Patent Publication Number: US-11391981-B2

Title: Display device with improved luminance and saturation

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/959,446 filed on Apr. 23, 2018. Further, this application claims priority from Japanese Application No. 2017-090318, filed on Apr. 28, 2017 and Japanese Application No. 2018-028944, filed on Feb. 21, 2018, the contents of which are incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a display device. 
     2. Description of the Related Art 
     As disclosed in Japanese Patent Application Laid-open Publication No. 2010-97176, a reflective display device that reflects external light to display a color image has been known. 
     The reflective display device typically combines light reflected from sub-pixels of red (R), green (G), and blue (B) to output light having a color other than the foregoing colors. However, yellow obtained by combining reflected light in red (R) and green (G) looks dingy, and obtaining required luminance and saturation has been a difficult task to achieve. 
     For the foregoing reasons, there is a need for a display device that can enhance the luminance and saturation of yellow. 
     SUMMARY 
     According to an aspect, a display device includes: a pixel including: a first sub-pixel including a color filter that transmits light having a spectrum peak falling on a spectrum of reddish green; a second sub-pixel including a second color filter that transmits light having a spectrum peak falling on a spectrum of bluish green; a third sub-pixel including a third color filter that transmits light having a spectrum peak falling on a spectrum of red; and a fourth sub-pixel including a fourth color filter that transmits light having a spectrum peak falling on a spectrum of blue. The first sub-pixel, the second sub-pixel, the third sub-pixel, and the fourth sub-pixel each include a reflective electrode that reflects light transmitted through the corresponding color filter. Each of the third sub-pixel and the fourth sub-pixel is greater in size than the first sub-pixel and the second sib-pixel. The first sub-pixel added to the second sub-pixel has a size equal to or greater than a size of the third sub-pixel. 
     According to another aspect, a display device includes: a pixel including: a first sub-pixel including a first color filter that transmits light having a spectrum peak falling on a spectrum of reddish green; a second sub-pixel including a second color filter that transmits light having a spectrum peak falling on a spectrum of bluish green; a third sub-pixel including a third color filter that transmits light having a spectrum peak falling on a spectrum of red; and a fourth sub-pixel including a fourth color filter that transmits light having a spectrum peak falling on a spectrum of blue. The first sub-pixel, the second sub-pixel, the third sub-pixel, and the fourth sub-pixel each include a reflective electrode that reflects light transmitted through the corresponding color filter. Each of the third sub-pixel and the fourth sub-pixel is greater in size than the first sub-pixel and the second sub-pixel. The first sub-pixel added to the second sub-pixel has a size equal to or greater than a size of the third sub-pixel and has a size equal to or greater than a size of the fourth sub-pixel. 
     According to another aspect, a display device includes: a pixel including: a first sub-pixel including a first color filter that transmits light having a spectrum peak falling on a spectrum of reddish green; a second, sub-pixel including a second color filter that transmits light having a spectrum peak falling on a spectrum of bluish green; a third sub-pixel including a third color filter that transmits light having a spectrum peak falling on a spectrum of red; and a fourth sub-pixel including a fourth color filter that transmits light having a spectrum peak falling on a spectrum of blue. The first sub-pixel, the second sub-pixel, the third sub-pixel, and the fourth sub-pixel each include a reflective electrode that reflects light transmitted through the corresponding color filter. When the pixel displays yellow having maximum luminance, the first sub-pixel, the second sub-pixel, and the third sub-pixel each exhibit maximum luminance. A total area of the first sub-pixel, the second sub-pixel, and the third sub-pixel is greater than twice an area of the fourth sub-pixel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view schematically illustrating a main configuration of a single sub-pixel; 
         FIG. 2  is a graph indicating exemplary spectra of red, reddish green, green, bluish green, and, blue; 
         FIG. 3  is a diagram illustrating exemplary shapes and sizes of sub-pixels included in a single pixel, an exemplary positional relation among the sub-pixels, and exemplary color filters of the respective sub-pixels; 
         FIG. 4  is a chart indicating relations among reproduced colors by a single pixel, R, G, and B gradation values applied as image signals, and the sub-pixels used for the output; 
         FIG. 5  is a chart indicating a schematic chromaticity diagram (xy chromaticity diagram) that represents a correspondence between yellow reproduced by a display device in an embodiment and the peaks of spectra of light transmitted through the color filter, the chromaticity diagram being plotted within chromaticity coordinates (xy chromaticity coordinates); 
         FIG. 6  is a chart indicating exemplary color reproducibility of the embodiment and that of a comparative example in an L*a*b* color space; 
         FIG. 7  is a diagram illustrating exemplary shapes and sizes of sub-pixels included in a single pixel, an exemplary positional relation among the sub-pixels, and exemplary color filters of the respective sub-pixels; 
         FIG. 8  is a diagram illustrating exemplary shapes and sizes of sub-pixels included in a single pixel, an exemplary positional relation among the sub-pixels, and exemplary color filters of the respective sub-pixels; 
         FIG. 9  is a schematic diagram illustrating, in an sRGB color space, a method for determining reddish green and bluish green according to an area ratio of the sub-pixels included in each of different types of a single pixel; 
         FIG. 10  is a diagram illustrating an example of dividing each sub-pixel into a plurality of regions having different areas for area coverage modulation; 
         FIG. 11  is a diagram illustrating another example of dividing each sub-pixel into a plurality of regions having different areas for area coverage modulation; 
         FIG. 12  is a diagram illustrating an exemplary circuit configuration of a display device in the embodiment; 
         FIG. 13  is a cross-sectional view schematically illustrating a sub-divided pixel; 
         FIG. 14  is a block diagram illustrating an exemplary circuit configuration of the pixel employing a memory in pixel (MIP) technology; 
         FIG. 15  is a timing chart for explaining an operation of the pixel employing the MIP technology; 
         FIG. 16  is a block diagram illustrating an exemplary configuration of a signal processing circuit; and 
         FIG. 17  is a diagram schematically illustrating an exemplary relation among external light, reflected light, and user&#39;s viewpoints when a plurality of display devices are disposed in juxtaposition. 
     
    
    
     DETAILED DESCRIPTION 
     Modes (embodiments) for carrying out the present disclosure will be described below in detail with reference to the drawings. The disclosure is given by way of example only, and various changes made without departing from the spirit of the disclosure and easily conceivable by those skilled in the art naturally fall within the scope of the present disclosure. The drawings may possibly illustrate the width, the thickness, the shape, and other elements of each unit more schematically than the actual aspect to simplify the explanation. These elements, however, are given by way of example only and are not intended to limit interpretation of the present disclosure. In the specification and the drawings, components similar to those previously described with reference to a preceding drawing are denoted by like reference numerals, and overlapping explanation thereof will be appropriately omitted. In this disclosure, when an element A is described as being, “on” another element B, the element A can be directly on the other element B, or there can be one or more elements between the element A and the other element B. 
       FIG. 1  is a perspective view schematically illustrating a main configuration of a single sub-pixel  15 .  FIG. 2  is a graph indicating exemplary spectra of red, reddish green, green, bluish green, and blue. The sub-pixel  15  includes a color filter  20  and a reflective electrode  40 . The color filter  20  has light transmissivity. The color filter  20  has a predetermined peak of a spectrum of light OL to be transmitted out of external light IL. Specifically, the peak of the spectrum of the light OL to be transmitted through the color filter  20  falls on either one of the spectrum of reddish green (e.g., first red green RG 1 ), the spectrum of bluish green (e.g., first blue green BG 1 ), the spectrum of red (e.g., red R 1 ), and the spectrum of blue (e.g., blue B 1 ). The reflective electrode  40  reflects the light OL that is transmitted through the color filter  20 . As exemplified in  FIG. 2 , the peak of the spectrum of the first red green RG 1  and the peak of the spectrum of the first blue green BG 1  each have a portion overlapping with the peak of the spectrum of light viewed as green G. The spectrum of the first red green RG 1  is closer to the spectrum of the red R 1  (on the long wavelength side) than the spectrum of the first blue green BG 1  and the spectrum of the green G are. The spectrum of the first blue green BG 1  is closer to the spectrum of the blue B 1  (on the short wavelength side) than the spectrum of the first red green RG 1  and the spectrum of the green G are. 
     A liquid crystal layer  30  is disposed between the color filter  20  and the reflective electrode  40 . The liquid crystal layer  30  includes liquid crystal having an orientation determined according to a voltage applied thereto by the reflective electrode  40 , for example. The liquid crystal layer  30  varies a degree of transmission of the light OL that passes between the color filter  20  and the reflective electrode  40  according to the orientation. A light modulation layer  90  may be disposed on the opposite side of the liquid crystal layer  30  across the color filter  20 . The light modulation layer  90  modulates, for example, a scattering direction of the light OL emitted from the display device. 
       FIG. 3  is a diagram illustrating exemplary shapes and sizes of the sub-pixels  15  included in a single pixel  10 , an exemplary positional relation among the sub-pixels  15 , and exemplary color filters  20  of the respective sub-pixels  15 . 
