Patent Publication Number: US-10777113-B2

Title: Display device

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims priority from Japanese Application No. 2014-241877, filed on Nov. 28, 2014, the contents of which are incorporated by reference herein in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The present invention relates to a display device. 
     2. Description of the Related Art 
     Display devices using four colors, i.e., red (R), green (G), blue (B), and white (W) as colors of a plurality of sub-pixels constituting a pixel are publicly known. By including the W sub-pixel in addition to the R, G, and B sub-pixels, the display device can display a color including a white component more brightly. 
     However, the display device in which the pixel is constituted of sub-pixels of four colors includes the W sub-pixel, so that an area of a display region that can be allocated to the R, G, and B sub-pixels is reduced by an area of the W sub-pixel. Therefore, as compared with a display device in which the pixel is constituted only of the R, G, B sub-pixels, the display device described above has a problem that luminance of at least one or more colors among the three colors having large output values is lowered, such as luminance of a color (single color) represented by using any of the R, G, B sub-pixels. 
     Such a problem as described above is not limited to the display device using the four colors of R, G, B, and W as colors of sub-pixels, but is common to any display devices using four or more colors as colors of sub-pixels. In other words, in the display device including sub-pixels of four or more colors, an area of the sub-pixels that can be allocated to three colors, i.e., a first color, a second color, and a third color among the four or more colors is smaller as compared to the display device including the sub-pixels of only three colors. 
     For the foregoing reasons, there is a need for a display device that includes sub-pixels of four colors, i.e., a first color, a second color, a third color, and a fourth color, and can increase luminance of the first color, the second color, and the third color. Further, there is a need for a display device that can achieve an effect obtained by using the fourth color in addition to the first color, the second color, and the third color as the colors of the sub-pixels, while achieving higher luminance of the first color, the second color, and the third color at the same time. 
     SUMMARY 
     A display device includes a display unit in which a plurality of pixels are arranged. One pixel includes four sub-pixels, and the display unit includes: a pixel including one each of four sub-pixels of four different colors that are a first color, a second color, a third color, and a fourth color; and a pixel including four sub-pixels, where two of the four sub-pixels are identical and are one of sub-pixels of the first color, the second color, and the third color, and remaining two of the four sub-pixels are different two of the sub-pixels of the first color, the second color, and the third color but are not one of the identical sub-pixels. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating a configuration example of a display device according to a first embodiment for implementing the present invention; 
         FIG. 2  is a conceptual diagram of an image display panel and an image display panel drive circuit of the display device according to the first embodiment; 
         FIG. 3  is a diagram illustrating a pixel arrangement of a part of the image display panel according to the first embodiment; 
         FIG. 4  is a diagram illustrating a pixel arrangement of a part of the image display panel according to the first embodiment in a wider range than that in  FIG. 3 ; 
         FIG. 5  is a diagram illustrating an image display panel of a conventional RGBW-type; 
         FIG. 6  is a diagram illustrating an image display panel of a conventional RGB-type; 
         FIG. 7  is a diagram illustrating a pixel arrangement of a part of an image display panel according to a modification of the first embodiment; 
         FIG. 8  is a diagram illustrating a pixel arrangement of a part of an image display panel according to a second embodiment; 
         FIG. 9  is a diagram illustrating a pixel arrangement of a part of an image display panel according to a modification of the second embodiment; 
         FIG. 10  is a diagram illustrating a pixel arrangement of a part of an image display panel according to a third embodiment; 
         FIG. 11  is a diagram illustrating a pixel arrangement of a part of an image display panel according to a fourth embodiment; 
         FIG. 12  is a diagram illustrating an example of an electronic apparatus to which the display device according to each embodiment is applied; and 
         FIG. 13  is a diagram illustrating an example of an electronic apparatus to which the display device according to each embodiment is applied. 
     
    
    
     DETAILED DESCRIPTION 
     The following describes preferred embodiments for implementing the present invention in detail with reference to the accompanying drawings. The present invention is not limited to the embodiments described below. Components described below include a component that is easily conceivable by those skilled in the art, a component that is substantially identical thereto. Furthermore, the components described below may be appropriately combined. The disclosure is merely an example, and the present invention naturally encompasses an appropriate modification maintaining the gist of the invention that is easily conceivable by those skilled in the art. To further clarify the description, a width, a thickness, a shape, and the like of each component may be schematically illustrated in the drawings as compared with an actual aspect. However, this is merely an example and interpretation of the invention is not limited thereto. The same element as that described in the drawing that has already been discussed is denoted by the same reference numeral through the description and the drawings, and detailed description thereof will not be repeated in some cases. 
     First Embodiment 
       FIG. 1  is a block diagram illustrating a configuration example of a display device according to a first embodiment for implementing the present invention.  FIG. 2  is a conceptual diagram of an image display panel and an image display panel drive circuit of the display device according to the first embodiment. As illustrated in  FIG. 1 , a display device  10  includes a signal processing unit  20  that receives an input signal (for example, RGB data) and performs predetermined data conversion processing on the input signal to be output, an image display panel  40  that displays an image, an image display panel drive circuit  30  that controls driving of the image display panel  40  based on an output signal output from the signal processing unit  20 , and a light source unit  50  that illuminates the image display panel  40  from a back surface thereof, for example. 
