Patent Publication Number: US-9835909-B2

Title: Display device having cyclically-arrayed sub-pixels

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a Continuation of application Ser. No. 14/711,013, filed May 13, 2015, and claims priority from Japanese Application No. 2014-102869, filed on May 16, 2014, the contents of which are incorporated by reference herein in their entirety. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present invention relates to display devices. 
     2. Description of the Related Art 
     In recent years, demand for display devices in mobile devices such as cellular phones and electronic paper has been increasing. In a display device, a single pixel includes a plurality of sub pixels and the sub pixels each emit light in colors different from one another, and by switching the display of the respective sub pixels on and off, various colors are displayed with one pixel. In such a display device, display characteristics such as resolution and luminance have been improved year after year. However, as the resolution becomes higher, a numerical aperture decreases. Hence, there are problems in that it needs to increase the luminance of a backlight when trying to achieve high luminance, and whereby the power consumption of the backlight increases. To improve the situation, there has been a technology that adds white pixels that are the fourth sub pixel, in addition to the conventional sub pixels of red, green, and blue (see Japanese Patent Application Laid-open Publication No. 2011-154323 (JP-A-2011-154323)). This technology decreases the value of current for the backlight as much as the white pixels improve the luminance, and thus reduces the power consumption. When the value of current for the backlight is not decreased, because the luminance is improved by the white pixels, by using this, the visibility under the outdoor daylight can be improved. 
     The technology disclosed in JP-A-2011-154323 describes a display device that includes an image display panel composed of pixels each composed of a first sub pixel, a second sub pixel, a third sub pixel, and a fourth sub pixel and arrayed in a two-dimensional matrix, and a signal processor that receives an input signal and outputs an output signal. In JP-A-2011-154323, FIGS. 2, 22, and 23 illustrate the arrays of the first sub pixels, the second sub pixels, the third sub pixels, and the fourth sub pixels. In the pixel arrays disclosed in JP-A-2011-154323, however, the numerical aperture may be reduced as pixel density becomes higher. 
     For the foregoing reasons, there is a need for a display device in which first sub pixels, second sub pixels, third sub pixels and fourth sub pixels are arranged and in which pixel density cam become higher. 
     SUMMARY 
     According to an aspect, a display device includes: a display unit in which pixels including three sub pixels out of a first sub pixel, a second sub pixel, a third sub pixel, and a fourth sub pixel are arranged and in which a first column of the sub pixels, a second column of the sub pixels arrayed next to the first column, a third column of the sub pixels arrayed next to the second column, and a fourth column of the sub pixels arrayed next to the third column are cyclically arrayed; a plurality of signal lines extending in a column direction that lies along at least one of the first column, the second column, the third column, and the fourth column; and a plurality of scan lines extending in a row direction that intersects with the column direction. The first sub pixel and the second sub pixel arranged in juxtaposition between the adjacent scan lines are lined alternately in the column direction in at least one of the first column and the third column. At least one of the third sub pixel and the fourth sub pixel is arranged between the adjacent scan lines in at least one of the second column and the fourth column. The first sub pixel, the second sub pixel, the third sub pixel, and the fourth sub pixel are included in an identical row of the pixels and in the first column, the second column, the third column, and the fourth column. A first pixel that is in an identical row of the pixels and includes sub pixels of the first column and the second column includes a sub pixel not present in a second pixel that is adjacent to the first pixel in the row direction and is included in the third column and the fourth column. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating one example of a configuration of a display device according to an embodiment; 
         FIG. 2  is a conceptual diagram of an image display panel and an image-display-panel drive circuit in the embodiment; 
         FIG. 3  is an explanatory diagram illustrating a pixel array of the image display panel in the embodiment; 
         FIG. 4  is a block diagram for explaining a signal processor of the display device in the embodiment; 
         FIG. 5  is a conceptual diagram of an extended HSV color space extendable by the display device in the embodiment; 
         FIG. 6  is a conceptual diagram illustrating the relation between the hue and saturation in the extended HSV color space; 
         FIG. 7  is a table for explaining panel drive of the display device in the embodiment; 
         FIG. 8  is an explanatory chart illustrating the relation between the resolution and the diagonal length of a sub pixel; 
         FIG. 9  is a diagram for explaining the size of a pixel according to a first comparative example; 
         FIG. 10  is a diagram for explaining the size of a pixel according to a second comparative example; 
         FIG. 11  is a diagram for explaining the size of a pixel according to a third comparative example; 
         FIG. 12  is a diagram for explaining the size of a pixel in the embodiment; 
         FIG. 13  is a conceptual diagram of an image display panel and an image-display-panel drive circuit according to a first modification of the embodiment; 
         FIG. 14  is a diagram illustrating a pixel array of the image display panel in the first modification of the embodiment; 
         FIG. 15  is a table for explaining panel drive of the display device in the first modification of the embodiment; 
         FIG. 16  is a block diagram illustrating one example of the configuration of a display device according to a second modification of the embodiment; 
         FIG. 17  is a schematic diagram for schematically explaining a cross-section of the image display panel in the second modification of the embodiment; 
         FIG. 18  is a diagram illustrating a pixel array of the image display panel in the second modification of the embodiment; 
         FIG. 19  is a diagram illustrating one example of an electronic apparatus including the display device in the embodiment; and 
         FIG. 20  is a diagram illustrating one example of an electronic apparatus including the display device in the embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to the accompanying drawings, a mode to implement the invention (an embodiment) will be described in detail. The content of the following exemplary embodiments described is not intended to limit the scope of the invention. The constituent elements described in the following include those that a person skilled in the art can easily assume or that are substantially the same. The constituent elements described in the following can further be combined as appropriate. Note that the disclosure is a mere example in any case, and appropriate modifications retaining the spirit of the invention that a person skilled in the art can easily assume are naturally included within the scope of the invention. Although the drawings may be schematically illustrated in terms of width, thickness, shape, and others of parts as compared with the actual modes to further clarify the explanation, the drawings are examples anyway and are not intended to limit the interpretation of the invention. In the description and each of the drawings, the constituent elements the same as those previously described concerning the previously described drawings are given the same reference symbols or numerals and their detailed explanations may be omitted as appropriate. 
       FIG. 1  is a block diagram illustrating one example of a configuration of a display device according to an embodiment.  FIG. 2  is a diagram illustrating a pixel array of the image display panel in the embodiment.  FIG. 3  is a conceptual diagram of an image display panel and an image-display-panel drive circuit in the embodiment.  FIG. 4  is a block diagram for explaining a signal processor of the display device in the embodiment. 
     As illustrated in  FIG. 1 , a display device  10  includes a signal processor  20  that receives an input signal (RGB data) from an image output unit  12  of a control device  11  and executes predetermined data conversion processing on the signal to be output, an image display panel  30  that displays an image based on an output signal output from the signal processor  20 , an image-display-panel drive circuit  40  that controls driving of the image display panel  30  (display unit), a light source device  50  that illuminates the image display panel  30  from its back surface, and a light-source-device control circuit  60  that controls driving of the light source device  50 . 
     The signal processor  20  is an arithmetic processor that controls the operation of the image display panel  30  and the light source device  50 . The signal processor  20  is coupled to the image-display-panel drive circuit  40  for driving the image display panel  30  and the light-source-device control circuit  60  for driving the light source device  50 . The signal processor  20  processes an input signal received from the outside and generates an output signal Sout and a light-source device control signal Spwm. That is, the signal processor  20  converts and generates the input signal into an output signal composed of color components of a first color, a second color, a third color, and a fourth color, and outputs the generated output signal to the image display panel  30 . The signal processor  20  outputs the generated output signal to the image-display-panel drive circuit  40  and outputs the generated light-source device control signal to the light-source-device control circuit  60 . The foregoing processing of color conversion by the signal processor  20  is one example in any case, and is not intended to limit the interpretation of the invention. 
     As illustrated in  FIGS. 2 and 3 , in the image display panel  30 , with a pixel  48 A and a pixel  48 B as a pair of pixels, pixels  48  of P 0 ×Q 0  pieces (P 0  pieces in the row direction and Q 0  pieces in the column direction) are arrayed in a two-dimensional matrix. The example illustrated in  FIGS. 2 and 3  is an example in which the pixels  48 A and the pixels  48 B provided in plurality are arrayed alternately in the row direction and in the column direction in a two-dimensional coordinate system of X and Y, and the pixels  48  are arrayed in a matrix. In this example, the row direction is an X direction and the column direction is a Y direction. 
     As illustrated in  FIG. 3 , the pixel  48 A includes, out of 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, three of the first sub pixel  49 R, the second sub pixel  49 G, and the third sub pixel  49 B. The pixel  48 B includes, out of 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, three of the first sub pixel  49 R, the second sub pixel  49 G, and the fourth sub pixel  49 W. The image display panel  30  includes scan lines Gp+1, Gp+2, and Gp+3 extending in the X direction and signal lines Sq+1, Sq+2, Sq+3, Sq+4, Sq+5, Sq+6, and Sq+7 extending in the Y direction. 