     The pixel  10  includes a first sub-pixel  11 , a second sub-pixel  12 , a third sub-pixel  13 , and a fourth sub-pixel  14 . The first sub-pixel  11  includes a first color filter  20 RG 1 . The second sub-pixel  12  includes a second color filter  20 BG 1 . The third sub-pixel  13  includes a third color filter  20 R 1 . The fourth sub-pixel  14  includes a fourth color filter  20 B 1 . The peak of the spectrum of the light transmitted through the first color filter  20 RG 1  falls on the spectrum of the reddish green (first red green RG 1 ). The peak of the spectrum of the light transmitted through the second color filter  20 BG 1  falls on the spectrum of the bluish green (first blue green BG 1 ). The peak of the spectrum of the light transmitted through the third color filter  20 R 1  falls on the spectrum of the red (red R 1 ). The peak of the spectrum of the light transmitted through the fourth color filter  20 B 1  falls on the spectrum of the blue (blue B 1 ). The pixel has a square shape in a plan view, and includes the sub-pixels in the respective four colors in respective regions obtained by sectioning the square pixel region. The sub-pixels each have a square or rectangular shape in a plan view (hereinafter referred to as a rectangle). The four rectangles are combined to form the square pixel. A light shielding layer such as a black matrix may be disposed in regions between the sub-pixels and an outer edge of the pixel, but this light shielding layer occupies only a small area of the pixel. Thus, when describing the shapes or combination of the sub-pixels or the shape of the pixel, such a light shielding layer may be substantially disregarded as a linear object constituting an outer edge of the pixel or the sub-pixel. 
     In the following description, the term “color filter  20 ” will be used to describe the color filter  20  when the peak of the spectrum of the light OL to be transmitted is not differentiated. When the peak of the spectrum of the light OL to be transmitted is differentiated, the color filter  20  will be described as, for example, the first color filter  20 RG 1 , the second color filter  20 BG 1 , the third color filter  20 R 1 , or the fourth color filter  20 B 1 , where appropriate. The light OL that has been transmitted through the color filter  20  is viewed as light in the color corresponding to the peak of the spectrum of the light to be transmitted through the color filter  20 . The term “sub-pixel  15 ” will be used when the sub-pixel  15  is not differentiated among the first sub-pixel  11 , the second sub-pixel  12 , the third sub-pixel  13 , and the fourth sub-pixel  14 , for example, by the colors of the color filters  20  included in the respective sub-pixels  15 . The first sub-pixel  11 , the second sub-pixel  12 , the third sub-pixel  13 , and the fourth sub-pixel  14  each include the reflective electrode  40  as illustrated in  FIG. 1 , which is omitted in  FIG. 3 . 
     The third sub-pixel  13  and the fourth sub-pixel  14  are each greater in size than the first sub-pixel  11  and the second sub-pixel  12 . The first sub-pixel  11  added to the second sub-pixel  12  has a size equal to or greater than a size of the third sub-pixel  13 . The fourth sub-pixel  14  is greater in size than the third sub-pixel  13 . The first sub-pixel  11  is identical in size to the second sub-pixel  12 . When an area ratio of the first sub-pixel  11 , the second sub-pixel  12 , the third sub-pixel  13 , and the fourth sub-pixel  14  is expressed as A to B to C to D, the following expressions hold: 0.65≤A=B&lt;1.0, 1.0≤C&lt;D, D=4−(A+B+C), and D≤1.7.  FIG. 3  exemplifies a case in which the expression of A to B to C to D=0.744 to 0.744 to 1.130 to 1.382 holds. In this case, the first sub-pixel  11  added to the second sub-pixel  12  has a size equal to or greater than a size of the third sub-pixel  13  and has a size equal to or greater than a size of the fourth sub-pixel  14 . In the embodiment, the first sub-pixel shares part of a side with the fourth sub-pixel. In contrast, the second sub-pixel and the third sub-pixel share no side. More specifically, a side shared between the first sub-pixel and the second sub-pixel coincides with an intermediate line dividing the pixel laterally into half. In contrast, a side shared between the third sub-pixel and the fourth sub-pixel is shifted toward the first sub-pixel with respect to the intermediate line. As a result, the first sub-pixel and the fourth sub-pixel share part of the side. 
       FIG. 4  is a chart indicating relations among reproduced colors by a single pixel, R, G, and B gradation values applied as image signals, and the sub-pixels used for the output. When the input gradation values of R, G, and B are expressed as (R, G, B)=(n, n, n), the reproduced color is white and the first sub-pixel  11 , the second sub-pixel  12 , the third sub-pixel  13 , and the fourth sub-pixel  14  are used for the output. When the input gradation values of R, G, and B are expressed as (R, G, B)=(n, 0, 0), the reproduced color is red and the third sub-pixel  13  is used for the output. When the input gradation values of R, G, and B are expressed as (R, G, B)=(0, n, 0), the reproduced color is green and the first sub-pixel  11  and the second sub-pixel  12  are used for the output. When the input gradation values of R, G, and B are expressed as (R, G, B)=(0, 0, n), the reproduced color is blue and the fourth sub-pixel  14  is used for the output. When the input gradation values of R, G, and B are expressed as (R, G, B)=(m, m, 0), the reproduced color is yellow and the first sub-pixel  11 , the second sub-pixel  12 , and the third sub-pixel  13  are used for the output. When the input gradation values of R, G, and B are expressed as (R, G, B)=(0, m, m), the reproduced color is cyan and the first sub-pixel  11 , the second sub-pixel  12 , and the fourth sub-pixel  14  are used for the output. When the input gradation values of R, G, and B are expressed as (R, G, B)=(m, 0, m), the reproduced color is magenta and the third sub-pixel  13  and the fourth sub-pixel  14  are used for the output. In this manner, the display device in the embodiment reproduces yellow through the combination of the first sub-pixel  11 , the second sub-pixel  12 , and the third sub-pixel  13 . The display device in the embodiment reproduces green through the combination of the first sub-pixel  11  and the second sub-pixel  12 . The display device in the embodiment reproduces cyan through the combination of the first sub-pixel  11 , the second sub-pixel  12 , and the fourth sub-pixel  14 . The display device in the embodiment reproduces magenta through the combination of the third sub-pixel  13  and the fourth sub-pixel  14 . The display device in the embodiment reproduces red using the third sub-pixel  13 . The display device in the embodiment reproduces blue using the fourth sub-pixel  14 . 
       FIG. 5  is a chart indicating a schematic chromaticity diagram (xy chromaticity diagram) that represents a correspondence between yellow reproduced by the display device in the embodiment and the peaks of the spectra of the light OL transmitted through the color filter  20 , the chromaticity diagram being plotted within chromaticity coordinates (xy chromaticity coordinates). In  FIG. 5 , the solid-line triangle having three vertexes of R, G, and B represents a color space that indicates colors that can be reproduced by sub-pixels of respective three colors of the conventional red (R), conventional green (G), and conventional blue (B) included in the conventional display device, with respect to the reproduction of yellow Y having predetermined luminance and saturation required for a display device. Such a conventional display device is unable to reproduce the yellow Y. Specifically, the luminance and saturation of yellow to be reproduced by the conventional display device are unable to exceed luminance and saturation on a straight line connecting the conventional red (R) and the conventional green (G) with respect to a white point (W), and at least either one of the luminance and saturation fails to reach the value to reproduce the yellow Y. Even when the conventional display device includes sub-pixels of four colors of white (W) added to the conventional red (R), the conventional green (G), and the conventional blue (B), increasing saturation of the yellow Y using the sub-pixel of white (W) is a difficult task to achieve. 
     Trying to reproduce the yellow Y using the sub-pixels of three colors by a conventional technology requires the conventional red (R) and the conventional green (G) to be shifted to red (e.g., R 1 ) and green (e.g., G 1 ) that can reproduce the yellow Y. However, shifting the conventional red (R) and the conventional green (G) to the red (e.g., R 1 ) and the green (e.g., G 1 ) that can reproduce the yellow Y by simply targeting the reproduction of the yellow Y causes the white point (W) to be shifted toward the yellow Y. Specifically, setting the red (e.g., R 1 ) and the green (e.g., G 1 ) by targeting the reproduction of the yellow Y in the conventional display device causes a color reproduced by lighting all sub-pixels to be tinged with yellow as a whole, resulting in changing color reproducibility.  FIG. 5  schematically indicates the white point (W) before being shifted toward the yellow Y using a black dot.  FIG. 5  further indicates the white point after having been shifted toward the yellow Y using a blank dot outlined by the broken line and denoted as W 1 . Setting the red (e.g., R 1 ) and the green (e.g., G 1 ) by targeting the reproduction of the yellow Y means to further darken these colors, and reduce light transmission efficiency of the color filter  20  and luminance, resulting in dark yellow. 
     Trying to achieve the luminance and the saturation corresponding to the yellow Y by adding the yellow sub-pixel to the pixel of the conventional display device still causes the color reproduced by lighting all sub-pixels to be tinged with yellow as a whole, resulting in changing color reproducibility. 