     The signal processing unit  20  controls operations of the image display panel  40  and the light source unit  50  in synchronization with each other. The signal processing unit  20  is coupled to the image display panel drive circuit  30  for driving the image display panel  40 , and to the light source unit  50  that illuminates the image display panel  40 . The signal processing unit  20  processes the input signal input from the outside to generate the output signal and a light source control signal. More specifically, the signal processing unit  20  converts, for example, an input value (input signal) of an input hue-saturation-value (HSV) color space indicated by the input signal into an extended value (output signal) of an extended HSV color space extended with components of a first color, a second color, a third color, and a fourth color to be generated, and outputs an output signal based on the extended value to the image display panel drive circuit  30 . The signal processing unit  20  outputs the light source control signal corresponding to the output signal to the light source unit  50 . 
     As illustrated in  FIGS. 1 and 2 , in the image display panel  40 , a plurality of pixels  48  are arrayed in a two-dimensional matrix. In the example illustrated in  FIG. 2  the pixels  48  are arrayed in a matrix on an XY two-dimensional coordinate system. In this example, a row direction is the X-direction, and a column direction is the Y-direction. In this way, the pixels  48  are arranged in a matrix along two directions intersecting with each other (the row direction and the column direction). As illustrated in  FIG. 2 , one pixel  48  includes a plurality of sub-pixels  49 . The sub-pixels  49  will be described below. 
     The image display panel drive circuit  30  includes a signal output circuit  31  and a scanning circuit  32 . The image display panel drive circuit  30  holds video signals using the signal output circuit  31 , and sequentially outputs the video signals to the image display panel  40 . The signal output circuit  31  is electrically coupled to the image display panel  40  via a wiring DTL. The image display panel drive circuit  30  performs control, by using the scanning circuit  32 , to turn ON or OFF a switching element (for example, a thin film transistor (TFT)) for controlling an operation of a sub-pixel (for example, display luminance, and in this case, light transmittance) in the image display panel  40 . The scanning circuit  32  is electrically coupled to the image display panel  40  via a wiring SCL. 
     The light source unit  50  includes a light source such as a light emitting diode (LED), and illuminates the image display panel  40  in response to supply of electric power and the light source control signal output from the signal processing unit  20 . The light source unit  50  is arranged, for example, on the back surface of the image display panel  40 , and emits light toward the image display panel  40  to illuminate the image display panel  40 . The light source unit  50  adjusts electric current and a voltage to be supplied to the light source unit  50 , and a duty ratio of a signal based on the light source control signal, and controls a quantity of light (light intensity) emitted to the image display panel  40 . The light source unit  50  may be arranged on the front surface of the image display panel  40  as a front light. When a self-luminous display device such as an organic light emitting diode (OLED) display device is used as the image display panel  40 , the light source unit  50  is not required. 
       FIG. 3  is a diagram illustrating a pixel arrangement of a part of the image display panel according to the first embodiment. As illustrated in  FIGS. 2 and 3 , the pixel  48  includes four sub-pixels  49 . The pixel  48  includes at least a first sub-pixel  49 R, a second sub-pixel  49 G, and a third sub-pixel  49 B. Some of the pixels  48  (pixels  48 W) further include a fourth sub-pixel  49 W. The four sub-pixels included in the pixel  48  are continuously arranged along a certain direction (for example, the row direction). 
     The first sub-pixel  49 R displays a first color component (for example, red as a first primary color). The second sub-pixel  49 G displays a second color component (for example, green as a second primary color). The third sub-pixel  49 B displays a third color component (for example, blue as a third primary color). The fourth sub-pixel  49 W displays a fourth color component (i.e., white). 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 from one another, they are collectively referred to as the sub-pixels  49 . As described above, in the first embodiment, the first color, the second color, and the third color correspond to red, green and blue, respectively. The fourth color corresponds to white in the first embodiment. 
     In the first embodiment, the components of the first color, the second color, the third color, and the fourth color of the extended HSV color space indicated by the output signal are assumed to correspond to the respective color components 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. However, the color components of the output signal do not necessarily directly correspond to the color components of the sub-pixels  49 . For example, maximum luminance of a single color that can be achieved by at least one of the color components of the sub-pixels  49  may be higher than maximum luminance of the single color that is defined in the extended HSV color space indicated by the output signal. 
     More specifically, the display device  10  is a transmissive color liquid crystal display device, for example. The image display panel  40  is a color liquid crystal display panel in which a first color filter that transmits the first primary color is arranged between the first sub-pixel  49 R and an image observer, a second color filter that transmits the second primary color is arranged between the second sub-pixel  49 G and the image observer, and a third color filter that transmits the third primary 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. A transparent resin layer may be provided to the fourth sub-pixel  49 W in place of the color filter. 
     In the example illustrated in  FIG. 3 , four sub-pixels  49  each having an equal area are arranged as a stripe array. However, the stripe array is merely an example, and the embodiment is not limited thereto. The structure and arrangement of four sub-pixels  49  included in one pixel  48  are not specifically limited. For example, in the image display panel  40 , the four sub-pixels  49  may be arranged as an array that is similar to a diagonal array (mosaic array), a delta array (triangle array), or a rectangle array. The four sub-pixels do not necessarily have the equal area. 
     Typically, an array similar to the stripe array is suitable for displaying data and/or character strings in a personal computer and the like. On the other hand, an array similar to the mosaic array is suitable for displaying a natural image in a video camera recorder, a digital still camera, or the like. These relations between arrays and products are merely examples, and the embodiment is not limited thereto. The relations are optional. 
