the horizontal direction for each target region (step S 44 ), and then ends the current process. The chunk determining unit  76  decides the maximum value among the pixel index values 1/α 1  of the pixels determined to be consecutive as the chunk index value 1/α 2  in the horizontal direction. 
     Next, a method of calculating (deciding) the chunk index value 1/α 2  in the vertical direction will be described.  FIG. 11  is a flowchart for describing a vertical-direction the chunk index value calculation process. In the signal processing unit  20 , the chunk determining unit  76  performs the consecutiveness determination using the vertical direction as the determination direction Z, calculates the chunk index value 1/α 2  in the vertical direction based on the determination result of the consecutiveness determination. 
     The chunk determining unit  76  extracts the pixel index value 1/α 1  of the starting pixel  48   s  (step S 62 ), and determines whether or not the pixel index value 1/α 1  of the starting pixel  48   s  is equal to or larger than a threshold value (step S 64 ). When the pixel index value 1/α 1  of the starting pixel  48   s  is determined to be neither equal to nor larger than the threshold value (No in step S 64 ), that is, when the pixel index value 1/α 1  is determined to be smaller than the threshold value, the chunk determining unit  76  proceeds to step S 76 . 
     When the pixel index value 1/α 1  of the starting pixel  48   s  is determined to be equal to or larger than the threshold value (Yes in step S 64 ), the chunk determining unit  76  decides the consecutiveness determination value for the consecutiveness determination (step S 65 ). In the first embodiment, the consecutiveness determination value is the upper boundary value Up and the lower boundary value Bo calculated based on the pixel index value 1/α 1  of the starting pixel  48   s.    
     After the consecutiveness determination value is decided, the chunk determining unit  76  stores the flag and the pixel index value 1/α 1  of the starting pixel  48   s  and the consecutiveness determination value in a FIFO, RAM, or the like (step S 66 ), extracts the pixel index value 1/α 1  of the sampling point neighboring in the vertical direction (step S 68 ), and determines whether or not the pixel at the sampling point is consecutive (step S 70 ). The consecutiveness determines method is the same as that in the horizontal direction. 
     When the pixel at the sampling point is determined to be inconsecutive (No in step S 70 ), the chunk determining unit  76  holds the sampling flag, and associates information of inconsecutiveness with the target sampling point (step S 72 ), and proceeds to step S 76 . When the pixel at the sampling point is determined to be consecutive (Yes in step S 70 ), the chunk determining unit  76  associates information of consecutiveness with the target sampling point, stores the pixel index value 1/α 1  of the sampling point (step S 74 ), and proceeds to step S 76 . 
     When determination of the sampling point is performed, the chunk determining unit  76  determines whether or not it has reached the boundary of the region in the vertical direction (step S 76 ). When it is determined to have not reached the boundary of the region in the vertical direction (No in step S 76 ), the chunk determining unit  76  returns to step S 62 , and performs the same process as described above on the next sampling point. When it is determined to have reached the boundary of the region in the vertical direction (Yes in step S 76 ), the chunk determining unit  76  determines whether or not it has reached the boundary of the image, that is, the end of the image display panel  40  (step S 80 ). 
     When it is determined to have not reached the boundary of the image (No in step S 80 ), the chunk determining unit  76  returns to step S 62 . When it is determined to have reached the boundary of the image (Yes in step S 80 ), the chunk determining unit  76  determines whether or not the vertical-direction consecutiveness determination ends, that is, whether or not the consecutiveness determination has performed on all the sampling points of the image (step S 82 ). 
     When the vertical-direction consecutiveness determination is determined not to end (No in step S 82 ), the chunk determining unit  76  shifts to a next line, (step S 84 ), and then returns to step S 62 . When the vertical-direction consecutiveness determination is determined to end (Yes in step S 82 ), the chunk determining unit  76  decides the chunk index value 1/α 2  in the vertical direction for each target region (step S 86 ), and then ends the current process. The chunk determining unit  76  decides the maximum value among the pixel index values 1/α 1  of the pixels determined to be consecutive as the chunk index value 1/α 2  in the vertical direction. 
     Region Index Value Calculation Process 
     Next, a process of calculating the region index value 1/α 3  through the region index value calculating unit  80  will be described. 
     The region index value calculating unit  80  acquires the information of the pixel index value 1/α 1  of the pixel  48  in the target region from the pixel index value calculating unit  74 , and acquires the hue information of the pixel  48  in the target region from the hue determining unit  73 . The region index value calculating unit  80  calculates the region index value 1/α 3  serving as the index value of the entire target region based on the information of the pixel index value 1/α 1  and the hue information using a predetermined algorithm. Here, an example of a predetermined algorithm is described, but not limited to. In the predetermined algorithm, a distribution of the pixel index values 1/α 1  of the pixels  48  in the target region is calculated. And pixel index values are extracted so that the number of pixels which have pixel index values equal or larger than the extracted pixel index values are higher than predetermined number of pixels. And a largest pixel index value 1/α 1  among the extracted pixel index values is decided as the region index value 1/α 3 . The region index value 1/α 3  is a value common to all the pixels  48  in the target region. When there are a plurality of target regions, the region index value calculating unit  80  calculates the region index value 1/α 3  for all the target regions. 
     Region Light Irradiation Value Calculation Process 
     Next, a process of calculating the region index value 1/α 3  through the light irradiation amount deciding unit  82  will be described. 
     The light irradiation amount deciding unit  82  acquires the information of the chunk index value 1/α 2  from the chunk index value calculating unit  78 , and acquires the information of the region index value 1/α 3  from the region index value calculating unit  80 . The light irradiation amount deciding unit  82  compares the value of the chunk index value 1/α 2  with the value of the region index value 1/α 3  in the target region. The light irradiation amount deciding unit  82  decides one of the value of the chunk index value 1/α 2  in the target region and the value of the region index value 1/α 3  in the target region, by which the irradiation amount of light of the light source unit  60  is increased, as the region light irradiation value 1/α. The region light irradiation value 1/α is a value common to all the pixels  48  in the target region. When there are a plurality of target regions, the light irradiation amount deciding unit  82  calculates the region light irradiation value 1/α for all the target regions. 
     The process flow of calculating the region light irradiation value 1/α described above will be described below with reference to a flowchart.  FIG. 12  is a flowchart illustrating the region light irradiation value calculation process. In the signal processing unit  20 , the pixel index value calculating unit  74  calculates the pixel index values 1/α 1  of the respective pixels (step S 90 ). The region index value calculating unit  80  decides the region index value 1/α 3  for each target region based on the calculate pixel index values 1/α 1  of the respective pixels (step S 92 ). The chunk index value calculating unit  78  calculates the chunk index value 1/α 2  (step S 94 ) based on the calculate pixel index values 1/α 1  of the respective pixels. Here, the process of step S 92  and the process of step S 94  may be performed in parallel or sequentially. 
     When the chunk index value 1/α 2  and the region index value 1/α 3  are decided, the signal processing unit  20  determines whether or not there is a valid sample (step S 96 ). Specifically, it is determined whether or not the number of samples, that is, the number of samplings that can be determined to be valid as a result of analysis is larger than 0 (zero). In the signal processing unit  20 , when it is determined that there is no valid sample (No in step S 96 ), that is, when the number of valid samplings is determined to be 0 (zero), the light irradiation amount deciding unit  82  decides a predetermined default value as the region light irradiation value 1/α (step S 98 ), and then ends the current process. Here, for example, 8′h20 may be used as the default value. The valid sample is a group of pixels determined to be consecutive among the pixels at the sampling points, that is, a chunk. When there is no valid sample, it indicates that there is no pixel determined to be consecutive, that is, that no chunk has been detected. 