     As illustrated in  FIG. 3 , a first column, a second column arrayed next to the first column, a third column arrayed next to the second column, and a fourth column arrayed next to the third column are cyclically arrayed in the X direction. In the first column and the third column, the first sub pixel  49 R and the second sub pixel  49 G, which are both arranged between the adjacent scan line Gp+1 and the scan line Gp+2, are lined alternately in the Y direction. In the second column and the fourth column, either the third sub pixel  49 B or the fourth sub pixel  49 W is arranged between the adjacent scan line Gp+1 and the scan line Gp+2, and the third sub pixel  49 B and the fourth sub pixel  49 W are lined alternately in the Y direction. The third sub pixel  49 B and the fourth sub pixel  49 W are also arranged alternately in the second column and the fourth column in the row direction. 
     The scan line Gp+1 is coupled to a switching element (not depicted) of the second sub pixel  49 G that is one of the first sub pixel  49 R and the second sub pixel  49 G in the pixel  48 B, and is coupled to a switching element of the first sub pixel  49 R that is one of the first sub pixel  49 R and the second sub pixel  49 G in the pixel  48 A of the next row. The scan line Gp+1 is further coupled to a switching element of the third sub pixel  49 B of the second column in the pixel  48 A and a switching element of the fourth sub pixel  49 W of the fourth column in the pixel  48 B. The switching element of the third sub pixel  49 B may be coupled not to the scan line Gp+1 but to the scan line Gp+2. The switching element of the fourth sub pixel  49 W of the fourth column may be coupled not to the scan line Gp+1 but to the scan line Gp+2. 
     The scan line Gp+2 is coupled to the switching element of the second sub pixel  49 G that is one of the first sub pixel  49 R and the second sub pixel  49 G in the pixel  48 A, and is coupled to the switching element of the first sub pixel  49 R that is one of the first sub pixel  49 R and the second sub pixel  49 G in the pixel  48 B in the next row. The scan line Gp+2 is further coupled to the switching element of the third sub pixel  49 B of the fourth column in the pixel  48 A, and to that of the second sub pixel  49 W of the fourth column in the pixel  48 B. 
     The scan line Gp+3 is coupled to the switching element of the second sub pixel  49 G that is one of the first sub pixel  49 R and the second sub pixel  49 G in the pixel  48 B, and is coupled to the switching element (not depicted) of the first sub pixel  49 R that is one of the first sub pixel  49 R and the second sub pixel  49 G in the pixel  48 A in the next row. The scan line Gp+3 is further coupled to the third sub pixel  49 B of the fourth column in the pixel  48 A, and to the fourth sub pixel  49 W of the second column in the pixel  48 B. 
     As just described, out of three of the first sub pixel  49 R, the second sub pixel  49 G, and the third sub pixel  49 B included in a single pixel  48 A, the second sub pixel  49 G is coupled to a scan line different from that of the other sub pixels. Out of three of the first sub pixel  49 R, the second sub pixel  49 G, and the fourth sub pixel  49 W included in a single pixel  48 B, the second sub pixel  49 G is coupled to a scan line different from that of the other sub pixels. 
     That is, the scan line to which the first sub pixel  49 R, which is one of the first sub pixel  49 R and the second sub pixel  49 G included in a single pixel  48 A, and the third sub pixel  49 B included in that pixel  48 A are coupled is different from the scan line to which the second sub pixel  49 G, which is the other included in that pixel, is coupled. The scan line to which the first sub pixel  49 R, which is one of the first sub pixel  49 R and the second sub pixel  49 G included in a single pixel  48 B, and the fourth sub pixel  49 W included in that pixel  48 B are coupled is different from the scan line to which the second sub pixel  49 G, which is the other included in that pixel, is coupled. 
     The signal line Sq+1 is coupled to the switching elements of the first sub pixels  49 R of the first column. The signal line Sq+2 is coupled to the switching elements of the second sub pixels  49 G of the first column. The signal line Sq+3 is coupled to the switching elements of the third sub pixels  49 B and the fourth sub pixels  49 W of the second column. The signal line Sq+4 is coupled to the switching elements of the first sub pixels  49 R of the third column. The signal line Sq+5 is coupled to the switching elements of the second sub pixels  49 G of the third column. The signal line Sq+6 is coupled to the switching elements of the third sub pixels  49 B and the fourth sub pixels  49 W of the fourth column. The signal line Sq+7 is the same as the signal line Sq+1. The distance between the signal line Sq+2 and the signal line Sq+1 is greater than the distance between the signal line Sq+2 and the signal line Sq+3. Thus, the distance between the signal line Sq+2 and the signal line Sq+1 is different from the distance between the signal line Sq+2 and the signal line Sq+3. In the same manner, the distance between the signal line Sq+5 and the signal line Sq+4 is greater than the distance between the signal line Sq+5 and the signal line Sq+6. Thus, the distance between the signal line Sq+5 and the signal line Sq+4 is different from the distance between the signal line Sq+5 and the signal line Sq+6. 
     By this configuration, between the sub pixels  49  of the first column and the sub pixels  49  of the second column, two of the signal line Sq+2 and the signal line Sq+3 are arranged. Between the sub pixels  49  of the third column and the sub pixels  49  of the fourth column, two of the signal line Sq+5 and the signal line Sq+6 are arranged. The fourth sub pixel  49 W is of luminance higher than the first sub pixel  49 R and the second sub pixel  49 G are, and the influence of an effective aperture width on the luminance is smaller than that of the first sub pixel  49 R and the second sub pixel  49 G. Thus, by making the effective aperture widths of the first sub pixel  49 R and the second sub pixel  49 G in the row direction (X direction) larger than the effective aperture width of the fourth sub pixel  49 W, the numerical apertures of the first sub pixel  49 R and the second sub pixel  49 G can be increased. In the column direction (Y direction), the third sub pixel  49 B and the fourth sub pixel  49 W are arranged alternately. Consequently, the effective aperture widths of the first sub pixel  49 R and the second sub pixel  49 G in the row direction (X direction) are larger than the effective aperture width of the third sub pixel  49 B. The effective aperture width of the third sub pixel  49 B in the column direction (Y direction) is larger than the effective aperture width of the first sub pixel  49 R or the second sub pixel  49 G. Thus, the luminance of the third sub pixel  49 B that displays the third color component, which has a lower visual sensitivity of human as compared with the first sub pixel  49 R and the second sub pixel  49 G, can be supplemented. The luminance of the fourth sub pixel  49 W can further supplement the luminance of the third sub pixel  49 B. As just described, it is desirable that two of the signal line Sq+2 and the signal line Sq+3 be biased toward the fourth sub pixel  49 W side. In the same manner, it is desirable that the wiring arrangement of two of the signal line Sq+5 and the signal line Sq+6 be biased toward the fourth sub pixel  49 W side. Thus, it is desirable that the wiring arrangement of the two of the signal line Sq+2 and the signal line Sq+3 and the two of the signal line Sq+5 and the signal line Sq+6 be biased toward the high luminance side. 
     The pixel  48  includes the first sub pixels  49 R, the second sub pixels  49 G, the third sub pixel  49 B, and the fourth sub pixel  49 W. The first sub pixel  49 R displays a first color component (for example, red as the first primary color). The second sub pixel  49 G displays a second color component (for example, green as the second primary color). The third sub pixel  49 B displays a third color component (for example, blue as the third primary color). The fourth sub pixel  49 W displays a fourth color component (for example, white). In the following description, when it is not necessary 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 individually, they are referred to as sub pixels  49 . The above-described image output unit  12  outputs, as an input signal to the signal processor  20 , RGB data that can be displayed by the first color component, the second color component, and the third color component in the pixel  48 . The first color component, the second color component, the third color component, and the fourth component are not limited to the primary colors and may be complementary colors. 
     As illustrated in  FIG. 3 , the pixels  48 A and the pixels  48 B are arranged alternately in the row direction (X direction) and in the column direction (Y direction). The arrangement of the pixels  48 A and the pixels  48 B is not limited to this. For example, while the pixels  48 A and the pixels  48 B are arranged alternately in the row direction (X direction), the pixels  48 A may be arranged continuously in the column direction (Y direction) and the pixels  48 B may be arranged continuously in the column direction (Y direction). Alternatively, while the pixels  48 A and the pixels  48 B are arranged alternately in the column direction (Y direction), the pixels  48 A may be arranged continuously in the row direction (X direction) and the pixels  48 B may be arranged continuously in the row direction (X direction). In any of the arrangements of the pixels  48 A and the pixels  48 B, the number of third sub pixels  49 B and the number of fourth sub pixels  49 W are equal in two pixels in the row direction (X direction) and in two pixels in the column direction (Y direction), and thus the color can be balanced even when the third color component is replaced with the fourth color component. Even in other pixel arrangements, if the arrangement of the pixels  48 A and the pixels  48 B are made such that the number of third sub pixels  49 B and the number of fourth sub pixels  49 W are equal in four pixels in the row direction (X direction) and in four pixels in the column direction (Y direction), the color can be balanced even when the third color component is replaced with the fourth color component. 
     The display device  10  is, more specifically, a transmissive color liquid crystal display device. The image display panel  30  is a color liquid crystal display panel, and a first color filter that lets the first primary color pass through is arranged between the first sub pixels  49 R and an image viewer, a second color filter that lets the second primary color pass through is arranged between the second sub pixels  49 G and the image viewer, and a third color filter that lets the third primary color pass through is arranged between the third sub pixels  49 B and the image viewer. In the image display panel  30 , no color filter is arranged between the fourth sub pixels  49 W and the image viewer. For the fourth sub pixels  49 W, a transparent resin layer may be provided in place of a color filter. As just described, in the image display panel  30 , by providing the transparent resin layer, the occurrence of a large step at the fourth sub pixels  49 W by not providing a color filter for the fourth sub pixels  49 W can be suppressed. The display device  10  may be a display device that lights its light-emitting body such as an organic light emitting diode (OLED). 