     The pixels  48  include the pixel  48 W including one each 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 pixels  48 R,  48 G, and  48 B each including four sub-pixels, where two of the sub-pixels are identical and are one of the first sub-pixel  49 R, the second sub-pixel  49 G, and the third sub-pixel  49 B and the remaining two sub-pixels are different two of the first sub-pixel  49 R, the second sub-pixel  49 G, and the third sub-pixel  49 B but are not one of the identical sub-pixels. A pixel including two first sub-pixels  49 R, one second sub-pixel  49 G, and one third sub-pixel  49 B is assumed to be the pixel  48 R. A pixel including two second sub-pixels  49 G, one first sub-pixel  49 R, and one third sub-pixel  49 B is assumed to be the pixel  48 G. A pixel including two third sub-pixels  49 B, one first sub-pixel  49 R, and one second sub-pixel  49 G is assumed to be the pixel  48 B. When it is not necessary to distinguish the pixels  48 R,  48 G,  48 B, and  48 W from one another, they are collectively referred to as the pixels  48 . Unless specifically described, reference numerals of the pixels  48 R,  48 G,  48 B, and  48 W are used only for distinguishing the numbers of the first sub-pixels  49 R, the second sub-pixels  49 G, the third sub-pixels  49 B, and the fourth sub-pixels  49 W included in each of the pixels, and are not used for distinguishing arrangement orders of these sub-pixels  49 . 
       FIG. 4  is a diagram illustrating a pixel arrangement of a part of the image display panel  40  according to the first embodiment in a wider range than that in  FIG. 3 . In  FIG. 4  and some other figures, the reference numerals related to the sub-pixels  49  are omitted. In  FIG. 4 , a rectangle in which “R” is described represents the first sub-pixel  49 R, a rectangle in which “G” is described represents the second sub-pixel  49 G, a rectangle in which “B” is described represents the third sub-pixel  49 B, and a rectangle in which “W” is described represents the fourth sub-pixel  49 W. In  FIG. 4  and some other figures, the reference numerals for distinguishing the pixels  48 R,  48 G,  48 B, and  48 W from one another are written on part of the rectangles representing the sub-pixels  49 . In the image display panel  40 , a pixel column (R column) in which the pixels  48 R and the pixels  48 W are alternately arranged along the column direction, a pixel column (G column) in which the pixels  48 G and the pixels  48 W are alternately arranged along the column direction, and a pixel column (B column) in which the pixels  48 B and the pixels  48 W are alternately arranged along the column direction, and the R, G, and B columns are periodically arranged in this order along the row direction. Further, in the image display panel  40 , the pixels  48 R,  48 W,  48 B,  48 W,  48 G, and  48 W are periodically arranged in this order along the row direction. 
     The following describes a more specific arrangement of the pixels  48 R,  48 G,  48 B, and  48 W with reference to  FIG. 4 . In the description of an adjacent relation between a certain pixel  48  and another pixel  48  and an adjacent relation between a certain sub-pixel  49  and another sub-pixel  49 , with reference to  FIG. 4 , the arrangement of the pixel  48  adjacent to the right side of a certain pixel  48  in the row direction may be referred to as “adjacently right”, and the arrangement of the pixel  48  adjacent to the lower side of a certain pixel  48  in the column direction may be referred to as “adjacently below”. Similarly, the arrangement of the sub-pixels  49  adjacent to the upper side and the lower side of a certain sub-pixel  49  in the column direction may be referred to as “vertically adjacent sides”. 
     The pixel  48 W of the G column is arranged adjacently right of the pixel  48 R. The pixel  48 B is arranged adjacently right of the pixel  48 W of the G column. The pixel  48 W of the R column is arranged adjacently right of the pixel  48 B. The pixel  48 G is arranged adjacently right of the pixel  48 W of the R column. The pixel  48 W of the B column is arranged adjacently right of the pixel  48 G. The pixel  48 R is arranged adjacently right of the pixel  48 W of the B column. Subsequently, until reaching the right end of a pixel row included in the image display panel  40 , the pixels are arranged in this order along the row direction. In the example illustrated in  FIG. 4 , the pixel column at the left end is the R column, so that the pixel  48  at the left end of each row is the pixel  48 R or the pixel  48 W of the R column. However, this arrangement is merely an example, and the embodiment is not limited thereto. The pixel column at the left end may be any pixel column (for example, the G column or the B column). 
     The pixel  48 W of the R column is arranged adjacently below the pixel  48 R. The pixel  48 R is arranged adjacently below the pixel  48 W of the R column. The pixel  48 W of the G column is arranged adjacently below the pixel  48 G. The pixel  48 G is arranged adjacently below the pixel  48 W of the G column. The pixel  48 W of the B column is arranged adjacently below the pixel  48 B. The pixel  48 B is arranged adjacently below the pixel  48 W of the B column. In each of the R column, the G column, and the B column, the pixels are arranged in this order along the column direction. In this way, in the image display panel  40 , the pixels  48 W are arranged in a hound&#39;s-tooth check pattern (like a checkered pattern). In other words, the pixel (pixel  48 W) including the sub-pixel of the fourth color (fourth sub-pixel  49 W) and the pixels (the pixels  48 R,  48 G, and  48 B) not including the sub-pixel of the fourth color are alternately arranged along at least one of two directions (in the first embodiment, the row direction and the column direction). 
     The first sub-pixel  49 R, the second sub-pixel  49 G, and the third sub-pixel  49 B in the pixel  48 R are arranged in the order of, from the left to the right of the stripe array, the first sub-pixel  49 R, the first sub-pixel  49 R, the second sub-pixel  49 G, and the third sub-pixel  49 B. Similarly, the first sub-pixel  49 R, the second sub-pixel  49 G, and the third sub-pixel  49 B in the pixel  48 G are arranged in the order of the first sub-pixel  49 R, the second sub-pixel  49 G, the second sub-pixel  49 G, and the third sub-pixel  49 B. The first sub-pixel  49 R, the second sub-pixel  49 G, and the third sub-pixel  49 B in the pixel  48 B are arranged in the order of the first sub-pixel  49 R, the second sub-pixel  49 G, the third sub-pixel  49 B, and the third sub-pixel  49 B. In this way, two sub-pixels  49  of the same color included in one pixel  48  are adjacent to each other. 