     In the display device according to the embodiment, on the other hand, the first sub-pixel  11  includes the first color filter  20 RG 1 , and the second sub-pixel  12  includes the second color filter  20 BG 1 . The peak of the spectrum of the light transmitted through the first color filter  20 RG 1  falls on the spectrum of the reddish green (first red green RG 1 ). The peak of the spectrum of the light transmitted through the second color filter  20 BG 1  falls on the spectrum of the bluish green (first blue green BG 1 ). The peak of the spectrum of the light transmitted through the third color filter  20 R 1  falls on the spectrum of the red (red R 1 ). The peak of the spectrum of the light transmitted through the fourth color filter  20 B 1  falls on the spectrum of the blue (blue B 1 ). More specifically, by representing the peak of the spectrum of the light that passes through the first color filter on the chromaticity coordinates (RG 1  in  FIG. 5 ), the x-coordinate of the peak is between the x-coordinate of the white point and the x-coordinate of the red (R 1  in  FIG. 5 ) corresponding to the third color filter  20 R 1 . Similarly, by representing the peak of the spectrum of the light that passes through the second color filter on the chromaticity coordinates (BG 1  in  FIG. 5 ), the x-coordinate of the peak is between the x-coordinate of the white point and the x-coordinate of the blue (B 1  in  FIG. 5 ) corresponding to the fourth color filter  20 B 1 . Thus, the embodiment obtains a blue component through the second sub-pixel  12  and the fourth sub-pixel  14 , thereby preventing the white point (W) from being shifted toward the yellow Y. The embodiment reproduces yellow through the combination of the first sub-pixel  11 , the second sub-pixel  12 , and the third sub-pixel  13 . Specifically, the peaks of the spectra of light transmitted through the first color filter  20 RG 1 , the second color filter  20 BG 1 , and the third color filter  20 R 1 , respectively, are set such that a combined color of the first red green RG 1 , the first blue green BG 1 , and the red R 1  is the yellow Y. This configuration allows the yellow Y to be reproduced using the three sub-pixels  15  out of the four sub-pixels  15  of the single pixel  10 . Thus, the embodiment allows the area of the sub-pixels  15  used for reproducing the yellow Y to be easily increased as compared with a case in which two colors (R and G) are used out of the sub-pixels of three colors of the conventional red (R), the conventional green (G), and the conventional blue (B). Specifically, the embodiment allows larger part of the color filter  20  and the reflective electrode  40  combining the first sub-pixel  11 , the second sub-pixel  12 , and the third sub-pixel  13  out of a display area of the single pixel  10  to be easily allocated to the reproduction of the yellow Y, thereby reliably achieving the luminance and the saturation of the yellow Y. Further, the embodiment also enhances the luminance and the saturation of cyan. Additionally, as compared with a configuration including a sub-pixel of white (W), the embodiment allows the third sub-pixel  13  including the third color filter  20 R 1  corresponding to the red (R 1 ) to be easily enlarged, thereby enhancing the reproducibility of primary colors. 
     The embodiment allows the light transmission efficiency of the first color filter  20 RG 1  transmitting the light whose spectrum peak corresponds to the reddish green (e.g., first red green RG 1 ) to be easily increased. Thus, the embodiment uses the first sub-pixel  11  including the first color filter  20 RG 1  for the reproduction of the yellow Y, thereby reliably achieving the luminance and the saturation of the yellow Y. 
     In the display device including the reflective electrode  40  like the display device in the embodiment, a reflection factor and contrast of the light OL reflected by the reflective electrode  40  remain constant. Meanwhile, the visual quality of colors of an image output by the display device depends on the light source color and luminous intensity of the external light IL. Thus, when the external light IL is obtained under a bright environment, for example, the visual quality of colors of the image tends to be good. In contrast, when the external light IL is obtained under a dark environment, it is relatively difficult to exhibit reliable visibility. The color filter  20  does not completely transmit the external light IL regardless of the peak of the spectrum of the light OL to be transmitted, and absorbs at least part of the external light IL. Trying to darken the reproduced color using the color filter  20  increases a ratio of an absorbed part of the external light IL. Thus, the display device that outputs an image through reflection of the light OL by the reflective electrode  40  is required to balance the saturation and the luminance by setting the peaks of the spectra of the light OL transmitted through the color filters  20  and adjusting an area ratio of the color filters  20  having different peaks. In other words, the display device that outputs the image through reflection of the light OL by the reflective electrode  40  has an extreme difficulty in adjusting colors and luminance by adjusting the light source, which can be achieved by a display device having other configurations permitting selection and adjustments of the light source. Application of the present embodiment to even such a display device that outputs the image through reflection of the light OL by the reflective electrode  40  can still reliably obtain the luminance and saturation of the yellow Y. 
     In the embodiment, the area ratio of the first color filter  20 RG 1 , the second color filter  20 BG 1 , the third color filter  20 R 1 , and the fourth color filter  20 B 1 , and the spectra of the first red green RG 1 , the first blue green BG 1 , the red R 1 , and the blue B 1  are determined depending on the required white point W and the required luminance and the saturation of the yellow Y. The blue B 1  in the embodiment and the conventional blue (B), which are identical to each other in  FIG. 5 , may be different from each other. The red R 1  in the embodiment and the conventional red (R), which are identical to each other in  FIG. 5 , may be different from each other. Although the combination of the first red green RG 1  and the first blue green BG 1  reproduces the conventional green (G) in  FIG. 5 , the combination of the first red green RG 1  and the first blue green BG 1  may reproduce green that is different from the conventional green (G). 
       FIG. 6  is a chart indicating exemplary color reproducibility of the embodiment and that of a comparative example in an L*a*b* color space. In  FIG. 6 , SNAP indicates yellow, green, cyan, blue, magenta, and red specified by the Specifications for Newsprint Advertising Production. A display device in the comparative example is an RGBW reflective display device that includes sub-pixels of four colors, i.e., white (W) in addition to the conventional red (R), the conventional green (G), and the conventional blue (B). The display device in the embodiment described with reference to  FIGS. 1 to 5  can reproduce the yellow Y that is brighter and more vivid than yellow OY to be reproduced by the display device in the comparative example. The display device in the embodiment can satisfy the demand in advertisement or the like by reproducing the bright and vivid yellow Y as required. 
       FIG. 7  is a diagram illustrating exemplary shapes and sizes of sub-pixels  15  included in a single pixel  10 A, an exemplary positional relation among the sub-pixels  15 , and exemplary color filters  20  of the respective sub-pixels  15 .  FIG. 8  is a diagram illustrating exemplary shapes and sizes of sub-pixels  15  included in a single pixel  10 B, an exemplary positional relation among the sub-pixels  15 , and exemplary color filters  20  of the respective sub-pixels  15 . The display device in the embodiment may include, in place of the pixel  10  illustrated in  FIG. 3 , the pixel  10 A illustrated in  FIG. 7  or the pixel  10 B illustrated in  FIG. 8 . 
     The pixel  10 A illustrated in  FIG. 7  includes a first sub-pixel  11 A, a second sub-pixel  12 A, a third sub-pixel  13 A, and a fourth sub-pixel  14 A. The first sub-pixel  11 A includes a first color filter  20 RG 2 . The second sub-pixel  12 A includes a second color filter  20 BG 2 . The peak of the spectrum of the light transmitted through the first color filter  20 RG 2  falls on the spectrum of the reddish green (second red green RG 2 ). The peak of the spectrum of the light transmitted through the second color filter  20 BG 2  falls on the spectrum of the bluish green (second blue Green RG 2 ). The third sub-pixel  13 A includes the third color filter  20 R 1 , similarly to the third sub-pixel  13  illustrated in  FIG. 3 . The fourth sub-pixel  14 A includes the fourth color filter  20 B 1 , similarly to the fourth sub-pixel  14  illustrated in  FIG. 3 . The third sub-pixel  13 A and the fourth sub-pixel  14 A are each greater in size than the first sub-pixel  11 A and the second sub-pixel  12 A. The first sub-pixel  11 A added to the second sub-pixel  12 A has a size equal to or greater than a size of the third sub-pixel  13 A and has a size equal to or greater than a size of the fourth sub-pixel  14 A. The fourth sub-pixel  14 A is greater in size than the third sub-pixel  13 A. The second sub-pixel  12 A is greater in size than the first sub-pixel  11 A. When an area ratio of the first sub-pixel  11 A, the second sub-pixel  12 A, the third sub-pixel  13 A, and the fourth sub-pixel  14 A is expressed as E to F to G to H, the following expressions hold: 0.65≤E&lt;F&lt;1.0, 1.0≤G=H, and H&lt;1.7. Further, the expression of E to F=G to H holds in the example illustrated in  FIG. 7 , but E to F may be a different ratio from that of G to H. A configuration in which the expression of E to F=C to H holds makes it easy to dispose a signal line  61  and a scanning line  62  (see  FIG. 12 ) at a position corresponding to a boundary between sub-pixels  15  having different color filters  20 .  FIG. 7  illustrates an exemplary case in which the ratio obtained through rounding each value to the third decimal places is expressed as E to F to G to H=0.669 to 0.819 to 1.130 to 1.382. In this case, the first sub-pixel  11  added to the second sub-pixel  12  has a size equal to or greater than a size of the third sub-pixel  13  and has a size equal to or greater than a size of the fourth sub-pixel  14 . Color reproduction by the pixel  10 A illustrated in  FIG. 7  can be described by reading the first sub-pixel  11 , the second sub-pixel  12 , the third sub-pixel  13 , and the fourth sub-pixel  14  described with reference to  FIG. 4  as the first sub-pixel  11 A, the second sub-pixel  12 A, the third sub-pixel  13 A, and the fourth sub-pixel  14 A, respectively. In such a pixel, the sub-pixels that are diagonally opposite to each other share no side. More specifically, the pixel is divided into four regions by one vertical line that divides the pixel laterally and one horizontal line that divides the pixel vertically. The vertical line is shifted toward the first sub-pixel (left edge side of the pixel) with respect to a centerline that laterally divides the pixel into half. The horizontal line is shifted toward the first sub-pixel (upper edge side of the pixel) with respect to a centerline that vertically divides the pixel into half. This configuration makes the magnitude relation of E&lt;F≤G&lt;H hold. 