     As illustrated in  FIG. 4 , the signal processor  20  includes a gamma conversion unit  21  that receives an input signal Sin (RGB data) from the image output unit  12 , and an image analyzer  22 , a data converter  23 , a decimation and color correction unit  24 , an inverse gamma conversion unit  25 , and a light source controller  26 . The gamma conversion unit  21  performs gamma conversion processing on the input signal Sin (RGB data). The image analyzer  22  calculates, based on the input value after the gamma conversion processing, control information Sa for an extension coefficient α, which will be described later, and calculates, based on the extension coefficient α, the light-source device control signal Spwm. The light source controller  26  controls the light-source-device control circuit  60  by a control signal Sb 1  based on the light-source device control signal Spwm. 
     The data converter  23  determines and outputs, based on the input values for which gamma conversion has been performed and the control information Sa for the extension coefficient α, an intermediate output signal Smid for each of the sub pixels  49  in all of the pixels  48 . The decimation and color correction unit  24  performs decimation processing so as to make the signal fit the pixel array of the image display panel  30  and performs color correction. For example, the decimation and color correction unit  24  performs, on display data to be displayed on the pixel  48 A including color information on the first color component, the second color component, the third color component, and the fourth color component, the processing of decimating the information on the fourth color component that is not displayable on the pixel  48 A. In the same manner, the decimation and color correction unit  24  performs, on the display data to be displayed on the pixel  48 B including the color information on the first color component, the second color component, the third color component, and the fourth color component, the processing of decimating the information on the third color component that is not displayable on the pixel  48 B. Alternatively, the decimation and color correction unit  24  decimates the information on the fourth color component from the display data to be displayed on the pixel  48 A including the color information on the first color component, the second color component, the third color component, and the fourth color component. In addition, the decimation and color correction unit  24  performs correction processing to add the information on the fourth color component that is not displayable on the pixel  48 A to the display data to be displayed on the adjacent pixel  48 B. In the same manner, the decimation and color correction unit  24  decimates the information on the third color component from the display data to be displayed on the pixel  48 B including the color information on the first color component, the second color component, the third color component, and the fourth color component. The decimation and color correction unit  24  further performs correction processing to add the information on the third color component that is not displayable on the pixel  48 B to the display data to be displayed on the adjacent pixel  48 A. The inverse gamma conversion unit  25  inputs, to the image-display-panel drive circuit  40 , the output signal Sout in which inverse gamma conversion has been performed based on the processing information on the decimation and color correction unit  24 . The gamma conversion processing  21  and the inverse gamma conversion unit  25  are not essential, and the gamma conversion processing and the inverse gamma conversion processing may not be performed. 
     The image-display-panel drive circuit  40  includes a signal output circuit  41  and a scanning circuit  42 . In the image-display-panel drive circuit  40 , the signal output circuit  41  holds video signals to be sequentially output to the image display panel  30 . The signal output circuit  41  is electrically coupled to the image display panel  30  via wiring DTL. In the image-display-panel drive circuit  40 , the scanning circuit  42  controls ON/OFF of a switching element (for example, a thin film transistor (TFT)) for controlling an operation of the sub pixel (light transmittance) in the image display panel  30 . The scanning circuit  42  is electrically coupled to the image display panel  30  via wiring SCL. 
     The light source device  50  is arranged on a back surface of the image display panel  30 , and illuminates the image display panel  30  by irradiating the image display panel  30  with light. The light source device  50  irradiates the entire surface of the image display panel  30  with light to illuminate the image display panel  30 . The light-source-device control circuit  60  controls irradiation light quantity and the like of the light output from the light source device  50 . Specifically, the light-source-device control circuit  60  adjusts a voltage or a duty ratio to be supplied to the light source device  50  based on the light-source-device control signal output from the signal processor  20  to control the light quantity (light intensity) of the light with which the image display panel  30  is irradiated. The following describes a processing operation executed by the display device  10 , more specifically, the signal processor  20 . 
       FIG. 5  is a conceptual diagram of an extended HSV color space extendable by the display device according to the embodiment.  FIG. 6  is a conceptual diagram illustrating a relation between the hue and saturation in the extended HSV color space. The signal processor  20  receives an input signal that is information of an image to be displayed input from the outside. The input signal includes the information of the image (color) to be displayed at its position for each pixel as the input signal. Specifically, in the image display panel  30  in which P 0 ×Q 0  pixels  48  are arranged in a matrix, with respect to the (p,q)-th pixel  48  (where 1≦p≦P 0 , 1≦q≦Q 0 ), the signal processor  20  receives a signal including an input signal of the first sub pixel  49 R the signal value of which is x 1-(p,q) , an input signal of the second sub pixel  49 G the signal value of which is x 2-(p,q) , and an input signal of the third sub pixel  49 B the signal value of which is x 3-(p,q)  (refer to  FIG. 1 ). 
     The signal processor  20  illustrated in  FIG. 1  generates, by processing the input signal, an output signal of first sub pixels (signal value X 1-(p,q) ) to determine the display gradation of the first sub pixels  49 R, an output signal of second sub pixels (signal value X 2-(p,q) ) to determine the display gradation of the second sub pixels  49 G, an output signal of third sub pixels (signal value X 3-(p,q) ) to determine the display gradation of the third sub pixels  49 B, and an output signal of fourth sub pixels (signal value X 4-(p,q) ) to determine the display gradation of the fourth sub pixels  49 W, and outputs the signals to the image-display-panel drive circuit  40 . 
     The display device  10 , as illustrated in  FIG. 5 , can expand the dynamic range of brightness in an HSV color space (extended HSV color space), by providing the fourth sub pixels  49 W that output the fourth color component (for example, white) in the pixels  48 . That is, as illustrated in  FIG. 5 , it is in a shape in which, in an HSV color space in a columnar shape that can be displayed on the first sub pixel  49 R, the second sub pixel  49 G, and the third sub pixel  49 B, a solid in an approximately trapezoidal shape for which a maximum of the value V (also referred to as brightness) becomes low as the saturation S increases is placed. 
     The signal processor  20  stores therein maximum values Vmax(S) of brightness with the saturation S as a variable in the HSV color space which has been expanded by adding the fourth color component (for example, white). That is, the signal processor  20  stores therein the maximum values Vmax(S) of brightness for respective coordinates (values) of the saturation and hue concerning the solid shape of the HSV color space illustrated in  FIG. 5 . Because the input signal includes input signals of the first sub pixel  49 R, the second sub pixel  49 G, and the third sub pixel  49 B, the HSV color space of the input signal is in a columnar shape, that is, the same shape as the columnar shape portion of the extended HSV color space. 
     The signal processor  20  then calculates an output signal of the first sub pixels  49 R (signal value X 1-(p,q) ) based on at least the input signal (signal value x 1-(p,q) ) and the extension coefficient α of the first sub pixels  49 R, and outputs it to the first sub pixels  49 R. The signal processor  20  calculates an output signal of the second sub pixels  49 G (signal value X 2-(p,q) ) based on at least the input signal (signal value x 2-(p,q) ) and the extension coefficient α of the second sub pixels  49 G, and outputs it to the second sub pixels  49 G. The signal processor  20  calculates an output signal of the third sub pixels  49 B (signal value X 3-(p,q) ) based on at least the input signal (signal value x 3-(p,q) ) and the extension coefficient α of the third sub pixels  49 B, and outputs it to the third sub pixels  49 B. The signal processor  20  further calculates an output signal of the fourth sub pixels  49 W (signal value X 4-(p,q) ) based on the input signal of the first sub pixels  49 R (signal value x 1-(p,q) ) based on the input signal of the second sub pixels  49 G (signal value x 2-(p,q) ) and the input signal of the third sub pixels  49 B (signal value x 3-(p,q) ), and outputs it to the fourth sub pixels  49 W. 
     Specifically, the signal processor  20  calculates the output signal of the first sub pixels  49 R based on the extension coefficient α of the first sub pixels  49 R and the output signal of the fourth sub pixels  49 W, calculates the output signal of the second sub pixels  49 G based on the extension coefficient α of the second sub pixels  49 G and the output signal of the fourth sub pixels  49 W, and calculates the output signal of the third sub pixels  49 B based on the extension coefficient α of the third sub pixels  49 B and the output signal of the fourth sub pixels  49 W. 
     That is, assuming that χ is a constant dependent of the display device  10 , the signal processor  20  obtains, from the following Expression (1) to Expression (3), the signal value X 1-(p,q)  that is the output signal of the first sub pixels  49 R, the signal value X 2-(p,q)  that is the output signal of the second sub pixels  49 G, and the signal value X 3-(p,q)  that is the output signal of the third sub pixels  49 B, for the (p,q)-th pixel (or a combination of the first sub pixel  49 R, the second sub pixel  49 G, and the third sub pixel  49 B).
 