     When it is determined that there is a valid sample (Yes in step S 96 ), that is, that the number of valid samplings is 1 or more, the signal processing unit  20  determines whether or not the region index value 1/α 3  is larger than the chunk index value 1/α 2  (step S 100 ). In the signal processing unit  20 , when the region index value 1/α 3  is determined to be larger than the chunk index value 1/α 2  (Yes in step S 100 ), the light irradiation amount deciding unit  82  decides the region index value 1/α 3  as the region light irradiation value 1/α (step S 102 ), and then ends the current process. In the signal processing unit  20 , when the region index value 1/α 3  is determined to be the chunk index value 1/α 2  or less (No step S 100 ), the light irradiation amount deciding unit  82  decides the chunk index value 1/α 2  as the region light irradiation value 1/α (step S 104 ), and then ends the current process. That is, the signal processing unit  20  sets the larger value as the region light irradiation value 1/α. 
     Region Lighting Amount Decision Process 
     Next, a process of deciding a region lighting amount LA will be described. The LD storage unit  83  stores the luminance distribution information LD of the light source  62 . As illustrated in  FIGS. 3 and 4 , a plurality of light sources  62  differ in the luminance distribution (the intensity distribution of light). Thus a luminance value of the entire surface of the light source unit  60 , which is detected when each of the light sources  62  is turned on with a predetermined lighting amount, is stored as the luminance distribution information LD. The luminance distribution information will be described with reference to  FIGS. 13 and 14 . 
       FIG. 13  is a schematic diagram for describing the luminance distribution information. As illustrated in  FIG. 13 , the luminance distribution information LD is information obtained by dividing the image display surface (or the emission surface  102  of the light source unit  60 ) of the image display panel  40  into a plurality of regions  104 , that is, m×n regions (m is an arbitrary integer satisfying 1≦m≦P 0 , and n is an arbitrary integer satisfying 1≦n≦Q 0 ). And the luminance distribution information LD is information obtained by storing the luminance value (the intensity value of light) of the light source unit  60  detected for each region  104 . The number of regions  104  is arbitrarily set to the extent that the number of pixels is a maximum number. When the region  104  corresponds to one pixel, the luminance value of the pixel unit is stored in the luminance distribution information LD. When the region  104  corresponds to a plurality of pixels, a pixel at a predetermined position in the region  104  is set as a representative pixel, and the luminance value of the light source unit  60  in the representative pixel is stored. In the example of  FIG. 13 , a luminance value L 1  is set to the luminance value of the representative pixel of the region  104  inside a distribution line of luminance (L 1 ) indicating the luminance value L 1 . The LD storage unit  83  stores the luminance distribution information LD in which the luminance values of the m×n regions  104  are set in a table form for each light source  62 . In the following description, the luminance distribution information LD of the table form is referred to as a “light source look-up table LUT (LUT).” Since the light source look-up table LUT is information unique to the display device  10 , the light source look-up table LUT is generated in advance and stored in the LD storage unit  83 . 
       FIG. 14  is a diagram illustrating the light source look-up table. The light source look-up table LUT is prepared for each of the light sources  62 A to  62 J. A light source look-up table LUT A  is one in which the luminance value when only a light source  62 A is turned on is recorded in a table form by the m×n regions. Similarly, the same light source look-up table LUT is set for a light sources  62 B to  62 J. In  FIG. 14 , the light source look-up table LUT I  for the light source  621  and the light source look-up table LUT J  for the light source  62 J are illustrated. Using the luminance value of the representative pixel representing a predetermined region  104 , it is possible to reduce the size of the light source look-up table LUT and reduce a storage capacity of the LD storage unit  83 . When the luminance value of each pixel is unnecessary, it can be calculated by performing an interpolation operation. The light source look-up table LUT is information when one light source  62  is turned on, but, for example, a light source look-up table when a set of the light sources  62 A and  62 B or a set of the light sources  62 C and  62 D is simultaneously turned on may be generated and stored. Thus, it is possible to save a work of generating the light source look-up table LUT and reduce the storage capacity of the LD storage unit  83 . 
     The light source look-up table LUT may be set in a state in which the luminance value is corrected to correspond to luminance unevenness correction. Using the light source look-up table LUT, the luminance unevenness correction can be performed at the same time as decision of a lighting pattern. 
     The light irradiation amount deciding unit  82  decides the region lighting amount 1/α′ serving as the lighting amount (the lighting pattern) of each light source  62  based on the region light irradiation value 1/α and the light source look-up table LUT stored in the LD storage unit  83 . The region lighting amount 1/α′ may be obtained by an operation. The region lighting amount 1/α′ may be decided such that the tentative region lighting amount is set, and luminance distribution information at the time of driving with the tentative region lighting amount is calculated using the light source look-up table LUT, compared with the region light irradiation value 1/α, and corrected. The light irradiation amount deciding unit  82  generates the light source control signal SBL based on the region lighting amount 1/α′, and outputs the light source control signal SBL to the light source unit  60 . 
     The light irradiation amount deciding unit  82  calculates the pixel light irradiation amount 1/α 0  for each pixel, using the region lighting amount 1/α′ and the light source look-up table LUT stored in the LD storage unit  83 . The pixel light irradiation amount 1/α 0  is the luminance value (the irradiation amount of light) of the light source unit  60  when each light source  62  is turned on with the region lighting amount 1/α′. First, the luminance distribution information LD of the respective light sources at the time of driving when the light source  62  is turned on with the region lighting amount 1/α′ is calculated using the light source look-up table LUT. When information of the pixel unit is not obtained from the light source look-up table LUT, the interpolation operation is performed, and the luminance distribution information LD of the respective light sources at the time of driving is calculated. Then, the luminance distribution information LD of the respective light sources at the time of driving is combined to obtain the luminance distribution information LD of the light source  62  at the time of driving. The pixel light irradiation amount 1/α 0  is set to the calculated luminance distribution information LD of the sidelight light source  62  at the time of driving in units of pixels. 
     Output Signal Generation Process 
     Next, an output signal generation process will be described. First, the signal processing unit  20  calculates the expansion coefficient α 0  based on the value of the pixel light irradiation amount 1/α 0  through the expansion coefficient calculating unit  84 . The expansion coefficient α 0  is a reciprocal of the pixel light irradiation amount 1/α 0 . The expansion coefficient α 0  is a value set for each pixel. 
     The output signal generating unit  86  of the signal processing unit  20  generates an output signal (a signal value X 1-(p,q) ) of the first sub-pixel for determining a display gradation of the first sub-pixel  49 R. The output signal generating unit  86  of the signal processing unit  20  generates an output signal (a signal value X 2-(p,q) ) of the second sub-pixel for determining a display gradation of the second sub-pixel  49 G. The output signal generating unit  86  of the signal processing unit  20  generates an output signal (a signal value X 3-(p,q) ) of the third sub-pixel for determining a display gradation of the third sub-pixel  49 B. The output signal generating unit  86  of the signal processing unit  20  generates an output signal (signal value X 4-(p,q) ) of the fourth sub-pixel for determining a display gradation of the fourth sub-pixel  49 W. The output signal generating unit  86  of the signal processing unit  20  outputs the output signals to the image display panel driving unit  30 . The output signal generation process performed by the signal processing unit  20  will specifically be described below. 
     After the expansion coefficient α 0  is calculated, the output signal generating unit  86  of the signal processing unit  20  calculates an output signal value X 4-(p,q)  of the fourth sub-pixel, based on at least the input signal (the signal value x 1-(p,q)  of the first sub-pixel, the input signal (the signal value x 2-(p,q) ) of the second sub-pixel, and the input signal (the signal value x 3-(p,q) ) of the third sub-pixel. More specifically, the output signal generating unit  86  of the signal processing unit  20  calculates the output signal value X 4-(p,q)  of the fourth sub-pixel based on the product of Min (p,q)  and the expansion coefficient α 0 . Specifically, the signal processing unit  20  may obtain the signal value X 4-(p,q)  based on the following Equation (4). In Equation (4), the product of Min (p,q)  and the expansion coefficient α 0  is divided by χ, but the present invention is not limited thereto.
 