     The first sub-pixels  49 R are arranged on the vertically adjacent sides of the fourth sub-pixel  49 W included in the pixel  48 W of the R column. Therefore, as illustrated in  FIG. 4 , among the columns of the sub-pixels  49  arranged in the order of the first sub-pixel  49 R, the first sub-pixel  49 R, the second sub-pixel  49 G, and the third sub-pixel  49 B along the row direction in the R column, the first sub-pixels  49 R included in one of the columns where the first sub-pixels  49 R belong to (for example, the column of the first sub-pixels  49 R adjacent to the second sub-pixels  49 G) are alternately replaced with the fourth sub-pixel  49 W. Similarly, the second sub-pixels  49 G are arranged on the vertically adjacent sides of the fourth sub-pixel  49 W included in the pixel  48 W of the G column. The third sub-pixels  49 B are arranged on the vertically adjacent sides of the fourth sub-pixel  49 W included in the pixel  48 W of the B column. In this way, in the column of the sub-pixels  49  in which the fourth sub-pixels  49 W are arranged, the fourth sub-pixels  49 W are arranged every other row. 
     An arrangement interval of the fourth sub-pixels  49 W in the row direction has a predetermined periodicity. More specifically, as illustrated in  FIG. 4  for example, the fourth sub-pixel  49 W included in the pixel  48 W of the B column is arranged on the right side of the fourth sub-pixel  49 W included in the pixel  48 W of the R column at an interval of every eight other sub-pixels  49  (the first sub-pixel  49 R, the second sub-pixel  49 G, or the third sub-pixel  49 B). The fourth sub-pixel  49 W included in the pixel  48 W of the G column is arranged on the right side of the fourth sub-pixel  49 W included in the pixel  48 W of the B column at an interval of every six other sub-pixels  49 . The fourth sub-pixel  49 W included in the pixel  48 W of the R column is arranged on the right side of the fourth sub-pixel  49 W included in the pixel  48 W of the G column at an interval of every seven other sub-pixels  49 . In this way, the sub-pixels of the fourth color (fourth sub-pixels  49 W) are arranged at a predetermined cycle along at least one of two directions (in the first embodiment, the row direction and the column direction). 
     Since the fourth sub-pixels  49 W are arranged in the manner described above, the arrangement order 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 may be different depending on which column among the R column, the G column, and the B column the pixel  48 W belongs to. In the pixel  48 W of the R column and the pixel  48 W of the G column, the first sub-pixel  49 R, the fourth sub-pixel  49 W, the second sub-pixel  49 G, and the third sub-pixel  49 B are arranged in this order from the left to the right of the stripe array. In the pixel  48 W of the B column, the first sub-pixel  49 R, the second sub-pixel  49 G, the fourth sub-pixel  49 W, and the third sub-pixel  49 B are arranged in this order. These arrangement orders are merely an example, and the embodiment is not limited thereto. For example, the arrangement order 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 in the pixel  48 W of the G column may be an arrangement order of the first sub-pixel  49 R, the second sub-pixel  49 G, the fourth sub-pixel  49 W, and the third sub-pixel  49 B. 
     The number of the sub-pixels of the first color (first sub-pixels  49 R), the number of the sub-pixels of the second color (second sub-pixels  49 G), and the number of the sub-pixels of the third color (third sub-pixels  49 B) are the same. More specifically, a ratio among the number of the first sub-pixels  49 R, the number of the second sub-pixels  49 G, the number of the third sub-pixels  49 B, and the number of the fourth sub-pixels  49 W is 7:7:7:3. 
       FIG. 5  is a diagram illustrating the image display panel  40  of the conventional RGBW-type. In the image display panel  40  of the RGBW-type in which all the pixels  48  are the pixels  48 W as illustrated in  FIG. 5 , the ratio among the number of the first sub-pixels  49 R, the number of the second sub-pixels  49 G, the number of the third sub-pixels  49 B, and the number of the fourth sub-pixels  49 W is 1:1:1:1. Under the condition that a difference between the image display panel  40  according to the first embodiment illustrated in  FIG. 4  and the image display panel  40  of the conventional type illustrated in  FIG. 5  is only the color of the sub-pixel  49 , the luminance of the first color component, the second color component, and the third color component in the image display panel  40  according to the first embodiment is 7/6 times higher than that of the first color component, the second color component, and the third color component in the image display panel  40  of the conventional type. In this way, according to the first embodiment, the luminance of the first color, the second color, and the third color can be further increased. 
       FIG. 6  is a diagram illustrating the image display panel  40  of the conventional RGB-type. As illustrated in  FIG. 6 , the image display panel  40  of the conventional RGB-type constituted of a pixel  48 RGB including only the first sub-pixel  49 R, the second sub-pixel  49 G, and the third sub-pixel  49 B does not include the fourth sub-pixel  49 W, so that an effect of including the fourth color component (for example, improvement in the luminance) cannot be achieved. On the other hand, the image display panel  40  according to the first embodiment includes the fourth sub-pixel  49 W, so that the effect of including the fourth color component can be exhibited. In this way, according to the first embodiment, the effect obtained by using the fourth color in addition to the first color, the second color, and the third color as the color of the sub-pixel  49 , and higher luminance of the first color, the second color, and the third color, can be achieved at the same time. 