 X   1-(p,q)   =α·x   1-(p,q)   −χ·X   4-(p,q)   (1)
 
 X   2-(p,q)   =α·x   2-(p,q)   −χ·X   4-(p,q)   (2)
 
 X   3-(p,q)   =α·x   3-(p,q)   −χ·X   4-(p,q)   (3)
 
     The signal processor  20  obtains the maximum value Vmax(S) of brightness with the saturation S, as a variable, in the HSV color space expanded by adding the fourth color, and obtains the saturation S and brightness V(S) in a plurality of pixels based on the input signal values of the sub pixels in those pixels. The signal processor  20  then determines the extension coefficient α such that the ratio of the pixels, for which the extended brightness value obtained by the product of the brightness V(S) and the extension coefficient α exceeds the maximum value Vmax(S), to the total pixels is equal to or smaller than a limit value β (Limit value). The limit value β is, with respect to a maximum of brightness in the extended HSV color space, an upper limit (ratio) of the ratio of width in which the combination of the values of hue and saturation exceeds the maximum. 
     The saturation S and the brightness V(S) are expressed by S=(Max−Min)/Max and V(S)=Max, respectively. The saturation S can assume the value of 0 to 1, and the brightness V(S) can assume the value of 0 to (2 n −1), in which the n is the number of display gradation bits. The Max is a maximum value of the input signal values of three sub pixels, which are the input signal value of the first sub pixel, the input signal value of the second sub pixel, and the input signal value of the third sub pixel, to a pixel. The Min is a minimum value of the input signal values of three sub pixels, which are the input signal value of the first sub pixel, the input signal value of the second sub pixel, and the input signal value of the third sub pixel, to the pixel. The hue H is represented by 0° to 360° as illustrated in  FIG. 6 . From 0° toward 360°, it represents red, yellow, green, cyan, blue, magenta, and red. In the embodiment, the region including an angle of 0° is defined as red, the region including an angle of 120° is defined as green, and the region including an angle of 240° is defined as blue. 
     According to the embodiment, the signal value X 4-(p,q)  can be obtained based on a product of Min (p,q)  and the expansion coefficient α. Specifically, the signal value X 4-(p,q)  can be obtained based on the following Expression (4). In Expression (4), the product of Min (p,q)  and the expansion coefficient α is divided by χ. However, the embodiment is not limited thereto. χ will be described later. The expansion coefficient α is determined for each image display frame.
 
 X   4-(p,q) =Min (p,q) ·α/χ  (4)
 
     Generally, in the (p,q)-th pixel, the saturation S (p,q)  and the brightness V(S) (p,q)  in the cylindrical HSV color space can be obtained from the following Expressions (5) and (6) based on the input signal (signal value x 1-(p,q) ) of the first sub pixel  49 R, the input signal (signal value x 2-(p,q) ) of the second sub pixel  49 G, and the input signal (signal value x 3-(p,q) ) of the third sub pixel  49 B.
 
 S   (p,q) =(Max (p,q) −Min (p,q) )/Max (p,q)   (5)
 
 V ( S ) (p,q) =Max (p,q)   (6)
 
     In the above expressions, Max (p,q)  represents the maximum value among the input signal values of three sub pixels  49  (x 1-(p,q) , x 2-(p,q) , and x 3-(p,q) ), and Min (p,q)  represents the minimum value among the input signal values of the three sub pixels  49  (x 1-(p,q) , x 2-(p,q) , and x 3-(p,q) ). In the embodiment, n is assumed to be 8. That is, the display gradation bit number is assumed to be 8 bits (a value of the display gradation is assumed to be 256 gradations, that is, 0 to 255). 
     It is assumed that no color filter is arranged for the fourth sub pixels  49 W that display white. Furthermore, when a signal having a value equivalent to a maximum signal value of the output signal of the first sub pixels is input to the first sub pixels  49 R, a signal having a value equivalent to a maximum signal value of the output signal of the second sub pixels is input to the second sub pixels  49 G, and a signal having a value equivalent to a maximum signal value of the output signal of the third sub pixels is input to the third sub pixels  49 B, the luminance of the aggregate of the first sub pixels  49 R, the second sub pixels  49 G, and the third sub pixels  49 B provided in the pixel  48  or a group of pixels  48  is defined as BN 1-3 . When a signal having a value equivalent to a maximum signal value of the output signal of the fourth sub pixel  49 W is input to the fourth sub pixels  49 W provided in the pixel  48  or a group of pixels  48 , the luminance of the fourth sub pixels  49 W is defined as BN 4 . That is, the white of maximum luminance is displayed by the aggregate of the first sub pixels  49 R, the second sub pixels  49 G, and the third sub pixels  49 B, and the luminance of this white is expressed by BN 1-3 . Consequently, assuming that χ is a constant dependent of the display device  10 , the constant χ is expressed by χ=BN 4 /BN 1-3 . 
     Specifically, the luminance BN 4  when the input signal having a value of display gradation 255 is assumed to be input to the fourth sub pixel  49 W is 1.5 times the luminance BN 1-3  of white when the input signals having values of display gradation 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, χ is 1.5 in the embodiment. 
     If the signal value X 4-(p,q)  is given by Expression (4) above, Vmax(S) can be represented by the following Expressions (7) and (8). 
     When S≦S 0 ,
 