 X   4-(p,q) =Min (p,q) ·α 0 /χ  (4)
 
     χ is a constant depending on the display device  10 . No color filter is arranged for the fourth sub-pixel  49 W that displays white. The fourth sub-pixel  49 W that displays the fourth color is higher in brightness than the first sub-pixel  49 R that displays the first color, the second sub-pixel  49 G that displays the second color, and the third sub-pixel  49 B that displays the third color when they are irradiated with light with the same light source lighting amount. When a signal having a value corresponding to the maximum signal value of the output signal of the first sub-pixel  49 R is input to the first sub-pixel  49 R, a signal having a value corresponding to the maximum signal value of the output signal of the second sub-pixel  49 G is input to the second sub-pixel  49 G, and a signal having a value corresponding to the maximum signal value of the output signal of the third sub-pixel  49 B is input to the third sub-pixel  49 B, luminance of an aggregate of the first sub-pixel  49 R, the second sub-pixel  49 G, and the third sub-pixel  49 B included in the pixel  48  or a group of pixels  48  is assumed to be BN 1-3 . When a signal having a value corresponding to the maximum signal value of the output signal of the fourth sub-pixel  49 W is input to the fourth sub-pixel  49 W included in the pixel  48  or a group of pixels  48 , the luminance of the fourth sub-pixel  49 W is assumed to be BN 4 . That is, white of the maximum luminance is displayed by the aggregate of the first sub-pixel  49 R, the second sub-pixel  49 G, and the third sub-pixel  49 B, and the luminance of the white is indicated by BN 1-3 . In this case, when χ is a constant depending on the display device  10 , the constant χ is indicated by χ=BN 4 /BN 1-3 . 
     Specifically, the luminance BN 4  when the input signal having the display gradation value of 255 is assumed to be input to the fourth sub-pixel  49 W is, for example, 1.5 times the luminance BN 1-3  of white when the input signals having the display gradation values such as the signal value x 1-(p,q) =255, the signal value x 2-(p,q) =255, and the signal value x 3-(p,q) =255 are input to the aggregate of the first sub-pixel  49 R, the second sub-pixel  49 G, and the third sub-pixel  49 B. That is, in the first embodiment, χ=1.5. 
     Then, the output signal generating unit  86  of the signal processing unit  20  calculates the output signal (the signal value X 1-(p,q) ) of the first sub-pixel based on at least the input signal of the first sub-pixel (the signal value x 1-(p,q) ) and the expansion coefficient α 0 . The output signal generating unit  86  of the signal processing unit  20  calculates the output signal (the signal value X 2-(p,q) ) of the second sub-pixel based on at least the input signal (the signal value x 2-(p,q) ) of the second sub-pixel and the expansion coefficient α 0 . The output signal generating unit  86  of the signal processing unit  20  calculates the output signal (the signal value X 3-(p,q)  of the third sub-pixel based on at least the input signal (the signal value x 3-(p,q)  of the third sub-pixel and the expansion coefficient α 0 . 
     Specifically, the signal processing unit  20  calculates the output signal of the first sub-pixel based on the input signal of the first sub-pixel, the expansion coefficient α 0 , and the output signal of the fourth sub-pixel. The signal processing unit  20  calculates the output signal of the second sub-pixel based on the input signal of the second sub-pixel, the expansion coefficient α 0 , and the output signal of the fourth sub-pixel. The signal processing unit  20  calculates the output signal of the third sub-pixel based on the input signal of the third sub-pixel, the expansion coefficient α 0 , and the output signal of the fourth sub-pixel. 
     In other words, the signal processing unit  20  calculates the output signal value X 1-(p,q)  of the first sub-pixel, the output signal value X 2-(p,q)  of the second sub-pixel, and the output signal value X 3-(p,q)  of the third sub-pixel which are supplied to the (p,q)-th pixel  48  (or the set of the first sub-pixel  49 R, the second sub-pixel  49 G, and the third sub-pixel  49 B) using Equations (5) to (7), respectively, when χ is a constant depending on the display device  10 .
 
 X   1-(p,q) =α 0   ·x   1-(p,q)   −χ·X   4-(p,q)   (5)
 
 X   2-(p,q) =α 0   ·x   2-(p,q)   −χ·X   4-(p,q)   (6)
 
 X   3-(p,q) =α 0   ·x   3-(p,q)   −χ·X   4-(p,q)   (7)
 
As described above, the signal processing unit  20  generates the output signals of the sub-pixels  49 . Next, a method (expansion process) of obtaining the signal values X 1-(p,q) , X 2-(p,q) , X 3-(p,q) , and X 4-(p,q)  that are the output signals of the (p,q)-th pixel  48  will be described. The following processes are performed to keep a ratio of the luminance of the first primary color displayed by (the first sub-pixel  49 R+the fourth sub-pixel  49 W), the luminance of the second primary color displayed by (the second sub-pixel  49 G+the fourth sub-pixel  49 W), and the luminance of the third primary color displayed by (the third sub-pixel  49 B+the fourth sub-pixel  49 W). The processes are performed to keep (maintain) a color tone as well. In addition, the processes are performed to keep (maintain) gradation-luminance characteristics (gamma characteristics, γ characteristics). When all of the input signal values are 0 or small values in any one of the pixels  48  or a group of the pixels  48 , the expansion coefficient α 0  may be obtained without including such a pixel  48  or a group of pixels  48 .
 