     As described above, the signal processing unit  20  converts, for example, the input value (input signal) of the input HSV color space indicated by the input signal into the extended value (output signal) of the extended HSV color space extended with components of the first color, the second color, the third color, and the fourth color to be generated, and outputs the output signal based on the extended value to the image display panel drive circuit. In this case, since the pixel  48 R, the pixel  48 G, and the pixel  48 B do not include the fourth sub-pixel  49 W, the image display panel  40  cannot output the fourth color component. Thus, in the first embodiment, exception processing is performed on the pixel not including the fourth sub-pixel  49 W. More specifically, as for the pixel  48 R, the pixel  48 G, and the pixel  48 B, the image display panel  40  may output the first color component, the second color component, and the third color component disregarding the fourth color component, for example. The signal processing unit  20  may output the output signal corresponding to the pixel  48 R, the pixel  48 G, and the pixel  48 B as the output signal corresponding to a color that can be extended only with the first color, the second color, and the third color in the extended HSV color space. The signal processing unit  20  may adjust the luminance using the fourth sub-pixel  49 W in a pixel group unit of a predetermined combination. More specifically, in a case of the pixel arrangement illustrated in  FIG. 4 , for example, 2 pixels×3 pixels (row direction×column direction) are assumed to constitute one pixel group, a luminance component that can be converted into the fourth color in the pixel group and can be extended with the fourth sub-pixel  49 W included in the pixel group may be distributed to the fourth sub-pixel  49 W included in the pixel group, and the luminance of the other color components may be reduced by the luminance distributed to the fourth sub-pixel  49 W. When a combination of the first color, the second color, and the third color constituting the input signal is red, green, and blue (RGB), an example of the luminance component that can be converted into the fourth color is a color component of a mixed color of all of the color components (white obtained by mixing RGB) corresponding to the smallest value among the luminance values of the color components indicated by the input signal. As a specific example, assuming that the input signal of RGB is “100, 100, and 50”, the luminance component therein that can be converted into white is “50, 50, and 50”. Distribution of each color in such conversion is appropriately set according to the first color, the second color, the third color, and the fourth color. 
     As described above, according to the first embodiment, the image display panel  40  functioning as a display unit includes the pixel (for example, the pixel  48 W) including one each of four sub-pixels of four colors, i.e., the first color, the second color, the third color, and the fourth color that are different from one another (for example, 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 pixels (for example, the pixel  48 R, the pixel  48 G, and the pixel  48 B) each including four sub-pixels, where two of the sub-pixels are identical and are one of the sub-pixels of the first color, the second color, and the third color, and the remaining two sub-pixels are different two of the sub-pixels of the first color, the second color, and the third color but are not one of the identical sub-pixels. Accordingly, under the condition that the sub-pixels of four colors, i.e., the first color, the second color, the third color, and the fourth color are included, the luminance of the first color, the second color, and the third color can be further increased. According to the first embodiment, the effect obtained by using the fourth color in addition to the first color, the second color, and the third color as the color of the sub-pixel, and higher luminance of the first color, the second color, and the third color, can be achieved at the same time. 
     The sub-pixels of the fourth color (for example, the fourth sub-pixels  49 W) are arranged at a predetermined cycle along at least one of the two directions, so that the sub-pixels of the fourth color can be distributively arranged without being concentrated on a part of the display unit. 
     The pixel (pixel  48 W) including the sub-pixel of the fourth color (fourth sub-pixel  49 W) and the pixels not including the sub-pixel of the fourth color (the pixel  48 R, the pixel  48 G, and the pixel  48 B) are alternately arranged along at least one of the two directions, so that the pixels including the sub-pixel of the fourth color can be distributively arranged without being concentrated on a part of the display unit. 
     The number of the sub-pixels of the first color (first sub-pixels  49 R), the number of the sub-pixels of the second color (second sub-pixels  49 G), and the number of the sub-pixels of the third color (third sub-pixels  49 B) are the same, so that the luminance of these colors can be further increased while preventing biased increase in the luminance of a specific color among the first color, the second color, and the third color. 
     The two sub-pixels  49  of the same color included in one pixel  48  are adjacent to each other, so that the luminance of the color of the two sub-pixels  49  in a region of the adjacent two sub-pixels  49  can be further increased. 
     Modification of First Embodiment 
       FIG. 7  is a diagram illustrating a pixel arrangement of a part of the image display panel  40  according to a modification of the first embodiment. As illustrated in  FIG. 7 , the second sub-pixel  49 G and the fourth sub-pixel  49 W in the pixel  48 W of  FIG. 4  according to the first embodiment may be replaced with each other. In  FIG. 7 , 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 in the pixel  48 W are arranged in the order of, from the left to the right of the stripe array, the first sub-pixel  49 R, the second sub-pixel  49 G, the fourth sub-pixel  49 W, and the third sub-pixel  49 B. 
     In  FIG. 7 , the arrangement interval of the fourth sub-pixels  49 W in the row direction has a predetermined periodicity. More specifically, as illustrated in  FIG. 7  for example, the fourth sub-pixel  49 W included in the pixel  48 W of the B column is arranged on the right side of the fourth sub-pixel  49 W included in the pixel  48 W of the R column at an interval of every seven other sub-pixels  49  (the first sub-pixel  49 R, the second sub-pixel  49 G, or the third sub-pixel  49 B). The fourth sub-pixel  49 W included in the pixel  48 W of the G column is arranged on the right side of the fourth sub-pixel  49 W included in the pixel  48 W of the B column at an interval of every seven other sub-pixels  49 . The fourth sub-pixel  49 W included in the pixel  48 W of the R column is arranged on the right side of the fourth sub-pixel  49 W included in the pixel  48 W of the G column at an interval of every seven other sub-pixels  49 . In this way, the sub-pixels of the fourth color (fourth sub-pixels  49 W) are arranged at a predetermined cycle along at least one of the two directions (in the modification of the first embodiment, the row direction and the column direction). 