     The pixel  10 B illustrated in  FIG. 8  includes a first sub-pixel  11 B, a second sub-pixel  12 B, a third sub-pixel  13 B, and a fourth sub-pixel  14 B. The first sub-pixel  11 B includes a first color filter  20 RG 3 . The second sub-pixel  12 B includes a second color filter  20 BG 3 . The peak of the spectrum of the light transmitted through the first color filter  20 RG 3  falls on the spectrum of the reddish green (third red green RG 3 ). The peak of the spectrum of the light transmitted through the second color filter  20 BG 3  falls on the spectrum of the bluish green (third blue green BG 3 ). The third sub-pixel  13 B includes the third color filter  20 R 1 , similarly to the third sub-pixel  13  illustrated in  FIG. 3 . The fourth sub-pixel  14 B includes the fourth color filter  20 B 1 , similarly to the fourth sub-pixel  14  illustrated in  FIG. 3 . The third sub-pixel  13 B and the fourth sub-pixel  14 B are each greater in size than the first sub-pixel  11 B and the second sub-pixel  12 B. The first sub-pixel  11 B added to the second sub-pixel  12 B has a size equal to or greater than a size of the third sub-pixel  13 B and has a size equal to or greater than a size of the fourth sub-pixel  14 B. The third sub-pixel  13 B is identical in size to the fourth sub-pixel  14 B. The first sub-pixel  11 B is identical in size to the second sub-pixel  12 B. When an area ratio of the first sub-pixel  11 B, the second sub-pixel  12 B, the third sub-pixel  13 B, and the fourth sub-pixel  14 B is expressed as I to J to K to L, the following expressions hold: 0.65≤I=J&lt;1.0, and 1.0≤K=L≤1.35.  FIG. 8  illustrates an exemplary case in which the expression of I to J to K to L=0.744 to 0.744 to 1.256 to 1.256 holds. In this case, the first sub-pixel  11  added to the second sub-pixel  12  has a size equal to or greater than a size of the third sub-pixel  13  and has a size equal to or greater than a size of the fourth sub-pixel  14 . Color reproduction by the pixel  10 B illustrated in  FIG. 8  can be described by reading the first sub-pixel  11 , the second sub-pixel  12 , the third sub-pixel  13 , and the fourth sub-pixel  14  described with reference to  FIG. 4  as the first sub-pixel  11 B, the second sub-pixel  12 B, the third sub-pixel  13 B, and the fourth sub-pixel  14 B, respectively. In such a pixel, the sub-pixels that are diagonally opposite to each other share no side. More specifically, the pixel is divided into four regions by one vertical line that divides the pixel laterally and one horizontal line that divides the pixel vertically. The vertical line coincides with a centerline that laterally divides the pixel into half. The horizontal line is shifted toward the first sub-pixel (upper edge side of the pixel) with respect to a centerline that vertically divides the pixel into half. This configuration makes the magnitude relation of I=J&lt;K=L hold. 
       FIG. 9  is a schematic diagram illustrating, in an sRGB color space, a method for determining reddish green and bluish green according to the area ratio of the sub-pixels  15  included in each of the pixel  10 , the pixel  10 A, and the pixel  10 B.  FIG. 9  illustrates a dash-single-dot line GL that couples the green G, which is a combined color of the first red green RG 1  and the first blue green BG 1 , with the white point W, while illustrating a broken line PL on the yellow side on which a hue angle is in the positive direction with respect to the dash-single-dot line GL.  FIG. 9  illustrates a broken line ML on the cyan side on which the hue angle is in the negative direction with respect to the dash-single-dot line GL. 
     The first sub-pixel  11 A of the pixel  10 A illustrated in  FIG. 7  is smaller in size than the first sub-pixel  11  of the pixel  10  illustrated in  FIG. 3 . The second sub-pixel  12 A of the pixel  10 A illustrated in  FIG. 7  is greater in size than the second sub-pixel  12  of the pixel  10  illustrated in  FIG. 3 . Assume an arrangement in which the color filters  20  of the first sub-pixel  11 A and the second sub-pixel  12 A included in the pixel  10 A illustrated in  FIG. 7  are the same as the color filters  20  of the first sub-pixel  11  and the second sub-pixel  12  included in the pixel  10  illustrated in  FIG. 3 . This arrangement decreases the area allocated to a red component by a relative amount of the reduced first sub-pixel  11 A, and increases the area allocated to a blue component by a relative amount of the enlarged second sub-pixel  12 A. As illustrated in  FIG. 9 , the hue angle of the second red green RG 2  corresponding to the peak of the spectrum of the light transmitted through the first color filter  20 RG 2  included in the first sub-pixel  11 A illustrated in  FIG. 7  is on the positive side relative to the hue angle of the first red green RG 1  corresponding to the peak of the spectrum of the light transmitted through the first color filter  20 RG 1  included in the first sub-pixel  11  illustrated in  FIG. 3 . The hue angle of the second blue green BG 2  corresponding to the peak of the spectrum of the light transmitted through the second color filter  20 BG 2  included in the second sub-pixel  12 A illustrated in  FIG. 7  is on the positive side relative to the hue angle of the first blue green BG 1  corresponding to the peak of the spectrum of the light transmitted through the second color filter  20 BG 1  included in the second sub-pixel  12  illustrated in  FIG. 3 . This configuration allows even the pixel  10 A illustrated in  FIG. 7  to achieve the required yellow Y, white point W, and green G equivalent to those in the pixel  10  illustrated in  FIG. 3 . 
     The third sub-pixel  13 B of the pixel  10 B illustrated in  FIG. 8  is greater in size than the third sub-pixel  13  of the pixel  10  illustrated in  FIG. 3 . The fourth sub-pixel  14 B of the pixel  10 B illustrated in  FIG. 8  is smaller in size than the fourth sub-pixel  14  of the pixel  10  illustrated in  FIG. 3 . Assume an arrangement in which the color filters  20  of the first sub-pixel  11 B and the second sub-pixel  12 B included in the pixel  10 B illustrated in  FIG. 8  are the same as the color filters  20  of the first sub-pixel  11  and the second sub-pixel  12  included in the pixel  10  illustrated in  FIG. 3 . This arrangement increases the area allocated to the red component by a relative amount of the enlarged third sub-pixel  13 B, and decreases the area allocated to the blue component by a relative amount of the reduced fourth sub-pixel  14 B. As illustrated in  FIG. 9 , the hue angle of the third red green RG 3  corresponding to the peak of the spectrum of the light transmitted through the first color filter  20 RG 3  included in the first sub-pixel  11 B illustrated in  FIG. 8  is on the negative side relative to the hue angle of the first red green RG 1  corresponding to the peak of the spectrum of the light transmitted through the first color filter  20 RG 1  included in the first sub-pixel  11  illustrated in  FIG. 3 . The hue angle of the third blue green BG 3  corresponding to the peak of the spectrum of the light transmitted through the second color filter  20 BG 3  included in the second sub-pixel  12 B illustrated in  FIG. 8  is on the negative side relative to the hue angle of the first blue green BG 1  corresponding to the peak of the spectrum of the light transmitted through the second color filter  20 BG 1  included in the second sub-pixel  12  illustrated in  FIG. 3 . This configuration allows even the pixel  10 B illustrated in  FIG. 8  to achieve the required yellow Y, white point W, and green G equivalent to those in the pixel  10  illustrated in  FIG. 3 . 
     The first red green RG 1 , the second red green RG 2 , and the third red green RG 3  have hue on the positive side with respect to the green G and on the negative side with respect to the red R 1 . The first blue green BG 1 , the second blue green BG 2 , and the third blue green BG 3  have hue on the negative side with respect to the green G and on the positive side with respect to the blue B 1 . 