     First Process 
     First, in the signal processing unit  20 , the expansion coefficient calculating unit  84  calculates the expansion coefficient α 0  for each pixel based on the pixel light irradiation amount 1/α 0  of the target region. 
     Second Process 
     Then, the signal processing unit  20  calculates the signal value X 4-(p,q)  in the (p,q)-th pixel  48  based on at least the signal value x 1-(p,q) , the signal value x 2-(p,q) , and the signal value x 3-(p,q) . In the first embodiment, the signal processing unit  20  decides the signal value X 4-(p,q)  based on Min (p,q) , the expansion coefficient α 0 , and the constant χ. More specifically, the signal processing unit  20  calculates the signal value X 4-(p,q)  based on Equation (4) as described above. The signal processing unit  20  calculates the signal value X 4-(p,q)  for all the pixels  48  in the target region. 
     Third Process 
     Then, the signal processing unit  20  obtains the signal value X 1-(p,q)  in the (p,q)-th pixel  48  based on the signal value x 1-(p,q) , the expansion coefficient α 0 , and the signal value X 4-(p,q) . The signal processing unit  20  obtains the signal value X 2-(p,q)  in the (p,q)-th pixel  48  based on the signal value x 2-(p,q) , the expansion coefficient α 0 , and the signal value X 4-(p,q) . The signal processing unit  20  obtains the signal value X 3-(p,q)  in the (p,q)-th pixel  48  based on the signal value x 3-(p,q) , the expansion coefficient α 0 , and the signal value X 4-(p,q) . Specifically, the signal processing unit  20  obtains the signal value X 1-(p,q) , the signal value X 2-(p,q) , and the signal value X 3-(p,q)  in the (p,q)-th pixel  48  based on Equations (5) to (7) described above. 
     The output signal generating unit  86  of the signal processing unit  20  generates the output signals for each target region through the above process, and outputs the generated output signals to the image display panel driving unit  30 . 
     As described above, in the display device  10 , the signal processing unit  20  includes the pixel index value calculating unit  74  that calculates the pixel index value 1/α 1  based on the input signal for each pixel. The signal processing unit  20  includes the chunk determining unit  76  that performs the consecutiveness determination which determines whether or not the pixel, having the pixel index value 1/α 1  between the upper boundary value Up and the lower boundary value Bo is consecutive to the starting pixel  48   s , and determines the regions of the pixels determined to be consecutive as a chunk. The signal processing unit  20  includes the chunk index value calculating unit  78  that calculates the chunk index value 1/α 2  based on the pixel index values 1/α 1  of the pixels  48  included in the chunk. The signal processing unit  20  includes the region index value calculating unit  80  that calculates the region index value 1/α 3  based on the pixel index values 1/α 1  of all the pixels  48  in the target region. The signal processing unit  20  includes the light irradiation amount deciding unit  82  compares the chunk index value 1/α 2  with the region index value 1/α 3 , and decides the irradiation amount of light (the region light irradiation value 1/α) of the light source unit in the target region based on the value by which the irradiation amount of light is increased. 
       FIGS. 15 and 16  are explanatory diagrams for describing an example of the irradiation amount of light of the pixel displayed on the display device. The display device  10  can suppress the occurrence of the deterioration in the display quality, by using the chunk index value 1/α 2  calculated by performing the chunk detection in addition to the region index value 1/α 3  calculated using a predetermined algorithm when the region light irradiation value 1/α indicating the irradiation amount of light from the light source unit  60  is calculated. In other words, as in a region  170  illustrated in  FIG. 15 , when the reduction amount of electric power is reduced and the display quality is maintained by the predetermined algorithm, there is no change. Whereas as in a region  180  illustrated in  FIG. 16 , when the reduction amount of electric power is increased and the display quantity is deteriorated by the predetermined algorithm, the display quality can be maintained by reducing the reduction amount of electric power through the chunk detection. In the case of an image illustrated in  FIG. 15 , the region index value 1/α 3  is calculated in association with a predetermined number or more of pixels  172  that are dispersed, by using a predetermined algorithm. The chunk index value 1/α 2  is calculated in association with a pixel  174  (chunk) serving as an aggregate of pixels through the chunk index value calculating unit  78 . As the region index value 1/α 3  has the higher value, the region index value 1/α 3  is decided as the region light irradiation value 1/α of the region  170 . In the case of an image illustrated in  FIG. 16 , the region index value 1/α 3  is calculated in association with a predetermined number or more of pixels  186  using a predetermined algorithm. And the chunk index value 1/α 2  is calculated in association with a pixel  184  (chunk) serving as an aggregate of pixels through the chunk index value calculating unit  78 . As the chunk index value 1/α 2  has the higher value, the chunk index value 1/α 2  is decided as the region light irradiation value 1/α of the region  180 . Thus, the chunk determining unit  76  can appropriately detect a case in which the pixels that are small in number but have the high pixel index value 1/α 1  are aggregated as illustrated in  FIG. 16 , so as to reduce the power consumption while suppressing the deterioration in the display quality. It is possible to detect the chunk through the simple process using the determination based on the consecutiveness of the pixel. 
     The display device  10  determines the pixel  48 , as the consecutive pixel, in which the pixel index value 1/α 1  is within a predetermined range (between the upper boundary value Up and the lower boundary value Bo) from the value of the pixel index value 1/α 1  of the starting pixel  48   s . In other words, the display device  10  decides a boundary value for deciding whether or not the pixel is consecutive, based on the pixel index value 1/α 1  of the starting pixel  48   s . For example, when the boundary value for deciding whether or not the pixel is consecutive is decided regardless of the pixel index value 1/α 1  of the starting pixel  48   s , even the pixel having the pixel index value 1/α 1  close to that of the starting pixel  48   s  is determined to be inconsecutive when it is out of the range of the boundary value. However, the display device  10  decides the boundary value based on the pixel index value 1/α 1  of the starting pixel  48   s  and thus can appropriately determine whether or not a pixel having the pixel index value 1/α 1  close to the value is consecutive. Thus, the display device  10  can appropriately perform the chunk detection and reduce the power consumption while suppressing the deterioration in the display quality. 
     The chunk determining unit  76  performs the consecutiveness determination on the pixels in the determination direction Z from the starting pixel  48   s  sequentially along the determination direction Z. The chunk determining unit  76  determines the determination pixel  48   u  to be consecutive from the starting pixel  48   s  when the pixel index value 1/α 1  of the immediately previous pixel  48   t  serving as the pixel that has undergone the consecutiveness determination immediately before the determination pixel  48   u  is between the upper boundary value Up and the lower boundary value Bo. The pixel index value 1/α 1  of the determination pixel  48   u  is the value between the upper boundary value Up and the lower boundary value Bo. When the pixels  48  at all the sampling point from the starting pixel  48   s  to the determination pixel  48   u  are determined to be consecutive, the chunk determining unit  76  determines the determination pixel  48   u  to be consecutive. Thus, the display device  10  can more appropriately perform the consecutiveness determination. 
     When the pixel is determined to be inconsecutive in the consecutiveness determination, the chunk determining unit  76  suspends the consecutiveness determination, and resumes the consecutiveness determination using the pixel determined to be inconsecutive as the starting pixel. The chunk determining unit  76  newly resumes the consecutiveness determination after the consecutiveness determination is suspended and thus can detect, for example, even a plurality of groups of pixels that differ in luminance and are included in the screen as a chunk. Thus, the display device  10  can perform the chunk detection more appropriately. 
     The chunk index value calculating unit  78  decides the maximum value among the pixel index values 1/α 1  of the respective pixels included in the chunk as the chunk index value 1/α 2 . The chunk index value calculating unit  78  can increase the value of the chunk index value 1/α 2  and thus more appropriately reduce the power consumption while suppressing the deterioration in the display quality. 
     The chunk determining unit  76  performs the chunk determination in the horizontal direction.  FIGS. 17 to 19  are explanatory diagrams for describing an example in which the horizontal-direction chunk determination is performed. The chunk determining unit  76  can determine a region  116  in which pixels  114  having the high pixel index value 1/α 1  are consecutive in the horizontal direction as illustrated in  FIG. 17  as a chunk by performing the horizontal-direction process illustrated in  FIG. 10 . Specifically, the pixel index value 1/α 1  at a sampling point  112  in the region  116  is determined to be consecutive and determined as a chunk. The pixel  114  having the high pixel index value 1/α 1  is, for example, a pixel in which gradations of two color components of three colors, that is, primary colors of yellow, green, and red or RGB are high, and a gradation of the remaining one component is close to 0 (zero) in an image having a high saturation. The chunk determining unit  76  determines that there is no chunk in a region  119  in which the pixels  114  having the high pixel index value 1/α 1  are inconsecutive as illustrated in  FIG. 17  by performing the horizontal-direction process illustrated in  FIG. 10 . 