     In two adjacent columns of the pixels  48 , three columns of the sub-pixels  49  are interposed between the column of the sub-pixels  49  where the fourth sub-pixels  49 W are arranged in one of the adjacent two columns and the column of the sub-pixels  49  where the fourth sub-pixels  49 W are arranged in the other one of the adjacent two columns. In this way, according to the modification of the first embodiment, the fourth sub-pixels  49 W are arranged at regular intervals. 
     According to the modification of the first embodiment, the same effect as that of the first embodiment can be obtained. More specifically, under the condition that the sub-pixels of four colors, i.e., the first color, the second color, the third color, and the fourth color are included, the luminance of the first color, the second color, and the third color can be further increased. According to the modification of the first embodiment, the effect obtained by using the fourth color in addition to the first color, the second color, and the third color as the color of the sub-pixel, and higher luminance of the first color, the second color, and the third color, can be achieved at the same time. The sub-pixels of the fourth color can be distributively arranged without being concentrated on a part of the display unit. The luminance of the first color, the second color, and the third color can be further increased while preventing biased increase in the luminance of a specific color among these colors. The luminance of the color of the two adjacent sub-pixels  49  in a region of the two sub-pixels  49  can be further increased. The fourth sub-pixels  49 W are arranged at regular intervals, so that the sub-pixels of the fourth color can be distributively arranged more uniformly. 
     Second Embodiment 
     Next, the following describes a second embodiment for implementing the present invention. The same component as that of the first embodiment may be denoted by the same reference numeral, and the description thereof may be omitted.  FIG. 8  is a diagram illustrating a pixel arrangement of a part of the image display panel  40  according to the second embodiment. The range illustrated in  FIG. 8  corresponds to the range illustrated in  FIG. 4 . As illustrated in  FIG. 8 , the arrangement of the sub-pixels  49  of the B column according to the second embodiment is such that the second sub-pixel  49 G of the B column in the first embodiment is replaced with the third sub-pixel  49 B or the fourth sub-pixel  49 W of the B column. Except this difference in the arrangement, the second embodiment is the same as the first embodiment. 
     More specifically, the first sub-pixel  49 R, the second sub-pixel  49 G, and the third sub-pixel  49 B in the pixel  48 B of the B column are arranged in the order of, from the left to the right of the stripe array, the first sub-pixel  49 R, the third sub-pixel  49 B, the second sub-pixel  49 G, and the third sub-pixel  49 B. Similarly, 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 in the pixel  48 W of the B column are arranged in the order of the first sub-pixel  49 R, the fourth sub-pixel  49 W, the second sub-pixel  49 G, and the third sub-pixel  49 B. 
     According to the arrangement of the sub-pixels  49  of the B column as described above, in the second embodiment, the fourth sub-pixel  49 W included in the pixel  48 W of the B column is arranged on the right side of the fourth sub-pixel  49 W included in the pixel  48 W of the R column at an interval of every seven other sub-pixels  49  (the first sub-pixel  49 R, the second sub-pixel  49 G, or the third sub-pixel  49 B). The fourth sub-pixel  49 W included in the pixel  48 W of the G column is arranged on the right side of the fourth sub-pixel  49 W included in the pixel  48 W of the B column at an interval of every seven other sub-pixels  49 . The fourth sub-pixel  49 W included in the pixel  48 W of the R column is arranged on the right side of the fourth sub-pixel  49 W included in the pixel  48 W of the G column at an interval of every seven other sub-pixels  49 . In two adjacent columns of the pixels  48 , three columns of the sub-pixels  49  are interposed between the column of the sub-pixels  49  where the fourth sub-pixels  49 W are arranged in one of the adjacent two columns and the column of the sub-pixels  49  where the fourth sub-pixels  49 W are arranged in the other one of the adjacent two columns. In this way, according to the second embodiment, the fourth sub-pixels  49 W are arranged at regular intervals. 
     According to the second embodiment, in addition to obtaining the same effect as that of the first embodiment, the fourth sub-pixels  49 W are arranged at regular intervals, so that the sub-pixels of the fourth color can be distributively arranged more uniformly. 
     Modification of Second Embodiment 
       FIG. 9  is a diagram illustrating a pixel arrangement of a part of the image display panel  40  according to a modification of the second embodiment. As illustrated in  FIG. 9 , the third sub-pixel  49 B and the fourth sub-pixel  49 W in the pixel  48 W of  FIG. 8  may be replaced with each other. In  FIG. 9 , 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 in the pixel  48 W are arranged in the order of, from the left to the right of the stripe array, the first sub-pixel  49 R, the second sub-pixel  49 G, the fourth sub-pixel  49 W, and the third sub-pixel  49 B. 
     According to the arrangement of the pixels  48 W as described above, in the modification of the second embodiment, the fourth sub-pixel  49 W included in the pixel  48 W of the B column is arranged on the right side of the fourth sub-pixel  49 W included in the pixel  48 W of the R column at an interval of every seven other sub-pixels  49  (the first sub-pixel  49 R, the second sub-pixel  49 G, or the third sub-pixel  49 B). The fourth sub-pixel  49 W included in the pixel  48 W of the G column is arranged on the right side of the fourth sub-pixel  49 W included in the pixel  48 W of the B column at an interval of every seven other sub-pixels  49 . The fourth sub-pixel  49 W included in the pixel  48 W of the R column is arranged on the right side of the fourth sub-pixel  49 W included in the pixel  48 W of the G column at an interval of every seven other sub-pixels  49 . In two adjacent columns of the pixels  48 , three columns of the sub-pixels  49  are interposed between the column of the sub-pixels  49  where the fourth sub-pixels  49 W are arranged in one of the adjacent two columns and the column of the sub-pixels  49  where the fourth sub-pixels  49 W are arranged in the other one of the adjacent two columns. In this way, according to the modification of the second embodiment, the fourth sub-pixels  49 W are arranged at regular intervals. 