     As exemplified in  FIGS. 3, 7, and 8 , in the display device in the embodiment, the four sub-pixels  15  included in the single pixel  10 ,  10 A, or  10 B have two or more different types of areas. The sub-pixel  15  including a color filter  20  having a relatively high luminous efficacy has a size equal to or smaller than a size of the sub-pixel  15  including a color filter  20  having a relatively low luminous efficacy. Specifically, the first color filter  20 RG 1  has a luminous efficacy relatively higher than a luminous efficacy of the second color filter  20 BG 1 . The first color filter  20 RG 2  has a luminous efficacy relatively higher than a luminous efficacy of the second color filter  20 BG 2 . The first color filter  20 RG 3  has a luminous efficacy relatively higher than a luminous efficacy of the second color filter  20 BG 3 . Further, the first red green RG 1 , the second red green RG 2 , and the third red green RG 3 , and the first blue green BG 1 , the second blue green BG 2 , and the third blue green BG 3  each have a luminous efficacy relatively higher than a luminous efficacy of the red R 1 . The red R 1  has a luminous efficacy relatively higher than a luminous efficacy of the blue B 1 . For the reproduction of yellow, the display device in the embodiment uses three sub-pixels  15  excluding the fourth sub-pixel (e.g., fourth sub-pixel  14 ) that includes the fourth color filter  20 B 1 . A total area of the three sub-pixels  15  used for reproducing the yellow Y may be equal to or greater than twice the area of the fourth sub-pixel. Alternatively, the three sub-pixels other than the fourth sub-pixel may be used to reproduce yellow regardless of the gradation value or the three sub-pixels other than the fourth sub-pixel may be used to reproduce yellow having a predetermined gradation value or higher. The yellow having the predetermined gradation value or higher refers to yellow having relatively high luminance and saturation as required, that is, yellow exceeding a predetermined halftone. This configuration uses the first sub-pixel (e.g., first sub-pixel  11 ) and the third sub-pixel (e.g., third sub-pixel  13 ) to reproduce yellow having the halftone or lower. 
     The sub-pixels  15  having a relatively high luminance efficacy are adjacent to each other in the X-direction or the Y-direction. For example, in  FIG. 3 , the first sub-pixel  11  is adjacent to the second sub-pixel  12 . In  FIG. 7 , the first sub-pixel  11 A is adjacent to the second sub-pixel  12 A. In  FIG. 8 , the first sub-pixel  11 B is adjacent to the second sub-pixel  12 B. 
     In the following description, the hue of the light OL transmitted through the color filter  20  included in a single sub-pixel  15  is regarded as a reference. The two sub-pixels  15  disposed in juxtaposition to one sub-pixel  15  transmit the light OL having a hue closer to the reference than the remaining one sub-pixel  15  does. The sub-pixels  15  are juxtaposed in the X-direction or the Y-direction. For example, in  FIG. 3 , the hue (first blue green BG 1 ) of the second sub-pixel  12  and the hue (red R 1 ) of the third sub-pixel  13  are closer to the hue (first red green RG 1 ) of the first sub-pixel  11  than the hue (blue B 1 ) of the fourth sub-pixel  14  disposed in a diagonal direction of the first sub-pixel  11  is. The hue (first blue green BG 1 ) of the second sub-pixel  12  and the hue (red R 1 ) of the third sub-pixel  13  are closer to the hue (blue B 1 ) of the fourth sub-pixel  14  than the hue (first red green RG 1 ) of the first sub-pixel  11  disposed in a diagonal direction of the fourth sub-pixel  14  is. The diagonal direction extends along the X-Y plane and intersects the X-direction and the Y-direction. Further, the hue (first red green RG 1 ) of the first sub-pixel  11  and the hue (blue B 1 ) of the fourth sub-pixel  14  are closer to the hue (first blue green BG 1 ) of the second sub-pixel  12  than the hue (red R 1 ) of the third sub-pixel  13  disposed in a diagonal direction of the second sub-pixel  12  is. The hue (first red green RG 1 ) of the first sub-pixel  11  and the hue (blue B 1 ) of the fourth sub-pixel  14  are closer to the hue (red R 1 ) of the third sub-pixel  13  than the hue (first blue green BG 1 ) of the second sub-pixel  12  disposed in a diagonal direction of the third sub-pixel  13  is. Relations of hues among the sub-pixels  15  illustrated in  FIG. 7  can be described by reading the first sub-pixel  11 , the second sub-pixel  12 , the third sub-pixel  13 , and the fourth sub-pixel  14  described with reference to  FIG. 3  as the first sub-pixel  11 A, the second sub-pixel  12 A, the third sub-pixel  13 A, and the fourth sub-pixel  14 A, respectively. Relations of hues among the sub-pixels  15  illustrated in  FIG. 8  can be described by reading the first sub-pixel  11 , the second sub-pixel  12 , the third sub-pixel  13 , and the fourth sub-pixel  14  described with reference to  FIG. 3  as the first sub-pixel  11 B, the second sub-pixel  12 B, the third sub-pixel  13 B, and the fourth sub-pixel  14 B, respectively. 
       FIG. 10  is a diagram illustrating an example of dividing each sub-pixel  15  into a plurality of regions having different areas for area coverage modulation. In the display device in the embodiment, a pixel  10 C includes a first sub-pixel  11 C, a second sub-pixel  12 C, a third sub-pixel  13 C, and a fourth sub-pixel  14 C, for example, as illustrated in  FIG. 10 . The first sub-pixel  11 C including the first color filter  20 RG 1  includes three regions having different areas including a first sub-divided pixel  111 , a second sub-divided pixel  112 , and a third sub-divided pixel  113 . The first sub-divided pixel  111 , the second sub-divided pixel  112 , and the third sub-divided pixel  113  have an area ratio of, for example, 1 to 2 to 4 (=2 0  to 2 1  to 2 2 ). The first sub-pixel  11 D has gradation performance of three bits (eight gradations) through combinations of whether each of the first sub-divided pixel  111 , the second sub-divided pixel  112 , and the third sub-divided pixel  113  transmits light. More specifically, area coverage modulation performed through the combination patters of whether each of the first sub-divided pixel  111 , the second sub-divided pixel  112 , and the third sub-divided pixel  113  transmits light is expressed as “0 to 0 to 0”, “1 to 0 to 0”, “0 to 1 to 0”, “1 to 1 to 0”, “0 to 0 to 1”, “1 to 0 to 1”, “0 to 1 to 1”, and “1 to 1 to 1” in ascending order of an output gradation, where 1 denotes that the specific sub-divided pixel transmits light and 0 denotes that the specific sub-divided pixel does not transmit light. A black matrix  23  (see  FIG. 13 ) is disposed between the sub-pixels  15 . For example, the black matrix  23  is disposed among a plurality of color filters  20 . For example, the black matrix  23  may be a black filter or may be configured such that the color filters of two adjacent sub-pixels are superimposed on top of one another to reduce a transmission factor in the overlapping part. The black matrix  23  may be omitted. A ratio of area coverage modulation by the sub-divided pixels (e.g., 1 to 2 to 4) corresponds to an aperture ratio in a plan view. Thus, in a configuration including the black matrix  23 , the ratio of area coverage modulation corresponds to a ratio of openings on which the black matrix  23  is not disposed. In a configuration without black matrix  23 , the ratio of area coverage modulation corresponds to an area ratio of the reflective electrodes  40  included in the respective sub-divided pixels. Specific shapes of the reflective electrodes  40  vary depending on how the sub-pixel is divided. For example, in  FIG. 10 , the reflective electrodes  40  having a rectangular shape, an L-shape, and an L-shape are provided from the central side of the pixel  10 C with the respective sub-divided pixels. 
     The second sub-pixel  12 C including the second color filter  20 BG 1  includes a plurality of sub-divided pixels that may be a first sub-divided pixel  121 , a second sub-divided pixel  122 , and a third sub-divided pixel  123 . The third sub-pixel  13 C including the third color filter  20 R 1  includes a plurality of sub-divided pixels that may be a first sub-divided pixel  131 , a second sub-divided pixel  132 , and a third sub-divided pixel  133 . The fourth sub-pixel  14 C including the fourth color filter  20 B 1  includes a plurality of sub-divided pixels that may be a first sub-divided pixel  141 , a second sub-divided pixel  142 , and a third sub-divided pixel  143 . The second sub-pixel  12 C, the third sub-pixel  13 C, and the fourth sub-pixel  14 C each achieve the area coverage modulation through the same mechanism as that of the first sub-pixel  11 C. 
     The first sub-pixel  11 C, the second sub-pixel  12 C, the third sub-pixel  13 C, and the fourth sub-pixel  14 C are configured in the same manner as the first sub-pixel  11 , the second sub-pixel  12 , the third sub-pixel  13 , and the fourth sub-pixel  14  described above, respectively, except that the first sub-pixel  11 C, the second sub-pixel  12 C, the third sub-pixel  13 C, and the fourth sub-pixel  14 C each include the sub-divided pixels. The sub-pixels  15  included in the pixel  10 A illustrated in  FIG. 7  and the pixel  10 B illustrated in  FIG. 8  may each be divided into a plurality of sub-divided pixels like the sub-pixels  15  included in the pixel  10 C illustrated in  FIG. 10 . 