       FIG. 18  illustrates an example in which a chunk  122  in which the pixels  114  having the high pixel index value 1/α 1  are aggregated straddles a plurality of regions  104  surrounded by a range  120 .  FIG. 19  is an enlarged view of the range  120 . The chunk determining unit  76  performs the horizontal-direction process illustrated in  FIG. 10  and holds the pixel index value 1/α 1  and the flag even after it has reached the boundary in the horizontal direction. Thus, even when the chunk  122  extends from the neighboring regions  104  as illustrated in  FIGS. 18 and 19 , the chunk determination result is held to be beyond the parting line  106  in the horizontal direction as indicated by a solid line  124 , and thus the chunk in the adjacent region  104  can reliably be detected. 
     The chunk determining unit  76  performs the chunk determination in the vertical direction.  FIG. 20  is an explanatory diagram for describing an example in which the vertical-direction chunk determination is performed. The chunk determining unit  76  can determine that a chunk of regions  150 ,  152 , and  154  in which the pixels  114  having the high pixel index value 1/α 1  are consecutive in the vertical direction as illustrated in  FIG. 20  is a chunk by performing the vertical-direction process illustrated in  FIG. 11 . The chunk determining unit  76  determines that regions  156 ,  158 , and  158  in which the pixels  114  having the high pixel index value 1/α 1  are inconsecutive in the vertical direction are not a chunk by performing the process illustrated in  FIG. 11 . 
     Second Embodiment 
     Next, a second embodiment will be described. A display device  10 A according to the second embodiment differs from that of the first embodiment in a determination method of the consecutiveness determination. In the second embodiment, a description of portions common to those of the first embodiment will be omitted. 
     The chunk determining unit  76  arranged in the display device  10 A according to the second embodiment differs from the chunk determining unit  76  according to the first embodiment in the consecutiveness determination value for the consecutiveness determination. The consecutiveness determination value according to the first embodiment includes the upper boundary value Up and the lower boundary value Bo. But the consecutiveness determination value according to the second embodiment includes a temporary boundary value Te, an upper limit boundary value L up , and a lower limit boundary value L bo  in addition to the upper boundary value Up and the lower boundary value Bo. 
     The chunk determining unit  76  calculates the upper boundary value Up and the lower boundary value Bo based on the pixel index value 1/α 1  of the starting pixel  48   s  through the same method as in the first embodiment. When there is an immediately previous pixel  48   t  that has undergone the consecutiveness determination immediately before the determination pixel  48   u , the chunk determining unit  76  calculates the temporary boundary value Te based on the pixel index value 1/α 1  of the immediately previous pixel  48   t . The temporary boundary value Te is a value that is out of the range between the upper boundary value Up and the lower boundary value Bo and differs from the pixel index value 1/α 1  of the immediately previous pixel  48   t  by a predetermined value A 3 . The predetermined value A 3  is a previously set value that is equal to the predetermined values A 1  and A 2 , serving as the difference between the upper boundary value Up and the pixel index value 1/α 1  of the starting pixel  48   s , and the difference between the lower boundary value Bo and the pixel index value 1/α 1  of the starting pixel  48   s . But the predetermined value A 3  is not limited thereto and may be a different value or may be changed, for example, according to a setting of an operator or the like. 
     The chunk determining unit  76  decides a value larger than the upper boundary value Up as the temporary boundary value Te, when the pixel index value 1/α 1  of the immediately previous pixel  48   t  is larger than the pixel index value 1/α 1  of the starting pixel  48   s . The chunk determining unit  76  decides a value smaller than the lower boundary value Bo as the temporary boundary value Te when the pixel index value 1/α 1  of the immediately previous pixel  48   t  is smaller than the pixel index value 1/α 1  of the starting pixel  48   s.    
     Although the pixel index value 1/α 1  of the determination pixel  48   u  is not the value between the upper boundary value Up and the lower boundary value Bo, when the pixel index value 1/α 1  of the determination pixel  48   u  is the value between the pixel index value 1/α 1  of the immediately previous pixel  48   t  and the temporary boundary value Te, the chunk determining unit  76  determines the determination pixel  48   u  to be the pixel consecutive to the starting pixel  48   s . In further detail, when the temporary boundary value Te is a value larger than the upper boundary value Up (the pixel index value 1/α 1  of the immediately previous pixel  48   t  is larger than the pixel index value 1/α 1  of the starting pixel  48   s ), the chunk determining unit  76  determines the determination pixel  48   u  to be the pixel consecutive to the starting pixel  48   s , if the pixel index value 1/α 1  of the determination pixel  48   u  is a value between the lower boundary value Bo and the temporary boundary value Te (equal to or larger than the lower boundary value Bo and equal to or less than the temporary boundary value Te). When the temporary boundary value Te is a value larger than the lower boundary value Bo (the pixel index value 1/α 1  of the immediately previous pixel  48   t  is smaller than the pixel index value 1/α 1  of the starting pixel  48   s ), the chunk determining unit  76  determines the determination pixel  48   u  to be the pixel consecutive to the starting pixel  48   s , if the pixel index value 1/α 1  of the determination pixel  48   u  is a value between the upper boundary value Up and the temporary boundary value Te (equal to or larger than the temporary boundary value Te and equal to or less than the upper boundary value Up). 
     As described above, the temporary boundary value Te is an extended boundary value that is applied only to the pixel  48  that undergoes the consecutiveness determination after the immediately previous pixel  48   t , based on the pixel index value 1/α 1  of the immediately previous pixel  48   t . Since the temporary boundary value Te is calculated based on the pixel index value 1/α 1  of the immediately previous pixel  48   t , the temporary boundary value Te may differ according to the sampling point. 
     In addition, the chunk determining unit  76  calculates the upper limit boundary value L up  and the lower limit boundary value L bo  based on the pixel index value 1/α 1  of the starting pixel  48   s . The upper limit boundary value L up  is a value larger than the upper boundary value Up, and the lower limit boundary value L bo  is a value smaller than the lower boundary value Bo. The chunk determining unit  76  decides a value larger than the upper boundary value Up by a predetermined value A 4  as the upper limit boundary value L up . The chunk determining unit  76  decides a value smaller than the lower boundary value Bo by a predetermined value A 5  as the lower limit boundary value L bo . The predetermined values A 4  and A 5  are a previously set value that is equal to the predetermined values A 1  and A 2 , but the predetermined values A 4  and A 5  are not limited thereto and may be a different value or may be changed, for example, a setting or an operator or the like. 
     Although the pixel index value 1/α 1  of the determination pixel  48   u  is the value between the pixel index value 1/α 1  of the immediately previous pixel  48   t  and the temporary boundary value Te, when the pixel index value 1/α 1  of the determination pixel  48   u  is a value out of the range between the upper limit boundary value L up  and the lower limit boundary value L bo  (equal to or larger than the lower limit boundary value L bo  and equal to or less than the upper limit boundary value L up ), the chunk determining unit  76  determines the determination pixel  48   u  to be inconsecutive to the starting pixel  48   s . In other words, the chunk determining unit  76  increases the consecutiveness determination range through the temporary boundary value Te, while limiting an upper limit value and a lower limit value of an increased consecutiveness determination to the upper limit boundary value L up  and the lower limit boundary value L bo . 
       FIG. 21  is an explanatory diagram illustrating an example for describing the consecutiveness determination according to the second embodiment. An example of the consecutiveness determination according to the second embodiment will be described with reference to  FIG. 21 . In  FIG. 21 , a horizontal axis indicates each pixel  48  at the sampling point, and a vertical axis indicates the pixel index value 1/α 1  of each pixel  48  at the sampling point. In other words,  FIG. 21  illustrates the pixel index value 1/α 1  of each pixel  48  at the sampling point, similarly to  FIG. 8 . 
     When the consecutiveness determination is performed by selecting the pixel  48   a1  as the starting pixel  48   s  as illustrated in  FIG. 21 , the chunk determining unit  76  calculates the upper boundary value Up a1  and the lower boundary value Bo a1 , an upper limit boundary value L upa1 , and a lower limit boundary value L boa1  of the pixel  48   a1 , based on the pixel index value 1/α 1  of the pixel  48   a1 . 
     The chunk determining unit  76  determines whether or not the pixel at each sampling point is consecutive to the pixel  48   a1  in the determination direction Z of the pixel  48   a1 . The pixels  48   a2  and  48   a3  are consecutive to the pixel  48   a1  since the pixel index value 1/α 1  is a value between the upper boundary value Up a1  and the lower boundary value Bo a1  of the pixel  48   a1 . 
     On the other hand, in the pixel  48   a4 , the pixel index value 1/α 1  is larger than the upper boundary value Up a1 . The pixel index value 1/α 1  of the pixel  48   a4  is a value that is equal to or less than a temporary boundary value Te a4  calculated based on the pixel index value 1/α 1  of the pixel  48   a3  serving as the immediately previous pixel and equal to or less than the upper limit boundary value L upa1 . Thus, the pixel index value 1/α 1  of the pixel  48   a4  is not the value between the upper boundary value Up a1  and the lower boundary value Bo a1 , but the value between the pixel index value 1/α 1  of the pixel  48   a3  and the temporary boundary value Te a4 , the pixel  48   a4  is determined to be consecutive to the pixel  48   a1 . 