     According to the modification of the second embodiment, in addition to obtaining the same effect as that of the first embodiment, the fourth sub-pixels  49 W are arranged at regular intervals, so that the sub-pixels of the fourth color can be distributively arranged more uniformly. 
     Third Embodiment 
     Next, the following describes a third embodiment for implementing the present invention. The same component as that of the first embodiment may be denoted by the same reference numeral, and the description thereof may be omitted.  FIG. 10  is a diagram illustrating a pixel arrangement of a part of the image display panel  40  according to the third embodiment. As illustrated in  FIG. 10 , in the third embodiment, the pixel columns along the row direction are arranged in the order of, from the left, the B column, the R column, the G column, the G column, the B column, and the R column. In the image display panel  40  according to the third embodiment, sets of the pixel columns arranged in this order (the B column, the R column, the G column, the G column, the B column, and the R column) are periodically arranged along the row direction. 
     In the third embodiment, the pixels  48 W are not arranged at every other pixel in the row direction. More specifically, for example, in the uppermost pixel row in  FIG. 10 , the pixel  48 B, the pixel  48 W of the R column, the pixel  48 G, the pixel  48 W of the G column, the pixel  48 W of the B column, and the pixel  48 R are arranged in this order from the left end of the sets of the pixel columns. In this case, when the pixel  48 W is represented as “present” and pixels other than the pixel  48 W are represented as “absent”, the pixels are represented as “absent”, “present”, “absent”, “present”, “present”, and “absent” in this order. In the third embodiment, the fourth sub-pixel  49 W included in the pixel  48 W of the G column is arranged on the right side of the fourth sub-pixel  49 W included in the pixel  48 W of the R column at an interval of every seven other sub-pixels  49  (the first sub-pixel  49 R, the second sub-pixel  49 G, or the third sub-pixel  49 B). Except this difference in the arrangement of the pixel columns and the pixel  48 W (fourth sub-pixel  49 W), the third embodiment is the same as the first embodiment. For confirmation, in the third embodiment, the pixels  48 W are arranged at every other pixel in the column direction similarly to the first embodiment. 
     According to the third embodiment, the same effect as that of the first embodiment can be exhibited. 
     Fourth Embodiment 
     Next, the following describes a fourth embodiment for implementing the present invention. The same component as that of the first embodiment may be denoted by the same reference numeral, and the description thereof may be omitted.  FIG. 11  is a diagram illustrating a pixel arrangement of a part of the image display panel  40  according to the fourth embodiment. As illustrated in  FIG. 11 , the image display panel  40  according to the fourth embodiment includes a pixel column (W column) constituted of only the pixels  48 W. The W column is a pixel column in which the pixel  48 W including the sub-pixels  49  arranged in the order of the fourth sub-pixel  49 W, the first sub-pixel  49 R, the second sub-pixel  49 G, and the third sub-pixel  49 B from the left to the right of the stripe array and the pixel  48 W including the sub-pixels  49  arranged in the order of the third sub-pixel  49 B, the first sub-pixel  49 R, the second sub-pixel  49 G, and the fourth sub-pixel  49 W from the left to the right of the stripe array are alternately arranged in the column direction. In the example illustrated in  FIG. 11 , the pixel columns are arranged along the row direction in the order of the B column, the R column, the W column, the G column, the R column, and the W column, from the left. In the image display panel  40  according to the fourth embodiment, the sets of the pixel columns arranged in this order are periodically arranged along the row direction. 
     In the fourth embodiment, among the number of the sub-pixels of the first color (first sub-pixels  49 R), the number of the sub-pixels of the second color (second sub-pixels  49 G), and the number of the sub-pixels of the third color (third sub-pixels  49 B), the number of the sub-pixels  49  of at least one of the colors is different from the number of the sub-pixels of the other colors. More specifically, in the example illustrated in  FIG. 11 , a ratio among the number of the first sub-pixels  49 R, the number of the second sub-pixels  49 G, the number of the third sub-pixels  49 B, and the number of the fourth sub-pixels  49 W is 14:13:13:8. The example illustrated in  FIG. 11  is applied to the image display panel  40  which shows a tendency of color reproduction such that the first color component is deficient as compared with the second color component and the third color component when the number of the sub-pixels of the first color (first sub-pixels  49 R), the number of the sub-pixels of the second color (second sub-pixels  49 G), and the number of the sub-pixels of the third color (third sub-pixels  49 B) are the same as described in the first to third embodiments. In this way, according to the fourth embodiment, color balance of the image display panel  40  can be adjusted by adjusting the ratio of the color components in the sub-pixels  49 . In the example illustrated in  FIG. 11 , the number of the first sub-pixels  49 R is relatively large in the sub-pixels  49  to further enhance the first color component. However, this is merely an example, and distribution of the color components in the sub-pixels  49  according to the fourth embodiment is not limited thereto. For example, to further enhance the second color component, either or both of the number and the arrangement of the first sub-pixels  49 R may be replaced with those of the second sub-pixels  49 G illustrated in  FIG. 11 . The same applies to a case of further enhancing the third color component. In the fourth embodiment, the distribution of the sub-pixels  49  of the respective color components is appropriately determined according to a tendency of excess and deficiency of the color components. However, in the fourth embodiment, a condition is applied such that the fourth sub-pixels  49 W are necessarily provided to one or more pixels among a plurality of pixels included in the image display panel  40 , and are not provided to all the pixels  48 . Also applied is a condition that, in the fourth embodiment, all the pixels  48  necessarily include one or more of each of the first sub-pixel  49 R, the second sub-pixel  49 G, and the third sub-pixel  49 B. Under such conditions, the ratio among the numbers 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 is adjusted. 