 V max( S )=(χ+1)·(2 n −1)  (7)
 
     When S 0 &lt;S≦1,
 
 V max( S )=(2 n −1)·(1/ S )  (8)
 
     In this case, S 0 =1/(χ+1). 
     The thus obtained maximum value Vmax(S) of the brightness using the saturation S as a variable in the HSV color space expanded by adding the fourth color component is stored in the signal processor  20  as a kind of look-up table, for example. Alternatively, the signal processor  20  obtains the maximum value Vmax(S) of the brightness using the saturation S as a variable in the expanded HSV color space as occasion demands. 
     Next, the following describes a method of obtaining the signal values X 1-(p,q) , X 2-(p,q) , X 3-(p,q) , and X 4-(p,q)  as output signals of the (p,q)-th pixel  48  (expansion processing). The following processing is performed to keep a ratio among the luminance of the first primary color displayed by (first sub pixel  49 R+fourth sub pixel  49 W), the luminance of the second primary color displayed by (second sub pixel  49 G+fourth sub pixel  49 W), and the luminance of the third primary color displayed by (third sub pixel  49 B+fourth sub pixel  49 W). The processing is performed to also keep (maintain) color tone. In addition, the processing is performed to keep (maintain) a gradation-luminance characteristic (gamma characteristic, γ characteristic). When all of the input signal values are 0 or smaller in any one of the pixels  48  and a group of the pixels  48 , the expansion coefficient α may be obtained without including such pixel  48  or a group of pixels  48 . 
     First Process 
     First, the signal processor  20  obtains the saturation S and the brightness V(S) in the pixels  48  based on the input signal values of the sub pixels  49  of the pixels  48 . Specifically, S (p,q)  and V(S) (p,q)  are obtained from Expressions (5) and (6) based on the signal value x 1-(p,q)  that is the input signal of the first sub pixel  49 R, the signal value x 2-(p,q)  that is the input signal of the second sub pixel  49 G, and the signal value x 3-(p,q)  that is the input signal of the third sub pixel  49 B, each of those signal values being input to the (p,q)-th pixel  48 . The signal processor  20  performs this processing on all of the pixels  48 . 
     Second Process 
     Next, the signal processor  20  obtains the expansion coefficient α(s) based on the Vmax(S)/V(S) obtained in the pixels  48 .
 
α( s )= V max( S )/ V ( S )  (9)
 