       FIG. 11  is a diagram illustrating another example of dividing each sub-pixel  15  into a plurality of regions having different areas for area coverage modulation. Shapes and arrangements of the sub-pixels  15  exemplified in  FIGS. 3, 7, 8, and 10  are illustrative only and can be modified as appropriate. As illustrated in  FIG. 11 , for example, a pixel  10 D includes the sub-pixels  15  including a third sub-pixel  13 D, a first sub-pixel  11 D, a second sub-pixel  12 D, and a fourth sub-pixel  14 D sequentially arranged from one end side in the X-direction. The sub-pixels  15  each have a stripe shape. These sub-pixels have widths in the X-direction, the relation of which is expressed as follows: width of the first sub-pixel=width of the second sub-pixel&lt;width of the third sub-pixel=width of the fourth sub-pixel. The first sub-pixel  11 D including the first color filter  20 RG 3  includes a plurality of sub-divided pixels that may be a first sub-divided pixel  11   a , second sub-divided pixels  11   b , and third sub-divided pixels  11   c . An area ratio among the central first sub-divided pixel  11   a , a pair of the upper and lower second sub-divided pixels  11   b , and a pair of the upper and lower third sub-divided pixels  11   c  is, for example, 1 to 2 to 4. The first sub-pixel  11 C has gradation performance of three bits (eight gradations) through combinations of whether each of the first sub-divided pixel  11   a , the second sub-divided pixel  11   b , and the third sub-divided pixel  11   c  transmits light. The second sub-pixel  12 D including the second color filter  20 BG 3  includes a plurality of sub-divided pixels that may be a first sub-divided pixel  12   a , second sub-divided pixels  12   b , and third sub-divided pixels  12   c . The third sub-pixel  13 D including the third color filter  20 R 1  includes a plurality of sub-divided pixels that may be a first sub-divided pixel  13   a , second sub-divided pixels  13   b , and third sub-divided pixels  13   c . The fourth sub-pixel  14 D including the fourth color filter  20 B 1  includes a plurality of sub-divided pixels that may be a first sub-divided pixel  14   a , second sub-divided pixels  14   b , and third sub-divided pixels  14   c . The second sub-pixel  12 D, the third sub-pixel  13 D, and the fourth sub-pixel  14 D each achieve the area coverage modulation through the same mechanism as that of the first sub-pixel  11 D. 
     The first sub-pixel  11 D, the second sub-pixel  12 D, the third sub-pixel  13 D, and the fourth sub-pixel  14 D are configured in the same manner as the first sub-pixel  11 B, the second sub-pixel  12 B, the third sub-pixel  13 B, and the fourth sub-pixel  14 B described above, respectively, except that the first sub-pixel  11 D, the second sub-pixel  12 D, the third sub-pixel  13 D, and the fourth sub-pixel  14 D each include the sub-divided pixels.  FIG. 11  illustrates a case in which an area ratio among the first sub-pixel  11 D, the second sub-pixel  12 D, the third sub-pixel  13 D, and the fourth sub-pixel  14 D is the same as that among the first sub-pixel  11 B, the second sub-pixel  12 B, the third sub-pixel  13 B, and the fourth sub-pixel  14 B illustrated in  FIG. 8 . However, the present disclosure is not limited thereto. The area ratio of the stripe-shaped sub-pixels  15  as illustrated in  FIG. 11  may be set to be the same as that of the first sub-pixel  11 , the second sub-pixel  12 , the third sub-pixel  13 , and the fourth sub-pixel  14  illustrated in  FIG. 3  or as that of the first sub-pixel  11 A, the second sub-pixel  12 A, the third sub-pixel  13 A, and the fourth sub-pixel  14 A illustrated in  FIG. 7 . Further, in the stripe-shaped sub-pixels  15  as illustrated in  FIG. 11 , two sub-pixels  15  adjacent to one sub-pixel  15  that serves as a reference preferably have a hue closer to the hue of the reference sub-pixel  15  than the hue of the remaining one sub-pixel  15 . In the example illustrated in  FIG. 11 , the one sub-pixel  15  that serves as the reference is the first sub-pixel  11 D or the second sub-pixel  12 G. 
     As described above, the sub-pixels  15  illustrated in  FIGS. 10 and 11  are each divided into a plurality of sub-divided pixels having different areas. Gradation expression for each of the sub-pixels  15  is performed through a combination of whether each of the sub-divided pixels transmits light. The number of sub-divided pixels included in a single sub-pixel  15  may be two, or four or more. Gradation performance of a single sub-pixel  15  in the area coverage modulation is indicated by the number of bits (N bits) corresponding to the number (N) of the sub-divided pixels, where N is a natural number of 2 or greater. Assuming that the area of the smallest sub-divided pixel is 1, the q-th (q-th bit) sub-divided pixel from the smallest sub-divided pixel has an area of 2 (q−1) . 
     The following describes a detailed configuration of a display device  1  in the embodiment with reference to  FIGS. 12 to 17 . In the description with reference to  FIGS. 12 to 17 , one of a plurality of sub-divided pixels will be referred to as a “sub-divided pixel  50 ”. 
       FIG. 12  is a diagram illustrating an exemplary circuit configuration of the display device in the embodiment. The X-direction in  FIG. 12  indicates a row direction of the display device  1 , and the Y-direction in  FIG. 12  indicates a column direction of the display device  1 . As illustrated in  FIG. 12 , the sub-divided pixel  50  includes, for example, a pixel transistor  51  employing a thin-film transistor (TFT), a liquid crystal capacitor  52 , and a holding capacitor  53 . The pixel transistor  51  has a gate electrode coupled with a scanning line  62  ( 62   1 ,  62   2 ,  62   3 , . . . ) and a source electrode coupled with a signal line  61  ( 61   1 ,  61   2 ,  61   3 , . . . ). 
     The liquid crystal capacitor  52  denotes a capacitance component of a liquid crystal material generated between the reflective electrode  40  provided for each sub-divided pixel  50  and a counter electrode  22  (see  FIG. 13 ) facing some of or all of the reflective electrodes  40 . The reflective electrode  40  is coupled with a drain electrode of the pixel transistor  51 . A common potential V COM  is applied to the counter electrode  22 . The common potential V COM  is inverted at predetermined cycle in order to inversely drive the sub-divided pixel  50  (see  FIG. 15 ). The holding capacitor  53  has two electrodes. One of the electrodes has a potential identical to that of the reflective electrode  40  and the other of the electrodes has a potential identical to that of the counter electrode  22 . 
     The pixel transistor  51  is coupled with the signal line  61  extending in the column direction and the scanning line  62  extending in the row direction. The sub-divided pixel  50  is at an intersection of the signal line  61  and the scanning line  62  in the display area OA. The signal lines  61  ( 61   1 ,  61   2 ,  61   3 , . . . ) each have one end coupled with an output terminal corresponding to each column of a signal output circuit  70 . The scanning lines  62  ( 62   1 ,  62   2 ,  62   3 , . . . ) each have one end coupled with an output terminal corresponding to each row of a scanning circuit  80 . The signal lines  61  ( 61   1 ,  61   2 ,  61   3 , . . . ) each transmit a signal for driving the sub-divided pixels  50 , i.e., a video signal output from the signal output circuit  70 , to the sub-divided pixels  50 , on a pixel column by pixel column basis. The scanning lines  62  ( 62   1 ,  62   2 ,  62   3 , . . . ) each transmit a signal for selecting the sub-divided pixels  50  row by row, i.e., a scanning signal output from the scanning circuit  80 , to each pixel row. 
     The signal output circuit  70  and the scanning circuit  80  are coupled with a signal processing circuit  100 . The signal processing circuit  100  calculates a gradation value (R 1 , RG, BG, and B 1  to be described later) of each of four sub-pixels  15  included in each pixel (e.g., pixel  10 ) according to the input gradation values of RGB. The signal processing circuit  100  outputs to the signal output circuit  70  a calculation result as area coverage modulation signals (Ro, RGo, BGo, and Bo) of each pixel. The signal output circuit  70  transmits to each sub-divided pixel  50  the video signal including the area coverage modulation signals (Ro, RGo, BGo, and Bo). The signal processing circuit  100  also outputs to the signal output circuit  70  and the scanning circuit  80  clock signals that synchronize operations of the signal output circuit  70  and the scanning circuit  80 . The scanning circuit  80  scans the sub-divided pixels  50  in synchronism with the video signal from the signal output circuit  70 . The embodiment may employ a configuration in which the signal output circuit  70  and the signal processing circuit  100  are included in a single IC chip  140 , or a configuration in which the signal output circuit  70  and the signal processing circuit  100  are individual circuit chips.  FIG. 12  illustrates circuit chips including the IC chip  140 , in a peripheral region SA of a first substrate  41  using a Chip-On-Glass (COG) technique. This is merely one example of implementation of the circuit chips, and the present disclosure is not limited thereto. The circuit chip may be mounted on, for example, a flexible printed circuit (FPC) coupled with the first substrate  41 , using a Chip-On-Film (COF) technique. 