     The pixel index value 1/α 1  of the pixel  48   a5  is a value that is larger than the upper boundary value Up a1  and equal to or less than a temporary boundary value Te a5  calculated based on the pixel index value 1/α 1  of the pixel  48   a4  serving as the immediately previous pixel. The pixel index value 1/α 1  of the pixel  48   a5  is larger than the upper limit boundary value L upa1 . In other words, since the pixel index value 1/α 1  of the pixel  48   a5  is the value between the pixel index value 1/α 1  of the pixel  48   a4  and the temporary boundary value Te a5  but not the value between the upper limit boundary value L upa1  and the lower limit boundary value L boa1 , the pixel  48   a5  is determined to be inconsecutive to the pixel  48   a1 . Even when the pixel index value 1/α 1  is the value between the upper limit boundary value L upa1  and the lower limit boundary value L boa1  or even when the pixel index value 1/α 1  is not the value between the pixel index value 1/α 1  of the immediately previous pixel  48  and the temporary boundary value Te, the pixel is determined to be inconsecutive. 
     The chunk determining unit  76  determines pixels from the pixels  48   a1  to the pixel  48   a4  to be consecutive, determines the pixel  48   a5  to be inconsecutive, and suspends the consecutiveness determination. The chunk determining unit  76  resumes the consecutiveness determination using the pixel  48   a5  as the new starting pixel  48   s.    
     The above-described consecutiveness determination process according to the second embodiment will be described with reference to flowcharts. First, the consecutiveness determination value calculation method will be described.  FIG. 22  is a flowchart for describing the consecutiveness determination value calculation method according to the second embodiment.  FIG. 22  is a flowchart for describing the calculation method according to the second embodiment in detail in the calculation of the consecutiveness determination value in step S 25  of  FIG. 10  and step S 65  of  FIG. 11 . As illustrated in  FIG. 22 , in the calculation of the consecutiveness determination value, the chunk determining unit  76  decides (calculates) the upper boundary value Up and the lower boundary value Bo based on the pixel index value 1/α 1  of the starting pixel  48   s  (step S 110 ). And the chunk determining unit  76  decides (calculates) the upper limit boundary value L up  and the lower limit boundary value L bo  based on the pixel index value 1/α 1  of the starting pixel  48   s  (step S 112 ). Step S 112  may be performed at the same time as step S 110 . 
     After the upper limit boundary value L up  and the lower limit boundary value L bo  are calculated, the chunk determining unit  76  determines whether or not there is an immediately previous pixel  48   t  that has undergone the consecutiveness determination immediately before the pixel that undergoes the consecutiveness determination (step S 114 ). When it is determined that there is the immediately previous pixel  48   t  (Yes in step S 114 ), the chunk determining unit  76  decides (calculates) the temporary boundary value Te based on the pixel index value 1/α 1  of the immediately previous pixel  48   t  (step S 116 ), and ends the consecutiveness determination value calculation process. Even when it is determined that there is no immediately previous pixel  48   t  (No in step S 114 ), the chunk determining unit  76  ends the consecutiveness determination value calculation process. Step S 114  may be performed only when it is determined that there is the immediately previous pixel  48   t.    
     Next, the consecutiveness determination method will be described.  FIG. 23  is a flowchart for describing the consecutiveness determination value calculation method according to the second embodiment.  FIG. 23  is a flowchart for describing the consecutiveness determination method according to the second embodiment in detail in the consecutiveness determination method in step S 28  of  FIG. 10  and step S 70  of  FIG. 11 . As illustrated in  FIG. 23 , the chunk determining unit  76  determines whether or not a relation of the lower boundary value Bo≦the pixel index value 1/α 1  of the sampling point≦the upper boundary value Up is satisfied (step S 120 ). When the relation of the lower boundary value Bo≦the pixel index value 1/α 1  of the sampling point≦the upper boundary value Up is satisfied (Yes in step S 120 ), the chunk determining unit  76  determines the pixel at the sampling point to be consecutive (step S 122 ), and then ends the process. 
     When the relation of the lower boundary value Bo≦the pixel index value 1/α 1  of the sampling point≦the upper boundary value Up is determined to be not satisfied (No in step S 120 ), the chunk determining unit  76  determines whether or not a relation of the lower limit boundary value L bo ≦the pixel index value 1/α 1  of the sampling point≦the upper limit boundary value L up  is satisfied (step S 124 ). When the relation of the lower limit boundary value L bo ≦the pixel index value 1/α 1  of the sampling point≦the upper limit boundary value L up  is not satisfied (No in step S 124 ), the chunk determining unit  76  determines the pixel at the sampling point to be inconsecutive (step S 126 ), and then ends the process. 
     When the relation of the lower limit boundary value L bo ≦the pixel index value 1/α 1  of the sampling point≦the upper limit boundary value L up  is satisfied (Yes in step S 124 ), the chunk determining unit  76  determines whether or not the pixel index value 1/α 1  of the sampling point is a value between the temporary boundary value Te and the pixel index value 1/α 1  of the immediately previous pixel  48   t  (step S 128 ). When the pixel index value 1/α 1  of the sampling point is the value between the temporary boundary value Te and the pixel index value 1/α 1  of the immediately previous pixel  48   t  (Yes in step S 128 ), the chunk determining unit  76  determines the pixel at the sampling point to be consecutive (step S 122 ), and then ends the process. When the pixel index value 1/α 1  of the sampling point is not the value between the temporary boundary value Te and the pixel index value 1/α 1  of the immediately previous pixel  48   t  (No in step S 128 ), the chunk determining unit  76  determines the pixel at the sampling point to be inconsecutive (step S 126 ), and then ends the process. 
     As described above, the chunk determining unit  76  of the display device  10 A according to the second embodiment determines the determination pixel  48   u  to be consecutive from the starting pixel  48   s , when the pixel index value 1/α 1  of the determination pixel  48   u  is a value between the pixel index value 1/α 1  of the immediately previous pixel  48   t  and the temporary boundary value Te. When the pixel index value 1/α 1  of the determination pixel  48   u  is not the value between the upper boundary value Up and the lower boundary value Bo but the value within the range of the temporary boundary value Te, the chunk determining unit  76  determines the determination pixel  48   u  to be consecutive. When the pixel index value 1/α 1  is the value that is apart from the starting pixel  48   s  but close to the pixel index value 1/α 1  of the immediately previous pixel  48   t  that has undergone the consecutiveness determination immediately previously, the chunk determining unit  76  determines the pixel to be consecutive. Thus, the chunk determining unit  76  can more appropriately perform the chunk detection. 
     The temporary boundary value Te is the value larger than the upper boundary value Up when the pixel index value 1/α 1  of the immediately previous pixel  48   t  is larger than the pixel index value 1/α 1  of the starting pixel  48   s . And the temporary boundary value Te is the value smaller than the lower boundary value Bo when the pixel index value 1/α 1  of the immediately previous pixel  48   t  is smaller than the pixel index value 1/α 1  of the starting pixel  48   s . The chunk determining unit  76  can appropriately increase the value range of the pixel index value 1/α 1  determined to be consecutive through the temporary boundary value Te and thus can more appropriately perform the chunk detection. 
     The chunk determining unit  76  determines the determination pixel  48   u  to be inconsecutive from the starting pixel  48   s , when the pixel index value 1/α 1  of the determination pixel  48   u  is the value that is between the pixel index value 1/α 1  of the immediately previous pixel  48   t  and the temporary boundary value Te, but out of the range between the lower limit boundary value L bo  and the upper limit boundary value L up . The chunk determining unit  76  increases the value range of the pixel index value 1/α 1  determined to be consecutive through the temporary boundary value Te and limits the lower limit boundary value L bo  and the upper limit boundary value L up . The chunk determining unit  76  can increase the value range of the pixel index value 1/α 1  determined to be consecutive to an appropriate range and thus can more appropriately perform the chunk detection. 
     Third Embodiment 
     Next, a third embodiment will be described. A display device  10 B according to the third embodiment differs from that of the first embodiment in the calculation method of the chunk index value 1/α 2 . In the third embodiment, a description of portions common to those of the first embodiment will be omitted. 
     A chunk index value calculating unit  78 B arranged in the display device  10 B according to the third embodiment decides a value between a maximum value and a minimum value of the pixel index values 1/α 1  of all the pixels  48  included in the chunk, as the chunk index value 1/α 2 . In further detail, the chunk index value calculating unit  78 B calculates the chunk index value 1/α 2  of the chunk based on an average of the pixel index values 1/α 1  of all the pixels  48  included in the chunk. Specifically, the chunk index value calculating unit  78 B decides an addition average value of the pixel index values 1/α 1  of all the pixels  48  included in the chunk as the chunk index value 1/α 2  of the chunk as indicated in the following Equation (8). 
     