     Then arranged are values of expansion coefficient α(s) obtained in the pixels (all of P 0 ×Q 0  pixels in the embodiment)  48  in ascending order, and it is assumed that the expansion coefficient α(s) corresponding to a range from the minimum value to β×P 0 ×Q 0  is the expansion coefficient α among the values of the P 0 ×Q 0  expansion coefficients α(s). In this way, the expansion coefficient α can be determined so that a ratio of the pixel in which the expanded value of the brightness obtained by multiplying the brightness V(S) by the expansion coefficient α exceeds the maximum value Vmax(S) to all the pixels is equal to or smaller than a predetermined value (β). 
     Third Process 
     Next, the signal processor  20  obtains 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)  of the input signals. In the embodiment, the signal processor  20  determines the signal value X 4-(p,q)  based on Min (p,q) , the expansion coefficient α, and the constant χ. More specifically, as described above, the signal processor  20  obtains the signal value X 4-(p,q)  based on Expression (4). The signal processor  20  obtains the signal value X 4-(p,q)  for all of the P 0 ×Q 0  pixels  48 . 
     Fourth Process 
     Subsequently, the signal processor  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, and the signal value X 4-(p,q) , 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, and the signal value X 4-(p,q) , and 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, and the signal value X 4-(p,q) . Specifically, the signal processor  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 Expressions (1) to (3) described above. 
     The signal processor  20  expands a value of Min (p,q)  with α as represented by Expression (4). In this way, the value of Min (p,q)  is expanded by α, so that the luminance of the white display sub pixel (fourth sub pixel  49 W) increases, and the luminance of the red, green and blue display sub pixels (corresponding to the first, second, and third sub pixels  49 R,  49 G, and  49 B, respectively) also increases as represented by the above expressions. Due to this, dullness of color can be prevented. That is, the luminance of the entire image is multiplied by α because the value of Min (p,q)  is expanded by α, compared with the case in which the value of Min (p,q)  is not expanded. Accordingly, for example, a static image and the like can be preferably displayed with high luminance. 
     The luminance displayed by the output signals X 1-(p,q) , X 2-(p,q) , X 3-(p,q) , and X 4-(p,q)  in the (p,q)-th pixel  48  is expanded α times the luminance formed by the input signals x 1-(p,q) , x 2-(p,q) , and x 3-(p,q) . Accordingly, the display device  10  may reduce the luminance of the pixel in the light source device  50  based on the expansion coefficient α so as to cause the luminance to be the same as that of the pixel  48  that is not expanded. Specifically, the luminance of the light source device  50  may be multiplied by (1/α). 
     As described above, the display device  10  according to the embodiment sets the limit value (Limit value) β for each frame of the input signals so as to set the expansion coefficient to a value that allows power consumption to be reduced while maintaining the display quality. 
     Panel Drive 
       FIG. 7  is a table for explaining panel drive of the display device in the embodiment.  FIG. 7  illustrates the display data of the intermediate output signal Smid that is output by the data converter  23  illustrated in  FIG. 4 , and the display data corresponding to the order of panel drive that is the output signal Sout processed by the decimation and color correction unit  24 . In  FIG. 7 , a single row represents a unit of row of respective sub pixels distinguished by the first sub pixel  49 R or the second sub pixel  49 G lined in the column direction of the sub pixels. As illustrated in  FIGS. 2 and 3 , the scanning circuit  42 , as a control device, transmits an image signal to be transmitted to the second sub pixels  49 G in the first column and the third column by shifting by one horizontal line of pixels (one row) from the image signal to be transmitted to the first sub pixels  49 R of the same pixels  48 A and pixels  48 B in which the second sub pixel  49 G is present. The decimation and color correction unit  24  illustrated in  FIG. 4  performs decimation and color correction to shift the image signal to be transmitted to the second sub pixels  49 G in the first column and the third column by one horizontal line of pixels (one row) from the image signal to be transmitted to the first sub pixels  49 R of the same pixels  48 A and pixels  48 B in which the second sub pixel  49 G is present. 
     As in the foregoing, the switching element of the third sub pixel  49 B can be coupled to either the scan line Gp+1 or the scan line Gp+2. The switching element of the fourth sub pixel  49 W of the fourth column can be coupled to either the scan line Gp+1 or the scan line Gp+2. When the switching element of the third sub pixel  49 B and the switching element of the fourth sub pixel  49 W of the fourth column are coupled to the scan line Gp+2, it is necessary to shift the display data of G(1,1) equivalent to the second sub pixel  49 G and B(1,1) equivalent to the third sub pixel  49 B out of the first pixel (1,1), and thus the storage capacity of a memory that temporarily stores therein the display data G(1,1) and B(1,1) is necessary. In contrast, when the switching element of the third sub pixel  49 B and the switching element of the fourth sub pixel  49 W of the fourth column are coupled to the scan line Gp+1 as illustrated in  FIG. 7 , it only needs to shift the display data of G(1,1) equivalent to the second sub pixel  49 G out of the first pixel (1,1), and thus the storage capacity of a memory that temporarily stores therein the display data G(1,1) can be reduced. Consequently, in the display device  10  in the embodiment, it is more preferable that the switching element of the third sub pixel  49 B and the switching element of the fourth sub pixel  49 W of the fourth column be coupled to the scan line Gp+1. 
     As in the foregoing, the display device  10  in the embodiment includes the image display panel  30  that includes the pixels  48 A and the pixels  48 B including three sub pixels  49  out of 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, and in which the first column, the second column arrayed next to the first column, the third column arrayed next to the second column, and the fourth column arrayed next to the third column are cyclically arrayed. The image display panel  30 , as a display unit, includes a plurality of signal lines Sq+1, Sq+2, Sq+3, Sq+4, Sq+5, Sq+6, and Sq+7 extending in the column direction (Y direction) that lies along at least one of the first column, the second column, the third column, and the fourth column, and a plurality of scan lines Gp+1, Gp+2, and Gp+3 extending in the row direction (X direction) that intersects with the column direction. 
     In the image display panel  30 , in at least one of the first column and the third column, the first sub pixel  49 R and the second sub pixel  49 G arranged in juxtaposition between the adjacent scan line Gp+1 and the scan line Gp+2 are lined alternately in the column direction, and in at least one of the second column and the fourth column, at least one of the third sub pixel  49 B and the fourth sub pixel  49 W is arranged between the adjacent scan line Gp+1 and the scan line Gp+2. An identical row of pixels and the first column, the second column, the third column, and the fourth column of sub pixels include 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, and the pixel  48 A (first pixel) that is the identical row of pixels and includes the sub pixels of the first column and the second column includes the third sub pixel  49 B that is not present in the pixel  48 B (second pixel) that is adjacent to the pixel  48 A in the row direction and included in the third column and the fourth column. The identical row of pixels means the row divided by the scan lines, or the row in units of the third sub pixel  49 B or the fourth sub pixel  49 W the numerical aperture of which has a larger numerical value. 
       FIG. 8  is an explanatory chart illustrating the relation between the resolution and the diagonal length of a sub pixel. The ordinate axis represents the resolution, the abscissa axis represents the diagonal length of a sub pixel, and an area of 500 pixels per inch (ppi, the number of pixels per inch) is indicated as A500. In  FIG. 8 , the VGA indicates the resolution in a state in which one pixel for display is arranged in a matrix of 640 by 480 pixels. The WVGA indicates the resolution in a state in which one pixel for display is arranged in a matrix of 800 by 480 pixels. The qHD (quarter HD) indicates the resolution in a state in which one pixel for display is arranged in a matrix of 960 by 540 pixels. The 720HD indicates the resolution in a state in which one pixel for display is arranged in a matrix of 1280 by 720 pixels. The Full-HD indicates the resolution in a state in which one pixel for display is arranged in a matrix of 1920 by 1080 pixels. The WQXGA indicates the resolution in a state in which one pixel for display is arranged in a matrix of 2560 by 1600 pixels.  FIG. 9  is a diagram for explaining the size of a pixel according to a first comparative example.  FIG. 10  is a diagram for explaining the size of a pixel according to a second comparative example.  FIG. 11  is a diagram for explaining the size of a pixel according to a third comparative example.  FIG. 12  is a diagram for explaining the size of a pixel in the embodiment. In the pixel illustrated in  FIG. 10  that includes the first sub pixel, the second sub pixel, the third sub pixel, and the fourth sub pixel, as compared in the same 500 ppi area, the aperture area Wb×Da is small with respect to the aperture area Wa×Da of a sub pixel in the pixel illustrated in  FIG. 9  that includes the first sub pixel, the second sub pixel, and the third sub pixel. In the pixel in the second comparative example illustrated in  FIG. 10 , as compared with the pixel in the first comparative example illustrated in  FIG. 9 , it may not be possible to ensure the numerical aperture when the pixel density is high. 
     In contrast, the pixel illustrated in  FIG. 11  is of a square pixel, and thus the lengths Wc and Wd can be ensured and the numerical aperture can be improved more than that of the pixel illustrated in  FIG. 10 . While the pixel illustrated in  FIG. 11  can be driven by increasing the number of signal lines without increasing the number of scan lines, the numerical aperture decreases because more signal lines are required than those of the pixel in the embodiment. The increase in signal lines results in a growth in the signal output circuit and is undesirable. Meanwhile, in the pixel illustrated in  FIG. 11 , when the number of scan lines is increased, the drive frequency increases (for example, twofold) and the power consumption may increase. Consequently, according to the pixel disclosed in  FIG. 18  in the above-described JP-A-2011-154323, although the length in the row direction can be made greater than that of the pixel in the second comparative example illustrated in  FIG. 10 , the respective apertures of the first sub pixel, the second sub pixel, the third sub pixel, and the fourth sub pixel are made in irregular shapes in practice to adjust the white chromaticity point, and thus the increase in pixel density has limitations. 