       FIG. 13  is a cross-sectional view schematically illustrating the sub-divided pixel  50 . The reflective electrode  40  faces the counter electrode  22  with the liquid crystal layer  30  interposed therebetween. The reflective electrode  40  is provided to the first substrate  41 . Specifically, wiring including the signal line  61 , and an insulation layer  42  are stacked on a surface of the first substrate  41 , the surface facing the liquid crystal layer  30 . The insulation layer  42  insulates one wiring from another wiring and from electrodes. The reflective electrode  40  is a film-shaped electrode formed on a surface of the insulation layer  42 . The counter electrode  22  and the color filter  20  are disposed on a second substrate  21 . Specifically, the color filter  20  is disposed on a surface of the second substrate  21 , the surface facing the liquid crystal layer  30 . The black matrix  23  is disposed among the color filters  20 . The counter electrode  22  is a film-shaped electrode formed on a surface of the color filter  20 . 
     The sub-divided pixel  50  illustrated in  FIG. 13  represents one of the sub-divided pixels provided for gradation expression by area coverage modulation described above with reference to  FIGS. 10 and 11 . Specifically, each of the sub-divided pixels includes an individual reflective electrode  40 . The reflective electrode  40  faces the counter electrode  22  with the liquid crystal layer  30  interposed therebetween. 
     The first substrate  41  and the second substrate  21  are, for example, glass substrates that transmit light. The counter electrode  22  transmits light and is formed of, for example, indium tin oxide (ITO). The reflective electrode  40  is a metal electrode that is formed of thin film silver (Ag), for example, and that reflects light. 
     The liquid crystal layer  30  is sealed with a sealing material, which is not illustrated. The sealing material seals the liquid crystal layer  30  by bonding the first substrate  41  and the second substrate  21  at their ends. A spacer, which is not illustrated, determines a distance between the reflective electrode  40  and the counter electrode  22 . An initial orientation state of liquid crystal molecules of the liquid crystal layer  30  is determined by orientation films (not illustrated) provided to the respective first and second substrates  41  and  21 . The liquid crystal molecules do not transmit light in the initial orientation state. The state of not transmitting light in the initial orientation state in which no electric field is applied to the liquid crystal layer  30  is referred to as normally black. 
     The spectrum of the light OL transmitted through the color filter  20  illustrated in  FIG. 13  has a peak that falls on either one of the spectrum of reddish green, the spectrum of bluish green, the spectrum of red, and the spectrum of blue, as described with reference to  FIGS. 3, 7 , and  8 . 
     As described above, the display device  1  includes: the first substrate  41  provided with the reflective electrode  40 ; the second substrate  21  provided with the color filter  20  and the translucent electrode (counter electrode  22 ); and the liquid crystal layer  30  disposed between the reflective electrode  40  and the translucent electrode. As described with reference to  FIG. 1 , the light modulation layer  90 , for example, to modulate the scattering direction of the light OL emitted from the display device, may be provided to the second substrate  21  on the opposite side of the liquid crystal layer  30 . The light modulation layer  90  includes, for example, a polarizing plate  91  and a scattering layer  92 . The polarizing plate  91  faces a display surface. The scattering layer  92  is disposed between the polarizing plate  91  and the second substrate  21 . The polarizing plate  91  prevents glare by transmitting beams of light polarized in a specific direction. The scattering layer  92  scatters the light OL reflected by the reflective electrode  40 . 
     The display device  1  in the embodiment employs the sub-divided pixel  50  according to a memory-in-pixel (MIP) technology to have a memory function. According to the MIP technology, the sub-divided pixel  50  has a memory to store data, thereby allowing the display device  1  to perform display in a memory display mode. The memory display mode allows the gradation of the sub-divided pixel  50  to be digitally displayed based on binary information (logic “1” and logic “0”) stored in the memory in the sub-divided pixel  50 . 
       FIG. 14  is a block diagram illustrating an exemplary circuit configuration of the sub-divided pixel  50  employing the MIP technology.  FIG. 15  is a timing chart for explaining an operation of the sub-divided pixel  50  employing the MIP technology. As illustrated in  FIG. 14 , the sub-divided pixel  50  includes a drive circuit  58  in addition to the liquid crystal capacitor (liquid crystal cell)  52 . The drive circuit  58  includes three switching devices  54 ,  55 , and  56  and a latch  57 . The drive circuit  58  has a static random access memory (SRAM) function. The sub-divided pixel  50  including the drive circuit  58  is configured to have the SRAM function. 
     The switching device  54  has one end coupled with the signal line  61 . The switching device  54  is turned ON (closed) by a scanning signal ϕV applied from the scanning circuit  80 , so that the drive circuit  58  obtains data SIG supplied from the signal output circuit  70  via the signal line  61 . The latch  57  includes inverters  571  and  572 . The inverters  571  and  572  are coupled in parallel with each other in directions opposite to each other. The latch  57  latches a potential corresponding to the data SIG obtained through the switching device  54 . 
     A control pulse XFRP having a phase opposite to that of the common potential V COM  is applied to one terminal of the switching device  55 . A control pulse FRP having a phase identical to that of the common potential V COM  is applied to one terminal of the switching device  56 . The switching devices  55  and  56  each have the other terminal coupled with a common connection node. The common connection node serves as an output node N out . Either one of the switching devices  55  and  56  is turned ON depending on a polarity of the holding potential of the latch  57 . Through the foregoing operation, the control pulse FRP or the control pulse XFRP is applied to the reflective electrode  40  while the common potential V COM  is being applied to the counter electrode  22  that generates the liquid crystal capacitor  52 . 
     When the holding potential of the latch  57  has a negative polarity, the pixel potential of the liquid crystal capacitor  52  is in the same phase with that of the common potential V COM , causing no potential difference between the reflective electrode  40  and the counter electrode  22 . Thus, no electric field is generated in the liquid crystal layer  30 . Consequently, the liquid crystal molecules are not twisted from the initial orientation state and the normally black state is maintained. As a result, light is not transmitted in this sub-divided pixel  50 . On the other hand, when the holding potential of the latch  57  has a positive polarity, the pixel potential of the liquid crystal capacitor  52  is in an opposite phase of that of the common potential V COM , causing a potential difference between the reflective electrode  40  and the counter electrode  22 . An electric field then is generated in the liquid crystal layer  30 . The electric field causes the liquid crystal molecules to be twisted from the initial orientation state and to change orientation thereof. Thus, light is transmitted in the sub-divided pixel  50  (light transmitted state). As described above, in the display device  1 , the sub-divided pixels each include a holder (latch  57 ) that holds a potential variable according to gradation expression. 
     In each sub-divided pixel  50 , the control pulse FRP or the control pulse XFRP is applied to the reflective electrode  40  generating the liquid crystal capacitor  52  when either one of the switching devices  55  and  56  is turned ON depending on the polarity of the holding potential of the latch  57 . Transmission of light is thereby controlled for the sub-divided pixel  50 . 
     The foregoing describes the example in which the sub-divided pixel  50  employs the SRAM as a memory incorporated in the sub-divided pixel  50 . The SRAM is, however, illustrative only and the embodiment may employ other types of memory, for example, a dynamic random access memory (DRAM). 
       FIG. 16  is a block diagram illustrating an exemplary configuration of the signal processing circuit. The signal processing circuit  100  includes a first processor  110 , a second processor  120 , and a look-up table (LUT)  115 . The first processor  110  identifies the gradation values (R 1 , RG, BG, and B 1 ) of the respective four sub-pixels  15  included in each pixel (e.g., pixel  10 ) according to the input gradation values of R, G, and B. The gradation value of “RG” out of the gradation values (R 1 , RG, BG, and B 1 ) of the respective four sub-pixels  15  is the gradation value of either one of the first red green RG 1 , the second red green RG 2 , and the third red green RG 3 , for example. 
     Specifically, “RG” corresponds to the peak of the spectrum of the light transmitted through the first color filter included in the first sub-pixel. The gradation value of “BG” is the gradation value of either one of, for example, the first blue green BG 1 , the second blue green BG 2 , and the third blue green BG 3 . Specifically, “BG” corresponds to the peak of the spectrum of the light transmitted through the second color filter included in the second sub-pixel. The gradation value of “R 1 ” is the gradation value of the red (R 1 ), for example. Specifically, “R 1 ” corresponds to the peak of the spectrum of the light transmitted through the third color filter included in the third sub-pixel. Further, the gradation value of “B 1 ” is the gradation value of the blue (B 1 ), for example. Specifically, “B 1 ” corresponds to the peak of the spectrum of the light transmitted through the fourth color filter included in the fourth sub-pixel. 