       
         
           
             
               
                 
                   
                     1 
                     / 
                     
                       α 
                       2 
                     
                   
                   = 
                   
                     
                       ∑ 
                       
                         k 
                         = 
                         1 
                       
                       n 
                     
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       
                         ( 
                         
                           1 
                           / 
                           
                             α 
                             
                               1 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               ak 
                             
                           
                         
                         ) 
                       
                       n 
                     
                   
                 
               
               
                 
                   ( 
                   8 
                   ) 
                 
               
             
           
         
       
     
     In Equation (8), n indicates the number of pixels  48  included in the chunk, that is, the number of pixels determined to be consecutive including the starting pixel  48   s . In Equation (8), 1/α 1ak  indicates the pixel index value 1/α 1  of any one of the pixels  48  of the chunk including the starting pixel  48   s.    
     The chunk index value calculating unit  78 B decides the addition average value of the pixel index values 1/α 1  of all the pixels  48  included in the chunk as the chunk index value 1/α 2  of the chunk as described above. But the present invention is not limited thereto, and, for example, a value obtained by adding a predetermined coefficient to the addition average value or by multiplying the addition average value by a predetermined coefficient or a value calculated using any other averaging process may be decided as the chunk index value 1/α 2  of the chunk. 
     The chunk index value calculating unit  78 B preferably decide the value between the maximum value and the minimum value of the pixel index values 1/α 1  of all the pixels  48  included in the chunk, as the chunk index value 1/α 2  of the chunk. The chunk index value calculating unit  78 B may calculates the chunk index value 1/α 2  based on a differential average value calculated by averaging differences between the pixel index value 1/α 1  of the determination pixel  48   u  and the pixel index value 1/α 1  of the starting pixel  48   s , and the pixel index value 1/α 1  of the starting pixel, for example. Here, the differential average value is a value obtained by calculating the difference value between the pixel index value 1/α 1  of the determination pixel  48   u  and the pixel index value 1/α 1  of the starting pixel  48   s  for each of the pixels  48  included in the chunk, and averaging the difference values. The chunk index value calculating unit  78 B calculates the chunk index value 1/α 2  by adding the differential average value to the pixel index value 1/α 1  of the starting pixel, for example. Specifically, the chunk index value calculating unit  78 B calculates the chunk index value 1/α 2  based on the following Equation (9), for example. 
     