     As illustrated in  FIG. 12 , in the pixel in the embodiment, as in the foregoing, an identical row of pixels and the first column, the second column, the third column, and the fourth column of sub pixels include the first sub pixels  49 R, the second sub pixels  49 G, the third sub pixel  49 B, and the fourth sub pixel  49 W, and the pixel  48 A (first pixel) that is the identical row of pixels and includes the sub pixels of the first column and the second column includes the third sub pixel  49 B that is not present in the pixel  48 B (second pixel) that is adjacent to the pixel  48 A in the row direction and included in the third column and the fourth column. The ratio of a single first sub pixel  49 R and a single third sub pixel  49 B is the same as that of a single second sub pixel  49 G and a single fourth sub pixel  49 W. Consequently, the aperture area of the first sub pixel  49 R is Dc×Wd, the aperture area of the second sub pixel  49 G is Dc×Wd, and the aperture area of the third sub pixel  49 B or the fourth sub pixel  49 W is Da×Wd. As illustrated in  FIG. 12 , in the pixel in the embodiment, when two of the adjacent pixel  48 A and the pixel  48 B are added, the respective areas of the first sub pixels  49 R, the second sub pixels  49 G, the third sub pixel  49 B, and the fourth sub pixel  49 W are Da×Wd=2×Dc×Wd, and thus the white chromaticity point can be adjusted. As in the foregoing, when two of the pixel  48 A and the pixel  48 B in the embodiment are combined, the first sub pixels  49 R, the second sub pixels  49 G, the third sub pixel  49 B, and the fourth sub pixel  49 W included in the identical row of pixels and the first column, the second column, the third column, and the fourth column of sub pixels have the same area. Furthermore, because the apertures are not necessary to be in irregular shapes, the display device  10  in the embodiment has excellent mass productivity and reduces cost. In the display device  10  in the embodiment, because the pixel pitch is to be large, flaws can be reduced. Furthermore, in the sub pixels  49  in the embodiment, because the pixel pitch is large, the viewing-angle color mixture is suppressed. 
     Because the pixels  48 A and  48 B in the embodiment are both arranged between the adjacent scan line Gp+1 and the scan line Gp+2, an increase in scan lines can be suppressed, and thus an increase in drive frequency can be suppressed. Consequently, the display device  10  in the embodiment yields low power consumption. 
     First Modification 
       FIG. 13  is a conceptual diagram of an image display panel and an image-display-panel drive circuit according to a first modification of the embodiment.  FIG. 14  is a diagram illustrating a pixel array of the image display panel in the first modification of the embodiment.  FIG. 15  is a table for explaining panel drive of the display device in the first modification of the embodiment. For the constituent elements the same as those in the foregoing, the detailed explanations will be omitted. 
     As illustrated in  FIGS. 13 and 14 , the pixel  48 A includes, out of 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, three of the first sub pixel  49 R, the second sub pixel  49 G, and the fourth sub pixel  49 W. The pixel  48 B includes, out of 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, three of the second sub pixel  49 G, the third sub pixel  49 B, and the fourth sub pixel  49 W. The image display panel  30  includes the scan lines Gp+1, Gp+2, and Gp+3 extending in the X direction and the signal lines Sq+1, Sq+2, Sq+3, Sq+4, Sq+5, Sq+6, and Sq+7 extending in the Y direction. An identical row of pixels and the first column, the second column, the third column, and the fourth column of sub pixels include 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, and the pixel  48 A (first pixel) that is the identical row of pixels and includes the sub pixels of the first column and the second column includes the first sub pixel  49 R that is not present in the pixel  48 B (second pixel) that is adjacent to the pixel  48 A in the row direction and included in the third column and the fourth column. That is, because the pixel  48 A and the pixel  48 B comparably include pixels of green component of high visual sensitivity and of white component, the display quality can be enhanced. 
     The fourth sub pixel  49 W has higher luminance than that of the first sub pixel  49 R, the second sub pixel  49 G, and the third sub pixel  49 B. The second sub pixel  49 G has higher luminance than that of the first sub pixel  49 R and the third sub pixel  49 B. Consequently, as illustrated in  FIGS. 13 and 14 , the pixel  48 A and the pixel  48 B are arranged such that the area of the second sub pixel  49 G, which has the highest luminance of the first sub pixel  49 R, the second sub pixel  49 G, and the third sub pixel  49 B, is larger when the areas of the sub pixels  49  occupying two of the pixels are compared. Such arrangement ensures the area of the sub pixels  49  of high luminance and makes deterioration in transmissive resolution difficult to see. 
     As illustrated in  FIGS. 13 and 14 , the first column, the second column arrayed next to the first column, the third column arrayed next to the second column, and the fourth column arrayed next to the third column are cyclically arrayed in the X direction. In the first column, the first sub pixel  49 R and the second sub pixel  49 G, which are both arranged between the adjacent scan line Gp+1 and the scan line Gp+2, are lined alternately in the Y direction. In the third column, the third sub pixel  49 B and the second sub pixel  49 G, which are both arranged between the adjacent scan line Gp+1 and the scan line Gp+2, are lined alternately in the Y direction. In the second column and the fourth column, the fourth sub pixel  49 W is arranged between the adjacent scan line Gp+1 and the scan line Gp+2, and is lined in the Y direction. 
     The scan line Gp+1 is coupled to the switching element of the third sub pixel  49 B that is one of the third sub pixel  49 B and the second sub pixel  49 G in the pixel  48 B, and is coupled to the switching element of the first sub pixel  49 R that is one of the first sub pixel  49 R and the second sub pixel  49 G in the adjacent pixel  48 A. The scan line Gp+1 is further coupled to the switching element of the fourth sub pixel  49 W. 
     The scan line Gp+2 is coupled to the switching element of the second sub pixel  49 G that is one of the first sub pixel  49 R and the second sub pixel  49 G in the pixel  48 A, and is coupled to the switching element of the third sub pixel  49 B that is one of the third sub pixel  49 B and the second sub pixel  49 G in the pixel  48 B in the next row. The scan line Gp+2 is further coupled to the switching element of the fourth sub pixel  49 W. 
     The scan line Gp+3 is coupled to the switching element of the second sub pixel  49 G that is one of the third sub pixel  49 B and the second sub pixel  49 G in the pixel  48 B, and is coupled to the switching element (not depicted) of the first sub pixel  49 R that is one of the first sub pixel  49 R and the second sub pixel  49 G in the pixel  48 A in the next row. The scan line Gp+3 is further coupled to the fourth sub pixel  49 W. 
     As just described, out of three of the first sub pixel  49 R, the second sub pixel  49 G, and the fourth sub pixel  49 W included in a single pixel  48 A, the second sub pixel  49 G is coupled to a scan line different from the other sub pixels. Out of three of the second sub pixel  49 G, the third sub pixel  49 B, and the fourth sub pixel  49 W included in a single pixel  48 B, the second sub pixel  49 G is coupled to a scan line different from the other sub pixels. 
     That is, the scan line to which the first sub pixel  49 R, which is one of the first sub pixel  49 R and the second sub pixel  49 G included in a single pixel  48 A, and the fourth sub pixel  49 W included in that pixel  48 A are coupled is different from the scan line to which the second sub pixel  49 G that is the other included in that pixel is coupled. The scan line to which the third sub pixel  49 B, which is one of the second sub pixel  49 G and the third sub pixel  49 B included in a single pixel  48 B, and the fourth sub pixel  49 W included in that pixel  48 B are coupled is different from the scan line to which the second sub pixel  49 G that is the other included in that pixel is coupled. 
     The signal line Sq+1 is coupled to the switching elements of the first sub pixels  49 R and the third sub pixels  49 B of the first column. The signal line Sq+2 is coupled to the switching elements of the second sub pixels  49 G of the first column. The signal line Sq+3 is coupled to the switching elements of the fourth sub pixels  49 W of the second column. The signal line Sq+4 is coupled to the switching elements of the third sub pixels  49 B and the first sub pixels  49 R of the third column. The signal line Sq+5 is coupled to the switching elements of the second sub pixels  49 G of the third column. The signal line Sq+6 is coupled to the switching element of the fourth sub pixel  49 W of the fourth column. The signal line Sq+7 is the same as the signal line Sq+1. The distance between the signal line Sq+2 and the signal line Sq+1 is greater than the distance between the signal line Sq+2 and the signal line Sq+3. Thus, the distance between the signal line Sq+2 and the signal line Sq+1 is different from the distance between the signal line Sq+2 and the signal line Sq+3. The effective aperture width of the first sub pixel  49 R or the effective aperture width of the second sub pixel  49 G in a single pixel  48 A is smaller than the effective aperture width of the fourth sub pixel  49 W in the pixel  48 A. In the same manner, the distance between the signal line Sq+5 and the signal line Sq+4 is greater than the distance between the signal line Sq+5 and the signal line Sq+6. Thus, the distance between the signal line Sq+5 and the signal line Sq+4 is different from the distance between the signal line Sq+5 and the signal line Sq+6. The effective aperture width of the first sub pixel  49 R or the effective aperture width of the second sub pixel  49 G in a single pixel  48 B is smaller than the effective aperture width of the third sub pixel  49 B in the pixel  48 B. 
     By this configuration, between the sub pixels  49  of the first column and the sub pixels  49  of the second column, two of the signal line Sq+2 and the signal line Sq+3 are arranged. Between the sub pixels  49  of the third column and the sub pixels  49  of the fourth column, two of the signal line Sq+5 and the signal line Sq+6 are arranged. The fourth sub pixel  49 W is of luminance higher than the first sub pixel  49 R, the second sub pixel  49 G, and the third sub pixel  49 B are, and the influence of the effective aperture width on the luminance is smaller than that of the first sub pixel  49 R, the second sub pixel  49 G, and the third sub pixel  49 B. Thus, by making the effective aperture widths of the first sub pixel  49 R, the second sub pixel  49 G, and the third sub pixel  49 B in the row direction (X direction) larger than the effective aperture width of the fourth sub pixel  49 W, the numeral apertures of the first sub pixel  49 R, the second sub pixel  49 G, and the third sub pixel  49 B can be increased. As just described, two of the signal line Sq+2 and the signal line Sq+3 are arranged being biased toward the fourth sub pixel  49 W side. In the same manner, the wiring arrangement of two of the signal line Sq+5 and the signal line Sq+6 are arranged being biased toward the fourth sub pixel  49 W side. 