     The LUT  115  is table data including the information on the gradation values of the respective four sub-pixels  15  predetermined for the gradation values of R, G, and B. The following describes an example in which the LUT  115  determines the gradation value of each of the first sub-pixel  11 , the second sub-pixel  12 , the third sub-pixel  13 , and the fourth sub-pixel  14  illustrated in  FIG. 3 . The first processor  110  refers to the LUT  115  and identifies the gradation values of (R 1 , RG 1 , BG 1 , and B 1 ) corresponding to the input gradation values of R, G, and B. For example, when the input gradation values of R, G, and B are expressed as (R, G, B)=(n, n, n) as illustrated in  FIG. 4 , the first processor  110  refers to the LUT  115  and identifies the gradation values as (R 1 , RG 1 , BG 1 , B 1 )=(n1, n2, n3, n4), where (n1, n2, n3, n4) represent colors of the first sub-pixel  11 , the second sub-pixel  12 , the third sub-pixel  13 , and the fourth sub-pixel  14  and are gradation values for reproducing colors corresponding to (R, G, B)=(n, n, n). The same applies to a case in which the input gradation values of R, G, and B are other gradation values. When the input gradation values of R, G, and B are expressed as (R, G, B)=(n, 0, 0), the first processor  110  identifies the gradation values as (R 1 , RG 1 , BG 1 , B 1 )=(n, 0, 0, 0). When the input gradation values of R, G, and B are expressed as (R, G, B)=(0, n, 0), the first processor  110  identifies the gradation values as (R 1 , RG 1 , BG 1 , B 1 )=(0, n5, n6, 0). When the input gradation values of B, G, and B are expressed as (R, G, B)=(0, 0, n), the first processor  110  identifies the gradation values as (R 1 , RG 1 , BG 1 , B 1 )=(0, 0, 0, n). When the input gradation values of R, G, and B are expressed as (R, G, B)=(m, m, 0), the first processor  110  identifies the gradation values as (R 1 , RG 1 , BG 1 , B 1 )=(m1, m2, m3, 0). When the input gradation values of R, G, and B are expressed as (R, G, B)=(0, m, m), the first processor  110  identifies the gradation values as (R 1 , RG 1 , BG 1 , B 1 )=(0, m4, m5, m6). When the input gradation values of R, G, and B are expressed as (R, G, B)=(m, 0, m), the first processor  110  identifies the gradation values as (R 1 , RG 1 , BG 1 , B 1 )=(m7, 0, 0, m8). 
     The second processor  120  outputs to the signal output circuit  70  the area coverage modulation signals (Ro, RGo, BGo, and Bo) corresponding to the respective sub-divided pixels associated with the gradation values (R 1 , RG, BG, and B 1 ) (e.g., R 1 , RG 1 , BG 1 , and B 1 ) of the respective four sub-pixels  15 . For example, when the gradation values of the colors of (R 1 , RG 1 , BG 1 , and B 1 ) identified by the first processor  110  are 8-bit numeric values (0 to 255), the second processor  120  divides the 8-bit numeric values into 2 N  segments for conversion into N-bit gradation values. When N=3, for example, a correspondence relation between the N-bit gradation values (0 to 7) and the 8-bit gradation values (0 to 255) may be classified as follows: 0: 0 to 31; 1: 32 to 63; 2: 64 to 95; 3: 96 to 127; 4: 128 to 159; 5: 160 to 191; 6: 192 to 223; and 7: 224 to 255. The foregoing classification example assumes the gradation values corresponding to a linear space ranging from 0 to 1.0 in which the gradation values are not subjected to gamma correction. When the gamma correction is performed, a classification may be changed. In accordance with the foregoing correspondence relation, the second processor  120  converts the 8-bit numeric values representing the gradation values of the colors of (R 1 , RG 1 , BG 1 , and B 1 ) into the corresponding N-bit gradation values. For example the second processor  120  converts the gradation values of (R 1 , RG 1 , BG 1 , B 1 )=(10, 100, 200, 255) to the area coverage modulation signals of (Ro, RGo, BGo, Bo)=(0, 4, 6, 7), and outputs the area coverage modulation signals to the signal output circuit  70 . The foregoing processing achieves expression of the input gradation values through the area coverage modulation. 
       FIG. 17  is a diagram schematically illustrating an exemplary relation among the external light IL, reflected light OL 1 , OL 2 , OL 3 , and OL 4 , and user&#39;s viewpoints H 1  and H 2  when a plurality of display devices  1 A and  1 B are disposed in juxtaposition. Each of the display devices  1 A and  1 B is the display device in the embodiment (e.g., display device  1 ). The reflected light OL 1 , OL 2 , OL 3 , and OL 4  represent beams of light OL having exit angles different from each other. As illustrated in  FIG. 17 , when the display devices  1 A and  1 B are disposed in juxtaposition, for example, beams of light OL having different exit angles from the display devices  1 A and  1 B may be viewed even with an incident angle of incident light IL on the display device  1 A being identical to an incident angle of incident light IL on the display device  1 B. In this case, with respect to the user&#39;s viewpoint H 1 , the reflected light OL from the display device  1 A is the reflected light OL 1 , and the reflected light OL from the display device  1 B is the reflected light OL 3 . Which of the reflected light OL 1  or the reflected light OL 2  from the display device  1 A is viewed by the user is changed depending on which of the user&#39;s viewpoint H 1  or the user&#39;s view point H 2  is assumed. Similarly, which of the reflected light OL 3  or the reflected light OL 4  from the display device  1 B is viewed by the user is changed depending on which of the user&#39;s viewpoint H 1  or the user&#39;s view point H 2  is assumed. Consequently, the exit angle of the light OL viewed by the user may vary depending on conditions, such as how the display devices  1 A and  1 B are disposed, and where the user&#39;s viewpoint is. Thus, the display device  1 A may be configured differently from the display device  1 B without departing from the scope of the present disclosure. For example, either one of the display devices  1 A and  1 B may employ the area ratio of the four sub-pixels  15  as illustrated in any one of  FIGS. 3, 7, and 8 , and the other of the display devices  1 A and  1 B may employ the area ratio of the four sub-pixels  15  as illustrated in the other one of  FIGS. 3, 7, and 8 . Alternatively, the correspondence relation between the input (gradation values of R, G, and B) and (R 1 , RG, BG, and B 1 ) in the LUT  115  of the display device  1 A may be made different from the correspondence relation between the input (gradation values of R, G, and B) and (R 1 , RG, BG, and B 1 ) in the LUT  115  of the display device  1 B. 
     As described above, in the reflective display device in the embodiment, the third sub-pixel and the fourth sub-pixel are each greater in size than the first sub-pixel and the second sub-pixel. The first sub-pixel added to the second sub-pixel has a size equal to or greater than the size of the third sub-pixel and has a size equal to or greater than the size of the fourth sub-pixel. The first sub-pixel includes the third color filter that has a spectrum peak falling on the spectrum of reddish green. The second sub-pixel includes the fourth color filter that has a spectrum peak falling on the spectrum of bluish green. The third sub-pixel includes the first color fitter that has a spectrum peak falling on the spectrum of red. The fourth sub-pixel includes the second color filter that has a spectrum peak falling on the spectrum of blue. The foregoing arrangements can further increase the luminance and saturation of yellow, thereby reliably achieving the required luminance and saturation of yellow (e.g., yellow Y). 
     Making the fourth sub-pixel greater in size than the third sub-pixel allows the hue of the spectrum of light transmitted through the color filters included in the first sub-pixel and the second sub-pixel to be more on the positive side. This configuration allows the light transmission efficiency of the color filters included in the first sub-pixel and the second sub-pixel to be more easily increased. Accordingly, the configuration further increases the luminance and saturation of yellow, thereby reliably achieving the required luminance and saturation of yellow (e.g., yellow Y). 
     Making the second sub-pixel greater in size than the first sub-pixel allows the hue of the spectrum of light transmitted through the color filter included in the first sub-pixel to be more on the positive side. This configuration allows the light transmission efficiency of the color filter included in the first sub-pixel to be more easily increased. Accordingly, the configuration further increases the luminance and saturation of yellow, thereby reliably achieving the required luminance and saturation of yellow (e.g., yellow Y). 
     The first sub-pixel, the second sub-pixel, and the third sub-pixel in combination reproduce yellow. This configuration car allocate a greater area of color filters and reflective electrodes combining the first sub-pixel, the second sub-pixel, and the third sub-pixel out of the display area of a single pixel to the reproduction of yellow. Consequently, the configuration can reliably achieve the required luminance and saturation of yellow (e.g., yellow Y). 
     The first sub-pixel and the second sub-pixel in combination reproduce green. This configuration can allocate a greater area of color filters and reflective electrodes combining the first sub-pixel and the second sub-pixel out of the display area of a single pixel to the reproduction of green. 
     The first sub-pixel is adjacent to the second sub-pixel. This arrangement allows green to be reproduced more uniformly. 
     A display device operable with lower power consumption can be provided by the sub-divided pixels performing the area coverage modulation 
     The sub-divided pixels each include a holder that holds a potential variable according to gradation expression. This configuration allows the display device to further reduce power consumption. 
     The present disclosure can naturally provide other advantageous effects that are provided by the aspects described in the embodiments above and are clearly defined by the description in the present specification or appropriately conceivable by those skilled in the art.