       
         
           
             
               
                 
                   
                     1 
                     / 
                     
                       α 
                       2 
                     
                   
                   = 
                   
                     
                       1 
                       / 
                       
                         α 
                         
                           1 
                           ⁢ 
                           a 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           0 
                         
                       
                     
                     + 
                     
                       
                         ∑ 
                         
                           k 
                           = 
                           1 
                         
                         n 
                       
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         
                           ( 
                           
                             
                               1 
                               / 
                               
                                 α 
                                 
                                   1 
                                   ⁢ 
                                   ak 
                                 
                               
                             
                             - 
                             
                               1 
                               / 
                               
                                 α 
                                 
                                   1 
                                   ⁢ 
                                   a 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   0 
                                 
                               
                             
                           
                           ) 
                         
                         
                           2 
                           ⁢ 
                           m 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   9 
                   ) 
                 
               
             
           
         
       
     
     1/α 1a0  in Equation (9) indicates the pixel index value 1/α 1  of the starting pixel  48   s , and 1/α 1ak  in Equation (9) indicates the pixel index value 1/α 1  of any one of the pixels  48  of the chunk including no starting pixel  48   s . In Equation (9), m indicates a value indicated by the following Equation (10).
 
 m= 1 (when  n= 1)
 
 m= 2 N  (when  n≧ 2)  (10)
 
     In Equation (10), N indicates a value indicated by the following Equation (11).
 
 N =Ceiling(√{square root over ( n )})  (11)
 
     In Equation (11), a function Ceiling(x) is a ceiling function for calculating a maximum integer having a value that does not exceed x. In other words, in Equation (11), N is a maximum integer that does not exceed a square root of n. 
     As described above, the chunk index value calculating unit  78 B uses a value of each factorial of 2 as m when the chunk index value 1/α 2  of the chunk is calculated based on Equation (9). Thus, the chunk index value calculating unit  78 B can suppress an operation capacity when the chunk index value 1/α 2  of the chunk is calculated based on Equation (9). When the number of consecutive pixels  48  is a predetermined number or more (when n is a predetermined value or more), the chunk index value calculating unit  78 B may calculate the chunk index value 1/α 2  using Equation (9) for the pixels  48  corresponding to the predetermined number or less. And the chunk index value calculating unit  78 B may decide the chunk index value 1/α 2  as the chunk index value 1/α 2  of the chunk. In this case, the predetermined number is, for example, 63 but not limited thereto. In this case, the chunk index value calculating unit  78 B can suppress the increase in an operand and thus suppress an operation capacity. In addition, since the operation is performed up to the predetermined number, a reduction in operation accuracy can be suppressed. In the chunk index value calculating unit  78 B, the calculation method of the chunk index value 1/α 2  is not limited to Equation (9) as long as the chunk index value 1/α 2  is calculated based on the differential average value and the pixel index value 1/α 1  of the starting pixel. 
     As described above, the chunk index value calculating unit  78 B decides the value between the maximum value and the minimum value of the pixel index values 1/α 1  of all the pixels  48  included in the chunk, as the chunk index value 1/α 2  of the chunk. The chunk index value calculating unit  78 B calculates the chunk index value 1/α 2  of the chunk based on the values of the pixel index values 1/α 1  of all the pixels  48  included in the chunk and thus can more appropriately reduce the power consumption while suppressing the deterioration in the display quality. 
     The chunk index value calculating unit  78 B calculates the chunk index value 1/α 2  based on the average of the pixel index values 1/α 1  of the pixels  48  of the chunk. The chunk index value calculating unit  78 B calculates the chunk index value 1/α 2  of the chunk based on the average of the pixel index values 1/α 1  of all the pixels  48  included in the chunk and thus can more appropriately reduce the power consumption while suppressing the deterioration in the display quality. 
     The chunk index value calculating unit  78 B may calculate the chunk index value 1/α 2  based on the differential average value, which is calculated by averaging the differences between the pixel index values 1/α 1  of the pixels  48  of the chunk and the pixel index value 1/α 1  of the starting pixel  48   s , and the pixel index value 1/α 1  of the starting pixel  48   s . The chunk index value calculating unit  78 B calculates the chunk index value 1/α 2  of the chunk based on the differential average value and thus can more appropriately reduce the power consumption while suppressing the deterioration in the display quality. 
     Application Examples 
     Next, an application example of the display device  10  according to the first embodiment will be described with reference to  FIGS. 24 and 25 .  FIGS. 24 and 25  are diagrams illustrating an example of an electronic apparatus to which the display device according to the first embodiment is applied. The display device  10  according to the first embodiment is applicable to electronic apparatuses of all fields such as car navigation systems illustrated in  FIG. 24 , television apparatuses, digital cameras, laptop personal computers, portable electronic apparatuses such as a mobile phone illustrated in  FIG. 25 , or video cameras. In other words, the display device  10  according to the first embodiment is applicable to electronic apparatuses of all fields that display video signals input from the outside or internally generated video signals as an image or video. The electronic apparatus includes the control device  11  (see  FIG. 1 ) that supplies the video signals to the display device and controls the operation of the display device. The present application example may also be applicable to the display devices according to the other embodiments described above in addition to the display device  10  according to the first embodiment. 
     The electronic apparatus illustrated in  FIG. 24  is a car navigation apparatus to which the display device  10  according to the first embodiment is applied. The display device  10  is installed on a dashboard  300  in a vehicle. Specifically, the display device  10  is installed on a portion of the dashboard  300  between a driver seat  311  and a passenger seat  312 . The display device  10  of the car navigation apparatus is used to perform a navigation display, a music operation screen display, a video reproduction display, or the like. 
     An electronic apparatus illustrated in  FIG. 25  is a portable information terminal to which the display device  10  according to the first embodiment is applied and that operates as a mobile computer, a multi-functional mobile phone, a mobile computer with a voice call function, or a mobile computer with a communication function and is also called a smartphone or a tablet terminal. The portable information terminal includes a display unit  561  on the surface of a housing  562 , for example. The display unit  561  includes the display device  10  according to the first embodiment and a touch detection (so-called a touch panel) function capable of detecting an external proximity object. 
     The exemplary embodiments according to the present invention have been described above, but the embodiments are not limited to content thereof. The components described above include components that are easily conceivable by those skilled in the art, substantially the same components, and equivalent ones. The components described above can appropriately be combined as well. In addition, various omissions, replacements or changes of the components can be made without departing from the gist of the embodiments described above.