       FIG. 15  illustrates the display data of the intermediate output signal Smid that is output by the data converter  23  illustrated in  FIG. 4 , and the display data corresponding to the order of panel drive that is the output signal Sout processed by the decimation and color correction unit  24 . As illustrated in  FIGS. 13 and 14 , the scanning circuit  42 , as a control device, transmits an image signal to be transmitted to the second sub pixels  49 G in the first column by shifting by one horizontal line of pixels (one row) from the image signal to be transmitted to the first sub pixels  49 R of the same pixels  48  in which the second sub pixel  49 G is present. The scanning circuit  42 , as the control device, transmits an image signal to be transmitted to the second sub pixels  49 G in the first column by shifting by one horizontal line of pixels (one row) from the image signal to be transmitted to the third sub pixels  49 B of the same pixels  48 B in which the second sub pixel  49 G is present. Consequently, the decimation and color correction unit  24  illustrated in  FIG. 4  performs decimation and color correction to shift the image signal to be transmitted to the second sub pixels  49 G in the first row or the third row by one horizontal line of pixels (one row) from the image signal to be transmitted to the first sub pixels  49 R of the same pixels  48 A and the third sub pixel  49 B of the pixels  48 B in which the second sub pixel  49 G is present. 
     Second Modification 
       FIG. 16  is a block diagram illustrating one example of the configuration of a display device according to a second modification of the embodiment.  FIG. 17  is a schematic diagram for schematically explaining a cross-section of the image display panel in the second modification of the embodiment.  FIG. 18  is a diagram illustrating a pixel array of the image display panel in the second modification of the embodiment. For the constituent elements the same as those in the foregoing, the detailed explanations will be omitted. 
     As illustrated in  FIG. 16 , the display device  10  in the second modification of the embodiment includes the signal processor  20  that receives an input signal (RGB data) from the image output unit  12  of the control device  11  and outputs it by performing a given data conversion processing, the image display panel  30  that displays an image based on the output signal output from the signal processor  20 , and the image-display-panel drive circuit  40  that controls the drive of the image display panel  30  (display unit). The display device  10  in the second modification of the embodiment is a reflective display device, and images can be displayed on the image display panel  30  by the light of a front light or by the environmental light from the outside. 
     As illustrated in  FIG. 17 , the image display panel  30  includes a first substrate (pixel substrate)  70 , a second substrate (counter substrate)  80  that is arranged facing the surface of the first substrate  70  in a perpendicular direction, and a liquid crystal layer  79  that is provided in an inserted manner between the first substrate  70  and the second substrate  80 . In the above-described embodiment, in the image display panel  30 , the light source device  50  is arranged on the side of the first substrate (pixel substrate)  70  opposite to the liquid crystal layer  79 . However, the image display panel in the second modification does not include the light source device  50 . 
     The first substrate  70  is a substrate on which various circuits are formed on a translucent substrate  71 , and on the translucent substrate  71 , includes a plurality of first electrodes (pixel electrode)  78 , which are arranged in a matrix, and a second electrode (common electrodes)  76 . As illustrated in  FIG. 17 , the first electrodes  78  and the second electrode  76  are insulated by an insulating layer  77  and face each other in the direction perpendicular to the surface of the translucent substrate  71 . The first electrodes  78  and the second electrode  76  are translucent electrodes formed of translucent conductive material (translucent conductive oxide) such as indium tin oxide (ITO). 
     When a thin-film transistor that is the switching element of each of the above-described sub pixels  49  is assumed as a transistor Tr, the first substrate  70  has a semiconductor layer in which the transistor Tr, which is the switching element of each of the above-described sub pixels  49 , is formed and wiring such as signal lines Sq (0≦q≦m) that supply a pixel signal to each of the first electrodes  78  and scan lines Gp (0≦p≦n) that drive the transistor Tr, being layer-stacked on the translucent substrate  71  and insulated by insulating layers  72 ,  73 , and  75 . 
     In the display device  10  in the second modification of the embodiment, as illustrated in  FIG. 3 , the pixel  48 A includes, out of 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, three of the first sub pixel  49 R, the second sub pixel  49 G, and the third sub pixel  49 B. The pixel  48 B includes, out of 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, three of the first sub pixel  49 R, the second sub pixel  49 G, and the fourth sub pixel  49 W. The image display panel  30  includes the scan lines Gp+1, Gp+2, and Gp+3 extending in the X direction and the signal lines Sq+1, Sq+2, Sq+3, Sq+4, Sq+5, Sq+6, and Sq+7 extending in the Y direction. The display device  10  in the second modification of the embodiment can increase, by arranging the pixels  48 A and the pixels  48 B as illustrated in  FIG. 3 , the reflectivity of reflected light L 2  that is incident light L 1  reflected on the first electrodes  78  in high-definition, even when transmitted light L 3  of the light source device  50  is not used. 
     As illustrated in  FIG. 17 , the signal lines Sq (0≦q≦m) are hard to affect the first electrodes  78  that act as reflectors. Consequently, without considering the effect in which the transmitted light L 3  of the light source device  50  is masked by the signal lines Sq (0≦q≦m), the arrangement of the pixels  48 A and the pixels  48 B as illustrated in  FIG. 18  is also possible, for example. 
     As illustrated in  FIG. 18 , between the sub pixels  49  of the first column and the sub pixels  49  of the second column, a single signal line Sq+3 is arranged. Between the sub pixels  49  of the second column and the sub pixels  49  of the third column, two of the signal line Sq+4 and the signal line Sq+5 are arranged. Between the sub pixels  49  of the third column and the sub pixels  49  of the fourth column, a single signal line Sq+6 is arranged. The distance between the signal line Sq+2 and the signal line Sq+1 is smaller than the distance between the signal line Sq+2 and the signal line Sq+3. Thus, the distance between the signal line Sq+1 and the signal line Sq+3 is substantially the same as the distance between the signal line Sq+2 and the signal line Sq+3. In the same manner, the distance between the signal line Sq+4 and the signal line Sq+6 is substantially the same as the distance between the signal line Sq+5 and the signal line Sq+6. In the case of a reflective liquid crystal display such as the display device  10  in the second modification of the embodiment, as illustrated in  FIG. 17 , because it has a reflecting layer (the first electrodes  78  in this example) between the signal lines and the display surface, the positions of the signal lines have no effect on the luminance of the external light. Consequently, the positions of the signal lines are arbitrary, and the signal lines may be arranged in an equal distance so as to run through the middle of the respective sub pixels. 
     In the display device  10  in the second modification of the embodiment, the second electrode (common electrodes) may be arranged an upper side. One of the first electrodes and the second electrode may be formed as a reflecting electrode. In the display device  10  in the second modification of the embodiment, one of the first electrodes  78  and the second electrode  76  may be arranged on the second substrate  80  and driven by a longitudinal electric field. As in the foregoing, the display device  10  in the embodiment may be reflective or transmissive, and the drive system of liquid crystals may be a transverse electric field or a longitudinal electric field. 
     Application Examples 
     With reference to  FIGS. 19 and 20 , the application examples of the display device  10  exemplified in the embodiment and the modifications will be described.  FIGS. 19 and 20  are diagrams illustrating examples of an electronic apparatus including the display device in the embodiment. The display device  10  in the embodiment can be applied to electronic apparatuses in all areas including car navigation systems such as one illustrated in  FIG. 19 , television apparatuses, digital cameras, notebook computers, handheld terminal devices such as a cellular phone illustrated in  FIG. 20 , and video cameras. In other words, the display device  10  in the embodiment can be applied to the electronic apparatuses in all areas that display a video signal received from the outside or generated internally, as an image or a video. The electronic apparatus includes the control device  11  (see  FIG. 1 ) that supplies a video signal to the display device and controls the operation of the display device. 
     The electronic apparatus illustrated in  FIG. 19  is a car navigation apparatus to which the display device  10  in the embodiment and the modifications is applied. The display device  10  is installed on a dashboard  300  inside a vehicle. Specifically, it is installed on the dashboard  300  between a driver seat  311  and a passenger seat  312 . The display device  10  of the car navigation apparatus is used for navigation display, music operation screen display, movie reproduction display, and others. 
     The electronic apparatus illustrated in  FIG. 20  is an information portable terminal, to which the display device  10  according to the embodiment and the modifications thereof is applied, which operates as a portable computer, a multifunctional cellular phone, a mobile computer allowing a voice communication, or a communicable portable computer, and may be called a smartphone or a tablet terminal in some cases. This information portable terminal includes a display unit  561  on a surface of a housing  562 , for example. The display unit  561  includes the display device  10  according to the embodiment and the modifications thereof and a touch detection (what is called a touch panel) function that can detect an external proximity object. 
     The embodiment is not limited to the above description. The components according to the embodiment described above include a component that is easily conceivable by those skilled in the art, substantially the same component, and what is called an equivalent. The components can be variously omitted, replaced, and modified without departing from the gist of the embodiment described above.