     According to the fourth embodiment, the color balance of the display unit (for example, the image display panel  40 ) can be adjusted by varying the ratio of the respective color components of the sub-pixels  49 . 
     Application Examples 
     Next, the following describes application examples of the display device  10  described in each embodiment with reference to  FIGS. 12 and 13 .  FIGS. 12 and 13  are diagrams each illustrating an example of an electronic apparatus to which the display device according to each embodiment is applied. The display device  10  according to each embodiment can be applied to electronic apparatuses in various fields such as a car navigation system illustrated in  FIG. 12 , a television apparatus, a digital camera, a laptop personal computer, a portable terminal device including a mobile phone illustrated in  FIG. 13 , or a video camera. In other words, the display device  10  according to each embodiment can be applied to electronic apparatuses in various fields that display a video signal input from the outside or a video signal generated inside as an image or video. The application examples can be applied to display devices according to other embodiments, modifications, and other examples other than the display device  10  according to each embodiment. 
     The electronic apparatus illustrated in  FIG. 12  is a car navigation device to which the display device  10  according to each embodiment is applied. The display device  10  is installed on a dashboard  300  inside an automobile. More specifically, the display device  10  is installed on the dashboard  300  between a driver&#39;s seat  311  and a passenger seat  312 . The display device  10  of the car navigation device is utilized for displaying navigation, displaying a music operation screen, reproducing and displaying movies, or the like. 
     The electronic apparatus illustrated in  FIG. 13  is a portable information terminal that operates as a mobile computer, a multifunctional mobile phone, a mobile computer capable of making a voice call, or a mobile computer capable of performing communications, to which the display device  10  according to each embodiment is applied, and may be referred to as what is called a smartphone or a tablet terminal. The portable information 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 each embodiment and has a touch detection (i.e., a touch panel) function capable of detecting an external proximity object. 
     Even though the embodiments and the modifications of the present invention have been described above, the embodiments and the modifications are not limited thereto. The components described above include a component that is easily conceivable by those skilled in the art, a component that is substantially identical thereto, and a component within a range of equivalents. The components described above can also be appropriately combined with one another. In addition, the components can be omitted, replaced, and modified in various manners without departing from the gist of the embodiments and the modifications described above. For example, the display device  10  may include a self-luminous image display panel  40  that lights a self-luminous body such as an organic light-emitting diode (OLED). The color for each sub-pixel (the first color, the second color, the third color, or the fourth color) can be determined using a luminescent material, instead of the color filter. 
     In the above embodiments, the HSV color space is employed as a color space of the color indicated by the input signal and the output signal. However, the HSV color space is merely an example of a color space that can be employed according to the present invention, and the embodiments are not limited thereto. Another color space may also be employed. The colors of the sub-pixels are not limited to red, green, blue, and white. At least one of these colors may be replaced with another color. As a specific example, a color such as yellow (Y) may be employed in place of white. In place of three primary colors including red, green, and blue, colors such as cyan (C), magenta (M), and yellow (Y) may be employed. 
     The present invention naturally encompasses other working effects caused by the aspects described in the above embodiments that are clear from the description herein or that are appropriately conceivable by those skilled in the art. 
     The present invention includes the following aspects: 
     (1) A display device comprising a display unit in which a plurality of pixels are arranged, 
     wherein one pixel includes four sub-pixels, and 
     wherein the display unit includes:
         a pixel including one each of four sub-pixels of four different colors that are a first color, a second color, a third color, and a fourth color; and   a pixel including four sub-pixels, where two of the four sub-pixels are identical and are one of sub-pixels of the first color, the second color, and the third color, and remaining two of the four sub-pixels are different two of the sub-pixels of the first color, the second color, and the third color but are not one of the identical sub-pixels.
 
(2) The display device according to (1),
       

     wherein the plurality of pixels are arranged in a matrix along two directions intersecting with each other, and 
     wherein sub-pixels of the fourth color are arranged at a predetermined cycle along at least one of the two directions. 
     (3) The display device according to either (1) or (2), 
     wherein the plurality of pixels are arranged in a matrix along two directions intersecting with each other, and 
     wherein a pixel including a sub-pixel of the fourth color and a pixel not including the sub-pixel of the fourth color are alternately arranged along at least one of the two directions. 
     (4) The display device according to either (1) or (2), wherein a number of sub-pixels of the first color, a number of sub-pixels of the second color, and a number of sub-pixels of the third color are equal. 
     (5) The display device according to either (1) or (2), wherein, among a number of sub-pixels of the first color, a number of sub-pixels of the second color, and a number of sub-pixels of the third color, a number of sub-pixels of at least one of the colors is different from a number of sub-pixels of the other colors.
 
(6) The display device according to either (1) or (2), wherein two sub-pixels of identical color included in one pixel are adjacent to each other.
 
(7) The display device according to either (1) or (2), wherein the first color, the second color, and the third color are red, green, and blue, respectively.
 
(8) The display device according to either (1) or (2), wherein the fourth color is white.
 
(9) The display device according to either (1) or (2), wherein the four sub-pixels included in the one pixel are continuously arranged along a certain direction.